Solar system sizing

Laura22

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Joined
Apr 7, 2022
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3
Hi, I am new to this and trying to size my cables and fuses, and need help with it all. Sorry for the multiple questions in one post.
12v system for campervan, 2 leisure batteries to be wired in paralled - I don't know how to size the cable between the batteries. Below the datasheet of the leisure batteries. https://static1.squarespace.com/sta.../1638288981046/Roamer-Datasheet-460Smart2.pdf

Solar system 3*345w (series) - 4AWG/25mm2> mppt 150/70 > Kill switch 80a > fuse 80a > busbar (lynx 1000)+/->leisure battery. Distance between mppt and busbar/batteries less then 2m.
Do I need a circuit break between pv and mppt? Is cable sizing and fusing correct?

Starter battery -4AWG/25mm2> B2B orion 12/12-30 non-isolated> Kill switch 60a >fuse 60a > busbar +/- > leisure Battery. Distance between charger and start battery is 8m.
Do I need a circuit break between starter battery and charger? Is cable sizing and fusing correct?

Multiplus12/3000/120-16 -1AWG/50mm2> Kill switch 400a > fuse 400a > busbar +/- > leisure battery. distance between inverter and busbar/batteries less then 2m. Is cable sizing and fusing correct?

12v fuse box- 8awg/10mm2 > kill switch 30a > fuse 30a > busbar +/-> leisure battery. distance between inverter and busbar/batteries less then 2m. Is cable sizing and fusing correct?

Is me wanting to place multiple kill switches not a good idea? I haven't purcharse yet the invertor, do you recommend the Multiplus12/3000/120-50 instead? Do my leisure batteries need a fuse between them?

Thank you so much for reading all this.
 

MichaelK

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Mar 21, 2020
Messages
2,124
Those are very large batteries! At 460Ah each, wired in parallel, that amounts to 920Ah. Assuming a 1/4thC charging rate is appropriate, you could go with 920Ah/4 = 230A.

With three panels, it would make sense to wire them in parallel. What is the Voc for each panel? I'm not recommending three in series because you haven't provided that information, so I don't know if the Voc will exceed 150V with your winter lows? With three parallel solar strings, each solar string will need it's own fuse or breaker. Then another fuse breaker between the controller and the batteries.

I assume the panels will be laying flat on the roof? If so, derate the output to 60%. That would be [(345W X panels)/13Vcharging] X 60%=48A.

I would never recommend a 3000W 12V inverter. That's just an advertising gimmic, and not a real production value you can ever expect to get. 3000W/12V=250A. That is a frightening amperage. I would not buy anything that is not UL/CE listed.

Here is an ampicity chart. I would say that 1AWG to the inverter is very inadequate. I am using 0000 (that's 4/0 in this chart) for my inverter connections. I'd be using 4 gauge between the controller and the batteries.
1649514684752.png
 

Rocketman

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Joined
Sep 27, 2020
Messages
711
I have that inverter in my MotorHome- Victron 3000 12v.
The manual wants two positives and two negatives of 1/0 (if I remember correctly) or a single 4/0 (which is what I have).

If you can fit one more solar panel - look at four in a 2p2s - otherwise three is fine in 3p.

You do want an easy way to “turn the sun off” for maintenance - a circuit breaker between panels and SCC does that job.

Good luck - let us know about any other questions.
 

WYtreasure

It's not happy hour, I'm just like this.
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Nov 23, 2021
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1,681
Location
Thunder Basin Wyoming
Hi, I am new to this and trying to size my cables and fuses, and need help with it all. Sorry for the multiple questions in one post.
12v system for campervan, 2 leisure batteries to be wired in paralled - I don't know how to size the cable between the batteries. Below the datasheet of the leisure batteries. https://static1.squarespace.com/sta.../1638288981046/Roamer-Datasheet-460Smart2.pdf

Solar system 3*345w (series) - 4AWG/25mm2> mppt 150/70 > Kill switch 80a > fuse 80a > busbar (lynx 1000)+/->leisure battery. Distance between mppt and busbar/batteries less then 2m.
Do I need a circuit break between pv and mppt? Is cable sizing and fusing correct?
I believe you want a Class-T Fuse to be the first item when coming off your leisure battery.
Hopefully you are planning to use a "Kill switch" which is rated for use "under load" in every instance where you call for a "Kill switch".

Starter battery -4AWG/25mm2> B2B orion 12/12-30 non-isolated> Kill switch 60a >fuse 60a > busbar +/- > leisure Battery. Distance between charger and start battery is 8m.
Do I need a circuit break between starter battery and charger? Is cable sizing and fusing correct?

