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Another Travel Trailer Solar Build Schematic - That needs review by all you DC Power Gurus

Dan Sinclair

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Mar 7, 2020
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I am installing a solar system that is a completely separate system from the factory DC system that comes with our travel trailer. The secondary system is intended to supply 120V power to a couple of 120V receptacles when dry camping. The original DC system will supply all 12V requirements as it did from the factory. I did add a second cheap battery that matches the original cheap battery of the original system as well as an ammeter to monitor the original DC system. The new system has 4 - 100W solar panels, a 2200 watt inverter, a 40 Amp MPPT Solar Controller and two SOK 100AH LiFePO4 Batteries. I have questions regarding the following on my wiring diagram attached.
1 - Do my Grounds look correct? See Green wires, they are terminating where original ground is tied to frame.
2 - The original DC system has a Battery cut off switch on the positive side, I am placing the cut off on the negative side on the new as shown on wiring diagram that came with the switch?
3 - Do my fuses/circuit breakers look correct?
Thanks for looking I appreciate it!
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Post the specs for the panels (Voc, Vmpp, Isc, Impp) and the max input voltage of your SCC. And confirm the panel configuration. Is it 4S or something else?

I would suggest some changes to the wiring layout. The "+ bus" should be connected to the fuse on the battery positive. Then everything should connect to the bus bar. Right now you have two wires going to the battery and a bunch of other things going to the bus bar. Same with the "- bus". That should be connected directly to the shunt and then everything should connect to the bus bar. In other words, the shore power converter charger should be wired to the bus bars like everything else.

There needs to be proper sized fuse between the inverter and the "+ bus".

There should be a breaker on the positive wire between the solar panels and the SCC to act as a disconnect. Make sure the breaker can handle the full Voc of the panels. Don't forget the Voc rises in colder temperatures.

Most people put the battery cutoff switch on the positive lead but I suppose it works on the negative wire.

The two SOK batteries in parallel support a 200A continuous discharge and 400A surge for 3 seconds. The 2200W inverter at max will draw about 180A. Add a few more loads and you could go over 200A. That might cause a nuisance trip of the fuse. Then again, the 200A fuse does prevent the batteries from discharging at too high a current. If you never plan to use the full 2200W of the inverter then the 200A fuse is probably good. A 225A fuse might give you a little wiggle room. The 2/0 wire can be fused up to 300A.

Make sure your 2/0 wire runs are no more than 20' round trip. The 2/0 wire is good for 200A up to 20' total round trip if you want to keep the voltage drop low (which you do for those critical paths).

Make sure the 8AWG wire from the SCC is less than 10' roundtrip to best handle the 40A. If longer you should use 6AWG.

Is the 12V socket your only DC load in this LiFePO4 setup?
 
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Post the specs for the panels (Voc, Vmpp, Isc, Impp) and the max input voltage of your SCC. And confirm the panel configuration. Is it 4S or something else?

I would suggest some changes to the wiring layout. The "+ bus" should be connected directly to the battery positive. Then everything should connect to the bus bar. Right now you have two wires going to the battery and a bunch of other things going to the bus bar. Same with the "- bus". That should be connected directly to the shunt and then everything should connect to the bus bar. In other words, the shore power converter charger should be wired to the bus bars like everything else.

There needs to be proper sized fuse between the inverter and the "+ bus".

There should be a breaker on the positive wire between the solar panels and the SCC to act as a disconnect. Make sure the breaker can handle the full Voc of the panels. Don't forget the Voc rises in colder temperatures.

Most people put the battery cutoff switch on the positive lead but I suppose it works on the negative wire.

The two SOK batteries in parallel support a 200A continuous discharge and 400A surge for 3 seconds. The 2200W inverter at max will draw about 180A. Add a few more loads and you could go over 200A. That might cause a nuisance trip of the fuse. Then again, the 200A fuse does prevent the batteries from discharging at too high a current. If you never plan to use the full 2200W of the inverter then the 200A fuse is probably good. A 225A fuse might give you a little wiggle room. The 2/0 wire can be fused up to 300A.

