4 PV Panels in Parallel- Fuse calculation

[Feenalicious]

MRBF--nice

For the fusing on circuits connected to the batteries, it would be safest to fuse as close to the battery as possible. A dual fuse block like this one could be loaded with the fuses appropriate for the charge controller and inverter, and mount right to the battery terminal.

As always, if you bump the fuse size up anywhere for whatever reason, make sure the conductor size in increased to match.

OMG Sensij, a dual fuse block that mounts right onto the battery terminal...I'm in heaven, thank you.

[posplayr]

Excellent, thank you!

I think both manufactures are essentially giving you the same answer if interpreted correctly.

The Naturepower 2000W recommends a 300 amp fuse which implies 2000/12V=166.7 amps giving a Surge/Continuous rating of 300/166.7=1.8:1


The Sunforce 650 is telling you it will trip out on 650W continuous and 1200W surge so these convert to amps as well but just as easily 1200W/650W=1.85:1

Note both of these are manufacturer's numbers which says more about their respective invertor designs and how they design for surge than how they arrived at the wiring recommendations.

For the Sunforce: 650W/12V*(1.85:1)=100 amps fuse rating. That is the minimum requirement and so long as you flip the internal overload of the invertor and not your fuses you will save money on fuses.

If the invertor fails and the overload protection fails, would you rather have a 125 amp fuse in series or a 100 amp fuse? I think 100A.

[sensij]

Unfortunately, I couldn't find a mfg recommendation for the Sunforce 650.
Thank you!

Is the inverter you are talking about this one? It looks like it will shutdown if you try to power more than 650 W continuous or 1200 W surge.

Although it doesn't give a fuse rating, you can estimate one from what it is drawing. 650 W / 12 V = 54 A continuous. For a continuous load, you should be sized 1.25X, so 54 * 1.25 = 68 A. Therefore, the minimum fuse between the battery and inverter should be 70 A. However, as Mike mentioned, if you go with 70 A and you have loads that surge higher (up to 1200 W), you may have some nuisance tripping (depends somewhat on the type of fuse used).

Since you are using 1/0 to mitigate voltage drop, you can see it can be used safely in a 150 A circuit with 75 deg rated terminations (they will be marked), or 125 A if the terminations are not marked. To be safe, I'd say that the maximum fuse should be no more than 125 A, especially since the surge load that will cause the inverter to trip out is ~100 A. The question, then, is where do you want the circuit to break if a fault occurs or if you try to power something that draws more than the inverter can handle? If you want the fuse to also protect the inverter (the fuse's primary purpose is to protect the conductor), I would size it at 100 A if you have any inductive loads that might hard start (compressor, pump, etc), or maybe slightly smaller if your loads are mostly resistive. If you would rather let the inverter shut down be your first line of defense, then that fuse could be 125 A.

Just for completeness (I think others have answered)

Between the panels and the combiner, no fuse required for 2x2.

Between the combiner and charge controller, no fuse required for 2x2, but your math was right, the circuit rating is ~18 A and a 20 A fuse would be appropriate. Your conductors for that circuit would need to be at least 12 AWG.

Between the charge controller and batteries, if the rated current is 40 A, then fuse size should be 1.25*40 = 50 A, probably with 6 AWG although it is possible 8 AWG could be ok if all the terminations are marked for it.

For the fusing on circuits connected to the batteries, it would be safest to fuse as close to the battery as possible. A dual fuse block like this one could be loaded with the fuses appropriate for the charge controller and inverter, and mount right to the battery terminal.

As always, if you bump the fuse size up anywhere for whatever reason, make sure the conductor size in increased to match.

[Feenalicious]

Since nobody is answering you I'll try to provide a little guidance. I would be tempted to use the smallest fuse possible anywhere without blowing that fuse of flipping that breaker. Wire size is usually sized to avoid voltage drops and power drops over long distance and the current it is capable of carrying might be much higher than you even need. So as you say the fuse is for the wire, you don't need to make the fuse higher than you need. It is just a safety concern.

