# Re: [EVDL] Re commendations for Li-ion Cooling



## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> [email protected] wrote:
> >
> > 1) Get a longer string of smaller Ah batteries to parallel the Li-ion
> > cells at pretty much the same voltage
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> [email protected] wrote:
> >
> > If you read my post from yesterday, you know that my cells are heating up
> > to 55-degrees C in 35-degree C ambient air. Anyone have recommendations
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

Looks like I wasn't clear enough, so let me explain the rationales between
the two choices better. =


For Option 1, the PbA string would be in parallel with the LCP cells. It
would only *assist* the LCP cells. So there'd still be current flowing
through the LCP cells and heating them, though not as much. Since it would
be the same voltage as the LCP cell string, it would have to be of a lower
Ah rating than Option 2 for size and weight reasons. =


For Option 2, I'd put in just enough PbA to get me up that hill at the end
of the commute, drawing all the current from the PbA string alone. This
way, the LCP cells don't get hot at all. In fact, they could be cooling
down during that period. If anything dies an earlier heat death, it's the
PbA batteries, which are cheaper to replace. Also, because of the way the
space would work out, the higher Ah string would have a little bit more
total Kwh than the higher-voltage, lower-Ah string. =


And please don't take this the wrong way, because I'm not looking to start
a flame. But I've been reading and posting on this list for many years. I
can assure you that even with the New Math they taught when I was in
grammar school, I understand the basics of
"half-the-voltage-twice-the-current" by now. 

Finally, no, I'm not going to drive slower and hold up traffic for 6 miles
on a narrow road. I know I'm asking a lot of the EV, but I want to do what
I can to make it work, and not have people cursing at me for the sluggish
electric car that's slowing them down when they have to follow it on their
way home from work every night. =


Bill

Original Message:
-----------------
From: fsabolich [email protected]
Date: Tue, 26 Aug 2008 09:58:53 -0700 (PDT)
To: [email protected]
Subject: Re: [EVDL] Re commendations for Li-ion Cooling







> [email protected] wrote:
> > =
> 
> > 1) Get a longer string of smaller Ah batteries to parallel the Li-ion
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

Yes, I got them for a great price. Plus, I have an 88-mile commute each
day, and I wanted all the energy that I could get. Finally, LFP cells from
ThunderSky did not yet exist when I purchased the LCP cells.

Bill

Original Message:
-----------------
From: fsabolich [email protected]
Date: Tue, 26 Aug 2008 10:20:10 -0700 (PDT)
To: [email protected]
Subject: Re: [EVDL] Re commendations for Li-ion Cooling







> [email protected] wrote:
> >
> > If you read my post from yesterday, you know that my cells are heating up
> > to 55-degrees C in 35-degree C ambient air. Anyone have recommendations
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> [email protected] wrote:
> > For Option 1, the PbA string would be in parallel with the LCP cells. It
> > would only *assist* the LCP cells.
> >
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

Lee, thanks for this. I read it multiple times, and I think maybe the 
Pack A and Pack B got mixed up in the text. The tags above the picture 
didn't seem to match the picture, and then the A's and B's seemed to 
jump in the description. I've modified the text and ASCII art to be the 
way I think you meant, but I could be totally wrong. Could you review 
the paragraphs below to see if I got the A's and B's right?

Thanks.

