# Planning Microcar 15Kw conversion



## Normsthename (Jul 13, 2008)

Anyone got any ideas?

Thanks

Andy


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## TheSGC (Nov 15, 2007)

What is the top speed you are looking for? Since that car is rather small, a 6.7" motor should work, like an ADC K91-4003 and run it at 72 volts. 

Motors are usually rated at their continuous power, not there peak. So a 20 HP continuous motor would be overkill for that microcar. (20 HP electric is what is used in 5000 lbs pickup trucks) The K91-4003 is rated at 8.5 HP continous at 72 volts and 22 HP peak at that voltage, so it would be about the same, if not better than the original ICE.


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## Normsthename (Jul 13, 2008)

Thanks TheSGC 


> What is the top speed you are looking for?


With the current 15Kw (20HP) ICE Engine fitted it will do 68mph, so I was assuming replacing it with an electric motor of the same power it would give it similar performance?
It would slow it a little with the extra weight of the batteries etc. but then it would have much improved torque over the ICE Engine?
I estimate the weight of the vehicle with the batteries fitted would be approx. 525KG depending on the size of battery selected.

To be honest, all the commuting that I do the road speed limits are a maximum of 40mph, so as long as it could do this comfortably I would be happy 

Thanks

Andy


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## TheSGC (Nov 15, 2007)

You can run the K91-4003 up to 96 volts for more HP (10 HP continuous, 35 Peak) and that should get that Microcar up to 65 MPH no problem. I am using that motor in my Civic, which will be about 1200 KG, and it should bring my EV to 55 MPH safely according to the EV Calculator.


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## Normsthename (Jul 13, 2008)

To keep the car in the same classification, the power cannot exceed 15Kw
I am a little a little confused on the difference between Motors and voltages.
There are some motors generating 8 HP Continuous and have a Peak of 15HP running on 72V
Then another companies Motor generates exactly the same power (8 & 15) but it is only running on 48V
Which is the best option to go with?

I found this kit on the 'Net', it is designed for "Small EV's like Go-Karts and Motorcycles" it looks like it could do the job for my light car?

http://www.beepscom.com/product_p/ki-72v-m9-k-r.htm

Andy


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## Jeremy (Jul 12, 2008)

I'm using that Mars ME0709 motor in my motorcycle conversion (the motor is only $500 from the manufacturer, Mars Electric LLC, BTW). It is going in a UK legal moped. It is rated as a 5kW motor, but will deliver about 7.5kW at 48V and around 15kW at 96V.

Motor ratings are usually based on the amount of power that the motor will deliver continuously, which is a function of the current flowing through the windings. This is usually a function of the ability of the motor to get rid of waste heat. Upping the voltage increases the maximum power available, but doesn't change the maximum allowable continuous power.

In a road vehicle this isn't a problem at all as the ratio of average power to maximum power will be low, probably around 20%. For example, a car that delivers around 50mpg only uses an average power of about 8 to 10hp, even though it may have a maximum power of 60 to 80hp or more.

My guess is that an ME0709, run at around 72V will give you plenty of performance in such a light vehicle. For a controller I would go for something like the Alltrax 7234, at around $480. A contactor is pretty cheap, maybe $40 or so and a pot box throttle maybe another $90 if you buy one, less if you make one.

Batteries are the killer, because you'll want to keep the weight down. I'm using a 48V, 40Ah LiFePO4 pack, which will deliver around 150 amps maximum and weighs about 22kg. You'll need more capacity than this, but I would guess that a 72V 60Ah pack would be just about OK and would weigh about 50kg. The motor weighs about 15kg, the controller and contactor will weigh around another 6 or 7kg. Overall I think this would easily fit within the tight weight restrictions you may face in order to remain within the capability of the structure and suspension limits, as the 500cc engine and full fuel tank probably weighs about the same.

The snag with this much lithium is the cost, LiFePO4 cells don't come cheap! You could use lead acid, but the weight and volume would be very significantly increased, plus the usable capacity might be less, due to peukert effect.

