What size of fuse is required for this small 24V system?

[Silver_Is_Money]

For a system consisting of a 1,500 Watt 24V inverter, 4 x 240 Watt solar panels, and 4 x 320 AH 6V batteries, plus a 40A charge controller, what is the proper size of fuse that should reside between the battery bank and the inverter?

Would this system offer a good balance of components? My overall average daily sunshine is 4 hours and December averages to 2.1 hours.

[paulcheung]

I would use 80 to 100 amps fuse, make sure the wire rating is larger than the fuse by about 25%.

320 AH at 24 volts battery bank, you should only draw no more than 400 watts continuously. the inverter is too large for the battery bank but if you can limit the power consumption will be fine. You should only have 1000 watts inverter for that 320AH 24 volts bank. I don't know your daily consumption so can't comment on the sun hours and the panels if it is enough.

[Silver_Is_Money]

I would use 80 to 100 amps fuse, make sure the wire rating is larger than the fuse by about 25%.

320 AH at 24 volts battery bank, you should only draw no more than 400 watts continuously. the inverter is too large for the battery bank but if you can limit the power consumption will be fine. You should only have 1000 watts inverter for that 320AH 24 volts bank. I don't know your daily consumption so can't comment on the sun hours and the panels if it is enough.

Thank you! What link in the chain determines that only 400 Watts can be drawn continuously? And what happens if I was to draw perhaps up to 1,400 watts periodically, such as running a microwave for 1.25 minutes to heat a cup of coffee for example?

[Sunking]

For a system consisting of a 1,500 Watt 24V inverter, 4 x 240 Watt solar panels, and 4 x 320 AH 6V batteries, plus a 40A charge controller, what is the proper size of fuse that should reside between the battery bank and the inverter?

You should not ask that question here. Look in the owners manual and it will tell you. Most likely something on the order of 75 to 100 amps using a minimum #4 AWG.

Would this system offer a good balance of components? My overall average daily sunshine is 4 hours and December averages to 2.1 hours.

As far as the balance goes is OK. Inverter is a bit large, but what no one knows is if it will work or not as you have no specified how many watt hours a day you need.

What I can tell you is with your poor solar insolation with a 960 watt panel can only provide you with 1.4 Kwh per day.

[paulcheung]

http://www.solarpaneltalk.com/showthread.php?11906-Peukert-Law-Batteries-and-You

That will explain it.

[Sunking]

Thank you! What link in the chain determines that only 400 Watts can be drawn continuously? And what happens if I was to draw perhaps up to 1,400 watts periodically, such as running a microwave for 1.25 minutes to heat a cup of coffee for example?

Don't worry about it. Paul is mistaken.

The weak link is the FLA battery at 320 AH you normally limit discharge current to about C/8 where C = battery AH capacity and 8 is hour discharge rate So C/8 is 320 AH / 8 = 40 amps. Well 40 amps x 24 volts is 960 watts which is why I said your Inverter is a bit large. You can get away running the Inverter for short periods of time at night, and no problem during bright daylight.

[Silver_Is_Money]

Don't worry about it. Paul is mistaken.

The weak link is the FLA battery at 320 AH you normally limit discharge current to about C/8 where C = battery AH capacity and 8 is hour discharge rate So C/8 is 320 AH / 8 = 40 amps. Well 40 amps x 24 volts is 960 watts which is why I said your Inverter is a bit large. You can get away running the Inverter for short periods of time at night, and no problem during bright daylight.

Would an AGM battery bank be more appropriate for a 1,500 Watt inverter (all other things remaining the same)?

[paulcheung]

Well Dereck,

To size the battery to work continuously we have to use the 20 hours rate so the battery can provide the full capacity. when it use C/8 discharge rate. The battery will discharged in no time. You teach me that.

[Sunking]

Well Dereck,

To size the battery to work continuously we have to use the 20 hours rate so the battery can provide the full capacity. when it use C/8 discharge rate. The battery will discharged in no time. You teach me that.

Paul I understand that ole friend. But you did make and error in calculation of how much the battery can supply or C/8. That is all I was pointing out. YOu are correct if he discharges for extended periods of time is going to significantly effect capacity. But he is talking minutes, not hours.

[Sunking]

Would an AGM battery bank be more appropriate for a 1,500 Watt inverter (all other things remaining the same)?

Yes if you can afford them. AGM have lower internal resistance and depending on which manufacture and model some can supply C/2 currents. Generically C/4 or twice FLA.

But the catch is AGM cost twice as much as FLA and only last about half as long. So in the end cost you some 4 times more.

[SunEagle]

Would an AGM battery bank be more appropriate for a 1,500 Watt inverter (all other things remaining the same)?

It is not necessarily the battery chemistry that determines the size of your inverter it is the Ah and voltage rating. Also over sizing the inverter (even for short time high wattage loads) can drain your battery faster due to the higher "no load" wattage losses with just the inverter on. A 1500 watt inverter with a even a 5% no load loss will use 75 watts just sitting there. It's a vampire load which reduces the amount your battery can deliver.

[Amy@altE]

For sizing the fuse between inverter and battery. Inverter wattage / lowest operating battery voltage x 1.25. Here's my best guess, check the inverter specs for your operating range. 1500W / 20V x 1.25 = 93A, round up to 100A.

[SunEagle]

For sizing the fuse between inverter and battery. Inverter wattage / lowest operating battery voltage x 1.25. Here's my best guess, check the inverter specs for your operating range. 1500W / 20V x 1.25 = 93A, round up to 100A.

Most inverters have a higher rating for short durations. A 1500W could go to 3000W so the fuse & wire may need to be able to handle a higher amp rating for whatever duration the inverter is rated to perform at.

[Amy@altE]

Most inverters have a higher rating for short durations. A 1500W could go to 3000W so the fuse & wire may need to be able to handle a higher amp rating for whatever duration the inverter is rated to perform at.

The fuses used are slow blow fuses. See the attached graph. The Xantrex fuse can handle 250% of its rating for 10 seconds, over 300% for 1 second. Xantrex Fuse.jpg

[Amy@altE]

For sizing the fuse between inverter and battery. Inverter wattage / lowest operating battery voltage x 1.25. Here's my best guess, check the inverter specs for your operating range. 1500W / 20V x 1.25 = 93A, round up to 100A.

Sorry, I forgot a variable. Inverter wattage / lowest operating battery voltage / inverter efficiency x 1.25. 1500W / 20V / 85% x 1.25 = 110A.

(NEC 690.8(A)4) Stand-Alone Inverter Input Circuit Current. Stand-alone inverters are nearly constant-output voltage devices. As the input battery voltage decreases, the input battery current increases to maintain a constant ac output power. The input current for such inverters is calculated by taking the rated full-power output of the inverter in watts and dividing it by the lowest operating battery voltage and then by the rated efficiency of the inverter under those operating conditions.)