With that in mind, your first step might be to just scale down the fuse rating that the 2000 watt manufacture recommended. 60/2000*300=90 amps. In the simplest of terms this should make sense because the whole point of going from 2000W to 600W was to reduce current. Remember you could have delivered much more power with a smaller wire at a higher voltage. So the fuse should scale by power which his proportional to current for the same voltage.

Another way to look at this is that 2000 watts at 12V is 166 amps and now you have a 600 watts at 12V which is 50 amps. Naturepower is suggesting a 2:1 ratio between the fuse rating and the average current. Using the same guide you would have a 100 amp fuse using the 600 watt invertor.

Make sure that nothing can pull/push current from/to the battery pack without going through a fuse.

Excellent, thank you!

[Feenalicious]

is this a fuse at the input port of the controller, or a fuse at each string of PV (combiner box fuse)? Just 2 arrays in parallel don't need combiner fuses, but using a circuit breaker makes for easier diagnosis of any array problems
for combiner fuse, the PV panels often have a "series fuse" rating on them - seat of the pants guess would be about 8 amps.
For Controller solar fuse, seat of the pants guess would be about 15A, and use wire that would be safe at that amperage. If you use 20a fuse, got to use heavier wire to handle 20A. Generally, you size the wire to have low loss for your expensive PV power.

--yes this fuse is at the controller input.

Inverters can consume some pretty high surge power spikes (my 1Kw pump may pull 7Kw when starting) and using too small of a fuse can cause nuisance blowing. So use wire larger than the fuse rating, and the fuse no larger than the Mfg. Recommended for your inverter.

Unfortunately, I couldn't find a mfg recommendation for the Sunforce 650.
Thank you!

[posplayr]

The instructions in my charge controller manual tell me to use a 40-amp fuse between the battery bank and the charge controller because it is a 40-amp controller. Between the solar panels and charge controller, it says to multiply the total amperage of the solar panels by a "sizing factor" of 1.56. Each panel =5.75A. If I connect my panels in series/parallel then the first two panels in series = 5.75A and the second two panels in series = 5.75A. These are then connected in parallel so adding 5.75+5.75= 11.5A for the four. 11.5*1.56= 17.94 so a 20-amp fuse would go here. Sound right?

Before when I was using the Naturepower 2000W inverter it said to use a 300Adc fuse between the battery bank and inverter. I've switched to my Sunforce 650W 12V inverter after receiving advice here. The instructions in the Sunforce inverter manual don't mention a fuse at all. This manual directs me to use 1/0 or 2/0 wire between the battery bank and inverter because the inverter is more than 6 feet from the batteries. I'm using 1/0 gauge wire. 1/0 gauge can safely handle 170A per the tables I looked at. Since the fuse is meant to protect the wires, should I put a 150A fuse in?

Since nobody is answering you I'll try to provide a little guidance. I would be tempted to use the smallest fuse possible anywhere without blowing that fuse of flipping that breaker. Wire size is usually sized to avoid voltage drops and power drops over long distance and the current it is capable of carrying might be much higher than you even need. So as you say the fuse is for the wire, you don't need to make the fuse higher than you need. It is just a safety concern.

With that in mind, your first step might be to just scale down the fuse rating that the 2000 watt manufacture recommended. 60/2000*300=90 amps. In the simplest of terms this should make sense because the whole point of going from 2000W to 600W was to reduce current. Remember you could have delivered much more power with a smaller wire at a higher voltage. So the fuse should scale by power which his proportional to current for the same voltage.

Another way to look at this is that 2000 watts at 12V is 166 amps and now you have a 600 watts at 12V which is 50 amps. Naturepower is suggesting a 2:1 ratio between the fuse rating and the average current. Using the same guide you would have a 100 amp fuse using the 600 watt invertor.

Make sure that nothing can pull/push current from/to the battery pack without going through a fuse.

