12v to 48v Converter Wire Gauge

[dmholmes]

I'm looking at discharging LiFePO batteries into power stations MPPT. This boost converter meets the voltage requirements but the first review is saying that the input wire gauge will not handle the amperage. I checked and the 32a max amperage looks adequate for 12 AWG with 105 degree insulation. Is that correct? Did the reviewer not take the insulation temperature rating into account?

 

[rmaddy]

That converter puts out 48.0V at 8A which is 384W. Assuming your batteries are as low as 12V then the input would be 384W / 12V = 32A but it's probably a bit more due to conversion losses. Assume 35A to be safe. Of course when your batteries are at 13.4V then the amperage will be a little lower. For 30A you would want 10AWG. For 40A you would want 8AWG. And this is with high quality marine grade wire rated for 105ºC. 12AWG shouldn't be used for more than 25A. This all assumes fairly short wires (under 6 feet roundtrip). That's all based on the nice Blue Sea wire and fuse chart. Though putting the numbers into their app I get 12AWG. I entered 12V, 32A, 6 feet total wire, 3% voltage drop, 105ºC insulation, single fused wire. But one telling factor is if you enter 90ºC insulation it suggests 10AWG. This means that 12AWG may work but it will likely be very hot. Remember that a wire at 100ºC won't melt the insulation if it's rated for 105ºC but the 100ºC wire will boil water and burn you badly.

 

[RCinFLA]

For spec sheet:

Input Rated Voltage:	DC 12V
Input Voltage Range	DC 10V ~ 25V
Output Voltage	DC 48V 8A
Output Rated Power	384W
Efficiency	97% (half load); 96% (full load)
Output Peak Power	480W

I am not sure I would believe the 96% efficiency for a boost converter. Usually they use an output rectifier diode. It is theoretically possible to use a synchronous rectifier but it is more difficult for a boost converter compared to a buck converter.

Anyway, using the published specs, For 48v @ 8 amps = 384 watts / 0.96 = 400 watts input power required. With 16 watt loss the case will get fairly hot.

400w/12v = 33.3 amps input current. For six feet pair of #12 you will have 0.65v wire voltage drop. Now you really have 11.35v on input which will give lower boost efficiency and greater required input current.

400w/11.35v is now 35 amps input, assuming same 96% efficiency which will not be the case at lower input voltage.

6 foot pair #12 gives 0.65v wire drop, with 22 watts of input wire heating/loss.
6 foot pair #10 gives 0.42 v wire drop, with 14 watts of input wire heating/loss.
6 foot pair #8 gives 0.26 v wire drop, with 9 watts of input wire heating/loss.

You can ratio the loss based on your actual wire pair length relative to the 6 foot pair example.

 

[dmholmes]

That converter puts out 48.0V (not 24 as your title states) at 8A which is 384W. Assuming your batteries are as low as 12V then the input would be 384W / 12V = 32A but it's probably a bit more due to conversion losses. Assume 35A to be safe. Of course when your batteries are at 13.4V then the amperage will be a little lower. For 30A you would want 10AWG. For 40A you would want 8AWG. And this is with high quality marine grade wire rated for 105ºC. 12AWG shouldn't be used for more than 25A. This all assumes fairly short wires (under 6 feet roundtrip). That's all based on the nice Blue Sea wire and fuse chart. Though putting the numbers into their app I get 12AWG. I entered 12V, 32A, 6 feet total wire, 3% voltage drop, 105ºC insulation, single fused wire. But one telling factor is if you enter 90ºC insulation it suggests 10AWG. This means that 12AWG may work but it will likely be very hot. Remember that a wire at 100ºC won't melt the insulation if it's rated for 105ºC but the 100ºC wire will boil water and burn you badly.

Thank you, title corrected.

I can use the proper wire gauge for the add ons but it looks like the short wires built-in are not adequate. I wonder how they can even sell this?

 

[rmaddy]

Thank you, title corrected.

I can use the proper wire gauge for the add ons but it looks like the short wires built-in are not adequate. I wonder how they can even sell this?

I have a 24V-12V DC-DC converter with leads that are a size too small as well. I just cut them as short as possible leaving just enough to butt splice the proper sized wire.

I was going to recommend a high quality product like the Victron Orion but they don't seem to have a 12V->48V converter.

 

[dmholmes]

I was going to recommend a high quality product like the Victron Orion but they don't seem to have a 12V->48V converter.

I've been looking at that route also. Doesn't have to be 48v but I'm trying to get a higher charging rate than just connecting the battery to the MPPT input (~100w). The power stations I have max out at 10a or 12a for the MPPT input.

 

[rmaddy]

It might help a lot if you take a step back and describe what problem you are trying to solve. I'm not sure why you would plug a battery into the PV input of a charge controller.

 

[dmholmes]

It might help a lot if you take a step back and describe what problem you are trying to solve. I'm not sure why you would plug a battery into the PV input of a charge controller.

Far from optimal I know, but it's a cheapish way of extending the runtime. Otherwise I have to use an inverter on the battery to use the power station's AC charger.

 

[dmholmes]

That's all based on the nice Blue Sea wire and fuse chart. Though putting the numbers into their app I get 12AWG. I entered 12V, 32A, 6 feet total wire, 3% voltage drop, 105ºC insulation, single fused wire. But one telling factor is if you enter 90ºC insulation it suggests 10AWG. This means that 12AWG may work but it will likely be very hot. Remember that a wire at 100ºC won't melt the insulation if it's rated for 105ºC but the 100ºC wire will boil water and burn you badly.

I put the same entries into their app and website, but even with 35 amps and 90ºC insulation it still gives me 12 AWG wire. I had to enter 75ºC insulation to get it to recommend 10 AWG. Am I missing another setting?

 

[rmaddy]

I put the same entries into their app and website, but even with 35 amps and 90ºC insulation it still gives me 12 AWG wire. I had to enter 75ºC insulation to get it to recommend 10 AWG. Am I missing another setting?

12V, 35A, 6 feet, 3%, 90ºC, Not in engine room, 1 wire in bundle, 1440 minutes duration, and fused. That gives me 10AWG in the app. Same values but 32A gives me 12AWG.

 

[dmholmes]

Would this 24v converter (240w) be safer? If I enter <= 22 amps in the calculator with same settings used for the other converter it recommends AWG 14, which is what this converter has. But if you enter 23 amps it recommends AWG 12.

 

[rmaddy]

I thought you needed 12V->48V?

Don't forget that the amp rating on these is the max. If you only pull, for example, 48V at 6A instead of the full 8A on the original 12-48V converter then it's only 24 amps on the 12V end. Don't max it out and the wire should be ok.

 

[dmholmes]

I thought you needed 12V->48V?

Don't forget that the amp rating on these is the max. If you only pull, for example, 48V at 6A instead of the full 8A on the original 12-48V converter then it's only 24 amps on the 12V end. Don't max it out and the wire should be ok.

My apologies for the odd use case here. I'm trying to charge a power station via the PV input from a standalone 12V LiFePO battery or the 12V battery in a hybrid vehicle in case of power outage. The power station will take 300W 11–75V DC 10A max. So without the boost converter I can only charge it at ~100W. I'm hoping to increase that a bit.

I was looking at the 48V converter, or at least 36V, to be able to charge my other power station which needs at least 36V.