Hey all, I’m having trouble connecting my antbms controlled battery to my sabvoton. If I power up the discharge mosfets and connect the battery, there is a large spark and the bms short circuit protection is triggered. If I leave the wires connected and try to power up the discharge mosfet, the controller caps suck out the power and the bms precharge never succeeds. Can I place this 10w precharge resistor in between the positive wire like shown below? My idea is that I only need to hold it for a few seconds, allowing the controller to charge the caps and avoid the short circuit problem with the bms. I’ve read through previous threads about precharge but I want to confirm that this will work as a temporary solution?
Temporary precharge circuit
- Thread starter Yermommy
- Start date
larsb
1 MW
Yes, a precharge resistor in the battery to bms circuit for a few seconds will do the job
JackFlorey
100 kW
Depends on the resistance, of course. Too low a resistance and you will still trigger short protection; too high and you won't precharge enough.Yermommy said:
JackFlorey said:
Gotcha. I measured 1000ohms resistance with a multimeter on the ceramic resistor. 72v battery divided by 1000ohms = .072amps of current. 72v X .072a = 5.182w. The resistor is rated for 10w so I think I’m good. Just nervous because I don’t like big sparks haha.
larsb
1 MW
JackFlorey said:
Too high precharge resistance and precharge will take longer than your patience (it will always precharge enough with time)
JackFlorey
100 kW
Unfortunately not always.larsb said:
All controllers have a quiescent current draw - the current drawn by the processor, gate drivers, display etc. If the draw is high enough, and the resistor is large enough, then the caps never charge.
Let's take an example. A controller takes 1 watt to operate (quiescent current) and has a buck converter to generate housekeeping. Buck converters are much more efficient than linear regulators (good for range) but they have a tendency to draw more current at low voltages.
Let's say this particular controller operates at 60 volts normally and the buck converter starts working at 12 volts. That means at 12 volts the controller will be drawing (1/12)=83ma at 12 volts. If you use a 1K resistor, once the buck converter starts working, the voltage at the input will drop dramatically, since the resistor can only supply 48ma at that current. So what happens at that point is that the input voltage drops until the buck converter shuts off, then the voltage rises, then it restarts, then the voltage drops again.
Using a 470 ohm resistor would solve the problem in that case. (Also other options will work, like increasing the LVD of the buck converter.)
larsb
1 MW
I see your logic but in all controllers i’ve had, never had this problem even though i just used whatever resistor i had at hand. Must be dependent on hardware solution also, those controllers that have an on off switch will not draw sleep current until active, rc esc:s and simpler controllers might.
DogDipstick
100 kW
Precharge choice maths:
http://liionbms.com/php/precharge.php
My problem when trying to do it " quick and dirty" without a dedicated ( precharger) circuit, or resistance(er) wired across the contact, is the precharge dissipates (discharges) by the time I put down the donor resistor I had on hand, and the controller / battery ZAPS! anyway when I go to plug the system in.
I mean, a common home oil burner motor, or sump pump motor, the inrush can be seen on a AC/DC clamp meter peak and hold... . usually. Air compressor motor. Ect. I have begun precharging my chargers too, playing with dc. Buck converters and boost converters too. IDK if it matters but the spark.. grrrrrrrr. I see a very high peak on the clamp. You can too if your meter is fast.
The XT90-s does help with my impulsivity to plug whatever into wherever whenever i feel so entitled to... Lol... Has helped but i have also worn few out ( at the voltages I have played with, big sparks, erode contacts,...) . Like larsb said i really think the timing calculation thing matters.
I do this with little alligator leads. Not by hand. That way I dont have to pay attention.
Goddamn that zap gets to me. Big 200v+ capacitors are no joke.
http://liionbms.com/php/precharge.php
My problem when trying to do it " quick and dirty" without a dedicated ( precharger) circuit, or resistance(er) wired across the contact, is the precharge dissipates (discharges) by the time I put down the donor resistor I had on hand, and the controller / battery ZAPS! anyway when I go to plug the system in.
I mean, a common home oil burner motor, or sump pump motor, the inrush can be seen on a AC/DC clamp meter peak and hold... . usually. Air compressor motor. Ect. I have begun precharging my chargers too, playing with dc. Buck converters and boost converters too. IDK if it matters but the spark.. grrrrrrrr. I see a very high peak on the clamp. You can too if your meter is fast.
The XT90-s does help with my impulsivity to plug whatever into wherever whenever i feel so entitled to... Lol... Has helped but i have also worn few out ( at the voltages I have played with, big sparks, erode contacts,...) . Like larsb said i really think the timing calculation thing matters.
I do this with little alligator leads. Not by hand. That way I dont have to pay attention.
Goddamn that zap gets to me. Big 200v+ capacitors are no joke.
Ianhill
1 MW
- Joined
- Sep 25, 2015
- Messages
- 2,871
I got a flipsky watercooled antispark on off switch and put it on a heatsink so far so good and a bonus is it turns itself on and off without having to touch the switch.
It picks up current flow when the motor spins and turns on then off after its preset time, it only breaks the positive and passes the negative through but thats plenty for a setup thats got bms.
Ive got it fitted on a brushed razor scooter build i found a 60v 3kw controller for lead acid brushed motors £25 and in uk i had a 48v 1000w lying around so pulled the trigger.
I thought id need the vesc to function its in off feature but no the controller leaks enough to work it, for a brushed setup its quite potent 16s highest ive seen on a setup like this, ive just finished it all up waiting on a length of brake hose long enough to do the job and get some serious miles on it but from testing its lethal its geared low 24mph top speed spins 5600rpm and left a big burn out on my carpet to my surprise the throttle had gone live when i pushed the scooter and activated the auto on.
Bit lethal really caught me out went to put the grip on the bars and up the wall it went.
It picks up current flow when the motor spins and turns on then off after its preset time, it only breaks the positive and passes the negative through but thats plenty for a setup thats got bms.
Ive got it fitted on a brushed razor scooter build i found a 60v 3kw controller for lead acid brushed motors £25 and in uk i had a 48v 1000w lying around so pulled the trigger.
I thought id need the vesc to function its in off feature but no the controller leaks enough to work it, for a brushed setup its quite potent 16s highest ive seen on a setup like this, ive just finished it all up waiting on a length of brake hose long enough to do the job and get some serious miles on it but from testing its lethal its geared low 24mph top speed spins 5600rpm and left a big burn out on my carpet to my surprise the throttle had gone live when i pushed the scooter and activated the auto on.
Bit lethal really caught me out went to put the grip on the bars and up the wall it went.
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