1920W + 1200Ah 12V System

[NomadNorman]

I am having an overland trailer custom built and am planning out my solar system. I'd appreciate feedback on this build that someone else designed for me. The trailer will have 12v fridge, 1x12v roof a/c, and roof space will be roughly 7'x20', minus the a/c. It will be 50A.

I am undecided on batteries but leaning towards 3xEG4 12v 400Ah server racks which will be placed underneath the bed, well insulated.

4XQ CELLS, Q.PEAK DUO XL G10.3/BFG 480W, PV MODULES

Victron Energy SmartSolar MPPT 150/85-Tr VE.Can

Victron Energy Battery switch ON/OFF 275A

Victron Energy MultiPlus-II 12/3000/120-50 2x120V (UL)

Victron Energy RJ45 UTP Cable 0.9m

Victron Energy Interface MK3-USB (VE.Bus to USB)

Victron Energy Cerbo GX

Victron Energy GX Touch 70

Victron Energy Lynx Distributor (M8)

Victron Energy Lynx Shunt VE.Can (M8)

Victron Energy MEGA-fuse 100A/32V (package of 5 pcs)

Victron Energy MEGA-fuse 250A/32V (package of 5 pcs)

 

[John Frum]

It will be 50A.

Do you mean the shore power plug will be 50amp 120/240VAC?

 

[NomadNorman]

Yes, and all 110v outlets will operate from inverter.

 

[John Frum]

Since the eg4 batteries https://signaturesolar.com/eg4-lifepower4-lithium-battery-12v-400ah/ have an on off switch, a separate disconnect switch is not required.

3000va ~= 2400 watts.
2400 ac watts / .85 conversion factor / 12 volts low cutoff = 235.294117647 inverter amps
235.294117647 inverter amps + 50 dc distribution amps = 285.294117647 service amps
235.294117647 inverter amps / .8 fuse headroom = 356.617647059 fault amps

That means a 300 amp mega fuse on the inverter branch circuit and a 400 amp ANL or class-t fuse on the battery feeder circuit.

 

[John Frum]

If you are not going to have a lynx power_in to the left of the lynx_shunt I suggest you use a Victron smart shunt instead and save yourself so cash.

 

[NomadNorman]

Since the eg4 batteries https://signaturesolar.com/eg4-lifepower4-lithium-battery-12v-400ah/ have an on off switch, a separate disconnect switch is not required.

3000va ~= 2400 watts.
2400 ac watts / .85 conversion factor / 12 volts low cutoff = 235.294117647 inverter amps
235.294117647 inverter amps + 50 dc distribution amps = 285.294117647 service amps
235.294117647 inverter amps / .8 fuse headroom = 356.617647059 fault amps

That means a 300 amp mega fuse on the inverter branch circuit and a 400 amp ANL or class-t fuse on the battery feeder circuit.

Ahh, good catch! I didn't realize there was a shutoff on these EG4 but you're right. Thanks. I'm not 100% settled on this battery yet.

 

[John Frum]

The solar strings are very simple, IMO combiner boxes are not required.
I think Y cables and double pole single throw switches would be sufficient.

 

[NomadNorman]

The solar strings are very simple, IMO combiner boxes are not required.
I think Y cables and double pole single throw switches would be sufficient.

That would save me about $400 on the 2xMidNite Solar combiners/breakers. Is that the only reason?

 

[NomadNorman]

If you are not going to have a lynx power_in to the left of the lynx_shunt I suggest you use a Victron smart shunt instead and save yourself so cash.

I'll have to ask my designer about that, not sure I understand why the Lynx Shunt is needed either.

Thanks for your input John!!

 

[John Frum]

That would save me about $400 on the 2xMidNite Solar combiners/breakers. Is that the only reason?

I'm assuming the strings are configured in series so they don't need over-current protection and they essentially one unit so they don't need/can't be individually disconnected.

 

[John Frum]

I'll have to ask my designer about that, not sure I understand why the Lynx Shunt is needed either.

Thanks for your input John!!

It does current accounting in and out of the battery.
If these batteries have a smart bms with a bluetooth interface a discrete shunt of any flavor will be basically redundant.

 

[John Frum]

If you don't need that shunt it simplifies the topology greatly.

 

[John Frum]

You should probably put a victron battery protect on the dc distribution branch.

 

[NomadNorman]

You should probably put a victron battery protect on the dc distribution branch.

Hmm, why is that John? I don't see these used much.

 

[John Frum]

Hmm, why is that John? I don't see these used much.

The inverter has a built in configurable low voltage disconnect which we usually set for 12 volts.
The dc distribution center doesn't have this function so it will draw your batteries down until they disconnect at ~10 volts.
The low knee for an LFP battery starts at ~3.1 volts per cell.
Drawing a battery deep into the low knee will really mess with cell balance.
It also causes differential stress on the weakest cell which just makes it weaker.
The next time you charge it up its much more likely to trip on cell over-voltage.

 

[NomadNorman]

That means a 300 amp mega fuse on the inverter branch circuit and a 400 amp ANL or class-t fuse on the battery feeder circuit.

Hey John, was thinking about this and can't understand why I would need both the 300A (I actually think I need 400A per the Victron manual) mega fuse and a 400A ANL both? As long as I have the single 400A between battery and inverter aren't I good?

 

[John Frum]

Hey John, was thinking about this and can't understand why I would need both the 300A (I actually think I need 400A per the Victron manual) mega fuse and a 400A ANL both? As long as I have the single 400A between battery and inverter aren't I good?

If they are the same awg then technically you don't need a fuse on that branch but it is best practice.
The idea is if a fault occurs on the branch circuit that the fuse may isolate the fault to that branch.
Bussman calls it selective coordination.

Bussman: Selecting Protective Devices

Free PDF teaching how to select and use over current protection devices: Based upon the 2017 NEC® This comprehensive guide to electrical overcurrent protection and electrical design considerations is based on the 2017 NEC®. With over 300 pages...

diysolarforum.com

Littelfuse calls it fault isolation.

 

[NomadNorman]

If they are the same awg then technically you don't need a fuse on that branch but it is best practice.
The idea is if a fault occurs on the branch circuit that the fuse will isolate the fault to that branch.
Bussman calls it selective coordination.

Bussman: Selecting Protective Devices

Free PDF teaching how to select and use over current protection devices: Based upon the 2017 NEC® This comprehensive guide to electrical overcurrent protection and electrical design considerations is based on the 2017 NEC®. With over 300 pages...

diysolarforum.com

Littelfuse calls it fault isolation.

Awesome, thanks again John...and for the link too. You've been very helpful!