# 700kW burst on LiFePo4?



## somanywelps (Jan 25, 2012)

Is it possible in any sane manner? (pouches, cylindrical, plastic cells)?

I figure that as long as I'm going to make an electric DD, I may as well make it fun to drive.

Note that this is a theoretical calculation, I'm open to figuring out what the real peak load would be:

2x Kostov 9" 220V (dual assembly)
2x Netgain 260V 1400A controllers or an emotorworks 1500A 600V controller(still in development) (either at 230-250V per motor and 1400A)


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## icec0o1 (Sep 3, 2009)

Yes, and the math is fairly simple.

The prismatic A123 20ah cells have 30C rating. So you take 700KW and divide it by 30 and you get 23.3 kwh pack that you'd need to assemble, from those cells.


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## major (Apr 4, 2008)

icec0o1 said:


> Yes, and the math is fairly simple.
> 
> The prismatic A123 20ah cells have 30C rating. So you take 700KW and divide it by 30 and you get 23.3 kwh pack that you'd need to assemble, from those cells.


Hi icec,

When you include sag (voltage drop due to internal resistance), the nominal energy for the pack will likely be about 35 to 40 kWh to realize a true 700 kW.

What is a DD 

major


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## icec0o1 (Sep 3, 2009)

major said:


> Hi icec,
> 
> When you include sag (voltage drop due to internal resistance), the nominal energy for the pack will likely be about 35 to 40 kWh to realize a true 700 kW.
> 
> ...


Yes, I forgot that but I doubt the voltage would drop much below 2.8V? That's a 13-15% drop so he'd need 26-27kwh pack, 30 at worst?


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## Tedktis (Jan 20, 2012)

Very interesting set-up. Anyone run dual Kostovs? What kind of range and acceleration? What kind of batteries and what did the conversion costin parts? 

What about using a Zilla 2k controller since they are DC motors?


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## EVfun (Mar 14, 2010)

There are a number of racers getting to or exceeding the 700 kW level. Shawn Lawless has "Lemon Juice" and John Metric has DC Plasma. Ron Adamowicz had Warp Factor II, currently being rebuilt for this racing season. 

One place to go looking for some of the fastest EVs is on the NEDRA web site. I suspect a number of the posted records will fall this season -- as soon as some of the cars can back up their times. It is very early in a very promising the 2012 racing season.


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## DJBecker (Nov 3, 2010)

icec0o1 said:


> Yes, I forgot that but I doubt the voltage would drop much below 2.8V? That's a 13-15% drop so he'd need 26-27kwh pack, 30 at worst?


At a 30C rate I would expect the cells to drop below 2.4V. Perhaps well below.

A 30C rate is a full discharge in 120 seconds.


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## Bowser330 (Jun 15, 2008)

DJBecker said:


> At a 30C rate I would expect the cells to drop below 2.4V. Perhaps well below.
> 
> A 30C rate is a full discharge in 120 seconds.


I have read that the grey market 20AH cells sagged to 2.3V @ 20C cont. or 25C burst....


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## somanywelps (Jan 25, 2012)

icec0o1 said:


> Yes, and the math is fairly simple.
> 
> The prismatic A123 20ah cells have 30C rating. So you take 700KW and divide it by 30 and you get 23.3 kwh pack that you'd need to assemble, from those cells.


I completely forgot about A123, I was looking through all the pouch type cells. 

500+ cells at once might get me a little leverage

Is there a good place to order from or at least to start research?


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## Bowser330 (Jun 15, 2008)

somanywelps said:


> I completely forgot about A123, I was looking through all the pouch type cells.
> 
> 500+ cells at once might get me a little leverage
> 
> Is there a good place to order from or at least to start research?


jack and others have obtained them from victopower

they are grey market A123 20AH cells that are being sold for an insane 1$/AH, cheaper than Calbs!


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## John Metric (Feb 26, 2009)

somanywelps said:


> Is it possible in any sane manner? (pouches, cylindrical, plastic cells)?
> 2x Kostov 9" 220V (dual assembly)
> 2x Netgain 260V 1400A controllers or an emotorworks 1500A 600V controller(still in development) (either at 230-250V per motor and 1400A)


I concur on your calcs. 
700,000 / 250V /2 = 1400 Amps from the battery to supply each motor at 220V and 1590amps
A good rule of thumb on a full sag pack (just big enough to get the amps needed) is the charge voltage needs to be twice the motor voltage. So you are at 440V charged, out of zillas range.
or you need a LOT more battery Ahr. Also, if 30C is the burst rate, 2800Amps/30C is a 93Ahr pack. This is a huge LiFeP pack. 

