Aha, thanks Roger for clarification. In any case, simple recalibration should take care of the issue.
Victor Roger Stockton wrote: > > Victor Tikhonov [mailto:[EMAIL PROTECTED]] wrote: > > > 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. > > With modern high-frequency PWM controllers, the battery current is not > as described; in the example Victor suggests, the battery current with > your DCP controller should be pretty much 200A with perhaps 20A of > ripple at the 20kHz (or so) switching frequency (actually, 50% duty is > the worst case scenario, so the ripple might be a bit higher % of the > average under this case and better everywhere else; Rich or Damon will > know for sure). > > The big current spikes are sourced by the controller's bus caps so that > the battery sees essentially only the average current; this is one of > the big advantages of modern high-frequency PWM controllers over > low-frequency ones such as the GE EV-1 SCR controller (switching at > 50-300Hz, Victor's description is right on the money for it. > > Your analog meter isn't likely to respond to the ~20kHz ripple on the > current signal anyway, so its inaccuracy may be inherent to the meter or > shunt that feeds it. > > Cheers, > > Roger.