Jeremy


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## Normsthename (Jul 13, 2008)

Hi Jeremy
Thanks for your input 
When you say "a 72V 60Ah pack" does that mean 6 x 12v batteries wired together?
I have seen some conversions where they have used 6 x 12v Deep Cycle batteries.
If this was suitable for my conversion, I would fit 3 x under the bonnet (Hood) and the other 3 x in the rear boot (Trunk)
How do you calculate the estimated range and size of Battery required if I was using that motor @ 72V?
I am considering keeping the CVT Transmission of the microcar, with the ICE Fitted it works superb and I think it would help with the performance and range.

Where are you located in the UK?
Your UK legal moped sounds interesting! what is the donor bike that you are using?
With the power that you are talking about, it will be a Flying machine 

Thanks

Andy


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## Jeremy (Jul 12, 2008)

The cells I'm using aren't lead acid, they are Lithium Ferrous Phosphate, LiFePO4 for short. They have a much higher energy density than lead acid cells and also a very much greater usable capacity (lead acid batteries tend to only have about 60% to 75% of their rated capacity that is usable in an EV, LiFePO4 have better than 90% usable capacity). The cell voltage of a LiFePO4 cell is 3.2V, whereas a lead acid cell is 2V. Car batteries are usually lead acis and are made up of 6 cells in series to give 12V. My 48V pack is made up from 16 LiFePO4 cells in series (actually it's 16 sub-packs of 4 cells in parallel connected in series).

I think you might well find that lead acid batteries will be a bit too heavy, even though they are cheap. A typical 55Ah deep discharge 12V lead acid battery (the Optima yellow top - a pretty good AGM battery) is going to weigh about 20kg, so 6 of them will weigh in at around 120kg. These will give you a usable capacity of maybe 40Ah or so for a weight that is far more than double that of a 60Ah LiFePO4 cells pack. They will be a lot cheaper though, maybe half the price of the LiFePO4 cells. On the other hand, decent LiFePO4 cells will have about two or three times the cycle life..........

Range depends on terrain, weight, maximum speed and driving style. There's an EV calculator here: http://www.evconvert.com/tools/evcalc/ that will help you work it out. For my bike (with it's light weight and lower drag then a small car) I'm aiming for a range of around 20 - 25 miles or from the 40Ah pack.

I'd bin the transmission, for the sort of speed range you need and the light weight of the car I think you'll find it just soaks up power for little or no gain. CVTs are notoriously inefficient and efficiency is everything with an EV.

I am in the UK, near Salisbury. The donor bike for my conversion is an old RD50MX I picked up from eBay as a basket case box of bits (but with a valid V5). Here's a couple of pics of progress so far:


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## Normsthename (Jul 13, 2008)

The battery you suggested sounds OK
Funds will not allow for anything too expensive....
I would be happy if the batteries weighed 120KG
The car would end up weighing a total of approx. 500kg which would be the same as the ICE Version carrying 2 x 165lb passengers which it has done and coped well!
Hopefully the Electric motor torque would go some way to compensate for the weight.
I think I will try it with the CVT to begin with, it would not be a difficult job to convert it to direct drive if it did'nt work.....
I just think that the gearing would help the top speed and range.

Your bike looks great! 
Will you be registering it as a motorcycle?
Reason I am asking is because a Moped has to have a maximum speed of 50kmh, and I think that yours will easily do that!

Andy


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## Normsthename (Jul 13, 2008)

Just checked the price of the Optima yellow top 55ah Battery and the cheapest I could find were £190 in Vat 
So that would work out to £1140 for the Batteries...... 

Andy


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## Jeremy (Jul 12, 2008)

The Optima's are pretty well proven, so may well be OK for you, although the range will likely be quite modest with just 6 of the 55Ah ones. That price looks about OK probably about half the price of the equivalent capacity in LiFePO4......... My 48V, 40Ah LiFePO4 pack has cost me around £800, and that's using the cheapest cells I could get (imported from China), me welding the cells together to form the pack and building my own BMS.

