# 72v systems in small car!



## Tesseract (Sep 27, 2008)

Yabert said:


> For science (and by interest) I have try my car with a 72v systems!
> 
> Well, in fact my Smart Fortwo currently used a 154v nominal 80Ah battery pack, but with 72v Alltrax controller in mind, I have set my Soliton 1 to 72v and 450A max on motor side (Warp Impulse 9)....


That's not as fair as you might think. Firstly, and most importantly, by using a 154V nominal pack but limiting motor voltage to 72V there will be no apparent sag. Secondly, 450A is "tits out" for the Alltrax, but for the Soliton1 it's just loafing along without a care in the world, even if only cooled by its fans.

You could probably better simulate the performance of a lower-power controller by judiciously setting the _zero current_ and _full load_ minimum battery voltage settings so that they start limiting motor current when there is a little bit of actual sag, but that sounds like a lot of work to me.


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## Ziggythewiz (May 16, 2010)

Tesseract said:


> That's not as fair as you might think. Firstly, and most importantly, by using a 154V nominal pack but limiting motor voltage to 72V there will be no apparent sag.


Yeah, I'd say if you want to see what 72V does for you, just hook up the 72. Especially for a 0-30, you're probably not putting much over 72 to the motor even if running a full pack.


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## Yabert (Feb 7, 2010)

Tesseract said:


> That's not as fair as you might think. Firstly, and most importantly, by using a 154V nominal pack but limiting motor voltage to 72V there will be no apparent sag.


Well, it why I use 72v. 83 volts nominal will sag at 72v under load!
I think a good 26s lithium battery pack is able to maintain a voltage over 2.77v per cell at around 2-3C discharge. Let say 26s of 100Ah or 130Ah prismatic cell! It's not irrealistic.

I'm maybe a bit optimistic about peak power capability of 72v battery pack and Alltrax controller because it's probably not a part of pleasure for this small controller to push 450A in motor compare to the Soliton1.

But this small one is able to push at least 200A in motor for long time (1h) and that's all that need a small car to roll around 60 mph at 72v.


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## EVfun (Mar 14, 2010)

I don't think I would run 26 LiFePO4 cells into a 72 volt controller. That is an 83 volt nominal pack and if that was a good idea why didn't they just call it an 80 volt controller? 

It is expecting a 72 volt nominal pack -- not more than about 66 volts at full load. 24 big CALB cells would be about 68 volts at 450 amps and about as far as I would be comfortable pushing a 72 volt controller. I figure about 4 LiFePO4 cells per 12 volts in controller rating unless there are published limits which would take precedence over any rule of thumb. 

I suggest trying it again at 66 to 68 motor volts. It will clip a little off the speeds and I think would be a lot more representative of a more normal Lithium powered Altrax 72 volt nominal system.


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## DaveAK (Jun 28, 2009)

EVfun said:


> I don't think I would run 26 LiFePO4 cells into a 72 volt controller. That is an 83 volt nominal pack and if that was a good idea why didn't they just call it an 80 volt controller?


It's rated up to 90V. Or at least I should say that it can be programmed to have an overvoltage cutoff of 90V. That would mean that you would have to charge 26 cells to no more than 3.46/cell, or bleed off any excess charge so that resting was below 90V, but that's how you'd get the absolute maximum from the controller.


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## EVfun (Mar 14, 2010)

Of course with your controller you can do what you want, but I wouldn't use up all the headway. There is some reason it is called a 72 volt controller and not a 78 volt controller. Every time the MOSFETs inside switch off the voltage inside spikes up a little higher than pack voltage. The higher the current being switched off the more overshoot there is. The manufacturer wrote their ratings with this in mind. We have to interpret them a bit when running a Lithium pack as most where designed with Lead packs in mind (the Soliton may be the first on-road controller built with Lithium batteries in mind.) 

