# 24v to 12v



## Jack in VA (Jul 24, 2003)

I was given a small (12"x24") solar panel(arco).Has no specs on it but determined it's 24v. I also have half a dozen 12v gel-cell batteries, also given to me. So, so far I have zero $ invested. What's the cheapest way to convert to 12v to keep batteries charged, or just run directly to 12v appliance, such as a 12v fan(s). I've seen 24v to 12v converters for as cheap as $30 and complete units that convert and charge control etc for $130. Not sure how I'd even use this, but one thought was to run directly a fan or two in my small greenhouse. I'm assuming it would only need to run when the sun is shining, so storage shouldn't be an issue.
Would be nice to charge the batteries, which would primarily be used for power outages, or maybe some outdoor lighting. Could I "manually" charge the batteries just by running the panel thru a converter and "watching" it with a voltmeter? Right now this is just a toy for me, so I don't wanna spend too much. Have I made any sense? BTW, I do have a cheap 300w inverter.


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## wy_white_wolf (Oct 14, 2004)

1. Get a 24V charge controller and charge the batteries in pairs wired in series. When using then wire the pair parrallel so the drain tha same amount. Max VOP (voltage output) needs to be at least 36volts for this. Most 24v panels have a VOP between 38 and 40 volts.

2. Whats the max VOP of the panel? If you can find a 12v charge controller that can handle the VOP of the panel on the input side you could charge the batteries without a convertor (one at a time or all wired parallel).

No matter which way you go make sure the charge controller is for gel cells. The voltage requirements on them is slightly different then lead acid batteries.


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## Jim-mi (May 15, 2002)

I highly dought that the old Arco is wired for 24.
You might see close to that with "open circuit" voltage readings . . .but not 24 in that size pannel


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## Jack in VA (Jul 24, 2003)

I'm reading about 40v open circuit. I've heard something about using diodes instead of a charge controller, in a pinch, but not sure about this.


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## wy_white_wolf (Oct 14, 2004)

40V open ciruit would be for 24v systems. You got that right. 

Diodes only control the direction of flow, not the quality. They are needed to keep the panel from discharging the batteries at night if the charge controller doesn't have them built in.

Don't know what kind of problems you would have with a 24VDC-12VDC convertor.

You really have to watch them trying to charge without a charge controller. I think you could only get about 80% charge in the batteries since you'd have a hard time float charging them (not even sure about float chargeing gel cells). 

Might be easier to check the voltage before charging and figure out how long it would take to charge. You would need to know the amp rating of the panel for that.

If you watch Ebay 24v controllers come up every once in a while.


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## PD-Riverman (May 24, 2007)

Jack in VA said:


> I was given a small (12"x24") solar panel(arco).Has no specs on it but determined it's 24v. I also have half a dozen 12v gel-cell batteries, also given to me. So, so far I have zero $ invested. What's the cheapest way to convert to 12v to keep batteries charged, or just run directly to 12v appliance, such as a 12v fan(s). I've seen 24v to 12v converters for as cheap as $30 and complete units that convert and charge control etc for $130. Not sure how I'd even use this, but one thought was to run directly a fan or two in my small greenhouse. I'm assuming it would only need to run when the sun is shining, so storage shouldn't be an issue.
> Would be nice to charge the batteries, which would primarily be used for power outages, or maybe some outdoor lighting. Could I "manually" charge the batteries just by running the panel thru a converter and "watching" it with a voltmeter? Right now this is just a toy for me, so I don't wanna spend too much. Have I made any sense? BTW, I do have a cheap 300w inverter.


'

Jack, Most 24 to 12 volt regulators will probably "Fry" from the 40 volts. If you don't want to spend any money and You want to "Play" just hook two 12 volt batteries in series and watch/check them with a volt meter. You can keep changing the batteries around as you use them. If you are not going to use the batteries just unhook the panel. I have had a battery hooked to a 15 watt panel without a charge controller for several years with no problem, but I do use the battery every night for lights and it was a free gel cell battery taken out a computer battery back-up system. Just Play And Have Fun. If You decide later---then you can spend the money.


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## Jim-mi (May 15, 2002)

If you have the right multimeter then do a short circut currant test. 
With that small a pannel the SC won't be much.

BTW that $30 24-12 converter is a can of smoke just waiting to go pooofff


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## Blu3duk (Jun 2, 2002)

I dont own any stock n the company but I like the Xantrex invertors, and if and when i go to setting up a system i like the bigger ones that are set up for the 48 volt systems which will kick the juice out at a smooth 110 AC and even 220, the one a friend has hooked to a pair 24 volt forklift batteries will run a small industrial shop..... but he only has it hooked up for his house trailer currently, though his shop will be completed this summer.... so he sez.

and yes i know the OP wants to just convert from 24 to 12 volt and such a stepdown convertor probably exists but why go that way unless you already have the 12 volt appliances installed? if you are gonna kick it to another voltage go for the invertor and go to AC is what ive been told..... though i know you lose efficiency.

William


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