Circuit breaker size for a 4x 6 volt battery @ 24 volt battery bank

[john95]

My system

4x 320 watt 24 volt panels voc 45.9 each panel
1x Outback FlexMax 80 charge controller
4x 6 volt Crown 235 Ah battery 24 volt battery bank
1x Go Power 1500 watt 24 volt inverter

Is it ok to install the same capacity breaker between the panels and charger, battery to inverter and charger to battery?

Your help will be appreciated.

[SunEagle]

First off how are you wiring those 4 320w panels? If they are either all in series or 2 pairs in parallel you really do not need any fusing between the panels and CC.

The size of the fuse should be less amps then the rating of the wire. That is what fuses are used for. To protect the wire.

If you plan on adding more panel wattage then you will need to run a wire rated at least 80amps (since that is the output of the CC) but a better solution is to make that wire rated 100Amp. Then you can use a 70 to 80A fuse to protect it.

The wire between the battery and inverter should be rated at least 65amps since the calculation for a 1500w 24v inverter can generate 62.5amps. Although most inverters have a "surge" rating which can be double the normal watt rating. That could mean a 3000 watts at 24volt or 125amps. Again it would be smart to run wire rated about 100amps and use a 70 to 80 amp fuse to protect it.

So in your case both sets of fuses could be the same at 70 to 80Amp as long as you use 100amp wire.

[john95]

Thanks for your answer! I'm planning to wiring the 4 panels in series (4x320=1280 watt @24v). I want to keep the whole system @ 24 volts to keep all components happy.
Now, what size of wire is rated 100 amp? I guess that Go power 1500 watt 24 volts inverter is size 4, which should be more suitable?
I already ordered all components above. I'm just getting the miscellaneous stuff on your advice. I probably install next week or as soon as I get the components. I'm very excited about this small solar project.

[Sunking]

I'm planning to wiring the 4 panels in series (4x320=1280 watt @24v). I want to keep the whole system @ 24 volts to keep all components happy.

You cannot wire all 4 panels in series as that likely exceeds the Charge Controller Voc limit of 150 Voc. You will want to run those panels 2S2P. That will give you roughly 72 volts @ 18 amps. Since there are only 2 parallel strings does not require or need any fuses between the panel and controller. Only thing you have to worry about is wire size vs distance. Minimum requirement is 12 AWG up to 30-feet 1-way.

Now, what size of wire is rated 100 amp? I guess that Go power 1500 watt 24 volts inverter is size 4, which should be more suitable?
I already ordered all components above. I'm just getting the miscellaneous stuff on your advice. I probably install next week or as soon as I get the components. I'm very excited about this small solar project.

Depends on what the wire insulation type is being 75, 90, or 105 degree C. 75 and 90 degree is 4 AWG and 105 is 4 AWG. However you only care about minimum size to er safe, PLUS line losses. You want to keep line losses to 3% or less. Minimum wire size depends on the Fuse Size connected. So a 100 amp fuse can be either 6 or 4 AWG depending on what temp the wire insulations is. Example at 24 volt battery with a 100 amp fuse if you use 90 degree 6 AWG you can go up to 17 feet 1-Way. If you use 4 AWG 90 degree wire you can go up to 25 feet.

Don't sweat the details. Use this calculator as it is one of the better ones for fixed DC voltages of 12, 24, and 36 volts. Just enter the data and it will tell you what to use. But I can tell you right now.

Use 105 Degree cable
Between Controller and Battery you will need an 80 amp Fuse and 8 AWG wire up to 14-feet 1-way Fuse is installed directly on the BATTERY TERM POST
Between Battery and Inverter use 100 Amp Fuse on 6 AWG wire up to 17-feet 1-Way.

Or to make life easy buy 75, 90, or 105 degree 4 AWG and you are good up to 100 amps or less up to 30-feet 1-way.

Or you can use a chart, but be aware it is made for 12 volts. For 24 volts just double the Distance in the 3% column. Easy peazy

[john95]

Thanks for your help Sunking, so far so good.

Some more questions please:

Will the inverter need a circuit breaker for the AC to loads and if so, which one good be a suitable one for AC for this 1500 watt inverter? Or the inverter shuts it self off in case an overload?

What type of MC4 connectors and how many do I need to wiring the 4 panels 2S2P? Thanks again.

[Sunking]

Thanks for your help Sunking, so far so good.

You are welcome.

Some more questions please:

Will the inverter need a circuit breaker for the AC to loads....

No. Your Inverter cannot generate enough fault current to operate a fuse or breaker. You Inverter's internal circuitry will shut itself down if to much current demand. A 1000 watt Inverter can only deliver about 8 amps at 120 VAC. What would happen to 15 or 20 amp fuse do with 8 amps flowing?

Nothing. It takes 6 times the Breaker rating for Instantaneous trip. No way can the Inverter deliver 90 to 120 amps. Would not even trip a 8 amp breaker if they made one. You woul dhave to use a 1 amp breaker and of course than means no more than 120 watts for your 1000 watt Inverter.

What almost all Inverters use is a GFCI Circuit Breaker. Or I should say any Inverter made for mobile applications which is what you are using. It requires no ground to operate. It looks at the current between the two conductors. If the Current is EQUAL, no problem. If there is any difference, there is a problem and it trips immediately because current is going somewhere it SHOULD NOT BE GOING.

What type of MC4 connectors and how many do I need to wiring the 4 panels 2S2P? Thanks again.

Does not matter how they are wired. Each panel requires 2 connectors. 4 panels x 2 connectors = 8 Plus 2 for the Feeder, so 10 in total.

[john95]

You are welcome.



No. Your Inverter cannot generate enough fault current to operate a fuse or breaker. You Inverter's internal circuitry will shut itself down if to much current demand. A 1000 watt Inverter can only deliver about 8 amps at 120 VAC. What would happen to 15 or 20 amp fuse do with 8 amps flowing?

Nothing. It takes 6 times the Breaker rating for Instantaneous trip. No way can the Inverter deliver 90 to 120 amps. Would not even trip a 8 amp breaker if they made one. You woul dhave to use a 1 amp breaker and of course than means no more than 120 watts for your 1000 watt Inverter.

What almost all Inverters use is a GFCI Circuit Breaker. Or I should say any Inverter made for mobile applications which is what you are using. It requires no ground to operate. It looks at the current between the two conductors. If the Current is EQUAL, no problem. If there is any difference, there is a problem and it trips immediately because current is going somewhere it SHOULD NOT BE GOING.

Great! Thanks for such a clear explanation.

Does not matter how they are wired. Each panel requires 2 connectors. 4 panels x 2 connectors = 8 Plus 2 for the Feeder, so 10 in total.

I'll buy 10 connectors. I"m getting the panels tomorrow.