DC to DC Charging and Inverter Wiring Diagram and Feedback

[slosquirrel]

Recently installed a Epoch 300Ah battery, Victron BMV 712 battery monitor / smart shunt, and hooked up a Victron smart dongle to the overland solar MPPT controller in my 2020 Front Dinette Grandby.

Moving onto the next phase which is DC to DC charger and inverter. Developed the attached wiring diagram based on what I've seen others do, but looking to solicit feedback to make sure I'm not missing anything before I pull the trigger on ordering all the parts / pieces (though I did already score a deal on a Victron 12V|1200VA inverter on FB marketplace).

If you have experience and are willing to provide feedback I'd greatly appreciate it!

EDIT: Didn't realize how small it would show up, but if you click on the image below it'll expand)

 

[Jon R]

First of all - nice diagram!

Two things I noted:

1) The camper battery positive should have a fuse/CB as close to the battery as practical, sized to protect the smallest otherwise unprotected wire in the circuit.

2) The circuit breakers associated with the dc to dc charger do not have the recommended margin if you are going to run the XS at 50 amps. The wire from the truck battery is going to see about 55 amps. Following the 80% industry rating recommendation for continuous loads, a 70 or 80 amp breaker would be more appropriate. Even for the 50 amps on the output wire a 60 amp CB is not quite large enough to meet the recommendation. The issues caused by not following that recommendation are possible nuisance trips and deterioration of the breaker due to long term heat exposure.

 

[Vic Harder]

Agreed, nice diagram. What are the two items below that Orion? They look like thermal breakers?

 

[Jon R]

Agreed, nice diagram. What are the two items below that Orion? They look like thermal breakers?

I think they are small bus bars allowing the change from 2 awg wire to 6 awg wire.

 

[K7MDL]

You may be fine with the 60A breakers. I have a 50A charger and 6AWG wire, measured voltage drops and currents, I never saw more than 42A input from my alternator. YOur may be better or worse.

The charger output is current limited at 50A, unlike a battery with very high short circuit current possible. If your power into the converter is limited so will the output be limited.

Assuming your battery is close to the bus bars, a fuse/breaker is not required there but everything coming off the bus bars should be protected according to their wire size. I see some smaller wires are not protected. The fuses should be close to the bus bar since you are protecting the wire.

 

[slosquirrel]

First of all - nice diagram!

Two things I noted:

1) The camper battery positive should have a fuse/CB as close to the battery as practical, sized to protect the smallest otherwise unprotected wire in the circuit.

2) The circuit breakers associated with the dc to dc charger do not have the recommended margin if you are going to run the XS at 50 amps. The wire from the truck battery is going to see about 55 amps. Following the 80% industry rating recommendation for continuous loads, a 70 or 80 amp breaker would be more appropriate. Even for the 50 amps on the output wire a 60 amp CB is not quite large enough to meet the recommendation. The issues caused by not following that recommendation are possible nuisance trips and deterioration of the breaker due to long term heat exposure.

Jon R,

Thanks for the kudos and feedback.

1) Battery positive will have a 250A MRBF (Marine Rated Battery Fuse) on the Terminal Block (MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems)

2) Good feedback on the DC to DC circuit breakers. The 70A version cost ~$1 less than the 60A version so I'll upgrade both to 70A.

 

[slosquirrel]

I think they are small bus bars allowing the change from 2 awg wire to 6 awg wire.

Vic / Jon R,

Correct, they are small (200A) bus bars to switch from 2AWG to 6AWG just before the DC to DC Charger. I read somewhere that the Orion XS 50 accepts a MAX of 6AWG, but just looked at the manual online and it looks like it accepts a 4AWG.

 

[slosquirrel]

You may be fine with the 60A breakers. I have a 50A charger and 6AWG wire, measured voltage drops and currents, I never saw more than 42A input from my alternator. YOur may be better or worse.

The charger output is current limited at 50A, unlike a battery with very high short circuit current possible. If your power into the converter is limited so will the output be limited.

