Battery pack

Submitted: Tuesday, Nov 12, 2002 at 01:00
ThreadID: 2352 Views:1441 Replies:6 FollowUps:7
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When I plug a power pack (which came with my Waeco fridge) into my cig. lighter my ignition light immediatly comes on. Does my vehicle think its now on ? I presume that the power is now flowing into my vehicle. Is this likely to cause a problem? I guess if I left it like this it would eventually flatten the power pack. How can I prevent this?
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Reply By: OziExplorer - Tuesday, Nov 12, 2002 at 01:00

Tuesday, Nov 12, 2002 at 01:00
The only way to prevent this happening, would be to put a small Bosch type mini-relay into the ingnition circuit, so when the ignition was switched off, it would disconnect/unlatch the relay and allow the contacts to go open circuit.

You could put a suitable size diode into the lighter circuit, however, this is not the preferable route, as a diode will drop the voltage .6 volt to your appliances and also to your battery that needs to be charged. .6 volt does not sound like much, but it is approximately 20% of the charge of your battery.
AnswerID: 8425

Follow Up By: Member - Nigel - Tuesday, Nov 12, 2002 at 01:00

Tuesday, Nov 12, 2002 at 01:00
You'd have to think carefully about how a relay was wired up, as the voltage from the battery pack may keep the relay switched on after the ignition switch is turned off.
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Follow Up By: Savvas - Wednesday, Nov 13, 2002 at 01:00

Wednesday, Nov 13, 2002 at 01:00
Sorry to be a pedant...but 0.6v is only 5% of the nominal 12v charge. The effect should be minimal on the appliances and battery.
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Follow Up By: Member - Nigel - Wednesday, Nov 13, 2002 at 01:00

Wednesday, Nov 13, 2002 at 01:00
Savvas, do you run your battery down to 0 volts?

A battery is considered totally flat at 11.89 volts (with no load and rested for a while) and fully charged at 12.65 volts. That leaves a usable range of 0.76 volts - do you really want to lose 0.6 volts of that?

BTW those are the voltages quoted by the manufacturers.
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Follow Up By: Oziexplorer - Wednesday, Nov 13, 2002 at 01:00

Wednesday, Nov 13, 2002 at 01:00
Savvas a bit of research on the internet about the effects of .6 volt on a 12vDC automotive style lead acid battery will surprise you. My statement is perfectly correct about the percentage. What is more, that is on the conservative side, as the modern batteries it can be has high as 31%.
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Reply By: Steve - Tuesday, Nov 12, 2002 at 01:00

Tuesday, Nov 12, 2002 at 01:00
Blackie: what make of vehicle are you using/talking about ?
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Follow Up By: Blackie - Tuesday, Nov 12, 2002 at 01:00

Tuesday, Nov 12, 2002 at 01:00
Its an '88 RR EFI.
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Reply By: Steve - Tuesday, Nov 12, 2002 at 01:00

Tuesday, Nov 12, 2002 at 01:00
Sorry, no comments other than that I don't want to start a flame war !! other than that I reckon you will never solve the problems with that unit....
AnswerID: 8449

Reply By: Eric - Tuesday, Nov 12, 2002 at 01:00

Tuesday, Nov 12, 2002 at 01:00
Blackie.
I am not familiar with RR ccts but every other vehicle has the lighter conected to the acc terminal of the ignition switch and there is no connection between acc and ign when the switch is off. I suggest you wire your lighter the same way or you will have a very flat power pack and possible damage to you electric fuel pump.
Eric.
AnswerID: 8458

Reply By: Savvas - Wednesday, Nov 13, 2002 at 01:00

Wednesday, Nov 13, 2002 at 01:00
Blackie ... Excuse the dumb question here. Why are you plugging the waeco power pack into the cigarette lighter with the ignition turned off anyway?
AnswerID: 8461

Reply By: Savvas - Wednesday, Nov 13, 2002 at 01:00

Wednesday, Nov 13, 2002 at 01:00
Oops...pressed submit too quickly.

I'd rig up a little adaptor between the power pack and the cigarette lighter that has an appropriate diode inline. This should prevent current flowing from the power pack back into the vehicle electrics, and you won't have to modify the vehicle wiring.

All you need is a cigarette lighter socket, cigarette lighter plug, some appropriately rated figure 8 wire, and an appropriate diode placed inline on the +ve wire. You could pick up all this stuff from Jaycar, Dick Smith, etc.
AnswerID: 8462

Follow Up By: Oziexplorer - Wednesday, Nov 13, 2002 at 01:00

Wednesday, Nov 13, 2002 at 01:00
Savvas under *NO* (shouting from top of hill) would you want to use a diode between the battery and the cigarette lighter. You cannot afford to loose .6 volt. You would need a Schottky diode, and for one of the required capacity would cost to many dollars. Schottky diodes are not normally used over forward currents of 1 amp. However, even a Schottky diode would not satisfy me. Any charge loss is to much.

The battery will not get properly charged to peak voltage.
It is no big deal to put a Bosch type mini-relay directly from the ignition circuit.

Personally, I would much prefer to see a better quality polarised plug and socket to connect that battery to the vehicle to charge. Cigarette lighters are generally shockers.
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Follow Up By: Savvas - Thursday, Nov 14, 2002 at 01:00

Thursday, Nov 14, 2002 at 01:00
Oziexplorer...I agree with you that cigarette lighters are shockers.

However, I must still be missing something here. I'm guessing that the power pack is plugged into the cigarette lighter to charge the power pack. Hence I would only do that when the vehicle is running and the alternator is charging. Therefore, I wouldn't expect either battery to go flat.

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