EREV - A Horsepower Math Problem?

[chriserx]

We don't know exactly how they arrived at that EPA standard rating, such as the SPEED of the vehicle, or the TERRAIN, or the TEMPS, or the WIND, but it most likely certainly would NOT include TOWING of any sort, or any additional weight in the truck, such as 5 passengers, etc.

Unless I'm misinterpreting, the EPA test cycle is known.

https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-testing

https://www.ecfr.gov/current/title-40/chapter-I/subchapter-Q/part-600/subpart-B/section-600.116-12

and let's assume the battery pack is rated at an EPA 350 miles range(just as an example)

I realize you stress 'as an example', but did you sanity check this? My BEV L doesn't even get close to this.

if the Generator engine needs to then produce that same kWh of power, over that same 6.37 hours, it will need to output 240v @ ________ the WHOLE time.

It would more likely be at the pack voltage and not the L2 voltage, but the answer is 22 kw, or using your setup 91.7A

But I agree with your basic premise, EPA test cycles are decent for gas vehicles but way too optimistic on EVs. I personally estimate a usable pack size of 50 kwh (2 hours at 55 plus change) and a generator output of 100-250 kw continuous. 100 if they go with efficiency and 250 for high performance applications

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[b.go]

It's going to weigh 9000 lbs.

 

[hturnerfamily]

"I realize you stress 'as an example', but did you sanity check this? My BEV L doesn't even get close to this."
Exactly - I was just trying to simplify the 'math' using an example where 1/2 the miles are from the battery, and the other 1/2 from the generator/engine... some EV's do, though...

"It would more likely be at the pack voltage and not the L2 voltage, but the answer is 22 kw, or using your setup 91.7A"
I'm trying to wrap my brain around some type of 400+volt generator... give me some examples of some, especially something that would fit in the frunk area.

"But I agree with your basic premise, EPA test cycles are decent for gas vehicles but way too optimistic on EVs. I personally estimate a usable pack size of 50 kwh (2 hours at 55 plus change) and a generator output of 100-250 kw continuous. 100 if they go with efficiency and 250 for high performance applications"
Why would you assume such a much smaller size of battery pack, especially one on an EV Truck?... this would seem to defeat the whole purpose of the platform.
I would like to see, too, some examples of some 100-250kw continuous Generators... it seems like a very tall order for a vehicle.

RAM says that they are using the 3.6L Pentastar® V6 engine with a liquid-cooled 92-kilowatt-hour battery pack paired with a 130-kilowatt generator.

 

[mr.Magoo]

and a generator output of 100-250 kw continuous. 100 if they go with efficiency and 250 for high performance applications

So something like this ?

 

[P-38]

The engine won't have any mechanical connection to the wheels (some will argue that cables are mechanical, just because this is the internet, but I mean driveshaft, etc.).

Well you see...the engine sits on motor mounts which attach to the frame and the frame is attached to the wheels thru various parts so there 100% is a mechanical connection...

 

[Lytning]

I honestly don’t understand the “importance” of how the ICE is “connected” to the wheels. The ICE is physically connected to the generator, and is the only source of power to drive the generator. Whether the generator output flows through the HV battery, or somehow bypasses the HV battery, when the HV battery is at its minimum allowable SOC, the ICE-driven generator will be the only source of power to the wheels. And that is why the size of the ICE and generator matter so much.

 

[Newton]

Plenty of pure battery EVs get more than 350 miles of range, including the Silverado (492) and the Lucid (512). It won't be too long before that is the range that we all expect - I was super happy that my 2019 e-Golf got a rating of 120 miles which is now pathetic.

Voltage is not the issue for a generator, a Van de Graaff generator is a simple mechanical device that can generate thousands of volts at a very low current. The issue is the kW rating, and the electric motors that drive trucks can consume 500 kW in larger vehicles such as the Silverado - and you usually have two of them. If you want a generator that can do this for any length of time, it has to be a large block diesel with a lot of torque at the low end. In addition, the alternator that converts mechanical to electrical energy has to be very large with a bunch of copper in the windings and lots of metal to dissipate the heat.

