E-Mountainbike Project

[J57ltr]

Typically you charge a Pb battery to 2.4V per cell so a 21.6V power supply. Most 24V power supplies are adjustable into that range. All you have to do is limit the current to a point lower than the output current of the power supply.

Say you have a 24V power supply rated at 5 amps You would need a resistor rated at about 5 ohms and 120W. That's a little on the large side and a pretty high charge current. about a 1 to 1.5 amp rate is a little better for up to about 12 Ah. So you would still need 5 ohms but only about 40 watts. Basically the resistor would limit the current coming out of the power supply and keep it from tripping or just smoking.

http://www.mpja.com/prodinfo.asp?number=16008+PS

Jeff

[BL_RV0]

I don't have a 24v PS though. Mine's 13.8v and 8.5a. Works fine for me, so I have no plans to upgrade it.

[J57ltr]

That was just in case you wanted to charge both batteries at the same time or if you wanted to use the 18V battery.

Jeff

[BL_RV0]

I was thinking of charging them as a 12v 24ah setup. Would that work with my current PS?

[J57ltr]

With what you have yes, the only thing you have to worry about is that the lower the voltage on the batteries the more current they are going to draw, so it might trip the PS when you first start to charge them. The only other thing you have to worry about is charging them too fast. I think a 12 Ah battery is recommended to be charge at about 2.5 amps max, but with them in parallel that would be 5 amps. If you have an adjustable power supply (most are) you can lower the voltage and watch the current drop and then slowly increase it until you are at the 14.4V value. I have been using a regular car charger the maintance free kind with a couple of resistors in series with the + output.

Or I will use my 60 amp power supply and just watch the gauges set it for about 1 amp charge and when the current drops I increase the voltage till I am back to 1 amp then repeat until I am at 14.4.

The maintance free charger is the easiest way since it will only go to 14.4V

You could get a 24V power supply and charge them in series and not have to remove the batteries and reconnect them.

Cheaper ones:

http://www.mpja.com/prodinfo.asp?number=16854+PS

http://www.mpja.com/prodinfo.asp?number=16855+PS

Jeff