lsjpeng

Just got my new CC ICE2 80HV. I love its data logger function, but the current reading seems higher than my Eagle Tree data logger. Since my job relates to a lot of tool calibrations, so I like to share how I calibrate these current readings.

Figure 1 shows the setup. ICE2 80HV, Eagle Tree and Watts Up are series together, so the current is the same.

Current standard is read from a calibrated current shunt (1mV=1Amp), voltage across this current shunt is picked up by a calibrated Keithley 2010 precision multimeter. Each measurement is repeat twice in opposite polarity to eliminate the thermal noise. Table shows the results: just as I suspected, the current reading from CC ICE2 80HV data logger is off by ~4.5% at high current (>30A) range, while Eagle Tree and Watts Up are off less than 1.4%.

Well, the calibration will NOT improve anything, just curious how accurate those numbers are.

DaveL322

Luke,

I noticed the same thing several years ago when I started running the ICE ESCs - logging showed higher amps and mah than my Eagletree. What amount of the differences do you think could be attributed to connectors / solder joints?

Regards,

Dave

lsjpeng

Dave:

Not sure, since all of them are series together, so the current is the same. My best guess is the software, or the way how it calculates the current. There are many other ICE2 80HV in my area, I might try to test the others to see if it is a systematic shift. If so, it may relate to CC's calibration equipment.

Luke

lsjpeng

Conversion factor:
This is a parameter to let me convert my ICE2 80HV current reading to the real current.
Plot the standard current vs. ICE2 80HV current reading using Excel, then add trend line and show the fitting equation. For this ESC, the conversion formula is: Real current (A) = 0.9548 x ICE2 reading

wingster

My Feedback: (26)

Any idea if the voltage measurements are OK?

lsjpeng

Voltage measurements are affected by length of cable, number of connectors etc. Each contact causes mV range drop. But a briefly check, they are statistically matched.
Voltage conversion factor:
Watts Up: 1.0007xWattsUp reading (V)
EagleTree: 1.0054xEagleTree reading (V)
ICE2 80HV: 1.0061xICE2 reading (V)

Not surprise..... WatssUp is closer to the battery, and ICE2 is at the far end; the reading is lower than the voltage at battery side.
I believe (not try yet), if I series them (to the battery) one each time to minimize the cable length and # of contactors, the voltage reading should be the same

Luke

bjr_93tz

Got an interesting question,

When measuring the "DC" voltage across the shunt, does your Keithly 2010 return the average voltage or the RMS voltage, given it's a PWM signal (unless the duty cycle is 100%) and we're using the DC range?

At a guess I'd bet that the CC ESC is using a PCB track as a shunt, +- 5% accuracy for hobby applications seems reasonable.

Cheers
Brett

DaveL322

FWIW,

When I first started running the ICE ESCs, they did seem pretty consistent ESC to ESC, and the voltage and RPM readings were very closely matched to the Eagletree and an optical tach.

Regards,

Bill Clark

thats alot better than my ICE100. My ET read 65 and the ICE read 85 if I remember correctly. I have never used the ICE logger on my HV80

bjr_93tz

Just to satisfy my own curiousity re the RMS vs Average on the DC range, I dug out some gear and had a play. I figured an 8kHz squarewave with suitable DC offset and varying duty cycle would would be close enough to what would be measured across a shunt. It turns out that a Fluke 175 (and probably every other meter) on the DC volts range measures Average voltage, not true RMS.

What does that mean to us?

If you measure the voltage drop across a 0.001 ohm shunt resistor where 1millivolt = 1amp, then the displayed value will be the average current which is useful for determining how fast you're draining the battery and how much electrical power is going into the motor. What it doesn't tell you is how much you're heating up your battery, esc and motor windings because it's the RMS value of current that decides that.

eg for ~142mV peak
25% duty cycle gave 36mv average and 73mv RMS
50% duty cycle gave 71mv average and 103mv RMS, with a boatload of assumptions to simplify things, at 50% duty cycle you're motor is producing half the torque (half the current) but the windings are heating up like your passing 73% of the current.
Note: The RMS values are calculated as Fluke 175 don't return true RMS values for squarewaves or high frequencies.

OK, it probably makes no difference to anyone here, but it's interesting nonetheless, especially to a student a couple of weeks back that couldn't figure out why 6 amps DC (average) from a mains powered 1/2 controlled rectifier didn't heat up an element the same as 6 amps (RMS) from a Variac...