capacitor blow out
capacitor blow out
Dear All,
We just set up our brand new 2x60A board.
We got
packetserial mixed pwm going from the library examples
All was going well for about 60 seconds.
The motors were going round appropriately.
However. After then there was a pop/bang and smoke came out of a capacitor. All was lost in front of my eyes.
Before i put in a new capacitor or buy a new board...
Is this due to a regenerative braking voltage spike.
Can someone suggest a good diode to stop this happening again.
I was using a diode, but it must have been the wrong specification.
These are LARGE motors with a high moment of inertia. hence the regen is probably quite significant
We just set up our brand new 2x60A board.
We got
packetserial mixed pwm going from the library examples
All was going well for about 60 seconds.
The motors were going round appropriately.
However. After then there was a pop/bang and smoke came out of a capacitor. All was lost in front of my eyes.
Before i put in a new capacitor or buy a new board...
Is this due to a regenerative braking voltage spike.
Can someone suggest a good diode to stop this happening again.
I was using a diode, but it must have been the wrong specification.
These are LARGE motors with a high moment of inertia. hence the regen is probably quite significant
Re: capacitor blow out
p.s. it was the small capacitors near to the mode button...
either C1 or C20
either C1 or C20
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Basicmicro Support
- Posts: 1594
- Joined: Thu Feb 26, 2015 9:45 pm
Re: capacitor blow out
I recommend you send the board in so we can repair it. I suspect you may be right regen killed it but it is most likely it took out the switching regulator as well if that small cap was damaged.
Send it to our contact address and include your contact information and return address inside the box.
Give me your motor model information and how you had everything wired up(power supply(make/model), battery, wire gauge/length etc).
Send it to our contact address and include your contact information and return address inside the box.
Give me your motor model information and how you had everything wired up(power supply(make/model), battery, wire gauge/length etc).
Re: capacitor blow out
On closer inpection, i think you are correct
it is not the capacitors but the chip.
As you can see in these pictures.
Does this confirm that it is a regenerative issue?
Set-up
2x 24V 70A motors. These are big boys capable of 4.1Nm continous.
wire gauge: Metric 25mmsquare. Each connection is 1250mm long
Batteries: 2x Mastervolt 90Ah AGM 12V in series to produce 24V
Blue Sea ML-24V isolation switch with a power diode accross it: MagnaChip MPJC2CA200U40, Dual Diode Module, Common Cathode, 400V 400A, 100ns, 2-Pin 3DM-2NI
it is not the capacitors but the chip.
As you can see in these pictures.
Does this confirm that it is a regenerative issue?
Set-up
2x 24V 70A motors. These are big boys capable of 4.1Nm continous.
wire gauge: Metric 25mmsquare. Each connection is 1250mm long
Batteries: 2x Mastervolt 90Ah AGM 12V in series to produce 24V
Blue Sea ML-24V isolation switch with a power diode accross it: MagnaChip MPJC2CA200U40, Dual Diode Module, Common Cathode, 400V 400A, 100ns, 2-Pin 3DM-2NI
-
Basicmicro Support
- Posts: 1594
- Joined: Thu Feb 26, 2015 9:45 pm
Re: capacitor blow out
Most likely, yes. If the voltage from regen goes over 42v it will pop the regulator almost every time. Hopefully it died in a way that didnt allow the raw voltage through to the rest of the board. Usually it doesnt and we can just replace the one chip but sometimes we arent so lucky and it takes out every thing on the 5v rail.
As for the motors, the rating on the motors is usually the continuous current rating. If thats 70a the stall current on those motors may be anywhere from 3 to 5 times higher. I recommend you determine the actual stall current. use a variable voltage power supply and multimeter. Set the power supply to around 1v and setup the multimeter to measure the current the 1v produces across one of the motors. Then multiply that by 25. That is your stall current at full charge on the batteries.
Usually lead acid batteries will handle regen energy fine but if the motors are big enough they may not. In that case you may have no choice but to add an active voltage clamp(basically a power switch, lareg watt/low ohm resistor and large electrolitic cap). At a minimum I'd set the maximum main battery voltage on the roboclaw to 2v above the main battery voltage at full charge. If the voltage rises above that the Roboclaw will put the motors into braking which will prevent further voltage rise but can be rough on the motors.
Also, your wire gauge looks fine but I'd shorten up the battery wire to the absolute minimum you can use.
As for the motors, the rating on the motors is usually the continuous current rating. If thats 70a the stall current on those motors may be anywhere from 3 to 5 times higher. I recommend you determine the actual stall current. use a variable voltage power supply and multimeter. Set the power supply to around 1v and setup the multimeter to measure the current the 1v produces across one of the motors. Then multiply that by 25. That is your stall current at full charge on the batteries.
Usually lead acid batteries will handle regen energy fine but if the motors are big enough they may not. In that case you may have no choice but to add an active voltage clamp(basically a power switch, lareg watt/low ohm resistor and large electrolitic cap). At a minimum I'd set the maximum main battery voltage on the roboclaw to 2v above the main battery voltage at full charge. If the voltage rises above that the Roboclaw will put the motors into braking which will prevent further voltage rise but can be rough on the motors.
Also, your wire gauge looks fine but I'd shorten up the battery wire to the absolute minimum you can use.