The CVT will waste maybe 10% of your available power and I really don't think you will need it at all, as the Mars has masses of zero speed torque (more than the max torque of the old 500cc ICE engine, I suspect). That Mars motor will only rev up to about 3400rpm maximum under load at 72V, which is way lower than the ICE it's replacing, I suspect. If you want to retain the transmission, then maybe using a motor with a much higher kV would make sense, the ME0709 has a loaded kV of around 48 (52 off load). Going for a motor with a kV of around 80 or so might make more sense for driving the CVT.

I'm retaining the registration as a moped, as the speed is restricted by the motor kV. I've geared it so that it can't exceed the restricted speed on 48V, although obviously it's acceleration will be just a tad better than it was with the old 50cc two stroke motor. I've worked out that I could easily change the gearing to allow it to go up to about 55 - 60mph on the 48V pack and still have reasonably good acceleration. Any more speed would need more volts.

Jeremy


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## MalcolmB (Jun 10, 2008)

Andy

If you want some relatively cheap batteries just to try things out there are some ex backup power supply batteries going fairly cheap on ebay (UK) item number 180221264009. These batteries generally lead an easy life and are replaced as a matter of course every few years

They're Hawker Odyssey 42Ah. I bought a pallet of 10 from this buyer recently for £200 including delivery. They're all holding a full charge (12.85-13V eight hours after charging) though I haven't actually used them under heavy load yet.

Personally I think the Mars motor will be a little underpowered for your Microcar, but it depends what sort of acceleration and top speed you want.


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## Normsthename (Jul 13, 2008)

I checked the specs of the ICE Petrol engine that is fitted, and got the following figures :-

Max Power 13.6-15 kW (ECE) 4200-5000 rpm
Max torque  36-38 Nm (rpm) 2200-3000 rpm

I think that to use the CVT as efficiently as possible, I would need a motor with similar RPM as the ICE (4200-5000 rpm) 

I would possibly need to use a chain and sprockets to replace the CVT & Vee Belt 
At least it would allow me to get the optimum gearing 

Andy


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## Normsthename (Jul 13, 2008)

Hi MalcolmB 
Thanks for the info about the batteries, they sound like a Bargain!


> Personally I think the Mars motor will be a little underpowered for your Microcar


The standard ICE engine only puts out 15Kw (21 BHP)
I have two options :-
1) Keep the power output to a maximum of 15Kw and keep the car in the same classification
2) Replace with a more powerful engine, I would need to change the vehicle classification on the Logbook.

I only have a full motorcycle licence and I am limited to the regulations I can drive. 

Andy


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## Jeremy (Jul 12, 2008)

At 200 amps the ME0709 will give you around 36Nm of torque, which is pretty much what you get from the existing motor and remains within your 15kW limit on 72V. The torque constant for this motor is about 0.18 Nm per amp, so you can work out the torque for any particular current.

If you adjusted the gearing to allow the motor to run up to it's max loaded rpm on 72V, which is around 3400, then I'm reasonably sure that you would get overall performance that isn't far off that produced by the existing ICE. 

To be sure, then it would help to know the gear ratio range of the CVT, including the final drive, as then it would be possible to reverse engineer the sort of likely performance you might get with direct drive and no CVT, at a fixed ratio drive that allows max motor rpm at your anticipated max speed.

Jeremy


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## barryfiatman (Jan 3, 2014)

We were considering something similar.
We have a 1980 50cc micro-car called an ERAD, the difference is that it is belt drive using expanding cones etc.
The original engine is 2hp so we cannot go much higher, the top speed is 45kmh. 
The motor which I have chosen from Aliexpress will fit instead of the engine, and a set of 2x100v lithium batteries and control unit etc.
The only problem in France is that I have to take it for Govt examination to see if it is safe.
Yours is a bit more modern.
Barry


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