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Discussion Starter #1
I first became aware of EV conversions only last year. I was enthralled by the concept and started my research. That's how I found this fantastic forum.
My first intention was to buy an older Range Rover to convert. With knowledge gained from this forum, I moved quickly from that idea to using my Jeep Grand Cherokee instead. Then to a Dodge Intrepid and finally to my current plan to use a Mercedes S-class (W220).
This new thread will be about the S-class conversion.

Why did I choose the S-class?
We'll, it's big & roomy, It's very aerodynamic (cd of 0.27), it's a RWD & I believe it has enough room for a 50+ Kwh battery pack.
I hope to put the 11-12 inch repurposed forklift motor motor in the transmission tunnel. If the tunnel isn't wide enough, I'll have to cut metal.
The plan is for direct drive to the rear wheels. The rear diff will need to take a new gear and pinion of about 6:1 ratio (stock is 2.86:1 x 1.93 Torque convertor factor).
If the Merc rear diff can't take a gear & pinion of that size, I'll have to replace it with a diff that can.
One of the significant challenges will be sorting out which functions of the ECM to ignore and those which may need to work to keep the car running.
Once again, this is a fantastic forum and I've learned so much here.
I look forward to comments and constructive feedback.
 

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Hi

Why do you want such a high ratio diff?

Forklift motors are good for about 5000 rpm - but you do need a fair amount of volts for that
And that is really for people like me who are stretching things - 4500 rpm would be more "sensible"

a 2.86:1 would be pretty damn good - if you want more torque then put two 11 inch motors in there

I'm using a 4.2:1 diff and I'm hitting 5300 rpm at the end of the 1/8th at 93.5 mph

A 2.86:1 with the same size tyres would be 3600 rpm at 93 mph

If you go 6:1 it would be 7500 rpm at 93 mph and the motor would have exploded!

With a 6:1 diff the "sensible" max speed would be 4500 rpm and 55 mph - I'm using 225/45/17 tyres - yours may be a bit bigger but not by much
 

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Discussion Starter #3
Hi

Why do you want such a high ratio diff?

Forklift motors are good for about 5000 rpm - but you do need a fair amount of volts for that
And that is really for people like me who are stretching things - 4500 rpm would be more "sensible"

a 2.86:1 would be pretty damn good - if you want more torque then put two 11 inch motors in there

I'm using a 4.2:1 diff and I'm hitting 5300 rpm at the end of the 1/8th at 93.5 mph

A 2.86:1 with the same size tyres would be 3600 rpm at 93 mph

If you go 6:1 it would be 7500 rpm at 93 mph and the motor would have exploded!

With a 6:1 diff the "sensible" max speed would be 4500 rpm and 55 mph - I'm using 225/45/17 tyres - yours may be a bit bigger but not by much
Thanks for the input Duncan, much obliged... If I follow your reasoning, I won't have to replace the stock diff and that would be a relief for sure!
My calcs involved taking the ICE rmp at 70mph ( 2400), running it through 5th gear (0.9:1),then through the torque convertor (1.93:1), then through the final drive at 2.86:1. I'll have no gearbox in the conversion. The lift motors' "sensible" rpm on the highway would much higher than the ICE - 4500 or thereabouts, so I thought I'd have to more than match the torque convertor multiplied by the final drive ratio, to get the same speed at the wheels. I hope your wealth of knowledge and practical experience trumps my calculations though, as that will save me a lot of hassle!
Thanks again Duncan,
Greg.
 

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This seems like a really roundabout and awkward way to look at the speeds and gear ratios. Just pick a top road speed, work out the wheel speed (in rpm) for that road speed, pick a corresponding motor speed (again in rpm) and divide the two speeds to get a ratio.

  1. A 2005 (last year of the W220 S-Class) base S430 has 225/55R17 tires (a few % taller than Duncan's), which turn 780 revolutions per mile. So if your top speed is to be 70 mph, that's 910 rpm.
  2. Take Duncan's advice and plan on 4500 rpm at that speed.
  3. 4500/910 = 4.95
Of course you won't find exactly a 4.95:1 final drive ratio, and probably won't find anything more than about 4:1. Apparently in 2005 an S430 came with 2.65:1 or 3.07:1 ratios, but some other Mercedes model using the same differential probably came with a shorter (higher reduction number) ratio. You could plan on the 3.07:1, and work out likely performance with that... realizing at a 70 mph it will only be turning 2800 rpm, and the maximum torque to the wheels will only be three times the maximum motor output torque.
 

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The thing to remember is that in the forklift the motor will be doing about 1400 rpm max

If you want to go faster you need to bump the voltage up - 4500 rpm is over three times the "normal rpm" - and will need over three times the voltage - more than that if you are going to increase the current as well - so for an 11 inch 48 volt motor you will need 200 volts +

An "S Class" is a big machine a LOT larger than my device
But you do have a lot of space in the transmission tunnel

I would be thinking about leaving the current diff but installing two 11 inch motors in line in the tunnel

That would mean that you could supply each motor with 150v and 500 amps -

Here (NZ) the motors go for $200 each and the Paul & Sabrina controller kits are about $600

Or you could go for both motors in series and use one of the P & S high voltage controllers with a 300+v battery

Using two motors would reduce the duty cycle
 

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Discussion Starter #6
This seems like a really roundabout and awkward way to look at the speeds and gear ratios. Just pick a top road speed, work out the wheel speed (in rpm) for that road speed, pick a corresponding motor speed (again in rpm) and divide the two speeds to get a ratio.

