Fuel 2 Electric - Converting the GMC to an EV

[Andreas]

I will have my '76 Eleganza II converted to electric. The way to go will be a renewed Tesla LDU with 455 horsepower instead of the old V8-engine and transmission, combined with 200 kWh LiFePo-Batteries, most in the frame and some in the motorcompartment. Should give a range of 4 hours driving at highway speed.
I am curious if here are other people who have done something similar with their moho and are willing to share experiences. So far i only know of one GMC moho, that has been converted already.

 

[Christo]

I will have my '76 Eleganza II converted to electric. The way to go will be a renewed Tesla LDU with 455 horsepower instead of the old V8-engine and transmission, combined with 200 kWh LiFePo-Batteries, most in the frame and some in the motorcompartment. Should give a range of 4 hours driving at highway speed.
I am curious if here are other people who have done something similar with their moho and are willing to share experiences. So far i only know of one GMC moho, that has been converted already.

Interesting! How did you figure the battery and motor requirements?

 

[Andreas]

Hi Christo, that wasn't too difficult: Most classic car conversions are done this way. Used Tesla motors are easy to get and the LDU from Model S and X is a little bit heavier and stronger built than the newer SDU, which is used in the smaller Models 3 and Y. The Tesla motor can be fitted right between the front axels where the final drive used to be. Only the drive shafts and the motor mounts have to be special crafted.
The size of the battery is planned to be around 200 kWh, because we think the moho will consume around 40-50 kWh per 100 km, which is at least twice as much as an electric car does at highway speed. First we thought about used Tesla or VW LiIon-batteries, but then decided for new LiFePo-batteries. They are much more flexible to install and to manage, and even cheeper. They weight a bit more, but thats no problem because the GMC can carry a lot of load when you have got rid of all the old fossil stuff: engine, trans, cooler, fueltanks, gastank, onan...

 

[billvv]

What happens when climbing I-5 over the 4000' elevation gain to the Siskiyou Summit?

 

[Christo]

This thread talks about needing 60 HP sustained: https://www.gmcmotorhome.org/threads/electric-conversion.70876/

I believe the GMCMH has a frontal area of about 70 square feet, and you're at maybe 9k pounds if you remove all the existing ICE gear (Olds engine/trans is about 1k pounds by itself)

I'm thinking you'll actually need about 400kwh of batteries for 4 hours of range at just 60 mph, which will add about 6k pounds of weight. If that's right, there's a chassis/tire problem, setting aside the significant cost and charging time concerns. Hm.

 

[Andreas]

N

What happens when climbing I-5 over the 4000' elevation gain to the Siskiyou Summit?

Not shure id i get the question right, Bill. Never heard of any ev having problems with climbing or height.
With 455 horsepower from the very robust Tesla motor that will be easy. Of cause the power consumption will get higher, but thats physics, same with fuel.

 

[Andreas]

This thread talks about needing 60 HP sustained: https://www.gmcmotorhome.org/threads/electric-conversion.70876/

I believe the GMCMH has a frontal area of about 70 square feet, and you're at maybe 9k pounds if you remove all the existing ICE gear (Olds engine/trans is about 1k pounds by itself)

I'm thinking you'll actually need about 400kwh of batteries for 4 hours of range at just 60 mph, which will add about 6k pounds of weight. If that's right, there's a chassis/tire problem, setting aside the significant cost and charging time concerns. Hm.

How do you come to that idea, Christo? Half of it is realistic.

 

[Christo]

N

Not shure id i get the question right, Bill. Never heard of any ev having problems with climbing or height.
With 455 horsepower from the very robust Tesla motor that will be easy. Of cause the power consumption will get higher, but thats physics, same with fuel.

And of course, it's more involved than just power consumption. It's also the ability of the batteries to deliver the sustained amperage without overheating.

 

[Andreas]

And of course, it's more involved than just power consumption. It's also the ability of the batteries to deliver the sustained amperage without overheating.

The batteries will of course be temperated - same as usual in other ev's. For example when charging at a supercharger they are cooled to make fast charging possible. I charge my Tesla from 10% to 80% in 15-20 min - just enough time to go pee and have a coffee. The three times bigger batterie in the moho will of course require some additional charging time. But, its a moho, i can cook my own coffee in it and take a nap or go with the dogs.

 

[Christo]

I found an updated coefficient of drag for the GMCMH of .39, which reduces the battery requirements significantly. Looks more like 250 kWh (minimum) based on the following calcs. How does this compare with your assumptions:

Key Parameters:
• Base vehicle weight: 9,000 lbs ≈ 4,082 kg
• Frontal area: 70 square feet ≈ 6.5 m²
• Target range: 240 miles
• Drag coefficient (C_d): 0.39
• Speed: 60 mph (26.8 m/s)
• Tesla LDU efficiency: approximately 85-90%



Battery Capacity for 240-Mile Range:
For 240 miles at 60 mph:
• Time = 240 miles ÷ 60 mph = 4 hours
• Energy needed = 63.1 kW × 4 h ≈ 252.4 kWh

