Blog 6: Now for some initial data

RE: Blog 6: Now for some initial data

dang74 — Sun, 15 May 2022 03:51:53 GMT

Earlier today I was reading blog#2. Back then you were concerned that you were in over your head. I am so glad pushed ahead. I had some frustration and self doubt during my road tests so I can totally relate. Things seem to be progressing now, and hey, you have the ability to read data, but best of all, you are learning new things and solving problems as they emerge, and there in lies the real reward.

RE: Blog 6: Now for some initial data

colporteur — Thu, 28 Apr 2022 16:38:57 GMT

I really appreciate michaelkellett & misaz lending me your expertise. I ran the python script again using the following configuration, to measure both current and voltage.

max.configure(sample_rate_khz=.5, digital_filter=128, measure_current=True, measure_voltage=True) with the following results. I had to add the sample_rate or the script errored out. This makes it slightly different than what misaz provided.

The readings are much more stable.

Break..Break... I could carry this question to another post but I got lazy:o

Why am I unable to measure the current with a Fluke 77 VOM using the 300mA range?

I tried using two different meters to read the current. Only when set to the 10amp range on the meters will they produce a reading of 0.07 and 0.06 on the other. If I attempt to use the 300mA on the Fluke meter and 250mA on a second different meter they indicate out of range.

The reading would suggest the current is within the lower range of the VOM's, Any suggestion on why are they not able to provide a reading?

RE: Blog 6: Now for some initial data

dougw — Wed, 27 Apr 2022 13:20:58 GMT

The readings seem to make sense, although timing of conversions and filtering may affect results. If you multiply voltage times current you will get an idea of the power consumed in each state. If the load is more or less constant (no load except friction), the speed will be proportional to power. Back EMF of the motor, which is proportional to speed will reduce the effective applied voltage, which tends to reduce current through the motor.

RE: Blog 6: Now for some initial data

michaelkellett — Wed, 27 Apr 2022 09:36:07 GMT

Do you have a scope - might be worth checking the nature of the applied voltage and the current ?

Looking at your results the current measurments fluctuate too much to be happy with them

Can you measure a a lot faster ?

(I would have hoped for >100 readings per second.)

Looking at your 12V readings the voltage is quite stable for the six readings but the current is still at the end dropping - would be really nice if you kept going with more readings until it settles.

Having said that, 6 samples would span 25 seconds which is a long time constant for the current to vary over .......

More data needed.

Suggested step 1.

Repeat experiment but take at least 20 readings per voltage.

BTW - what is th loco doing (on rails, upside down etc)