MRBF fuses for battery parallel connection?

[JanC]

Hi,

I'm upgrading my solar system after about 8 months since I built it with one extra lithium battery that I will wire in parallel with the older one. The battery is Elkersolutions lifepo4 24v 100Ah. Currently I have one 300A MRBF fuse right on the positive terminal and I'm using a 2/0 AWG wire.

If I understand correctly, the reason for adding a fuses between each lithium battery is to protect the wires connecting them together. I attached a drawing of how I would fuse it. Is this the correct way to do it and would the same 300A MRBF fuse be suitable?

Thanks

 

[Steve_S]

You can use an MRBF on the Battery + terminal.
If the battery is 24V/100AH, it should be fused to 200A as the BMS will exceed that for surge.
You can have 24V/100AH & 24V/300AH in parallel as well without issues, as long as your charge profile is proper.

For Parallel Battery Packs (non server-rack / telecom type) it is easiest & best to connect the batteries to a BusBar with equal length wire and fuse the batteries at the Busbar. You can use the standard 300A Busbar pairs or even buy busbars designed for use with MRBF fuses.
Busbar with MRBF: https://www.bluesea.com/products/5196/MRBF_Surface_Mount_Fuse_Block_-_Common_Source

Alternately you can just use two High Quality Busbars and offset one (the + bar) by adding a 1.5cm spacer under it so the entire assembly looks like this, nice & tidy.

These busbars below are from Pike Industries https://pikeind.com/industries-busbars/


A Typical "Component" based System with batteries in Parallel. Showing 4S/12V Batteries as example.

 

[solarstuff]

You can use an MRBF on the Battery + terminal.
If the battery is 24V/100AH, it should be fused to 200A as the BMS will exceed that for surge.
You can have 24V/100AH & 24V/300AH in parallel as well without issues, as long as your charge profile is proper.

For Parallel Battery Packs (non server-rack / telecom type) it is easiest & best to connect the batteries to a BusBar with equal length wire and fuse the batteries at the Busbar. You can use the standard 300A Busbar pairs or even buy busbars designed for use with MRBF fuses.
Busbar with MRBF: https://www.bluesea.com/products/5196/MRBF_Surface_Mount_Fuse_Block_-_Common_Source

Alternately you can just use two High Quality Busbars and offset one (the + bar) by adding a 1.5cm spacer under it so the entire assembly looks like this, nice & tidy.

These busbars below are from Pike Industries https://pikeind.com/industries-busbars/
View attachment 166850

A Typical "Component" based System with batteries in Parallel. Showing 4S/12V Batteries as example.
View attachment 166851

Hey Steve, This part confuses me:
You offered that
"If the battery is 24V/100AH, it should be fused to 200A as the BMS will exceed that for surge"

I was thinking of paralleling 2x200a 24v batteries (both have 200a bms).

Does that mean you recommend 400a fuses on each battery positive? I thought .25 headroom was all that was required (meaning a 250a fuse).

I don't want to pull the max my inverter can, but don't want to waste fuses... so please advise?

 

[Steve_S]

Almost ALL BMS' are capable of 2X surge handling for "moments" and that will not trigger a fuse or breaker. This is something that is Best Avoided, never push a BMS past design limits, in fact, best to not exceed 80% capacity handling. If you have a bank of batteries that makes life a lot easier as they will all share/divide load/charge proportionately...

My 174's & 280's in my bank were all fused to 150A (6 packs). With my final revision build, all 6 280AH packs are getting 200A BMS, and fused for 200A, even the DC Breakers on the boxes are 200A.

With the TWO 200A Packs with 200A BMS, use a same sized fuse.

 

[gr8pix]

Almost ALL BMS' are capable of 2X surge handling for "moments" and that will not trigger a fuse or breaker. This is something that is Best Avoided, never push a BMS past design limits, in fact, best to not exceed 80% capacity handling. If you have a bank of batteries that makes life a lot easier as they will all share/divide load/charge proportionately...

My 174's & 280's in my bank were all fused to 150A (6 packs). With my final revision build, all 6 280AH packs are getting 200A BMS, and fused for 200A, even the DC Breakers on the boxes are 200A.

