Van Build - Design Check: Have I sized my battery fuse correctly?

[shrekqween]

I am not sure about is whether or not to size my battery bolt on fuse based on the 700W Inverter or the DC Fuse Block. Right now I have it at 80A, sized by the inverter:

700W/12V = 58.83A

58.83 x 1.25 = 72.92A -> round up to 80A

If I were to size based on the fuse block, I imagine I'd have to go with a 125A.

Please correct me! Thanks

 

[mikefitz]

The 'master' fuse at the SOC battery idealy should have a higher fault current withstand. The MEGA is only good for 2000 amps, better would be a MRBF fuse on a Blue Sea holder, directly on the battery post. ( MRBF rated at 10000 amps at 12v)
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A
With inverter efficiency the current will be higher than your calculation, and house loads also, fuse value 100/125 amps would be good. (note the SOK is rated for 100 amps continuous, a fault together with BMS failure could allow the battery to deliver 1000s of amps).

Fit your other fuses near or incorporated with the positive buss bar, 60A for the Renogy and 40A for the fuseblock feed.

Wiring error, all battery negative should pass the shunt, remove the connection from the battery negative to buss bar.

Once operational you will have a better idea of managing power use. You may need some care using the inverter at full power together with all house 12v loads as you could exceed the 100 amps limit on the battery.

Investigate USB and laptop charging via 12v power converters, fed via fuses in the 12v fuseblock . This will be more efficient than using the inverter.


Mike

 

[John Frum]

I am not sure about is whether or not to size my battery bolt on fuse based on the 700W Inverter or the DC Fuse Block. Right now I have it at 80A, sized by the inverter:

700W/12V = 58.83A

58.83 x 1.25 = 72.92A -> round up to 80A

If I were to size based on the fuse block, I imagine I'd have to go with a 125A.

Please correct me! Thanks
View attachment 130346

A mega fuse does not have the breaking capacity for a 12 volt LFP battery.
Also the inverter alone can pull up to ~80 amps.
Suggest you use an MRBF fuse right on the battery positive terminal.
You can fuse the 4 awg as high as 150 amps.
Also your inverter circuit is not fused.
This is tecnically ok as long as you use 4 awg wire.
Better to fuse the inverter circuit as close to the busbar as possible.
Mega fuses are fine for branch circuits.
6 awg can be fused as high as 100 amps
4 awg can be fused as high as 150 amps
This assumes the cables are pure copper in free air with insulation rated to 90C or better.

 

[shrekqween]

The 'master' fuse at the SOC battery idealy should have a higher fault current withstand. The MEGA is only good for 2000 amps, better would be a MRBF fuse on a Blue Sea holder, directly on the battery post. ( MRBF rated at 10000 amps at 12v)
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A
With inverter efficiency the current will be higher than your calculation, and house loads also, fuse value 100/125 amps would be good. (note the SOK is rated for 100 amps continuous, a fault together with BMS failure could allow the battery to deliver 1000s of amps).

Fit your other fuses near or incorporated with the positive buss bar, 60A for the Renogy and 40A for the fuseblock feed.

Wiring error, all battery negative should pass the shunt, remove the connection from the battery negative to buss bar.

Once operational you will have a better idea of managing power use. You may need some care using the inverter at full power together with all house 12v loads as you could exceed the 100 amps limit on the battery.

Investigate USB and laptop charging via 12v power converters, fed via fuses in the 12v fuseblock . This will be more efficient than using the inverter.


Mike

Mike,

Thank you so much for taking the time to review this! Sounds good, I will purchase either a 100A or 125A MRBF fuse to replace the MEGA on the battery terminal. (If you would recommend one amperage rating more than the other, please let me know).

For the fuseblock feed, how did you arrive at 40A for that?

Ah, great catch! I will remove that wire that goes directly from the negative terminal of the battery to the negative busbar.

Good to note. I am sure I will need to make adjustments to my use as I learn what my consumption looks like.

Yes, I will look into that as well.

Again, thank you so much for your feedback! It's super helpful!


Michelle

 

[shrekqween]

A mega fuse does not have the breaking capacity for a 12 volt LFP battery.
Also the inverter alone can pull up to ~80 amps.
Suggest you use an MRBF fuse right on the battery positive terminal.
You can fuse the 4 awg as high as 150 amps.
Also your inverter circuit is not fused.
This is tecnically ok as long as you use 4 awg wire.
Better to fuse the inverter circuit as close to the busbar as possible.
Mega fuses are fine for branch circuits.
6 awg can be fused as high as 100 amps
4 awg can be fused as high as 150 amps
This assumes the cables are pure copper in free air with insulation rated to 90C or better.

Thank you so much for your review! I really appreciate it!

I will be switching to an MRBF fuse for the battery - thanks for the suggestion.
Gotcha, I will add in another fuse for the inverter - probably will go with the 80 fuse there. Let me know if you would recommend something other.
Would you also recommend adding a fuse to the fuse block circuit?
Yes, getting pure copper for everything!

Thanks again

Michelle

 

[mikefitz]

Fuse block feed fuse at 40A is a guess, could be lower. Most fuse blocks have a limit on total current capacity and you need to protect the feed cable.
In a camper system the high-power energy source is the battery. Overcurrent protection should be provided for any connecting cable and whatever is on the end of that cable.
Having a second fuse in the inverter feed is useful but technically not needed with 4awg as protection is provided by the battery MRBF fuse.

With the cables used, there seems oversized cable in some areas. In itself not a problem, but more expense and perhaps termination issues.
Renogy cables could be 6 awg, fuse block feed 8 awg, use 4 awg for inverter although 6 awg fused at lower than 100A could be used for short runs,
For cooler use 10 awg or 8 awg for long run, they don't like volt drops.

Apart from the over looked cable bypassing the shunt your original circuit was functional and resionably safe. The suggestions for enhanced fusing and placement adds a higher level of safety.

Mike

 

[shrekqween]

Fuse block feed fuse at 40A is a guess, could be lower. Most fuse blocks have a limit on total current capacity and you need to protect the feed cable.
In a camper system the high-power energy source is the battery. Overcurrent protection should be provided for any connecting cable and whatever is on the end of that cable.
Having a second fuse in the inverter feed is useful but technically not needed with 4awg as protection is provided by the battery MRBF fuse.

With the cables used, there seems oversized cable in some areas. In itself not a problem, but more expense and perhaps termination issues.
Renogy cables could be 6 awg, fuse block feed 8 awg, use 4 awg for inverter although 6 awg fused at lower than 100A could be used for short runs,
For cooler use 10 awg or 8 awg for long run, they don't like volt drops.

Apart from the over looked cable bypassing the shunt your original circuit was functional and resionably safe. The suggestions for enhanced fusing and placement adds a higher level of safety.

Mike

Fantastic. Well, I will add that an appropriate sized fuse block fuse in, as well as one for the inverter (just for safe measure).

Gotcha, yeah initially I was following Will's 400W System with Alternator Charging pretty closely, where he said to use 4awg pretty much everywhere except the inverter and solar panels. I will definitely reassess what I should for the wire sizing, so I appreciate you highlighting this.

Again, this was so kind of you to take the time to review and give your feedback. I really appreciate it!!

Thank you,

Michelle

 

[John Frum]

Would you also recommend adding a fuse to the fuse block circuit?

Yes, I suggest 100 amp fuse for the fuse block feeder.

@shrekqween have you already purchased your components?

 

[shrekqween]

Yes, I suggest 100 amp fuse for the fuse block feeder.

@shrekqween have you already purchased your components?

Sounds good!

Yes, purchased and have pretty much everything - last bit of things are trickling in.