The electric GMC fully imagined -

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hertfordnc

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Apr 1, 2012
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I have participated in lots of meandering conversations on this so I thought i would put all my silly thoughts in one place.

I think a 300-400 mi range electric GMC is totally doable.

Some of these numbers are just guesses so feel free to challenge them.

A Tesla S weighs 4200 lb with a 1200 lb battery. A GMC weighs around 11,000 lb give or take.


The engine, transmission, exhaust, cooling, tanks, generator and fluids weighs over 2300 lb.

One Tesla motor only weighs 110 lb. So, by my guess, two motors and three batteries would only add 1700lb net after you removed all the ICE stuff.

The drag coefficient of a GMC with a clean roof is .30 - the Tesla S is .24


To do this today would be at least $60,000 in used parts but in a few years when there are a pile of EV parts in junkyards the math is there and the GMC is an excellent candidate.

I used Tesla because the numbers are readily available but Amazon ordered 100,000 Rivian electric trucks. That will also contribute the parts supply.
 
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hertfordnc said:
I have participated in lots of meandering conversations on this so I thought i would put all my silly thoughts in one place.

I think a 300-400 mi range electric GMC is totally doable.

Some of these numbers are just guesses so feel free to challenge them.

A Tesla S weighs 4200 lb with a 1200 lb battery. A GMC weighs around 11,000 lb give or take.


The engine, transmission, exhaust, cooling, tanks, generator and fluids weighs over 2300 lb.

One Tesla motor only weighs 110 lb. So, by my guess, two motors and three batteries would only add 1700lb net after you removed all the ICE stuff.

The drag coefficient of a GMC with a clean roof is .30 - the Tesla S is .24


To do this today would be at least $60,000 in used parts but in a few years when there are a pile of EV parts in junkyards the math is there and the GMC is an excellent candidate.

I used Tesla because the numbers are readily available but Amazon ordered 100,000 Rivian electric trucks. That will also contribute the parts supply.
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Interesting thought experiment, thanks! One question, given that I don't know much about aerodynamics: Can we directly compare the coefficients of drag or do we have to take the GMC's much larger frontal area vs the Tesla into account when determining how much power is required to move it through the air?
 
gerryg said:
Drag force is proportional to frontal area times the drag coefficient. So yes, the drag force on the gmc will be much larger.
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Are you sure it works that way? To my understanding drag coefficient is fixed number- .30 on the GMC, (.316 on a Dodge minivan). A VW bus might have less frontal area but it will have a lot more drag.

So if the power to weight ratio is the same then the vehicle with lower CD will be more efficient.

I don't claim actual knowledge, i work with engineers and today I asked one of them to unpack this exact question and that's what i came away with.
 
The full story is here https://en.wikipedia.org/wiki/Automobile_drag_coefficient

Drag coefficient (Cd) is used to compare shapes. It does not take into account the size of the shape. To compare properly you need to calculate the drag area (Cd x A) to take into account the size. The area is (I think) the silhouette area looking from the front.

Comparing the 2003 Hummer
Cd = 0.57
CdA = 26.5 sq ft

1991/2 Toyota Camry
Cd = 0.33
CdA = 7.57 sq ft

The shape of the Hummer has less then twice the coefficient of the Camry but because the Hummer is so much bigger the drag is more than 3 1/2 times.

The drag area of a Tesla is about 6.2 sq.ft. (approx. 0.24 x 26 sq.ft)

I figure the drag area of the motorhome would be 0.3 x 48 sq.ft or about 14.4 sq.ft
 
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Start with a gutted 23 and you can get the weight down much further (and you can build back the interior lighter). I would go with the Hummer electric motor (not the Tesla). The Hummer weighs about the same as a stripped 230. I feel like the drag coefficient, while important, isn't the huge point of focus that it's being made out to be, unless the goal is really just covering long distances via the highway (which for many with a motorhome, it's not).
 
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It is good to see thoughtful conversation regarding an inevitable GMC-EV. It will happen sooner or later, and most likely in my lifetime. The early ones will have limited mileage and be expensive conversions, but that will change with time and technology.

I have a couple of thoughts and/or questions on the topic.

