# Planning a Mk1 AH Sprite Conversion



## Duncan (Dec 8, 2008)

Hi
I like the old Frogeye 

How much - ranges from ~ $3000 - up
Transmissions
I went direct drive - with a light car end enough power you don't need a gearbox

The main cooling problem is the controller, need liquid cooling at about 700 amps 

http://www.diyelectriccar.com/forum...-dubious-device-44370p2.html?highlight=duncan

That is my beast - bit lighter than a Sprite
I have $3000 of batteries - gives about 25 miles range
Performance - a LOT faster than a 1275cc Sprite
(But NOT ENOUGH!) 
I am going to upgrade the controller
With an 11 inch motor I will need about 700 amps to spin the back tires

This is all DC
AC is sorta better but you have to add a zero to the price


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## nimblemotors (Oct 1, 2010)

I have a 71 Midget with extensive modifications. I have reduced its weight almost in half from 1800 lbs to 900lbs. There really isn't anything that has not been replaced and lightened. It has a Suzuki 1.0L 3-cyl and 5-speed. 
Pic shows the bugeye inspired but aerodynamic front end. 
It also has a chopped and raked carbon fiber hardtop. 

I suppose I would consider converting it to electric for you, as it will be sold eventually, it is still not completed. In any case, I am familiar with the cars.










Google electric midget and you'll find a website on an EV conversion.
It is a typical EV conversion, just swap out the engine with an electric motor. Not much inspiration there. He lost his trunk, and there is no other place to secure things in a soft top midget, but then a true bugeye has no trunk,
which is kinda a dumb design flaw. 
A 9in motor is probably overkill for such a light car particularly with a transmission, which has the advantage of a built-in reverse.

An idea is to flip the rearend over and put the motor in the back, like a VW, and put all the batteries in the engine compartment, so you still have a useable trunk. Maybe even use an actual VW transaxle. 
Or use a lightweight transverse transaxle out of a Geo Metro, with a 8in DC motor. Hmm, I just happen to have one of those in my garage...
A pic of it is attached, note the size comparison with a Prius transaxle next to it, and the main prius motor in the lower right. 




Kevin Evans said:


> So, I have about no idea where to start with this. Never done a conversion before, but I have experience with some auto mechanics and I do have access to a few shops, and EE/ME advice from my coworkers. I have an "okay" amount of knowledge on electronics, mostly stuff from college (low current, low voltage), as well as some hobby electronics (embedded boring stuff). Dunno if it'll help me much though.
> 
> Anyway, I am looking to purchase a 1959-61 AH Sprite. I have looked at a few in the area (already fixed up), and I think I would be able to fit a decent-sized motor as well as plenty of batteries in there. I am still deciding on which motor to use. I have a budget of around $10,000-$20,000 currently, but I don't mind sinking in some more money. I still have to acquire a Sprite, and there aren't many around here.
> 
> ...


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## Duncan (Dec 8, 2008)

I will beg to differ 
_A 9in motor is probably overkill for such a light car particularly with a transmission,_
A 9 inch is just about right!

I am using an 11 inch in a lighter car!

_I have reduced its weight almost in half from 1800 lbs to 900lbs._

Knowing how those cars are constructed I simply don't believe it - have you weighed it??

That is less than Caterham 7 with a motorbike engine!!


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## nimblemotors (Oct 1, 2010)

Then I would say you have built a slow and heavy car,
and should not be proud of your mistakes.

Did you not read the part where I said every part of this car has been modified/lightened??



Duncan said:


> I will beg to differ
> _A 9in motor is probably overkill for such a light car particularly with a transmission,_
> A 9 inch is just about right!
> 
> ...


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## Duncan (Dec 8, 2008)

900 lbs would be a superb result - but it would not be a Sprite!