So that is the technical challenge that you have to overcome in an EREV. If you had a pure diesel electric (no battery) such as a train the generator would have to be impractically large for a light truck. In any case, a diesel would probably be at least as expensive as simply adding batteries, but the cheaper gasoline engines are not really suited for large generators - they die quickly. Charging the batteries with a lower power generator while running doesn't really help the user because you will still eventually run out and have to go to the dreaded fast charger. In the mind of the scared EV novice, running out after 500 miles is just the same as running out after 80 miles.

The only hint I see of this future is Fords recently released EREV Bronco in China which apparently solves the problem by simply having poor performance when it is running on generator-only. It feels a little deceptive to talk about a "758 mile range" when many of those miles have much less performance than when the battery is running. I do not know how bad it is, but someone who is used to driving 85 will be pretty unhappy once their top speed is limited to 50 until they go to the dreaded fast charger.

Obviously the engineers will try to do something better than that but they run into a fundamental problem - converting mechanical energy to electrical energy and then back to mechanical energy is going to be less efficient than the already inefficient mechanical ICE arrangement. (One real design issue for generators is heat dissipation in the alternator - and that heat represents energy loss.) If you are limited to the same size of engine that the ICE truck has, you are going to have less power than the equivalent ICE when you are in generator mode. If the solution is to have two levels of performance, I do not see how this satisfies the truck user. You don't want to lose power after you have driven your trailer 100 miles to the mountains.

 

[Firn]

I honestly don’t understand the “importance” of how the ICE is “connected” to the wheels. The ICE is physically connected to the generator, and is the only source of power to drive the generator. Whether the generator output flows through the HV battery, or somehow bypasses the HV battery, when the HV battery is at its minimum allowable SOC, the ICE-driven generator will be the only source of power to the wheels. And that is why the size of the ICE and generator matter so much.

Because you dont have to run the battery to minimum SOC. Thats just computer logic to balance generstor output and battery output. Ultimately though the battery HAS to be available, the demand placed on the system is highly variable and the battery provides that variation.

No reason that at 50% SOC the generstor kicks on full time, and at 25% SOC speed and acceleratiin are limited. Or 75% and 50%. After that its just giving the drivers some settings to bias the system one way or another.

 

[Newton]

In the end, I think that the EREV is a psychological (and political) solution rather than an engineering one. I have met people in California who are as surprised that I'm coming from Canada in an EV as if I told them that I had walked. They don't know that compared to my EV6 the Lightning has pathetic range and a glacial charging rate, but it is more comfortable so we take it on long trips. These are the people that Ford is halfheartedly trying to convert, and I'm kind of worried that they will have a worse experience than those of use with pure EVs. That may be the point, though...

 

[Newton]

Because you dont have to run the battery to minimum SOC. Thats just computer logic to balance generstor output and battery output. Ultimately though the battery HAS to be available, the demand placed on the system is highly variable and the battery provides that variation.

No reason that at 50% SOC the generstor kicks on full time, and at 25% SOC speed and acceleratiin are limited. Or 75% and 50%. After that its just giving the drivers some settings to bias the system one way or another.

I agree that if you want any kind of decent performance the battery has to be available, but I'm not sure that is what happens.

If we want to speculate about these systems we need to know the output of the generator in kW, and we don't know it for either of the two EREV truck systems that are in or close to production. You cannot know this from the HP rating of the gas engine, as I have said often.

So, consider this to be wild speculation based on some knowledge. I believe that the Ramcharger is a 30kW system based on some information and speculation. In one report, I read that they can send 30kW to a house in an emergency. The Pentastar V6 has a displacement of 3.7L which would be too small for a 50kW Diesel generator (4.5L for this 50kW) but about right for approximately a 30kW generator. I know that I am comparing different technologies but a diesel engine will always be capable of more torque than a similar displacement gasoline.

I also looked at the dimensions of the Ford Ecoboost V6 which I think is the largest engine that fits in the F-150 compared to the dimensions of the diesel generators and again, roughly 30kW is all that I think can fit. This is of course very speculative and rough but I'd say that 30kW is in the ballpark and even trying to get that much from a gasoline engine that is specifically designed to be light is ... bold.

