Repairing a shunt on a mainboard

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ebike11

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HI guys
I have a 50A controller and unfortunately I have to lower the amps rather than increasing the amps that most people do via shunt mod. There are 3 shunt bars side by side. I snipped off a small part of one on the shunt but I still needed to lower the amps because the battery pack that I have only has cells with a continuous discharge of 30A. Its a small build for another bike. I tried snipping a bit more off from the shunt bars but I accidently severed the remaining 2 bars and there is a gap in the center. What could I use along with solder to make the connection again? The original shunt bars are pretty stiff.
Thx
 
docw009 said:
Why not copper wire?
Click to expand...

Yes i will try tomorrow and solder
So the controllet stopped working after all 3 shunts were cut. Is that a normal thing for it to do?
 
Shunt are sense wires, the less shunt material the less current while the more shunt material (soldering equal amounts to each shunt) the more current. I would have just cut one shunt out of the 3 to reduce to 2/3 of total. So if your controller was 45A, it would now be 30A, is my best guess. They would be in parallel, so 10//10=5 and 10//10//10 is 5//10 is 3.33 total so cutting one out is 10/10=5 so more resistance. Parallel resistance equation^^^^^^^^^^^^^^^^^^^^
 
DogDipstick said:
https://endless-sphere.com/forums/viewtopic.php?t=31643

Best shunt mod thread I have found yet. Explains alot on how they work typically.

... and by cutting all three... you would increase resistance and reduce current (to zero apparently lol).
Click to expand...

Yes when I cut one and tested, the bike ran fine. Then I cut the other 2 shunts in half causing a gap and the bike never moved when the throttle was twisted. I soldered the shunts together, but still nothing. Would something have caused no power signal to the motor? maybe cutting all 3 shunts allowed something else to malfunction?
I see no burnt marks on the board
 
Obviously you don't know what value the shunts were, but have you searched to see if someone else has reported their value? What controller is it? Can you post a picture of what they look like?

If the controller is trying to read the phase current but you effectively changed the resistance to infinity then the voltage across it will be high and could activate the hardware protection, assuming it has that.

I would have expected that bridging each shunt with solder would have temporarily restored operation as long as nothing else was damaged.
 
The 5v circuit may be defective now, first thing to test.

Cutting all the shunts was not the best idea of the month. :wink:
To restore (at least one), I would have soldered on it a jumper of copper wire about the same gauge.
 
bww129 said:
Obviously you don't know what value the shunts were, but have you searched to see if someone else has reported their value? What controller is it? Can you post a picture of what they look like?

If the controller is trying to read the phase current but you effectively changed the resistance to infinity then the voltage across it will be high and could activate the hardware protection, assuming it has that.

I would have expected that bridging each shunt with solder would have temporarily restored operation as long as nothing else was damaged.
Click to expand...

its a 72V greentime controller 45A model, but I cant find it in his store now
Yes I bridged with solder but Im assuming something else must have got damaged :(
 
MadRhino said:
The 5v circuit may be defective now, first thing to test.

Cutting all the shunts was not the best idea of the month. :wink:
To restore (at least one), I would have soldered on it a jumper of copper wire about the same gauge.
Click to expand...

Yeah, not the best idea for sure. I did solder after the damage was done but nothing.
Where is the 5V circuit usually located?
i can upload of the opened controller if needed thx
 
Time to just buy a new one, to use while you work on this one. Unless you have a spare already.
 
Yep, good to have spares, for a commuter especially.

Test the 5v circuit on throttle, or phase red/black
 
FWIW, the shunts *are* the battery-negative connection for the controller.

Without the shunts, there's no power.

Wiring across the shunts restores power but leaves the controller unable to know how much current is flowing, and thus unable to protect itself against overcurrent, and vulnerable to failure upon any usage.
 
amberwolf said:
FWIW, the shunts *are* the battery-negative connection for the controller.

Without the shunts, there's no power.

