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Old 06-20-2021, 05:18 PM   #1
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12 volt or 24 volt system?

Hi, I've heard from some that a 24 volt system is more efficient/better than a 12 volt system.

I have 1,360 watts of solar. I planned on getting 6 golf cart batteries that are 6 volts each and pairing them to be 3 batteries at 12 volts. I then learned that I would likely need 2 charge controllers to handle that power in a 12v system.

Theoretically, if we got 8 batteries and paired them together to be 2 sets at 24 volts... What would be the pros and cons? Would it be worth the time, space, money, and weight?

Can someone explain to me why a 24 volt system is better or worse?

Thanks!

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Old 06-20-2021, 05:40 PM   #2
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Originally Posted by Ross&Hailey View Post
Hi, I've heard from some that a 24 volt system is more efficient/better than a 12 volt system.
Depends on your application/needs.

Quote:
Originally Posted by Ross&Hailey View Post
I have 1,360 watts of solar. I planned on getting 6 golf cart batteries that are 6 volts each and pairing them to be 3 batteries at 12 volts. I then learned that I would likely need 2 charge controllers to handle that power in a 12v system.
This is because 1360W / 12V = 113.33A, so you'd need either one charge controller capable of over 100A, or enough controllers to add up to that number.

My rule is 100A- 1200W charge/discharge, look at 24V, and 2400W charge/discharge, look at 48V. There are potential benefits to go 24V in your case.

Quote:
Originally Posted by Ross&Hailey View Post
Theoretically, if we got 8 batteries and paired them together to be 2 sets at 24 volts... What would be the pros and cons? Would it be worth the time, space, money, and weight?

Can someone explain to me why a 24 volt system is better or worse?
Pros to 24V:
  • Halve your amperage requirements for all charge controllers and wires. Therefore, you can use smaller wire for the same load at 12V, or, use the same-size wire you'd need at 12V and suffer less losses.
  • Inverters have to work less hard to convert voltage. At 12V a leap to 120V is 10x, to 240V / split phase is 20x- at 24V this is halved, making the inverter more efficient. Same if your inverter also charges!
  • Some DC appliances like mini fridges take 24V natively, which is a win for efficiency.
  • Batteries are less stressed by needing half the amperage for the same load, which is another win for efficiency. Especially for lead acid, a battery drawing .5C will yield (slightly) more energy than a battery drawing 1C, for instance.
Cons to 24V:
  • You need to convert to 12V for 12V appliances. On the flip side, this can improve performance and the lifespan of equipment by feeding 12VDC appliances a consistent voltage rather than the typical range lead acid batteries- roughly 11V - 14.4V.
  • Fewer devices take 24V DC natively than those that are available in 12V DC.
  • Due to the added components for conversion, the resulting system is more complex in that regard.
  • Batteries wired in series will not equalize like those wired in parallel. Over time they may drift apart, requiring balancing.

Overall, given that you anticipate charging at over 1200W, I'd recommend 24V. If you anticipate heavy inverter use or to wire your inverter into an AC distribution panel, I'd recommend 24V doubly so.

I run 48V in my full time rig and 12V in my shorty.
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Old 06-20-2021, 06:07 PM   #3
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Originally Posted by kazetsukai View Post
Depends on your application/needs.

This is because 1360W / 12V = 113.33A, so you'd need either one charge controller capable of over 100A, or enough controllers to add up to that number.

My rule is 100A- 1200W charge/discharge, look at 24V, and 2400W charge/discharge, look at 48V. There are potential benefits to go 24V in your case.