A Caterham 7 is about as light as you can go for a road car - 
and the lightest of those with no weather equipment a motorbike engine and a frame that is a bit too light is about 450 Kg - 990lbs
(one of my friends used to have to change her chassis every year)

A Sprite has a heavy steel chassis and body
You can replace all sorts of bits but unless you are running a spaceframe with a very light fiberglass body and no interior you are not going there


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## samwichse (Jan 28, 2012)

He has done some pretty extensive lightening work on the midget. His build thread is here:
http://ecomodder.com/forum/showthread.php/mg-midget-geo-metro-3cyl-mgeo-15091.html


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## Duncan (Dec 8, 2008)

I have now read his thread - its quite impressive

BUT - as I thought he has NOT weighed his car 
The weight estimate is based on weight removed - and that simply does not work!

If I compare him to my car
He still has the heavy steel chassis - mine is a lot lighter - I can pick it up and carry it
(and that includes all of the floorpan and bulkheads
He has a "50lb" fiberglass front - mine is 15Kg
He has a 150lb engine + gearbox - I have a motor (102Kg) no gearbox - a wash
He has a windscreen, door, bootlid, fuel tank, radiator....
I don't
I do have 50Kg of batteries

My car weighs (actual weight) 710Kg 1562lbs

I could believe 1200lbs for his car - 900lbs is just too far

Many years ago (when I built my two liter twin cam mini) kit car manufacturers used to quote very low numbers for their cars 
These were always estimates based on taking an inaccurate initial weight and subtracting

After a few years on the road I made my mini into a rack car
It had a 5 liter fuel tank, no doors no windscreen and a motorcycle battery
I could pick the back of my mini up (both rear wheels would leave the ground) 
It was still a lot more than 900lbs


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## nimblemotors (Oct 1, 2010)

Duncan said:


> I have now read his thread - its quite impressive


Thanks, what kind of car do you have?


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## Duncan (Dec 8, 2008)

nimblemotors said:


> Thanks, what kind of car do you have?


Duncan's Dubious Device 

http://www.diyelectriccar.com/forum...-dubious-device-44370p2.html?highlight=duncan

It's a Lotus 7 type thing,
Now road legal (been on the road for 16 months)
Great fun - But I need more torque!
Should be getting a new (experimental) controller soon


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## dougingraham (Jul 26, 2011)

Looks like the thread got hijacked a little so hopefully this will bring it back on topic.



Kevin Evans said:


> I still have to acquire a Sprite, and there aren't many around here.


I have only seen two and one of those was a conversion. Probably a quite rare car these days.



Kevin Evans said:


> Ideally, I'd like about 50+ miles on a charge, and something relatively easy to drive.


With a Lithium conversion the 50 miles is pretty easy.



Kevin Evans said:


> I have like a billion questions, but here it goes:
> 
> 
> How much do people typically spend on a conversion?
> ...


I spent $19000 excluding the cost of the donor car which I already owned. I could have spent less and still been happy with the car as a daily driver. I would do things a little differently today and probably spend a couple thousand more which would needlessly increase the performance. You always want more. The goal was at least as fast as the top end model in the last year the car was made. I way exceed that now.

I kept both the transmission and the clutch for a number of reasons. Without the clutch shifts are slow and I wanted the car to be superior to when it had the wankel in it.. If you eliminate the transmission then that problem goes away. The amount of torque needed would depend on exactly what you expect for acceleration and the mass of the EV. Probably some sort of rule of thumb could be devised to answer this question but it is complicated. In my case I would like the acceleration to be what I see somewhere between 2nd and 3rd gear. 2nd gear torque at the face of the tires would be just below the weight of the car and 3rd gear torque is about half of that. The problem with fixing my final drive ratio to that of 3rd gear is top speed. The rev limiter would stop me at 68 mph (5500 rpm) and even before that happens the torque starts to fall off at 49 mph (4000 rpm). A higher voltage pack would help me out in widening the torque band. It would be a balancing act to find the right final drive ratio such that you could get rid of the transmission. I have a WarP 9 and can feed it 1000 amps. It isn't totally clear what the actual torque is because I have seen different number published but the one I use in the calculations is 277 ft-lbs. I don't think this is quite enough to go without a transmission in a 2600 lb car. If I never went on the highway it would be enough. If you decide to try to eliminate the transmission and use a Series DC motor because of the high torque you will have the problem of the final drive ratio. In my case the total reduction in 3rd is 5.6 and you will not find that to be an easy reduction to obtain. The other problem will be reverse. With your typical Series DC motor you need three full power contactors on the motor to switch the direction. Unless you have a motor with interpoles (Netgain WarP 11HV or one of the Kostov motors) the timing of the motor is advanced for forward operation. When operating the motor in reverse the timing that is advanced in forward is now retarded timing and can cause damage to the comm and brushes. Warp9 is about $2000 and Warp11 is about $3000 and you need at least 1000 amps. So you are looking at a $3000 motor control. In your car if you keep the gearbox you get a lot more options. You can use any of the HPEVS AC systems and get good performance. You can use a WarP9 with a 500 amp motor controller without any reversing contactors because you can still use the reverse in the transmission. Because a conversion is already difficult enough any problems that can be eliminated help. For your first conversion I suggest keeping both the clutch and transmission because it is easier. (You were probably thinking that it would be easier to leave them off.)

