# 1971 mg midget ev



## Gregabrams (Mar 25, 2012)

I want to make my 1971 mg midget to electric. I want to have a 40 mile range and a cruising speed of 45. Which motor, controller, battery charger, batteries, and converter do I need? Also, what voltage should it run at? Any advice is greatly appreciated. Also, what would this conversion probably cost me?

Greg


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## Yabert (Feb 7, 2010)

Hi Greg

Let say 45 miles at 45 mph.... it's one hour of traveling. At 225 wh/mile you will need 10 Kwh of energy storage (battery). 
Now it's better to don't discharge the battery over 80%, so that give 12.7 Kwh. That represent the minimum requirement and you can store this energy with 40 100Ah cells (40 x 3.2v = 128v x 100Ah = 12.8 Kwh). It's a bit under 5K$ of Lifepo4 cells.

If you think you will never need to go on highway or need good performance, you can try a 72v conversion with 560$ controller (Alltrax SPM72400) and Impulse 9 (1700$) or used forklift motor (100-500$).
Your battery requirement will be the same 12.7 Kwh, so 12700 / 76v (24 x 3.2v) = 167Ah. 

If no, go for a 120 or 144v conversion. That will give you better power capability... so posibility of faster acceleration and higher top speed but for shortened period of time. (Same period of time at 45 mph)


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## tomofreno (Mar 3, 2009)

gottdi said:


> Be wary of some forklift motors. Not all mind you but some. As Yabert failed to tell you about his incident with a failed forklift motor even though he mentioned using or possibly getting one to use. If you do go the forklift route then you need to do some homework first. Learn from others mistakes. Yaberts failure was NOT a common failure at all but one to be on the look out for in case you decide that route. Still, get a good 9" motor if you can. An 11" may be too over kill in that little car.


A 9" motor is overkill for the stated requirements. Dtbaker has an 8" in his Swift with 120V and gets good performance.


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## Yabert (Feb 7, 2010)

gottdi said:


> 72 volts is just crap performance. Don't go there. Been there, done that. Unless you want a golf cart.


Right, 33Kw of peak power and around 33 hp peak at motor shaft (after battery sag and efficiency lost) give crappy perfomance...... like a 2000 lbs golf cart able to drive 60-70 mph..
All depend of budget and performance requirement!




> As Yabert failed to tell you about his incident with a failed forklift motor even though he mentioned using or possibly getting one to use


Strange than you talk about my forklift motor incident because any serie motor (Warp, GE or kostov) can be destructed by overspeeding in unload condition. Please don't mix things!


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## Ziggythewiz (May 16, 2010)

gottdi said:


> I disagree. A 9" motor is not overkill for most applications. Very few applications should use smaller. Just because you can does not mean you should. If you stick with a smaller motor your limiting your ability to upgrade too.


I run my 6.7" at 45 mph every day, and can take it up to 70 if I feel like it.

My motor wouldn't need an upgrade until the charger, controller, and batteries have all been upgraded first.

Some people do have budgets.


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## Ziggythewiz (May 16, 2010)

Everything's relative. My bug's too heavy now, but when new it was quicker than anything else I've ever driven. Actually, I don't even use most of my bug's performance anyway, so it's rather a moot question. I killed my first pack pretty quick hot rodding around all the time, so I'm being nicer to the batteries now.

I wouldn't expect someone with multiple 11"s laying around to understand.


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## fb_bf (Jul 6, 2011)

I'm the new owner of the Pete's midget. I just saw this thread. His/ my car has the warp9 impulse motor. I believe this is a beefed up 8 inch design. It is a perfect motor for the midget because at 500 amps it delivers the same torque as the original gas engine. It fits in the car so that it can use the stock engine mounts so the installation is clean. I'm running a 120 volt pack and can deliver 500 amps out to 4200 rpm. I believe the top speed to be rpm limited (5000) at 83 mph. My recent measured runs at 50 mph with the luggage rack removed and the top up showed I'm using 183 wh/m. I'm at 5000ft elevation, so I have 15% less drag than at sealevel. This was measured using the logging from the the Soliton Jr. and measured in both directions and averaged to account for the slight incline in the road. I would encourage the original posted to take a look at my site. I now have a lot of inforamtion about the conversion including costs, and will be happy to help with any questions.


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## fb_bf (Jul 6, 2011)

Pete,

The car is running great. I found that the emergency brake cable was sticking, so after fixing it, the car will simply roll out of the garage if I don't stop it. I also did measurements of with and without the lugage rack that was bolted to the trunk. The results showed that the rack was costing between 4% and 7% drag at 50mph and 60 mph. So it's gone. I also just finished removing the steel from the front and rear bumpers. I shaved off 43 lbs, and the bumpers look the same. I'll be posting pictures and instructions on how to do this on my site either today or tomorrow. I sold my gas midget about a month ago and have about 1800 miles on my electric midget. I hope we're not steeling the tread. I am convinced that midgets make for a great choice of a conversion car.


