I'm not sure why battery voltage would affect C rate. Sure, it affects absolute amps being drawn from the battery. However, if it's the same kWh battery, then the higher voltage battery will have a lower AH rating -- and thus the C rate (which is the amperage relative to the Ah capacity) will be the same. For example, drawing 100A from a 250 volt 100AH battery is the same C rate (1) as drawing 250 amps from a 100 volt 250AH battery. Both are the same kWh of battery storage, and both are the same kW to the motor, and both are the same C rate (and presumably, the same voltage sag in percentage, if the cells behave the same as the same C rate).
Increasing the kWh capacity of the battery is a different question, and could be done either by using more cells of the same AH (higher voltage battery), or the same number of higher AH cells -- either way decreases the C rate the same for the same kW of draw. Z On Thu, Dec 27, 2012 at 10:47 PM, Ing. Marco Gaxiola < [email protected]> wrote: > Jeff; I think that Rick Miller refers when say to use a high batt voltaje > for a low motor voltaje is a valid idea if you think in 'power' drawn by > the motor. > > In his 250V batt example; lets suppouse that the motor requires an X amp > rate, lets say 100AMP in 170V, that would be 17KWatts. That energy flowing > in the motor-controller side would be same 17KWatts in the > battery-controller side (plus a minimum lost inside the controller) > > But those 17KWatts on the controller-battery side would be arround 68AMP > beeing drawn from the batts; > > There it makes sense the C rate, and power. You could put the max power > in the motor, but have batts and controller 32% more relaxed than Normal. > Please correct my theory.. > > Rick, the only minimal 'insignificant' problem on all this avobe, > either it works or not; would be the Regen. It would be impossible to > achieve, since the controller could boost/step dn voltage from batteries > but could never buck/step up voltage from motor. > > > Marco Gaxiola > ...facebook/EvMarch > > > > Enviado desde mi iPhone > > El 27/12/2012, a las 09:11 p.m., Jeff Major <[email protected]> escribió: > > > Hi Rick, > > > > Sure you could run a higher voltage battery and set a lower output > voltage using an AC controller. It is done all the time when motor speed is > less than base. You could set the controller to a maximum motor phase > voltage lower than the normal .707 Vb. Or accomplish the same thing by > setting a maximum frequency. I am not sure why you would want to. AC > motors do not have the voltage limitation seen with the DC commutator. > > > > The 3 phase bridge inverter used as the AC controller can be thought of > as 6 Buck converters. Or like a DC controller for each 1/2 phase. So the > AC controller has as much control over motor voltage as a DC motor > controller. > > > > I guess I don't follow your logic with regards to > > max power, C rating and all that. How would setting an artificially low > voltage at the controller output help get more power out of the > > controller? > > > > I wouldn't say that AC lacks flexibility but rather DC is less complex > there easier for people to apply to different situations. AC drives > require tuning to the specific motor which is often best done by the pros > at the place putting the system together. Once that is done the AC drive > package is very flexible w/r/t applications and features. > > > > Regards, > > > > Jeff M > > > > > > ----- Original Message ----- > > From: "[email protected]" <[email protected]> > > To: [email protected] > > Cc: > > Sent: Thursday, December 27, 2012 2:33 PM > > Subject: Re: [EVDL] 9" motor Mishap > > > > Can AC controllers function as voltage transformers in order to allow > the > > use of a higher voltage battery pack in order to compensate for battery > sag > > that might keep you from achieving max power and holding that power to > max > > set RPM in your controller output. > > For example a modern 300V input DC controller can easily be set to an > > output voltage to match a lower motor voltage requirements. 250V in > 170V out > > for a 9". The advantage here would be to reduce battery currents and > keep > > them within their proper C ratings. This way you get every Kw of > controller > > you paid for right up to your set RPM. > > Does this make any sense or have I missed something? Is there a lack of > > flexibility with AC or do I just have to plan better? > > > > Rick Miller > > -------------- next part -------------- > > An HTML attachment was scrubbed... > > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20121227/d91a37cb/attachment.htm > > > > _______________________________________________ > > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA ( > http://groups.yahoo.com/group/NEDRA) > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20121228/c6c17a36/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
