Anyone ever tried wiring two 12V loads in series to run off a 24V battery bank?

[garybeck]

I have some challenges designing a PV system for a remote village in Haiti. the loads are: refrigerator, lights, fans, cell phone chargers. I want to keep everything DC for a multitude of reasons.

things would be a little easier if I could go with 24 V battery instead of 12V. it would help with the wire size, fuse, disconnects.... most loads for this system can run 12 or 24, except we want to have some power for cellphone chargers and I don't know of any 24V cell chargers. these common 12V chargers are everywhere:

https://www.qualitylogoproducts.com/tradeshow-promotions/usb-car-adapter-extralarge-276280.jpg

i had an idea, if I wire two of them together in series, i basically create a 24V cell phone charger. the only issue is that both of them have to be in use at the same time. or maybe just having both connected is good enough, and one in use at a time would work.

has anyone tried anything like this?

thanks
gary in vermont (heading to haiti in one month)

[foo1bar]

Get a 24V to 12V converter/regulator.
ex:

https://www.amazon.com/Nextrox-Converter-Regulator-Step-Down/dp/B00BWKXTUU

(No idea if that's a good one or a crappy one - just an example of the category you should be looking for)

Even if both chargers are in use at the "same time", one cell phone will finish charging before the other does - and you'll probably wind up with one of them seeing 20V and the other 4V and fry something.

[Sunking]

Will not work.

[garybeck]

Get a 24V to 12V converter/regulator.
ex:

https://www.amazon.com/Nextrox-Converter-Regulator-Step-Down/dp/B00BWKXTUU

(No idea if that's a good one or a crappy one - just an example of the category you should be looking for)

Even if both chargers are in use at the "same time", one cell phone will finish charging before the other does - and you'll probably wind up with one of them seeing 20V and the other 4V and fry something.

thanks, i talked to my friend who is an electrical engineer and he said the same thing! so I could use one of those regulators, or a battery equalizer

[Mike90250]

...or a battery equalizer

What the heck is a battery equalizer ? I know what Equalizing a Battery is, but something is lost in the translation..

[inetdog]

What the heck is a battery equalizer ? I know what Equalizing a Battery is, but something is lost in the translation..

Links have been posted to a "battery equalizer" which connects to three points on a 24V battery bank, -, midpoint and +.
Instead of regulating 24 down to 12 it uses a current mirror arrangement to draw equal current from both halves of the bank into a DC to DC converter from the upper half which drives the load in parallel with the lower half.
Instead of regulating, the output voltage goes down to remain 1/2 of the total bank voltage.
In theory it can be more efficient, but that is just theory.

Not sure whether it also serves to equalize end of charge voltage when the net flow is into the bank (just between - and + terminals.)

[Mike90250]

Ah, a redneck cell balancer. Got it. Thanks
I'd be more confident of a 24-12 down-converter - much simpler.

[Bala]

These were fitted to some of the truck I work on, I have thrown a few in the bin.

If you search Redarc CE10 you will find them.

The REDARC 10A Charge Equaliser is designed to manage a high current 12 volt supply in a 24 volt vehicle. It allows 12 volts to be be tapped from series batteries while still maintaining eqaal charge

[garybeck]

What the heck is a battery equalizer ? I know what Equalizing a Battery is, but something is lost in the translation..

this is a battery equalizer. not sure if it's available anymore. kind of an old catalog

[littleharbor]

Vanner appears to still be in business. I bought one of their 60 amp equalizer versions a while back. I can say this, they are quite heavy and appear solidly built, for whatever that's worth. I never have used it as it appears to be intended for a 2-12 volt battery bank, maybe what you would find in a vehicle with a 24 volt system. For a higher count 24 volt battery bank I'm not sure how well it would work as it looks like it balances voltage between TWO batteries. I found one picture with a diagram , added here



Vanner battery equalizer.jpg

[littleharbor]

Spec sheet. Vanner spec sheet.jpg

[garybeck]

Vanner has different models. some are for two 12V battery banks. some are for what i'm trying to do - one 24V battery bank with 12V loads, like this one:

http://www.vanner.com/brochures/Battery-Equalizer-PB-6-01.pdf

bottom line is they are more expensive than a 24V - 12V converter which are a lot more efficient than they used to be, so I'll probably go with the latter.

[foo1bar]

I never have used it as it appears to be intended for a 2-12 volt battery bank, maybe what you would find in a vehicle with a 24 volt system. For a higher count 24 volt battery bank I'm not sure how well it would work as it looks like it balances voltage between TWO batteries.

Whether it's physically four 6V units or two 12V units or six 4V units I believe you still could treat it as a two 12V sections and use this equipment.
And if it's used that way from the beginning I don't think it'd be much different results between those scenarios... After all, a 12V battery is made up of six individual 2V cells that are wired together. So four 6V units is still electrically the same as a pair of 12V - just slightly different physical packaging to make it easier to transport, etc.

I don't know enough about this equipment to know if it's a good idea or not in general. I'd probably go with the 24V->12V converter if they're cheaper for good enough quality (cheaper, familiar (to me) technology.) I'd want to see what the efficiency differences are before I chose.

[littleharbor]

So if you have more than one string of batteries ,then what? This is what I am concerned about. You still are only splitting between two 12 volt sections in one string, leaving the other string(s) unbalanced in relation to the string with the battery equalizer.

[foo1bar]

So if you have more than one string of batteries ,then what? This is what I am concerned about. You still are only splitting between two 12 volt sections in one string, leaving the other string(s) unbalanced in relation to the string with the battery equalizer.

You mean if you have four 12V units to make a 24V system and the midpoint isn't connected between the two strings?
Yeah, I'm not sure what that'd do here.
I'd guess that if you were not currently getting sun (or other charging source) that you'd have current flow out of the 2nd set and into the set with the connection.
It'd be a bit weird...

I think the solution to that is the advice I've seen given here multiple times - don't do parallel batteries.