[funkyronster]

Hi guys

I am willing to do my research and am not looking to be lazy, but a few opinions from experienced folk would help me greatly.

I am an active member of a group of classic motorhome (RV) enthusiasts in the UK. These vans are Mercedes based 1985 to 1995, rear wheel drive. Classic Mercedes 5 cylinder diesels producing 95hp. The vans weigh between 3.5 and 4.5 tons fully loaded. I estimate that the engine and gearbox weighs about a ton - maybe a bit less, and without the engine and gearbox, there would be quite a decent size void up front.

There has been some talk for a while now about the feasibility of conversion to EV. The writing is on the wall over here for old polluting diesels - we are already banned from London and most EU cities.

In terms of range around 50 miles would be OK, obviously the more the merrier. Campsites over here generally have 6, 10 or 12 amp 240v supplies, plus there are the normal recharge points starting to appear for production EVs - Nissan leaf etc ...

There would also be space for some sort of gasoline generator, and solar panels on the roof, but I doubt you could get more than about 500w of solar, assuming the sun shines. However there are plenty of retired folk who would just stay in one place until they had a charge to move on! The requirements for an RV would be quite a bit less than those for a commercial delivery vehicle with a defined duty cycle. With diesel costing $6 a gallon over here, present costs are around 40c a mile.

So far my basic thinking has led me to think that the engine and gearbox could be removed and replaced by a DC traction motor directly connected to the propshaft. I have read that these motors will also generate power through regenerative braking. But then there is the matter of the vehicle's other systems - in particular the servo systems for the brakes and steering, which are driven by the fanbelt. Could these be retained and driven by a modified system using power take off, or even by a motor with a through drive shaft to the front as well as to the rear propshaft?

The rest of these vehicles are pretty straightforward - there are no electronic sensors or ecus. Controls are just the basics - 3 pedals, a wheel and the stick.

I have a reasonable grasp of the technology involved, but where I am completely clueless is the area of cost. I know prices are coming down as the technology become more mainstream, but I still have no idea on the cost per kw, the motors, and the ancillary systems required to do such a conversion.

I believe I have the contacts and access to engineering facilities to do most of the work as a DIY project. My family business gives me access to engineering facilities, including laser cutting and metal fabrication.

Like I said - I am not looking for a free blueprint - but a few ideas on the costs of the major components would be a great help to inform my thinking.

Thanks guys

Ron

 

[Kevin Sharpe]

Like I said - I am not looking for a free blueprint - but a few ideas on the costs of the major components would be a great help to inform my thinking.

Come and talk to Anne from New Electric (here) at the Fully Charged Live Show in June (here). Anne is working on a series of vehicles very similar to what you describe

 

[Duncan]

Hi Ron

How much do you want to spend?
How fast do you want to go?

I would be thinking about stuffing a Leaf motor/transmission unit in the back and another one in the front
You may get away with just one - but two would give more power
The two Leaf battery packs would give a big vehicle like that about 80 miles range

So two crashed Leafs to get you started

You could also look at Tesla - or any of the current production EV's as a source of parts

Another way would be to use the old Forklift motors - I use one in my car
I would probably use three of them bolted together to make a long skinny cylindrical motor inside the transmission tunnel - possibly four with a short propshaft to the rear diff
Still use Leaf or Tesla batteries

 

[MattsAwesomeStuff]

diesels producing 95hp. The vans weigh between 3.5 and 4.5 tons fully loaded.

Dat power:weight ratio...

I estimate that the engine and gearbox weighs about a ton - maybe a bit less, and without the engine and gearbox, there would be quite a decent size void up front.

Roughly-speaking, a traction motor from a forklift is going to be around 200lbs, and you can probably hold it to 95hp just fine with some air cooling.

The battery pack on a Tesla is around 1000lbs for 80kwh-ish.
The battery pack on a Leaf is around 480lbs for 24kwh-ish.

That includes all the wiring, frame, etc stuff around the pack which is probably 1/3 to 1/2 of the weight.

A motorhome is probably going to use... maybe 1000watt-hours per mile? (3x what a small car uses? Is that about right for fuel efficiency? 10-15 mpg? It should be comparable).

So to get 50 miles of range at highway speed you're going to need a pack that's around 1000 lbs ballpark probably. Keep it under 45 miles an hour, you'd double your range.

Campsites over here generally have 6, 10 or 12 amp 240v supplies

240v * 12 amps = 2880 watts. Your pack will be ~55kwh for the range you want, so, that would take 19 hours to charge from empty, flat out.

