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[Taxi_Driver]

Charge a 12v lead acid battery (90 or 110AH).....from the omega? And no fitting it as main battery isnt an option.

I could use a 150w invertor connected to a battery charger and all slung in the boot......where the battery will be. But seems a unefficient to me. Ive had a search on the interwebby to see if theres a 12v-12v charger/lead thingy but carnt find anything  :-/

Any ideas?

Cheers

[Martin_1962]

Caravan split charge relay

[Taxi_Driver]

Caravan split charge relay

How does that work Martin? Does it limit current? Coz i did think of connecting it to the omega 12v.....but a flat 90-110AH battery is going to want to take a lot of current initially.... :-/

Did think of just connecting it to rear ciggie lighter.......but think it will just pop the 10amp fuse

[Martin_1962]

Caravan split charge relay

How does that work Martin? Does it limit current? Coz i did think of connecting it to the omega 12v.....but a flat 90-110AH battery is going to want to take a lot of current initially.... :-/

Did think of just connecting it to rear ciggie lighter.......but think it will just pop the 10amp fuse

HUmm made a mistake - still need charging kit as well!

However check this site

http://www.towsure.com/product/562-Fridge/Battery_Combination_Relay

[lee4206]

Could try this  http://www.tradingdirect.co.uk/gadgets_easy_start.asp     and cut the plug off of one end and put croc clips on.    

lee

[Elite Pete]

Could try this  http://www.tradingdirect.co.uk/gadgets_easy_start.asp     and cut the plug off of one end and put croc clips on.    

lee

Don't mention crocodile clips, you'll give Tunnie a stiffy ::) ;D

[Ken T]

One way would be to tap into a suitable fused power source, the cig lighter is fused at 10A, and stick a resistor in series to limit the charging current. For example a 1R resistor would limit the max charge to 12-14A, but as your battery is unlikely to be totally flat then it wouldn't pass that much. One rated at 10W would be suitable, and Maplins sell them for £0.40. This has the dissadvantage that charging will take a while, say if the battery is up at 10V and the supply is 14V, then max charge is only 4A, so could take a while to fully charge. If the battery will not be below say 6V, you could decrease the resistor to 0.5R (put 2 in parallel). Mind you the crap, sorry thin leads they tend to use on cig lighters leads probably couldn't pass 10A without melting, so you could probably just connect it directly to the battery without any problems. And as a bonus the charging leads would get nice and warm.  

[Kevin Wood]

Depends if the battery is going to be permanently mounted to the car or if it's just a temporary arrangement and also how quick you need it to charge. In addition, if there's going to be load on it during charging.  For a permanent installation I would run a decent, thick cable from the car battery through a fuse to the rear of the car, with a caravan split charge relay or similar to enable charge to the second battery when the car battery volts rise.

You want to drop as few volts in this cable as possible because if there's too much drop the battery won't reach a fully charged state. If you need to draw load from the battery during charging it might be wise to take this from the end of this cable at the front of the car to minimise voltage drop at the battery end.

For a temporary set up, something to plug into the cigar lighter may do the job, depending on the voltage at that socket with the other loads in the car drawing current. You might find the lighter socket delivers insufficient voltage (less than 13.8 and the battery won't reach full charge) to charge the battery. You may well find that the resistance in the circuit is enough to prevent the current getting excessive, since the battery "looks" like a voltage source of up to 12.5v with an internal resistance. This means that you're only dropping a volt or so across the resistance of the circuit instead of the full 12 volts - unless you start with a totally flat battery, of course.

If it's a temporary lashup and you've got an inverter and a battery charger handy it might be the easiest solution. At least you know the charge to the battery will be under control.

Kevin

[Markjay]

Wouldn't the alt be overloaded with charging a 90-110Ah battery...?

[Kevin Wood]

Wouldn't the alt be overloaded with charging a 90-110Ah battery...?

