[brian_]

What I'm thinking of is a trailer for trips. Probably double-axle. It would have:
1. An internal combustion engine, possibly the same one that's in the van now...

My idea is that, in town, the van is a pure EV. When I go on a trip, I hook up the trailer which converts it into a hybrid.

I get the idea of a hybrid spread between the van and trailer, but there's no reason to use the huge original van engine, because that engine is sized for peak load rather than average load.

You could make a generator trailer, but that means you need the whole engine on there, plus a generator large enough to power the vehicle at highway speeds (maybe 20hp for your van? 25? That's 15-18kw)...

The van with trailer will need more power than that. At the same time, there's no point in an 18 kW generator on a 200+ horsepower engine. The generator needs to have more capacity than the average load over the trip, and the engine needs to be sized to operate efficiently at that power level.

I have serious doubts as to whether a 25hp engine could move this thing fully loaded (per my description above, plus trailer) at 65 mph for hours, and if I'm traveling from town to town it would be hours. Even if you're using the on-board electric drive to even out the high-power stretches. I'd go so far as to doubt that a 4-cylinder auto engine could do it without really stressing. I wouldn't mind a little 5L Cummins diesel though.

Right, 25 hp isn't enough, but something much less than the van's current engine is suitable. If you're using up to a kilowatt-hour per mile, and averaging a mile a minute (60 mph), that's 60 kw or 80 hp.

A Cummins 5L (the V8 engine in the Nissan Titan XD diesel) is not "little" by any rational measurement. It would be heavier than the van's current engine. If you really like diesel, the GM "baby" Duramax 2.8 from the Colorado/Canyon, or the Ford small Powerstroke 5-cylinder from the Transit would be a better match, but I think an automotive 2-litre would be better.

I could consider having the van's motors capable of pulling the loaded van and trailer combined at highway speed continuously, I can see where this might simplify things a bit and may even save money on build cost.

Because this is a series hybrid, and even for pure EV operation without the trailer, the van's motors are going to need to be large.

 

[brian_]

Push trailers

... So what people do is build a "push trailer". Meaning you drive the trailer wheels with the actual engine. The ghetto way of doing this is to just take the front end of a FWD car, stopping just after after the windshield. A little bit of hotwiring and you're done.

If your motor has regenerative breaking, you can still charge the batteries this way too by applying the brakes while being pushed, though your throttle and brake arrangement gets a bit sketchy that way...

It has been done, but a lot of unsound things have been done - that doesn't make it advisable. "Sketchy" is the nicest word that I can think of for this scheme.

There are actually articulated buses (essentially a bus towing a passenger-carrying trailer) with the engine in the back (so, the trailer) pushing the whole thing... but they are not nearly as crude as those "push trailers".

By the way, powering one axle with an engine while charging with a generator driven by another axle is called "through the road" hybrid charging. It is a bad idea with both axles on the same vehicle, but with the driver on the trailer and the drag on the tow vehicle it's really bad.

 

[brian_]

Van projects

There are a couple of van projects in the forum:
1967 VW Split Screen Van - "ICE Breaker" (a little VW van)
Tesla powered Mercedes Vito (a Mercedes Metris - a usable van, but still smaller than a full-size)
Neither of these builders plans (as far as I know) any kind of generator trailer.

 

[brian_]

Engine options

If I'll need another engine for this, I think I'd rather get something designed for a generator than something designed for an automobile. Given a diesel's maintenance cycle and overall simplicity, I'd rather go that route than with gasoline.

Any modern diesel is certainly more complex than a gasoline engine. If you want an engine designed for optimal efficiency at the desired power level, that would be a gasoline engine from a Toyota hybrid.

I can see your point about average power. And I was thinking of the inline v6 diesel found in 90s Dodge trucks. My father had one, it would pull like a mule. You're probably right about it being bigger than the original van engine in terms of power and torque, but it was pretty small in terms of physical size per unit power. If there's a 4-liter version of that, or even 3-liter I'd be interested.

Inline and V are opposite things; I assume that you mean the Cummins B-series inline 6, originally called the 6B (then 6BT when turbocharged). The current version (called the ISB for commercial applications) is still used in 2500 and larger Ram trucks, but it is now much more complex and powerful. The B-series started as a 5.9 litre and has grown (to 6.7 litres). It is not small for its power, by comparison with anything other than an even larger diesel.