LiFePO4 Battery Configuration (assuming use of 100% capacity which isn't practical in real world)
• Battery weight: 252,400 Wh ÷ 100 Wh/kg ≈ 2,524 kg (5,563 lbs)
• Cell configuration: Approximately 11-12 parallel strings of 280Ah cells
• System voltage: Typically 400-800V to match Tesla LDU requirements

Total Vehicle Weight:
• Base RV weight: 9,000 lbs
• Battery weight: 5,563 lbs
• Total: 14,563 lbs (6,606 kg)

 

[tmsnyder]

I found an updated coefficient of drag for the GMCMH of .39, which reduces the battery requirements significantly. Looks more like 250 kWh (minimum) based on the following calcs. How does this compare with your assumptions:

Key Parameters:
• Base vehicle weight: 9,000 lbs ≈ 4,082 kg
• Frontal area: 70 square feet ≈ 6.5 m²
• Target range: 240 miles
• Drag coefficient (C_d): 0.39
• Speed: 60 mph (26.8 m/s)
• Tesla LDU efficiency: approximately 85-90%

View attachment 18565

Battery Capacity for 240-Mile Range:
For 240 miles at 60 mph:
• Time = 240 miles ÷ 60 mph = 4 hours
• Energy needed = 63.1 kW × 4 h ≈ 252.4 kWh

LiFePO4 Battery Configuration (assuming use of 100% capacity which isn't practical in real world)
• Battery weight: 252,400 Wh ÷ 100 Wh/kg ≈ 2,524 kg (5,563 lbs)
• Cell configuration: Approximately 11-12 parallel strings of 280Ah cells
• System voltage: Typically 400-800V to match Tesla LDU requirements

Total Vehicle Weight:
• Base RV weight: 9,000 lbs
• Battery weight: 5,563 lbs
• Total: 14,563 lbs (6,606 kg)

That C(drag) was measured in a wind tunnel but the model was 'clean' with no bumpers sticking out scooping air, rear view mirrors sticking out, roof pods and A/Cs .

A more realistic Cd would be 0.7

 

[tmsnyder]

This thread talks about needing 60 HP sustained: https://www.gmcmotorhome.org/threads/electric-conversion.70876/

I believe the GMCMH has a frontal area of about 70 square feet, and you're at maybe 9k pounds if you remove all the existing ICE gear (Olds engine/trans is about 1k pounds by itself)

I'm thinking you'll actually need about 400kwh of batteries for 4 hours of range at just 60 mph, which will add about 6k pounds of weight. If that's right, there's a chassis/tire problem, setting aside the significant cost and charging time concerns. Hm.

Based on the fuel consumption of our coaches, I calculated the horsepower required just to cruise down a flat highway at 65 mph was more like 90 HP

 

[tmsnyder]

The batteries will of course be temperated - same as usual in other ev's. For example when charging at a supercharger they are cooled to make fast charging possible. I charge my Tesla from 10% to 80% in 15-20 min - just enough time to go pee and have a coffee. The three times bigger batterie in the moho will of course require some additional charging time. But, its a moho, i can cook my own coffee in it and take a nap or go with the dogs.

Hi Andreas,

Sounds like a great project! I hope you move forward with it (no pun intended!)

Do the calcs, make the assumptions you need to make and build it, this is how progress happens. Maybe some part of it won't work, but this is how we learn.

The fastest cars at the 1/8 track near me are the Teslas, they have some serious power.

Please keep us up to date on your progress.

Todd

 

[Richard RV]

I will have my '76 Eleganza II converted to electric. The way to go will be a renewed Tesla LDU with 455 horsepower instead of the old V8-engine and transmission, combined with 200 kWh LiFePo-Batteries, most in the frame and some in the motorcompartment. Should give a range of 4 hours driving at highway speed.
I am curious if here are other people who have done something similar with their moho and are willing to share experiences. So far i only know of one GMC moho, that has been converted already.

There are people that very conscientiously strive to lighten their GMCs. One 23' was under 9000 pounds and a 26' was just under 10,000. With some effort and expenditure I'd think a GMC EV could have a curb weight pretty close to the OEM GVWR.

The goalposts are constantly moving and there's denser energy storage batteries around the corner. Mercedes is doing some very interesting things.

2027 Mercedes-AMG GT 4-Door Coupe EV Is A 1,153-HP Showcase Of What Electric Performance Cars Can Do - Jalopnik

The new-generation AMG GT 4-Door has axial-flux motors, 600 kW charging, a huge level of customization for driving dynamics, and a whole lot more.

www.jalopnik.com

Axial flux in hub motors, active control everything, ridiculously fast charging time, etc, etc.

It'll be less than $200K and I'd buy one except for 2 things:
1). 0 to 60 mph seems sluggish at 2.0 seconds
2). I'd be dead right around 2.1 seconds.

 

[Christo]

That C(drag) was measured in a wind tunnel but the model was 'clean' with no bumpers sticking out scooping air, rear view mirrors sticking out, roof pods and A/Cs .

A more realistic Cd would be 0.7

The wind tunnel test was .31, so I raised it about 25%. Maybe not enough, but it's certainly more aerodynamic than a typical boxy RV.

 

[Eric S.]

