# Cycle Analyst Shunt Problem - Solved!



## PTCruisin (Nov 19, 2009)

Since installing a Cycle Analyst (CA) on my car last September, I have had much difficulty in getting the 500A/50mV current shunt to zero-out or read accurately. So, yesterday I decided to rewire the shunt so that I could monitor all current (both charge and discharge) on the 38s LiFePO4 pack.

As I was finishing up the wiring I noticed that the connections between the shunt and the controller were not snug. After tightening up the connection bolts, the Amp reading on the CA was very stable, and easily zeroed. When I plugged in the charger, the amp display indicated -9.6A (flowing into the cells) and the kW display indicated 1.2kW, which is what I have measured countless times for the 1.5kW Elcon charger with another meter. 

Apparently, the loose connections were adding small amounts of resistance in series with the shunt and causing the erratic readout of current on the CA.

Lesson learned: Loose connections bad!!!!


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## dtbaker (Jan 5, 2008)

interesting indeed... I will check mine again. It might just be that the connectors I put on those super-fine wires aren't making a good electrical contact.... but I got a couple higher resistance resistors from the CA people yesterday; I am somewhat hesitant to attempt to install as the frigging things are microscopic. I have never tried soldering anything so small....


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## Roy Von Rogers (Mar 21, 2009)

dtbaker said:


> interesting indeed... I will check mine again. It might just be that the connectors I put on those super-fine wires aren't making a good electrical contact.... but I got a couple higher resistance resistors from the CA people yesterday; I am somewhat hesitant to attempt to install as the frigging things are microscopic. I have never tried soldering anything so small....


 
Lol....I work on small stuff once in a while, those resistors/diodes,transistors etc are so small I have to use a tootpick to hold them down while soldering, cause if I breath to close, it blows off the board.

Roy


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## ElectriCar (Jun 15, 2008)

A shunt is a VERY SMALL value resistor between the two terminals which creates a very small voltage at high amperage. Not only should your connections be tight but it won't hurt to brush the shunt terminal and wire connector with a wire brush LIGHTLY to remove any oxidation before connecting them up. Soldering the wires to the connectors will make the connection even better. I just installed my shunt today.


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## PTCruisin (Nov 19, 2009)

ElectriCar said:


> A shunt is a VERY SMALL value resistor between the two terminals which creates a very small voltage at high amperage. Not only should your connections be tight but it won't hurt to brush the shunt terminal and wire connector with a wire brush LIGHTLY to remove any oxidation before connecting them up. Soldering the wires to the connectors will make the connection even better. I just installed my shunt today.



Good advice, ElectriCar. I can't believe the difference I'm seeing now that the shunt resistance is greater than the connections. The current value displayed on the CA is accurate to 0.1A now, at least at the low end. I've been able to confirm many of the parasitic current draws (lights, wipers, brakes, etc.) with both the CA and a clap-on ammeter.


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