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diy solar

Please check my fuses

orangedoughnut

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Oct 25, 2021
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Hey all,

Could I get a sanity check on my system before I throw it together? I also had a few specific questions below.

solar-setup.png

So, questions:
  • Do I need an additional fuse between the solar array and the Growatt?
  • Do I need an additional fuse between the batteries and the Growatt?
    • The Growatt has a 60A max charge rate and the batteries only have a 50A max charge rate.
    • Also, in the Mobile Solar book, there is a solar charge controller fuse (in this case, 80A charge controller, so 100A fuse), but I'm not sure whether that still applies since I have no stand-alone charge controller.
  • Am I overpaneled for the batteries? Do I need to remove a panel to drop below 50A?
    • Max battery charge rate = 50A
    • 1400W solar / 24V battery voltage = 58.3A
Any input or advice would be very welcome. I'm a little nervous -- this will be my first solar system. Thanks!
 
Hey all,

Could I get a sanity check on my system before I throw it together? I also had a few specific questions below.

View attachment 77194

So, questions:
  • Do I need an additional fuse between the solar array and the Growatt?
  • Do I need an additional fuse between the batteries and the Growatt?
    • The Growatt has a 60A max charge rate and the batteries only have a 50A max charge rate.
    • Also, in the Mobile Solar book, there is a solar charge controller fuse (in this case, 80A charge controller, so 100A fuse), but I'm not sure whether that still applies since I have no stand-alone charge controller.
  • Am I overpaneled for the batteries? Do I need to remove a panel to drop below 50A?
    • Max battery charge rate = 50A
    • 1400W solar / 24V battery voltage = 58.3A
Any input or advice would be very welcome. I'm a little nervous -- this will be my first solar system. Thanks!
Does the Growwatt manual specify a fuse size?
200A is a reasonable size, but you could probably get away with 175A.

However, the wire size is too small. If you are using marine grade wire, the smallest wire for 200A would be 1/0AWG.

1640565879402.png

If you use wire rated for lower temps, it would have to be higher.

Are those Lead Acid Batteries? If so, ANL should be fine.

In the diagram, there are 3 Strings of 2 panels. For this arrangement, there should be a fuse on each string.

Please see this resource to figure it out:

Do I need an additional fuse between the solar array and the Growatt?
No, but you should put in a disconnect switch. (See the resource I referenced above)

Do I need an additional fuse between the batteries and the Growatt?
  • The Growatt has a 60A max charge rate and the batteries only have a 50A max charge rate.
No, but you should program the growatt to have a max 50 Grid+Solar charge rate.

Also, in the Mobile Solar book, there is a solar charge controller fuse (in this case, 80A charge controller, so 100A fuse), but I'm not sure whether that still applies since I have no stand-alone charge controller.
No. (See the resource I referenced above)

Am I overpaneled for the batteries? Do I need to remove a panel to drop below 50A?
  • Max battery charge rate = 50A
  • 1400W solar / 24V battery voltage = 58.3A
You do not need to remove a panel. Just program the Growatt to max out the Solar+Grid charging at 50A.
 
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Thanks for the reply! I read through the fuses and wiring guide you linked. Hopefully I got it right this time.

solar-setup-v2.png

A few more questions (I swear this thing is 10% practical project and 90% learning experience):
  • Can you recommend any particular combiner boxes? Looks like I'm going to need one for the panel string fuses/breakers and bus bars.
  • My batteries are LiFePO4, so definitely a Class T fuse between the battery and inverter/charger. Should the other fuse/breakers be any particular kind?
  • The manual for the Growatt recommends 6 AWG for the solar to inverter/charger, but I can't really figure out why. I've ordered an 8 AWG wire for that leg and I'd have to custom make a 6 AWG, from what I can tell. Is it worth going with the 6 AWG or will an 8 AWG do the job?
  • Same with the AC input: the heaviest prefab extension cord I can find is 10 AWG and the manual says 8 AWG. Do I need to custom make one?
Thanks again!
 
Whoops!!! I completely missed the fact that there are dissimilar solar panels in the same array! That can be a big problem.

