Supposedly the diodes are there to protect the BMS... Basically the BMS is a circuit board with mosfets and fancy magic stuff that manages the lithium cell. Basicallly the lithium cells output runs through the bms, which then goes to the ebike motor. I am connecting to lithium cells in series with their respective bms systems. Is this circuit valid, and is it necessary to have the diodes. thanks. The thing is supposedly, if one bms trips, the diodes would prevent full voltage of both battery from flowing through a bms and blowing it up. I think?!
Lithium Battery BMS circuit??!
- Thread starter umeshamin
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ptonsparky
Tom
- Occupation
- EC - retired
Obviously above my pay grade. What is BMS?
ron
Senior Member
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- New York, 40.7514,-73.9925
In this case, BMS is battery monitoring system. due to volatility of some li-ion chemistries, UL requires a battery monitoring system and an output contactor on some li-ion containers so if it senses a thermal runaway condition, or other issue (such as overcharging, etc), it opens that cell or container to keep it from catching fire and spreading to the rest of the place
Any Updates??
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ron
Senior Member
- Location
- New York, 40.7514,-73.9925
When you use words like fancy magic stuff, the BMS designs for li-ion batteries are proprietary and it sounds like to are modifying the circuitry in some undocumented fashion, I'm not sure that anyone will be able to comment if it is ok.
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- Placerville, CA, USA
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- Retired PV System Designer
FWIW the more common use of the initialism BMS is for Battery Management System, stressing that it is doing more than just monitoring. An integral component, whether done with active or passive circuitry, is to both prevent overcharge of individual cells, taking into account temperature for those chemistries that are prone to thermal runaway and to prevent over discharge which can permanently damage the cells. A low voltage cut-off at the cell lever rather than based on the total string voltage.
You get one BMS per 'battery'.
Are you connecting them in series on the cell level or just stacking batteries?
Say for example we take eight of my Makita 18 volt Lxt drill batteries and stack them (connect in series), each has a BMS, each is charged by plugging it into a charger.
There is a little BMS board, with diodes in each battery.
I'll have a 120VDC for 5 amp hours.
When its flat dead I'l have to disassemble it and charge them one at a time.
If I decide to crack the case open and connect all the cells to make a new 120V battery then we need a new custom BMS to control the thing.
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