Is that significant for acceleration? My numbers suggest otherwise.
1 farad means that drawing 1 amp makes the voltage drop 1V/sec.
Series caps divide their capacitance. A 120V system with 10x 4 farad
caps in series is 0.4 farads. So under an acceleration where you try to
draw 100A from the cap, the voltage will drop 250V/sec. It sounds like
there will be only a delay of a few milliseconds before the batt+cap
voltage ends up at the voltage the batt would drop to anyways.
In other words if the batt is 30V lower when loaded down, the 10x 4
farad caps in series can supplement all of 12 amp-seconds between the
higher and lower voltage states. 12 amps over 1 sec, 1 amp over 12 sec,
100 amps over 0.12 sec.
It might help stiffen the battery against current ripple- but the total
capacitance is insignificant for acceleration.
Danny
----- Original Message -----
From: Michael T Kadie <
[email protected]>
Date: Friday, August 31, 2007 12:51 pm
Subject: Re: [EVDL] A123 Battery Feasibility
To: 'Electric Vehicle Discussion List' <
[email protected]>
> For short burst of acceleration coupled to a 12 volt'ish battery
> system I
> don't think you will be able to beat the competition stereo
> capacitors. 1-4
> farads for a very affordable price. <note not nearly enough juice
> for the
> quarter, but enough for quick response to pass someone, also will help
> extend range of batteries>
> The thing about a123 batteries are they are light for what you get.
> However
> to have more umph than the lead acid / agm you need to buy enough
> of them
> that you can probably run the vehicle on the a123 (figure 100 amps
> and 3
> volt per cell at $10-20 each, a good lead acid will produce 500
> amps, so
> that means you need 10 times the system voltage divide by 3 or 3
> times the
> system voltage to get any benefit). I love them (using them in
> 2SSIC) but
> they do not seem to be a way to save any money.
>
> KD
>
> -----Original Message-----
> From: Jack Murray [mailto:
[email protected]]
> Sent: Thursday, August 30, 2007 9:04 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] A123 Battery Feasibility
>
> yep, a capacitor thingy is a better approach than using A123, the
> caps can
> take the abuse of constant charge discharge. and while it would be
> complicated, it will also be very expensive, so if you consider how
> muchlifespan it improves the cheap batteries, you might be better
> off to buy a
> few sets of batteries than pay for the caps and complications.
> But if they are expensive batteries, e.g. some low-rate Lithium, it
> might be
> worthwhile to improve their lifetime by lowering their amp draws.
> If you
> are trying to go fast and don't care as much about cost, then it
> might be
> worthwhile approach in any case. I've been toying with some ideas,
> andmight try them out on an R/C car.
>
> Jack
>
> Timothy Balcer wrote:
> > Actually there is a discussion of using AGMs + Floodies in buddy
> pairs
> > for just the same idea. A veddy nice list member looks like he is
> > going to bench a pair and get some numbers on this scenario.
> >
> > As far as using A123s as an 'acceleration pack', that's been
> discussed
> > as well. It's called a Hybrid pack, and such a thing has the
> potential
> > to be absolutely fraught with difficulties.
> >
> > If order for this sort of thing to work -very- well, the pack
> control
> > would have to be based on amps demanded, and so it would have to
> be a
> > controller that had that smarts in it tp handle this scenario.
> >
> > In order for it to work -reasonably- well (which is to say, it
> would
> > work, but not be elegant), you could spend a lot of time thinking
> > about balancing currents and battery voltages for unequal pairs,
> set
> > up faux 'buddy pairs' and go to town. The A123s would be a bit
> abused
> > by this treatment though.
> >
> > All of this is predicated on the idea that the 'demand' battery
> (A123
> > in your case) has a lower internal resistance than the 'float'
> battery
> > and so would provide most of the current for short durations of
> high
> > demand. Once demand went down to below a certain threshold
> (depending
> > on your 'float' battery) then current would start to flow from
> the
> > float battery. If the demand were low enough, the float battery
> would
> > recharge the demand battery as well as supply current to the
> > controller.
> >
> > I am actually working out a way to use NiCD floodies as a demand
> pack
> > myself. They are very resistant to abuse and have a pretty low
> > internal resistance.
> >
> > What I've been learning is that you really have to think hard
> about
> > how you match up batteries, otherwise you'll end up with one or
> the
> > other cooked off by current runaway or overuse.
> >
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> >
>
>
>
>
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