Make sure your 2/0 wire runs are no more than 20' round trip. The 2/0 wire is good for 200A up to 20' total round trip if you want to keep the voltage drop low (which you do for those critical paths).

Make sure the 8AWG wire from the SCC is less than 10' roundtrip to best handle the 40A. If longer you should use 6AWG.

Is the 12V socket your only DC load in this LiFePO4 setup?
Wow, Thank you so much, I will revise and repost and also post panel specs. I really appreciate you taking the time to look at this!
 
Glad to help. I just noticed one misstatement in my previous post. The "+ bus" should not be connected directly to the battery positive. The "+ bus" should be connected to the battery fuse. I edited my post to reflect that.

battery positive -> battery fuse (200A) -> + bus -> everything

battery negative -> shunt -> - bus -> everything
 
Wow, Thank you so much, I will revise and repost and also post panel specs. I really appreciate you taking the time to look at this!
Glad to help. I just noticed one misstatement in my previous post. The "+ bus" should not be connected directly to the battery positive. The "+ bus" should be connected to the battery fuse. I edited my post to reflect that.

battery positive -> battery fuse (200A) -> + bus -> everything

battery negative -> shunt -> - bus -> everything
So question - Each Panel’s VOC is 22.6V, four panels with 2 Ea in Series, Grouped in parallel. Does the panel VOC double or quadruple when wired like this. Reason for asking is size of breaker, is a 50A sufficient? Thanks Again. I will be posting an updated schematic with the changes from your suggestions later this evening.
 
So question - Each Panel’s VOC is 22.6V, four panels with 2 Ea in Series, Grouped in parallel. Does the panel VOC double or quadruple when wired like this. Reason for asking is size of breaker, is a 50A sufficient? Thanks Again. I will be posting an updated schematic with the changes from your suggestions later this evening.
I have updated the schematic but still a work in progress.
 
The panels don't really determine the breaker after the SCC. The amperage of the SCC is the determining factor. Since it's a 40A SCC the 50A fuse is what you want.

The max input voltage of the SCC is the really important number that you haven't posted yet. With your panels in 2S2P the Voc is double that of a single panel. It's just like with batteries. Voltage in series is added while the amps stay the same. Amperage in parallel is added while the volts stay the same. With panels in 2S2P you double the volts due to the 2S and you double the amps due to the 2P.

So a panel with a Voc of 22.6V means your 2S2P will have a Voc of 45.2V. Maybe about 48 or 49V in cold weather. As long as your SCC has a max input voltage of 55V or more you are good.
 
The panels don't really determine the breaker after the SCC. The amperage of the SCC is the determining factor. Since it's a 40A SCC the 50A fuse is what you want.

The max input voltage of the SCC is the really important number that you haven't posted yet. With your panels in 2S2P the Voc is double that of a single panel. It's just like with batteries. Voltage in series is added while the amps stay the same. Amperage in parallel is added while the volts stay the same. With panels in 2S2P you double the volts due to the 2S and you double the amps due to the 2P.

So a panel with a Voc of 22.6V means your 2S2P will have a Voc of 45.2V. Maybe about 48 or 49V in cold weather. As long as your SCC has a max input voltage of 55V or more you are good.
I put it on the SCC (in very small print) but it has a max solar input V - 100 VDC
 
I put it on the SCC (in very small print) but it has a max solar input V - 100 VDC
I really value your input on this as I know nothing, just been doing as much reading as this old brain can handle. With that said for some reason I keep on looking at the grounds from the neg side of the battery off of the shunt, does that look correct to you? Also still wondering about the battery shut off, I will post a pic of info that came with switch that shows it on neg side? Thanks, Can I buy you a beer?

