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Old 01-10-2017, 11:12 PM   #1
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Charging a car battery


I have a 13.8V 3A power source. Can I charge a car battery with that?

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Old 01-11-2017, 01:02 AM   #2
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Re: Charging a car battery


It will be slow but it will charge a car battery.
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Old 01-11-2017, 01:26 AM   #3
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Re: Charging a car battery


That would make a good trickle charger for a larger battery.
If your car isn't starting it could take all day to charge it.
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Old 01-11-2017, 07:24 AM   #4
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Re: Charging a car battery


How would I know when it is done charging? I don't want to damage the battery or blow anything up. I think an actual "charger" would have some circuitry to shut itself off automatically.
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Old 01-11-2017, 07:59 AM   #5
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Re: Charging a car battery


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Originally Posted by mathmonger View Post
How would I know when it is done charging? I don't want to damage the battery or blow anything up. I think an actual "charger" would have some circuitry to shut itself off automatically.
Yes a real battery charger will have protection circuits, then trickle charge to keep it topped up. That's just a bit lower then what your charger puts out anyways, so you'd be waiting a real long time before you have a problem. As long as you monitor it, it'll be fine.

Why are you asking anyways? Why not just get an off the shelf charger?

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Old 01-11-2017, 08:56 AM   #6
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Re: Charging a car battery


You can get an offbrand battery float charger from Harbor Freight for $9 or a Battery Tender Jr online for around $25. I'd go that route and take the worry out of ruining the battery by over charging.
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Old 01-11-2017, 10:08 AM   #7
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Re: Charging a car battery


Yeah... Sentimental attachment to this power supply. It's kind of a cool thing that not everybody has. I'd like to do something with it. I have an inverter, so my one idea is to make a little portable power pack.

My other idea is something like this:
http://www.instructables.com/id/Elec...val-aka-Magic/
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Old 01-11-2017, 11:06 AM   #8
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Re: Charging a car battery


For the portable power pack, I would not use a car battery. Their life is shortened by deep discharges. You would get better performance from a marine/RV deep cycle battery.

I would not use a small power supply to charge a car sized battery that had been significantly discharged. it would simply take too long for my taste. You would be better off with a real battery charger. Something like a 2/10/50 or larger.

The 3A power supply would be much better suited for the rust removal project.
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Old 01-11-2017, 11:36 AM   #9
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Re: Charging a car battery


I've had one of these to maintain my ZTR for about 5 years and it works very well, also will charge a dead battery overnight, and analyzes,charges, and tells you when the battery is fully charged, and go's into matainence mode, much better to slow charge a battery at 3amp then fast charge.

http://www.sears.com/diehard-battery...p-02871219000P
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Old 01-11-2017, 04:05 PM   #10
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Re: Charging a car battery


Repeated charging of a battery with that particular 3amp power supply (not a charger) will lead to sulfation of the plates. The 13.8 voltage is two low for 12v FLA or AGM batteries, particularly in the bulk and absorbtion charge stages. The voltage is much closer to a stage 3 or float charge voltage.

If you don't hit the battery with a equalization charge periodically, it will die sooner than necessary.
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Old 01-11-2017, 07:40 PM   #11
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Re: Charging a car battery


How to determine when the battery is fully charged:

http://www.aa1car.com/library/2003/us20310.htm

Print off that table and post it in your garage. Note temperature note.
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Old 01-11-2017, 09:39 PM   #12
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Re: Charging a car battery


Quote:
Originally Posted by Oso954 View Post
Repeated charging of a battery with that particular 3amp power supply (not a charger) will lead to sulfation of the plates. The 13.8 voltage is two low for 12v FLA or AGM batteries, particularly in the bulk and absorbtion charge stages. The voltage is much closer to a stage 3 or float charge voltage.

If you don't hit the battery with a equalization charge periodically, it will die sooner than necessary.
Hey... Oso.... could you explain equalization charge to me...

(Thanks... My wifes car is a BMW known to have an electric drain problem when trips are repeated and short. I have a shumacher charger, and have to charge it every so often, Just want to learn more.)

I'm using a Bosch FLA.
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Old 01-11-2017, 10:21 PM   #13
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Re: Charging a car battery


An equalizing charge is nothing more than a deliberate overcharge to remove sulfate crystals that build up on the plates over time. Left unchecked, sulfation can reduce the overall capacity of the battery and render the battery unserviceable in extreme cases. An equalizing charge also reverses acid stratification, a condition where acid concentration is greater at the bottom of the battery than at the top.


http://batteryuniversity.com/learn/a...alizing_charge
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Old 01-12-2017, 11:34 AM   #14
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Re: Charging a car battery


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Originally Posted by Oso954 View Post
Repeated charging of a battery with that particular 3amp power supply (not a charger) will lead to sulfation of the plates. The 13.8 voltage is two low for 12v FLA or AGM batteries, particularly in the bulk and absorbtion charge stages. The voltage is much closer to a stage 3 or float charge voltage.

If you don't hit the battery with a equalization charge periodically, it will die sooner than necessary.


Should have added mine has a desulfator built in also.

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