kenkoh
Solar Enthusiast
Gone through Will's book again and the guides are mainly for 12v systems. Thanks.
Is there a wire/fuse size chart for 24v?
- Thread starter kenkoh
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24v fuseing is the same as 12v just that your amperage is half what 12v would be for the same wattage. If you are calculating amps the fuses are the same as they would be for 12v at the same amperage.
kenkoh
Solar Enthusiast
But the wire size are different for the same length, say for a 1500w inverter to battery the wire is 1 awg for 12v but 4 awg for 24v. Is there a wire size chart specifically for that?
It's based on amperage. 1500W / 12V / 85% = 150A. 1500W / 24V / 85% = 75A. It's those different amperages that give you the different wire size.
kenkoh
Solar Enthusiast
I see. Thank you again. I just found this calculator today, can I trust it? https://www.explorist.life/wire-sizing-calculator/
Confederate Sun
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Yes he's reputable.
kenkoh
Solar Enthusiast
Would I use a 80a fuse for the 24v 1500w inverter?
Hedges
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Fuses have a current rating, a voltage rating, and an "AIC" rating. The last one is how much short-circuit current they can interrupt, which depends on voltage. So switching from 12V design to 24V, need to take that into account.
1500W / 24V / 90% x 1.25 margin x 1.12 ripple factor = 97A
I would use a 100A fuse.
If this is lithium battery, 24V is reasonably close to low voltage operation. If lead-acid, substitute 20V in the equation.
90% is assumed inverter efficiency. Look up its reported efficiency at 100% load (will be less than quoted peak, perhaps twice the efficiency loss.)
25% larger is standard margin to avoid nuisance tripping.
12% larger is my contribution to the art. Turns out current powering an inverter is not steady-state DC, rather looks like a rectified sine wave. Its Irms value (which heats wires and fuses) is almost 12% higher than its "mean" value, which delivers power.
"Is there a wire/fuse size chart for 24v?"
Ampacity of wire remains the same (minimum size for a given amperage), based on heating, insulation temperature rating, bundles that prevent airflow.
Voltage drop due to current remains the same, but with system 24V rather than 12V, you can tolerate twice the voltage drop.
1500W / 24V / 90% x 1.25 margin x 1.12 ripple factor = 97A
I would use a 100A fuse.
If this is lithium battery, 24V is reasonably close to low voltage operation. If lead-acid, substitute 20V in the equation.
90% is assumed inverter efficiency. Look up its reported efficiency at 100% load (will be less than quoted peak, perhaps twice the efficiency loss.)
25% larger is standard margin to avoid nuisance tripping.
12% larger is my contribution to the art. Turns out current powering an inverter is not steady-state DC, rather looks like a rectified sine wave. Its Irms value (which heats wires and fuses) is almost 12% higher than its "mean" value, which delivers power.
"Is there a wire/fuse size chart for 24v?"
Ampacity of wire remains the same (minimum size for a given amperage), based on heating, insulation temperature rating, bundles that prevent airflow.
Voltage drop due to current remains the same, but with system 24V rather than 12V, you can tolerate twice the voltage drop.
It's a 75A load so an 80A fuse is too close and you risk nuisance trips. 75A x 125% = 94A so a 100A fuse would be a good choice. 4AWG wire can safely be fused at 100A so you are good.
kenkoh
Solar Enthusiast
So instead of a 175a fuse, I'll use a 90a fuse on a 24v 1500w inverter correct?
kenkoh
Solar Enthusiast
Using the formula, does this PDF look right?
Most of your wire choices are too small.
1000W / 24V / 85% = 50A. Use 6AWG.
1200W / 24V / 85% = 60A. Use 6AWG.
1500W / 24V / 85% = 75A. Use 4AWG.
2000W / 24V / 85% = 100A. 4AWG is borderline. I'd use 2AWG.
