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Re: (ET) Alltrax DCX300 ET in E20
The archives has some better numbers but...
If I calculate right, the shunt should be less than 1 milliohm
(0.775mohms). With 150A of cuurent, that's a liitle over 100mV. I think
the meter is 100mV full scale so this seems right.
The shunt then should dissipate 15W at full power. That's pretty warm
for the cable, and real warm for the sheet copper shunt. I think the
problem may be in the shunt connections - I have had that problem. Say
you have 0.01 ohms in a bad connection; that would be 225 W at 150A
power draw. That's a lot of heat. But the fuse would still hold because
150A is not a crazy load if it's being dropped in the motor (and say, a
snowblower), which can handle it. If the meter is seeing the shunt
resistance plus the bad connection resistance, it would see (150 * 0.01)
= 1.5V which would hard peg the 100mV meter movement and could probably
burn it out. Though it indicates enormous power (until it smokes), it's
a false reading. I don't know much about the solid-state controllers,
but I could see how this scenario may cause it problems since a lot of
power is being dropped outside the motor, and the controller thinks it's
all in the motor.
I would take a close look at all high power conections, esp at the shunt.
Another possibility is a short somewhere that bypasses the fuse.
- SteveS
Raymon Ellis wrote:
Jim Coate wrote that the power meter is connected in parallel with the
shunt and measures the voltage drop across the shunt. My meter which
blew was connected that way. I don’t however know what the effective
resistance was of the copper shunt. The shunt was purchases after the
original copper shunt turned red hot and actually blazed with the
first controller failure. Right now I get of crazy resistance readings
across the shunt which was connected parallel to the blown meter. I
don’t trust the shunt or my testing ohmmeter. Now someone please tell
me why the original in-line fuse did not blow with the large surge of
current? Does an old original wire type fuse remain effective to
protect? When I connect my replacement controller I will use a new
in-line fuse which Steve Richardson is sending in the package. Further
comments from all will be appreciated. Raymon
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