[Mike90250]

The instructions in my charge controller manual tell me to use a 40-amp fuse between the battery bank and the charge controller because it is a 40-amp controller. Between the solar panels and charge controller, it says to multiply the total amperage of the solar panels by a "sizing factor" of 1.56. Each panel =5.75A. If I connect my panels in series/parallel then the first two panels in series = 5.75A and the second two panels in series = 5.75A. These are then connected in parallel so adding 5.75+5.75= 11.5A for the four. 11.5*1.56= 17.94 so a 20-amp fuse would go here. Sound right?

is this a fuse at the input port of the controller, or a fuse at each string of PV (combiner box fuse)? Just 2 arrays in parallel don't need combiner fuses, but using a circuit breaker makes for easier diagnosis of any array problems
for combiner fuse, the PV panels often have a "series fuse" rating on them - seat of the pants guess would be about 8 amps.
For Controller solar fuse, seat of the pants guess would be about 15A, and use wire that would be safe at that amperage. If you use 20a fuse, got to use heavier wire to handle 20A. Generally, you size the wire to have low loss for your expensive PV power.

For the wire between the controller and battery, I'd use a 45A fuse, because a 40a fuse @ 40a will eventually weaken and blow.
Use wire rated for 45A (or the size of the fuse).

Before when I was using the Naturepower 2000W inverter it said to use a 300Adc fuse between the battery bank and inverter. I've switched to my Sunforce 650W 12V inverter after receiving advice here. The instructions in the Sunforce inverter manual don't mention a fuse at all. This manual directs me to use 1/0 or 2/0 wire between the battery bank and inverter because the inverter is more than 6 feet from the batteries. I'm using 1/0 gauge wire. 1/0 gauge can safely handle 170A per the tables I looked at. Since the fuse is meant to protect the wires, should I put a 150A fuse in?

Inverters can consume some pretty high surge power spikes (my 1Kw pump may pull 7Kw when starting) and using too small of a fuse can cause nuisance blowing. So use wire larger than the fuse rating, and the fuse no larger than the Mfg. Recommended for your inverter.

[Feenalicious]

And now back to fusing

The instructions in my charge controller manual tell me to use a 40-amp fuse between the battery bank and the charge controller because it is a 40-amp controller. Between the solar panels and charge controller, it says to multiply the total amperage of the solar panels by a "sizing factor" of 1.56. Each panel =5.75A. If I connect my panels in series/parallel then the first two panels in series = 5.75A and the second two panels in series = 5.75A. These are then connected in parallel so adding 5.75+5.75= 11.5A for the four. 11.5*1.56= 17.94 so a 20-amp fuse would go here. Sound right?

Before when I was using the Naturepower 2000W inverter it said to use a 300Adc fuse between the battery bank and inverter. I've switched to my Sunforce 650W 12V inverter after receiving advice here. The instructions in the Sunforce inverter manual don't mention a fuse at all. This manual directs me to use 1/0 or 2/0 wire between the battery bank and inverter because the inverter is more than 6 feet from the batteries. I'm using 1/0 gauge wire. 1/0 gauge can safely handle 170A per the tables I looked at. Since the fuse is meant to protect the wires, should I put a 150A fuse in?

[posplayr]

They mean 5 ft apart, not 5' "round trip," meaning 2.5' apart, right?
I was looking at some wire gauge tables and online calculators and they use the distance there and back instead of one way. It got me wondering.

DC Input Cable:
• Low resistance wire (copper) is required for all the DC connections between the inverter and
the battery bank.
• For 38210, 38310, uses minimum #2 AWG wire with maximum cable length of 5 feet.
• For 38215, use minimum #1/0 AWG wire with maximum cable length of 5 feet.
• For 38320, use minimum #2/0 AWG wire with a maximum cable length of 5 feet.

I would guess it means two conductors side by side equal in length to 5 foot (10 foot of wire).

You can always run a wire calculator to see why it has to be that think. Also if you let the connection get dirty you can start a fire. You know that as well. The wire will not burn, but the cable end can melt the top of solder slug out of a battery.

[Feenalicious]

Distance between battery and inverter

Not sure what happned to my other post, so here is a retry. Manual says needs no more than 5 ft of #2/0 wire

They mean 5 ft apart, not 5' "round trip," meaning 2.5' apart, right?
I was looking at some wire gauge tables and online calculators and they use the distance there and back instead of one way. It got me wondering.

