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[Dave DND]

Much has been said on the forum about the internal rechargeable powersounder battery and its failings, but knowing that there is a wealth of expertise on here, I have a few thoughts, and was wondering if any of you have similar opinions or thoughts?

One of the symptoms, sorry, let me rephrase that, one of the indications, that something is wrong with the internal powersounder battery is when the internal voltage drops below its designated threshold and its monitoring circuit will start to emit a few beeps.

In my experience, this usually indicates either a faulty powersounder battery, or, more significantly, a low voltage on the main car battery - (Go with me on this for a minute ) If the Main Battery is also dipping below its threshold voltage, although it may be able to crank and start the car and appear that all is well, the monitored voltage may still be below what the siren is expecting, and it may start to beep (sometimes).

This is not an uncommon scenario when cars are left for long periods of time and the battery is not keeping up its charge as simply not being driven enough.

In order to try and determine why the battry packs are failing, I have had a thought - could be utter rubbish, but this is why I`m asking for some thoughts.

If the main car battery is left to deteriorate by insufficient charge, and constant short journeys, we all know that it will eventually knacker itself fairly quickly - SO . .  If it did, and was constantly left in a poor state, what effect would that have on a secondary battery that was connected directly to it? ie: powersounder battery?  Would the constant lower voltage of the main battery cause any form of loss in voltage of the powersounder battery to a point where prolonged heat and current could become an issue as the two tried to charge each other - and if so, would sustained exposure to this cause the powersounder battery to fail and leak ?

In other words, are the powersounders failing because the main battery or charge is not adequately maintained ?

 :-?

[Marks DTM Calib]

Interesting one.

On the power sounder battery side of things, it will be very dependent on the charge circuit used.

If it is (and I know its not) a modern uber duper smart controler then it will keep it in tip top condition no matter what (as these can also boost volts using flyback on the switcher coils as well as reduce volts)

What I cant recall is the power sounder battery voltage (is it 6v in total ?).

If significantly lower then the car battery then it should be ok.

I would infer that the charge circuit in the power sounder is a pretty simple affair with I suspect nothing more than a constant V and I arrangement with the V regulation coming from the main circuit regulator and the I probably from a resistor!

A car battery generaly wont crank the car once its down to about 10.5-11V.

So it may well be not related.

THE most important part of any rechargeable circuit is the charger and the one in the power sounder (as per most domestic items) has been done very much at a cost (given the time when it was developed)

[Jimbob]

Interesting theory

when ours went, the thing had never made a single beep prior to the incident.  No warning whatsoever

The car had been stood for 24 hours odd prior to the fire.

The car battery was 11 or so volts when I checked it the next day (sure it was just under 12) :-/

http://www.omegaowners.com/forum/YaBB.pl?num=1259433462/0

[Dave DND]

The car battery was 11 or so volts when I checked it the next day (sure it was just under 12)

And that is EXACTLY my point . . .

Could the low voltage of the car battery have been a contributary factor in what happened next ?

 :-?

[Dave DND]

A car battery generaly wont crank the car once its down to about 10.5-11V.

But a battery at say, 11.5v would be enough to start the car, but would not be seen as adequate enough to keep the powersounder charged -

As you say, interesting theory . . . .

 :-?

[Marks DTM Calib]

A car battery generaly wont crank the car once its down to about 10.5-11V.

But a battery at say, 11.5v would be enough to start the car, but would not be seen as adequate enough to keep the powersounder charged -

As you say, interesting theory . . . .

 :-?

If we consider a battery at say 13.4V starts the car well then at 10.5V you only have 60% (it will actualy be worse than this as the internal resistance of a discharged battery rises) of the starter power.....and hence it more often than not wont start it.

Yet the power sounder battery may well still be fine (we need to find out how many V's it is) and charging ok.

What I infer may be happening is that the power sounder batteries are dying and maybe have a short circuit cell in them.....this then ups the charge current (on a basic charge circuit) and boils the others or cooks the onboard resistor.

It maybe worse than we originaly thought and the charge circuit could be so simple that there is actualy no voltage reg at all and it relies on the reality that the vehicle supply volts never goues about 14ish V's....and has only a series resistor (god help us!)

That would be bad in the case of an alternator reg failure resulting in high charge volts. 

[zirk]

No nothing about the power sounder back up supply, but whats the normal voltage of the PS Batteries?.

[Dave DND]

I`m thinking more along the lines of the main battery voltage being just a fraction lower than the voltage threshold set by the powersounder battery, and the main battery is now being seen as a LOAD that is draining the powersounder, albeit at a miniscule and insignificant current, but a load none the less.

Although probably in microamps, or the odd milliamp at most, would it be enough to cause the small powersounder battery to overheat and break down?

If it starts to overheat and boil, then the acid leaks, wrecks the board and eventually combusts, that bit we all know.

For a rechargeable battery to fail is pretty unusual, and because they have lasted a while, build quality can be almost (!) ruled out - also, If it was one type of sounder that failed, fair enough, but as there are several versions using different battery configurations and types, then surely it has to be something external to it, ie: the car !!

