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Re: battery help
by Morgan LaMoore
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Joe,
I'd disagree. If you're using a battery with higher voltage, the controller
can use a lower duty cycle to get the same speed. Lower duty cycle means
less average current drawn from the batteries. Less current drawn from the
batteries means longer range. In an ideal world, they would trade off
perfectly, and your range would depend on only capacity (in Watt-hours, not
amp-hours).
Of course, the real world has inefficiencies and imperfections that mess
with things. At higher currents, you lose much more power in the wires (I^2R
losses); higher voltage at lower currents lowers these losses. At higher
voltages, you may get more iron losses from the magnetics (depending on type
of motor), or the motor controller may be less efficient if it is running at
a very low duty cycle. So you have to find a balance between voltage and
current. You don't see many EV's putting 15 6V batteries in parallel!
What matters is energy storage, not just amp storage. Energy is what makes
the world go.
-Morgan LaMoore
On 8/16/07, Joseph T. <jat1793@...> wrote:
>
> John,
>
> I know where you are coming from, but I think you might be
> incorrect. (sorry!) Here's a run down:
>
> More amp-HOURS is what provides more range. An amp-HOUR is
> one amp running for one hour, so more amp-hours means that the battery
> can run longer, and therefore give you more range.
>
> Adding more batteries, or making the battery cells larger
> will increase range. Now, when you add more batteries you do increase
> voltage and range. However, you can have a battery pack with more
> volts have less range than a battery pack with LESS volts. How? The
> battery with less voltage can have more amp-hours, and because it has
> more amp-hours, and therefore a longer running time, it gives the
> vehicle more range. You can though, increase range by adding more
> batteries, which also gives you more voltage.
>
> I think a better, and easier way, to measure how far battery pack
> will take you is simply with kilowatt-hours.
>
> On 8/16/07, John A. Evans - N0HJ <jaevans@...> wrote:
> > Hi David et al.,
> >
> > I have a question about your statement that voltage is unimportant for
> > range. I realize that providing current determines range (as long as
> > you can provide X amps, you can keep going) and that voltage equates to
> > speed. However, doesn't adding additional series batteries (like going
> > from say, 96V to 108V) add capacity and thus increase range? Since you
> > have more batteries/lead, don't they provide more capacity and hence
> > more range? It is certainly easier for 18 6volt golf cart batteries to
> > provide, say, 200 amps than it is for 16 6volt batteries. I've heard
> > folks argue that adding batteries won't give extra range, so I thought
> > I'd ask for clarification.
> >
> > tnx,
> > john
> >
> > David Roden wrote:
> > > Voltage is unimportant for range.
> >
> > _______________________________________________
> > For subscription options, see
> > http://lists.sjsu.edu/mailman/listinfo/ev
> >
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
I'd disagree. If you're using a battery with higher voltage, the controller
can use a lower duty cycle to get the same speed. Lower duty cycle means
less average current drawn from the batteries. Less current drawn from the
batteries means longer range. In an ideal world, they would trade off
perfectly, and your range would depend on only capacity (in Watt-hours, not
amp-hours).
Of course, the real world has inefficiencies and imperfections that mess
with things. At higher currents, you lose much more power in the wires (I^2R
losses); higher voltage at lower currents lowers these losses. At higher
voltages, you may get more iron losses from the magnetics (depending on type
of motor), or the motor controller may be less efficient if it is running at
a very low duty cycle. So you have to find a balance between voltage and
current. You don't see many EV's putting 15 6V batteries in parallel!
What matters is energy storage, not just amp storage. Energy is what makes
the world go.
-Morgan LaMoore
On 8/16/07, Joseph T. <jat1793@...> wrote:
>
> John,
>
> I know where you are coming from, but I think you might be
> incorrect. (sorry!) Here's a run down:
>
> More amp-HOURS is what provides more range. An amp-HOUR is
> one amp running for one hour, so more amp-hours means that the battery
> can run longer, and therefore give you more range.
>
> Adding more batteries, or making the battery cells larger
> will increase range. Now, when you add more batteries you do increase
> voltage and range. However, you can have a battery pack with more
> volts have less range than a battery pack with LESS volts. How? The
> battery with less voltage can have more amp-hours, and because it has
> more amp-hours, and therefore a longer running time, it gives the
> vehicle more range. You can though, increase range by adding more
> batteries, which also gives you more voltage.
>
> I think a better, and easier way, to measure how far battery pack
> will take you is simply with kilowatt-hours.
>
> On 8/16/07, John A. Evans - N0HJ <jaevans@...> wrote:
> > Hi David et al.,
> >
> > I have a question about your statement that voltage is unimportant for
> > range. I realize that providing current determines range (as long as
> > you can provide X amps, you can keep going) and that voltage equates to
> > speed. However, doesn't adding additional series batteries (like going
> > from say, 96V to 108V) add capacity and thus increase range? Since you
> > have more batteries/lead, don't they provide more capacity and hence
> > more range? It is certainly easier for 18 6volt golf cart batteries to
> > provide, say, 200 amps than it is for 16 6volt batteries. I've heard
> > folks argue that adding batteries won't give extra range, so I thought
> > I'd ask for clarification.
> >
> > tnx,
> > john
> >
> > David Roden wrote:
> > > Voltage is unimportant for range.
> >
> > _______________________________________________
> > For subscription options, see
> > http://lists.sjsu.edu/mailman/listinfo/ev
> >
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
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