Bill
> For example, suppose you have two 120v packs. Pack A has low amphour 
> capacity, but is very good at supplying high currents. Pack B is the 
> opposite; it is optimized for amphour capacity, but has poor peak 
> current capability. It is used to get your range.
>
> Wire pack A to your motor and controller normally. It is used for fast 
> acceleration and hill-climbing, but only provides a range of a few miles 
> with it alone.
>
> Wire pack B to a switchmode DC/DC converter (switchmode so it works with 
> a DC input). Connect its isolated output in series with pack B, to 
> charge pack A. Operate this power supply as a battery charger, to 
> continually charge pack A to a good float voltage, at a maximum current 
> that's safe for pack B. For example,
>
> pack A: 120vdc, 10ah, 500a peak
> pack B: 120vdc, 100ah, 50a peak
> DC/DC: 120vdc input, 0-15vdc at 50a output (750w max)
> _________________________ ____________________
> | | _________ | | | ____|_____
> | |_| |__| | | | B+ |____
> __|__+ |+in -out| | __|__+ | M+| _|_
> ___ pack B | DC/DC | | ___ pack A |controller| (___) motor
> | 120v _|-in +out|_____| | 120v | M-|____|
> | - | |_________| | - |__________|
> |__________|______________________|_______________|B-
>
> Start with both packs fully charged. The DC/DC starts charging pack A; 
> its voltage immediately rises to float voltage (say 135v) at which it 
> draws a low current (say 1a). Pack B supplies 1.1a to do this; 0.1a to 
> power the DC/DC to make 1a on its output, plus 1a because it's in series 
> with the DC/DC's 1a output. The DC/DC adjusts its output voltage to 
> 135v-120v = 15v to do this.
>
> Now suppose you "floor it". Pack A delivers 500a to the controller, and 
> sags to 110v to do it. The DC/DC sees the pack A voltage drop, and 
> raises its output to its 50a current limit. Doing so loads pack B to 50a 
> plus whatever the DC/DC needs at its input. Let's say pack B sags to 
> 100v under its 50a load. The DC/DC needs to output 110v-100v = 10v at 
> 50a. The DC/DC needs 100v at 5a to deliver 10v at 50a. So, pack B 
> supplies 50a+5a = 55a.
>
> This is very crude, but you get the idea. You need to arrange the DC/DC 
> and pack voltages so pack B can deliver a nice smooth current to pack A 
> without requiring too much or too little voltage from the DC/DC.
>
> 

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> Bill Dennis wrote:
> > Lee, thanks for this. I read it multiple times, and I think maybe the
> > Pack A and Pack B got mixed up in the text.
> 
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

I tried doing some google searches to answer your push or pull
question.......

>From my experience with semiconductors and heat sinks -- we preferred to
push the air down,
or through the heat sink instead of pull.

I can think of one reasons for sure  --- 
longevity of the fan -- it will be operating in a cooler environment.

You do want to be sure that you are not drawing a hotter source of air to
the batteries.

I've seen system failures in micro-electronics where a hot air from one part
of the system
was drawn into an area that was expecting a cooler ambient -- and started
failing.

So don't blow air over your controller, then pick up that air and move it
across your batts -- for example.

cheers,

Mike






> [email protected] wrote:
> >
> > Roger,
> > We had a bit of cooler weather here today, so I took the car out for a
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> [email protected] wrote:
> 
> 
> 
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> txhokie4life wrote:
> > While a very cool (sorry for the pun) concept, wouldn't the heating of the
> > parafin hold the heat in the system
> > and the battery pack would then be in a higher ambient situation and not
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

Lee, I've been thinking about your proposal. If I'm understanding 
correctly, the higher-Ah pack would have to supply almost all the 
average, "normal" driving amps, because the lower Ah pack can go only a 
few miles on its own. In your scenario, that's somewhere around 50A. 
In my conversion, conversely, 100A is the normal freeway current draw 
(for example, my partial commute last week lasted a little over an hour 
and used 105 Ah). So to make your plan work, I'd need a 100A-capable 
DC/DC converter, is that correct? Those seem hard to come by. Do you 
know of any? If not, is the next best thing to parallel multiple Vicor 
bricks?

Thanks.

Bill



> Lee Hart wrote:
> > [email protected] wrote:
> >
> >> For Option 1, the PbA string would be in parallel with the LCP cells. It
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> Txhokie4life wrote:
> 
> > My understanding of systems like this is that you take the
> > water and then heat exchange it elsewhere.......
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

PCM cooling sounds interesting... I=B4m not sure if this company has =

been mentioned:

http://www.allcelltech.com/

-Osmo


Roger Stockton kirjoitti 28.8.2008 kello 9.14:



> > Txhokie4life wrote:
> >
> >> My understanding of systems like this is that you take the
> >> water and then heat exchange it elsewhere.......
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> Bill Dennis wrote:
> > Lee, I've been thinking about your proposal. If I'm understanding
> > correctly, the higher-Ah pack would have to supply almost all the
> > average, "normal" driving amps, because the lower Ah pack can go only a
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

How well would this work with a pack of lead-acid batteries? Sounds
like it might be a good solution for colder weather: absorb the heat
from daily driving into the paraffin, then allow the paraffin to
release the heat back into the batteries at night to keep them warm.