There is a 4-cylinder version of the B-series, called the 4B. With the same bore and stroke, it is a 4-litre. It is an enormous and heavy paint-shaker, used in many delivery vans and similar commercial vehicles. There is no version which meets modern emissions standards, but it might be suitable in power output.

 

[brian_]

Transmission?

I know most DIYers take off the engine and keep the transmission, putting the motor right where the engine was, but I think that will likely just add a lot of weight and complexity to the drive train and take up a lot of room. I see most people here seem to use just one gear most of the time anyway. I can see how it would be a much simpler conversion that way, just saying I don't like the compromise.

All good reasoning, and especially valid with the weight and complexity and issues of an automatic transmission, but be sure that the overall drive ratio is right. Modern motors need to run faster to get enough power than they would with just the rear axle's final drive ratio for reduction.

 

[brian_]

That tesla powered mercedes build looks like what I was thinking, only I don't think both of those sides are motors. Not sure what the other can is. But I thought I overbuilt when I weld crap together, this guy is outrageous.

That's a typical Tesla drive unit. One side is the single motor (which drives a differential through two stages of reduction gearing); the other side is the inverter/controller, housed in a metal can.

Those are both much smaller vans than I have.

Yes, they are relatively small. That's a problem in finding a motor - even the large Tesla Model S motor would be marginal for the large loaded van pulling a trailer.

I've read enough though to know that the bigger the vehicle the more it's worthwhile to convert it to an EV, even though the conversion cost is higher.

If the benefit of conversion is saving money on fuel, or reducing fossil fuel consumption, then yes there is more to be saved.

The main point of my query seems to hold water though, the idea of a generator on a trailer that converts a pure EV into a hybrid. Especially attractive is the idea of storing luggage on the trailer too. We always end up with 3 coolers, baby supplies, a couple pack-and-plays and pretty much an entire daycare in the van all folded up.

One challenge is weight distribution, with the big fixed weight of the engine and variable cargo load. Where do you put things so that the weight distribution is suitable under all conditions?

I'm thinking that the first step is to get a plan to convert the van itself, and price that out. There's a ton of room under the floor of the van, still protected by the frame. Not sure if I could swing actual EV battery packs, but there's lots of room for them if I can. I'd probably need some sort of cover under them to prevent damage from rocks and dirt though. Things have changed a bit since I first started researching this years back.

A complete EV pack won't fit, but repackaged modules of production EVs is the current trend in conversions.

 

[brian_]

Put the engine at the desired center of gravity. Put the fuel roughly the same place, just like a commercial trailer generator. Luggage goes around the outside.

Correctly loading a trailer is not complicated, just necessary. The only post-loading variable here is fuel. You pack the trailer with the correct hitch weight, and if the fuel tank COG is right in front of the axle then the trailer maintains correct balance the whole trip.

If the fuel tank is at the centre of gravity, then the engine can't be behind the fuel tank (the trailer would have negative tongue weight without cargo), so it must be ahead of the fuel tank. That's pretty front-heavy. A more practical configuration would put the fuel at the axle, and the engine and generator immediately in front of that.

Of course the fuel could be on top or under the genset, but that's not reasonable for a large tank. It could also go in saddle tanks on each side, I suppose.

Even then, the cargo is all going in front and rear trunks on the trailer. That can work, but doesn't sound like a convenient thing to use, and requires attention to distribution between front and rear. On the other hand, if this is a simple build, the front and rear cargo compartments can just be off-the-shelf cargo boxes.

 

[brian_]

Re: Engine options

I can't say I've looked at a modern diesel, but the ones from the 90s are much simpler than a gas engine if you discount the mechanical injectors. I know that the newer injectors are computerized, with some sort of actuator instead of a mechanical pump. To me, that means simpler.

The problem is that a mechanical injection pump is more complex than a complete gasoline injection system plus a complete ignition system. Modern diesels use electronic injection systems which are similar to gasoline injection systems but at much higher pressure; modern ignition systems have no moving parts and routinely go for the life of the vehicle without failure or repair... and a couple hundred thousand kilometres without even changing the plugs.

