EREV - A Horsepower Math Problem?

[bthanos]

Methinks you'll need to find a charger before you hit 0 and then go get gas. Also I bet that "700 miles" will be at lower speeds and not 70mph+

For road trip usage the only sensible usage model is to stop for gas, filling the generator and rely on it to maintain the battery at a useable level for the road ahead. There’s no way I would stop for 30 mins to charge AND stop at a gas station. Ergo , the generator sizing will be plentiful to be overcoming the discharge of the vehicle in motion. And you can safely assume the frunk is the place the generator will get installed.

People will use this like a hybrid, maybe charge at home for daily commutes.

And in that use case your carrying around the weight of the ice motor and generator when it’s not running at all.

I’ll stick with my ER Lightning BEV thanks.

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[Lytning]

I believe Ford even mentioned a locomotive in their release for those still confused maybe this helps or maybe it will confuse you more!

A diesel locomotive operates by converting diesel fuel into mechanical energy through a diesel engine, which powers electric generators that drive traction motors to move the train.

Great catch on the locomotive correlation from the announcement!

 

[Wendy]

This math and assumptions in this are all wrong.

You’re confusing peak power output vs average output.

Let's start with some of these assumptions:

It's not designed to drain the battery down to zero and then start the range extender. That doesn't make any sense. The range extender will likely be an atkinson cycle 4 cylinder, maybe 6 cylinder engine. The default way for it to run would be at a set RPM for maximum efficiency. There will probably also be a max power engine parameter to run as well.

There will be an algorithm that looks at remaining battery range, and expected loads and determine when to kick on the range extender. Something like: when you're just driving around, when the battery gets to 20% remaining, the range extender kicks on in efficiency mode to try to maintain the charge between 20-40%. You can still extract all the power that you would when it's not on! This is designed so it doesn't ever have to go into "turtle" mode.

If you're towing something, the vehicle would see the increase power demand and maybe kick on the range extender at 40% instead. If it sees sustained load for a long time (ie. you're towing up a mountain or something), maybe it operates the range extender at max output as opposed to max efficiency.

Either way, the range extender is going to attempt to estimate future power demand and kick on when needed in various operating modes to maintain a minimum base level in the batterie so that you get full power (or at least very very close to full power) at all times.


Let's take your hypothetical example.

If you average 2 mi/kWh, , you're traveling 60 mph, and you travel 120 miles, you're consuming 60 kWh of the battery in the course of 2 hours. That's a power draw of 30 kW on average.

There's no need to talk about voltage or amperage. kW is a measure of power. The atkinson 4 cylinder in the Ford Maverick makes 162 horsepower. That's 119 kW. That's likely peak power. There are some efficiency loss in converting it for the battery too (say 10%? Not sure if that's right, but let's use it as a placeholder). It's more than plenty to maintain a 30 kW draw from the battery. Let's say you're towing: again, if you average 1.0 mi/kWh in a Lightning towing a heavy load, you could easily output that with the Maverick motor.

The batteries act as a buffer to allow for huge power demand. The generator just needs to keep up with the average power consumption, not the peak.

I saw someone quote the RamCharge, saying it has a 130kw generator. If some of the recent math is correct that you need 35kw ~ 70kw to keep driving at 70mph then this could be filling you up at twice the rate you are depleting.

I think what will be interesting is, as you say above, the range extender needs to know when to kick in and at what level to keep the battery. I can just imagine the Guess-o-Meter they will have to build to get that right!

 

[Mal106]

GM brought back the Bolt but not the Volt for good reason. Shame to see Ford and Ram go down that rathole.

 

[Nikos]

I'm curious... They say the truck will have a "700 mile range"... So What if you're doing a 1500 mile road trip? Will the battery be depleted after 700 miles, AND the gas tank is empty as well, meaning you need to go to a gas station AND a DCFC? Or will the truck be able to play "catch up" and recharge itself to a stable point once you refuel with gas and continue on your road trip.

