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Dual-motor Austin Mini

90K views 168 replies 42 participants last post by  galderdi 
#1 · (Edited)
I've been talking about this for long enough and I've changed my mind about how to do it countless times, but I've finally made a start on my Mini conversion.
I've got to come clean first and say it's not a completely authentic Mini, as it was rebodied some years ago with a glass fibre shell. Otherwise it's a Mini through and through, complete with leaks, ageing 1275 A-series engine and gokart handling.

She's currently buried outside under 12 inches of snow, but I've bought a spare front subframe so that I can get the motors mounted and refurbish the front running gear over winter. I found a couple of Prestolite 7" motors a while back, via an ebay contact. They're rated at 130A continuous at 36V. I've advanced them by eight degrees and plan to run them at around 120V each.

The motors have actually been shortened by around 40mm since I took the photo below. This was done by removing the internal fan, and machining back the alloy "legs" on the drive end. It was the only way I could get the two motors to fit across the subframe and also gave me a decent length of plain shaft to mount the drive sprocket on. I'm not going to worry about whether it's unbalanced the motors yet...
Each of the motors will drive a chain sprocket mounted on the inboard ends of the half shafts, so no gearbox, no diff. I'm busy making up two pairs of bearing carriers that will each support a short shaft with a sprocket on one end and a CV joint on the other. I'll post some photos in a few days when I've got something worth showing.

Now to the first of many daft questions: I want to keep this conversion as simple (and hopefully cheap) as possible. I've been looking at options for providing vacuum and 12V power and the simplest way I can see to do that would be to use the tail shaft on one motor to drive a mechanical vacuum pump, and use the tail shaft on the other to drive a lightweight alternator. The question is, if I have the motors wired in series to a single controller, is the small difference in load on each motor likely to cause any problems?
 

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#103 ·
Hi Malcolm,

Get some degreaser on the commutator (brake cleaner perhaps?), oil can cause all sorts of commutation problems as well as causing damage to the commutator if run at power.
TBH I've always been a little surprised this doesn't happen more often, I guess we're lucky that most EV's don't tend to be very oily..
 
#104 ·
Hi Steve, good to hear from you!

Thanks, I'll give the commutator a rub down with isopropyl alcohol. Yes, when you think of the industrial environments that some of these motors work in I'm also surprised they don't fail more often.

Is your MX-5 still running well?
 
#105 ·
Hi Steve, good to hear from you!

Thanks, I'll give the commutator a rub down with isopropyl alcohol. Yes, when you think of the industrial environments that some of these motors work in I'm also surprised they don't fail more often.

Is your MX-5 still running well?
Just giving the MX5 a service after it's first year of use - the heater element died (actually it melted the plastic and dropped out of the airflow) and it's getting to that time of year when you really WANT a heater!
Also lost a cell (or 1 bank of parallel cells) - though luckily the LVC system caught it before I poked 1000A through it! Easy to swap these lipo cells over however, it will be back on the road this week.
 
#107 ·
Thanks Doug, the same thing crossed my mind, but both motors are neutrally timed at the moment. I reset them to neutral a while back as I'll be using a low-voltage pack for a while - until I win the lottery.

I test ran the motors on the bench for several hours in their current configuration and there was no problem at all.
 
#108 ·
She works!! :D

I've just had my first drive in an electric car :D Drove up and down my street this morning in the Mini. I've got to say after all the time and thought I've put into this project and all the imagined problems, it was almost an anti-climax. No fireworks, no clouds of smoke, no wild surges of power. She just glides along serenely accompanied by the sound of an old milk float and the odd thump from the suspension :)

My main worry was torque steer, since the motors are wired in a parallel to a single Alltrax. I did a couple of full-lock turns and the steering feels just the same as it did with the ICE. Obviously I'll have to do more testing, but it looks encouraging so far.

The performance isn't anything to shout about at the moment, but it feels perfectly adequate for town driving.

I did find one small problem though. I installed a forward/reverse gear lever in the transmission tunnel just in front of the handbrake. The handbrake was on when I did the installation, and I never thought to check clearance with the handbrake off. Now I can only select reverse when the handbrake is on... I guess that's one way of making sure I've come to a complete stop before I go into reverse :eek:

Still a few little jobs to do, minor details you know, such as wiring the instruments and chargers, fitting the dash, interior carpet, exterior paint...
 
#109 ·
Excellent news Malcomb! Been looking forward immensely to this! How about some pics?! Keen to see your final motor installation, and some pics of what your plan is for mounting batteries. Love the thought of an EV Mini! Was looking at the thread about the Toyota/Lexus electric rear transaxle and thinking that would drive a light fiberglass Mini a treat! Be a little rocket! :D
Congrats sir!
 
#112 ·
Thanks gents :)

No video and very few pics at the moment, I've been too busy. Here are a couple of pics of the engine bay though. I still need to fit terminal boots and tidy up the wiring. I've just sent details off to PlugInsure to get an insurance quote. They'll be getting sick of us UK tinkerers soon...
 

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#118 ·
Big day tomorrow, I have the Mini booked in for its MOT (roadworthiness test)! I've got loads of little jobs done, fixing lights, replacing the windscreen washer and a seat belt etc. Hopefully I haven't missed anything.