I`m more puzzled that this is fairly commonplace here, but problems are with both original and replaced batteries, so that leads me to beleive that its something we are either doing, or not noticing that is causing this powersounder to fail.

[Entwood]

Not sure if this adds anything or not ....

When my powersounder started to play up first indications were random alarms, followed within 48 hours by the infamous "beeps"on shut down.

I replaced the powersounder with a new one, this was May 09 so 14 months ago. The removed one was AFAIK original fit, so was 8 years old

False alarms stopped, and obviously, no beeps.

Battery is the same one , alternator has not been touched, car usage pattern is the same.

I've had no other electrical problems (touch wood) and the car electrical system works quite hard when towing as it runs the fridge in the 'van and the cool box on the rear seat .. and I've towed 18 weekends this year so far.

HTH

[Dave DND]

OK, for those of you who have been unfortunate enough to witness this first hand, some questions:

What time of year was it?
What time of day was it?
What was the weather / temperature?
Is the car used for long / short journeys?
When was the Battery last replaced?
Have you heard any "beeps" from the sounder?

As a guess, I bet that conditions were cold and the battery is a few years old - if so, this kind of adds weight to my theory as temperature can have quite an impact on battery voltage.

 :-?

[Dave DND]

Not sure if this adds anything or not ....

When my powersounder started to play up first indications were random alarms, followed within 48 hours by the infamous "beeps"on shut down.

I replaced the powersounder with a new one, this was May 09 so 14 months ago. The removed one was AFAIK original fit, so was 8 years old

False alarms stopped, and obviously, no beeps.

Battery is the same one , alternator has not been touched, car usage pattern is the same.

I've had no other electrical problems (touch wood) and the car electrical system works quite hard when towing as it runs the fridge in the 'van and the cool box on the rear seat .. and I've towed 18 weekends this year so far.

HTH

So it could be that the main battery takes a little while to break down the powersounder battery, and the problem is only noticeable on powersounder batteries that are past their best and now starting to deteriorate rapidly?

Batteries certainly don`t last forever, and it could be that your "new" powersounder batteries were in good enough condition to mask any faults for a few years to come?

 :-/

Or, of course it could be that you genuinely had a faulty powersounder ?

 :-?

[Entwood]

1) May 09
2) False alarms - Early Morning (around 2 am)
3) Can't remember but cool /damp I think
4) Good mixture of both
5) Over 2 1/2 years .. ie   not by me !!!
6) yes .. 48 hours after the false alarms started but only on switching off the engine - which I think was the PS complaining about a voltage drop as the charging circuit switched off.

PS was replaced   

I'm about to go out and put a multimeter on the system just to see what the readings are ... back shortly .

EDIT :

Car has not been started for  2 days :

Battery voltage before cranking = 12.09 v
Battery voltage @ 600 rpm  = 13.65 v
Battery voltage @ 2000 rpm. initially 13.89 but rising very slowly, after 2 minutes it was 13.96 and still rising (what I'd expect as the battery becomes charged - should top out at 14.3 if I left it long enough )

So I think the battery / electrical system is about right ... does that help at all ?

My personal take on the PS problem is that the batteries fail, possibly due to the "memory factor" of rechargeables, which all the stuff I've read says you should fully discharge a rechargeable every so often .. never happens to a PS battery (and I know that "rule" only applies to older rechargeables .. but thats whats in the PS) !!

Just my thoughts .. nowt else .... 

[Dave DND]

My personal take on the PS problem is that the batteries fail, possibly due to the "memory factor" of rechargeables, which all the stuff I've read says you should fully discharge a rechargeable every so often .. never happens to a PS battery (and I know that "rule" only applies to older rechargeables .. but thats whats in the PS) !!

Just my thoughts .. nowt else .... 

Battery readings would suggest to me that all is well with your car.

I understand where you are coming from with the memory effect, and I know that powersounders are never run down

However,

There are millions of rechargeable batteries in circulation, and if they kept spontaneously combusting, then someone would have noticed by now - and they would all have been withdrawn - and yet a fairly small group of people are experiencing an exceptionaly high percentage of failures - that does not seem to me like the battery failing, more like the circumstances under which its failing.

[Marks DTM Calib]

I susepct that its not the batteries actulay going up thats the issue.

I would think that it is either a failing battery over stressing a poorly designed charger circuit or the battery leaking and damaging components on the board.

There is certainly a diode in the circuit to stop the power sounder batteries from driving back out onto the vehicle supply.

Perhaps its time I cracked open the one on the shelf in the garage for a closer look 

[Dave DND]

I susepct that its not the batteries actulay going up thats the issue.

I would think that it is either a failing battery over stressing a poorly designed charger circuit or the battery leaking and damaging components on the board.

There is certainly a diode in the circuit to stop the power sounder batteries from driving back out onto the vehicle supply.

Perhaps its time I cracked open the one on the shelf in the garage for a closer look 

Good idea - if I had one here I would be doing the same

just a thought

wonder if that diode is ok, or leaky ?
If it was allowing current to flow in either direction, then theoretically it could cause the problem? 