Multiplus12/3000/120-16 -1AWG/50mm2> Kill switch 400a > fuse 400a > busbar +/- > leisure battery. distance between inverter and busbar/batteries less then 2m. Is cable sizing and fusing correct?

12v fuse box- 8awg/10mm2 > kill switch 30a > fuse 30a > busbar +/-> leisure battery. distance between inverter and busbar/batteries less then 2m. Is cable sizing and fusing correct?

Is me wanting to place multiple kill switches not a good idea? I haven't purcharse yet the invertor, do you recommend the Multiplus12/3000/120-50 instead? Do my leisure batteries need a fuse between them?

Thank you so much for reading all this.
I think multiple kill switches are a good idea, provided they are of the proper size and type. A $10 or $15 kill switch is most likely the wrong type.

What country are we discussing here?
 

Laura22

New Member
Joined
Apr 7, 2022
Messages
3
Those are very large batteries! At 460Ah each, wired in parallel, that amounts to 920Ah. Assuming a 1/4thC charging rate is appropriate, you could go with 920Ah/4 = 230A.

With three panels, it would make sense to wire them in parallel. What is the Voc for each panel? I'm not recommending three in series because you haven't provided that information, so I don't know if the Voc will exceed 150V with your winter lows? With three parallel solar strings, each solar string will need it's own fuse or breaker. Then another fuse breaker between the controller and the batteries.

I assume the panels will be laying flat on the roof? If so, derate the output to 60%. That would be [(345W X panels)/13Vcharging] X 60%=48A.

I would never recommend a 3000W 12V inverter. That's just an advertising gimmic, and not a real production value you can ever expect to get. 3000W/12V=250A. That is a frightening amperage. I would not buy anything that is not UL/CE listed.

Here is an ampicity chart. I would say that 1AWG to the inverter is very inadequate. I am using 0000 (that's 4/0 in this chart) for my inverter connections. I'd be using 4 gauge between the controller and the batteries.
View attachment 90508
Voc for 1 solar panel is 40.45V. Each solar panel will be fused with 20a in line. What would be the benefit of parallel wiring vs series?
I have that inverter in my MotorHome- Victron 3000 12v.
The manual wants two positives and two negatives of 1/0 (if I remember correctly) or a single 4/0 (which is what I have).

If you can fit one more solar panel - look at four in a 2p2s - otherwise three is fine in 3p.

You do want an easy way to “turn the sun off” for maintenance - a circuit breaker between panels and SCC does that job.

Good luck - let us know about any other questions.

I will use 4/0 between batteries and towards invertor so I don't have to use 2 cables and the t-fuse. Thank you :)
I believe you want a Class-T Fuse to be the first item when coming off your leisure battery.
Hopefully you are planning to use a "Kill switch" which is rated for use "under load" in every instance where you call for a "Kill switch".


I think multiple kill switches are a good idea, provided they are of the proper size and type. A $10 or $15 kill switch is most likely the wrong type.

What country are we discussing here?
Currently in UK for 1 year, then Europe and South America.

Thank you so much for your help :)
 
Last edited:

Rocketman

Solar Addict
Joined
Sep 27, 2020
Messages
711
With parallel wiring of solar panels - from the combined point your volts will be the same (Voc 40.45) add the amps together (approx 10 each *3 = 30 amps.

FYI - for series wiring you add the volts (Voc = 121.35 ) and the amps will stay the same (approx 10amps (your post never stated the exact amps - but that will be close).

For the wires to parallel the batteries… the best way is to connect each battery to the Lynx busbar with its own cables. Those cables need to be exactly the same length and size. Their size needs to be half the 4/0 size so either 1/0 or 2/0 (I would go 2/0). Or you could just use 4/0 cable on them if it’s easier to manage just one cable size and connectors rather than two sizes.
 

MichaelK

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Mar 21, 2020
Messages
2,124
Please correct me if I am wrong, but isn't this Victron Multiplus12/3000 a hybrid inverter that has AC input, but no DC solar input? The charger mentioned in it's specifications appears to be powered via incoming grid AC.

So, for this unit to function with solar panels, you'll need a separate charge controller to charge the batteries independently of the inverter/charger.

So, this is where you question about parallel/series becomes very important.

Voc for 1 solar panel is 40.45V. Each solar panel will be fused with 20a in line. What would be the benefit of parallel wiring vs series?

Solar controllers are made in various models that all have different maximal voltages and amperages to meet the needs of individual users. Prices go up as either the voltage limit or amp limit go up. A budget controller may be limited to 100V and 20A, whereas the higher capacity model from the same manufacturer might have a 100A limit at 200V. So, the details are important here.