3000W / 24V / 85% = 150A. 1AWG minimum. I'd use 1/0AWG if you will regularly use loads over 2500W.
The fuse should be 125% - 156% (upper value includes ripple effect calculation) times the amperage. Round up to nearest available fuse size. You seem to have good fuse choices though several of the listed sizes won't be available.
You should also be using Class T fuses for a 24V LiFePO₄ setup.
1000W / 24V / 85% = 50A. Use 6AWG.
1200W / 24V / 85% = 60A. Use 6AWG.
1500W / 24V / 85% = 75A. Use 4AWG.
2000W / 24V / 85% = 100A. 4AWG is borderline. I'd use 2AWG.
3000W / 24V / 85% = 150A. 1AWG minimum. I'd use 1/0AWG if you will regularly use loads over 2500W.
The fuse should be 125% - 156% (upper value includes ripple effect calculation) times the amperage. Round up to nearest available fuse size. You seem to have good fuse choices though several of the listed sizes won't be available.
You should also be using Class T fuses for a 24V LiFePO₄ setup.
kenkoh
Solar Enthusiast
Does this look right? I over gauge by 1:
24V 1200W use 8 AWG (6 feet) and 90A fuse
24V 1500W use 4 AWG (6 feet) and 100A fuse
24V 2000W use 2 AWG (6 feet) and 150A fuse
24V 3000W use 2 AWG (6 feet) and 215A fuse
kenkoh
Solar Enthusiast
Yes I've corrected from your post above thank you so much.
Hedges
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That shows 115A fuse for 24V, 1500W. That would be fine with suitable wire. Thicker is better. What's the largest gauge that will fit in terminals? How about 2/0?
The pictures show a SOK battery (thought not two for 24V). They show a fuse that may not be good enough for Lithium, which can deliver perhaps 5x the short-circuit current of lead-acid. We like class-T fuses as rmaddy said. They are rated to interrupt 20,000A shorts.
Actually they are Battle Born batteries, not that it really matters.
As I stated earlier, 1500W at 24V can be 75A so the 115A fuse works fine. I suggested 4AWG for the 75A load. A 115A fuse is fine for 8AWG or thicker.
Why 2/0AWG for a 75A load?
Hedges
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Yeah, that's what it says. Switching between browsers to see it and going by memory when typing, because .pdf doesn't open in chrome.
Definitely thicker than needed. But minimizes voltage drop if inverter has any surge capability.
Single conductor in free air, 90 degree:
6 awg for up to 105A, 4 awg up to 140A
6 awg 0.4 ohms per 1000'
Table of equivalent AWG Wire and Resistance per foot
AWG Chart of Approximate equivalent Cross-Sections of Wire, American Wire Gauge by Resistance per 1000 feet
www.interfacebus.com
If 10' away, 20' round trip, 0.008 ohms x 75A = 0.6V drop, 2.5% of 24V
If surge current 2x, 1.2V drop, 5%
The percentage is loss in energy efficiency. The voltage reduces what inverter gets (and current has to go up by the percentage.)
So 6AWG is just under 3%. I suggested using 4AWG for 75A so well under 3%. So again, why suggest 2/0AWG for 75A when 4AWG, even 6AWG gets you under 3% VD? I'm a big believer is using larger wire than strictly needed but no need to severely over do it.
Hedges
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You're right, smaller would be fine.
For AC runs I usually go by ampacity. Although in conduit, derating for extra conductors requires larger.
For inverter input I like to make it as big as reasonable, unless $$ get in the way.
I have 2/0 on a nominally 125A circuit, 6kW 48V. I had the cable on hand anyway, and it should help when putting out surge current.
For AC runs I usually go by ampacity. Although in conduit, derating for extra conductors requires larger.
For inverter input I like to make it as big as reasonable, unless $$ get in the way.
I have 2/0 on a nominally 125A circuit, 6kW 48V. I had the cable on hand anyway, and it should help when putting out surge current.
