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Discussion Starter #1
here's my thought process:

The volt is literally designed for this exact use case of being a generator to charge a system that's in active use. If paired with Volt cells in a conversion, would it even be that difficult?

of course you'd need to replicate the high voltage cabling that exist in the Volt, although no idea if the ICE engine in there goes through the normal plug in charging system, or a totally separate system when it's acting as a generator for the batteries.

also an entire 4 cylinder car engine on a trailer is...not small, but i can't see it weighing in over 1000 lbs for the engine, short heavily mufflered exhaust, a small gas tank, cooling loop with a radiator, the necessary cabling, and a fiberglass cowl on top to keep the weather out.
Engine testing stands are a thing and they're pretty darn compact...

prices on car part for these engines are between 500 and 1000, not great but not terrible.

Of course, the hard part will be fooling the engine into running when it's totally outside of a normal Volt. I imagine there's a lot of ECU and charge controller hacking i'm glossing over.





thing is, the volt's internal generator is 45kw, so that little thing has as much electric generator capability as this 4000+ pound, $27,000 diesel monstrosity
https://www.coloradostandby.com/winco-mobile-towable-generators-rp55-45kw-diesel-generator
and at 45kw you should be able to maintain charge for most motor setups at cruising highway speeds


So how crazy is this? has anyone even researched it yet?
 

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I don't think GM went to much effort to optimize the engine for the Volt; Toyota's -FXE engines might be a better example. In any case, the engine has no idea what its output is being used for, so you don't need to use the Volt (or Prius, or other similar powertrain) and any engine can work... you just want one which is very efficient when running at the planned power. Having said that, generating while the vehicle is stationary is a normal mode for these vehicles, and some people use a Prius that way.

Running a generator trailer to power an EV creates a series hybrid. There is a good reason that GM went to some trouble to avoid that mode of operation (the Volt normally runs as a power-split hybrid): inefficiency.

The onboard charging system to accept plug-in power is mostly an AC to DC converter; the control of power from the motor-generators to the battery is unrelated to the plug-in part, and regulated by the inverter/controllers for each motor-generator.

Sure, the engine, all accessories (cooling system, exhaust system, etc), generator, inverter/controller, fuel tank, trailer structure, trailer chassis, and body might reasonably be not much more than half a ton.

If concerned about weight, carrying around the Volt's entire transaxle and only using a small fraction of it (one of the motor-generators) doesn't make a lot of sense to me.

I don't know why anyone would want a small fuel tank; the trailer is for long-range use, so it should have a larger tank than a conventional car would have.


The "diesel monstrosity' is heavy because it is intended to run at full power continuously, all day and every day, efficiently.
 

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Discussion Starter #4
My thought was that by using the transaxle you maintain all the optimizations (however lazy) gm did to get that thing to push out 45kw, also to reduce cost since the motor+transaxle is only like $750 from a wrecker.... whereas using the engine but putting your own generator on it means you need to find a pretty darn good generator and make an adapter plate etc. The two things you get at that point (over using the stock transaxle) are more control over the generator, and saving maybe a hundred pounds or so since you don't have the extra motor dead weight compared to a smaller motor + adapters. But for the lower overall cost and the lower need for bespoke controllers, I think using the stock transaxel is worth it.
Of course, it shifts your effort into making the transaxel firmware do what you want in terms of pushing kilowatts when you want it.

The small fuel tank is for safety (less volume of boom boom), but I guess having a stronger tank isn't too difficult or heavy. Keep in mind these engines get a solid 40 mpg in generator mode, so a 5 gallon tiny tank still gets you 200 miles of range assuming your highway cruising isn't drawing more than 45kw (I'll admit I'm not actually sure what the numbers are on power draw at 60mph).... Although on that same token you could go freaking 800 miles on a single 20 gallon tank! Solid 13 hours of straight driving without dipping into batteries, holy cow.