Motor cooling is often done with an internal fan but there are motors designed to be liquid cooled. I don't have any additional cooling beyond the internal fans and my daily driving does not require it. Even at highway speeds for the five minutes I do this the motor does not heat up excessively. Maybe I would have an issue if I had a terrible headwind on a 115 degree day but I think I would be hiding from the heat in a vehicle with air conditioning in that case. I guess the answer is that it depends. I suspect that unless you have more than a 10 minutes on the highway you might need some additional cooling with a Series DC. The motor controllers however do usually need some outside cooling.

I don't know how to answer your question about standard layout. You can check out similar conversion to what you want to do but from my three trips to EVCCon and having done my own conversion the approaches taken are as varied as the builders. I went to the first EVCCon hoping I would learn how other people did things. It was tremendously valuable. One thing I discovered was that I didn't yet know the questions that needed answers. Since there is a club in your area you have projects you can go look at and see how people solved the problem you are facing at that moment. You also have this forum to consult. There is no one absolute correct way to do something.


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## nimblemotors (Oct 1, 2010)

Let me add that there is little point in using an original bugeye for an EV conversion, unless you already have one that is a beater.
They don't have a trunk as I said, or rollup windows.
The key feature is the front end body design.
The later model Sprites and Midgets are plentiful, particularly the 73+ rubber bumper midgets that nobody wants, there was one for sale locally for $400 with no motor a few months ago. You can swap the front end of them with a bugeye front end and get the bugeye look, and then have a trunk and rollup windows, a no-brainer really. Leave the original bugeyes to the restorers.

Regarding a clutch, none of my EVs have clutches, and I find it 'stupid' to keep a clutch in an electric car, there is no point to it, they wear out, but most importantly is that it requires a flywheel which was invented for a gas motor. An electric motor already has a very hefty weight to it that needs to spinup, and just as importantly spin DOWN when you stop, and a flywheel just adds even more weight making it more inefficient to accelerate and decelerate. The first thing you notice when driving an EV is that when you lift the throttle that car just keeps on going from inertia, whereas a gas motor will decelerate very quickly. Regen braking with an A/C motor adjusts for this difference.
Easier shifting? Get an automatic transmission dude. Safety disconnect? God I hope your car is not that unsafe to need a clutch for safety.

Just my opinion of course.


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## MN Driver (Sep 29, 2009)

I find it hard to consider a clutch to be pointless or stupid.

Matching the speed of the input and output shafts of the transmission with the synchronizers takes more time and wears them out. I consider a car that I can shift quickly to be a safety benefit and I'd like to operate a transmission where I shift it without extra load that it wasn't designed for. I'd prefer not to downshift and need to spin the motor up via the synchronizers.

I drove a clutchless EV once and quickly decided that this was not the route I was going to take. I want a car that I can shift quickly and make driving maneuvers without requiring additional time to shift. Not to mention if I want to accelerate quickly starting in a low gear and make an upshift or two along the way that I can accelerate from a stop to highway speed as quickly as possible, this is part of the fun of driving in a sporty fashion, which in my opnion, is more fun.