The old Curtis 1221B works up to 150 volts input, but I don't recommend running them with 43 LiFePO4 cells. I would be very uncomfortable running a controller over about 2 LiFePO4 cells for every 6 volts of rated nominal voltage.


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## DaveAK (Jun 28, 2009)

EVfun said:


> Of course with your controller you can do what you want, but I wouldn't use up all the headway. There is some reason it is called a 72 volt controller and not a 78 volt controller. Every time the MOSFETs inside switch off the voltage inside spikes up a little higher than pack voltage. The higher the current being switched off the more overshoot there is. The manufacturer wrote their ratings with this in mind. We have to interpret them a bit when running a Lithium pack as most where designed with Lead packs in mind (the Soliton may be the first on-road controller built with Lithium batteries in mind.)
> 
> The old Curtis 1221B works up to 150 volts input, but I don't recommend running them with 43 LiFePO4 cells. I would be very uncomfortable running a controller over about 2 LiFePO4 cells for every 6 volts of rated nominal voltage.


Well each to their own of course. 90V is the manufacturers maximium rating, that's all I'm saying. You can run it with 26 cells if you want, or not. I imagine it's called a 72V controller more for market conventions than absolute design criteria. It's not inconceivable that its 90V maximum rating includes sufficient headway. And of course there's nothing to say that at 90V it isn't running on the ragged edge. That would be a question for Alltrax.


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## Yabert (Feb 7, 2010)

EVfun said:


> I suggest trying it again at 66 to 68 motor volts. It will clip a little off the speeds and I think would be a lot more representative of a more normal Lithium powered Altrax 72 volt nominal system.


I think you are right.... But I also think Dave is right!



> 90V is the manufacturers maximium rating, that's all I'm saying. You can run it with 26 cells if you want, or not. I imagine it's called a 72V controller more for market conventions than absolute design criteria. It's not inconceivable that its 90V maximum rating includes sufficient headway. And of course there's nothing to say that at 90V it isn't running on the ragged edge. That would be a question for Alltrax.


So, because we agree about tipical cell can sag at 2.75v under load, I think it's a really good idea to simulate a 24s (76.8v nominal) by limiting motor voltage to 66v and retry the road test.

And like that, any 72v conversion build with 24S or 26S will have his proper results.
24S battery sag to 66v and 26S battery sag to 72v.


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## Yabert (Feb 7, 2010)

I took an hour today to try a 24s simulation.

I set the Soliton to 66 max motor volt and 450A limit.... and I took the road:

-89 km/h (55 mph) in third gear.
-102 km/h (63 mph) in fourth gear.
-0-56 km/h (0-35 mph) in only 6-7 sec. in second gear...

I like the result and I need to add than 66v at cruising speed isn't representative because I recorded 110-115A in third gear to maintain speed and 145-150A in fourth gear (from approximately 148v with my current battery pack in this poor and cold winter conditions).
And most prismatic cell (100Ah to 200Ah) can stay around 3v at 1C to 3C.
3v x 24S = 72v and 3v x 26S = 78v.... so, the speeds reached during my first test are good.


Enjoy the data!...


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## rwaudio (May 22, 2008)

Yabert said:


> I took an hour today to try a 24s simulation.
> 
> I set the Soliton to 66 max motor volt and 450A limit.... and I took the road:
> 
> ...



If a small pack was made with the A123 20ah pouches they maintain 3.2v (or higher) at 2C until about 60-70% DOD (30-40% SOC)

Testing related to the attached graph was 38A CC discharge (2C based on a capacity of ~19Ah) The cell was charged to 3.65v with a CC CV curve at 40A and turning off at c/20, it sits for a couple minutes then a 2C discharge to 2.25v, then charged again. The cell barely gets above ambient temperature the whole time.