I have been reading everyone’s opinions and assumptions of what this EREV Lightning will be. None of us know what this truck will look like externally or internally. On your post though the intent is to never deplete the battery to below 25%, I assume.
The generator will engage to provide power at around 50% SOC. It will try to maintain that level as best as it can.
Ehat Ford will build in this assumption is still a mystery. Judging by what they have done before by marketing the Lightning, all of us need to be aware to block the misinformation and understand how this EREV truck really works. When I studying the RAM Recharge, I was seeing the ugly side of marketing not telling the truth and capabilities of the truck.
Putting it in clear terms, as soon as you hook your 6000lb trailer or camper on your EREV truck, you basically starting your Gas Generator shortly after pulling away from your home or working site or camping spot. The smaller the battery(HVB), the quicker the gas generator comes on line.
All of us eventually will find out what this new EREV truck is all about.
We are treading in swampy waters folks. We all need to see this product in flesh. I like my Lightning the way it is. I do my towing occasionally and I will tow even more in 2026.
I have so many questions for Ford but I know like all of us have, we will not get any answers any time soon.
Expect a flashy intro event in a year or so. In the meantime enjoy your Lightnings.

 

[CavRider]

Yeah, good point.

This is the exact kind of reason why GM is trying to push everyone to use the in-car navigation as opposed to something like CarPlay. Even though they would need to pry CarPlay from my cold dead hands, I totally get why they're pushing in that direction

Ha ha. That's funny. They (GM) are pushing use of in car nav so that they (GM) have possession of your location data instead of Apple.

 

[Mal106]

Native nav is and will always be there Android Auto and Apple Carplay are just eye candy. Sure they communicate with the vehicle but that doesn't negate the fact that the vehicle can do it's own thing.

 

[Mal106]

If the Ram has a 90 or so KWH battery how will they, or Ford, be able to build an EREV without just adding the cost of an engine and generator to what a Lightning SR would cost? The price of a Lightning was a major barrier.

 

[PJnc284]

If the Ram has a 90 or so KWH battery how will they, or Ford, be able to build an EREV without just adding the cost of an engine and generator to what a Lightning SR would cost? The price of a Lightning was a major barrier.

Don't think they said anything about it actually being affordable for the average joe. That's supposed to be the midsize truck's job but my money's on not getting one for 30k.

 

[gregoryhcain]

I ran the numbers and came up with higher hp requirements than did Gemini, but either way the amount of power to keep a truck rolling is substantial. I think Gemini underestimated the energy losses. When using the power to run an EREV you will have both losses charging the battery and discharging.

Anyway here’s what Gemini says is the power to keep a F150 rolling at various speeds:

“
To maintain a constant speed of 60 mph on a level road, a typical gasoline-powered Ford F-150 requires approximately 25 to 35 horsepower (hp).


While these trucks have engines capable of 325 to over 700 hp, that massive power is only used for acceleration or towing. At a steady cruise, the engine only needs to produce enough power to overcome two main forces: Aerodynamic Drag and Rolling Resistance.


The Physics Breakdown


To calculate this, we look at the power required at the wheels (\bm{P_{wheels}}) and then factor in the efficiency of the drivetrain.


1. Aerodynamic Drag (\bm{F_d})


For a large vehicle like an F-150, air resistance is the biggest hurdle at 60 mph.


• Formula: \bm{F_d = \frac{1}{2} \cdot \rho \cdot v^2 \cdot C_d \cdot A}


• Drag Coefficient (\bm{C_d}): Approx 0.44 to 0.46 (Trucks are "blocky" and less aerodynamic than cars).


• Frontal Area (\bm{A}): Approx 31.5 to 35 sq ft.


• Speed (\bm{v}): 60 mph (88 feet per second).


• Result: At 60 mph, aerodynamic drag consumes about 18–22 hp.


2. Rolling Resistance (\bm{F_{rr}})


This is the friction between the tires and the road.


• Formula: \bm{F_{rr} = C_{rr} \cdot m \cdot g}


• Weight (\bm{m}): A typical F-150 weighs about 5,000 lbs.


• Rolling Coefficient (\bm{C_{rr}}): Approx 0.010 to 0.015 for standard highway tires.


• Result: Rolling resistance consumes about 8–10 hp.


3. Total Power at the Wheels


• Sum: \bm{20\text{ hp (Air)} + 9\text{ hp (Tires)} = \mathbf{29\text{ hp}}}


Why the Engine Works Harder


The number above is the power needed at the wheels. To provide 29 hp to the ground, the engine must produce more because of:


• Drivetrain Loss: About 15–20% of power is lost through the transmission, driveshaft, and differentials.


• Accessories: The alternator, water pump, and air conditioning also draw a few horsepower.


Estimated Engine Output at 60 mph: 34–40 hp.


Comparison Table: Power Required vs. Speed


As speed increases, the power required rises exponentially because aerodynamic drag increases with the cube of velocity (\bm{P \propto v^3}).

 

[chl]

If the generator is like the GM Volt, the small gas engine actually WAS connected to the drive train to assist, in the GEN 2 version, which akin to a "plug-in hybrid" in inconvenience - needed an EVSE AND a gas station.

