Fuses / disconnects / breakers for 2 LV6548 system

[timselectric]

When using buss bars like that, it's not that critical to connect to opposite corners. It's not like multiple connections with wires and lugs.

 

[FilterGuy]

When using buss bars like that, it's not that critical to connect to opposite corners. It's not like multiple connections with wires and lugs.

That is only true if the bus bars are very heavy duty (and therefore offer little resistance). I just assume they are not heavy enough and hook things up diagonally.

 

[timselectric]

Understandable
I'm just assuming that in 25 years, I'm not going to be worried that one battery is slightly degraded more than the other. I'm sure that I will probably have switched to using a zero point module, by then. lol
(Not sure how many people will get that reference)

 

[CamoGreg]

I don't trust those breakers.
I asked their support and he said he would get back with an answer and has not yet replied.
Until he does I will recommend a class t breaker as close as possible to the positive battery terminal.

I've went ahead and installed 150A MRBF fuses and 300A BlueSea terminal blocks on my 3 EG4 batteries.
Simply because Signature Solar seems reluctant to commit to the quality of their breaker function.

On the Lifepower4 versions, there isn't enough room to get the MRBF block between the plastic and on to the positive battery post. I had to mill 1mm off each side of the mounting tang to have it fit. (Could have used a disk sander since 1mm isn't much.)

Then there's a 300A Class T at the very beginning of the positive trunk line that runs to the Victron Distributor. The VE Distributor has 125A mega fuses for each inverter and both SCC since that's the smallest they make.
Wire was sized up for those fuses and to keep resistance down. That is also the recommended inverter fuse size per Victron. The SCCs are only capable of 85A. I would have preferred a 100A fuse, but using what I could get.

The MRBF on the EG4 battery terminal may not be necessary. But it should protect if the breakers aren't up to the task.
For $100, I think it's worth the cost and effort.

 

[John Frum]

I've went ahead and installed 150A MRBF fuses and 300A BlueSea terminal blocks on my 3 EG4 batteries.

MRBF fuses only have an AIC of 2,000 amps at 58 volts.
Even conservative estimates of the dead short amperage start at 5,000 amps.

My estimate comes from a plot I saw of a dead short on a single LFP cell.
The initial seconds were at or above 100C until the vent burst.
100C * 100 amp hours is 10,000 amps.
Lets say all the joinery drops that in half to 5,000 amps.

5,000 amps * 51.2 volts = 256,000 watts
256000 watts / 1440 watts = 177.777777778 ceramic heaters at full bore.

 

[CamoGreg]

I'd like to see Signature Solar or Will intentionally short the EG4 to see how the breaker performs.
Similar to this.

 

[John Frum]

I'd like to see Signature Solar or Will intentionally short the EG4 to see how the breaker performs.
Similar to this.

Good video.
I have an hypothesis.

400ah * 100c / 2 pack resistance(WAG) = ~20000 dead short amps

The voltage drop over 15 feet of 8 awg copper at 20000 amps is going to be massive.
As the voltage drops the the fuse's AIC goes up.

 

[Texican]

OK... now your freaking me out, I have 6 of the eg4s

 

[CamoGreg]

I have an hypothesis.

400ah * 100c / 2 pack resistance(WAG) = ~20000 dead short amps

The voltage drop over 15 feet of 8 awg copper at 20000 amps is going to be massive.
As the voltage drops the the fuse's AIC goes up.

Others in the video comments had the same hypothesis. Basically calling the 8awg wire a big resistor.

 

[CamoGreg]

OK... now your freaking me out, I have 6 of the eg4s

Welcome to my world.

I like what the SOK rack battery did with including an internal Class T fuse. Solved a bunch of questions.

I don't know if I have the space to include 3 other big honking Class T fuse holders. I went with MRBF fuses because it seemed a reasonable alternative. There is a breaker but I'm leary of someone just saying "yeah, those Chinese breakers are fine."

So far I have the 125A battery breaker, MRBF fuses on each battery, a 300A Class T protecting the entire battery bank and a 250A 125VDC heavy duty breaker as a disconnect switch.

In your case, (6) Class T fuses and holders would set you back about $85 each. Plus another for the entire bank. 7x$85 = $595

 

[timselectric]

If for some reason the breaker didn't trip. The BMS, would shutdown or the fets would burn. I don't have to trust the breaker, it's not the weakest link.

