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[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.