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Old 30-08-2018, 07:37   #1
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24v to 12 v

A friend has a 120 amp 24v alternator feeding a 40 amp solar controller to charge 12v batteries.

Would it be better to have a 24v to 12v converter, and should it be 120 amp?


Thank you for any comments...
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Old 30-08-2018, 08:25   #2
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Re: 24v to 12 v

That seems like a real kludge. How is the alternator output controlled?

Why not just use a 12v alternator to start with?

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Old 30-08-2018, 08:36   #3
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Re: 24v to 12 v

Alternators, the same as solar panels don't actually output 12v, they output much more. They then require regulation to bring the voltage down to suitable charging voltages. An unregulated alternator will destroy a battery pretty quickly. A smart charger will regulate the voltage to accommodate battery types and their state of charge while your most basic regulator will pick a charging voltage and you get down to that. Most alternators have these basic regulators inbuilt. I don't know what kind of solar controller you are using but as long as it brings the voltage down to somewhere under 14.4v it should be fine.
Hopefully you will get more comprehensive advice from more of an expert than me!
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Old 30-08-2018, 11:03   #4
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Re: 24v to 12 v

You would need a 240a regulator. As that is the 12v output rating.... not input rating.

Is he running that between a 24vbattery and 12v battery? Or direct from an alt? I can't see the later working to regulate the alt.

If the alt was charging a 24v battery a dc - dc charger would be best.
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Old 30-08-2018, 11:08   #5
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Re: 24v to 12 v

well feeding 100 plus amps into a 40 amp controller might be an issue.
not sure why the dual voltage, just thought it simpler to use a voltage converter rated at alt amps… this is for charging 12v bank.
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Old 30-08-2018, 17:01   #6
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Re: 24v to 12 v

"well feeding 100 plus amps into a 40 amp controller might be an issue."
No real problem there. Either it will blow a fuse, or start a fire. Either way, the problem will be over shortly.

Your friend REALLY might want to do the math: Pay for the fire damage? Or put in properly matched components, even if that means paying an electrician?
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