What kind of LiFePo batteries are you thinking of using? If you are thinking standard plastic-case off-the shelf LiFePo's you may have some significant cooling issues, both for driving and for charging. Nissan found out the hard way that air-cooled lithium batteries in the Leaf did not last very long. The Leaf's batteries were encased in metal housings for better heat transfer, but air cooling of these battery modules was simply not sufficient and the batteries suffered serious degradation if fast-charged or run in high-temperature environments. Perhaps you've already considered this, but just suggesting to consider thermal transfer seriously. Also, what is your plan for cooling the motor, and for heating/air conditioning of the cockpit? Power steering? Brake vacuum assist?

 

[Andreas]

I found an updated coefficient of drag for the GMCMH of .39, which reduces the battery requirements significantly. Looks more like 250 kWh (minimum) based on the following calcs. How does this compare with your assumptions:

Key Parameters:
• Base vehicle weight: 9,000 lbs ≈ 4,082 kg
• Frontal area: 70 square feet ≈ 6.5 m²
• Target range: 240 miles
• Drag coefficient (C_d): 0.39
• Speed: 60 mph (26.8 m/s)
• Tesla LDU efficiency: approximately 85-90%

View attachment 18565

Battery Capacity for 240-Mile Range:
For 240 miles at 60 mph:
• Time = 240 miles ÷ 60 mph = 4 hours
• Energy needed = 63.1 kW × 4 h ≈ 252.4 kWh

LiFePO4 Battery Configuration (assuming use of 100% capacity which isn't practical in real world)
• Battery weight: 252,400 Wh ÷ 100 Wh/kg ≈ 2,524 kg (5,563 lbs)
• Cell configuration: Approximately 11-12 parallel strings of 280Ah cells
• System voltage: Typically 400-800V to match Tesla LDU requirements

Total Vehicle Weight:
• Base RV weight: 9,000 lbs
• Battery weight: 5,563 lbs
• Total: 14,563 lbs (6,606 kg)

Hey, Christo, that's a very interesting find! Thank you for that.
I have not calculated in a comparable way, i just asked a lot of ev-conversion experienced people. They all said something around 40 and 50 kW per 100 km (or per hour if driving 60 mph). When i make long trips in my Tesla, for example 2500 km from northern Germany to Greece, i never drive more then 3,5 hours, then make a short pause. Thats how we came to planning with 200 kWh of battery capacity.
And when it really comes out that it consumes more, so what, i just make pause a little earlier. Charging stations can be found nearly everywhere nowerdays. Or drive a little slower - it's a moho classic, not a race car. (Driving slower makes a real big difference even with a very streamlined Tesla. )

There is one very important thing that has improved a lot since the calculation you have found, Christo: the weight of the batteries is much less, we plan with 1000kg only.
Years ago on a vacation trip we took a chance to weigh our moho, it was 4500 kg including all the holyday stuff and 2 irish wolfhounds on board.
So after the conversion it should not be very much heavier, and will still be a lot under its allowed weightcarrying capacity.

 

[Andreas]

Hi Andreas,

Sounds like a great project! I hope you move forward with it (no pun intended!)

Do the calcs, make the assumptions you need to make and build it, this is how progress happens. Maybe some part of it won't work, but this is how we learn.

The fastest cars at the 1/8 track near me are the Teslas, they have some serious power.

Please keep us up to date on your progress.

Todd

I will do so, Todd.
First thing will be installing new brakes - doing the complete disc-brake kit from gmcrvparts, because the original brakes are too weak as you shurely all agree. With a Tesla motor the moho will be much more agile - therefore better brakes are a must.
That i hope to do during this summer. Afterwards i have to drive it 500 km to the company that will do the conversion. They plan to finish the job including achieving road-legality in spring 2027.
It all will take a lot of time - could go quicker if anyone had done this before and could provide ready made parts like battery housings, motor mount a.s.o. DOES ANYONE HERE KNOW SOMEONE?

 

[Andreas]

What kind of LiFePo batteries are you thinking of using? If you are thinking standard plastic-case off-the shelf LiFePo's you may have some significant cooling issues, both for driving and for charging. Nissan found out the hard way that air-cooled lithium batteries in the Leaf did not last very long. The Leaf's batteries were encased in metal housings for better heat transfer, but air cooling of these battery modules was simply not sufficient and the batteries suffered serious degradation if fast-charged or run in high-temperature environments. Perhaps you've already considered this, but just suggesting to consider thermal transfer seriously. Also, what is your plan for cooling the motor, and for heating/air conditioning of the cockpit? Power steering? Brake vacuum assist?

Hey Eric,
since the projekt is just about to start, we have not discussed in detail how exactly the battery (and motor) cooling will be done, but it will be with water like in the other evs out there, and yes, you are right, it must be done. EVs are very efficient, but a little bit of energy will always be lost in form of heat, so a little radiator will be necessary anyway.
The air condition compressor will be exchanged with an electric one, and a vacuum pump comes for brake booster and power steering (and wipers if i keep them original). These are normal parts in electric vehicles.

 

[Keith V]

Why wpuld better brakes be necessary? Wouldnt you mostly be using regenerative braking?