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Reply to "Addicted to BlueRail"

@gunrunnerjohn: I re-ran the test by hooking up directly to my KW transformer and connecting directly through a bridge into the DC inputs of the motor.

I started out at 8VAC to let the chassis cruise across the track for a "baseline"...got about 1.5 amps for this part.

Then I let it roll into a bumper and gradually I cranked the voltage up to 12VAC.  The wheels slipped and grabbed a bit, giving me around 3.5amps for that period, until they finally locked up and I was at full stall with around 4.5amps.

So My previous "ramp" test was obviously flawed, but even here I'm only peaking at 4.5 amps or so.  However, I realized that the equivalent DC Voltage is only around 0.7 times AC voltage (or something like that, for a full wave bridge), so maybe I need to re-run the test with 17 or 18VAC to really simulate 12VDC at the motor during stall.  I will do that later this evening, but I'm still thinking I wont get anywhere near 14 amps.

EDIT (Everything below): After brushing up a bit more, I'm pretty sure I got the AC-DC voltage conversion backwards.  Assuming the bridge as 1.4volt drop across the diodes, I believe the Vdc=1.4*(VAC-2*0.7). So to get around 12.8V DC to the motor leads, I should set my transformer 10.5V (subject to things like the actual forward voltage drop of the diodes being 0.7V, the efficiency of the bridge, etc.) 

But in the end, after all the calculations and assumptions, I realized that I *actually have a tool to measure the DC current and DC amps across the bridge legs!* (Duh!)

So I simply set my transformer to an AC voltage that resulted in measurement of 12.8VDC across the bridge.  Interestingly, this voltage was 14.9VAC, not the 10 or so I expected.

Then I measured the current across the DC leads of the bridge attached to the motor leads at stall.  And that current was right at 3 amps. 

So I'm fairly confident that I can make the 4amp Tsunami decoder work.

(YMMV!)

Original video trying to measure AC amps (wrong way):



Updated video measuring DC amps directly (the right way I think):

Attachments

Videos (2)
20210405_120706
20210405_150217_1
Last edited by Jeff_the_Coaster_Guy

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