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## Ziggythewiz (May 16, 2010)

Is that the final battery box or just a temp job? (shape and placement don't look optimal)


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## Ziggythewiz (May 16, 2010)

Gotcha...makes sense. So what are you testing with it? I bet with the right gear ratio dual 11's could make it take flight.


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## fb_bf (Jul 6, 2011)

gottdi said:


> Let me know when you post the photos.


I've posted the instructions and pictures on my site on how to remove the steel portions out of the rubber bumpers. This will be of more interest to the MG crowd. I have added my wiring diagram to the site, so EV converters might like looking that over. 
I did measure my change in drag with the top up and down. 50 mph seemed like a sweet spot with the top up. I recorded 183wh/m at 50 mph. With the top down, That value jumped 22%!. At 60 mph the increased drag from driving top down went down to 12%. I'm trying to be careful taking these measurements for accuracy sake. The differences I saw make me suspicious of my accuracy. I'll keep taking data as I change things, so eventually I'll get a better feel on the accuracy of all of this.


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## RE Farmer (Aug 8, 2009)

Getting back to Greg's original question... I have a different setup.

I'm using an HPEVS AC31/Curtis 1238-7501. At $4300, not the cheapest way to go, but it fits nicely. I don't recall if Pete or Frank stating the final weight for Midge, but 183Wh/mi sounds about right given an estimated driving wt. of 1850# with driver (Wh/mi ~=10% of the vehicle wt.). 

I'm a little under 1100# in the de-ICE'd state. My planned battery pack is 36 SE100's, split into two 18 cell packs; one (19"x28"x6.5") where the original tank was and a similar pack directly over the motor. Note these cells will be lying on their sides so the packs will be 6.5" tall; not optimum but space for anything is a premium in the the midget.


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## fb_bf (Jul 6, 2011)

RE Farmer said:


> Getting back to Greg's original question... I have a different setup.
> 
> I'm using an HPEVS AC31/Curtis 1238-7501. At $4300, not the cheapest way to go, but it fits nicely. I don't recall if Pete or Frank stating the final weight for Midge, but 183Wh/mi sounds about right given an estimated driving wt. of 1850# with driver (Wh/mi ~=10% of the vehicle wt.).


I'll be real interested in your AC setup. I keep thinking if you can get 15% or maybe even 20% extra range in city driving from regen, then you could justify the cost of the AC system by buying less batteries and you would keep the weight down. It seems that your motor will have enough torque to do a decent job on keeping a realistic midget acceleration. My car ended up at 2020lbs, and I weigh 145lbs. The newer midgets are heavier to begin with, and I have a full interior and top plus 475lbs of batteries.


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## RE Farmer (Aug 8, 2009)

Frank,
Besides a lighter de-ICE weight, my pack will be ~250# and the AC31 is just 85#; that's ~300# less (~15% of your driving wt.) right there. I'm striving for minimum practical weight with my build - that's one of the major reasons for going AC. 

Regen was also a factor for going AC, not for increasing range but to save on brakes. Unless you do a lot of stop & go (or "jack-rabbit" style) driving, regen is marginal for increasing range - driving technique has a greater effect on range. 

OT: I saw your post in the MG Midget Forum about removing the steel from your RB. I was surprised you didn't catch a lot of flack for "ruining" a classic. BTW, Greg, the MG Experience Forum is a good source of info/help on all things MG. (http://www.mgexperience.net/phorum/list.php?3)


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## fb_bf (Jul 6, 2011)

RE Farmer said:


> Frank,
> Besides a lighter de-ICE weight, my pack will be ~250# and the AC31 is just 85#; that's ~300# less (~15% of your driving wt.) right there. I'm striving for minimum practical weight with my build - that's one of the major reasons for going AC.
> 
> Regen was also a factor for going AC, not for increasing range but to save on brakes. Unless you do a lot of stop & go (or "jack-rabbit" style) driving, regen is marginal for increasing range - driving technique has a greater effect on range.
> ...


Do you have an estimate of your peak torque you'll get. I have my estimate at 80 ft-lbs. (500amps) I find myself driving the car where I use about 300 amps for regular acceleration. Regular meaning what I've been used to driving my gas midget at. This should be about 40 ft-lbs. That should give you an idea of what yours will drive like.
Do you know why you don't get more out of regen? what makes it so you have to have big hills and fast stops? Why is it not effective during normal deceleration?
I've had mostly positive remarks from the MG community. I'm striving to keep the car's driving characteristics like a gas midget, and I think that helps. From the outside, and inside of my car you can't tell it's electric.