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## motor guy (Dec 17, 2008)

hello all

72 volt, we have it working in our 5945 lbs chevy truck. it is also using an automatic.

you can see pics of our 72 volt truck on our web sit. photo gallery.
topekaelectricmotor.com

thanks kevin


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## MBEV (Sep 28, 2008)

Those interested in 72 volt systems may find some of the data at my site interesting as well……

The switch to SE180Ah cells over a year ago has made an enormous difference in all areas except my bank account. Note that the weight of this EV is less then 700kg and only 4th and reverse gears are used.

http://www.mightyboyev.com/Li-Ion%20Upgrade%20On%20Road%20Data%20Results%20final%20set%20Dec%204%202010.htm

The complete build home page is at http://www.mightyboyev.com/

The PakTrakr was pretty much a waste of money and I would do my monitoring differently next time.

Cheers
Bruce


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## mechman600 (Oct 16, 2010)

There are a few examples out there of guys running an Alltrax 7245 (72V/450A) with an 84 volt system in the evalbum. One guy's is switchable between 72/84. He starts off at 72 and once the surface charge is gone switches to 84.


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## MBEV (Sep 28, 2008)

Hi gottdi,

I would say it comes back to a number of things……

Firstly, “Power to Weight” ratio, the Suzuki Mightyboy is a Japanese 'K-class' or Kei Jidosha vehicle and hence smaller and lighter than most people realize. It has a larger then recommended motor for its weight (ADC 8”). The vehicles on road whr/km figure is fairly low 110 w-h/km _(or 187 w-h/mile)._

Secondly, the gearbox/transaxle/wheel diameter ratios by luck worked in my favour. The small light 12”x4.5” wheels/tires help keep the unsprung mass to a minimum.

Thirdly, I spent a lot of time on the high current wiring, keeping the cables larger than normal and as short as possible also crimping and soldering all connection lugs (some details of this can be found on my site….). I check all leads with a 4 post milliohm meter. Extra special attention was also spent preparing and connecting the battery/controller/motor high current terminals. The result is very little voltage drop when the larger 400 amp plus currents are needed.

Having said all this I also think 96 volts would be the best as well and keep the currents a bit lower. The vehicle top speed would also benefit from the higher voltage.

I see Alltrax are about to release their new SPD controller range and the 650 amp -72 volt model SPD-72650 looks great for future 72 volt conversions. Checkout http://www.alltraxinc.com/Products_SPM.html . I think the maximum voltage is the same as the AXE 72 volt models currently being sold. Too bad they don’t make a 96 volt version of these.

Could I inquire into the pricing of the Leaf? In Australia the price seems very high with little rebates if any. You are a luck man!!

Regards

Bruce


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## Yabert (Feb 7, 2010)

Thanks MBEV to share the performance of your 72v systems and let people know that it works well in your small car.

Really nice and clean build.


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## Yabert (Feb 7, 2010)

Ok guys, I'm interested to complete this thread with my last experiments and datas. 

My 865 Kg (1900 lbs) car need around 7 Kw to maintain 35 mph. That represent 85 to 95 Amps from 24s or 26s battery pack.
And it need aound 16 Kw to maintain 60 mph. That represent 200 to 220 Amps from 24s or 26s battery.

Finally, I need around 20 to 30 Kw to confortably accelerate with crazy traffic. 10 to 15 Kw is enough on small street. 

So, my conclusion is that a 72v conversion is absolutely acceptable for a sub 900 Kg (2000 lbs) car with low performance requirement and no highway driving.

I think it's now especially true since Alltrax sell news 72v controller capable of 500A (575) and 650A (740).
It's respectively over 41 and 53 Kw peak at controller with proper battery pack. That seem a good performance perspective for a light car.


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## MalcolmB (Jun 10, 2008)

Thanks for the information Yabert. This is an interesting thread for me, as I'm planning to test the Mini with an Alltrax 7245 and 26s of 70Ah (7x10 Ah) LifeBatt cells. I know it's pushing the little Alltrax to the edge, but someone has to do it.