If we use 30kW as a benchmark then we can go even further out on the speculative limb to see what the managers are thinking while the engineers cringe. The Lightning is rated at about 2.6 mi/kWh from the EPA (Lariat 320mi/131kWh). At that rate, one hour of driving will generate a (absolute maximum) of 78 miles of charge so if you keep it under 80 you can drive as much as you have gas in the tank + the electric range.

Unfortunately it is not that simple, beginning with the fact that I rarely see numbers that high and certainly not when towing. Additionally in the heavy towing cases that the EREV is supposed to solve, the battery will be hot which limits how much charging you can do.

The really hard problem to solve is that 30kW is not going to drive the electric motors very well, and while it is driving the motors it is not charging the battery. So once the battery is down it stays down until you fast charge. The assumption when they say things like "700 mile combined range" is that you can just go to a gas station and fill up - but that is not true. You will have to go to both a gas station and a charger for the next leg of your 1400 mile trip.

To make this work as a driver, I think you are going to have to be very aware of your current usage, expected usage, and plan on turning on the 'charger' much earlier than you think - probably at the beginning of your trip. For customers who already have difficulty with route planning ("just use ABRP!" we say so often) this is going to be even more off-putting.

The really big question for me is "how well does it drive with the battery completely empty?" Can I tow my (imaginary) big rig up Washington Pass, and at what speed?

 

[hturnerfamily]

yes, those are agreed points that most of us have little to go on, at least yet...

from the very beginning, an advertised '700 miles Combined range' can be a little misleading, at least to those unaware of all the REAL elements to this idea. I doubt that anyone assuming that you can then drive 80+mph on the Interstates for the whole 700 miles is going to be pleased with the 'real' outcome... they'll be stopping to fast charge about 200 miles in. They'll have seen the battery SOC dropping like a rock, and yet the Generator is, yes, running. Still, it won't look good, and range anxiety will still be a thing.

You can get range anxiety at 50 miles in, and you can just as easily get it at 300 miles in.

A Generator that could possibly drive the vehicle at the same speeds and for the same miles might as well be your ONLY power source, since, well, WHY then would you need a battery??

The Generator's ONLY job is to recharge the battery pack. It is NOT to drive the truck.

 

[chriserx]

A Generator that could possibly drive the vehicle at the same speeds and for the same miles might as well be your ONLY power source, since, well, WHY then would you need a battery??

To run HVAC at a stop, to store regen braking, to store 'excess' power generated, to enhance efficiency by running the generator at it's most efficient output, to combine battery power and gen power in a way some supercars have for performance reasons. And this is just what I came up with in under a minute, imagine what an actual engineer could with time. I don't disagree with your sentiment, just playing devils advocate.

 

[Firn]

I agree that if you want any kind of decent performance the battery has to be available, but I'm not sure that is what happens.

If we want to speculate about these systems we need to know the output of the generator in kW, and we don't know it for either of the two EREV truck systems that are in or close to production. You cannot know this from the HP rating of the gas engine, as I have said often.

So, consider this to be wild speculation based on some knowledge. I believe that the Ramcharger is a 30kW system based on some information and speculation. In one report, I read that they can send 30kW to a house in an emergency. The Pentastar V6 has a displacement of 3.7L which would be too small for a 50kW Diesel generator (4.5L for this 50kW) but about right for approximately a 30kW generator. I know that I am comparing different technologies but a diesel engine will always be capable of more torque than a similar displacement gasoline.

I also looked at the dimensions of the Ford Ecoboost V6 which I think is the largest engine that fits in the F-150 compared to the dimensions of the diesel generators and again, roughly 30kW is all that I think can fit. This is of course very speculative and rough but I'd say that 30kW is in the ballpark and even trying to get that much from a gasoline engine that is specifically designed to be light is ... bold.

If we use 30kW as a benchmark then we can go even further out on the speculative limb to see what the managers are thinking while the engineers cringe. The Lightning is rated at about 2.6 mi/kWh from the EPA (Lariat 320mi/131kWh). At that rate, one hour of driving will generate a (absolute maximum) of 78 miles of charge so if you keep it under 80 you can drive as much as you have gas in the tank + the electric range.

Unfortunately it is not that simple, beginning with the fact that I rarely see numbers that high and certainly not when towing. Additionally in the heavy towing cases that the EREV is supposed to solve, the battery will be hot which limits how much charging you can do.

