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Discussion Starter #1
An idea that I have had, along with many others, is to have a hybrid
battery pack. I've always thought it should work like this: Two
completely separate battery packs, with separate charging systems. Use
a switch to choose which pack you want.

So I've thought, why not just use a "cheap" golf cart battery pack for
range, then separately have a very light, very low amp-hour, A123 pack
for hard acceleration. Of course this raises questions like....

Do A123 batteries require using special balancers and chargers?

What is available in the market for balancing/charging A123 battery packs?

And....

If you had two battery packs and used a switch to choose which one you
are using, the controller will suddenly be receiving no power while
you are switching be the two battery packs.
Would suddenly taking away the power from the controller be harmful?

If it is, then you'd have to do turn off the whole car, then switch to
the other pack, and then turn on the car. But that sounds like it
would take too long if the whole point of the A123 pack is too
accelerate!

Is there some fancy capacitor thingy to solve this?

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Discussion Starter #2
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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Discussion Starter #3
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 much
lifespan 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, and might 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.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


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Discussion Starter #4
Joseph T. wrote:
> An idea that I have had, along with many others, is to have a hybrid
> battery pack. I've always thought it should work like this: Two
> completely separate battery packs, with separate charging systems. Use
> a switch to choose which pack you want.
>
> So I've thought, why not just use a "cheap" golf cart battery pack for
> range, then separately have a very light, very low amp-hour, A123 pack
> for hard acceleration.

Yes, that's the basic idea. Of course, people want to skimp and only
have one charging system, or one controller. But this can lead to problems.

Given that we have so little experience with hybrid battery packs, I
think it makes sense to do as you suggest -- have a separate charger for
each pack, optimized for that type of battery.

It also makes sense to have some sort of system, either manual or
automatic, to select when and how much load current each pack supplies.
You can't count on just paralleling them, or using diodes to common them
until you know more about exactly how they will behave.

> Of course this raises questions like....
>
> Do A123 batteries require using special balancers and chargers?

Yes. They are lithium cells, and so have pretty strict charging and
balancing requirements.

> What is available in the market for balancing/charging A123 battery
> packs?

Not much yet. Consumers don't use individual A123 cells, so there really
aren't any chargers for them. They are being used by large companies,
who supply their own charging and balancing systems as part of the "deal".

> If you had two battery packs and used a switch to choose which one you
> are using, the controller will suddenly be receiving no power while
> you are switching be the two battery packs. Would suddenly taking away
> the power from the controller be harmful?

Not in and of itself. The controller has big capacitors on its input to
protect it from sudden changes. But you would want to release the
throttle before switching pack voltages, so the motor is at zero current.

You may also need a precharge circuit to gradually move the controller's
input from one pack's voltage to the other. Trying to switch them
instantaneously leads to very large peak currents in the capacitors,
which is hard on them (as well as whatever you used to switch packs).

But, all this is relatively straightforward, and only takes a fraction
of a second.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Discussion Starter #5
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 much
lifespan 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, and
might 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.
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>




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Discussion Starter #7
If it were possible to load share both packs during acceleration, I don't
see the point in switching out the floodies. Ideally, I'd like to be able
to pull 500 amps from an AGM pack, and 250 from a floodie pack
simultaneously. I suspect it would take a disconnect switch and two
separate charging systems to fully charge them.

Now if the floodies were in a trailer, so you could disconnect it at the
drag strip, then I could see accelerating with just the lightweight pack :).
The thousand pound weight reduction should make up for the lower available
current, especially if you're limited by the controller anyway.

Marty
----- Original Message -----
From: "Joseph T. " <[email protected]>
To: <[email protected]>
Sent: Thursday, August 30, 2007 7:15 PM
Subject: [EVDL] A123 Battery Feasibility


