24v series single battery 12v

Majkhands

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I have a 12 volt peltier cooler I would like to connect to a single 12v battery. The load is minimal but continuous. I would expect the system would balance itself considering the large cables connecting the two in series.
For small load circuits I do not see a problem. Please enlighten me.
Thank you.
 

rmaddy

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Your question is really unclear.

Are you saying that you have two 12V batteries connected in series to make a 24V bank? And are you then asking if you can connect a 12V load to just one of the two 12V batteries?

If that's your plan you need to change your plan. Never connect loads to just one battery in a series of batteries. It's really important that batteries in series always be at the same voltage and SOC. Adding a load to one of the batteries prevents this from happening. In the end you cause under charging and over discharging of one battery and over charging and under discharging of the other.

The proper solution would be to get a 24V -> 12V DC-DC converter added into your 24V system. Connect a 12V fuse panel to the converter. Then wire up your 12V loads to the 12V fuse panel.
 

Majkhands

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Thank you ready. Yes that is what I intended to convey. I have 24-12 converters. They are 40 amp and I am using a 10amp power controller. I am concerned that is an extreme mismatch. I believe I risk melting the controller despite under 10amp circuits being run.
 

rmaddy

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What is a 10A power controller?

You have more than one 24V->12V DC-DC converters?

Perhaps you should post a schematic of your setup.
 

Majkhands

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Hello again rmaddy,
I am off grid and playing with this system. I followed Will's 4kw system with all of his recommended components.
I recently sold most of the panels to upgrade to larger wattage. Until they arrive, I still have small circuits to run for my aquaponics systems, led lighting and other small draws.
I require a surprisingly small amount of power in my world. 4k is over kill. But hey I love solar.
Sorry power controller is charge controller, 10 amp PMW cheap extra component lying around.
 

rmaddy

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OK. I'm not sure what your concern is between the solar charge controller (SCC) and the 24V->12V DC-DC converters. They have nothing to do with each other. The SCC is charging your batteries (I assume the SCC is 24V). The DC-DC converter is being powered by your batteries.

As long as your loads don't drain the battery faster than your SCC can recharge the batteries you should be fine. Worse case, if everything is setup correctly, your batteries will cutoff and your loads will stop receiving power when the battery voltage gets too low. But it's not going to affect your SCC at all.

Also keep in mind that a 40A DC-DC converter can supply up to 40A on the 12V end. If you only connect 5A or 10A of loads to the converter then your converter will only provide those 5 or 10 amps. And the 24V side of the converter will only be drawing (roughly) half that many amps from the battery.
 

Majkhands

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I have connected the converter directly to the batteries but the load attached appears to drain the battery too far. Using the batteries to extend the lighting in the greenhouse now that the days are growing shorter.
I tried connecting the converter to the output side of the charge controller but it popped and fried the controller. It was a cheap one so I was not concerned.
I wondered if using the resistor trick may have prevented the pop and saved the system.
Thank you for all of your help. I have ideas about ways the system might work then come here to find out why those ideas are not functional. I realize just because it works for now is not a good long term solution.
So far it is small loads with little risk. Mostly 12v and a few amps. I enjoy the education in those mistakes. I am not willing to play with real power and circuits, in that manner, we all know the outcome.
Again, thank you.
 

rmaddy

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What kind and size batteries do you have?

If you only have 12V loads why are your batteries setup for 24V?

Can your SCC handle 12V and 24V? Many will autodetect the correct voltage.

If you only have 12V loads and your SCC works with 12V then I would put the batteries in parallel and then you can eliminate the 24V->12V DC-DC converter.
 

Majkhands

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My panels are 24v. A concern to me at first, until I realized the advantages.
My cheap charge controllers are auto 12, 24v. The 24v do not step down so the converter comes into play. The world is setup for 12vdc or 110ac. The other voltages at first seem to comical things, but I appreciate them now. I hesitate to exceed 24v because of the shock risk, but I have experienced the bite of 110vac frequently enough not to be concerned any more.
I do have larger future loads, including industrial 3 phase 480 equipment. That is the reason for the upgrade panels.
I am working my way to industrial scale solar arrays the slow way, with hands on experience.
For now until I am more experienced I live in the safe zone of under 30v.
 

MisterSandals

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My panels are 24v. A concern to me at first, until I realized the advantages.
My cheap charge controllers are auto 12, 24v. The 24v do not step down so the converter comes into play.
So you have a 24V to 12V converter between your SCC and battery?

That’s probably not a good idea% Your SCC is specifically designed to detect battery voltage (12 or 24v) when it is connected (first, always before SCC). And it is specifically designed to charge the battery.

It is NOT designed to power a converter. In fact, it probably has no idea what voltage your battery is because it is likely hidden by the converter.

You are using your tools wrong because you do not understand how they work.
 

Majkhands

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I have every confidence you are correct, I do not know where the converter goes. I have had it connected directly to my battery bank all summer. While it has worked stepping down 24v to 12v it has degraded used batteries. Chalked up to experience. They are now cores for the replacement new ones, once I sm clear how it us all wired correctly.
My expectation is it should be wired to the output of the SCC. I tried that the first time but sparked and blew the SCC. It may have been the internal fuse, but I don't remember. I did not wire it between the SCC and the battery connection. I am confident that would confuse the controller, no way to measure the batterys voltage. A ghost drain as it were.
Part of the reason for this detailed share is to demonstrate what does not work and why so others will not need to explore this path.
As a side note. I sold one of the panels to n electrician, he did not know if you could draw a 12v circuit as I questioned in the first part of this post. I was not as disappointed I did not know if a professional did not either. That is the reason I tried it and questioned it here.
 

MisterSandals

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My expectation is it should be wired to the output of the SCC. I
What are you using the converter for?
Are your loads 12V?

It sounds like you created a 24V battery bank without understanding that your SCC can charge a 12V battery with a panel that produces 36V.
MPPT SCCs do this better but a PWM will work much better than whatever the converter was messing up.

Is there a reason you cannot wire your batteries to 12V (in parallel) and use your 12V battery bank as it is intended?
 

Short_Shot

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The panel voltage is irrelevant relative to the battery voltage as long as you have a solar charge controller between the two.

You can put 500 volt panels on a 12 volt battery with the appropriate charge controller.

The charge controller accepts the panel input up to whatever voltage its rated for.

It then outputs the appropriate voltage for your battery, assuming it's rated for that. 12v solar controller on 12v battery, 24v controller for 24v battery, and so forth.

Edit: clarified statement about panel and battery voltage relative importance.
 
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Majkhands

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Thank you both. I assumed if I connected a 12v battery bank to a SCC that was receiving 24v(36v) from the panels I would fry the batteries immediately.
I read the instruction as limited as they were. Read all the posts I could find here and did not know the SCC was capable of stepping down the output to the battery.
If that is the case I do not need a converter in the system at all.
It shows ask a silly question and learn something very useful.
Thank you I will hook it up tomorrow.
 

Majkhands

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I knew those were the rules, now it makes sense why.
I assumed it would damage the SCC if were not hooked up first.
 
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