# Battery Configuration for Warp 9/Soliton 1



## Tesseract (Sep 27, 2008)

bdmiko said:


> ...
> So if I understand dougingraham's comments correctly, the 120ah x 269V is preferable to 180ah x 179V. Correct?
> ...


Not necessarily. Both configurations deliver exactly the same peak power (and energy) so they will likely behave almost identically with respect to driving "feel". The reason why is because of the following: 

1) motor torque is proportional to motor current; 
2) RPM is proportional to voltage at a given current level (ie - higher torque requires more voltage for a given RPM); 
3) battery current must be limited to prevent damage to the cells; 
4) all motor controllers (including inverters) act as constant power devices, so if output (motor) current is higher than input (battery) current then output voltage must be lower than battery voltage. 

For example, the WarP-9 delivers around 240 lb-ft of torque at 1000A and will require about 50V per 1000 rpm at that current. E.g. - you will need to apply ~150V across the motor to hit 3000 rpm at 1000A. If your cells are rated for 3C, the 2p pack can deliver 360A while the 3p pack can deliver 540A. When you factor all of this together you find that the 2p pack can deliver 1000A to the motor until motor voltage reaches 100V (around 2000 rpm) while the 3p pack can deliver 1000A to the motor until motor voltage reaches 98V (or close enough to 2000 rpm to not matter).

There are other considerations involved in selecting battery pack voltage vs. Ah capacity, but, generally speaking, any combination of cells that gets you to a total voltage somewhere between 180V and 240V will be a good match for the typical 9" DC motor with advanced brush timing (like the WarP-9). For a higher voltage, neutrally timed motor such as made by Kostov you will want to reduce motor current but increase battery voltage up in the range of 220V to 300V.


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## dougingraham (Jul 26, 2011)

bdmiko said:


> I am hoping to get some feedback on the best battery layout for my conversion. What I have are 168 60ah lithiums (3.2V nominal).
> 
> My original plan was to run 3 batteries in parallel to effectively build a 180ah battery and then string 56 of them in series for a total of 179 volts. However on a different thread I just read dougingraham comments which got me thinking I should run 2 batteries in parallel for a 120ah battery and then string 84 of them together for a total of 269 volts.
> 
> ...


I would run the 84S2P arrangement. You will get a wider torque band that will be sag free even on a fairly cold winter day (if you have those.) If you go to a a 3P arrangement you will notice if the batteries sag and you will be limiting the torque band. 56S3P would give you a nominal voltage of 179.2 but if you get a 25% sag (you probably wont) would drop the voltage the motor sees to 134.4 volts.

After break in turn the motor amps up to 1000 (or whatever lesser point still makes you happy). I would limit it to 500 or so amps for the first few days at least.
Set the motor volts to 170 (or as high as 192 if you are feeling frisky).
Set the RPM limit to 6000.
Set the battery current to 120 times the pulse C rating. Probably 8C which gives 960 amps.
Set the low battery value to 2.0 volts * 84 = 168 volts.
Set the low running voltage to 3.0 volts * 84 = 252 volts. (Evnetics has a different name for this and I can't remember what it is.)

Set the Slew rate to 3000. You can bump it up if the shifting delay bothers you.

Set the motor power to 170 kw.


The difference between the 2P and the 3P arrangements would be minimal in practice and I think you would be happy either way. You might find that your charger or DC-DC converter will work at the lower voltage better making the 3P configuration more acceptable.


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## bdmiko (Jul 17, 2013)

dougingraham said:


> I would run the 84S2P arrangement. You will get a wider torque band that will be sag free even on a fairly cold winter day (if you have those.)


I was thinking along these same lines. It does get cold here but this car is going to be a fair weather vehicle.

One problem with the higher voltage is the higher expense. The charger is a PFC50 so I'm good there but my DC/DC converter cannot handle 300 volts and I would need additional minibms modules for the additional battery packs.



Tesseract said:


> the WarP-9 delivers around 240 lb-ft of torque at 1000A and will require about 50V per 1000 rpm at that current. E.g. - you will need to apply ~150V across the motor to hit 3000 rpm at 1000A. .