Assuming your battery is close to the bus bars, a fuse/breaker is not required there but everything coming off the bus bars should be protected according to their wire size. I see some smaller wires are not protected. The fuses should be close to the bus bar since you are protecting the wire.

I might just bump up to 70A circuit breakers. That way I know it's not limiting any power unnecessarily and will still trip in the event of a short circuit.

Everything should be fairly close with short cable runs, the only positive load not protected is going to the factory installed battery disconnect and 12V blue sea fuse block. I'll add up all the fuses in there and add another fuse in the line close to the positive bus bar.

 

[Jon R]

Jon R,

Thanks for the kudos and feedback.

1) Battery positive will have a 250A MRBF (Marine Rated Battery Fuse) on the Terminal Block (MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems)

2) Good feedback on the DC to DC circuit breakers. The 70A version cost ~$1 less than the 60A version so I'll upgrade both to 70A.

That 250 amp fuse at the battery is just above what the ABYC table says would be acceptable to protect 2 awg wire from excess heat in a hot short. It’s way too large for the 6 awg and 10 awg wire shown in the diagram as having at least short lengths only protected by the battery fuse. In addition, even if you had all 2 awg wire, why allow such high fault current if you don’t need to? A 250 amp fuse will allow all kinds of melting and sparks at the fault if a short to a grounded item occurs. You don’t want that in an enclosed sleeping space.

In this kind of installation I would suggest reducing the size of the battery fuse to just large enough to avoid nuisance trips with your highest expected operating current. That might be when the inverter is running at capacity, or could be when both the solar and truck chargers are providing maximum combined output. That may call for only a 100 amp fuse. I would suggest reducing that fuse size based on your analysis of the maximum expected operating current multiplied by 1.25 (the 80% rule I mentioned in my first post). This is just my opinion on a design choice. Others may have different advice on this.

 

[slosquirrel]

That 250 amp fuse at the battery is just above what the ABYC table says would be acceptable to protect 2 awg wire from excess heat in a hot short. It’s way too large for the 6 awg and 10 awg wire shown in the diagram as having at least short lengths only protected by the battery fuse. In addition, even if you had all 2 awg wire, why allow such high fault current if you don’t need to? A 250 amp fuse will allow all kinds of melting and sparks at the fault if a short to a grounded item occurs. You don’t want that in an enclosed sleeping space.

In this kind of installation I would suggest reducing the size of the battery fuse to just large enough to avoid nuisance trips with your highest expected operating current. That might be when the inverter is running at capacity, or could be when both the solar and truck chargers are providing maximum combined output. That may call for only a 100 amp fuse. I would suggest reducing that fuse size based on your analysis of the maximum expected operating current multiplied by 1.25 (the 80% rule I mentioned in my first post). This is just my opinion on a design choice. Others may have different advice on this.

Jon R,

Highest load will be the Victron 12v|1200VA inverter. Specs are:

• Max Wire Size: 2AWG
• Continuous Power: 1000W
• Peak Power (Surge): 2200W

My math:

• At 1000w (Continuous)
  • 1000w / 12v = 83.33A
  • 83.33A * 1.25 = 104.16A
• At 2200w (Peak / Surge)
  • 2200w / 12v = 183.33A
  • 183.33 * 1.25 = 229.16A

The surge is what's really throwing me off. I was planning a 175A MEGA fuse before the the inverter, but is that overkill? The inverter manual states it has an internal 200A fuse, I figured going a size lower (e.g. 175A) so it blows first was the right call?

All other loads off the positive bus bar will be fused properly based on wire gauge and expected loads.

Which actually brings up another question. Is there a fuse in the existing positive cable from the battery to factory installed 12V (12 terminal) fuse block? If so, I didn't see one. Wire looks to be 6-8 AWG? Looking at the fuse panel there's 11 blade fuses totaling 102.5A?

 

[Vic Harder]

When I fused my 3000W pure sine wave inverter (which can surge to crazy high numbers) I fused it at 250A (3000/12.5 = 240A). Of course, the inverter can draw more than the steady state when in surges, which it has when both the induction cooktop (1800W) and a hair dryer (I'm bald) were used at the same time. Those mega fuses make a nice bright spark when they go! Otherwise, the fuse has never popped.