I know I`m clutching at straws, but it would be good to get to the bottom of this one

[Entwood]

My personal take on the PS problem is that the batteries fail, possibly due to the "memory factor" of rechargeables, which all the stuff I've read says you should fully discharge a rechargeable every so often .. never happens to a PS battery (and I know that "rule" only applies to older rechargeables .. but thats whats in the PS) !!

Just my thoughts .. nowt else .... 

Battery readings would suggest to me that all is well with your car.

I understand where you are coming from with the memory effect, and I know that powersounders are never run down

However,

There are millions of rechargeable batteries in circulation, and if they kept spontaneously combusting, then someone would have noticed by now - and they would all have been withdrawn - and yet a fairly small group of people are experiencing an exceptionaly high percentage of failures - that does not seem to me like the battery failing, more like the circumstances under which its failing.

My thoughts ... probably rubbish ... I don't think the actual batteries would kick out enough power to ignite, especially if they are failing and not holding a charge - even though a directly shorted battery can put out a large current for a short time - I'm thinking that, because the batteries monitor the car battery - thats what sets the alarm off after all - it is the very large reserve of power from the CAR battery that actually causes the fires ... the PS batteries fail and shortcircuit .. so causing a very large drain/heat source inside the PS, which eventually ignites.

Now Mark DTM knows a lot more about electronics than I .. so perhaps he's right, and the short is not actually in the battery .. but the componenets trying "feed" a high current to a failed battery ??

[Dave DND]

I don't think the actual batteries would kick out enough power to ignite, especially if they are failing and not holding a charge

totally agree, but I don`t think its the power that is causing the ignition, I think its the temperature.

A very hot battery, albeit very small encased inside plastic - surely thats more than enough for combustion?

and that would also add credability to those that have combusted once removed from the car and stuck in the garage. Damage has already been done and they are now leaking and now "self contained"

[Entwood]

I don't think the actual batteries would kick out enough power to ignite, especially if they are failing and not holding a charge

totally agree, but I don`t think its the power that is causing the ignition, I think its the temperature.

A very hot battery, albeit very small encased inside plastic - surely thats more than enough for combustion?

and that would also add credability to those that have combusted once removed from the car and stuck in the garage. Damage has already been done and they are now leaking and now "self contained"

AH .. didn't realise some had gone up "on the shelf" .. I thought they were all "in car" and so drawing power from the car battery in attempting to charge ... blows my theory right out the window then ..

[Dave DND]

The ones that I am aware of going up on the shelf were all within a week of being removed as faulty. So its conceievable that these have already started to leak, been removed and they have been stored under ideal conditions for them to continue to burn.

 

but what caused the failure in the first place?

Thinking more on this diode - my thoughts are that although the batteries / sounder chassis have a few variations, I bet that the smaller components, diodes etc come from a  single source, and its certainly not uncommon for a diode to break down.

 :-/

Marks DTM, i`m presuming that its a dead sounder that you are disecting, and I would be very interested in any such diode type / readings if you could oblige

 

[feeutfo]

If it helps, mine only ever false alarmed on first start up on Monday morning after the car stood unused over the weekend.

After disection, the one in the guide, the board was fine and only slight leak on the battery showed. Kevin checked the voltages with a meter which showed a tired car battery, possibly original.

New car battery and the problems stopped. New PS  batterys where soldered in shortly after iirc. Although i was tempted to leave them to prove the car battery voltage dropping was the cause in my case.

Obviuosly with the ps monitoring car battery voltage it would be under highest load at start up on a cold morning. Then straining the tired car battery beyond the ps limit and the alarm goes off thinking the battery is being disconnected and the car stolen.

[Dave DND]

If it helps, mine only ever false alarmed on first start up on Monday morning after the car stood unused over the weekend.

After disection, the one in the guide, the board was fine and only slight leak on the battery showed. Kevin checked the voltages with a meter which showed a tired car battery, possibly original.

New car battery and the problems stopped. New PS  batterys where soldered in shortly after iirc. Although i was tempted to leave them to prove the car battery voltage dropping was the cause in my case.

Interesting - kind of works with my theory.

Obviuosly with the ps monitoring car battery voltage it would be under highest load at start up on a cold morning. Then straining the tired car battery beyond the ps limit and the alarm goes off thinking the battery is being disconnected and the car stolen.

Now this is where I think there is an issue -
If there is a sudden and rapid change in state of the voltage being monitored, disconnection, cranking etc etc, then the sounder will sound - but I`m wondering if there is a slight drain that causes the voltages to drop by such a small amount at a time, that the sounder would never actually sound, and depending on which battery was draining what, you would either end up with a flat main battery or a red hot powersounder battery.

I think this charging circuit really may be the key to this.

 :-/

[Kevin Wood]

I also find it hard to believe that the batteries are spontaneously combusting without being abused. I have seen the same type of battery in many applications. I have seen them leak and muller the PCB before but, as you say, they would be withdrawn if the problem were widespread.