Did you get the numbers (ie. 50V/1000RPM @ 1000A) when testing the Soliton 1? It would be great to have a chart showing the V, RPM at various amps. Do you know if there is a chart with this information?

I have a pretty good idea of the power requirements for my car based on similar conversions but it would be nice to have a power curve that shows the V/RPM at various amps.

David


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## dougingraham (Jul 26, 2011)

bdmiko said:


> I was thinking along these same lines. It does get cold here but this car is going to be a fair weather vehicle.
> 
> One problem with the higher voltage is the higher expense. The charger is a PFC50 so I'm good there but my DC/DC converter cannot handle 300 volts and I would need additional minibms modules for the additional battery packs.


What can the DC/DC converter handle? An 84S pack of LiFe cells would be 302.4 volts only with a top balanced pack when all the cells were at 3.6 volts during the CV portion of the charge. If you bottom balanced and charged conservatively to 3.45 volts per cell the peak voltage would be 289.8 and the pack would quickly settle to something less than 285 volts. If the DC/DC were disconnected during charge it would see peak voltages of around 286 volts after only a few minutes of settling.

The implication from the second paragraph above is that you have already purchased some bms modules. I personally don't see any need for a BMS in a DIY EV. They appear to cause more problems than they solve at a high initial cost. So to keep you from wasting anymore money I suggest the 56S3P arrangement. This will cut down the number of potential cell destroying failures by 1/3. This is a huge improvement in reliability.


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## Tesseract (Sep 27, 2008)

bdmiko said:


> ...Did you get the numbers (ie. 50V/1000RPM @ 1000A) when testing the Soliton 1? It would be great to have a chart showing the V, RPM at various amps. Do you know if there is a chart with this information?...


The numbers for the WarP-9 were obtained as a result of testing various other things a few years ago and not, specifically, the motor itself. I vaguely recall collecting more data at a couple other constant motor current values but hell if I know where that notebook is at now. I think fellow user GerhardRP did a lot of (over-) analysis of this, but, really, the simple rules of thumb already expressed and expanded upon below should suffice.

The first thumb rule is that above the "saturation current" (which begins around 200A for the WarP-9) the voltage required by the motor is a linear function of RPM while output torque is a linear function of the current (below saturation they are both square functions). There is also an offset to the required voltage as a result of "IR drop" but we'll ignore that for now as it comes out to around 6-7V at 1000A. 

Roughly speaking, then, if you reduce motor current to, e.g., 800A then you can expect the voltage per 1000 RPM to drop by 20% as well (i.e. - to around 40V/1krpm for the WarP-9).

Now, keep in mind that a WarP-9 can't take 1000A for very long - my informal recommendation is to keep time at that current to 10 seconds every 2 minutes max - and that it is inadvisable to apply maximum rated voltage at the same time as extreme overload current (note that 1000A is ~4x the continuous current rating of the WarP-9).

In fact, you want to be very careful about exceeding ~160V at the motor when running at 1000A, while at 800A you can probably push the voltage up to 180-190V. Thus, at 1000A you should not exceed ~3200 RPM while at 800A you should stay under ~4700 RPM (which is getting close to the maximum recommended RPM of the motor, anyway [which is somewhere between 5000 and 6500 RPM, depending on who you ask and when...  ]).

The series DC motor controller is basically a buck converter that can only output a voltage less than the input voltage (even with the switch on 100% of the time there will be a volt or two of drop across it) but which demands a current from the source that is less than or equal to the load. So what happens when the voltage applied to the motor approaches the battery voltage? Well, remember above where I mention that the voltage needed by the motor to run at a given RPM declines with current? Once the controller maxes out on output voltage the current (and therefore torque) from the motor must decline so that the demanded voltage matches what is available. This is called the "constant power" region of the speed/torque curve, btw, because torque is falling as RPM continues climbing. If you enter into this region while driving you will experience a progressive lessening of acceleration force, but you will continue to accelerate (at least until you reach a speed that demands more *power* than is available).