With the TWO 200A Packs with 200A BMS, use a same sized fuse.

Hi Steve_s, this is how the manufacturer suggests wiring these batteries in parallel. Where should these be fused?

 

[solarstuff]

Almost ALL BMS' are capable of 2X surge handling for "moments" and that will not trigger a fuse or breaker. This is something that is Best Avoided, never push a BMS past design limits, in fact, best to not exceed 80% capacity handling. If you have a bank of batteries that makes life a lot easier as they will all share/divide load/charge proportionately...

My 174's & 280's in my bank were all fused to 150A (6 packs). With my final revision build, all 6 280AH packs are getting 200A BMS, and fused for 200A, even the DC Breakers on the boxes are 200A.

With the TWO 200A Packs with 200A BMS, use a same sized fuse.

Thanks Steve,

Just so I don't jump to a conclusion: I'm ok with the two 250a fuses, each on a pos terminal, I specced out above then?

Or should I spec them for 225, just at little headroom above the max bms each can deliver, since I don't plan to ever deliver close to the 400 both could supply.

 

[solarstuff]

Thanks Steve,

Just so I don't jump to a conclusion: I'm ok with the two 250a fuses, each on a pos terminal, I specced out above then?

Or should I spec them for 225, just at little headroom above the max bms each can deliver, since I don't plan to ever deliver close to the 400 both could deliver.

UPDATE: I read the post twice and understand. 200a it is. Thanks, Steve

Almost ALL BMS' are capable of 2X surge handling for "moments" and that will not trigger a fuse or breaker. This is something that is Best Avoided, never push a BMS past design limits, in fact, best to not exceed 80% capacity handling. If you have a bank of batteries that makes life a lot easier as they will all share/divide load/charge proportionately...

My 174's & 280's in my bank were all fused to 150A (6 packs). With my final revision build, all 6 280AH packs are getting 200A BMS, and fused for 200A, even the DC Breakers on the boxes are 200A.

With the TWO 200A Packs with 200A BMS, use a same sized fuse.

 

[Steve_S]

Hi Steve_s, this is how the manufacturer suggests wiring these batteries in parallel. Where should these be fused?
View attachment 186653

In this instance, FUSE @ BUSBAR being the simplest.

 

[Steve_S]

Remember:
- Each Battery gets a Fuse/Breaker. Rated to MAX of BMS Rate (not for surge handling)
- Solar IN to SCC gets a Fuse/Breaker.
- Solar Out from independent Solar Charge Controller to BATT/Inverter also gets a Fuse/Breaker.
- From BATT Main DC Bus to Inverter gets a Fuse/Breaker rated to handle the MAX PULL from Batteries.

There is no compromise for safeties & protections. Only takes one tiny booboo to make for a REALLY BAD DAY !

 

[gr8pix]

I have been getting conflicting answers on this and I'm still unsure as to the fusing and the wire size to use on my system and the batteries are the same as Solarstuff's. There is also no mention of a fuse between the busbar and the disconnect switch where one is needed to protect that wire.
In my case I think the wiring from my battery manufacturer is off and wrong, as the trailer wires connecting the two positive & negative terminals are not needed as they are joined at the bus bar. After a lot of confusion and research, I came up with this. Am I wrong again?

 

[Steve_S]

That "T" is not needed there. The Batt Fuses deal with that.
There does have to be one "in front of Inverter" but that would be for the Max Pull of the inverter... ie 12V/3000W Inverter can pull 250A to deliver that, so Fuse/Breaker to handle that 250A.

PS, arent the battery wires supposed to go in in the bottom of the Lynx ?

 

[gr8pix]

Remember:
- Each Battery gets a Fuse/Breaker. Rated to MAX of BMS Rate (not for surge handling)

In my case each BMS is rated for 200A

- Solar IN to SCC gets a Fuse/Breaker.

I have been researching that a fusing is not needed here, but a 2 pole disconnect switch is. Nate explains it well and why here

- Solar Out from independent Solar Charge Controller to BATT/Inverter also gets a Fuse/Breaker.

In my case is fused in the LYNX with Mega fuse

- From BATT Main DC Bus to Inverter gets a Fuse/Breaker rated to handle the MAX PULL from Batteries.