  1. A 2005 (last year of the W220 S-Class) base S430 has 225/55R17 tires (a few % taller than Duncan's), which turn 780 revolutions per mile. So if your top speed is to be 70 mph, that's 910 rpm.
  2. Take Duncan's advice and plan on 4500 rpm at that speed.
  3. 4500/910 = 4.95
Of course you won't find a 4.95:1 final drive ratio. Apparently 2005 an S430 came with 2.65:1 or 3.07:1 ratios, but some other Mercedes model using the same differential probably came with a shorter (higher reduction number) ratio. You could plan on the 3.07:1, and work out likely performance with that... realizing at a 70 mph it will only be turning 2800 rpm, and the maximum torque to the wheels will only be three times the maximum motor output torque.
I like your method better than mine Brian... 😊
Using your calcs, a 4.95:1 final drive would be ideal as you suggested. Although Mercedes may not have a diff with that ratio, there are alot of gear & pinion kits in that range. I may have to get the carrier from another make, like a Jeep or Dodge Charger, but I think it's workable.
 

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Discussion Starter #7
The thing to remember is that in the forklift the motor will be doing about 1400 rpm max

If you want to go faster you need to bump the voltage up - 4500 rpm is over three times the "normal rpm" - and will need over three times the voltage - more than that if you are going to increase the current as well - so for an 11 inch 48 volt motor you will need 200 volts +

An "S Class" is a big machine a LOT larger than my device
But you do have a lot of space in the transmission tunnel

I would be thinking about leaving the current diff but installing two 11 inch motors in line in the tunnel

That would mean that you could supply each motor with 150v and 500 amps -

Here (NZ) the motors go for $200 each and the Paul & Sabrina controller kits are about $600

Or you could go for both motors in series and use one of the P & S high voltage controllers with a 300+v battery

Using two motors would reduce the duty cycle
Wish I could get one of those motors from NZ... Here in the States, used 12 inch motors are going for $500-$750 online. A refurbished one with a warranty sells for up to $1,200.
While on that tack, where can I order a Paul & Sabrina kit? My recent Internet searches give me the impression Paul doesn't make them any more.
 

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used 12 inch motors are going for $500-$750 online.
Anyone who's bothering to sell them, will want that much for them.

But you're approaching the problem wrong.

Just show up at a forklift repair/salvage place, and ask for a traction motor or if you could be allowed to pull a traction motor from a lift they're scrapping.

Usually it's not even worth their time to pull the motor off. They just send the whole carcass to a scrapyard.

Much of forklift repair is the yard buying junked lifts for their batteries, or trying to make 1 functional lift out of 2 dead ones. They might pull the mast and the safety features/lights (usually end up getting smashed, meaning the lift won't pass safety). Then they throw the other 10,000 pounds of it in the scrap metal bin.

The motor is almost never what fails.

A forklift is an essential piece of equipment. No one's going to buy a new motor for one, they'll just buy a working, used lift. No one's going to pay for labor time to swap in a used motor. Their warehouse downtime is far too costly to them to risk it.

So... most yards probably won't even bother pulling the motors off, no point in stocking them.

Just show up and tell them you're working on a fun science project, and ask if they have any old motors you could have if you did the work yourself (it's about an hour to pull a motor). If they're picky they may want you to pay scrap value (once it's out, it's worth more than scrap steel since it has copper in it). No more than $200.

I've picked up 7 in various sizes and I've paid $0 for the whole batch. "Let me know when you're done with everything you want on that, it's going in the metal bin after" is the extent of my constraints.
 

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Discussion Starter #9
used 12 inch motors are going for $500-$750 online.
Anyone who's bothering to sell them, will want that much for them.

But you're approaching the problem wrong.

Just show up at a forklift repair/salvage place, and ask for a traction motor or if you could be allowed to pull a traction motor from a lift they're scrapping.

Usually it's not even worth their time to pull the motor off. They just send the whole carcass to a scrapyard.
Thanks so much Matt. Duncan has similar views and it seems to work for him in New Zealand.
This looks like the best way forward for me to get a motor at reasonable cost.
 

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Wish I could get one of those motors from NZ... Here in the States, used 12 inch motors are going for $500-$750 online. A refurbished one with a warranty sells for up to $1,200.
While on that tack, where can I order a Paul & Sabrina kit? My recent Internet searches give me the impression Paul doesn't make them any more.

http://www.pandspowerelectronics.com/


Yes, he is making them. I just bought 2 of them
 

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Discussion Starter #11
Wish I could get one of those motors from NZ... Here in the States, used 12 inch motors are going for $500-$750 online. A refurbished one with a warranty sells for up to $1,200.
While on that tack, where can I order a Paul & Sabrina kit? My recent Internet searches give me the impression Paul doesn't make them any more.

http://www.pandspowerelectronics.com/


Yes, he is making them. I just bought 2 of them
So sorry, I missed your post yesterday.
I checked Paul and Sabrinas' website and this is the message currently..
"P&S is Moving! We can take no orders until April 30th"
No problems though, I can wait.

How hard is it to build a 750 - 1000A/ 144V controller? I can solder, but I believe there's some machining of metal involved. Was it an easy job to build the two you bought, or did you buy them fully assembled?
Thanks!
 
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