Re: AC Drive Sources?

[Victor Tikhonov <vtikhono@lsil.com>]

You are right, pound for pound in your example DOD is the same. And 
always will be if you parallel the same batteries in low voltage system. 

360VDC (30 batteries) will have the same DOD at the end of the same trip
as three paralleled strings of 10 batteries in case of equal power 120V
DC system.
 
The difference is, in case of AC you *have* to use high voltage,
while in the DC case above, you *have a tempting choice* to use just two
or
one 120V string for cutting initial cost/weight just to get it moving,
and
since the voltage is still the same, initially everything will work, and
apparently to the user pretty much the same (except the range).

People will do that, especially newbies without going in depth of
analyzing
consequences.

That was my point, perhaps I wasn't very clear.

Victor 

"VanDerWal, Peter" wrote:
> 
> >Regarding whether AC system will save you money in a long run compare
> >to DC setup - possibly. Depends on how you drive. The only difference
> >it makes - it forces you to use high voltage battery pack (At <200 VDC
> >pack voltage the drive performance will be really poor). So (for
> >for the same performance) currents are lower and (for fixed range) DOD
> >of your batteries is also lower.
> 
> That's not true.  Assuming you are using the same weight in batteries, to
> use a 240V system vs a 120V system requires you to use 12V batteries instead
> of 6V batteries.  Pound for pound 12V have about 1/2 the capacity of 6V
> batteries (usually less).
> 
> So even if your current draw is only 1/2 that of the lower voltage pack,
> it's still will bring the 12V batteries down to the same DOD.  I.e. 80Amps
> for 1 hr takes a 100 Ah cell down to the exact same DOD as 160 amps does
> with a 200 AH cell.  Furthermore 80 amps on a 100 AHr battery is just as
> hard on it as 160 amps is on a 200 AHr battery.
> 
> And that's if you use 12V AGM batteries.  The 12V flooded cells don't
> perform nearly that well.