I have a power sounder PCB on the bench and I believe I did trace the circuit to a certain extent a while back.

I reckon either the charging circuit is bad or, what I had observed on one of them, is that the battery had leaked conductive goo over the MOSFET (iirc) that drives the output transformer. It had started to conduct due to a partial gate-to-VCC short and had harmlessly flattened the battery in this case. Had that failure happened quicker, it might have sent enough current through the primary of the transformer (low DC resistance) to have ignited it, perhaps?

Anyway, I'll have a little play next time I'm bored and see what I can find out.

Batteries are 2 3.6v NiCd  packs in series IIRC.

Kevin

[JohnM]

My 2p - could be way off here.

First omega.  Sad main battery, car had been used daily on long, motorway runs.  Soon after that stopped main battery gave up.  When battery changed the sounder was allowed to go off (didn't do the ign - 15s procedure) - sounded nice and loud.  No alarm issues I can remember of. 

Second omega.  Had been standing for unknown time.  Battery charged okay (and is still running) sounder gave 3? beeps straight away.  Told just because main battery had been low/stood.  Did improved, warning beeps less became frequent - thought all was well.  Later, alarm problems - random alarms (alarm horn) couldn't find the cause (not helped by someone elses nearby going off) when one day arrived & parked up and the sounder was going off after a few mins.  Couldn't do a thing with it, ign on/off, even started up the sounder was squawking (parked somewhere out of the way).  All well (well flat?) on my return.  Seem to think it isn't fitted now - might have given a dying breath noise as it departed.

Now that one may have been murdered.  As whilst chasing the alarm problem I had that sparky moment and those reds? from one of the big blade fuses were seen on the pas pully.  The fuse was intact so I thought if that was the charging/monitor feed that was causing the alarm triggers, or lowering the main battery charge at least (I assume the 12v is monitored too).  In reality it may have part-shorted the charge feed - they were a good shower of sparks - and killed the nicads prematurely.

[TheBoy]

My PS is right in front of me. Sadly, its has been waterproofed with a potting compound by look of it.  I can see 6 batteries, presumably cheap, nasty nicads, so thats 7.2v

I know there are various types of PS that all do the same thing, so its possible some use other voltages - it's probably provided a simple 12v, 0v and some signalling to alarm ECU, with the internals being entirely up to the specific manufacturer of the PS.


I suspect the fire reports are probably where, over time, the batteries have leaks or vented, causing PCB damage?


Mine lasted about 10yrs before I removed it. It wasn't the usual failure, mine just used to occasionally go off whilst driving!

[Dave DND]

I suspect the fire reports are probably where, over time, the batteries have leaks or vented, causing PCB damage?

But I fear that is a very easily reached conclusion as to what has happened, without looking a bit more in depth as to the cause, and every time another one goes up, we (myself included) are all too quick to blame the powersounder and add this to the growing list of torched cars instead of looking into it further.

Old rechargeables simply do not leak or vent on such a scale as we see here on the forum, and even if they did, as the gooey acidic mess comes out, there would be little or no current left inside to cause a spark. Find a leaking nicad that still holds a good charge and prove me wrong !!

But you are right that there are various types of Powersounder that all do the same thing, and as they are all having the same fault, the problem MUST lie with something else on the car that is causing this to happen.

[doog]

When mine went it was....

What time of year was it?   winter
What time of day was it? 8.50am
What was the weather / temperature?  cold (frost)
Is the car used for long / short journeys? both
When was the Battery last replaced? 2 2 years previously
Have you heard any "beeps" from the sounder? no

note frosty roofs in picture  so it was cold at the time



Doug

[Dave DND]

When mine went it was....

What time of year was it?   winter
What time of day was it? 8.50am
What was the weather / temperature?  cold (frost)
Is the car used for long / short journeys? both
When was the Battery last replaced? 2 2 years previously
Have you heard any "beeps" from the sounder? no

note frosty roofs in picture  so it was cold at the time



Doug

Interesting -
From that I would suspect that your battery would certainly be below its normal voltage due to the very cold weather - still enough to start, but definately a volt or so down would be expected.

I think I may be on to something here then.

 :-/

Has anyone had one of these go up on a hot sunny day after a reasonable run and a good main battery?

 :-?

[Marks DTM Calib]

Well if the sounder batteries are 7.2V (6 off nicads) then its fair to assume that they are not driivng out into the main vehicle load.

I have a spare hour this evening, will crack mine open and pop a few pics up.

[Dave DND]

Well if the sounder batteries are 7.2V (6 off nicads) then its fair to assume that they are not driivng out into the main vehicle load.

Disagree - surely the transformer there could still theoretically allow it to happen ?

[TheBoy]

This is inside of mine...

[Dave DND]

TB,

Somehwere on the circuit board will be some form of diode protection for the charging circuit. I`m afraid that I do not know what shape / type / form it will take.

If there is any way to dig around and locate it, and if so, do you have a multimeter to take a forward and reverse reading from it ?

In theory, fire should not have altered the electrical characteristics of this diode component, so if it reads as short circuit or leaky, then that can only have happened pre-fire.