So far my basic thinking has led me to think that the engine and gearbox could be removed and replaced by a DC traction motor directly connected to the propshaft.

Because your vehicle is 8000 lbs, and only came with a 95hp motor... I'm a bit scared of it's inability to climb a hill. With a DC traction motor you'll get all your torque right from zero RPM... but to hold it at low revs and high power loads for long periods of time, it won't survive. You're going to need a gearbox in there I think, to give it a fighting chance on hills.

Then again... the tranny is probably so heavy that you could just throw a second electric motor on there instead perhaps.

I have read that these motors will also generate power through regenerative braking.

Incorrect. DC Traction motors do not regen.

The good news is that regen is almost worthless. It's not magical energy you make, it's only energy wasted from stopping. Since you're driving a brick, any time you want to stop, just letting off the pedal is going to bring you to a stop.

If you're in an area with lots of long (multi-mile-long) hill descents, maybe I'd say get a motor that can regen (a 3phase AC motor or "Brushless DC motor", same thing).

Generally people have this perception that regen is incredible but it's single-digit improvement in most cases.

But then there is the matter of the vehicle's other systems - in particular the servo systems for the brakes and steering, which are driven by the fanbelt. Could these be retained and driven by a modified system using power take off, or even by a motor with a through drive shaft to the front as well as to the rear propshaft?

They certainly exist and yes. No reason you couldn't. It would make for less modification.

I have a reasonable grasp of the technology involved, but where I am completely clueless is the area of cost. I know prices are coming down as the technology become more mainstream, but I still have no idea on the cost per kw, the motors, and the ancillary systems required to do such a conversion.

DC Traction motors from forklifts are generally available for Free-$200 depending on how purdy your dress is.

If you want an AC motor that can do regen, low-mid single-digit thousands for an OEM salvage.

Batteries are expensive-ish, but people find deals all the time. There's lots of confusion in the market, some scrappers don't know what to do with them, others do. You might pay $600, you might pay $10,000. But, generally somewhere in there, single-digit thousands for the battery pack.

Your controller you could build yourself for $600, or buy something in the $1500 range.

A charger you could build yourself for free or pay, I dunno, $100-1000 for.

You'll need cabling (a couple hundred perhaps) and contactors (a couple hundred more). Misc bits anywhere from free to a few hundred extra depending on your scrounging.


The big-ish 3 are usually Motor, Battery, Controller. Everything else is floor sweepings.

 

[brian_]

Medium-duty trucks are actually a decent target for electrification, because there is usually space to mount batteries (but perhaps not in an RV, which uses under-floor space for tanks and other services), because fuel consumption is high (so there is motivation to convert) and because performance expectations are usually moderate. That means that many thousands of electric trucks and buses of this size have been built (normally based on vehicles that are usually sold with a diesel engine) and so motors and other hardware are available.

Currently another forum member is discussing a motor and gearbox unit which could be suitable for this size of vehicle: BAE HybriDrive drive unit, large induction motor with planetary gearbox... Opinions?

In a recent thread - RV Project - suitable hardware was discussed. This was about a series hybrid, but as far as the motor and controller are concerned that's the same as straight battery-electric. Note that in that discussion existing production motors for medium-duty trucks were dismissed as unavailable... but they certainly exist and if you can find one (used), you have a suitable motor.

The main challenge, as discussed in other recent RV EV threads, is that electric vehicles are best suited to service in which they return to a charging station at the end of each day... and for many RV users, that is the exact opposite of how they travel.

 

[brian_]

Eliminate original transmission?

So far my basic thinking has led me to think that the engine and gearbox could be removed and replaced by a DC traction motor directly connected to the propshaft.

That leaves the final drive gearing (ring and pinion at the differential) as the only reduction gearing. For a large DC motor which is suitable only for relatively low rotational speed, this can work. If you use an motor that can run productively at 10,000 rpm (as in almost any modern EV), you need an additional stage of reduction gearing to get the full capability of the motor. The BAE HybriDrive unit which I mentioned in the previous post is a huge thing, and still includes a reduction gearset... but it is an induction motor, not a brushed DC motor.

 

[brian_]

Driving accessories

But then there is the matter of the vehicle's other systems - in particular the servo systems for the brakes and steering, which are driven by the fanbelt. Could these be retained and driven by a modified system using power take off, or even by a motor with a through drive shaft to the front as well as to the rear propshaft?