One last thing to consider is that the switching losses in the controller are proportional both to current AND voltage, so running at maximum allowed voltage is not necessarily the best approach, particularly if you don't need the range and/or your motor can't use the higher voltage.

Which inexorably leads to what I already wrote: either pack configuration will deliver the same performance, more or less. Switching losses in the controller will be lower with the 3p pack and the BMS will likely cost less. Conversely, the battery side wiring will have to be bigger to accommodate the higher average current of the 2p configuration.


* - if used, as controversy still rages on this point, though I am in the camp that thinks you are nuts not to run at least a monitoring system.


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## dougingraham (Jul 26, 2011)

This is an interesting case because the voltage of the 3P arrangement is still above what you need to keep the motor happy. And the voltage of the 2P arrangement is not so high that the controller efficiency is compromised. You would notice a decrease in performance with a 42S4P arrangement. I see the torque drop off with my 51 cell pack at about 3800 rpm. This is because the cells sag pretty badly at 1000 amps. My cells are 100 AH and you will have 180 AH in the 3P arrangement and you have an additional 10 volts so you will not see nearly the sag I am seeing. Like Tess says the 2P and 3P are so close you probably could't tell the difference when driving it under normal conditions. If the pack is below freezing then I think the higher voltage would be better because the motor probably won't see the severe sag due to the cold.


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## bdmiko (Jul 17, 2013)

Tesseract and dougingraham - thank you for the info and advice, it is just what I needed. Still haven't decided what battery configuration to use but I will post when I figure it out.

Tesseract - special thank you for the detailed write up. It answered quite a few questions that I've had about the way the controller works and the power requirements for the motor.

David


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## Tesseract (Sep 27, 2008)

I found a graph made by GerhardRP here that tells you pretty much all you want to know about the WarP-9's performance:


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## dougingraham (Jul 26, 2011)

Thanks Tess, that is a very useful chart. The voltage where the torque rolls off seems spot on from personal experience. Thanks also to Gerhard Randers-Pehrson for making it. I do have to question the torque scale as it looks like the torque should be in Ft-lbs rather than Nm. The numbers would line up closer with other test results. If Nm is correct then my car should not be as quick as it is.


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## Tesseract (Sep 27, 2008)

dougingraham said:


> ...the torque scale as it looks like the torque should be in Ft-lbs rather than Nm....


Now that you mention it, I agree. As I recall, 1000A results in somewhere between 220 and 240 lb-ft of torque from a WarP-9, with the sloppiness the result of summing the inaccuracies of the current measurement in the controller and the pressure measurement in the dyno.


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## major (Apr 4, 2008)

There seems to be two different performance curves for the WarP9 with different torq/amp characteristics. Both appear to be the format used by Netgain. They are undated and don't have any distinguishing identification.










And this










The second curve shows 67lb.ft. at 400A and the first shows only about 325A at 67lb.ft.  

major


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## EVfun (Mar 14, 2010)

Look at the motor part number. The first one is 00-08219 and the second one is 00-08219A. It looks like the motor was revised and the second one is more current. It makes sense to cut back the torque per amp a little as it increases the rpm per volt. Series wound motors tend to have a peak power point quite a few rpm lower than the gas engine they replace. Check out the difference in horsepower at 3000 rpm.


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## Tesseract (Sep 27, 2008)

EVfun said:


> Look at the motor part number. The first one is 00-08219 and the second one is 00-08219A. ...It makes sense to cut back the torque per amp a little as it increases the rpm per volt.


Good catch, and the most likely explanation is the simplest: the timing has been advanced more on the A version motors.


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## dtbaker (Jan 5, 2008)

yeah.... and the other thing I find frustrating is the curves are generated at 72 volts.... which none of us build. It would be a whole lot nicer to see actual dyno tests at 120v, 144v, 156v for 'normal' builds.

The other thing I am still curious about is the effect of the different brushes available on efficiency for 'normal' driving to maximize the miles/watthr. I haven't seen any really good clear test results on the different brushes for real world driving.


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