 :-?

[Kevin Wood]

I suspect the fire reports are probably where, over time, the batteries have leaks or vented, causing PCB damage?

But I fear that is a very easily reached conclusion as to what has happened, without looking a bit more in depth as to the cause, and every time another one goes up, we (myself included) are all too quick to blame the powersounder and add this to the growing list of torched cars instead of looking into it further.

Old rechargeables simply do not leak or vent on such a scale as we see here on the forum, and even if they did, as the gooey acidic mess comes out, there would be little or no current left inside to cause a spark. Find a leaking nicad that still holds a good charge and prove me wrong !!

But you are right that there are various types of Powersounder that all do the same thing, and as they are all having the same fault, the problem MUST lie with something else on the car that is causing this to happen.

I know this doesn't go anywhere towards explaining your observation of them combusting on the shelf, but when connected to an Omega they have access to an 80 A fused permanent 12v supply to aid combustion.

I have a PCB that I can connect up and experiment with variable supply voltages while watching the battery charging behaviour. I'll see if that turns anything up.

The link to the main alarm ECU is able to report back status of the power sounder as well as to activate / deactivate the alarm sounder. When a dying power sounder activates it gets logged in the main alarm ECU and a Tech 2 is also able to access diagnostic functions on the power sounder. (a test sounding can be commanded, and main and backup battery charge level can be shown IIRC).

EDIT:

Disagree - surely the transformer there could still theoretically allow it to happen ?

The transformer just steps up the squarewave output of the microcontroller on the PCB to a level suitable to drive the piezo sounder. I can't see a mechanism by which it would be rectified to generate a higher DC voltage.

Kevin

[Kevin Wood]

Another question:

Of the ones that have combusted - do we know what type of internals they had? I have seen at least 2 variants of sounder which aren't potted, each with different batteries, and I believe there is more than one type of potted internals based on the pictures I've seen posted.

Just thinking that, while they all fail given time (what product relying on NiCd batteries doesn't?) it's quite likely that only one design has the really fatal flaw that can start a fire.

Kevin

[Dave DND]

Kevin,

thanks for the transformer identification, I knew there was one in there, just not sure what for.

 

If you can, monitor the voltage and current on the rechargeable pack, and see what hapens as the main battery voltage is turned down -

Also, what is there in the way of diode protection?

How do the above readings react if the diode is shorted out ?

 :-?

[Dave DND]

Another question:

Of the ones that have combusted - do we know what type of internals they had? I have seen at least 2 variants of sounder which aren't potted, each with different batteries, and I believe there is more than one type of potted internals based on the pictures I've seen posted.

Just thinking that, while they all fail given time (what product relying on NiCd batteries doesn't?)
Kevin

I`ve also only seen 2 non potted versions, but have also seen 2 potted versions both with slightly different shaped outer casings - very subtle differences around the mouth of the siren, but unsure how different the internals are

it's quite likely that only one design has the really fatal flaw that can start a fire.

No, there are at least two diferent styles on this forum from the pictures I have seen
And thats what prompted me to start digging further . . . .

[TheBoy]

TB,

Somehwere on the circuit board will be some form of diode protection for the charging circuit. I`m afraid that I do not know what shape / type / form it will take.

If there is any way to dig around and locate it, and if so, do you have a multimeter to take a forward and reverse reading from it ?

In theory, fire should not have altered the electrical characteristics of this diode component, so if it reads as short circuit or leaky, then that can only have happened pre-fire.

 :-?

Not sure its worth it on mine, as mine wasn't the usual failure.  I suspect mine was just getting tired after 10yrs use.  It actually still works, but is prone to sounding the siren for now reason.

The pic was just to show that type, and the batts...

[Kevin Wood]

Had a prod at a power sounder board that still shows signs of life after the battery crud has been cleaned off.

2 12V supplies. Permanent and switched.

7.2V Ni Cd battery  (2 x 3.6V)

Battery is charged from the permanent 12V input at a rate of 15mA. Regulated between 14 and 16mA over the range of 10V - 16V input. Above that the charging is cut off. Almost as if there's an overcurrent/voltage protection circuit.

Current pretty much stable down to a short circuit where the NiCd battery should be.

Charging diminishes below 10V input and by 8V there's none, as expected. Alarm sounds below about 6V input, and whenever the power is disconnected. Alarm is silenced when both 12V supplies are restored.

The feed to the sounder (and most of the other circuitry) is fed via a pair of diodes so that it is fed from either the battery or the permanent 12V input, whichever has greatest voltage. Failure of one of these diodes could therefore result in 12V into the rechargeable battery or the rechargeable battery trying to drive the car electrics.

Alarm sounder transformer is indeed driven by what looks like a MOSFET straight from the junction of the 2 diodes. Transformer primary DC resistance is about 1.2 ohms. Feed to the MOSFET comes from a pin on the microcontroller which is toggled up and down to generate the tones.

I hope there isn't a DC path from the microcontroller to the MOSFET as this pin ending up in the wrong state due to a firmware glitch would result in combustion without a doubt.

