Battery current isn't a PWM square wave. Capacitors in the controller smooth the current flow. It's DC with an AC component.
Motor current is smoothed by the motor's inductance and would have a waveform similar to the battery current. A DC ammeter which in this case is a millivoltmeter connected to a shunt will read the DC component of the current and not respond to the AC component. The meter will indicate the DC or average value of the current. The Corbin ammeter might be inaccurate but not because the current is pulsating. It should be possible to compare readings of current indicated by the ammeter and by the E-meter. I'd be surprised if the difference were more than a few percent. Tom Shay ----- Original Message ----- From: "Victor Tikhonov" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Wednesday, October 09, 2002 5:26 PM Subject: Re: Sparrow Ammeter > John Lussmyer wrote: > > > > At 01:11 PM 10/9/2002 -0700, Victor Tikhonov stated: > > >How does your analog meter averages battery amps? It is not a DC, > > >it's PWM'ed DC so the error for odd wave form may be as much as 50%. > > > > The little analog amp meter in my Sparrow is small, and does seem to read > > 30-40% low most of the time. I have no idea what kind it is, or anything > > else about it. I do believe it measures battery amps, and not motor amps. > > Yes, its battery amps, but the number is not real. > > If you draw PWM 200A pulses 50% duty cycle (like > 200A-0A-200A-0A every 100us or so), the average current > is 200*0.5=100A but your analog movement meter may show 60...70A. > > A good way to check is to connect a scope to the shunt and get the > average voltage reading ar some load. Divide it by shunt resistance > and you'll get the current your analog meter should show. > > Victor > >
