https://endless-sphere.com/forums/viewtopic.php?f=2&t=84856&hilit=bms+switch
thanks. funny to see that i posted in that thread as well (w/o having read the first pages of course).amberwolf said:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=84856&hilit=bms+switch
izeman said:thanks. funny to see that i posted in that thread as well (w/o having read the first pages of course).amberwolf said:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=84856&hilit=bms+switch
imho i already tried to lift the gate signal (2y ago) and put a switch in line. can't remember why it didn't work. but i'll try again
izeman said:thanks for clarification. i would have directly pulled down GATE to GND to shut down the bms. so a toggle switch in the gate line, toggling the GATE between whatever it was connected to before, and GND. correct? or do i need the resistor?
izeman said:has anyone of you an idea where to add an ON/OFF switch to use the BMS as switch between battery and controller?
i put a switch between the thermal control switch which works, but you need to reset the bms afterwards to make it work again, so this method is not appropriate. any other ideas? i'd like to get rid of the extra inrush limiter i installed, it's just an additional component adding complexity to the system.
fechter said:izeman said:has anyone of you an idea where to add an ON/OFF switch to use the BMS as switch between battery and controller?
i put a switch between the thermal control switch which works, but you need to reset the bms afterwards to make it work again, so this method is not appropriate. any other ideas? i'd like to get rid of the extra inrush limiter i installed, it's just an additional component adding complexity to the system.
I've seen the temp sensor work if you add a resistor from B- to P- to bring the output up to pack voltage (this resets the BMS). This would be like a precharge resistor. Downside of this is the controller could still drain something through the BMS. If the controller is the type with it's own switch or display unit, this might be fine. Resistor would be something like 1k, 5W.
Inserting a SPDT switch in series with the gate drive should work fine if the controller caps aren't too big. The BMS gate drive is kind of wimpy and might switch on slow enough to blow the FETs against a large capacitive load. In the off position, the FET gate can just be grounded.
vex_zg said:in my opinion grounding the FET gate should be done only in conjunction with disconnecting the gate driver (otherwise you could keep the gate driver supplying current trying to keep the BMS on while you are trying to force it off)
so you would not recommend to do it? "large" caps and "low enough" leaves a lot room, and i don't want to blow the bms.fechter said:Inserting a SPDT switch in series with the gate drive should work fine if the controller caps aren't too big. The BMS gate drive is kind of wimpy and might switch on slow enough to blow the FETs against a large capacitive load. In the off position, the FET gate can just be grounded.
fechter said:vex_zg said:in my opinion grounding the FET gate should be done only in conjunction with disconnecting the gate driver (otherwise you could keep the gate driver supplying current trying to keep the BMS on while you are trying to force it off)
Yes, that's the idea. It would look like this:
This would require finding and cutting the trace that feeds the FET gates. I think this will actually work quite well but there is still the risk of blowing up the FETs with a big controller.
so you would not recommend to do it? "large" caps and "low enough" leaves a lot room, and i don't want to blow the bms.
velias said:Give it up and buy a new one!
You could have flipped burgers for the number of hours you have wasted on this to pay for another one.
it's 3x 220u @50v. so way below your 1000u threshold.fechter said:How big are your controller caps?
What voltage?
izeman said:it's 3x 220u @50v. so way below your 1000u threshold.
vex_zg said:regarding the pull down resistor for which fechter is proposing 4.7MOhm. ..
...yeah this value is not that critical. Yes it will cause continuous drain of the gate driver. But 100kOhm @ typically max 20V for Vgs will only incurr 0.2mA current. So I don't thin it would be stressing gate driver. I personally would put something between 0.1MOhm and 1MOhm
fechter said:izeman said:it's 3x 220u @50v. so way below your 1000u threshold.
I think it will be no problem.
A while back, I tested a solid state switch that works in a similar manner. Sort of wimpy gate drive to turn on. It worked fine at 60V into 1000uF. I tried a gigantic 10,000uF cap and it blew up. Based on what I've seen with the spot welder circuits, I think if you can turn the FETs on hard enough they will survive a massive amount of peak current. Basically you want them to be nearly fully on before the current rises. There will always be some inductance in the wiring that will delay the current.
vex_zg said:regarding the pull down resistor for which fechter is proposing 4.7MOhm. ..
...yeah this value is not that critical. Yes it will cause continuous drain of the gate driver. But 100kOhm @ typically max 20V for Vgs will only incurr 0.2mA current. So I don't thin it would be stressing gate driver. I personally would put something between 0.1MOhm and 1MOhm
The problem is there is no "gate driver", just a 4.7M resistor that goes to cell 3. Any resistance to ground and it will act like a voltage divider and reduce the gate voltage. What might be better is to just place a 15v zener diode from gate to source to protect the gate from stray voltages in the event the wire breaks or gets disconnected and just live with the possibility the gate could be charged when the wire breaks. The leakage in the zener diode would eventually drain the gate.
ha! now i understand #3 seems strange as voltage per cell can go down to 2.8v which means 8.4v at #3. a little low for full FET turn on, isn't it?fechter said:In the typical BMS, the gates get powered from a tap on cell #3, which is around 12v. No voltage regulator. From the cell 3 tap, it goes through a high value resistor to the gates and there are transistors which can pull the gates to ground.
fechter said:In the typical BMS, the gates get powered from a tap on cell #3, which is around 12v. No voltage regulator. From the cell 3 tap, it goes through a high value resistor to the gates and there are transistors which can pull the gates to ground.
vex_zg said:velias said:Give it up and buy a new one!
You could have flipped burgers for the number of hours you have wasted on this to pay for another one.
I guess most of ppl on this forum are more inclined towards learning and DIY vs. turnkey solutions. Repairing is good for environment