My battery pack is so small that it wouldn't make sense to go for a high-voltage system, as I know I couldn't resist using the increased performance. If I can get decent performance from 0-50 mph, i.e. town use, I'll be happy, for the time being at least.


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## Ziggythewiz (May 16, 2010)

Where does it stop though? Perhaps starting at 72V can help keep ones expectations and desires in check.

I started at 120, and can't wait to go 144.

Is there a voltage that's good enough? Maybe if you go OEM, but for the DIYer there's always going to be an upgrade on the horizon.


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## EVfun (Mar 14, 2010)

Ziggythewiz said:


> Where does it stop though? Perhaps starting at 72V can help keep ones expectations and desires in check.
> 
> I started at 120, and can't wait to go 144.
> 
> Is there a voltage that's good enough? Maybe if you go OEM, but for the DIYer there's always going to be an upgrade on the horizon.


I suppose enough is when the pack voltage under load is as high as the motor can handle. Above that you won't feel a difference because you will need to set the controller to limit motor voltage. The motor is a lot slower if you flash over the comm.


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## Yabert (Feb 7, 2010)

gottdi said:


> I don't think you will be as happy as you might think at this time. I thought I'd be happy with 72 volts and thought as many do that it would be just fine. Boy was I wrong. You will be itching for more real soon. But go ahead and do your setup because you already have the parts. It will be great fun but you will want more. Guaranteed.


All depend of weight. Can you really compare your 72v conversion with a 600-700 Kg (1320-1540 lbs) mini conversion equipped with a 150 lbs battery pack???


I know than higher voltage is better, but I actually don't know any high quality 96 to 156v controller available for low price. 
I think than SPM alltrax offer at 400-600$ is really hard to beat.

I think people need to distinguish between two thing:
-Low cost, low performance (less than 50 hp), not highway, 72v conversion (Alltrax controller for 400-600$)
-Mid / high cost 96 to 300v conversion (Soliton, Zilla, Warpdrive, Synkromotive controller for 1700 to 3000$ and more)... You can notice than I exclude Kelly and Curtis from choices...


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## motor guy (Dec 17, 2008)

hello all

are we talking ac power or dc power, motor style?

you all have seen the video of both of our trucks, 1 is dc and manuel trans - 48 cells 200 amphr, the other is 72 volt 3 phase motor with auto trans. 

they both will run highway speeds, 70 mph, the s10 is lighter by 1900 lbs. and will run faster than the 1/2 ton silverado. 75 mph is about the limit on the silverado. but for the around town and the occasional highway jont, it does a great job on deliveries, with power steering and auto trans,and ac to be cool.

our silverado truck weighs 5950 lbs and still does a great job. is it as fast as the zombie car, no, not even my wildest dreams, but the zombie car cant haul a 1500 lbs gearbox to the customer either.

you have to decide what you are wanting to accomplish with your build. there are pros and cons for everything built in this world. what works for one person might not for the next. just do the best reseach that you can and be proud of what you build.

we were told that our design ac motor on 72 volt with an auto trans, wouldnt work either, but you build and learn anyway. and if it does work, take the video and put it on youtube, so all can see. is our ac power truck the answer on evs, no, but it might help kick the can alittle further,to ware someone else might get the next big idea.

thanks 
kevin


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## ga2500ev (Apr 20, 2008)

gottdi said:


> Depends upon weight? Sort of. If it is fully only going to be a town car and really never on the highway then 72 could do but from experience I guarantee you will WANT more. Just because 72 volts could do the job does not mean you will not WANT more. I guarantee you will once you drive it. If you only need an in town car why not just go by a GEM or the like. Its just an in town street legal golf cart. Plenty of poop to do what you need there. But if you WANT a car then pony up and build a CAR not a CART.
> 
> I don't consider the Synkromotive an Expensive controller and I do consider it a top quality controller. A contender to all the top brands that is truly affordable.
> 
> ...