A totally separate charging circuit will add some complexity of a different charger on top of the plug in charger, but I can't imagine it's too bulky?

One thing I have no idea about is how would the wiring from the trailer to the batteries work? Would it just be some big ass cables with a really beefy super locked connector going from the generator inverter into the generator charger that'll live in the car? That's definitely need some bespoke stuff, including safety systems to pop connections and fuses in the case of a runaway trailer!

Also what is even involved in making a volt engine "just run" on command and the generator to just make power.
How much of the engine do you need to fool? How much of the original volt do you need?
Could you use a totally separate aftermarket ECU to run the engine and just not do anything to the generator, just get the high voltage cables and trust it'll make the power you want?

Please note I'm a complete idiot and I'm throwing out ideas to see what's feasible or not, hoping some folks come along to say "well actually" and set me straight.
 

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My thought was that by using the transaxle you maintain all the optimizations (however lazy) gm did to get that thing to push out 45kw..
No, the transaxle doesn't change how the engine operates; it would run exactly the same way with a just a generator, given suitable control logic. 45 kW is only 60 hp... that's trival for the engine.

... also to reduce cost since the motor+transaxle is only like $750 from a wrecker.... whereas using the engine but putting your own generator on it means you need to find a pretty darn good generator and make an adapter plate etc.
Yes, but you carry around a lot of hardware for that cost saving and convenience.

The small fuel tank is for safety (less volume of boom boom), but I guess having a stronger tank isn't too difficult or heavy. Keep in mind these engines get a solid 40 mpg in generator mode, so a 5 gallon tiny tank still gets you 200 miles of range assuming...
To me, 200 miles is unworkably short for highway travel, making any significant trip into a continual fuel stop planning exercise. You don't need to use all of the available range if you have more, but it lets you stop for fuel when you want, instead of when you need to.

One thing I have no idea about is how would the wiring from the trailer to the batteries work? Would it just be some big ass cables with a really beefy super locked connector going from the generator inverter into the generator charger that'll live in the car? That's definitely need some bespoke stuff, including safety systems to pop connections and fuses in the case of a runaway trailer!
Right... and I think you want a connection which will safely pull apart rather than get destroyed if the cable is pulled. Even the connection from a Level 2 charging station to an EV (which is fundamentally just a 240 V AC plug-in) has safety interlocking, and that's in a stationary application.
 

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So the Volt has a 45kW generator set on board? Wild! I spent weeks trying to find a 50kW genset for my truck, while planning a conversion. Only, I don't want to do a trailer, I wanted to install it permanently and use it as a series hybrid.

I figured on 50kW based on using a Tesla X drive unit. To drive my truck at the cruise speed I want, it will take about 67HP which is right at 50kW. This is really overkill, because I overestimated the vehicle weight. And, if it came to it, I could just cruise the speed limit.

Unfortunately, I also came to the conclusion that I would only be seeing about 18MPG max going this way, so I'm not going to do it. I have an alternative that will get me 40+mpg in the same truck, which currently gets 15mpg. The 15 year old V6 and 4 speed is coming out, and a modern V8 and 8 speed is going in. I'll look into the Volt drivetrain just the same, because if I can get what I want with electricity I'd rather go that way and what I want is 10 second quarter miles and 40+mpg cruising.

This is the link I used to figure out required HP. The field information needed like frontal area and cD can be found online. Frontal area, find you vehicle's height and width in inches online, multiply one by the other, then divide the answer by 144 to convert to square feet. Whatever it comes up with, multiply by 746 to get the wattage required to maintain speed.

http://www.wallaceracing.com/Calculate HP For Speed.php

This site does similar, but claims I need 10hp less to maintain speed.

http://www.tritrack.net/horsePower.html

Hope some of this helps.
 