1.) Brakes? Do you use a vacuum pump and keep the booster? or go with electric brakes?
2.) Power Steering? Electric like tesla?
3.) Electric AC on the road, battery drain.

If the weight issue could be worked out, I would like to keep the Onan and one fuel tank, so that I'm not stranded somewhere with dead batteries. Maybe even use the Onan going down the road to charge the batteries and get a little more range, more like a "hybrid" system. Time will tell.
 
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I would definitely keep the genny and a smaller fuel tank with an electric evMH. Ditching the gas tank and switching to propane only would make sense in this application (propane for generator, stove top, winter heat, and possibly backup H20 heat and back up propane fridge). If I could just snap my fingers and have a solution for my rig right now, I would love to see some sort of diesel hybrid option, but I think the technology for all electric (especially in regard to batteries) will advance so quickly that there would only be a 10-15 year window where the hybrid would make sense.
 
Russell said:
It is good to see thoughtful conversation regarding an inevitable GMC-EV. It will happen sooner or later, and most likely in my lifetime. The early ones will have limited mileage and be expensive conversions, but that will change with time and technology.

I have a couple of thoughts and/or questions on the topic.

1.) Brakes? Do you use a vacuum pump and keep the booster? or go with electric brakes?
2.) Power Steering? Electric like tesla?
3.) Electric AC on the road, battery drain.

If the weight issue could be worked out, I would like to keep the Onan and one fuel tank, so that I'm not stranded somewhere with dead batteries. Maybe even use the Onan going down the road to charge the batteries and get a little more range, more like a "hybrid" system. Time will tell.
Click to expand...
Another factor to bear in mind: Charging time. Prohibitive right now for long distance travel?
 
p.s. I believe the Rivian truck can be flat towed and will "capture" a charge while being towed. This kind of a solution applied to a smaller vehicle used as the MH house battery is a really interesting idea that could be applied in the *now* (as a *sort of* hybrid option).
 
Christo said:
Another factor to bear in mind: Charging time. Prohibitive right now for long distance travel?
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When's the last time you spent less than 20 minutes fueling up (filling tank, cleaning windows, stretching legs, walking dog)? I feel like another 10 minutes isn't that bad. The ev Hummer states a range of 350+ miles. DC fast charging states 60-100 miles per every 10 minutes. Who knows if they are *really* hitting those marks right out of the gate, but I'm betting even if they aren't now, they will be soon.
 
hertfordnc said:
I have participated in lots of meandering conversations on this so I thought i would put all my silly thoughts in one place.

I think a 300-400 mi range electric GMC is totally doable.

Some of these numbers are just guesses so feel free to challenge them.

A Tesla S weighs 4200 lb with a 1200 lb battery. A GMC weighs around 11,000 lb give or take.


The engine, transmission, exhaust, cooling, tanks, generator and fluids weighs over 2300 lb.

One Tesla motor only weighs 110 lb. So, by my guess, two motors and three batteries would only add 1700lb net after you removed all the ICE stuff.

The drag coefficient of a GMC with a clean roof is .30 - the Tesla S is .24


To do this today would be at least $60,000 in used parts but in a few years when there are a pile of EV parts in junkyards the math is there and the GMC is an excellent candidate.

I used Tesla because the numbers are readily available but Amazon ordered 100,000 Rivian electric trucks. That will also contribute the parts supply.
Click to expand...
I saw an article some time back that was talking about the testing of the "new" GMC Motorhome on track and in the wind tunnel. I wish I could call that article up now.
But the JUST that I got from it was how they found that the big brick, the GMC Motorhome actually had Better aerodynamics than the Corvette. It was suggested that these test numbers were quietly filed away because they didn't want it out that the Vette was not the most aerodynamic vehicle on the road and certainly not second to a big Brick like the GMC Motorhome.
-- The other thought is the battery.
We know that the VOLT with its 57 mile range charges on 120v ac for 12 hours
I don't have a number on the tesla or the BOLT but it takes a 240v ac charger to do it.
If the battery is to be increased in size by 3 times, how long is it going to take to charge that battery before you can travel.
If we assume a 300 mile range, that is roughly a 6 hour drive then you will be forced to stop for minimum half a day but assume much longer to recharge the battery banks.
Unless a new battery is developed, it just does not seem possible.
 