 

[CamoGreg]

I've seen video of applying over current to the EG4. The BMS shut down at 213 amps. The breaker never tripped.

That was a factor in my reasoning for using the MRBFs. I'd prefer to not use the BMS as first defense protection device.

 

[John Frum]

Welcome to my world.

I like what the SOK rack battery did with including an internal Class T fuse. Solved a bunch of questions.

I don't know if I have the space to include 3 other big honking Class T fuse holders. I went with MRBF fuses because it seemed a reasonable alternative. There is a breaker but I'm leary of someone just saying "yeah, those Chinese breakers are fine."

So far I have the 125A battery breaker, MRBF fuses on each battery, a 300A Class T protecting the entire battery bank and a 250A 125VDC heavy duty breaker as a disconnect switch.

In your case, (6) Class T fuses and holders would set you back about $85 each. Plus another for the entire bank. 7x$85 = $595

TFB1-150, 150A Class T Fuse Kit | DonRowe.com

The TFB1-150 offers 150 amps of over-current protection and provides safe operation of your inverter.

www.donrowe.com

$49.99 * 6 = $299.94

50 bucks to protect each battery and the rest of your system and your house and family.

 

[John Frum]

I've seen video of applying over current to the EG4. The BMS shut down at 213 amps. The breaker never tripped.

That was a factor in my reasoning for using the MRBFs. I'd prefer to not use the BMS as first defense protection device.

I trust a Fet based bms about as much as I trust that breaker.

 

[timselectric]

I trust a Fet based bms about as much as I trust that breaker.

I'm surprised that you trust a fuse. lol

 

[Hedges]

I've seen video of applying over current to the EG4. The BMS shut down at 213 amps. The breaker never tripped.

That was a factor in my reasoning for using the MRBFs. I'd prefer to not use the BMS as first defense protection device.

I trust a Fet based bms about as much as I trust that breaker.

Moderate overload, I would expect BMS to shut off before thermal delay of a breaker.
Severe overload (20,000A) is where we are at least curious if FET can shut it off.

Semiconductors may be able to take massive current for a very short time, if total deposited energy (Joules) doesn't heat them too much.
But transitioning from "on" (zero ohms) to "off" (infinite ohms) with that massive current means a lot of power deposited.

I'm surprised that you trust a fuse. lol

Tested by an NRTL to interrupt over-current beyond it's rating, they should be trustworthy. It is a conductor to vaporize and maybe some material to help quench the arc.
Just so long as a "holding company" doesn't decide to buy up Bussmann, LittleFuse, and other quality players.

If for some reason the breaker didn't trip. The BMS, would shutdown or the fets would burn. I don't have to trust the breaker, it's not the weakest link.

Have your FETS been tested by an NRTL to clear a fault?

So far I have the 125A battery breaker, MRBF fuses on each battery, a 300A Class T protecting the entire battery bank and a 250A 125VDC heavy duty breaker as a disconnect switch.

So long as a bolted fault can't occur where only protected by MRBF, that actually seems reasonable. I don't think any battery sinking current from its neighbors is going to blow a fuse, so that's not what it is for. Only BMS can protect it. If there is a fault after class T fuse that exceeds MRBF rating so it arcs, class T should also blow in a short time.

 

[timselectric]

I trust the fuse and breaker.

 

[John Frum]

So far I have the 125A battery breaker, MRBF fuses on each battery, a 300A Class T protecting the entire battery bank and a 250A 125VDC heavy duty breaker as a disconnect switch.

Is this your topo?
If yes, the short as shown would not be interuppted by the class_t fuse.

positive
|<->class_t_fuse<->rest_of_system
|-dead_short------------------------------->|
|<->mrbf_fuse<->breaker<->battery.1<->bms<->|
|<->mrbf_fuse<->breaker<->battery.2<->bms<->|
                   rest_of_system<->shunt<->|
                                     negative

 

[John Frum]

I trust the fuse and breaker.

If you trust the breaker then the fuse is superfluous, right?
Do you trust the BMS, if yes then the breaker is superfluous, right?

 

[timselectric]

you trust the breaker then the fuse is superfluous, right?

Yes

Do you trust the BMS, if yes then the breaker is superfluous, right?

The breaker doubles as a disconnect. And could possibly save the BMS.