> An idea that I have had, along with many others, is to have a hybrid
> battery pack. I've always thought it should work like this: Two
> completely separate battery packs, with separate charging systems. Use
> a switch to choose which pack you want.
>
> So I've thought, why not just use a "cheap" golf cart battery pack for
> range, then separately have a very light, very low amp-hour, A123 pack
> for hard acceleration. Of course this raises questions like....
>
> Do A123 batteries require using special balancers and chargers?
>
> What is available in the market for balancing/charging A123 battery packs?
>
> And....
>
> If you had two battery packs and used a switch to choose which one you
> are using, the controller will suddenly be receiving no power while
> you are switching be the two battery packs.
> Would suddenly taking away the power from the controller be harmful?
>
> If it is, then you'd have to do turn off the whole car, then switch to
> the other pack, and then turn on the car. But that sounds like it
> would take too long if the whole point of the A123 pack is too
> accelerate!
>
> Is there some fancy capacitor thingy to solve this?
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
>


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Discussion Starter #10
Is there any reason you couldn't use your charger as the "feed controller?"

----- Original Message ----
From: Bill Dube <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Sent: Friday, August 31, 2007 1:38:13 PM
Subject: Re: [EVDL] A123 Battery Feasibility

The hybrid pack concept has been discussed many times over the years.

Once you think it through, the they way to do it is to have
a higher voltage pack of flooded batteries, and a slightly lower
voltage pack of high-power batteries (like A123 or perhaps peppy
AGMs). You Connect the controller to the high-power pack in the
normal manner. You then put a second, much smaller, PWM controller
("feed" controller") from the floodie pack to the high-power pack.

You run the car with the high-power pack and then set the
feed controller to keep it topped up at a current rate that is
acceptable to the floodie pack.







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Discussion Starter #15
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.
> >
> > _______________________________________________
> > 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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Discussion Starter #16
This thread is an ideal example of why we need to get all of this
wisdom onto a darned Wiki! :)

Bill Dube offhandedly mentioned "Oh yeah, that problem was basically
solved a whole ago and the answer is this.." Wow! I mean, I would have
loved to have had that in a Wiki under 'Hybrid Battery Packs'
somewhere. It would have saved me a few hours of musing.

David, I suggest an EVDL approved Wiki, perhaps only accessible (for
edits and contributions) to EVDL/EAA/XXXorganization members. It's
free software, and instead of cobbled together FAQs it would be a
living repository where contributors could just post their musings
onto a community moderated board. The rate limiting factor would be
who you chose as editors. It would offload a lot of the repeat traffic
here, give us linkable material that is consistent, and allow for
collaboration way beyond what the EVDL allows.

I'd be happy to assist in setting it up and paying for it.. let me know!

--T

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Discussion Starter #19
> To Morgan, super cool that you got the A123 and flooded batteries
> working together. How do they work together? Are the batteries still
> in good "health"?
>

I didn't say that I've done it; I'm saying that's how I *would* do it
to ensure that it works as well as possible and you don't have
problems switching over.

> "You end up trying to accelerate a vehicle that
> is carrying the weight of the floodies with just the small A123 pack. I'm
> just a clueless newbie, but that sounds like trouble to me. "
>
> I am also a newb! I don't think it'd be a problem though. The A123
> batteries are so light, and yet so powerful, that I think they can
> easily pull around an EV loaded with batteries.
>

The problem is that battery power is rated relative to battery
capacity. So if you make an A123 pack with half the capacity, it also
has half the power. I don't know whether A123 are powerful enough that
a small, cheap pack could still have enough power to help accelerate
well.

-Morgan

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Discussion Starter #20
Big misconception here. Battery power and battery capacity are NOT
related directly if you are talking about different battery
technologies (even differing topologies within the same battery technology)

"Specific Power" is given in Watts/kg and tells you how much HP
(watts) you can draw from each kg of this type battery.

"Specific Energy" is given in Watt-hrs/kg and tells you how much
energy (capacity) you have in each kg of this type battery.

You can alter the internal geometry (like the paste thickness,
separator thickness, grid thickness) on any type of battery to
increase the specific power to the detriment of specific energy. You
can also do vice-versa. Basically, for a given battery technology,
you pick how much power you are willing to give up to gain capacity,
and you pick how much capacity to give up to gain power.

Bill Dube'

>The problem is that battery power is rated relative to battery
>capacity. So if you make an A123 pack with half the capacity, it also
>has half the power. I don't know whether A123 are powerful enough that
>a small, cheap pack could still have enough power to help accelerate
>well.
>
>-Morgan
>
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