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GatsbysCruiser said:
-- The other thought is the battery.
We know that the VOLT with its 57 mile range charges on 120v ac for 12 hours
I don't have a number on the tesla or the BOLT but it takes a 240v ac charger to do it.
If the battery is to be increased in size by 3 times, how long is it going to take to charge that battery before you can travel.
If we assume a 300 mile range, that is roughly a 6 hour drive then you will be forced to stop for minimum half a day but assume much longer to recharge the battery banks.
Unless a new battery is developed, it just does not seem possible.
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How fast you can charge the batteries depends on the battery chemistry, the charger and the available power to operate the charger.

I don't know the specs on Tesla batteries but I am familiar with Lithium Iron Phosphate (liFePO4 or LFP). You can typically charge a LFP at .5C meaning for a 100Ahr battery you can charge it at the rate of 50Amps (approx 750 watts). So a depleted battery will take about 2 hrs to charge. You can charge at higher rates, but your battery life will decrease significantly. Charging at lower rates will maximize the number of charge/discharge cycles. I typically charge my LFP house batteries at .2C (20amps) while my charger is capable of 60Amps (30Amps x 2 batteries).

If you have say 100KwHrs of battery pack and 50A at the campsite then you have 50A x 240V = 12Kw of possible charging power. 100KwHrs / 12Kw = 8.33Hours to discharge a depleted battery. But now you have no power to run your A/C, lights or anything else. So you need to reserve some power for that... say 4Kw. Now you have 8Kw for charging so you need 12.5 hours to charge. But nothing is 100% efficient, nor would (should) you fully deplete your battery. So 12 hours to charge a (say 20% State of Charge (SOC))100Kw battery pack from a 50A/240VAC source seems reasonable.

A charger capable of 12Kw would be a fair size. I Can't see putting one much larger into a GMC.

How far can you go on 80KwHr discharge? I recall somewhere it was calculated that a GMC takes about 25hp to travel at 55mph on level ground with no wind (someone can correct me on this). So at 746 watts/hp x 25 = about 20kw so you can travel for about 4 hours @ 55mph = 220 miles. So that's about the same as my rule of thumb to fill up when my gas tanks hit the 1/2 level = 200 - 250 miles per tank refill. Went we are heading to a destination, we will fill 2 to 3 times per day. When we are just exploring the area, then 200 miles is fine.

So you might want 200KwHr of battery capacity. Full charge when you leave home for a range of ~400 miles the first day. Then get a partial recharge for 200 miles the next day. Then say you stay at a campground for a couple of days and you can get a full recharge again. This is assuming that only a few people have electric RV's so the campground electrical system is not overloaded.

Anyway, that's just my farmboy mechanic with 40 years in electronics way of looking at it. I'm not an engineer nor an expert in anything, so I might be completely wrong.
 
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What I am having a hard time understanding is why people want to put a modern drive train into a fifty year old design. I personally (as a builder of composite boats) think that one could start with a fresh design, keep the TZE parts you like (High Cab and Low Floor and maybe less window area) and do it all out of composite. Ray Frank made the original motorhome that became Travco in 1961 with a fiberglass body on a steel frame. There are better materials and methods available to us now. I personally would consider this but for two small impediments in my case. I couldn't afford to buy the materials I would like to use and my body can't work that long and hard these days.
Matt
 
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Matt Colie said:
What I am having a hard time understanding is why people want to put a modern drive train into a fifty year old design. I personally (as a builder of composite boats) think that one could start with a fresh design, keep the TZE parts you like (High Cab and Low Floor and maybe less window area) and do it all out of composite. Ray Frank made the original motorhome that became Travco in 1961 with a fiberglass body on a steel frame. There are better materials and methods available to us now. I personally would consider this but for two small impediments in my case. I couldn't afford to buy the materials I would like to use and my body can't work that long and hard these days.
Matt
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I think the answer to this one is time, money, and effort. Starting from scratch vs. starting with a rolling frame and light (fiberglass) body are very, very different starting points. And if the body is already relatively aerodynamic and "cool..." why would one want to change it? There was a lot of engineering that went into the body and systems of the GMC that still work very well and would be major time/cost savers in building an EVMH.
 
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