I have a small battery charger that I installed in the enine compartment of my car.....its plugged into the same circuit as the block heater...it goes on when the block heater goes on (on a timer...goes on at about 4 am until I leave for work.) When not plugged in, the battery charger leads are isolated from the battery by a relay...but when power goes on, the leads are connected.

The output of the charger is 3 amps @ 12 V....its small, about 2 1/2 inches square. Red LED indicates when charging...when battery is charged, it switches to green..(trickle).

Is this bad to do..I mean charge the battery (warm the battery??) when it is connected to positive and neg. battery leads. I read in one of the posts that a car battery should be disconnected when charging to prevent damage to alternator. The charger i have is designed for battery-in-car charging, but I'm not sure if this could damage the alternator.

Thanks,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

What a great idea!

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Think Alternative Energy!
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The 3 amp charge is not doing much to charge the battery in that small amount of time, if your alternator is in reasonable shape. A trickle charge overnight is the best thing to do to your battery, I do my 240D & wife's Jetta overnight once or twice a month. It will not hurt your anternator, jumping a battery with another car or heaver duy charger can cause damage sometimes. But it's rare.

Well it's time to go plug the wife's Jetta into the charger.

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'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

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Nice idea.
I do not see any possible alternator damage with your system.

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I have a Solar Charger for my 99 VW Beetle TDI--I think its maybe a 1 amp(or less0.5A) and I never have a problem. I only use it here in Miami when I am out of town and the car will be sitting for a week or longer, unstarted. Mine plugs into the Cigerette lighter. No Problems!!

Don't most cars disable their outlets with the ignition turned off (all the way off/no key) ??? I know all ours do.....so how would the solar charger, (or any charger of that type) be effective if the power never reaches the battery? I'd think you'd have to have an outlet thats live all the time for it to work.....?

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Correct...

As I said earlier, I isolate both the pos. and neg. charger leads from the battery (when not plugged in) by use of a relay. Is this necessary, or recommended??? I did this based only on a gut feel that it would be preferable not to have the charger connected to the battery when not in use...that there may be a slight drain on battery, or possible damage to charger, or something like that. Is that the case, or is the relay totally unnecessary.

Thanks,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Battery chargers have a diode at the output for protection against back voltage- it conducts in one direction only, and presents a very high resistance in the other direction. Very high resistance, but not a complete open circuit- so it could conceivably discharge your battery if left long enough. The relay makes for better protection against this- now that you have it on there, you might as well leave it.

Dave

Mark it depends on the design of your charger, as to leaving on when charged. The one I use is designed for being left on the battery for long periods and will maintain the battery in a fully charged condition for extended periods.

As for most German cars of the 90's, the cig lighter stays hot when car is turned off. All VW's have been like this for 10 to 15 years. The .05 Amp solar charger that comes with VW's is too light duty to charge the battery much, but will carry the load of the electronic system drain while the car is parked. Someone who had to park a car for an extended period, can't remember exactly how long, but it was somewhere between 6 to 12 months. Anyway the battery, which was fairly new, drained durring this extended period.

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'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

As others observed charging at a low rate is usually quite safe and actually can be a good idea to help lessen the strain on the battery in cold weather. Do check the electrolyte level once in a while though because it can cause a slightly higher rate of evaporation.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
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