And the darn thing specified HIGH TEST PREMIUM GASOLINE.

Anyway, their sales numbers were...underwhelming:

https://gmauthority.com/blog/gm/chevrolet/volt/chevrolet-volt-sales-numbers/

I expect Ford will experience the same low demand, for all the reasons everyone has mentioned above.

More money down the drain on design and tooling and marketing.

I think they should can this boondoggle before it goes any further.

 

[reddog21]

I think they should can this boondoggle before it goes any further.

Then they should can the entire lighting program along with it.

 

[fhteagle]

If the generator is like the GM Volt, the small gas engine actually WAS connected to the drive train to assist,

That is correct for both Gen 1 and Gen 2, they both could mechanically send power from the engine to the wheels. The Gen 1 had a more limited speed/ torque request range where this clutch closure arrangement would be selected by the computers. There has been a ton of disinformation about this spread by even Volt owners. But it's well settled that this happened if you go to source GM docs.

But this does not sound like what Ford is proposing.

And the darn thing specified HIGH TEST PREMIUM GASOLINE.

This was true for Gen 1 only. Which is the variant I had. And I ran tests, and believe it or not the premium was equal or better $/mile.

I think they should can this boondoggle before it goes any further.

100% agreed.

 

[hturnerfamily]

I think the RAM REV will have a 'boost' option, which basically allows the Engine's Generator output to ADD TO the battery output to the MOTORS, such as when towing heavy loads up a steep grade...

They also essentially call this a PHEV, but, as we know, there are certainly major differences since these REVs do not directly drive the wheels... but, it's just a different 'routing' of power...

 

[chriserx]

I ran the numbers and came up with higher hp requirements than did Gemini, but either way the amount of power to keep a truck rolling is substantial. I think Gemini underestimated the energy losses. When using the power to run an EREV you will have both losses charging the battery and discharging.

Anyway here’s what Gemini says is the power to keep a F150 rolling at various speeds:

“
To maintain a constant speed of 60 mph on a level road, a typical gasoline-powered Ford F-150 requires approximately 25 to 35 horsepower (hp).


While these trucks have engines capable of 325 to over 700 hp, that massive power is only used for acceleration or towing. At a steady cruise, the engine only needs to produce enough power to overcome two main forces: Aerodynamic Drag and Rolling Resistance.


The Physics Breakdown


To calculate this, we look at the power required at the wheels (\bm{P_{wheels}}) and then factor in the efficiency of the drivetrain.


1. Aerodynamic Drag (\bm{F_d})


For a large vehicle like an F-150, air resistance is the biggest hurdle at 60 mph.


• Formula: \bm{F_d = \frac{1}{2} \cdot \rho \cdot v^2 \cdot C_d \cdot A}


• Drag Coefficient (\bm{C_d}): Approx 0.44 to 0.46 (Trucks are "blocky" and less aerodynamic than cars).


• Frontal Area (\bm{A}): Approx 31.5 to 35 sq ft.


• Speed (\bm{v}): 60 mph (88 feet per second).


• Result: At 60 mph, aerodynamic drag consumes about 18–22 hp.


2. Rolling Resistance (\bm{F_{rr}})


This is the friction between the tires and the road.


• Formula: \bm{F_{rr} = C_{rr} \cdot m \cdot g}


• Weight (\bm{m}): A typical F-150 weighs about 5,000 lbs.


• Rolling Coefficient (\bm{C_{rr}}): Approx 0.010 to 0.015 for standard highway tires.


• Result: Rolling resistance consumes about 8–10 hp.


3. Total Power at the Wheels


• Sum: \bm{20\text{ hp (Air)} + 9\text{ hp (Tires)} = \mathbf{29\text{ hp}}}


Why the Engine Works Harder


The number above is the power needed at the wheels. To provide 29 hp to the ground, the engine must produce more because of:


• Drivetrain Loss: About 15–20% of power is lost through the transmission, driveshaft, and differentials.


• Accessories: The alternator, water pump, and air conditioning also draw a few horsepower.


Estimated Engine Output at 60 mph: 34–40 hp.


Comparison Table: Power Required vs. Speed


As speed increases, the power required rises exponentially because aerodynamic drag increases with the cube of velocity (\bm{P \propto v^3}).

I'd say this was about right, at 100 mph I glanced at carscanner and motor output was roughly 90 kw, which puts it at 120 hp, wasn't willing to take my eyes off the road or do a longer term test other than that.

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