 

[slosquirrel]

When I fused my 3000W pure sine wave inverter (which can surge to crazy high numbers) I fused it at 250A (3000/12.5 = 240A). Of course, the inverter can draw more than the steady state when in surges, which it has when both the induction cooktop (1800W) and a hair dryer (I'm bald) were used at the same time. Those mega fuses make a nice bright spark when they go! Otherwise, the fuse has never popped.

Vic,

Based off your feedback I'm thinking of ditching the Mega Fuse and Switch / Disconnect at the Inverter and just installing a 120A-135A Blue Sea 187-Series MRCB. I shouldn't be fusing to peak / surge power.

I'll probably do something similar at the battery. Thinking either 150A or 200A. The 187 series circuit breakers are expensive, but require less components (and space).

 

[K7MDL]

My 2022 Front Dinette Hawk had 8AWG running from the rear batteries to the breaker under the front dinette seat next to the ACR. On the other side of the breaker is 10AWG outside to the truck and a short 10AWG to the fuse panel in the cabinet. There should be a fuse/breaker near the batteries in the back for that long a run. My Li battery is now under the dinette curing that problem and cutting out half of the wire length. I reused the old battery 8AWG to extend the solar panel raw to the solar charger input up front. I kept the old solar fuse in back.

 

[Vic Harder]

Vic,

Based off your feedback I'm thinking of ditching the Mega Fuse and Switch / Disconnect at the Inverter and just installing a 120A-135A Blue Sea 187-Series MRCB. I shouldn't be fusing to peak / surge power.

I'll probably do something similar at the battery. Thinking either 150A or 200A. The 187 series circuit breakers are expensive, but require less components (and space).

Correction: I noticed yesterday while rechecking my camper inventory that I used 300A fuse after the 250 popped.

 

[slosquirrel]

Correction: I noticed yesterday while rechecking my camper inventory that I used 300A fuse after the 250 popped.

Vic, thanks for checking that out. That should still just account for your 3000W at continuous load correct?

• (3000W / 12.5V) = 240A
• 240A * 1.25 = 300A

Going off that math it looks like my 1200VA (1000W) should be

• (1000W / 12.5V) = 80A
• 80A * 1.25 = 100A

I'm still thinking ~135A - 150A Blue Sea 187 Series MRCB might be the best bet?

From what I've read the Victron can handle higher than the 1000W continuous load rating and that would allow the inverter to surge to ~1350 - 1500W (well below the max surge rating of 2200W), all while still providing adequate protection for the 2AWG cable and the 200A internal fuse that the inverter has.

 

[Vic Harder]

Yes and keep in mind that breakers are sometime "slow blow". I like having a fuse in this circuit to go fast should something really go sideways.

And I rarely use more than 1800W. I got the 3000W because at 2000W unit would be running awfully close to max power. My two BattleBorn 100AH batteries each only put out 100A max, so really I am limited by the input current to 200A*12.5 = 2500W

 

[slosquirrel]

Revised my diagram based off feedback from all you great people and some others over on the Four Wheec Campers Owners FB group.

Revisions include:
- Increasing XS50 MRCB from 60A to 70A and changing them to 187-series from Blue Sea
- Trailer Vision Weatherproof Enclosures to the Anderson SB120 connectors.
- ScanStrut Cable Seal on camper penetration
- 100A Mega Fuse Block between new positive busbar and existing (factory installed) battery switch / 12v fuse block
- Inverter remote switch and VE.Direct Smart Dongle
- Dual MRBF terminal fuse block with separate feeds and battery switches for inverter (175A) and busbar (125A).

The Victron inverter is rated at 1000W continuous, but can surge up to 2200w. Fusing it at 175A will allow it to surge to ~1750W while still protecting the internal fuse.... But after looking at the wiring recommendations from Blue Sea looks like I may want to upsize the wire from the inverter to the battery, or reduce the fuse to ~150A.

Let me know if I missed anything, and thank you again for all the feedback!