How much MPG when charging off a generator?

[Cheburashka]

I got a Firman 3200W continuous generator and I'm charging my Model S at 3kW using the UMC at 24a/125v.

It has a 1.8gal tank.

Does anyone know how much range/miles it would add on a tank of gas? Wondering how big of a gas canister I should get...

 

[SSonnentag]

Probably in the mid 40's. My Chevy Volt got 44 mpg on its generator.

 

[livesmith]

I got a Firman 3200W continuous generator and I'm charging my Model S at 3kW using the UMC at 24a/125v.

It has a 1.8gal tank.

Does anyone know how much range/miles it would add on a tank of gas? Wondering how big of a gas canister I should get...

View attachment 1008036

That's an interesting question... I doubt you'll get much real idea until you run a tank full through. I only see that it says it can run for up to 9 hours at 25% load. I'm not at all sure how that translates at close to 100% load. Will it use up a tank in 2 or 3 hours?

Hmm... Here's some random thoughts on this limited vague info... that I still don't think will translate to reality...
If we say that you could charge at 1KW for 9 hours and burn 2 gallons of gas...
You'd probably be lucky to add 8KWH during that time...
And if you could get something like 333WH/mile... Then maybe you added 24 miles of range?

So, then you're around 12MPG... Again, wild numbers... But it wouldn't surprise me if it was that bad...

 

[livesmith]

Probably in the mid 40's. My Chevy Volt got 44 mpg on its generator.

I feel like that's really optimistic. In the Volt you've got a much more refined process... I was going to say that you're bypassing some conversions from the battery to the charger....
But actually... I think in what you're referring to in that form on the Volt, you're skipping the whole battery entirely. And... Actually, last I heard as much as the Volt was sold as an "EV", it still had mechanical means in some modes to connect the engine directly to the wheels just like the Prius, etc. So in that case, you're skipping the electric transfer entirely as well...

 

[ucmndd]

Probably in the mid 40's. My Chevy Volt got 44 mpg on its generator.

Not even close. Some rough assumptions:

Fuel consumption is not linear with load but it’s a reasonable estimate to think that you’ll use ~double the fuel at full load as you do at 25%. So say you have ~4 hours of runtime at 3kw. Honestly I think that’s generous and it’s probably less.

3kw for 4 hours is 12kwh. At ~3 miles per kWh for most Model S (including charge losses, etc) that’s 36 miles of range. Divided by 1.8 gallons equals ~20 MPG.

 

[SSonnentag]

Not even close. Some rough assumptions:

Fuel consumption is not linear with load but it’s a reasonable estimate to think that you’ll use ~double the fuel at full load as you do at 25%. So say you have ~4 hours of runtime at 3kw. Honestly I think that’s generous and it’s probably less.

3kw for 4 hours is 12kwh. At ~3 miles per kWh for most Model S (including charge losses, etc) that’s 36 miles of range. Divided by 1.8 gallons equals ~20 MPG.

So Chevy manages to get more than double your calculations somehow. Must be magic?

 

[ucmndd]

So Chevy manages to get more than double your calculations somehow. Must be magic?

It’s not even the slightest bit magic to think that a 1.4 liter four cylinder tuned precisely for this purpose connected directly to a HV battery is roughly twice as efficient as a portable generator that’s decidedly NOT designed to run at full load for long periods of time charging an EV through a mobile power cord at 24 amps.

It’s surprising that you seem confused by this.

 

[livesmith]

It’s not even the slightest bit magic to think that a 1.4 liter four cylinder tuned precisely for this purpose connected directly to a HV battery is roughly twice as efficient as a portable generator that’s decidedly NOT designed to run at full load for long periods of time charging an EV through a mobile power cord at 24 amps.

It’s surprising that you seem confused by this.

I'd also question that the Volt can get mpg in the 40s in a scenario where the Volt is strictly charging the battery and then later driving on only the battery.

Pretty sure the Volt is mostly skipping that process(and losses) entirely.