Wiring across the shunts restores power but leaves the controller unable to know how much current is flowing, and thus unable to protect itself against overcurrent, and vulnerable to failure upon any usage.
Click to expand...

thx for the info!
 
Unless there is something "great" about your controller, some feature that stands above the rest then just buy a new controller to suit your voltage and discharge amp requirements. Then you can go to www.mouser.com and by some shunts, guessing as to what ohmic (resistive/resistor value) it was stock. It will be a low ohmic value, like 0.10 or a 0.05 ohm or something along that lines, very low.
 
MadRhino said:
ebike11 said:
MadRhino said:
Test the 5v circuit on throttle, or phase red/black
Click to expand...

phase red/black? the phases wire are green, blue and yellow
Click to expand...
Sorry. Brain fart. I meant halls red/black.
Click to expand...

tested and I have 5v in both places. its weird why there is no signal..tested motor halls and coils. they are also both good
Its gotta be in the controller
 
Maybe you did mod the shunt resistance enough so, that the Amp signal is now reading a value that is out of the controller program setting.

I agree that you should have a spare controller to ride the bike while you are playing with this one.
 
MadRhino said:
Maybe you did mod the shunt resistance enough so, that the Amp signal is now reading a value that is out of the controller program setting.

I agree that you should have a spare controller to ride the bike while you are playing with this one.
Click to expand...

hi
in other words, i put too much solder over the shunts?
also this controller has no programming capabilities or bluetooth
 
Most controllers I've seen use something like a LM358 to measure the voltage across the shunt. Normally the input would be millivolts, but if the shunt resistors were all open circuit, the LM358 (or whatever is looking at the shunt voltage) could see full pack voltage and self-destruct.
 
ebike11 said:
MadRhino said:
Maybe you did mod the shunt resistance enough so, that the Amp signal is now reading a value that is out of the controller program setting.

I agree that you should have a spare controller to ride the bike while you are playing with this one.
Click to expand...

hi
in other words, i put too much solder over the shunts?
also this controller has no programming capabilities or bluetooth
Click to expand...

No, If you had lowered resistance of the shunt, the controller would be working, only not ‘knowing’ it is feeding higher power. But, if you raised the resistance of the shunt too high, the controller program could shut the power off, thinking the max Amp setting is attained or busted.

This can happen if you had replaced the copper shunt material with solder that has a higher resistance (lead has only 7% of copper conductivity, thin is about 15%). Normally we do the opposite. I mean we are ADDING solder to the copper shunt, to lower the shunt resistance slightly, or add an extra shunt to lower resistance considerably. This is tricking the controller thinking it is feeding power within its limit setting, when it is really feeding much more. Now, bridging with solder, you may have tricked it thinking it had reached the limit, even at rest.
 
MadRhino said:
ebike11 said:
MadRhino said:
Maybe you did mod the shunt resistance enough so, that the Amp signal is now reading a value that is out of the controller program setting.

I agree that you should have a spare controller to ride the bike while you are playing with this one.
Click to expand...

hi
in other words, i put too much solder over the shunts?
also this controller has no programming capabilities or bluetooth
Click to expand...

No, If you had lowered resistance of the shunt, the controller would be working, only not ‘knowing’ it is feeding higher power. But, if you raised the resistance of the shunt too high, the controller program could shut the power off, thinking the max Amp setting is attained or busted.

This can happen if you had replaced the copper shunt material with solder that has a higher resistance (lead has only 7% of copper conductivity, thin is about 15%). Normally we do the opposite. I mean we are ADDING solder to the copper shunt, to lower the shunt resistance slightly, or add an extra shunt to lower resistance considerably. This is tricking the controller thinking it is feeding power within its limit setting, when it is really feeding much more. Now, bridging with solder, you may have tricked it thinking it had reached the limit, even at rest.
Click to expand...

Thanks for that info MadRhino..hmm so I guess maybe I should remove all of the large glob of solder and start over. Maybe bridging the shunt gap with thin copper wire instead of bridging the gap with solder??
 
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