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I have a heavy 14.4V 1.5A heavy battery charger I would like to use to charge my car battery (over time, monitored for heat in a well ventilated area).

When I plug the battery to the charger as is, I believe it turns off as the led doesn't turn on and the Voltage I read is 10.8 which is what the battery is at. When I measure the charger on it's own I get 13V.

Can someone help me modify it to make it work? I'm comfertable soldering and researching if you don't feel like giving a specific answer :). Images of the transformer and circuit:

Transformer

Circuit

Details

Thanks in advance for any efforts :)

Edit - I sketched a diagram of the circuit on tinyCad, here it is: circuit

I noticed that there is an earth connection for the battery, but only 2 connections to the wall socket. I don't get how it would be earthed, but perhaps the third connection is needed to turn it on? It is directly connected to one of the switch's 4 'legs'.

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  • \$\begingroup\$ Less than 2a is usually considered a "Trickle Charger". Start with the car battery charged, then it may help hold a charge over time. \$\endgroup\$
    – Optionparty
    Commented Jan 18, 2015 at 0:23
  • \$\begingroup\$ Noted, I'll see if I can get it charged first. You believe once it's charged up this circuit will then work? I thought I should still be able to charge it now and would just take longer no? \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 0:26
  • \$\begingroup\$ Battery voltage should rise somewhat if charger working. Connection & operation of what appears to be a relay is not obvious. \$\endgroup\$
    – Russell McMahon ♦
    Commented Jan 18, 2015 at 0:39
  • \$\begingroup\$ Do you think it would work if I just take it apart, and connect the low voltage end to Rectifier-->Diode-->Capacitor-->battery (and add resistors if the aperage goes up)? \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 0:45
  • \$\begingroup\$ I just tested with the tool's battery that the charger is intended for - when I hook up the T connection it charges, and when I don't the switch kicks in. The battery is came with has 3 connections, + - and T. Any idea what I could I plug to the same terminal on the board to make it work ("To battery ground" in the diagram above)? \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 4:59

2 Answers 2

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It looks like you're trying to repurpose a charger that was originally intended for some sort of tool battery, judging from the socket built into the case.

It also appears that said battery leaked at some point into the charger, given all of the crud all over the case, contacts and PCB.

You really need to clean the corrosion off of everything, and verify that all of the connections on the PCB and the rest of the wiring are still good.

The relay is probably there to switch between "fast" and "trickle" charging modes, as indicated by the labels on the LEDs. It would be worth your while to trace out the circuit and draw a schematic diagram, so that we all have a reference for further discussion.

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  • \$\begingroup\$ Thanks, I will create a diagram and post it here. The mess is white paint that got in there a bit, I cleaned it with alcohol. \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 0:58
  • \$\begingroup\$ I made a diagram of the circuit and updated the post, would be happy to hear any feedback. I hope I got it all right, double and triple checked. \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 3:48
  • \$\begingroup\$ I just tested with the tool's battery that the charger is intended for - when I hook up the T connection it charges, and when I don't the switch kicks in. The battery is came with has 3 connections, + - and T. Any idea what I could I plug to the same terminal on the board to make it work ("To battery ground" in the diagram above)? \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 5:01
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The charger appears to be unfiltered, so it will produce pulsating DC - this is not a problem for battery charging. Your meter is probably reading a sort of average of the pulsating DC, hence the apparent low voltage.

In any case, a 1.5 Amp charger is grossly undersized for charging a car battery, particularly one as far discharged as your is. You should get a charger rated at 10 Amps or more for this application.

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  • \$\begingroup\$ Thanks for your response. From what I read up on, to recover a worn battery it should be charged at 14.4V 2A for a few days, it breaks up the sulphation on the plates and restores it to new condition. Isn't a low average also bad though, taking pulsating into account? From what I understand it's important that it's charging at a higher voltage than the battery itself. I also noticed there is no rectifier in there, how come it's putting out DC? \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 0:23
  • \$\begingroup\$ The large cylindrical things at the bottom left corner of the board are probably the rectifier diodes. If the battery is badly sulfated, you should probably replace it rather than trying to revive it, if you want it to be reliable in future. \$\endgroup\$
    – Peter Bennett
    Commented Jan 18, 2015 at 0:28
  • \$\begingroup\$ You restoration comment is for a "Desulfator" combined with a charger. That's not what you have. \$\endgroup\$
    – Optionparty
    Commented Jan 18, 2015 at 0:31
  • \$\begingroup\$ I'm doing this as a project, got very curious on the matter. @Optionparty - from what I understand, if you charge the battery at 2% RC 14.4V is what leads to Desulfate. Some chargers send pulses but this is not a must/proven to work better. I speak with little experience (just a week long obsession but I learn fast :) ). \$\endgroup\$
    – Gil
    Commented Jan 18, 2015 at 0:39
  • \$\begingroup\$ @Gil I have only read of pulse versions, and have never a conformation that any Desulfation actually works. A simple pulse ckt with short leads would be interesting to try, but I don't have the time, or I would. circuitlab.com/circuit/yr82k8/improved-desulfator \$\endgroup\$
    – Optionparty
    Commented Jan 18, 2015 at 20:17

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