Increase BMS limits?

[justinm001]

Are you talking about lifePower4 12v? Why do you say it is a 100A BMS?

Yes and because it has 100a BMS as in I can't pull over 100a from a single battery or 200a from a pair without them restarting.

 

[FilterGuy]

Yes and because it has 100a BMS as in I can't pull over 100a from a single battery or 200a from a pair without them restarting.

That is odd... You are sure it is not tripping on a start surge of over 200A each? Do you have other reasons to think it is a 100A BMS?

 

[justinm001]

I didn't see, are the 2 batteries in series or parallel?
If in parallel wouldn't 2 100 amp BMS produce 200 amps to the inverter?? Adding another battery with a 200 amp bms would provide 400 amps to the inverter.
Maybe start at the bottom the power chain with, buss bars, bigger cables, equal length cables. Maximize the existing power before adding more.

Parallel. Yes they produce 200a combined.

Don't think adding another battery with 200a bms would give me 400a as it should draw from all 3 equally thus blow the 100a bms batteries at 300a.

4/0 gauge cables with batteries next to eachother connecting lugs then a couple feet to a 1000a Lynx distribution.

 

[justinm001]

That is odd... You are sure it is not tripping on a start surge of over 200A each? Do you have other reasons to think it is a 100A BMS?

Pretty sure if I have the 1500w AC already running and turn off one battery switch it'll blow the bms

 

[FilterGuy]

Pretty sure if I have the 1500w AC already running and turn off one battery switch it'll blow the bms

Please try that and report the result.

 

[justinm001]

Please try that and report the result.

You're right it can handle 200a it seems. The problem is somehow my voltage gets low and when I get below like 11v my entire firefly system restarts which causes my ACs to restart since the thermostats use 12v and are fused on the firefly.

I noticed one of my lugs wasn't super tight so after tightening it I seem to not have as bad low voltage. I'm going to locktite the battery lugs and run each to a lynx distributor instead of wiring together then see if anymore issues.

 

[FilterGuy]

You're right it can handle 200a it seems. The problem is somehow my voltage gets low and when I get below like 11v my entire firefly system restarts which causes my ACs to restart since the thermostats use 12v and are fused on the firefly.

I noticed one of my lugs wasn't super tight so after tightening it I seem to not have as bad low voltage. I'm going to locktite the battery lugs and run each to a lynx distributor instead of wiring together then see if anymore issues.

All systems can have issues with the connections on the DC. Even a slightly resistive connection can create significant voltage drops at the currents we deal with. That is why it is so important to make sure all the connections are clean and properly torqued.

It is the worst on 12V systems for two reasons.
1) The working voltage range is narrower than on 24 & 48V systems so a voltage drop across a connection is more likely to cause issues.
2) On 12V systems the current is a lot higher for the same power, so the voltage drops tend to be a lot higher.

 

[sunshine_eggo]

You're right it can handle 200a it seems. The problem is somehow my voltage gets low and when I get below like 11v my entire firefly system restarts which causes my ACs to restart since the thermostats use 12v and are fused on the firefly.

I noticed one of my lugs wasn't super tight so after tightening it I seem to not have as bad low voltage. I'm going to locktite the battery lugs and run each to a lynx distributor instead of wiring together then see if anymore issues.

FFS, please do not do this unless you use green or something designed to break under torque.

All systems can have issues with the connections on the DC. Even a slightly resistive connection can create significant voltage drops at the currents we deal with. That is why it is so important to make sure all the connections are clean and properly torqued.

It is the worst on 12V systems for two reasons.
1) The working voltage range is narrower than on 24 & 48V systems so a voltage drop across a connection is more likely to cause issues.
2) On 12V systems the current is a lot higher for the same power, so the voltage drops tend to be a lot higher.

FWIW, Victron absolutely hates DC ripple. Their cable recommendations are typically larger than one might choose by current rating alone. They want superconductivity on their DC side, and they want slightly resisty on the AC side for parallel operations.

 

[justinm001]

FFS, please do not do this unless you use green or something designed to break under torque.



FWIW, Victron absolutely hates DC ripple. Their cable recommendations are typically larger than one might choose by current rating alone. They want superconductivity on their DC side, and they want slightly resisty on the AC side for parallel operations.

Yes I'll use orange which I use on various other things and will remove under torque. The 4/0 lugs just vibrate too much it seems. I also don't have the wires and lynx permanently mounted yet, still trying to find the best spot. Once I do that I'll also put rubber mounting things to hold the cables.

I still need to do a bit more testing to be sure that's the only issue

 

[wme]

Some really quick crude checks. With a digital volt meter set on 20v and a light load on the inverter, measure between the batteries + terminals. On 1 battery measure between + and the buss bar body, the buss bar body and the inverter, finally between the battery+ and the inverter. Repeat on the other battery.
0v everywhere and your golden, ANY voltage is a sign of power loss.