Multi battery charger design PROBLEM

Hi All

I'm wanting to build a charger that can charger multiple 12 lead acid (deep cycle) batteries off an alternator.

The below pic (charger2.jpg) shows the current setup, however this causes some problems, the alternator picks up the voltage from the highest battery and slows down charging, and therefore not supplying enough current for the other batteries.


With my design (charger1.jpg), I would use a uC to read the voltages independent, and with the use of relays isolating each battery so it can be charged separately. Basically on start up, it would charge batt1 until set point is reached, then engage batt2 before disconnecting batt1 and so one, and if all batteries are full then it would connect all batteries to the alternator to keep them maintained.

Does this sound like it could work, or are the any suggestion of a better way?

Thanks in advance!

I think that you are overcomplicating things, because you have misunderstood how voltage is distributed.

In you current setup, with the batteries in parallel, the voltage on all of the batteries is the same, assuming that you have thick enough wire joining them.

That's fine for charging lead acid batteries as they take what current they need to charge when fed from the 14.4 V of the alternator. If the voltage is below that, the alternator will be giving it's maximum output, so you're getting all you can hope for.

I wouldn't change what you are doing. If you are getting significantly different voltages on batteries that are in parallel, buy thicker wire.

I understand what you say, but in practice thing operate differently. Sometime batteries charge differently according to there condition, and especially when there is no load present.

You can charge a bunch of batteries in parallel , but when isolated they have different voltages ( when there is a short charge period). for this reason I want to charge them independently.

Lighty said:

You can charge a bunch of batteries in parallel , but when isolated they have different voltages ( when there is a short charge period).

Click to expand...

Does that mean that they even out after a longer charge period? The alternator will put out its maximum current until the voltage is up to 14.4 V or so. At that point the voltage is really as high as you should take a battery to, and all the batteries are at the same voltage, so you are charging all of them as fast as you can.

Separating the batteries can only decrease the current from the alternator.

If you want to go ahead, get a load of switches to do the switching manually, just so that you can find out how you want to charge the batteries, and how you would want an automatic system to work.

I still think that you will find that you will only slow down the charging.

To avoid mismatched charging voltages early in the charge cycle, configure the wiring so that there is equal voltage drop to each battery:

helo..anyone can help me....
anyone know how to design the smart charger..
the charger will be charged:
1-lead acid
2-nickel-cadmium
3-lithium-ion
4-lithium-polymer

Vo=1v~24v, I=4A
..please help me..=(