I don't know why so many people want to drive these accessories from the traction motor, and thus have no accessory power when stopped (that should be fun for the steering boost when parking) and force the accessory systems to vary speed in proportion to road speed. No production EV does this - they use separate electric motors to drive each accessory when required and at a suitable speed. Even the forklifts that people get their motors from for EV conversion projects use one motor (or two) to drive the wheels and a separate motor to drive the hydraulic pump... and maybe another one for steering.

The currently practical method to electrically power steering in a custom installation is an inline unit which installs in the steering column, although it is also reasonable to use an electrically-driven pump with the existing hydraulic power steering (using a pump from one of the many non-electric production cars which were built with electro-hydraulic power steering).

 

[brian_]

Which Mercedes van

I am an active member of a group of classic motorhome (RV) enthusiasts in the UK. These vans are Mercedes based 1985 to 1995, rear wheel drive. Classic Mercedes 5 cylinder diesels producing 95hp. The vans weigh between 3.5 and 4.5 tons fully loaded.

Just so I can picture this better, are we talking about Mercedes TN/T1 vans? The 95 hp 5-cylinder would be the top of the engine range for those, the top of the GVWR range matches, and in a quick search they seem to be common for caravans. There is also the larger second-generation T2 for the same period, and they seem to have been used for caravans as well.

We never got these vans in North America - the first Mercedes vans we saw were the first-generation Sprinters, after they had been available in Europe for a few years.

 

[brian_]

Range

The two Leaf battery packs would give a big vehicle like that about 800 miles range

I'm guessing that this is a typo, and was supposed to be 80 (eighty, not eight hundred) miles range for two Leaf packs at 24 kWh each. That would allow 600 Wh/mile, which is probably optimistic but roughly plausible.

 

[brian_]

fuel consumption

Is that about right for fuel efficiency? 10-15 mpg?

Yes, I think so...

With diesel costing $6 a gallon over here, present costs are around 40c a mile.

This implies 15 miles per gallon (presumably an imperial gallon, so 12.5 miles per US gallon).

Pretty good by our standards for a motorhome, but these are Class B or narrow-body Class C, not our barn-door Class C units, and engines are small. I suspect that highway driving speeds are pretty low, too.

 

[brian_]

two motors?

I would be thinking about stuffing a Leaf motor/transmission unit in the back and another one in the front

• With a live beam axle rear, the motor for the rear would at most be half-way back in the wheelbase, at the front of the final section of propeller shaft.
• A motor for the front wheels would be interesting, as it would require conversion of the front hubs and suspension for a driven front axle. This has been done as an aftermarket conversion, apparently using G-Wagen components.

Two motors is likely a good idea if using motors from electric cars; although a Leaf motor is rated by Nissan at 80 kW (107 hp), sustained operation at that level might not be reliable. If you have two motors anyway 4WD would be nice, but whether it is worth the conversion is not clear.

 

[MattsAwesomeStuff]

Brian - Why did you reply to the same thread back to back with 7 different posts rather than compose them all into one message?


Do you know you can quote whatever section you want just by adding


(quote) and then (/quote)? (In square brackets instead of round).

 

[brian_]

Brian - Why did you reply to the same thread back to back with 7 different posts rather than compose them all into one message?

I've done that (often, including post #10 of this thread) but the result can be quite long, and another member often responds by quoting the entire original post, losing any useful context. Keeping each post to a reasonably narrow range of subject material makes both the post and responses much more readable.

There is no quota or limit for the number of posts, so reducing the number of posts has no inherent benefit.

Think of an in-person conversation - do you save up everything you know about a subject then stream it all out in one uninterrupted statement, or do you have a back-and-forth exchange?

 

[funkyronster]

Dat power:weight ratio...


Because your vehicle is 8000 lbs, and only came with a 95hp motor... I'm a bit scared of it's inability to climb a hill.

Matt, big thanks for taking the time to reply - lots of food for thought there.

Yes these vans are famously underpowered - down to 10 to 20 mph on big hills, with a line of angry traffic behind! However on the flat or mild grades around 45 to 50 mph is fine on the open road.

 

[funkyronster]

Brian thank you very much for all the info.

Yes we are talking the Merc 5 cylinder T1/TN.

There are 2 reasons to pursue the possibility of EV - the first is emissions regulation, the second is running cost. I get 15mpg, average, UK gallon. Modern vans with ECU engines are returning double that, with lower emissions. I have been actively pursuing research to see whether it is possible to re-engine the van, but that is another subject!

 

[funkyronster]

Re auxilliary systems - yes, face palm moment, a diesel engine ticks over at rest, an electric motor doesn't!

Am I correct in assuming that in the EV world, clutches and traditional gearboxes are a thing of the past? You can't just replace a piston engine with an electric motor and use the existing gearbox for hills etc ...

