[ausev] Ive discovered my scooter is over unity!!!

[tomsmail at wtez.net]

I believe this is normal, and the low quality meter might be just excacerbating what's already there.  Aaron, I don't think you ever clarified if you meant that the pack voltage remains high after resting for several minutes with no load, or if you took a sample while on the road under load?

I see the same thing on my EV under load.  I use a good Fluke meter with logging and supposedly very good transient frequency response.  The controller has a very large capacitor and the pack leads are pretty long so the system is like a gigantic (RLC) oscillating network.  Current or Voltage (whichever one I happen to measure) bounce around and them damp after several seconds, whenever I sharply depress or release the accelerator pedal.  This occurs with or without regenerative braking turned on.  I can tweak the controller to make this go away - by limiting current or setting precharge circuit voltage thresholds to higher values.

For me, "several seconds" has been around 10 seconds.

Tom

p.s.  Al Gore uses the harbor freight meters to measure temperature ;-)

--- gkrysztopik at satx.rr.com wrote:

From: gary <gkrysztopik at satx.rr.com>
To: AustinEV News Announcements and General Discussion <ausev at austinev.org>
Subject: Re: [ausev] Ive discovered my scooter is over unity!!!
Date: Sat, 16 May 2009 08:40:53 -0500

Yes, I found that my magic $2.99 Harbor Freight DVM can create a lot of 
energy.  Sometimes my batteries go from 12.xx volts to 14.xx volts after 
charging.  I think GM uses these meters to measure fuel economy.

Gary Krysztopik
www.ZWheelz.com
www.aceaa.org
San Antonio, TX



Erik wrote:
> Some voltmeters also read funny in the presence of high frequency 
> noise.  An analog meter usually won't lie, but my harbor freight meter 
> can give some creative responses.
>
> On Fri, May 15, 2009 at 7:36 PM, Matt <mba at hazmat.com 
> <mailto:mba at hazmat.com>> wrote:
>
>     Most likely, the battery pack voltage is drooping under high
>     current (high
>     load), and the reference voltage for the battery meter is drooping as
>     well.  The measurement is only as accurate as its reference. I would
>     investigate how you are powering your voltage meter and where it
>     gets its
>     reference from.
>
>     Matt
>
>     On Fri, May 15, 2009 6:20 pm, Chris Robison wrote:
>     > Some questions:
>     >
>     > What is the make and model of your scooter? At what points in
>     the system
>     > are you placing your probes or clips? Can you reproduce the
>     behavior on
>     > a stand (with the rear wheel raised)?
>     >
>     > I could imagine motor regeneration causing temporarily higher
>     voltages,
>     > but if your 64V pack is "sitting" at 110V after shutting down,
>     I'd guess
>     > you either have a measurement error or a battery pack that won't
>     last
>     > long.
>     >
>     >   --chris
>     >
>     >
>     >
>     >
>     >
>     > Aaron Richardson wrote:
>     >> I put a volt meter on my pack to see how much its sagging under
>     load.  I
>     >> see the resting pack voltage is about 64V (5x12v SLA).  When I
>     >> accelerate the pack sags down to about 55 or so and then climbs
>     as the
>     >> scooter increases speed.  On a freshly charged pack it got to
>     110V!!
>     >>
>     >> I dont think Im inducing current into my sense wires because
>     the voltage
>     >> goes to 64V when I let off the accelerator and coast at high
>     speed.  It
>     >> seems this voltage it right.  If I shut the scooter off then
>     this is
>     >> where the pack sits.
>     >>
>     >> So, whats causing this voltage and can I trust the sag voltage
>     when the
>     >> scooter is moving very slowly?
>     >>
>     >> thanks,
>     >> Aaron
>     >>
>     >>
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