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Discussion Starter #8
the 45kw number i'm pulling right from that infographic on the volt engine



so it's accuracy is....hmmm..

also keep in mind if you aren't covering 100% of your cruising energy with the generator it's not that bad. The idea is to extend your range, not totally replace it with gas, which would be a pretty lofty goal and most of the time you'd be spinning a generator for nothing. If instead you get triple your standard range because you're consuming battery power at a third the rate, that takes your 100 mile range project to 300 miles instead!

but, have no clever electrical engineers tried anything like this yet? Generator trailer ideas keep popping up and going nowhere, it's pretty disheartening :(
 

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the 45kw number i'm pulling right from that infographic on the volt engine

...

so it's accuracy is....hmmm..
Marketing people frequently mess up technical content, but that image is from GM... it's probably trustworthy. 45 kW is entirely reasonable for the output side motor-generator in a power-split transmission for an engine of this size. It's probably capable of more than that; the total output of both motors is listed as 129 HP (96 kW), and the 45 kW value is for regenerative braking output, which may be limited by acceptable battery charging rate (rather than the motor-generator).
 

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... also keep in mind if you aren't covering 100% of your cruising energy with the generator it's not that bad. The idea is to extend your range, not totally replace it with gas, which would be a pretty lofty goal and most of the time you'd be spinning a generator for nothing. If instead you get triple your standard range because you're consuming battery power at a third the rate, that takes your 100 mile range project to 300 miles instead!
The generator only needs to cover the average power demand for range to be limited only by fuel. If the generator's continuous output matches the average, it will never idle; the generator will only idle most of the time if it is sized for peak power demand, rather than average.

The REX version of the BMW i3 is a series hybrid (as any EV with an added charging trailer would be); it has a little 25 kW engine (a 0.647 L two-cylinder from a scooter). If not deliberately hobbled by software limits set to game California regulations, it can keep up with cruising demand for the car as long as the fuel lasts.
 

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... but, have no clever electrical engineers tried anything like this yet? Generator trailer ideas keep popping up and going nowhere, it's pretty disheartening :(
I think most trained and experienced engineers would realize how rare suitable applications would be, given the efficiency and implementation issues, so they don't pursue the idea. And most of the details of a generator trailer are mechanically engineering issues, not electrical; the charging control is the only significant electrical technical challenge.

The BMW i3 is one of the very rare series hybrids in production; it is essentially the same as an EV plus a charging trailer, but is much more convenient to drive (except for the tiny fuel tank), and its poor fuel economy demonstrates why this sort of system is problematic. A larger engine would likely be more efficient, but the car-plus-trailer implementation would be an efficiency disadvantage due to rolling and aero drag.
 

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Discussion Starter #12
which may be limited by acceptable battery charging rate (rather than the motor-generator).
this is what i'm worried about with a chevy volt system. Can it actually push 45kw from the generator into the battery continuously? I think the regular volt can give enough juice to maintain highway driving without dipping into the battery....but doesn't the volt just have the gas engine "directly" (without the battery as a middle ground) power the wheel motor when at higher speeds?
I'm really hoping it's the former.
 

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this is what i'm worried about with a chevy volt system. Can it actually push 45kw from the generator into the battery continuously?
I don't see why not. It's not much compared to available engine power, and not surprising for the motor-generator. The inverter-controller will be sized to suit the application.

I think the regular volt can give enough juice to maintain highway driving without dipping into the battery....but doesn't the volt just have the gas engine "directly" (without the battery as a middle ground) power the wheel motor when at higher speeds?
I'm really hoping it's the former.
A Volt can accelerate hard up to and beyond typical highway speed without needing energy from the battery (although the battery needs to be functional - pull it out entirely and the car is likely dead).

The Volt transaxle has multiple operating modes, and the list of modes depends on the generation of Volt. Modes with a mechanical transmission path (the "power-split" feature of the transaxle, also used by the Prius and other Toyotas, Ford hybrids, and non-GM two-mode hybrids from BMW and others) are used for efficiency, not due to limitations of the motor-generator sizes.

The battery is always in the power flow, but only the net difference between what is generated and what is used goes into or out of the battery. This is true of any system which "floats" the battery, which is how all hybrids work.
 