One of your panels by itself has a Voc of 40.45, at room temperature. Two in series would be 80.9Voc, and three, 121.35Voc. At freezing the three numbers would be 45.3Voc, 90.6Voc, and 135.9Voc respectively. At a frigid -40degrees those numbers would be 50.5Voc, 101.1Voc, and 151.7Voc.

With a budget controller like an Epever 4210, you can not wire three in series because 121.35Voc exceeds the controllers 100V limit. Two in series might be OK, unless exposed to really cold -40degrees weather.

On the other hand, three panels in parallel would put out (345W X 3 panels/13Vcharging = 79.6A, which would exceed the 40A limit of the Epever 4210. Alternatively, a high capacity unit like the Tracer 8420AN could have all three panels wired in series even in the frigid winter cold because it has a voltage limit of 200V. Three panels in series would get transformed down to 79.6A, which is below the 80A limit of this controller.
 

Rocketman

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Joined
Sep 27, 2020
Messages
711
If you are looking at Victron equipment the SmartSolar MPPT 150/60 (or 70 would be fine on a 12v system. With flat panels you will never get close to 100% - you may want to save some money and get a 60 vs the 70.
The difference is the 150/60 can deliver 860watts - anything above that will be clipped. The 150/70 can deliver 1000watts.
 

Laura22

New Member
Joined
Apr 7, 2022
Messages
3
With parallel wiring of solar panels - from the combined point your volts will be the same (Voc 40.45) add the amps together (approx 10 each *3 = 30 amps.

FYI - for series wiring you add the volts (Voc = 121.35 ) and the amps will stay the same (approx 10amps (your post never stated the exact amps - but that will be close).

For the wires to parallel the batteries… the best way is to connect each battery to the Lynx busbar with its own cables. Those cables need to be exactly the same length and size. Their size needs to be half the 4/0 size so either 1/0 or 2/0 (I would go 2/0). Or you could just use 4/0 cable on them if it’s easier to manage just one cable size and connectors rather than two sizes.
this are the specs of one solar panel
  • Maximum Power (Pmax): 345W
  • Maximum Power Current (Ipm): 10.03A
  • Maximum Power Voltage (Vpm): 34.38V
  • Short Circuit Current (Isc): 10.49A
  • Power Output Tolerance (Pmax): 0/+5
  • Open Circuit Voltage (Voc): 40.94V
  • Nominal Operating Cell Temp. (NOCT): -40 to +85°C
  • Maximum System Voltage: 1500V DC
  • Maximum Efficiency: 20%
My question is why would parallel wiring - 30a at 34.38v would be better then 10.03a at 103v? and I can get advantage of cloudy days if wired in series.
I do have a victron mppt 150/70 as recommended for the solar array.
Thanks again :)
 

MichaelK

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Joined
Mar 21, 2020
Messages
2,124
If you are looking at Victron equipment the SmartSolar MPPT 150/60 (or 70 would be fine on a 12v system. With flat panels you will never get close to 100% - you may want to save some money and get a 60 vs the 70.
The difference is the 150/60 can deliver 860watts - anything above that will be clipped. The 150/70 can deliver 1000watts.
This statement is I think only partially correct. Yes, with flat laying panels the amperage will be lower. I usually apply a 60% derating for flat panels.
But, you should be expecting full voltage, even in relatively low light, and too high voltage, even at minute amperage levels is enough to damage some electronics.
 

MichaelK

Photon Sorcerer
Joined
Mar 21, 2020
Messages
2,124
My question is why would parallel wiring - 30a at 34.38v would be better then 10.03a at 103v? and I can get advantage of cloudy days if wired in series.
I do have a victron mppt 150/70 as recommended for the solar array.
:)
You don't seem to understand what I wrote in post #7.

One of your panels by itself has a Voc of 40.45, at room temperature. Two in series would be 80.9Voc, and three, 121.35Voc. At freezing the three numbers would be 45.3Voc, 90.6Voc, and 135.9Voc respectively. At a frigid -40degrees those numbers would be 50.5Voc, 101.1Voc, and 151.7Voc.

Three panels in series will only be 103V at room temperature, and that's under load. In the winter, the panels will be cooler, and their voltage will be higher. That being said, this really depends on your location? Where are you physically located; Texas, Montana, Spain, Norway? In my location, I can wire up to 4 panels in series, but that is because I know my winter lows have never passed zeroF, and I bought the 200V model. People that do not take their winter lows into account end up frying their electronics.
 
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