Discussion in 'Electronic Basics' started by [email protected], Aug 31, 2005.

1. ### Guest

We have a photo-voltaic system with a battery bank configured to 24
Volts. There were sound reasons for going this way, but it has made
headaches because 24 V equipment is hard to find and expensive to buy.

My question is this; when we have a few cloudy days and I need to
charge the battery bank, can I just wire up two 12 V chargers in series
to do the trick or is this too good to be true? Would it be likely to
damage the chargers? I would be running these off the dual outputs of a
gas generator.

Reason - 12 v chargers are readily available and cheap. 24 V chargers
are a special order and several hundred dollars.

Thanks for any help!

2. ### DBLEXPOSUREGuest

I would get the manufactures opinion. Not all chargers are created equal.

Check continuity from the negative charger terminal to the ground of the AC
cord, If you have continuity then you cannot connect two of them in series.

If the charger is floating the ground i.e. high resistance from (-) to
ground then, You might take the two 12v Charges, put some sort of dummy load
on them, (individually), say 100 or 50 Ohms. Then measure with your DVM the
DC volts from (-) of Chrgr A to (-) of Chrgr B, Hopefully you will get 0
volts. Do the same from (+) to (+), again, hopefully 0 volts. And now from
(-) of Chrgr A to (+) of chrgr B, Hopefully 12 Volts.

Now call the manufacturer and get an engineer on the horn and tell him you
are going to connect the two together in series and see if says, "no
problem"

I believe I have seen battery charger in the past that where able to do this
but can't remember the Manufacture. I would guess most chargers use a

Also, chargers these days can have some complicated output monitoring
circuitry to more efficiently charge you battery. Putting two in series may
disrupt how this circuitry works?

Good luck

Good luck..

3. ### mikeGuest

Do you have actual 24V batteries? OR series connected 12V?
If the latter and your chargers are isolated, you can probably put
one charger across each 12V. Your average cheapo battery charger like
for a car battery has a transformer and SCR to decide when charging is
done. It's likely to get upset connected in series.
You might be able to put two 12V smaller batteries as buffers on the
chargers and the whole series connected pile of stuff across your 24V
battery bank.
mike

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4. ### Jasen BettsGuest

If the chargers aren't earthed (most aren't earthed), and are of similar type,
that's a viable option.

It is probably better to hook the midpoint of the two chargers to the
midpoint of the two 12V batteries, as that way any slight mismatch between
the two chargers or the two batteries will of less consequence

if you're hoping to replace a "100 watt" solar panel (which can often be
expected to proudce somewhat less in real life) you're going to want about
half that so two 2A (aka 2000mA) chargers would be sufficient (because
chargers can run 24 hours unlike the photovoltaic cell)

Bye.
Jasen