 

[Emyr]

Re auxilliary systems - yes, face palm moment, a diesel engine ticks over at rest, an electric motor doesn't!

Am I correct in assuming that in the EV world, clutches and traditional gearboxes are a thing of the past? You can't just replace a piston engine with an electric motor and use the existing gearbox for hills etc ...

You can, but in a car conversion the standard clutch may not tolerate the torque for very long and if your electric powertrain can deliver enough torque at low speeds and also not reach its rev limit before cruising speed, you can lose the gearbox and save weight (and potentially use the gearbox location for the motor, leaving a motor's worth of extra free space under the bonnet).

 

[MattsAwesomeStuff]

and another member often responds by quoting the entire original post, losing any useful context.

Ahh, I haven't seen much of that, but if other forum-goers are poor at contexual quoting, yeah.

Think of an in-person conversation - do you save up everything you know about a subject then stream it all out in one uninterrupted statement, or do you have a back-and-forth exchange?

I see your point, and no I don't do that in conversation, but it's not a conversation. In conversation if you raise 5 points, I have to remember it in my head. In text I don't have to remember it, I can refer back to it. So in a forum I tailor my replies to this medium, not conversation.

Likewise, in conversation, do you make one statement, turn your back, end the conversation, walk away, approach the group talking a few minutes later and give another statement, turn your back, end the conversation, walk away, etc 5 times? Of course not. There wasn't a back and forth, just 5 isolated statements in a row. Just feels weird is all. Once upon a time forum etiquette discouraged this and it was considered poor form, but I think that was more to avoid repeated "bumping" of a thread to the top and to avoid padding your post count which, once upon a time was "prestigious" to have high post counts.

I dunno, not criticizing really, I just haven't really seen anyone else act that way and was curious why you chose to be different.

 

[brian_]

transmission considerations

Re auxilliary systems - yes, face palm moment, a diesel engine ticks over at rest, an electric motor doesn't!

Some people have actually used torque-converter automatics so the motor will turn at idle... a solution which made some sense long ago, but not now.

Am I correct in assuming that in the EV world, clutches and traditional gearboxes are a thing of the past? You can't just replace a piston engine with an electric motor and use the existing gearbox for hills etc ...

While production EVs are almost all single-speed (so no shifting, and no clutch), you can use the existing transmission and many conversions do... especially those using brushed DC motors which have a narrow powerband compared to high-voltage AC motors.

If you do retain a multi-speed transmission and expect to shift while moving, you then have the choice of using a clutch or not. That can be an extended discussion, which can be left until you know what your approach is for the transmission.

Yes these vans are famously underpowered - down to 10 to 20 mph on big hills, with a line of angry traffic behind! However on the flat or mild grades around 45 to 50 mph is fine on the open road.

This is a reason to retain at least a two-speed transmission, so that the motor can run fast enough for high power at sustained low speeds while climbing grades. If you use a single-speed configuration, you need to make sure that the gearing is tall enough (low enough reduction ratio) that the motor doesn't run too fast on a flat highway at 50 mph, yet low enough (high enough reduction ratio) that it can produce enough power to accelerate and climb grades from low speed.

A high-voltage AC motor can typically produce its full rated power over about a 4:1 ratio of speeds - you can choose whatever ratio makes that 13 to 50 mph, and everything is good.

This is much less of a concern for a typical electric car, which doesn't need the full motor power at low speed (because it would just spin tires), and doesn't need much of its potential power just to maintain speed - peak power is high compared to vehicle mass and is only used for short bursts of acceleration.

Some people seem fixated on that idea that electric motors produce high torque a low speed. Torque at the motor shaft is not enough: the force to move the vehicle is the product of motor torque and gear ratio, so if you have more reduction gearing you have more drive force, but that limits how fast vehicle can run without the motor going too fast (or just too fast for peak power).

 

[Kevin Sharpe]

Am I correct in assuming that in the EV world, clutches and traditional gearboxes are a thing of the past?

A lot depends on your skill set and the vehicle you are converting

I'd suggest you take a look at the BMW 840CI that Damien has converted several times.

The first successful conversion of this car used a Siemens IPV5135 motor (here), BMW 6 speed manual gearbox, and no clutch. I mention this because the Siemens motor was also used historically in the Ford Transit Connect Van (here), with a single speed Borg Warner Gearbox (here), and is being used in several commercial van conversions

Damien is currently converting the car to use a Tesla Drivetrain with single speed gearbox (here).

This video gives you some background on the Siemens version;