Brushed Controller Failure

[nutsandvolts]

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[fechter]

Sounds like shorted FETs.

When a brushed controller fails, it feeds full power to the motor instead of shorting out the battery. This is why there is frequently no visible damage. The motor keeps the FETs from exploding.

If you measure from Battery neg. to Motor neg., it should read open in one direction with the power off. If it reads close to zero both ways, then the FETs shorted somewhere.

Frequently there are several FETs in parallel. Most of the time, only one will actuall short out. You can't really test them without removing them from the board. Remove one by one and test each time you pull one out. You might get lucky and pull the bad one first.

[nutsandvolts]

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[Link]

With power off, I have continuity between neg battery lead and neg motor lead.
What do you mean in one direction?

The negative battery lead on a brushed controller is actually just a dead short to the motor's - lead. The controller only modulates the + side of things. That's the one you want to check.

[nutsandvolts]

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[TylerDurden]

Continuity is not sufficient. You need continuity in one direction only... that is: reversing the DMM probes to see if conduction occurs in each case. If you have continuity both ways (by swapping the probes), FETs are shorted.

@Link... I believe the brushies work on the negleg.

[nutsandvolts]

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[TylerDurden]

I thought a continuity test was not directional, but okay I tested both the neg and pos battery leads to motor leads, with the power off, I get continuity on both leads, both directions. So one or more FETs are probably blown?

If one were stupid enough to want to attempt this again (76V), with different FETs and main caps, what FET would be a good candidate?

Sounds like toast.

The stickies on Clyte controller repair have loads of info on FETs, caps and the other goodies that make controllers work.

For a 72V brushie, I'd look into the deal ES members get on ecrazyman controllers, rather than fixing the blown unit.

[gmouchawar]

only one MOSFET could be bad and you will get those symptoms. The trick is to know which one or do it by luck.
I apply power in the correct polarity to put my finger on the MOSFETS. The one that heats up is the bad one.
Currently the best choice for MOSFET is IR4110. If you need help in replacing them let me know.

[Link]

@Link... I believe the brushies work on the negleg.

Might depend on the controller. When I opened up my last-gen e-crazyman controller, the battery negative and the motor negative shared the same solder point.

And yeah, you might as well upgrade it while you're at it.

[johnb]

Might depend on the controller. When I opened up my last-gen e-crazyman controller, the battery negative and the motor negative shared the same solder point.

And yeah, you might as well upgrade it while you're at it.

On the Crystalyte controller it is the negative that gets switched.

[johnb]

only one MOSFET could be bad and you will get those symptoms. The trick is to know which one or do it by luck.
I apply power in the correct polarity to put my finger on the MOSFETS. The one that heats up is the bad one.
Currently the best choice for MOSFET is IR4110. If you need help in replacing them let me know.

That's a good trick. Didn't think of that. I went by luck when mine failed and got the bad one first time

[TylerDurden]

You might also try the inverted compressed duster gag... spray enough refrigerant/propellant to get frost to form on the components, then apply power... the frost will melt or evaporate on the hot components first.

Do not use butane.

[Link]

LOL, yeah, but you know that burning the stuff in air dusters produces hydrofluoric acid? Apparently one of the worst acids, health wise. Getting a concentrate of it over 2.5% of your skin is enough to kill you.

That would also explain why my lungs started to burn when I lit some of it up once. Would have been nice to know that at the time.

[nutsandvolts]

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[nutsandvolts]

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[nutsandvolts]

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[fechter]

Organ donor.

What happened when you tested it?

[nutsandvolts]

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[fechter]

Frequently the gate driver transistors blow at the same time. Yours sound like they are stuck on, however if the FETs are good and the controller is not powered, the resistance between the battery neg and motor neg wires should be high in one or both directions (swap the meter probes while measuring).

You can trace the circuit from the FET gates back to these transistors. There is usually a resistor in series with the gate first. These can blow too, but usually fail open. You can test resistance across them. Compare to the others.

The driver transistors are usually pretty small, and not expensive to replace.