The capacity of the battery doesn't really come into it. The alternator should current limit at a safe level so the more battery capacity you connect across it the longer it would take to charge it. Furthermore, if you use a caravan charging relay you'll only switch in the second battery when the main vehicle battery has fully charged and the alternator is powering the loads on the car with capacity to spare.

Kevin

[Markjay]

Wouldn't the alt be overloaded with charging a 90-110Ah battery...?

The capacity of the battery doesn't really come into it. The alternator should current limit at a safe level so the more battery capacity you connect across it the longer it would take to charge it. Furthermore, if you use a caravan charging relay you'll only switch in the second battery when the main vehicle battery has fully charged and the alternator is powering the loads on the car with capacity to spare.

Kevin

Okkky dokkky Kevin... I guess that's why we need you on this forum  

[Kevin Wood]

The capacity of the battery doesn't really come into it.

.. within reason, of course. If you set off at the start of every journey with a completely flat 110 ah battery in the boot I think the alternator would get the hump, but it's more down to how much charge you're going to be taking out of the battery than its capacity, and that depends on the application.

Kevin

[Taxi_Driver]

Depends if the battery is going to be permanently mounted to the car or if it's just a temporary arrangement and also how quick you need it to charge. In addition, if there's going to be load on it during charging.  For a permanent installation I would run a decent, thick cable from the car battery through a fuse to the rear of the car, with a caravan split charge relay or similar to enable charge to the second battery when the car battery volts rise.

You want to drop as few volts in this cable as possible because if there's too much drop the battery won't reach a fully charged state. If you need to draw load from the battery during charging it might be wise to take this from the end of this cable at the front of the car to minimise voltage drop at the battery end.

For a temporary set up, something to plug into the cigar lighter may do the job, depending on the voltage at that socket with the other loads in the car drawing current. You might find the lighter socket delivers insufficient voltage (less than 13.8 and the battery won't reach full charge) to charge the battery. You may well find that the resistance in the circuit is enough to prevent the current getting excessive, since the battery "looks" like a voltage source of up to 12.5v with an internal resistance. This means that you're only dropping a volt or so across the resistance of the circuit instead of the full 12 volts - unless you start with a totally flat battery, of course.

If it's a temporary lashup and you've got an inverter and a battery charger handy it might be the easiest solution. At least you know the charge to the battery will be under control.
Kevin

Thanks for the ideas guys  

The battery wont be totally flat.....it will only be charging in the boot.....and will be temp...Probably lowest voltage it will be drained to will be about 10v.
So probably will go the invertor and battery charger route.......however my battery charger says it draws max 150W, so will have to use 150W invertor to be on the safe side......tho 150W invertor will draw between 10-13 amps if on max load by the charger and the voltage at the rear ciggie socket.....so the rear ciggie lighter socket maybe out if it keeps popping the fuse for it (10A) Will have to try it.....and if it does, run fused wires from the car battery  

Also need to get a decent charge into the battery after about 1hr or so of charging.

[Auto Addict]

Charge a 12v lead acid battery (90 or 110AH).....from the omega? And no fitting it as main battery isnt an option.

I could use a 150w invertor connected to a battery charger and all slung in the boot......where the battery will be. But seems a unefficient to me. Ive had a search on the interwebby to see if theres a 12v-12v charger/lead thingy but carnt find anything  :-/

Any ideas?

Cheers

The question is.........WHY? :-?

[Taxi_Driver]

Charge a 12v lead acid battery (90 or 110AH).....from the omega? And no fitting it as main battery isnt an option.

I could use a 150w invertor connected to a battery charger and all slung in the boot......where the battery will be. But seems a unefficient to me. Ive had a search on the interwebby to see if theres a 12v-12v charger/lead thingy but carnt find anything  :-/

Any ideas?

Cheers

The question is.........WHY? :-?

I was wondering when someone was gonna ask  

Coz now that im a tent owner.....i was thinking of visiting a site, the week following the nealry in Wales meet.....that doesnt have electric hookup for the tent pitches.....and i wanted to take a portable TV....a 110AH lesiure battery should run it for 5-6hours possibly longer