MAX Pull = Inverter load ie: Multiplus II 24 V 120 x2 = 3000W / 20V cutoff / .85 efficiency = 176A

There is no compromise for safeties & protections. Only takes one tiny booboo to make for a REALLY BAD DAY !

No kidding this is a $tre$$ful Shit!!!!!

 

[gr8pix]

That "T" is not needed there. The Batt Fuses deal with that.

That saves some $$$

There does have to be one "in front of Inverter" but that would be for the Max Pull of the inverter... ie 12V/3000W Inverter can pull 250A to deliver that, so Fuse/Breaker to handle that 250A.

This will be fused in the Lynx

PS, arent the battery wires supposed to go in in the bottom of the Lynx ?

The battery can be connected anywhere along the positive & negative bus bars, Victron suggests the inverter be connected directly beside the battery on the busbar, I'm doing it this way to connect my disconnect switch as well as the Smartshunt to the end connectors for less wire and resistance.

 

[gr8pix]

There is a good article I came across here from 2006 on battery bank fusing, the photo of the burnt out boat really makes you take all of this seriously! https://pbase.com/mainecruising/battery_fusing

 

[Sabre36]

I have been getting conflicting answers on this and I'm still unsure as to the fusing and the wire size to use on my system and the batteries are the same as Solarstuff's. There is also no mention of a fuse between the busbar and the disconnect switch where one is needed to protect that wire.
In my case I think the wiring from my battery manufacturer is off and wrong, as the trailer wires connecting the two positive & negative terminals are not needed as they are joined at the bus bar. After a lot of confusion and research, I came up with this. Am I wrong again?
View attachment 186659

In a marine application the required AIC is 20,000A.

 

[Sabre36]

There is a good article I came across here from 2006 on battery bank fusing, the photo of the burnt out boat really makes you take all of this seriously! https://pbase.com/mainecruising/battery_fusing

That is a very old article on the old site.

https://marinehowto.com/battery-banks-over-current-protection/

 

[gr8pix]

That is a very old article on the old site.

https://marinehowto.com/battery-banks-over-current-protection/

Thanks, I like this article better. Much of the same photo's are used.

 

[JJJJ]

In my case I included a shut off for each battery in case I wanted to take one off line for maintenance. I then fed through the bottom of the Distributor. In this case I can add four batteries without stacking lugs. I then put my shunt and master shut off before the inverter.

 

[Steve_S]

I don't know about all the vids out there other than over 50% are bunk.... Will's are GOOD but I have seen some pretty scary crap by well knowns... not going there. I rely on the tech I have learned over the years from sources Like Midnite, Samlex, Victron as well as standards we adhered to at National Defence. 1 of which is Rule of 3, triple redundancy whenever possible. You should have seen my Server Farms ! But then again, if you had, you'd have to be shot.

I provide info as I know it to be and as applicable to my environment... Every region/area etc has it's own rules, regs, codes & whatnot, most are similar BUT there are differences. Use the information as you please....

I will make one suggestion, which should seem obvious, use common sense & DUE DILIGENCE with info provided to ensure you are OK... Sadly, some people advise terribly scary stuff, seems the get a kick out of it...

 

[gr8pix]

I don't know about all the vids out there other than over 50% are bunk.... Will's are GOOD but I have seen some pretty scary crap by well knowns... not going there. I rely on the tech I have learned over the years from sources Like Midnite, Samlex, Victron as well as standards we adhered to at National Defence. 1 of which is Rule of 3, triple redundancy whenever possible. You should have seen my Server Farms ! But then again, if you had, you'd have to be shot.

I provide info as I know it to be and as applicable to my environment... Every region/area etc has it's own rules, regs, codes & whatnot, most are similar BUT there are differences. Use the information as you please....

I will make one suggestion, which should seem obvious, use common sense & DUE DILIGENCE with info provided to ensure you are OK... Sadly, some people advise terribly scary stuff, seems the get a kick out of it...

As a newbie & fellow Canuk from Toronto, I walk softly & i won't shoot you, but I'm carrying a big insulated stick ? I really appreciate your input Steve!