Following up on Nathan Stowe's question regarding Speed and a 9in ADC motor, I found this very interesting thread on the EVDL. It turns out that just because your DC motor is rated for 144Volts doesn't mean your battery pack has to be 144Volts.
Re: Maximum ADC Voltage? by Roger Stockton May 26, 2008; 07:25pm :: Rate this Message: (use ratings to moderate[?])
James Massey wrote:
> So why didn't you say it that way, instead of saying it in a
> way that can be interpreted as though the motor wouldn't see
> pack voltage? With hundreds of new just-started-learning
> potential EVers reading this list, we must all be clear when
> we describe things to avoid confusion if at all possible.
You are correct, I could have expressed this more clearly. I think clarity is often sacrificed when we dip too deeply into technical details too early on in a newcomer's education ;^>
I thought it sufficient to explain that using a 192V pack does not mean the motor will necessarily *ever* see that full pack voltage.
> Except that unless the controller is an SCR based controller (has no
> capacitors) the batteries do not sag to the 'fully loaded
> voltage' on each pulse, but sags to a voltage that is
> proportional to the loading.
Yes, I did not mean "full loaded voltage" to suggest that the batteries will see maximum load current every time the switches are on, though I do appreciate that it might have read that way. I meant that the battery will sag to whatever loaded voltage is appropriate for the current being drawn at the time.
> >If the insulation isn't up to the job it will break down, if the
> >mechanical clearances are not good enough the motor will
> >flash over if conditions are right (or wrong, depending on
> >your point of view).
> >
> >Yes, this *might* be a consideration if one is running an
> >exceptionally high pack voltage.
>
> Or a motor with tired, old insulation, or a poorly made motor
> (built on a Friday or a Monday) that has nicks or other
> damage to the insulation (see Jim Husteds' photo gallery for
> examples of this). ...[show rest of quote]
Fair enough; if one is scrounging used motors they'd best make sure they are aware of what the motor is capable of handling in its present condition and not rely on nameplate data, etc.
> > The 192V suggested is unlikely to qualify. There are several
> > examples of others running 192-240V packs with bone stock
> > ADC and Warp motors, so I personally would not worry in the
> > least about the insulation holding up to the loaded voltage
> > of a 192V pack.
>
> Well, since Jim Husted would worry, and he is our motor guru,
> I'd defer to his worry.
Jim is indeed our motor guru, however he is not yet an EV guru. I could be mistaken, but I believe that his response was based on the assumption that someone was thinking of *running* their motor at 192V rather than using a 192V battery pack.
> The fact that some are running 192V
> does not mean that the much higher voltage is not slowly
> destroying their motors, or won't quickly destroy another
> motor of similar type but worse build quality. Any example of
> someone doing something does not mean that it is something
> that can always be got away with. Who set up their systems?
> are the motors really bone-stock, or have they been prepared
> by someone? How hard are they being driven? How well
> protected against road spray (or anything else that can cause
> corrosion) are they?
>
> A Jim Husted style prepared motor has been proven many a time
> to be fine in the short term for significantly higher
> voltages than 192V systems, but to state that 192V is 'likely
> to be fine' on a motor of unknown condition is easy to say if
> you don't have to pay the cost of repairs if it isn't. ...[show rest of quote]
I believe the original poster specifically asked about an ADC or Warp motor nameplated for operation to 144V. I stand by my comments that I would have no hesitation whatsoever about running a 192V pack with a ADC or Warp 8" or 9" motor. I will add the qualifier 'provided said motor is in proper operating condition'. This does not mean that I would recommend operating the motor at an average voltage of 160V or higher.
Running a 192V pack these days almost certainly means running a Zilla controller, and so I would strongly advise the poster to heed Jim's caution and limit the max motor voltage *below* 160V (e.g. even a 144V limit is unlikely to be a nuisance and will provide a measure of safety should one ever push the vehicle that hard).
The results of a few minutes spent browsing the EV Album:
Otmar's CaPope runs a 240V pack of AGMs with a pair of ADC 8" motors; I think it safe to say that it gets run reasonably hard as a testbed for the Zilla controllers.
JB Straubel's 944 also runs a 240V pack with a pair of ADC 8".
John Bryan runs a 192V pack with an ADC XP-1227A.
Byan Hall's 914 runs a 192V pack with a single ADC 8".
Bill Dube's Rabbit runs/ran a 192V pack with an ADC XP-1227.
Canadian Electric Vehicles built a Metro with 192V feeding an ADC 9".
Edward Ang's Paseo uses a 192V pack feeidng an ADC 8".
Mike Willmon's Mistubishi PU runs a 192V pack feeding a Warp 9.
Jeremy Green's CRX has a 192V pack feeding an ADC 9".
Dan Shoop's Sentra has a 192V pack feeding an ADC 9".
John Benson's 914 has a 192V pack feeding an ADC 9".
Etc, etc.
It seems to me that it is not at all unusual to run 192V or more with ADC or Warp 8" and 9" motors. Some of these vehicles are driven hard, and some have been in use for several years.
It is common practice to run a battery pack voltage at least somewhat higher than the motor nameplate rating since it will otherwise not be possible to achieve the rated RPM when the pack sags under load.
> So the answer to the original posters' question is 'maybe',
> if, if, if. So lets' do what we can to help him (I didn't
> keep the original post so I'm not sure who they are) answer
> the 'ifs' so they can then make an informed decision as to
> wether the risk is minimal of increased voltage.
Sure. The long list of EVers who are already running pack voltages of 192V+ with ADC and Warp 8" and 9" motors nameplated to 120V or 144V certainly suggests that the risk of following suit is minimal, unless of course one happens to be using a motor that is in poor condition or is defective. (In which case, it is likely to fail sooner or later even if the nameplate rating is not exceeded.)
I do not think this empirical evidence is at all at odds with our motor guru's warning. I think it simply indicates that our motors seldom operate at an average voltage near full pack voltage, and that they do not seem to be greatly bothered by instantaneous voltages over 160V during the brief on-time of the controller.
There is no argument that if one wishes to absolutely minimize the likelihood of harming their motor from overvoltage that limiting the pack voltage to 156V max is a useful step. Conveniently, there is economic justification for doing so, as there is a fairly steep step in controller cost once the pack exceeds 156V! ;^>
Cheers,
Roger.
