Can a car battery be kept charged with another car battery?

Hi All,

I have a car that is not located near any 120VAC power, so I cannot use a normal trickle charger to maintain my car's battery at full charge (the car sits for long periods). But can I use another (fully charged) lead acid car battery, or perhaps even one of those portable car jump starter units (like the Black and Decker VEC010BD

300 AMP JumpStarter), to keep my car's battery fully charged? Every week or so I would bring home the "charger battery" for a recharge, then hook it back up again to my car's battery through jumper cables. Is this possible, or are there some major pitfalls?

Thanks,

-Bill

Reply to
billcalley
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Reply to
AndyS

Andy writes: Sure, but there are a couple of tricks.

1) Use the portable battery to run a small inverter that will boost the output to a couple of volts higher than the portable battery voltage. Then use this higher voltage to charge the fixed battery , either thru a resistor or some time of current limiting regulator. 2) Use and additional portable battery in series with the first portable battery to provide a higher voltage, and proceed as above. 3) The simplest way, however, is to just connect the two batteries in parallel with a 1 ohm resistor in the positive leads. When the portable battery is "freshly charged" it will bring up the charge in the fixed battery, slowly. ( The one ohm is to limit the current so there's not any gassing). The portable battery will need to be charged regularly and this is only a trickle arrangement. But, if that's all you need, it is very simple.

Perhaps there are other suggestions, such as buying a solar array that will put a few hundred mils into the fixed battery. That would work OK as a trickle maintainer, but remember, it will only work for a few hours every day..... The internet will give you the average daily "full sun" numbers for various location. In Dallas, for instance, "full sun" only averages 5 1/2 hours per day. So don't use "peak sun" number for the array output without factoring this in.

Just a couple suggestions. I'd be interested in reading some of the other replies...... Lots of creative people on this group.

Andy W4OAH in Eureka, Texas

Reply to
AndyS

The most efficient would be to simply swap the batteries.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

or just bring the fresh battery when you actually need to start the car; consider disconnecting the in car battery to reduce "nuisance" loads from the car.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Reply to
no_one

I don't think you can charge one with another battery. The charged battery will only be 12 volts under load. You need 13.5 volts to charge normally. Any time a battery looses a great deal of power, it permanately looses power. It will not last. Jump starting is going to be very hard on the battery. You can use a battery with increased cells to charge a battery, or use two 12 volters and a regulator to deliver a lower charge, longer charge time. There is a FAQ or two on batteries which you shaould read. You can keep a battery trickle charged with a solar unit, which is what i should have done last winter. i have a very small solar unit, thats capable of keeping a battey topped off.

greg

Reply to
GregS

Hi Bill,

I think you can maintain your battery at a reasonable voltage to avoid damage, but I don't think that you can give it a full charge or maintain a full charge. You can use a head light bulb in series with the positive lead to limit the charge current. Make sure that the battery that is used for charging is in good condition and fully charged.

At low temperature the battery to be charged will only accept charge when the voltage is higher then the normal room temperature voltage (about -30 .. -50mV/degr C. for a 12V battery). So to avoid sulfation, you need to charge with higher voltage then your "charger battery" can give. So I agree with Andy to use a step up converter when you may expect low temperature conditions.

You may search on "lead acid battery maintenance" for having a table with charge voltage versus temperature and/or battery voltage versus capacity left.

If you have regular access to the battery, you may take it home, give it a full charge (at room temperature) and put it back. At low temperature, the self discharge is not that high for a f r e s h lead acid battery. You can leave it for about 6 months after giving it a full charge.

Best regards,

Wim PA3DJS

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Reply to
Wimpie

billcalley wrote in news: snipped-for-privacy@a26g2000pre.googlegroups.com:

Get one of those SOLAR panels that plug into the cigarette lighter socket.They are intended to keep a car battery charged,during storage.

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Jim Yanik
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Jim Yanik

innews: snipped-for-privacy@a26g2000pre.googlegroups.com:

Thanks guys -- your recommendations are great stuff! I'll have to look into which way to go next.

Very Best Regards,

-Bill

Reply to
billcalley

if the car's outdoors get one of those solar charging panels. they cost about the same as the battery and there's no maintenance.

or you could take the battery out,

or run a 12V cable (with a fuse at the car end) to somewhere where you can have a charger....

Bye. Jasen

Reply to
Jasen

You need slightly higher voltage than that battery you're attempting to charge. why not set up some 14..16 volt solar panels to keep the car's battery charged ? I know some one that does that now with their camper vehicle at a camp sight that does not have power all year round. it seems to work very nicely. He run's a low power 2 meter repeater from it.

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Reply to
Jamie

Get two 12V motorcycle batteries. Why? smaller, lighter. Hook them in series to give you 24V. Get two 12V lamps, say rated at 1 amp, hook them in series. Now connect the minus of the 24V pack to the minus of the 12V battery. Hook the two series 12V lamps between the plus terminals of the

24V pack and the 12V battery.

If your 12V battery is shorted, the worst that can happen is the two 12V lamps will light normally. This limites the current to, say, two amps. Otherwise the 12V battery will have a 1 amp or so trickle charge from the 24V pack. The amount of charge will be indicated by the brightness of the two bulbs. The capacity of the two smaller batteries must be sufficient to recharge your 12V battery to your satisfaction.

When you get home, recharge your motorcycle batteries.

Al

Reply to
Al

Would work best if the "charger battery" is like an enormous truck battery.

I've tried using the little portable items with a car that isn't driven frequently enough to charge the battery, and in the beginning when there was enough juice to start the car, for some reason just driving it around even for an hour on the highway wouldn't cause the car battery to fully charge, and eventually the car battery got low enough that the portable thing couldn't put it over the top to start the car.

Now I know what you're thinking, that the car battery had just died, because that's what I thought too; but I decided to give it one more chance and connected a little 5 amp Sears charger up for two days before the current meter looked like zero, and the battery has been able to start the car fine even with up to two weeks dead time (as long as I dared leave it) even in the winter. ??

Oh yeah, I had similar bad results with one of those little solar panel chargers that sit on the dashboard, at least in the winter. Summer, it seemed to do better.

Reply to
z

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