[Mike90250]

I see, I'm not utilizing a key benefit of the MPPT controller, the higher voltage I can get by putting the panels in series, right?

Once you get above 2x the battery voltage (in your case, over 25V solar panel voltage) losses in the inverter begin to increase, but if you have a long cable run from the PV, it may be worth it to put up with conversion losses instead of copper resistance loss.

My 170V PV array shows this effect but I could not add any more copper into existing conduit.

[sensij]

I wasn't really suggesting that using the 2000 W inverter with a smaller fuse was a good idea, just that it was better than using it unfused. With the wire sized for the full inverter rating, the insulation should hold up OK, but limiting the power reduces the risk of a problem at the terminations, which are hard to make properly for those who don't do it regularly (and have the right tools). The fuse isn't necessary, you could just pinkie swear never to load the inverter more than 600 W (or whatever), but the smaller inverter will be a better choice for a number of reasons (as others have said).

With respect to discharge rate, keep in mind that if you discharge at C/10 (40 amps = 480 W), that is a 10 hour rate, while the battery Ah rating is usually published at the C/20 rate (20 amps = 240 W). Discharging at the 10 hour rate may reduce the effective capacity somewhat. Based on the specs you shared, I think it might be this battery. The reserve capacity is the number of minutes a 25 A load can be maintained (100 A for four in parallel = 1200 W), a C/4 rate. 210 min = 3.5 hour * 25 A = 87.5 Ah per battery. You could figure C/10 capacity would be something less than 105 Ah, but more than 87.5 Ah.

Also be aware that it is difficult to wire four batteries in parallel and keep them perfectly balanced. If you must stay in this configuration, my very unqualified recommendation would be to rotate their position in the bank periodically so whatever mismatches exist in the wiring get distributed among all four of them over time, like rotating tires. I'm not going to defend that recommendation if others with more knowledge shoot it down.

[thastinger]

Much thanks, Thastinger. Yes, of course, I will be using the 650 Watt Inverter. Unfortunately, I started researching this solar project three months ago then shelved it until now. I've obviously forgotten most of what I learned. Can I trouble you to show me your calculations that gave you the 500W load number and the 153A passing through the cables? I need to understand this completely and that will give me a little "jump start" back into it.

Sure, you have a 12V 400AH battery bank. Following the guide of C8/C10 max discharge rate we get 400/10=40A which can be safely pulled from the battery bank or 50Amps with the C8 rate. So 40 amps at 12 volts is 480 Watts and 50 Amps at 12V is 600W.
The smaller inverter should run more efficiently at those levels than the 2000W fused down.

So, if you decided to stick to the no more than 20% depth of discharge on the battery bank, what could you do with that much power? Let's use 2 100W light bulbs to figure it out. You could drain 80 Amps from the bank assuming it was fully charged, 80Ax12V=960W. Let's assume your inverter is 92% efficient, so 960x.92=880W of useable power in the evening after the sun goes down. So you could run those 2 light bulbs for a bit over 4 hours. Expectation management is my point, it is a small system so be careful to manage your loads.

[Feenalicious]

fusing down

By "fusing down" the 2000 watt inverter you are limiting the amount of power it can draw because the fuse will open when too much current goes through the wire.

So technically you are converting that 2000 watt (2000w / 12volts = 167amps) to a 500 watt (500w / 12volt = 42amps) by putting in a 40amp fuse instead of a 160amp fuse.

Blowing fuses is not the best way to run a system (will eventually cause the wire insulation to fail) but it will limit the amount your draw with that 2000w inverter.

Lol, gotcha. Thanks.

[SunEagle]

Yes, switching to the 650W. Just wondering, what do you mean by "fuses the 2000W down...?"

By "fusing down" the 2000 watt inverter you are limiting the amount of power it can draw because the fuse will open when too much current goes through the wire.

So technically you are converting that 2000 watt (2000w / 12volts = 167amps) to a 500 watt (500w / 12volt = 42amps) by putting in a 40amp fuse instead of a 160amp fuse.

Blowing fuses is not the best way to run a system (will eventually cause the wire insulation to fail) but it will limit the amount your draw with that 2000w inverter.