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Old 04-19-2018, 07:30 PM   #1
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Why 12vdc over 24vdc?

I see everyone running 12volt systems in their skoolies. Wondering why?

24-->12 step down converters seem pretty cheap
You can run a smaller MPPT Charge Controller saving $$
24Vdc is supposed to be more efficient right?
I guess number of batteries in your bank may be a hinderance. Can't run 6 6v batteries and make 24v.

Is there any other reason not to run 24v?
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Old 04-19-2018, 07:35 PM   #2
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Quote:
Originally Posted by dspizzle View Post
I see everyone running 12volt systems in their skoolies. Wondering why?

24-->12 step down converters seem pretty cheap
You can run a smaller MPPT Charge Controller saving $$
24Vdc is supposed to be more efficient right?
I guess number of batteries in your bank may be a hinderance. Can't run 6 6v batteries and make 24v.

Is there any other reason not to run 24v?
I would hazard to guess it's because the vast majority of them are factory built for 12v. It's sort of the standard of the automotive industry, and manufacturers and school districts like being able to buy widely available, reasonably priced parts as opposed to special-order 24v parts.
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Old 04-19-2018, 07:38 PM   #3
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You can run 6V batteries in a 24V system.

You string 4 in series, then run as many of the strings in parallel that you like.
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Old 04-19-2018, 07:42 PM   #4
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The question was more for the house batteries. Why dont people run 24v systems more often?
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Old 04-19-2018, 07:52 PM   #5
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Originally Posted by dspizzle View Post
The question was more for the house batteries. Why dont people run 24v systems more often?
Because many more appliances and fittings are available for 12V, and at more reasonable prices, than can be found for 24V service.
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Old 04-19-2018, 08:20 PM   #6
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Makes sense. I kind of talked myself out of it simply by the number of Batteries I can have. Was planning on 6 6v. So 24v seems like a no go from that alone...
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Old 04-19-2018, 08:41 PM   #7
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Makes sense. I kind of talked myself out of it simply by the number of Batteries I can have. Was planning on 6 6v. So 24v seems like a no go from that alone...
Yes, you would need either 4 or 8.

Remember that batteries have the same amount of actual power in them regardless of the voltage it is delivered at.

So 4 x 6V 225 amp hour batteries have the same power whether they are configured as 12V @ 450 Amp hour, or 24V @ 225 Amp hour.

The measure that ignores voltage is kilowatt hours. If you run the numbers you will find they are the same.
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Old 04-19-2018, 09:10 PM   #8
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Right. I was more interested in regards to voltage loss, and wire sizing.

As I understand it, its much easier to have higher efficiency with a higher voltage. But maybe it doesn't make a big enough difference for the price.
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Old 04-19-2018, 09:35 PM   #9
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Right. I was more interested in regards to voltage loss, and wire sizing.

As I understand it, its much easier to have higher efficiency with a higher voltage. But maybe it doesn't make a big enough difference for the price.
Your understanding is correct. That's why long-distance transmission lines run anything up to 400 000 volts.

When we convert a bus it's a bit different. Do your calculations based upon a 3% maximum voltage drop then go up at least one size on the wire. We aren't buying enough for it to break the bank.

Vehicle manufacturers buy the stuff by the mile, so for them it makes sense to use the smallest wire that can be made to do the job. We have a little more luxury than that.
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Old 04-20-2018, 07:05 AM   #10
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In general the higher voltage systems are more efficient, not only in copper losses. Higher voltage means lower amperage for the same load.
The brushes in your starter / wiper / fan motor can live longer because of reduced current.

the switching transistors , mosfets, igbt's have less voltage drop with a lower current as well. so if you heavily rely on an inverter / solar charger / solar then higher voltage would make a lot of sense.


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