Pete,

Every time you come along I always chuckle. You are a true enthusiast. Sometimes I wonder what I actually would do if I had 10-15K USD to spend on a car. Choices are different when money is no object.

Every choice that I make is based on cost. My personal enthusiasm in this field is based solely on cost. I haven't spent more that 1500 USD total for any vehicle that I've driven for the last 6 years. Each was purchased with a problem, and the problem was cheaply fixed. 

I'm interested in the low voltage, low weight conversion precisely because of cost. 120V of 180 AH lithium cells would be lovely. But it's 10K.

I just bought a test pack last week. Fits perfectly into this discussion. Six 12V 35 Ah U1 AGM scooter batteries. Probably won't last 2 miles in the Geo I'm putting together. But I got them reconditioned for $160 out the door. If I can get a test run up the hill on my street and get to 40 Mph, that'll be an achievement.

The A123 Prismatic pouches looks to be the compromise. All lithium at at fraction of the cost. I figure that 90-120 cells in a 96V battery will end up being the winner.

Just my two cents. I'm still chuckling...

ga2500ev


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## Ziggythewiz (May 16, 2010)

ga2500ev said:


> The A123 Prismatic pouches looks to be the compromise. All lithium at at fraction of the cost. I figure that 90-120 cells in a 96V battery will end up being the winner.


I'd call it an alternative, but not a compromise, and not cheaper. The cell cost is the same and the tradeoff comes from a fully built cell ready to go in a battery box from a trusted supply chain vs a high performance pouch that needs extra hardware and a custom battery box to be used from a questionable supply chain with an uncertain future.

Option, yes, winner, too early to tell. I think it could be a winner if A123 went under and someone else got all the rights on liquidation and could provide them legit in the states for cheaper than larger prismatics.


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## motor guy (Dec 17, 2008)

hello all

thanks for the good thoughts and words.

our link to see both of our trucks is

topekaelectricmotor.com


thanks kevin


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## Yabert (Feb 7, 2010)

motor guy said:


> are we talking ac power or dc power, motor style?


Cheap DC. 
High cost controller and high weight motor isn't part of the discution. Good demonstration by the way!



> I just bought a test pack last week. Fits perfectly into this discussion. Six 12V 35 Ah U1 AGM scooter batteries


Hi ga2500ev 
Please just try to don't mix lead acid able to output 15-20 Kw of peak power with lithum pack able to output 30-40 Kw. I understand the cost wise.



> Just because 72 volts could do the job does not mean you will not WANT more.


I know... I currently drive a 100Kw Smart Fortwo and I would like to have a 200Kw... Human nature!!..

Oh! and by the way, no highway is relative because I actually cruise each day on highway with 15-20 Kw. That is often with less than 72v at motor terminals (controller pulsing the 154v battery nominal voltage).


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## ga2500ev (Apr 20, 2008)

Ziggythewiz said:


> I'd call it an alternative, but not a compromise, and not cheaper. The cell cost is the same and the tradeoff comes from a fully built cell ready to go in a battery box from a trusted supply chain vs a high performance pouch that needs extra hardware and a custom battery box to be used from a questionable supply chain with an uncertain future.


The lack of packaging and the cheaper cell cost makes it a much more flexible option. And the huge difference seems to be the maximum amp draw. The pouches can be pushed to 20C with absolutely no problems. The encased 40 and 60 Ah cells all have max current draw specifications of around 5C sustained. I routinely see postings warning not to average more than a 2C draw on the packaged cells.

It makes a huge difference because it becomes possible to capitalize packs in smaller, more flexible increments. While a 30 cell prismatic battery will have limited range, it will push 96V at upwards of 500A when required with absolutely no problem. Can be done at a cost of $750 or so plus the box. I cannot see any way to do that with 40A Calb or Sinopoly cells. Can't get the voltage nor the amperage at that cost.

I don't think I'm missing anything here. Am I?



> Option, yes, winner, too early to tell. I think it could be a winner if A123 went under and someone else got all the rights on liquidation and could provide them legit in the states for cheaper than larger prismatics.


