Gut Check Time...

[HRTKD]

I put together a diagram of my 12 volt system and I would like a check on if I have the right size protection devices included.

The solar panels in the diagram aren't what I'll be using. I can get a bigger bang for the limited roof space by going with two 320 watt Mission Solar panels and then two of something else, but I haven't figured out what that something else is yet. The other panels will probably go on their own charge controller.

The new system is on the left side of the diagram. Everything on the right (except for the solar panels at the top) is existing equipment and isn't going to change.

I don't pull much power at the same time. I added up everything in my trailer and if I turned on everything at the same time I could pull about 140 amps. Of course, I would never do that, so my maximum draw is much lower, probably no more than 90 amps. I would hit 90 only when running the coffee maker off of the inverter. My system is beefed up to ensure that I have plenty of runtime over a cold night - or nights - when the furnace is running almost constantly.

Specifications for the Mission Solar 320 watt panels

Temperature coefficient of Voc: -0.28% °C​

Temperature coefficient of power: -0.377% °C​

Temperature coefficient of Isc current: ±0.039% °C​

NOCT (nominal operating cell temperature): 46.09 ° C (± 2° C)​

Maximum Power Output: 320 Watts​

Max Operating Voltage (Vmpp): 34.22 Volts​

Max Operating Current (Imp): 9.351 Amps​

Open Circuit Voltage (Voc): 40.08 Volts​

Short Circuit Current (Isc): 10.028 Amps​

Module Efficiency: 18.94%​

Thanks. Don't be gentle.

 

[John Frum]

There is no means of disconnect between the panels and the scc.
Is the whole system isolated from the chassis?

 

[Deleted member 4428]

250 amp class t fuse is too large for 2/0 battery cable. 175 amp max.
50 amp Bussman 157 too large for 6ga wire. 40 amp max, 30 amp is safer.

 

[HRTKD]

There is no means of disconnect between the panels and the scc.
Is the whole system isolated from the chassis?

You are correct that there is no disconnect between the panels and the SCC. I was hoping to find a way to do that without a combiner box.

It's not shown, but the SCC will be grounded. I read in the Victron manual that they want the SCC grounded, but not the panels. I need to put a common ground distribution block in the diagram.

250 amp class t fuse is too large for 2/0 battery cable. 175 amp max.
50 amp Bussman 157 too large for 6ga wire. 40 amp max, 30 amp is safer.

I think I had a brain fart on the Bussman 157 and the wire. Might still be occurring. If I stepped down to 2 or 4 gauge wire, the 50 amp Bussman would be appropriate? The charge controller can potentially put out 50 amps.

 

[JoeHam]

You could consider something like this * with the appropriate sized wire *

250V Low-voltage C65H-DC Miniature Circuit Breaker For Solar Panels 16A/32A/63A(32A) - - Amazon.com

250V Low-voltage C65H-DC Miniature Circuit Breaker For Solar Panels 16A/32A/63A(32A) - - Amazon.com

www.amazon.com

 

[Deleted member 4428]

Brain fart? Is that the same as a Floriduhhhh moment
4ga works if the terminals of the SCC will accept that.

 

[John Frum]

2/0 awg pure copper rated for 105 celcius is rated for 330 amps.
6 awg pure copper rated for 105 celcius is rated for 120 amps.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

 

[HRTKD]

Brain fart? Is that the same as a Floriduhhhh moment
4ga works if the terminals of the SCC will accept that.

Crud, another brain fart. I knew the SCC wouldn't support any wire heavier than 6 awg. I don't know why I suggested that. Plan "C" would be to keep the 6 awg but change the circuit breaker to a lower amperage. I already have the 6 awg wire and lugs.

 

[svetz]

Sorry, know nothing about trailers, so please... don't anyone hurt themselves laughing at these... ?

1. I think NEC only requires a rapid shutdown on buildings, any value on a trailer?
2. AC Charger so the generator can charge the batteries?
3. GFCI circuit on Inverter?
4. AC Bus is the trailer load center?
5. Grounding?
6. Shutoff for the converter so you can run cable from the inverter output to the 30 Amp shore power input?
7. Brutal Acronym police: ATC is a typo of ATS?

 

[HRTKD]

2/0 awg pure copper rated for 105 celcius is rated for 330 amps.
6 awg pure copper rated for 105 celcius is rated for 120 amps.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

I think I used the same calculator, or one similar when figuring out which wire to use. Some of my stuff is coming from Bay Marine, so I know I at least saw their calculator.

My dual BMS configuration will allow a discharge of as much as 240 amps. The distance is going to be under 10'. That calculator said that 2/0 is "Excellent for most uses". Are you saying that 2/0 is OK or not?