I must double check the above.

The area around the MOSFET is one of the areas that was affected by battery leakage on this unit.

Kevin

[Dave DND]

Full set of Brownie points to Kevin !!!!

Battery is charged from the permanent 12V input at a rate of 15mA. Regulated between 14 and 16mA over the range of 10V - 16V input. Above that the charging is cut off. Almost as if there's an overcurrent/voltage protection circuit.

Current pretty much stable down to a short circuit where the NiCd battery should be.

About what I would have expected

Charging diminishes below 10V input and by 8V there's none, as expected. Alarm sounds below about 6V input, and whenever the power is disconnected. Alarm is silenced when both 12V supplies are restored.

Again as expected, but surprised that the low voltage "Beep" didn`t kick in - although a feature of the powersounder, its consistant with others who say that they have never heard it.

The feed to the sounder (and most of the other circuitry) is fed via a pair of diodes so that it is fed from either the battery or the permanent 12V input, whichever has greatest voltage. Failure of one of these diodes could therefore result in 12V into the rechargeable battery or the rechargeable battery trying to drive the car electrics.

Thats worrying !!
Do they read ok though?
Cheesy / cheap components ?

I hope there isn't a DC path from the microcontroller to the MOSFET as this pin ending up in the wrong state due to a firmware glitch would result in combustion without a doubt.

If you mean a software fault on the main Alarm control box, then you can pretty much rule that one out - the units are virtually indestructable and apart from a few dirty or worn out indicator relays, seldom give any cause for concern. The programming that is done to them for various alarm features etc, does not affect the firmware in any way whatsoever. The comminication between the two is done at around 5v IIRC. However, taking on board your comments, can you elaborate your theory any further with regards to this

The area around the MOSFET is one of the areas that was affected by battery leakage on this unit.

So another problem could occur from here once the battery had drained onto it?



Very interesting results . .   

[Kevin Wood]

Didn't check for beep. May well have missed it because I had the sounder disconnected to avoid the din but you can hear some feint screeching from the transformer when it kicks off.

Thats worrying !!
Do they read ok though?
Cheesy / cheap components ?

They were fine on this example but an example of what might go wrong. No sign of anything to mitigate against this (I would have liked to see a fuse on the PCB or  perhaps a zener or VDR across the input to protect against transients, fast chargers, etc.).

If you mean a software fault on the main Alarm control box, then you can pretty much rule that one out - the units are virtually indestructable and apart from a few dirty or worn out indicator relays, seldom give any cause for concern. The programming that is done to them for various alarm features etc, does not affect the firmware in any way whatsoever. The comminication between the two is done at around 5v IIRC. However, taking on board your comments, can you elaborate your theory any further with regards to this

I'm not referring to the main alarm unit. On the power sounder board is a small microcontroller and an E² memory chip. When the alarm sounds you get a squarewave which sweeps up and down in frequency on one of the output pins of the microcontroller. In other words, the firmware is toggling the pin up and down. This drives the MOSFET and via the transformer the alarm sounder so there is no oscillator outside the chip. The microcontroller directly generates the alarm sound. Now, let's say that microcontroller can enter a state where it leaves this pin active for longer then it should (due to low battery, voltage dipping during startup, etc.).This might burn out the transformer and cause a fire. Just a theory. I would have put a cap in series to break the DC path from the microcontroller myself but I will check that's the case.

So another problem could occur from here once the battery had drained onto it?

Yes, again, another theory but the gunge on this one had caused the mosfet to partially turn on, leading to a high drain on the battery. Nothing worse than that in this case but maybe...

Kevin

[Dave DND]

Interesting.

What blows most most of our theories out of the water however, is that there appears to be no other internal component faults except the battery itself, and so far replacement of that seems to bring the unit back to life.

Now, let's say that microcontroller can enter a state where it leaves this pin active for longer then it should (due to low battery, voltage dipping during startup, etc.).This might burn out the transformer and cause a fire. Just a theory.

Not sure the transformer would be so delicate, but wouldn`t this cause a continual drain on the battery and cause that to overheat instead?  Or, could continual drain / high useage of a rechargeable then cause it to leak? But either way, if that output was left in a high state wouldn`t that give some sort of audible tone?

Hang on . .  The sirens are know to "screetch" when they fail, aren`t they ?

the gunge on this one had caused the mosfet to partially turn on, leading to a high drain on the battery. Nothing worse than that in this case but maybe...

That is indeed one of the tell tale indications that the siren is knackered, but doesn`t help as to why the battery leaked on it in the first place.

Or maybe, this IS simply down to a bad design of battery pack that does start to leak over time.

Might be worth seeing if we can get hod of some other dead ones for you to perform an autopsy on, as you certainly have mastered the theory of operation I think, and would be good to make some comparisons.

Has anyone out there got any dead / blown / burnt out ones that we could disect ?

[Jimbob]

mine went in the bin sorry (it stank)

[Dave DND]

mine went in the bin sorry (it stank)

Is it still there? Or are you one of those who give blokes a bad name by actually emptying your garage bin once in a while?

