Battery fuse blown twice

[Gurusi]

Hey, about three or four days ago a 200amp T-class fuse blew on the connection between my 16s 280ah pack and the bus bar. I figured the headroom on my BMS was too high 18000 and the charge control amperage was too high 80Amp on each controller (split phase).

I ordered a replacement (coming tomorrow).

Just now I was doing some BMS work on the fuseless pack (increasing the fet opening time) when both inverters just shut down, restarted and showed the error for ‘no battery’. The second pack was not charging (as I heard no fet/relay noise), was fully charged and balancing. The inverters were calm and quiet as no major loads were running…

I checked the 2nd packs 200amp fuse and it has blown!

What could be the issue? Do I need to upgrade to 250amps? Could I have a short? I have no idea how to troubleshoot….

 

[Bluedog225]

Some photos will make this easier.

 

[Hedges]

How many watts are the inverter? What model?

Fuses often blow or might be partially blown when connecting inverter capacitor bank to battery. Do you have a precharge mechanism?

2nd pack - two batteries? When they get paralleled, are they the same voltage?

 

[timselectric]

If they weren't charging or discharging heavily.
The only reason for the fuse to blow is a short.

 

[Ampster]

I figured the headroom on my BMS was too high 18000 and the charge control amperage was too high 80Amp on each controller (split phase).

I have a hard time knowing what the "18000 refers to and the reference to "80 Amps on each controller(split phase) is confusing since I think of the controllers as DC and split phase as AC with entirely different voltages.
Amps are the issue here but for context when you describe the Amps clarify if you are talking AC or DC and what voltage you are seeing.

 

[Nobodybusiness]

Hey, about three or four days ago a 200amp T-class fuse blew on the connection between my 16s 280ah pack and the bus bar. I figured the headroom on my BMS was too high 18000 and the charge control amperage was too high 80Amp on each controller (split phase).

I ordered a replacement (coming tomorrow).

Just now I was doing some BMS work on the fuseless pack (increasing the fet opening time) when both inverters just shut down, restarted and showed the error for ‘no battery’. The second pack was not charging (as I heard no fet/relay noise), was fully charged and balancing. The inverters were calm and quiet as no major loads were running…

I checked the 2nd packs 200amp fuse and it has blown!

What could be the issue? Do I need to upgrade to 250amps? Could I have a short? I have no idea how to troubleshoot….

It might be as simple as a bare wire short somewhere.
Everything is fine until it gets moved a certain way then Bam!

 

[Gurusi]

Hey sorry for the late reply I was checking for things. Please see schematic attached and photos.

I do have a pre-charge as per guide in the download section. See photo

18000 (180amps) was as regard the maximum pack current voltage over protection on the bms.

80amps was in relation to the charge amps via each inverters charge controller

Yes both packs were identical, 16s 280ah in parallel. However only one was connected due to an earlier blown fuse.

Everything had been humming along all day…

 

[Supervstech]

With a parallel set, when one blows for an overload issue, the other will not be long behind.

 

[Gurusi]

If they weren't charging or discharging heavily.
The only reason for the fuse to blow is a short.

See more info just posted. How would I go about tracing a short?

 

[Gurusi]

With a parallel set, when one blows for an overload issue, the other will not be long behind.

The first blown fuse was about 5 days ago when I believe I overshoot my charge controller amps and the bms settings. However they could be both related and my settings were coincidental

 

[Supervstech]

271 max sustained amp draw from the equipment. Plus charging amps of 320 if connected to solar fully loaded...
Plus the charger you have connected, you said 80A...


It shouldn't have blows a parallel 200A fuse.
Unless the leads are not the same length.
Then the max load could have been on the system... idk, I would want to monitor the wire temps when system is again operational.

 

[Gurusi]

271 max sustained amp draw from the equipment. Plus charging amps of 320 if connected to solar fully loaded...
Plus the charger you have connected, you said 80A...


It shouldn't have blows a parallel 200A fuse.
Unless the leads are not the same length.
Then the max load could have been on the system... idk, I would want to monitor the wire temps when system is again operational.

Hey, yes 40amps each inverter (but no charging was happening when it blew). Wire lengths from the busbar to the battery packs are equal.

I guess I will double check all connections and monitor temps. Don’t really want to blow through fuses at 70cad a pop!

Would this primarily be the DC side? Do I need to check from the ac out to my main breaker?

 

[400bird]

What's with the conductors at the battery bolted to wood?

 

[Gurusi]

What's with the conductors at the battery bolted to wood?

They pass through to the other side of the wood to hook up to the bus bars (instead of curling over the top)

The copper bar is due to drilling the pass through connectors out of line with the positive lug…

 

[Hedges]

200A is about right for one 6500W inverter.
Two and two, would depend on how well current draw was balanced.

Have you drawn anywhere near 6500W or 13,000W continuous?
Did you ever check for or observe heating? Fuses will be hot if moderately overloaded long enough to blow.

For precharge, I saw a rotary switch in the drawing.
Off-On-On in the photo.
Is it impossible to turn on without precharge? Did it ever get connected without precharge?

An intermittent short is possible. Inspect. Are bare terminals too close inside inverter?

I'm inclined to think connected to capacitor bank without precharge weakened it.

 

[Gurusi]

200A is about right for one 6500W inverter.
Two and two, would depend on how well current draw was balanced.

Have you drawn anywhere near 6500W or 13,000W continuous?
Did you ever check for or observe heating? Fuses will be hot if moderately overloaded long enough to blow.

For precharge, I saw a rotary switch in the drawing.
Off-On-On in the photo.
Is it impossible to turn on without precharge? Did it ever get connected without precharge?

An intermittent short is possible. Inspect. Are bare terminals too close inside inverter?

I'm inclined to think connected to capacitor bank without precharge weakened it.

I have been up and running for 5 days, my maximum has been 6000W for approx 2hrs.

No difficulty with heat, although I only checked cabling, bms wires and cell bus bars (never took the shroud off the fuses).

The rotary precharge goes from off to pre charge and then on and then on again (Either Ons work). So you need to go via the precharge to get into an on state. I have ensured precharge during each connection.

I will start taking things apart tomorrow and see what I can find. I have a mass of photos during the process of the build but nothing looks out of place after reviewing.

I would rather it was an obvious issue than something small and difficult to pin down!

 

[Gurusi]

200A is about right for one 6500W inverter.
Two and two, would depend on how well current draw was balanced.

Have you drawn anywhere near 6500W or 13,000W continuous?
Did you ever check for or observe heating? Fuses will be hot if moderately overloaded long enough to blow.

For precharge, I saw a rotary switch in the drawing.
Off-On-On in the photo.
Is it impossible to turn on without precharge? Did it ever get connected without precharge?

An intermittent short is possible. Inspect. Are bare terminals too close inside inverter?

I'm inclined to think connected to capacitor bank without precharge weakened it.

 

[42OhmsPA]

Are you grounding the negative class T? Hard to tell for sure but looks like a bare ground and has me confused.

 

[timselectric]

I believe that is the shunt.

 

[Hedges]

6000W won't blow one fuse.

Those battery terminals are far apart, unlike some other brands we've seen pictures of.

How long does precharge take? If too long and you rotated switch too soon, it would be defeated.