Smart BMS: https://s.click.aliexpress.com/e/rhASYNF2
Does anyone have experience with these? I bought it thinking it was 200a continuous, but its only 200a burst and I think only 70a continuous.
So if I bypass discharge, I can still monitor my cells which is good, but can I still take advantage of low voltage and high voltage cut off? My thoughts are probably not but just thought I’d put it out there to the brain trust 
No you can’t.
This bms is a beast!!
Also, not sure your entire situation (environment, weight, build), but typically you won’t draw 35 amp constantly to each motor so you might be just fine with this on charge and discharge.
I checked the lonk to the bms and for $5 dollars you could get a 300a version. Does that still have only 70a continuous?
Apparently the 300a version is 120a continuous.
Unfortunately I have already purchased this one.
The build will be 4x 6374 maytechs and its gonna be pushed pretty hard. 70a definitely not enough.
Ive been speaking to a dude on FB who reckons it is possible but wanted to run it past you guys. Will try copy some of the conversation over here a bit later
That sucks. I bet you thought no need to get a 300a since 200a is more then enough and didn’t realize that wasn’t continuous.
My thoughts exactly
Some of what old mate had to say:
Glyph Iks
so perhaps you can use a 50A BMS for LVC, HVC, HCC, and balancing. Connect the -P of the 50A BMS to the Contactor switch coil and LVC will disconnect the Contactor switch that connects your direct feed from the battery to the motor controller(s).
This way you get a LVC disconnect on your direct draw, and HVC HCC and balancing during charging.
Does the motor have a temperature sensor?
Glyph Iks
hmmm, not really just stuff I have written about, I never read about anyone else doing this and I don’t have a thread on this subject. most of the higher end battery builders would know about this way of using a BMS for just charging or using a BMS to drive the Cell LVC (low voltage cutoff) and having the BMS keep a Contactor switch that connects the battery to the motor controller closed by connecting the coil switch to the “P-” port off the BMS.
That way as long as P- is live the Contactor switch that connects the battery and the motor controller is keep open by the current from P- passing though the Contactor coil. Then when LVC is tripped the contactor opens and you motor controller gets no current.
Glyph Iks
You would need something that stops the contractor from chattering. So a BMS that you can set the time to reset after a LVC is tripped. Here is an example of the software for the 8S-24S or 16-32S Ant BMS where in the app you can set the LVC or “Power under-voltage protection” and then you can set the delay by putting the “Power under-voltage recovery” higher than the LVC so that it will take like a minute to recover or make it so it can’t recover.
I have the non-slim version of this BMS in my bike project (it’s two PCBs stacked instead of one big one) and it’s been good so far (haven’t gotten the bike into a rideable state so only bench testing so far).
I do know that the supplied app can be pretty terrible depending on what version they have, but there’s a third party app called VBMS (Vortecks BMS) that works amazingly well. I think it was $7? on the play store.
I decided not to integrate the screen into the bike because all the vital info is available on my phone or on my cycle analyst dashboard.
Is it possible to ‘trick’ the BMS? For example, i’ll be running two unitys and some accessories… if i run the power direct from the battery to the unitys, but run the power for the accessories through the BMS, would the low voltage and high voltage cutoffs work by just disabling the accessories?
No because your unitys are directly connected to the battery
The low and high voltage protection would only work for the accessories
I wouldnt expect it to cut power to the escs, but accessories would turn off letting me know that something was wrong… like a slient alarm
That’s a interesting idea if the wiring checks out just as a visible warning.
If you can monitor voltages on your phone then is low voltage cutoff very necessary? A beast like this should never be run empty.
Its definitely good for safety if it has some kind of sudden issue
Yeah that would work.
To be honest, I dont like the idea of a BMS cutting power to my ESCs but I would like an indication if there is something wrong.
The unity supposedly takes care of low voltage cutoff, not sure about high voltage but im sure it would, but that would only work on a pack average.
The advantage of a discharge BMS is that it works per p group, so I would know if something was wrong with a particular p group without losing power to the motors
If you wire up the bms as charge only it will still take care of overvoltage in time of charging. You don’t want a bms to cut you out due to over voltage while driving anyway. That’s usually when you start riding with fully charged battery and break hard. Better overcharged the cells for some seconds than losing breaks…as min that’s my attention to it. Once you hit acceleration the cell voltage will drop anyway again.
Not sure if that’s possible, but you might be able to set up a undervoltage Alarm notification via app on your phone. This way you get a notification on your phone if one group goes down but the bms will not cut out.
whats this board for? that’a a ridiculous amount of power. what sort of wheels and gearing you using?
i have my board set up in this way. Unity is in bypass but all my lights are powered through the bms. This way if there is a problem with a single cell group then the lights turn off but im not thrown off the board
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@ducktaperules Excellent. I guess you rely on the unity power switch then for on/off rather than bms e-switch?
Here’s the loose build plan… Madness - 4wd Monster Build
yes unity for on/off switch. i have fallen before due to bms cut out. it happens right at the moment you put the power down and generally are committed to the acceleration. struggled to trust the board after this so never again will i ride a board that can cut from bms.
Hearing you there brother. My mistaken purchase has turned out to be a blessing in disguise.
