Is it OK to charge a car battery without disconnecting it from car wiring?

 

hi,
If you mean when the battery is in the car, it is OK to charge it.
E

 

hi,
If you mean when the battery is in the car, it is OK to charge it.
E

Thanks. The battery is dead, so I am hooking up an external charger to it.

 

Have done that myself many times.

 

If the battery is dead and been left like that over 24 hours, it will never recover fully. If it is very dead, the charger may refuse to charge.

 

the charger may refuse to charge.

Not likely if it's a dumb old charger like I have.


Long live the deciBel !

 

Is it OK to charge a car battery without disconnecting it from car wiring?

Yes - that's what the alternator does.

 

Yes - that's what the alternator does.

I routinely have charged batteries while installed and connected in the vehicle. Of course that is using a normal small 8 amp charger. With a super high power charger , say 20 amps or more, doing a quick charge, disconnecting may be smart.
And certainly if a regular wet cell battery goes totally flat it will not be as good after that.

 

I routinely have charged batteries while installed and connected in the vehicle. Of course that is using a normal small 8 amp charger. With a super high power charger , say 20 amps or more, doing a quick charge, disconnecting may be smart.
And certainly if a regular wet cell battery goes totally flat it will not be as good after that.

I tried with a small charger but disconnected the charger before actually starting the car - no luck but it was cold outside so the engine struggled and gave up. Now I have a larger power supply 20 Amp so want to try and start with this power supply connected while I try again to start - any thoughts?

 

I tried with a small charger but disconnected the charger before actually starting the car - no luck but it was cold outside so the engine struggled and gave up. Now I have a larger power supply 20 Amp so want to try and start with this power supply connected while I try again to start - any thoughts?

Depending on vehicle the start current is going to be very high, as much as a few hundred amps. Unless you have a good automotive charger with a start function this is not a good idea. You have a battery which is low to begin with. You have a 20 amp supply available across the battery. Then you place a load easily exceeding 100 amps (depending on vehicle) on the battery and connected charger. Something not good is likely to happen. Even with a smart charger which should disconnect with that load this is not a good idea.

Is it OK to charge a car battery without disconnecting it from car wiring?

This is not where we started. The answer to your original question was yes. We seem to have wandered off the path. There is a reason automotive chargers with the Start Boost function have a higher price ticket.

Ron

 

There is a reason automotive chargers with the Start Boost function have a higher price ticket.

None of the ones that can be carried around will ever start a car, even though that is their claim. It takes one on wheels that also takes a couple of people to lift it, to really start a car.

 

None of the ones that can be carried around will ever start a car, even though that is their claim. It takes one on wheels that also takes a couple of people to lift it, to really start a car.

Not on their own, but a relatively (and surprisingly) small booster can save your butt. My daughter's Subaru has a weird glitch where it'll run the battery down maybe once in 200 days. She has a little booster battery she plugs into the cigarette lighter (OK, "accessory port", there's no lighter) and it has saved her many times.

This shocks me and like you I would have predicted no success with such a thing. I speculate that it keeps voltage at the computer from falling too low while cranking with the drained, but not completely dead, main battery. My boat's battery will spin the starter just fine at 9V, but the engine will never start at that voltage because the computer won't let it. That's the source of my theory about the Subaru.

 

None of the ones that can be carried around will ever start a car, even though that is their claim. It takes one on wheels that also takes a couple of people to lift it, to really start a car.

I have one that literally fits in my pocket that has no problem starting my 1988 F-250 with a 460 c.i.d. (7.5 liter) engine in it, even when the battery is so drained that the solenoid will only click.

I was turned on to these little LiPo-based jump starters when I had the truck in the shop getting my lift gate installed and when I went to pick it up the battery, which was failing, couldn't turn over the motor. So the guy came out with the Microstart that was perhaps 2" by 1" by about 10" with these tiny little clips and my eyes went wide with disbelieve. I just knew that this wasn't going to work. He connected and the truck cranked like it had a new battery in it! Fired right off. Drove from there straight to an auto parts store and got a new battery.

But they aren't cheap -- he said that that one was $300. I bought a much cheaper one, about $80, and discovered that while it was useful if the battery got to the point where it was cranking slowly, it didn't have enough power to crank if it was below that. So I bought a $200 unit and it works as advertised. Not surprisingly, you can't crank very long with it, but it has always been enough to light it off -- even when my big charger (on wheels) can't do it with it's Start option, since it can only put out 200 A.

I'm still amazed by the thin lead wires and battery clips on those things -- but they actually handle the few seconds of current quite well.

 

Now I have a larger power supply 20 Amp so want to try and start with this power supply connected while I try again to start - any thoughts?

It would likely overload the supply some when cranking, but since that normally only takes a few seconds until the engine starts, I doubt that it will damage the supply.
A battery charger is typically designed to limit the current since the current can get very high when charging a dead battery.

 

My employer company proved otherwise: the 12 volt, 7.2 amp hour battery CAN deliver 100 amps for almost a minute, with a terminal voltage of over 9 volts. And a terminal voltage of over 11 volts for quite a few seconds. So if the only problem is a weak battery that should start a modern fuel injected auto engine. The booster battery MUST be in good condition and fully charged for that to be possible. And there is no promise of long battery life.
Our product used three of the 7.2 AH batteries in series, regulated down to 24 volts, to power in-vehicle cameras and lights for crash test filming. The system powered four 24 volt lights and two 20 amp film cameras for crash test recordings.

 

@wayneh @WBahn You guys are talking about something totally different than a battery charger. I was answering reloadron that was talking about a battery charger with a boost function. I have 2 of those and they won't help turn over a mostly discharged battery to help start a car. I also have one of the Li-po jump packs. They do work, but they aren't battery chargers.

The tread started talking about charging a battery in a car, but wasn't about jump packs.

 

None of the ones that can be carried around will ever start a car, even though that is their claim. It takes one on wheels that also takes a couple of people to lift it, to really start a car.

Agree, the good ones have wheels for a reason.

Ron