 

[Deleted member 4428]

Thanks SmoothJoey. One would think I was drinking or high. Sorry to say that's not the case. It's getting worse too because I know all this stuff.

 

[John Frum]

I think I used the same calculator, or one similar when figuring out which wire to use. Some of my stuff is coming from Bay Marine, so I know I at least saw their calculator.

My dual BMS configuration will allow a discharge of as much as 240 amps. The distance is going to be under 10'. That calculator said that 2/0 is "Excellent for most uses". Are you saying that 2/0 is OK or not?

Its fine for 10 feet round trip.
3/0 is indicated for 20 feet round trip.

 

[HRTKD]

Sorry, know nothing about trailers, so please... don't anyone hurt themselves laughing at these... ?

1. I think NEC only requires a rapid shutdown on buildings, any value on a trailer?
2. AC Charger so the generator can charge the batteries?
3. GFCI circuit on Inverter?
4. AC Bus is the trailer load center?
5. Grounding?
6. Shutoff for the converter so you can run cable from the inverter output to the 30 Amp shore power input?
7. Brutal Acronym police: ATC is a typo of ATS?

1. Standards? On a trailer? Minimal, but I am more likely to do things by the book than most people are. I'm more likely to overconfigure than underconfigure, when I know what minimum/ideal configuration standards are. I think I need to read through the Yacht electrical document.
2. Yes, the AC converter can be powered by either shore or generator.
3. Yes, the inverter has GFCI on the outlet on the inverter box and the remote outlet has that also I believe.
4. Correct. I'm not touching that part of the system. No changes I'm making directly integrate with the existing AC system. Not even the inverter.
5. Any product that has instructions to ground it will be grounded.
6. The converter has a dedicated circuit breaker on the AC bus.
7. I had no idea that my design tool had autocorrect.

 

[HRTKD]

Its fine for 10 feet round trip.
3/0 is indicated for 20 feet round trip.

Whew! The closet I'm putting all this in is right next to heart of where all the AC and DC systems in the trailer come from.

 

[svetz]

Regarding the rapid shutdown, NEC usually has great reasons for why things are in the code and it makes sense to follow them. That's why I was wondering if there would be value on a trailer...esp. as you're most likely to be your own volunteer fire department.

On #2... does the converter have a special circuit to charge Lithium batteries? Or is the output voltage high enough where CC/CV is done by the BMS and won't exceed the battery C-Rate?

 

[HRTKD]

On #2... does the converter have a special circuit to charge Lithium batteries? Or is the output voltage high enough where CC/CV is done by the BMS and won't exceed the battery C-Rate?

Good question. No, the current converter does NOT understand how to correctly charge a LiFePO4 battery. In fact, I question if it is even correctly charging my flooded lead acid batteries. But that's a different subject. Suffice it to say that I'm not confident in the converter and I will be disabling it altogether, selectively enabling it, or replacing it. The converter isn't being used that much. I rarely run the generator or connect to shore power. The existing sole solar panel does an OK job of charging the battery.

I'm going to admit my ignorance here with this question: Does a DIN rail that the circuit breaker suggested by @JoeHam in post #5 provide only a mounting solution? Or does it also provide some common power connection?

Here's why I'm asking (beside being ignorant). If I end up with two isolated solar strings coming into the diagram, can I put two sets of those breakers on the same DIN rail without causing problems? The two strings will likely go into their own solar charge controller. They shouldn't share a circuit until after the charge controller. I'm thinking the answer is an easy "No" because it looks like that dual breaker setup has + on one side and - on the other. If the circuit breakers were electrically tied into the DIN rail there would be significant sparks when I flipped the switch.

 

[JoeHam]

The DIN rail is a mechanical mount only.

No sparks ?

 

[HRTKD]

I should have no more than 25 amps coming in from my main string of solar panels. So the 32 amp circuit breaker is enough, right? I don't need the 63 amp circuit breaker?

If I put the circuit breaker in, the in-line fuses located at the panels are redundant?

 

[John Frum]

I see that you have a 50 amp breaker in front of a 50 amp solar charge controller.
Standard practice is to fuse someone between the capacity of the wire and 1.5 times the continuous load or in this case 75 amps.

 

[HRTKD]

I see that you have a 50 amp breaker in front of a 50 amp solar charge controller.
Standard practice is to fuse someone between the capacity of the wire and 1.5 times the continuous load or in this case 75 amps.

Ah, I can see where the breaker could trip if the solar charge controller gets close to its limit. I'll adjust that.