Only running on 60% of the battery pack at the moment, so the battery installation isn't complete. The batteries are secured in an angle iron frame with heavy-duty lashing straps and a square-section restraint bar. Since there's plenty of space either side at the moment I've installed the chargers here. I need to make up a proper cover for the fuse :eek:

I charged the pack up yesterday and the cells are closely enough balanced that the chargers shut down before any cell can trigger the cell-logs. The highest cell was around 3.53V and lowest around 3.47. The chargers just shut down for a minute or so and then repeat the charge cycle. I plan to use a timer to prevent them cycling endlessly. If any of the cells does get far enough ahead of the other to trigger a cell-log (3.6V) it activates a mains relay that shuts off the chargers.

Instrumentation is minimal right now. The speedo is the original tachometer, taking pulses from an inductive proximity sensor on the tail shaft of one of the motors. I worked out the speed at given rpm and then printed off a new dial for the tach.

I've fitted the old Cycle Analyst from my motorbike but realised that the new 400A 50mV shunt I fitted is outside its calibration range, so I'll probably get one of the ZEVA fuel gauge drivers. I'm also tempted by the EMW Android tablet display.

Still need to wire up a pair of analogue ammeters, one for each motor, just to check how they are sharing current under different conditions. I don't need accurate current reading, so I'll just use identical lengths of motor cable as shunts for each meter, to give readings for comparison (thanks for the tip Jozzer).

Loads of cosmetic work still to do, as you can see. It looks as if the Mini is going rusty, but that's just glue from the old carpet. Fibre glass doesn't rust as far as I know :D
 

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#119 ·
Good luck on the MOT!

Did you try both of the range settings in the Cycle Analyist?

Great way to bring an old classic back to life. I look forward to seeing it at one of the Brighton Mini runs one say;)
 
#121 ·
I'm road legal :D Passed the MOT with no advisories at all. I'm still waiting for the DVLA to approve the change of fuel type, but in the meantime I'm going to tax the Mini as an ICE, then claim back the road tax when the new log book comes through.

It was only a couple of miles to the testing station, but enough to confirm that I want more power. I'm still weighing up controller options, but at the moment leaning towards a Synkromotive. I really like the features and support of the Soliton Junior, but I don't think 600A split between the two motors will give me the performance I want. A Soliton 1 would be very nice, but is physically too big for the space I have available.

Steve: It's not actually a Cycle Analyst I'm using, it's the earlier version – the Drain Brain – and it only has one calibration range according to the manual.
It's a pity you live way down in the uncivilised south, I'd really like to drop in and see what you're up to :)

Mike: Thanks, hope you get your charger sorted out soon.
 
#124 ·
It was only a couple of miles to the testing station, but enough to confirm that I want more power. .
How much power do you really have with your small battery pack?
450A and 50v after sag (22 Kw)? I guess it's the main cause of underpower, right?

About controller, why don't simply add another cheap AXE 7245? Or trade your controller for a SPM 72650 (740A peak)?
 
#123 ·
Congrats!
Have you applied for the change to electric by post? Down here they usually give me a tax disk to walk away with and the docs follow later..

Shame indeed - you'd like it here, it's like an EV toyshop:)
 
#126 ·
Congrats!
Have you applied for the change to electric by post?
Yes, I sent the V5 off by post a couple of weeks ago. Called them today and they haven't processed it yet. I'd probably have been better off going to the local office.


Yabert said:
How much power do you really have with your small battery pack?
450A and 50v after sag (22 Kw)? I guess it's the main cause of underpower, right?

About controller, why don't simply add another cheap AXE 7245? Or trade your controller for a SPM 72650 (740A peak)?
Not sure about the power output yet. The lowest voltage I've seen so far is 67V, so possibly a bit more than 22 kW. Yes, another AXE 7245 would definitely make a big difference in low-speed acceleration for relatively little cost. I'm not really interested in going above 110 kph, but I would like decent torque from 0 to 95 kph, so I reckon I'll need more than 72V. I built the pack as 24V 50Ah modules with the intention of going to 120V as soon as I get a higher voltage controller. I have enough cells to go to 36s right now, so I'm looking for some more Lifebatt/PSI cells in good condition if anyone has any spare.
 
#132 ·
I just bought a Diahatsu Mira as somewhere to put my $12k worth of LifeTech's that have been sitting in the spare room for 2 years and also want to do a twin DC but running a series parallel switch.
Thanks! $12k worth of LifeTech eh? You've got too many toys mate, you need to share more :D
I was originally going to do series/parallel switching as well, but the wiring is messy enough already with two reversing contactors. I'm sure it could be simplified with a bit more planning though.
 
#133 ·
Im thinking 2 PM motors (maybe ME1003's) with a kelly controller as they have electronic reverse and regen, then making a mechanical series parallel sliding switch.
but then there may be arcing during the shift as the magnets might be inducing current on throttle off.
Can anyone clarify this ?

Also when 2 motors are in series are the number of turns effectively doubled ?
 
#135 ·
Thanks Rikard, and congratulations to you on getting married.

It's only classed as an electric car for taxation purposes in the UK. You notify the licensing agency that you have changed the fuel type to electric, and then you no longer have to pay annual road tax. I think it's a relic of the days when we had electric delivery trucks.
 
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