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## dougingraham (Jul 26, 2011)

nimblemotors said:


> LRegarding a clutch, none of my EVs have clutches, and I find it 'stupid' to keep a clutch in an electric car, there is no point to it, they wear out, but most importantly is that it requires a flywheel which was invented for a gas motor. An electric motor already has a very hefty weight to it that needs to spinup, and just as importantly spin DOWN when you stop, and a flywheel just adds even more weight making it more inefficient to accelerate and decelerate.


I am going to let you in on a secret. The clutch on an EV does not wear out. The bulk of the wear on the clutch in an ICE powered car comes from slipping the clutch when you start off from a standstill. There is almost no wear any other time.

I agree it would be better to not have a clutch but if you want a car that you are going to drive in a spirited fashion you need a clutch. The shifts just take too long. It is also somewhat hard on the synchros. I don't know if clutchless shifting will wear out the transmission prematurely or not. Probably not enough to worry about since if I didn't have a clutch I would most likely use 3rd gear 90% of the time. I am using a lightweight aluminum flywheel (a little less than 10 lbs) instead of the 25 lb one that was on the wankel. The pressure plate weighs more than the flywheel and there is not a significant amount of energy stored in the flywheel assembly with a light weight flywheel.

And here we go hijacking the thread again.


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## Duncan (Dec 8, 2008)

Continuing the hijack 

If you want a light car -
And you don't need a very high top speed - 

Then a direct drive is ideal 

With "normal" sized tires (24inch diameter) and a standard diff (4.1:1)
I hit our country wide speed limit at less than 4000rpm (100kph)
at 5000 rpm I would be doing 87mph 
at 6000 rpm I would be doing 104mph
My 11 inch motor should be OK at 5000rpm - a 9 inch motor should be OK at 6000rpm


at 277 ftlbs (at 1000 amps with a Warp 9) - I would get 1135ftlbs at the tires or 1135 lbs of thrust at the road surface
This will spin the tires of a car with 1400lbs weight on the rear tires

So with a light car - and if 100mph is enough - you don't need a gearbox

Reverse
I am using a standard reversing contactor off a forklift - 
With my timing advance I know that I should not go mad in reverse
So I don't go in for the type of autotest that uses reverse

For normal road use you really do not use much power in reverse,
Some of the motorbike engined Caterhams use a starter motor to get reverse

Losing the transmission enables you to put the motor where the gearbox should have gone leaving a nice big hole (where the engine used to be) for batteries


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## Moltenmetal (Mar 20, 2014)

From my amateur point of view, the clutch is a safety benefit for DC installations because the controllers can fuse on- and at that full on current hopefully you fuse would blow, but your contactor or disconnect may not be able to interrupt the current- depends what you're using if course. With an AC install, the flywheel mass shouldn't be an issue and the motor torques are lower than the DC series wound so the clutch should improve performance a lot. Some here have indicated gutless performance with AC50s in relatively lightweight cars, and I don't want to take any risk of that with the effort and dollars I'm putting into mine.


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## fb_bf (Jul 6, 2011)

I have a '77 midget converted to electric. You should go to my site and look it over. I have a lot of information, and I'd be glad to offer advice through emails or a phone call. I would agree that converting a bugeye sprite is probably not the way to go. They are classics, and finding one will be tough. A later Midget '66 to '79 is a better choice. I believe that if you want a drivable car then keeping the clutch and gearbox is a must. On my site I have pictures and data for the added performance of lightening the flywheel. I cut the entire OD off and brought it down to the OD of the pressure plate. It will never wear out. I start the car in first gear without slipping the clutch. Shifting is great, and it allowed me to use a Warp 9 impulse with less torque than the Warp 9 motor. With 120 volts of battery I don't limit the current until 4200 RPM. I have the controller set to shut down at 5,000 RPM. The car drives just like the gas version did. I use the soliton Jr controller so I'm limited to 550 amps, so it isn't a speed demon, but with 38 180AH cells I get over 100 miles of range. You could put in 38 100AH cells and get your 50 mile range you wanted and have a lighter and quicker car than mine. Good luck with your build.


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