I take it as I can get it. Legit drives up the price. Jack Ricard and others seem to be having good luck with VictPower so far. I waiting to see if any US group buys come in OK.

ga2500ev


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## Ziggythewiz (May 16, 2010)

ga2500ev said:


> The encased 40 and 60 Ah cells all have max current draw specifications of around 5C sustained. I routinely see postings warning not to average more than a 2C draw on the packaged cells.
> 
> It makes a huge difference because it becomes possible to capitalize packs in smaller, more flexible increments. While a 30 cell prismatic battery will have limited range, it will push 96V at upwards of 500A when required with absolutely no problem. Can be done at a cost of $750 or so plus the box.


What exactly do you need more than a sustained 300 amps for? Yes, the little pouches are more flexible, but they're also little. Your proposed pack will have a safe range of 5 miles.


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## ga2500ev (Apr 20, 2008)

Ziggythewiz said:


> What exactly do you need more than a sustained 300 amps for? Yes, the little pouches are more flexible, but they're also little. Your proposed pack will have a safe range of 5 miles.


I understand that. This thread from last year discusses the issue of current draw of small Ah encased cells. It has pages and pages and pages of discussion of the fact that the sustained draw of 2-3C is acceptable for small packs of encased cells. 

Here's the difference, the prismatic pouches can run with no problem at 15-20C. So that means that you can put together a 2P or 3P pack which matches up with 40 Ah - 60 Ah encased cells that has the sustainable draw to have regular usage, and the power draw to give sufficient acceleration.

So the bottom line is that while a prismatic pouch battery at the price of 60 Ah cells can be usable, the 60 Ah encased cells are not acceptable for normal small EV use. 

That's why it's possibly the winner.

ga2500ev


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## Yabert (Feb 7, 2010)

Hi, still me...
Because I have in mind another small car conversion, something cheap as 300$ forklift motor, 500$ Alltrax controller with 2000$ Chevy Volt battery pack, I've drove my Smart all week long with 70v - 450A setting in the controller. That should simulate well worst case of a 20S battery pack (can you imagine that, managing only 20 cells )

*Result:* 
Fully usable on the highway at 100-110 Km/h (62-68 mph) in 4e gear.
Top speed of close to 130 km/h (80 mph) in 5e gear.
Easely keep up with traffic in 2e gear from 0 to 60 km/h (0-37 mph).

So that seem really good to my idea of a nice and cheap small commuter car.
Thanks to the small Warp Impulse 9 who spin fairly fast despite this "low" voltage.

Details: 15-25°C, 865 kg car, mostly flat road here.


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## Woodsmith (Jun 5, 2008)

It is really good reading this thread again.

I am planning on no more then 72v on my truck, mainly because I have the donated 72v Curtis controller, and the battery cost will be reasonable.

My truck will be less then 550kg, plus pack weight, plus payload.
I only need 40mph top speed and reasonable acceleration for day to day traffic and the ability to climb a couple of hills at 30mph or better. The range needs only be 10miles minimum and 20 miles would see me happy.

Also I am legally limited to 15kw nominal power for this build so I am not ever going to have better performance anyway.

I have an 11" motor direct drive to a 3.91:1 rear axle on 21" diameter tyres.


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## bwjunkie (Jul 31, 2013)

I'm glad I stumbled on this thread.

I wanted to increase range of my 2200lb car (Winston 60ah 45s 144v DC SolitonJr) , but didn't want to double up to 90 batteries from 45. 

So I thought "maybe I can get away with 115v 36s, by buying 27 more batteries? (or even 102v 32s?)

Currently when I drive on the freeway I feel I have LOTS of headroom on power/speed, so...

It's experimental but I'm thinking it has a high chance of success?

bummer so far is I think I'll need a new charger since I don't think my Canbus enabled TC/elcon voltage can't be changed?

josh


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