 

[Jimbob]

lol it had to go, the acid stink got right up my nose whenever  I went in.

Sorry 

[Andy H]

When my main car battery required replacing last year (due to one dead cell) the power sounder was being triggered in full siren mode when the volts went low during a cold start. I can't remember whether it beeped as well  :-/

[Andy H]

7.2V Ni Cd battery  (2 x 3.6V)

Battery is charged from the permanent 12V input at a rate of 15mA. Regulated between 14 and 16mA over the range of 10V - 16V input. Above that the charging is cut off. Almost as if there's an overcurrent/voltage protection circuit.

Are there any markings indicating the capacity of the batteries? IIRC a safe charge rate would charge a NiCd in 10 hours so I wouldn't be surprised if the batteries were rated at 150 mAh. Continued charging at the 10 hour rate would destroy the cells in a few days so I presume the charging circuit must maintain a float voltage once they are fully charged.

My suspicion is that when the batteries get old then one cell will die first and the charging circuit will stay on at 15mA. What happens next depends on what the batteries do when they fail (ie where the acid goes )

[TheBoy]

I'm not sure the location is smart, seeing as its right under a drain, so water drips on it.  OK, so its supposedly waterproof, but....

[Jim Durham]

I'm new to the forum and am becoming concerned at hearing about this problem with the powersounder ( haven't had any myself up to now). Is it something I should be doing something about? I tend to be a "if its not broke don't fix it" driver.

[Dave DND]

I'm new to the forum and am becoming concerned at hearing about this problem with the powersounder ( haven't had any myself up to now). Is it something I should be doing something about? I tend to be a "if its not broke don't fix it" driver.

No, dont be too concerned about it - the powersounder gives quite few indications when something is wrong, from beeping and draining the car battery - only if it is continually ignored in a faulty state can things go horribly wrong.

The purpose of this particular thread, inlike the others, is to try and investigate the cause of the powersounder failure, rather than simply replacing a faulty one.

 

[Kevin Wood]

7.2V Ni Cd battery  (2 x 3.6V)

Battery is charged from the permanent 12V input at a rate of 15mA. Regulated between 14 and 16mA over the range of 10V - 16V input. Above that the charging is cut off. Almost as if there's an overcurrent/voltage protection circuit.

Are there any markings indicating the capacity of the batteries? IIRC a safe charge rate would charge a NiCd in 10 hours so I wouldn't be surprised if the batteries were rated at 150 mAh. Continued charging at the 10 hour rate would destroy the cells in a few days so I presume the charging circuit must maintain a float voltage once they are fully charged.

My suspicion is that when the batteries get old then one cell will die first and the charging circuit will stay on at 15mA. What happens next depends on what the batteries do when they fail (ie where the acid goes )

No evidence of the charge stopping when the batteries are full. I might try a long term test to see if there's a time-based limit but it looks to me like they charge at C/10 indefinitely.

Kevin

[Andy H]

Have you still got the old batteries in circuit? or are you testing with a resistor?

Two thoughts
1. if using a resistor you won't see a true float voltage
2. if using the batteries they will presumably need 10 hours of charge before they are fully charged (and I hope you have a working smoke alarm )

[Kevin Wood]

I was using batteries but not the originals. They did reach about 8v during testing (I suspect they are not in great condition - from the bottom of my junk box).

Kevin

[lee4206]

I have one if you're still after one.  I have no idea whats wrong with it (if anything)as its connected but has never gone off in the year ive had the car (the horn goes off occasionaly if i make it).
lee

[Kevin Wood]

Interesting... I've just been looking for a source of replacement batteries and came across some specs for those Varta Mempac batteries.

http://www.rapidonline.com/netalogue/specs/18-1575.pdf

Now, that isn't exactly the right battery but I suspect constructed from the same or similar cells.

Trickle charge 3.3mA

Overcharge 11mA continuous or 22mA for 1 Year @20^oC

We're charging them at 15mA in an environment where the temperature can go all over the place and I bet there's no temperature compensation on the charging circuit. So, the batteries are being "abused" in this case.

I need to find out if 15mA is the design charging current or if it's due to a fault / leakage on the PCB.

I have another board to try. It doesn't work but it might work enough to measure the charging current, I suppose?

Failing that I'll trace the circuit.

Kevin

[Dave DND]

Interesting... I've just been looking for a source of replacement batteries and came across some specs for those Varta Mempac batteries.

http://www.rapidonline.com/netalogue/specs/18-1575.pdf

Now, that isn't exactly the right battery but I suspect constructed from the same or similar cells.

Trickle charge 3.3mA

Overcharge 11mA continuous or 22mA for 1 Year @20^oC

We're charging them at 15mA in an environment where the temperature can go all over the place and I bet there's no temperature compensation on the charging circuit. So, the batteries are being "abused" in this case.

I need to find out if 15mA is the design charging current or if it's due to a fault / leakage on the PCB.

I have another board to try. It doesn't work but it might work enough to measure the charging current, I suppose?

