Huge Voltage spike when BMS cuts off

[team karst]

Ive got several mov 18V rated discs spread around my 12V buss. More for lightning than anything else. There are also automotive rated breakdown diodes out there too.

[CaptainRivet]

Originally Posted by Fuss

I’m doing a few experiments at the moment. 30v spike for my 24v bank.
Let’s not discuss that BMS cutoff should not happen, the thread is about voltage spikes with lifepo4.
Do you know what is the best protection to suppress spikes with lifepo4 installations.?
I did not test yet large inductive loads like electric motors, they might produce something similar.
It would be good for everyone on the forum to have a protection solution as these spikes I suspect are coming with inverter overload shutdown, shore power overload disconnect etc.

It’s the sort of fault that’s hard to measure and possibly damages sensitive devices nice and slowly so you don’t notice until…..

Any experts on this as it would be nice to solve.

Thats why you put senstive devices after an isolated DC2DC converter which galvanically isolates them so non of these 30V spike reaches these senstive electronics.
A buffer battery would also absorb these spikes, best combine both isolated DC2DC converter which does top up charging of a buffer battery.

[Fuss]

I'm experimenting and there is much more too it than just saying a buffer battery absorbs the spikes, it does not. By its very nature, it is small.
we all know about dc2dc Rivet that not the question, of course that works but some things are sensitive that you do not yet know about...like your cheap inverters that you recommend...they create even bigger voltage spikes. I'm using an old style Skylla so I see how important quality is as this one produces spikes too.
Your cheapo inverters will be spiking like crazy when their lvc occurs.
You should not be recommending them on this forum.

[CaptainRivet]

Originally Posted by Fuss

I'm experimenting and there is much more too it than just saying a buffer battery absorbs the spikes, it does not. By its very nature, it is small.
we all know about dc2dc Rivet that not the question, of course that works but some things are sensitive that you do not yet know about...like your cheap inverters that you recommend...they create even bigger voltage spikes. I'm using an old style Skylla so I see how important quality is as this one produces spikes too.
Your cheapo inverters will be spiking like crazy when their lvc occurs.
You should not be recommending them on this forum.

First a buffer battery absorbes spikes, its either its resistance if you use an agm or its charge capability if an LTO...thats one of the major functions a buffer does and thats why you use an lead starter as surge protector for your alternator and even a small 5AH motorbike AGM does the job even on a 200A alternator.

I use and recommend what works for me and other after a longer test periode and the budget inverter don't spike more then others, especially my edecoa which has actually a soft start that even a 4 times more expensive victron doesn't have and makes it a very good boost inverter for multis and quattros.
And these inverter are not senstive to spikes especially not an LF like the vevor.
And that the inverter doesn't do a LVC under full load which creates a spike with ALL inverters independent how much they cost, you can simply switch off of big loads with the right BMS before that....a measure i also do to prevent a LVC in systems i design. LCV and HCV are emergency measures which shouldn't happen in good designed system.
Well and what spikes comes on the input side of the DC2DC, problem solved.

And sure a Skylla spikes because its a lead charger where it doesn't matter as a lead is connected thats absorbing it, why wasting money then? And if you use that on a LFP sure it spikes because its switching under a huge load all the time. Thats shows its quality, other lead charger will go up in smoke....

Spikes on DC side will be produced by every motor (starter, alternator, pumps, windlass, compressors of fridge/freezer, DC watermaker) and devices with high power (inverter, charger, AC..) containing big trafos or semiconductors. And they go all on the input side of your DC2DC or in case of fridge/freezer compessors and sweet water pump on a seperate DC2DC and get stabilized 14.8V which gives them a)optimal working condition (and less AH in the end), b) life longer and c) their spikes are isolated from the rest of the system and d)can be even shut on and off via the remote of the DC2DC by a BMS.