CA3 - Phaserunner Speedo EMI Noise

Triketech

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Mar 31, 2015
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Bought the CA3 DPS about 9 months ago along with a Thun and mounted it on a Recumbent Trike to measure rider power and a lighted gauge. Worked great. Thats on my wife's trike.

Also have one on mine, along with a Phaserunner and MAC 10T.

Just finished installing a Phaserunner and MAC12T on my wife's trike. Speedo works fine unless the motor is running. Once the motor pulls over 10-15 watts there appears to be an inductive input to the speedo. The speedo is connected to the front wheel but setting the rear on a jackstand and running full throttle it shows 65 MPH.

I disconnect the speedo wire (previously added a JST connector) and route the wire away from all others, it still tracks motor switching speed.

If it were radiated susceptibility it would likely be an H Field (magnetic) rather than and E Field (inductive) if it was due to the Speedo wire. Its worth mentioning that the Phaserunner is about 6" from the CA3 on both trikes. Only having a problem on one of them.

Its also possible the 6 pin CA3 -Phaserunner cable is inductively coupling as it runs along the back of the Phaserunner. Depends on the sensitivity of the speedo pickup I suppose.

Anyone have some insight?
 
Ruled out EMI as the problem.
Powering the CA3 separate from the Phaserunner via the concentric plug output and connecting the throttle directly to the Phaserunner , the speedo works fine when the motor spins up.

Another strange thing is no matter what shunt resistance I set in the CA3 it shows -5W at standstill when plugged into the Phaserunner, although when running it gives a readout that could be accurate when value is set to 1m. Its a pet peeve of mine that the CA3 display shows a little case "m" rather than an upper case "M" for a Meg-Ω reading.

I get .4Ω between #3 (blue) & # 4 (white) on the 6-pin on the Phaserunner, close to what the 2nd working one reads.

Concerned its the Phaserunner. Kind of a bummer if it is.
 
The speed reading is a bit odd, as you added a connector to the Speed sensor, could you try adding a 1000pF ceramic capacitor to the connector and see if it filters out the noise?

The Phaserunner has a precision (i.e. 1%) 1.00mOhm (milliohm) shunt in it, so you should set the CA3 shunt to 1.000 mOhm. It is not Megaohm shunt (capital M). 1 milliohm = 0.001 ohm, when 40A of current is flowing across this shunt, there is a measurably a small voltage on either side of the shunt, to the tune of 40mV (0.04V). The CA3 takes this measurement, and amplifies it to a value the microcontroller onboard can display in more meaningful range (i.e. amps!). If the shunt was 1 Megaohm (1,000,000 Ohm), to try and push 40A through the resistor, you'd need 40,000,000V source!

Regarding your CA3 -ve watts reading, go into the CA3 setup Calibration screen, and find the heading that says "Zero Amps", press and hold the left button, and it will put the offset of the CA to zero, and get rid of that -5W offset.

Also, if you set your multimeter and just touch the probes together, you'll get a similar reading of 0.3 to 0.4 Ohm, this is because the shunt is too low of a resistance for your meter to read effectively when it's trying to measure Ohms.
 
I didn't realize they used an inline shunt rather than a bypass shunt. Then again it is relatively low voltage so I suppose that makes better sense (literally) to use.

Tried swapping the two CA3's. Its in the CA3 unit. I suspect maybe a bad solder joint on the ground lead to the PCB pad, but for the cost of my time to pull it apart and check I may as well just order a new CA3.

My Fluke seems to have pretty good low resistance accuracy without a bridge on the leads. When the gator clips are bound together it shows .05-.07 Ω. I have an old HP Milliohmeter but the probes are shot and too pricey to replace.

Thanks for the reply Robbie!
 
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