My pack is not LiFePO4 but LiFeCo Polymer. I chose LiPo as the lowest cost per kW. (not for daily driving however)
Go to my build thread in EV Performance and see the design charts for a LiPo pack that is right at this performance, 2800Amps and 220-240V. Check out the PVI diagram for overlapping the motor requirements and the battery output curve and the controller design limits.

I use 30.8Ahr 45C/90C RC LiPo pouches from A123-Korea/Polyquest
4.4Ahr 6S packs total arrangement 7P90S 3.7V cells 333V nominal

Metric


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## somanywelps (Jan 25, 2012)

I was under the impression (from Dow Kokam) that LiPo was more power dense, but more expensive than LiFePo4.


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## glaurung (Nov 11, 2009)

Stock 9" 220v will not live to see 1400amps, i would look for something bigger.


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## sourcefinder (Dec 17, 2010)

You should choose a higher voltage system. I run 300a continous and everything gets warm at this 3c. Higher voltage usually makes motor lighter at same power and gives you higher number of revolutions. Also efficiency is better because of magnetic reasons. And you loose less energy because of smaller current.

I would only use lifepo cells, they have little less energy than lipo, but they are save. When you discharge at 30c which is close to short circuit, voltage drops. So you need a very exact measuring system of left capacity, which cannot be exact enough to find the real zero ah remaining point when discharge time at 30c is only some seconds.

So watch out what happens when you have one lipo cell that is empty when the others still run under 30c. Will be a nice fire-party. So i wiuld choose lifepo.

I saw a thundersky lifepo 60ah that was wrong polarity in a serial pack. Did not explode or run out, the cell just got bigger and rounder.


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## MN Driver (Sep 29, 2009)

glaurung said:


> Stock 9" 220v will not live to see 1400amps, i would look for something bigger.


Ditto. It looks like the 9" 220v motor was designed with the 600 amp peak Soliton Jr in mind. It's smaller than a Warp and the model that competes with the Warp 9 is the Kostov 10" which looks to be a bit more powerful than the 9". The Warp 9 is about 9 1/4" and the Kostov 9 is a 220mm (8.66"). The Kostov 9 is wired for more torque per amp and a higher voltage in mind. I'd personally have an RPM transducer on that motor and run it at 250v to the motor(300v or higher battery to counter the sag). You might get away with them in parallel so each is seeing 700 amps. 1400*250 is still 350kw tho. They will melt in short order at 700kw. You need a bigger Kostov if you are going Kostov.


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## Batterypoweredtoad (Feb 5, 2008)

I think he was saying he was going to use two dual 220V 9" setups. So 4 motors in total.


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## somanywelps (Jan 25, 2012)

Batterypoweredtoad said:


> I think he was saying he was going to use two dual 220V 9" setups. So 4 motors in total.


No, it was 2 motors, but not at 1400A for more than a matter of seconds.

I should probably take a look at the new netgain Hyperdrive 9"s, but I can't find the spec sheet for them.

Edit: apparently they won't make the hyperdrive 9"s anymore, moving on...


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## drgrieve (Apr 14, 2011)

Dual K11's should fit the bill better.

http://kostov-motors.com/tractionmotors/kostovevmotors(ac-dc)/seriesdcmotorsforelectricvehicles/k11340v-dual-/


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## somanywelps (Jan 25, 2012)

drgrieve said:


> Dual K11's should fit the bill better.
> 
> http://kostov-motors.com/tractionmotors/kostovevmotors(ac-dc)/seriesdcmotorsforelectricvehicles/k11340v-dual-/


I was considering that.

I'd lose RPM and have to turn down the amps to not shred the transmission and clutch though (t-56 magnum, 700ft-lb limit).


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## FWD (Feb 3, 2012)

Bowser330 said:


> I have read that the grey market 20AH cells sagged to 2.3V @ 20C cont. or 25C burst....


where did you read this?
isee nothing like this only people that love these and comment about a steady voltage over the compleet discharge?

do you have any links?