Tim

------
Date: Wed, 27 Aug 2008 23:14:11 -0700
From: Roger Stockton <[email protected]>
Subject: Re: [EVDL] Re commendations for Li-ion Cooling

You're right about the water-based cooling system. The point of using
a phase change material is that it is a simple passive system that
doesn't require the bulk and complexity of plumbing and pumps and
radiators and thermostats, etc.

You want the phase change material to remain in contact with the
cells, not for it to flow elsewhere. The phase change material
absorbs heat as it warms, and warms until reaching is melting point,
but then remains at that temperature while absorbing significantly
more heat as it changes phase.

Paraffin wax will warm about twice as rapidly as the same weight in
water, but only until it reaches its melting point at 47-64C. Once at
this temperature, it requires 100x as much energy input to change
phase, and will not heat further until it has changed phase. So, if
it took 6mi of climbing to raise the pack from 25C to a melting point
of 50C, it would then take another 24mi of similar driving to melt the
paraffin so that the temperature could rise further.

In Bill's case, his pack is rising about 20C above ambient over the
course of 20mi+ of driving. Adding paraffin to his box would reduce
the amount of temperature rise just because the energy dissipated by
the cells must now warm the paraffin as well as the cells. IF the
cells warm sufficiently to reach the melting point of the paraffin (or
other phase change material), then the temperature essentially stops
rising since the energy input required to complete the phase change is
so much greater that it is likely that the battery will run flat
before the phase change completes.

Cheers,

Roger.

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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

> The approach I described puts the isolated output of the
> DC/DC in series 
> with the pack. This means it only has to supply 100a at the
> voltage 
> *difference* between the two packs; not 100a at the full
> pack voltage. 
> 100a at 120v is 1200 watts; you'd need an EV controller
> like a Curtis 
> 1221 to do this. 


But an EV controller is not isolated (not any that I know of). And can't be used as a battery charger (the lack of inductance of the battery pack won't allow the current limits to work fast enough).

Steven Ciciora




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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> On 28 Aug 2008 at 9:54, Tim Clevenger wrote:
> 
> > How well would this work with a pack of lead-acid batteries? Sounds
> > like it might be a good solution for colder weather: absorb the heat
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

Officer pulls you over, step out of the car sir, but officer, sir we could
smell the pina coladas two car's back. They are in here somewhere. Open the
trunk please!

Mark Grasser
Eliot, ME


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of EVDL Administrator
Sent: Thursday, August 28, 2008 2:49 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Re commendations for Li-ion Cooling



> On 28 Aug 2008 at 9:54, Tim Clevenger wrote:
> 
> > How well would this work with a pack of lead-acid batteries? Sounds
> > like it might be a good solution for colder weather: absorb the heat
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> Steven Ciciora wrote:
> ...
> > But an EV controller is not isolated (not any that I know of).
> 
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

>> The approach I described puts the isolated output of the DC/DC in
>> series with the pack. This means it only has to supply 100a at the 
>> voltage *difference* between the two packs; not 100a at the full 
>> pack voltage. 100a at 120v is 1200 watts; you'd need an EV
>> controller like a Curtis 1221 to do this.



> Steven Ciciora wrote:
> > But an EV controller is not isolated (not any that I know of). And
> > can't be used as a battery charger (the lack of inductance of the
> > battery pack won't allow the current limits to work fast enough).
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> Steven Ciciora wrote:
> >> But an EV controller is not isolated (not any that I know of).
> 
> Metric Mind wrote:
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> EVDL Administrator wrote:
> > I think the temperature would be too high for normal operation and good
> > cycle life. You might try coconut oil instead. It melts at 25 deg C, a
> > comfortable temperature for lead batteries.
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*



> Tim Clevenger wrote:
> 
> > How well would this work with a pack of lead-acid batteries?
> > Sounds like it might be a good solution for colder weather:
> ...


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## EVDL List (Jul 27, 2007)

*Re: [EVDL] Re commendations for Li-ion Cooling*

Lee,

What I meant, the 3 phase output is only connected to the motor stator
windings, so whole setup is floating vs. ground (which is not the case 
for non-isolated DC-DC controller). But adding DC-DC's output in series
wit hthe battery is very different application, I missed original
intent, so my comment actually does not apply to this situation.

Victor



> Lee Hart wrote:
> > Steven Ciciora wrote:
> >>> But an EV controller is not isolated (not any that I know of).
> >
> ...


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