Pros to 24V:
  • Halve your amperage requirements for all charge controllers and wires. Therefore, you can use smaller wire for the same load at 12V, or, use the same-size wire you'd need at 12V and suffer less losses.
  • Inverters have to work less hard to convert voltage. At 12V a leap to 120V is 10x, to 240V / split phase is 20x- at 24V this is halved, making the inverter more efficient. Same if your inverter also charges!
  • Some DC appliances like mini fridges take 24V natively, which is a win for efficiency.
  • Batteries are less stressed by needing half the amperage for the same load, which is another win for efficiency. Especially for lead acid, a battery drawing .5C will yield (slightly) more energy than a battery drawing 1C, for instance.
Cons to 24V:
  • You need to convert to 12V for 12V appliances. On the flip side, this can improve performance and the lifespan of equipment by feeding 12VDC appliances a consistent voltage rather than the typical range lead acid batteries- roughly 11V - 14.4V.
  • Fewer devices take 24V DC natively than those that are available in 12V DC.
  • Due to the added components for conversion, the resulting system is more complex in that regard.
  • Batteries wired in series will not equalize like those wired in parallel. Over time they may drift apart, requiring balancing.

Overall, given that you anticipate charging at over 1200W, I'd recommend 24V. If you anticipate heavy inverter use or to wire your inverter into an AC distribution panel, I'd recommend 24V doubly so.

I run 48V in my full time rig and 12V in my shorty.

Okay awesome! Are there batteries that would be a better bang for our buck in the 24 volt system? Originally we were planning on the FLA Duracell 6v golf cart batteries from Sam's club and getting 6 of them. But having 4 batteries in parallel seems a little crazier to me.
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Old 06-20-2021, 08:45 PM   #4
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Okay awesome! Are there batteries that would be a better bang for our buck in the 24 volt system? Originally we were planning on the FLA Duracell 6v golf cart batteries from Sam's club and getting 6 of them.
Link the ones you're thinking of, and I can give you a cost rundown of what you're thinking versus other options. This one for example:
https://www.samsclub.com/p/duracell-...plp_product_13



Claim: Minutes at 25 amps:395


395 minutes / 60 = 6.58 hours.
6.58 hours * 25 amps * 6 volts = 987Wh. Not sure if that's usable (the 50% SoC) rating or what.



$89.99 / 987Wh = $0.09 / Wh or $91.16 / kWh.



Lately I've been recommending EVE 280Ah (LiFePo4) cells, an 8S bank makes a very nice 24V setup for the cost. They have gotten a bit more expensive lately- around $0.18 / Wh or $184.70 / kWh delivered.


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Originally Posted by Ross&Hailey View Post
But having 4 batteries in parallel seems a little crazier to me.
You'd need 4 in series for 24V. 8 cells would be wired in 2P4S.
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Old 06-20-2021, 11:30 PM   #5
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Originally Posted by kazetsukai View Post
Link the ones you're thinking of, and I can give you a cost rundown of what you're thinking versus other options. This one for example:
https://www.samsclub.com/p/duracell-...plp_product_13



Claim: Minutes at 25 amps:395


395 minutes / 60 = 6.58 hours.
6.58 hours * 25 amps * 6 volts = 987Wh. Not sure if that's usable (the 50% SoC) rating or what.



$89.99 / 987Wh = $0.09 / Wh or $91.16 / kWh.



Lately I've been recommending EVE 280Ah (LiFePo4) cells, an 8S bank makes a very nice 24V setup for the cost. They have gotten a bit more expensive lately- around $0.18 / Wh or $184.70 / kWh delivered.


You'd need 4 in series for 24V. 8 cells would be wired in 2P4S.

Thats literally the battery I was going to link so thank you! That EVE LiFePo4 cell seems like a solid deal! Unfortunately I worry about the up front cost right now... I only have a few months more before I need to move into the bus and don't quite have the money for the LiFePo4 yet. I think I'll get the FLA for now, and IF I have bad luck with them I will save up for the Lithium later. Maybe in a year or two Lithium might go down in price even further.

This really helps me! I'm basically sold on the idea of the 24v system since I should be able to find a single charge controller that will handle the amps I need. Charge controllers are expensive enough I think it will roughly the same price between the inverter, charge controllers and batteries with a more efficient system.

Thank you!
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