The really hard problem to solve is that 30kW is not going to drive the electric motors very well, and while it is driving the motors it is not charging the battery. So once the battery is down it stays down until you fast charge. The assumption when they say things like "700 mile combined range" is that you can just go to a gas station and fill up - but that is not true. You will have to go to both a gas station and a charger for the next leg of your 1400 mile trip.

To make this work as a driver, I think you are going to have to be very aware of your current usage, expected usage, and plan on turning on the 'charger' much earlier than you think - probably at the beginning of your trip. For customers who already have difficulty with route planning ("just use ABRP!" we say so often) this is going to be even more off-putting.

The really big question for me is "how well does it drive with the battery completely empty?" Can I tow my (imaginary) big rig up Washington Pass, and at what speed?

Its a bit false to compare an industrial generator, something designed to be as cheap as possible and with few size or weight constrains, that is designed to run continuously (24/7) for years. With a device that needs to run intermittently and has a fairly fixed load profile. Money towards engineering and manufacturing can go a LONG way.

I know what you are saying but there IS some comparison between HP and KW so its not accurate to say a motor than can make 230kw wont be able to make 30kw. With what I can find the Volt and Prius have electrical generstor outputs in the 50kw range, so clearly it is possible to get more energy than 30kw.

Its also not accurate to say the alternator size HAS to be that big. Remember, out electric motors ARE generators and can put roughly 250kw each to the ground, and send a sizable portion of that back to the battery.

Bottom line 700 miles is MANY MANY times more than the SR lightning can achieve so its unlikely that EREV range is a "max effort" range consuming all fuel and all battery. Heck, 30kw wont even maintain the Lightning at 70mph. At even 70kw the truck can not only charge while driving, it can tow many different trailers AND still charge while driving. There is every reason to believe the system will be powerful enough to maintain at least level ground towing of medium trailers.

 

[hturnerfamily]

To run HVAC at a stop, to store regen braking, to store 'excess' power generated, to enhance efficiency by running the generator at it's most efficient output, to combine battery power and gen power in a way some supercars have for performance reasons. And this is just what I came up with in under a minute, imagine what an actual engineer could with time. I don't disagree with your sentiment, just playing devils advocate.

I don't disagree, but my point was actually just the premise that the Generator is somehow going to 'drive' the truck when the battery is low or depleted... or, maybe just when the owner WANTS to drive it that way - otherwise, that's called a HYBRID, like we've had for years.

If a generator/engine that can be placed within the Frunk and will be a large enough and consistent enough to power the truck down the road, then why not not just have a token 10kwh battery pack, or just a 1kwh battery pack... you'd be mostly relying on a generator/engine running 100% of the time.

I DO, though, disagree with the premise that the Generator/engine is going to be powerful enough to power the truck at 100% torque and hp you might expect... sounds like any 'generator power' directly to the motors will be simply for SUPPLEMENTAL support, with the battery output already at a HIGH output, for steep terrains and heavy loads, etc.
I'd like to be proven wrong, and that's o.k. if so... I'm good for knowing more exact ways and equipment involved in powering such a vehicle.

 

[chriserx]

I don't disagree, but my point was actually just the premise that the Generator is somehow going to 'drive' the truck when the battery is low or depleted... or, maybe just when the owner WANTS to drive it that way - otherwise, that's called a HYBRID, like we've had for years.

If a generator/engine that can be placed within the Frunk and will be a large enough and consistent enough to power the truck down the road, then why not not just have a token 10kwh battery pack, or just a 1kwh battery pack... you'd be mostly relying on a generator/engine running 100% of the time.

I'm not against what they're attempting even if I think it's a bit backwards, but it would allow them to maintain our software while getting potentially more sales from more traditional truck drivers and act as a bridge for nascent solid state battery tech to mature. I feel strongly that 50 kwh usable would be the sweet spot for this type of truck, a decent EV only range, decent buffer. Ford is likely going to aim for the current truck use average for its EV mark which is local trips, non towing and maybe 500-1000 lb load, 25 kwh would be good enough for this. But for EV marketing and a decent battery life expectancy I'd expect around 50 kwh

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