Failing that I'll trace the circuit.

Kevin

So how would temperature affect the charging current?

Would it rise in colder temperatures?

As is would initially appear as though these sounders tend to fail with colder weather rather than hot ?

[Kevin Wood]

So how would temperature affect the charging current?

Would it rise in colder temperatures?

As is would initially appear as though these sounders tend to fail with colder weather rather than hot ?

It will effect the terminal voltage so if there were a strategy to terminate the charge at a voltage threshold that would ideally be temperature dependant. It seems in this case that it just charges 24/7 so probably not an issue.

The maximum continuous charging current is specified at 20^oC so I would imagine it's derated either side of this, although the data sheet doesn't specify how. I would have thought they were more likely to suffer in high temperatures but who knows?

I have no idea why they are charging them so hard. They are on charge 24/7 and the only prospect of them being discharged is when the vehicle battery is disconnected (or flat).

There's always the possibility that a fault causes the charging current to rise, of course.

Kevin

[Kevin Wood]

In fact, considering that they are only achieving a 5 year life (ish?) from these devices, it beats me why they bothered with a rechargeable battery at all, and didn't just use a non-rechargeable Lithium battery. Ho, hum.

Kevin

[TheBoy]

In fact, considering that they are only achieving a 5 year life (ish?) from these devices, it beats me why they bothered with a rechargeable battery at all, and didn't just use a non-rechargeable Lithium battery. Ho, hum.

Kevin

Would a cheap lithium have the power to sound the PS?  Also, I guess its fair to say the alarm has to be able to recover from going off occasionally...

[Kevin Wood]

In fact, considering that they are only achieving a 5 year life (ish?) from these devices, it beats me why they bothered with a rechargeable battery at all, and didn't just use a non-rechargeable Lithium battery. Ho, hum.

Kevin

Would a cheap lithium have the power to sound the PS?  Also, I guess its fair to say the alarm has to be able to recover from going off occasionally...

9 times out of 10 the vehicle battery will be powering it. They are also quite efficient in terms of db sound per Watt of electrical power. I guess it comes down to cost. NiCd pack being cheaper.

Kevin

[Lampynoiseboy]

In fact, considering that they are only achieving a 5 year life (ish?) from these devices, it beats me why they bothered with a rechargeable battery at all, and didn't just use a non-rechargeable Lithium battery. Ho, hum.

Kevin

Would a cheap lithium have the power to sound the PS?  Also, I guess its fair to say the alarm has to be able to recover from going off occasionally...

9 times out of 10 the vehicle battery will be powering it. They are also quite efficient in terms of db sound per Watt of electrical power. I guess it comes down to cost. NiCd pack being cheaper.

Kevin

Would be an interesting experiment to replace with a lithium pack as suggested, and time the sounder before the pack discharges (Ear defenders anyone?). As a lot of the newer (& cheaper than when these were designed) batteries can hold a charge for a considerable time, could that be considered a long term solution?
We change or smoke detector batteries on an annual basis, so why not our PS's? Admittedly it's not easy due to construction of the PS, but I'm sure that a "how to" mod that could be written to make it easier each year?
Even basic soldering skills could facilitate an external battery pack if more power was required?

Again, insurance issues, but certainly better than no PS at all

Obviously a "proper" solution is preferable, and you guys have certainly spent time & effort, and have reached a lot of important conclusions, but if there is no answer, it's expensive, or can't be found maybe this could be considered?

[Osprey]

Scuse me for bumping an old thread but here’s one more bit of anecdotal data for Dave DND’s failing main battery theory. 

My battery was fine, or so I assumed, because the car started first time every time without hesitation.  But when I started hearing the four beeps, I checked properly: even after a full charge from a three-stage mains charger the battery wouldn’t hold more than 12.32V, and it started to sag noticeably on a few minutes of headlight load with the engine off. 

From what little I know of its recent history it is quite likely that the car has sat around unused for a month or more over the summer, probably on a tired battery.  So looks like another example that fits in with Dave’s picture of the PS battery failing after being put to the test by a suspect main battery.

[lightfj]

Just to add to the interesting talk on the powersounder, mine just went off last sunday afternoon. No apparent reason but stopped after a few minutes and went off again in no time flat. It continued to cycle and was not stopped by unlocking the car with the remote or even turning on the ignition or starting the engine. I removed it and lasted 3 minutes continuing to cycle before it died. I have since opened it up and it has Varta 3.6V 140mA batteries. One battery measured 0.40V and the other 1.90V. The car is a 2002 2.2 dti elite and has done 108K. Could the imbalance of the battery voltage have anything to do with it? Following Dave DND's exhaustine research details I offer this as additional info for his archives. If onebattery is not holding its charge compered to the other could it cause random triggering of the alarm?
Am going to replace both batteries and see what happens.
Thanks to all who post on this issue -its interesting.

[Kevin Wood]

The batteries are simply connected in series so an imbalance wouldn't cause any failure mode a failed pair wouldn't, IMHO.

Any signs of battery leakage?

Kevin