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## RE Farmer (Aug 8, 2009)

fb_bf said:


> Do you have an estimate of your peak torque you'll get. I have my estimate at 80 ft-lbs. (500amps) I find myself driving the car where I use about 300 amps for regular acceleration. Regular meaning what I've been used to driving my gas midget at. This should be about 40 ft-lbs. That should give you an idea of what yours will drive like.
> Do you know why you don't get more out of regen? what makes it so you have to have big hills and fast stops? Why is it not effective during normal deceleration?
> I've had mostly positive remarks from the MG community. I'm striving to keep the car's driving characteristics like a gas midget, and I think that helps. From the outside, and inside of my car you can't tell it's electric.


The AC31 actually has a bit more torq (~110 lb-ft peak) than the AC50, but it's only up to ~2000rpm vice ~3500rpm for the AC50.

My physics answer would be entropy, i.e. friction (heat) in the bearings, transmission (oil & gears), air, etc. If you're not exchanging potential energy (elevation) for kinetic E (speed) on hills, or heating brakes from rapid stops at each stop light/sign, then there's little advantage to regen. Technique (coasting as much as possible or as much as fellow drivers allow rather than heating brakes) is more effective. 

Having your controller's regen parameters set so it only provides braking (through a brake line pressure transducer) instead of the usual (ICE-style compression) off-throttle braking, will add to your mileage unless you're really good at feathering the accelerator pedal (again technique).


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## boatman (Apr 13, 2012)

Hi Electric Midget guys,
I too am looking into converting a 1500 Midget to electric, and have been very interested in the designs you guys have.
I'm hope I'm not hi jacking the thread, but hope any info would be valuable to Greg too.
I was considering going with a Lynch / Agni type motor, as it would save space in the engine bay for lower mounted batteries, and weight too. Any thoughts?

I too was considering side lying batteries where the current petrol tank is, and would be very interested in your design, RE Farmer.

Any tips or thoughts gratefully received.


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## DIYguy (Sep 18, 2008)

gottdi said:


> Im thinking that the Lynch/Agni type motor is too small. Now if you were able to connect two or three in series then maybe. A good choice would be the Warp9 or Warp9 Impulse sized motor. If you go AC I'd stick with using the AC50 size motor. Personal choice would be the Warp9 series motor or if you could get your hands on a 9" GE motor then that would be an excellent choice as well but they have only one shaft and not an aux shaft like the warp motors.


Hi guys, there are 9" GE motors out there with aux shafts also...


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## boatman (Apr 13, 2012)

Thanks for the motor advice, don't know much about GE motors, or AC for that matter. My initial thoughts had been for a 9" Warp motor, and there is a guy near here who is a distributor for them. However, in the UK the price for imported America gear is often much higher, so I thought locally sourced motors might be worth a look.
I suspected that the Lynch / Agni type motors might be too small for a Midget. I had read that both are producing more powerful versions soon, but I don't now how powerful they will be, expected dates or prices.


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## boatman (Apr 13, 2012)

Hi Greg,
did you you get any further with your ideas on a Midget conversion?

Boatman


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## fb_bf (Jul 6, 2011)

gottdi said:


> Im thinking that the Lynch/Agni type motor is too small. Now if you were able to connect two or three in series then maybe. A good choice would be the Warp9 or Warp9 Impulse sized motor. If you go AC I'd stick with using the AC50 size motor. Personal choice would be the Warp9 series motor or if you could get your hands on a 9" GE motor then that would be an excellent choice as well but they have only one shaft and not an aux shaft like the warp motors.


Check out this build for a dual Lynch motor http://www.diyelectriccar.com/garage/cars/278 I've been in contact with Paul because I was interested in his regen results. He gets a documented 15% range increase with in town driving.
Not sure where you did your research, but I think your numbers are a little off. Quote from Paul
"My motor is the LMC-2X2-D127, which means Lynch mounted two of their D127 motors in tandem. The weight is more like 50 pounds, and the torque at 200A is rated at about 67 ft-lbs. That makes more sense for the current comparison, since our cars are close to the same weight. There is one photo of the motor with covers removed on my EValbum page: http://www.evalbum.com/2224 "
Pete, he uses a Kelly controller with this motor. The normal torque for the 1500 midget engines was 88 ft-lbs. So this motor can probably match that torque at peak output, if not go higher. You'd start the build with 85 lbs less motor weight. You'll probably want to retain the clutch with a motor that has this kind of torque. Depending on your driving goals, as in you do mostly around town driving, you could use the regenerative braking to reduce your pack size and weight. It sound like that motor costs around $4,000., but maybe you could trade off some battery costs with a reduced pack.

If your interested in the trunk battery box, and my site doesn't show enough information on how I did it,contact me and I'll be glad to help. Right now, I'm trying to see if anyone has prints for the adapter plate for a midget. I've had about 3 people contact me and are looking for information on where to get a coupler and adapter. If anyone has this infromation, can they pass it on?


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## drgrieve (Apr 14, 2011)

boatman said:


> However, in the UK the price for imported America gear is often much higher, so I thought locally sourced motors might be worth a look.


Perhaps you can source Kostov motors cheaper as they are Europe based. Their 9" motor is 45 kg. Choice of different voltages to suit controller / battery choice.


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