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Before I decided on 2 Leaf motors, I was thinking of having one in the front acting as a generator being driven by a TDI. The torque curve for the TDI is ideally suited to driving a Leaf and I could generate 60kw with no problems. I had been thinking of the idea of the trailer with this system as well for long hauls.
 

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Before I decided on 2 Leaf motors, I was thinking of having one in the front acting as a generator being driven by a TDI. The torque curve for the TDI is ideally suited to driving a Leaf and I could generate 60kw with no problems. I had been thinking of the idea of the trailer with this system as well for long hauls.
Given the substantial size of this truck, you could even build the generator set on a skid to be carried on the truck's deck... not that it would avoid the inherent inefficiency of a series hybrid, but it would avoid towing a trailer (and the resulting aero drag).
 

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Given the substantial size of this truck, you could even build the generator set on a skid to be carried on the truck's deck... not that it would avoid the inherent inefficiency of a series hybrid, but it would avoid towing a trailer (and the resulting aero drag).

That would be nice but the bed will be taken up, most of the time during long distance travel, by a pop up hard top camper. I noticed that my current fuel economy with 1 tonne of solar panels on the back doesn't change much but towing a 14' Bigfoot camper is really bad so every effort will be taken to make the camper as aerodynamic as possible, hence the pop up.
 

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Given the substantial size of this truck, you could even build the generator set on a skid to be carried on the truck's deck...
That would be nice but the bed will be taken up, most of the time during long distance travel, by a pop up hard top camper. I noticed that my current fuel economy with 1 tonne of solar panels on the back doesn't change much but towing a 14' Bigfoot camper is really bad so every effort will be taken to make the camper as aerodynamic as possible, hence the pop up.
That makes sense. Fortunately, a generator trailer would be narrower (or much narrower, if by 14' you mean a later 17' Bigfoot with a 14' long body) than the Bigfoot, so it would not be the same aerodynamic problem. If the generator trailer would typically be used with the camper, but not always, it could be designed with a load deck on top (matched to the truck deck height?) so that when carrying the camper the trailer could carry cargo which would be in the aerodynamic "shadow" of the truck and camper.
 

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Given the substantial size of this truck, you could even build the generator set on a skid to be carried on the truck's deck... not that it would avoid the inherent inefficiency of a series hybrid, but it would avoid towing a trailer (and the resulting aero drag).

One thing to consider, the driven motor (generator) will not generate enough to drive the drive motor at 100 percent. You'd be looking at probably 80 percent by the time line losses and whatnot are taken into account. In the past I considered doing something similar only using Warp engines, and was looking at using a Warp 11 for the drive motor and a Warp 13 for the driven motor. I wanted the ability to run the drive motor at 100 percent, while still having enough juice to run the rest of the car. This may not actually be a concern for you, but it's something you should be aware of nonetheless.



I really wish the infrastructure and battery tech were at a point where you can stop at any corner gas station and fully recharge the battery in 5 minutes, going 100 percent would be a no brainer. Due to family and work I need to be able to jump in and drive 12 hours nonstop at the drop of a hat, so I'm probably going to be driving a gasser all my life because of it.
 

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That makes sense. Fortunately, a generator trailer would be narrower (or much narrower, if by 14' you mean a later 17' Bigfoot with a 14' long body) than the Bigfoot, so it would not be the same aerodynamic problem. If the generator trailer would typically be used with the camper, but not always, it could be designed with a load deck on top (matched to the truck deck height?) so that when carrying the camper the trailer could carry cargo which would be in the aerodynamic "shadow" of the truck and camper.
Yes, you are right. It is the 17ft Bigfoot with a 14ft body. I suspect the power trailer would be somewhat like the size of a bigger motorcycle trailer and could easily be designed to fit into the slipstream of the truck, even act as a drag reducer similar t those on the back of a semi trailer.
 
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