In the configuration shown, the Jinko panel will not contribute energy and will likely drain energy! The combined 74.4V of the Canadian Solar Panel is so much higher than the 49.8V of the Jinko panel that the current will flow backward through the Jinko. This means that adding the jinko to the array will actually *reduce* the total output of the array! The backflow can be stopped with blocking diodes, but that just means there will be no back-current..... but with the voltage difference, there won't be a forward current either.

The only reasonable way to mix these dissimilar panels is to use two controllers.

Sorry I did not catch this before.
 
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I have not tried to run numbers on everything else, but the only other thing I saw that you might want to consider changing is the Solar Disconnect.
As shown there is only one breaker on the positive line. This is the way I used to do it, but the NEC requirement is that both legs should be disconnected... so I now put two-pole disconnects in. If you are using breakers, you can get a ganged breaker that will work fine.
 
Can you recommend any particular combiner boxes? Looks like I'm going to need one for the panel string fuses/breakers and bus bars.
If the Jinko panel is removed, then there are only two strings, and the need for a combiner box is reduced/eliminated.
My batteries are LiFePO4, so definitely a Class T fuse between the battery and inverter/charger.
Good
Should the other fuse/breakers be any particular kind?
Well, The AC input breaker should be AC rated. (BTW: Does the Growatt have a breaker on the AC output? If not, you may want to add one.)
The configuration for the panels will probably be changing. If the new configuration needs breakers on each string (It may not), they should be DC rated. If the are polarized breakers, it is important to put the positive pole toward the charge controller.
The PV Disconnect breaker should be DC rated and should have a trip value at something greater than 1.56x the array Isc.
The manual for the Growatt recommends 6 AWG for the solar to inverter/charger, but I can't really figure out why. I've ordered an 8 AWG wire for that leg and I'd have to custom make a 6 AWG, from what I can tell. Is it worth going with the 6 AWG or will an 8 AWG do the job?
This needs to be discussed in two parts.
1) The circuits going from the panels to the combiner point. (These are called the source circuits)
  • For the Canadian Solar panels, the string ISC is 8.87A. 1.56x8.87=13.84A. For these, even a 12AWG would work if it is a short run. If the runs are longer, you may need to calculate the voltage drop to find out if a larger wire is needed.
  • For the Jinko panel, the Isc is 10.6A. 10.6*1.56=16.54. Again, 12AWG should work unless it is a really long run.
2) The circuit that goes from the combiner point to the controller. (This is called the output circuit).
Note: For this calculation, I will assume the Jinko is on a separate controller than the Canadian Solar.
  • The combined current of the Canadian solar array is 2x8.87A=17.74A. 1.56 x 17.74A=27.67A. For a very short run, this should be at least 10AWG. If the run is very long it should probably be 8AWG.
  • The Jinko is a single panel so the Source Circuit is also the Output circuit. As calculated above, 12AWG should be fine unless it is a long run.
You may ask why the manual recommends 6AWG. I would need to look up the Growatt manual to be sure, but I am guessing the 6AWG is what would be needed for the max PV config for the controller. If the actual config is smaller, the wires can be smaller.

Same with the AC input: the heaviest prefab extension cord I can find is 10 AWG and the manual says 8 AWG. Do I need to custom make one?
The reason for the larger wire is that when the inverter is in pass-through *and* charging the battery, it can be a lot of current.

The worst case scenario for your configuration is that the inverter is in pass-through mode and is charging the battery at 50A.
The 50 charge current translates to a worst case wattage of 28.5V x 50A = 1425W. Assuming the charger is 95% efficient, that translates into
(1425/.95)/120=12.5A.

Meanwhile, the 3000W load on the output of the inverter is drawing 3000/120=25A.

So.... the combined (worst case) current on the input is 32.5A... This would exceed the 30A rating of a 10AWG wire so 8AWG is needed on the input.
 
Welcome to the forum O

I purchased this Combiner box and MidNite Solar DC Fuses. Good quality and it leaves room for future expansion.

FilterGuy has numerous links at the bottom of his posts to help you, including:

 
FilterGuy has numerous links at the bottom of his posts to help you, including:
This is probably a better resource for a combiner box fuse sizing

 
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