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## major (Apr 4, 2008)

FWD said:


> where did you read this?
> isee nothing like this only people that love these and comment about a steady voltage over the compleet discharge?
> 
> do you have any links?


For my post #3, I found the internal resistance spec here: http://www.mavizen.com/A123.html It says R_int = 2 mΩ nominal. 

At 30C, I = 600A. Droop = I * R_int = 600A * 0.002Ω = 1.2V. V_cell = V_nom - I * R_int = 3.3V - 1.2V = 2.1V.


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## DIYguy (Sep 18, 2008)

FWD said:


> where did you read this?
> isee nothing like this only people that love these and comment about a steady voltage over the compleet discharge?
> 
> do you have any links?


Most batteries tend to give max peak output at a 50% voltage drop. So, thats about 1.6 volts for LiFePo. Most report that Li-poly is a lot stiffer however it's peak is likely the same. . . 50%. . . but in many cases, the tabs would melt off first.
If you want high C-rate and u want to use LiFePo, you need to look at cylindrical A123, not pouch. Cylindrical A123 cells will peak to about 70C.


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## Ziggythewiz (May 16, 2010)

DIYguy said:


> If you want high C-rate and u want to use LiFePo, you need to look at cylindrical A123, not pouch. Cylindrical A123 cells will peak to about 70C.


Got any links? I've heard lots about the pouches, but nothing on these. Screw cells similar to the headways would be much preferable.


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## frodus (Apr 12, 2008)

here's a link for ya:
www.a123systems.com

You've never heard of Cylindrical A123 M1 cells? They're the 26650 cells from dewalt packs.


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## Batterypoweredtoad (Feb 5, 2008)

DIYguy said:


> If you want high C-rate and u want to use LiFePo, you need to look at cylindrical A123, not pouch. Cylindrical A123 cells will peak to about 70C.


But that is 70C on 2.2 amp hours for the cylindrical instead of 30C on 20 amp hours for the pouches. A quick mental calc says you need about 4 cylindrical cells to match the power output of one pouch cell. Ease of pack building has to be considered.


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## somanywelps (Jan 25, 2012)

Can someone link to the thermal generation for a brushed DC motor?

I was just approximating using the wattage dumped into the motor (700kw in this case).

Current*Voltage=Power which is proportional to the heat generated, yes?


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## major (Apr 4, 2008)

somanywelps said:


> Can someone link to the thermal generation for a brushed DC motor?
> 
> I was just approximating using the wattage dumped into the motor (700kw in this case).
> 
> Current*Voltage=Power which is proportional to the heat generated, yes?


Off topic for this thread. But the motor power loss contributes to motor heat which is the electric power into the motor minus the mechanical power output of the motor, or the motor input power times (1 minus motor efficiency).


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## drgrieve (Apr 14, 2011)

somanywelps said:


> I was considering that.
> 
> I'd lose RPM and have to turn down the amps to not shred the transmission and clutch though (t-56 magnum, 700ft-lb limit).


If I go down the path of dual K11 I will forgo the transmission and clutch and go direct drive.


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## somanywelps (Jan 25, 2012)

major said:


> But the motor power loss contributes to motor heat which is the electric power into the motor minus the mechanical power output of the motor, or the motor input power times (1 minus motor efficiency).


If my interpretation is correct, [email protected] and [email protected] results in the same heat generation (approximately, I know the motors have efficiency curves).



drgrieve said:


> If I go down the path of dual K11 I will forgo the transmission and clutch and go direct drive.


It would be tricky due to the RPM limit, I'd probably have to get a custom 4.10 (LSD while I'm at it) differential and assume a top speed of 110-120mph or so.

Edit: http://www.diffsonline.com/product/gearsets.shtml

3.91 gear set?


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## Ziggythewiz (May 16, 2010)

frodus said:


> here's a link for ya:
> www.a123systems.com
> 
> You've never heard of Cylindrical A123 M1 cells? They're the 26650 cells from dewalt packs.


oh..yeah, those. I didn't realize those were 70C cells, and I thought you meant an off the shelf larger cylindrical cell that would actually be convenient, not overpriced toolpacks assembled into Teslesque nonsense.


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