Another dumb question can I put the wire from the battery at any location on the bus bar, I have four lugs on the bus bar, can it be attached to one of the middle ones, I would think so but? Also can I double up on one of the lugs of the bus bar?
 
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The ground wire near the battery should be attached to the "- bus" like everything else. The only thing attached to the shunt should be the battery on one end and the negative bus bar on the other end.

I don't think it matters which studs things get attached to on the bus bar. Though I think a lot of people put the battery on one end and then the device with the highest current goes closest to that connection and the wire with the lowest current goes on the furthest. That's probably being really over the top but...

You can put multiple wires on one lug. I wouldn't do more than two but that's me. If you do stack two or more, again, put the one with the highest current on first and the lowest current on top of the stack.
 
Can you tell me the proper gauge of wire to run for the grounds?

For each grounded device I used the same wire size as the + and - wires for its ground wire. Then I used the largest of those sizes to run the final ground wire from the bus bar to the trailer frame.

But I'm not really sure if that's the correct way to determine ground size.
 
run the final ground wire from the bus bar to the trailer frame.

But I'm not really sure if that's the correct way to determine ground size
You should have a ground path to the trailer frame. The ground from (to?) the inverter and to the frame should be the same size as the positive (+) cable. Device grounds should source at the negative bus or DC power distribution / fuse block.
Some cite a theory that the ‘ground’ can be smaller than the + cable “because + energy gets used up by the running accessories” but that is not entirely how that works irl.
 
I’m no expert so take some, all, or none of this. Won’t hurt my feelings. Installation is very neat and easy to follow unlike mine.
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Not sure of the quality of the T-Tocas Circuit Breakers, Check the reviews on those. Busman and Blue Sea are good, but others have done things like drop voltage or pop far above or below the rated capacity.

What type of power do you have? Lithium may not blink at an ANLE fuse and just arc across it.

For your 45 amp AC to DC converter, what is your plan to not have it charge itself? A transfer switch is one way. I have my inverter plugged into the Shore Power, so I trip the breaker to the converter. If I don’t bad things can happen.

A 2200 watt inverter is pretty ambitious through a 12 volt system. A 200 amp fuse may not cover the power, so bring spares. I have a 2000 watt inverter With a 200 amp fuse. When I run it at 1800 AC watts, about 2100 watts comes from the battery and I pull 155 amps.

If I were to do that with low SOC batteries, the volts would be lower and amps higher. Could go as high as 200 amps an that 1800 watt AC load if my battery voltage sags to the inverter cutoff of 10.5 amps. I have not run the high wattage loads except on a fully charged battery, so I don’t know what the sag voltage is when SOC is low. 4/0 wire for this.

A couple of your lugs are bare copper. I’ve found its not to hard to use nickel electrolysis to coat those To prevent corrosion.
 
Type of power 2 -100 AH SOK Lithium with 4 100 watt panels 2 panels wired in series grouped in parallel.
Hmmm I not think of the charger charging itself, is that a thing? Have not plugged it in yet
 
Why two systems? Sure complicates things.
Well the 20amp controller is for my original house batteries, had that first. Then I added the 40 amp that is for my lithium batteries for a separate system in my travel trailer. Added receptacles that are for the lithium setup only which we use when dry camping for our 110 power source, the lighting is still all tied into the original house 12 volt system. Seems to work well.
 
Well the 20amp controller is for my original house batteries, had that first. Then I added the 40 amp that is for my lithium batteries for a separate system in my travel trailer. Added receptacles that are for the lithium setup only which we use when dry camping for our 110 power source, the lighting is still all tied into the original house 12 volt system. Seems to work well.
Just asking. I wouldn't want to lug around an extra 100 lbs of batteries when you have 200aH of LFP goodness that can more than handle all your power needs.
 
wouldn't want to lug around an extra 100 lbs of batteries when you have 200aH of LFP goodness that can more than handle all your power needs.
He doesn’t have to lug them around; they’re factory installed in the RV.
What exactly is lfp goodness?!LOL
 
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