I’m in the process of upgrading my “old” boat power system. In this process I have bought victron solar panel 185W, smart mppt 20A and orion tr dc-dc 12-12 30A. Everything was great in this project until I wanted to “upgrade” my 12V “normal” service battery with lifepo4 one where I’ve got info from manufacturer that I need to protect lifepo4 battery from on-surge (inrush current) and off-surge (back-EMF) issues caused by equipment like water, bilge, macerator,… pumps on boat that can damage battery’s BMS components. It seems common issue and standard equipment but I’m not sure is there a victron product of the shelf that I can buy for this problem or some other community solution for these issues or it is diy project?
!! I’d send the battery back as not fit for service.
Do provide more information about this battery?
A good battery BMS would be capable of handling currents up to 0.5C reliably, and be equipped with over current protection in either direction.
Sorry if I was not clear. I didn’t order battery for this reason. They are fully transparent on this on their product pages. I’ve received this feedback from their customer support since I could read on product Q/A page that all of their batteries are not suitable for water pumps. On my question to explain why, they have explained that for this type of equipment and frequent switch on/off when in use, inrush current and off surge back EMF, can damage BMS/MOSFETs. They have suggested some “solutions” how to “fix” the issue. I have even “AId” to confirm and it looks like “known” problem. I’ve got the impression that they were talking from support experience/like from troubleshooting batteries that were returned as faulty/not operational and that issues caused by equipment like water pumps can’t easily be mitigated on the battery side.
Any back-EMF would indeed damage the BMS, ONLY IF you were to disconnect the BMS from the cells, while the motor was running, leaving the BMS connected to a free-spinning motor. Since the motor switching is happening downwards from the battery, how on earth would a back-EMF find its way to the battery and its BMS?
Inrush currents on the other side, do exist, however I never had issues with ANY BMS, even very small ones connected to big motors. If the can’t manage the inrush current, the would disconnect while the motor would start up. Best way to deal with inrush currents is get a “slow-start” motor, that usually means a motor with a built-in circuitry to do the job, like the newest power tools that ramp up slowly.
This is caused by designing the BMS FET’s to too low a specification, with no allowance for surge or external voltage variations. Even for a battery with 0.5C “continuous” capability, they can often safely produce 3C for 10s. this covers the start up of a water pump - some of which are quite heavy due to starting under load - typical in a marine setup. If the FET’s are only rated for the 0.5C current then they will overheat and fail in a poor BMS design. for the reverse voltage “Back EMF” spike, yes,if the fet’s remain on, then this spike causes an inrush current to the battery - if it exists. Normally the spike is on the motor side of the dc switch.
The thing that I don’t quite understand is why it seems that lifepo4 batteries are sold as great choice for service battery when to really protect BMS MOSFETs from basically standard equipment like water pump I need special approach like “relay + diode/TVS”.
Am I missing something
You don’t need anything special to “protect” the BMS, it will protect itself. As I already stated, I never had ANY BMS on ANY LFP battery (even small, cheap ones), fail due to inrush currents. Back-EMF simply doesn’t exist.