On top of that, modern diesels have both diesel particulate filter (DPF) and selective catalytic reduction (SCR) emissions control systems which are far more complex and less reliable than the catalytic converter on a gasoline engine. The problems of making a diesel to meet current emissions regulations are so extreme that Caterpillar dropped out of the business of manufacturing these engines for heavy trucks in response to the regulation changes - they just couldn't make it work economically and reliably. And of course most people have heard of Volkswagen's "dieselgate" nightmare. If you use an old engine you avoid all of that, but it's strange to promote EV conversion (which is often chosen for environmental reasons) then run a filthy engine. If you do, a pre-2007 common-rail electronic injection engine from a light commercial application (not something intended only for cars) is probably the most efficient and reliable choice... although I would want to avoid the parts prices of Mercedes engines.

With respect to efficiency I'm going to have to ask for proof. My dad's truck frequently pulled a 40 foot trailer with 20+ tons on it, and it still got 15 to 17 mpg. He drove it until it had 300k miles on it with minimal maintenance.


If your claims about gas engines being more efficient were true, or even if the efficiency were close to true, the commercial haulers (big trucks and trains) would be switching over.

A good diesel run as intended is more fuel-efficient than a gasoline engine under similar conditions. I was just pointing out that the engines which are available in light vehicles which are optimized for hybrid operation (nearly constant power at an engine speed unrelated to road speed) are those gasoline engines.

If you show me real-world proof that your gas engine is more efficient and more reliable than a diesel generator then I'll pay attention.

Modern gas engines in cars light trucks are more reliable than diesel engines in the same vehicles, due to the problems with current diesel emission controls. Of course heavy diesels are reliable (other than the emission controls), and there is no gasoline comparison (although they would be just as reliable) because diesels are cheaper to fuel - due to both fuel consumption and fuel pricing - so no one builds large commercial gasoline engines.

 

[brian_]

Right now I'm focused on a generator on a trailer, with storage and power cables.

If the van has suitable battery capacity for local use as a pure battery EV (running on battery power only), that capacity will be lots for series hybrid operation with the trailer. A plug-in hybrid car typically has about 16 kWh of capacity; the much bigger van with trailer would be a reasonable plug-in hybrid with about three times that capacity, and you'll want that for routine operation without the trailer anyway. Unless you want long battery-only range with the trailer, I don't see any need to make things complicated (and expensive) by putting more battery in the trailer.

The trailer could be treated as a mobile charging station for the van, but the van will need to accept a charge while driving, which is not normal for EVs. You do need the connection, but there are off-the-shelf connectors for high-rate DC charging of EVs at up to 400 volts and a couple hundred amps.

 

[brian_]

As I said I had planned to use a diesel generator set, not mate a generator I found to a motor I found somewhere else.

That gives you a matched set of engine and generator, but a genset with high enough output is going to be a massive thing, intended for stationary industrial operation.

 

[brian_]

I was thinking of putting raw 3-phase AC through the trailer connector. Thinking now on it that probably won't work so well, a generator set will probably be either 240 or 480, or maybe 400. There's probably no reason to route around that circuitry, and the EV charging circuitry will be set up for one of those too most likely.

If using a ready-made genset I can see doing this, preferably at 240 volts to match existing Level 2 EV charging standards... but 3-phase Level 2 charging is only used in Europe, as far as I know.

Multiple conversions are annoying and inefficient, which is why it would be nice to do it all on the generator trailer so that there is no conversion on the van side at all. If you can get a 3-phase alternator at a suitable voltage, you could rectify and regulate to the van's voltage without additional conversions. Of course the rectifier and inverter could be in either the trailer or the van.

An old-style generator set runs at a fixed speed to make 60 hertz (or 50 hertz outside of North America) power, and so doesn't run at its most efficient speed for the load of the moment. A current "inverter" generator runs at variable speed, produces high-frequency 3-phase AC (which the vehicle's charger likely won't handle well), and rectifies that to feed an inverter to produce the desired output. Feeding the final output of an inverter generator set to the van means an unnecessary inverter stage.

If you want the option of using the trailer as a mobile generator to power stuff other than the van (such as powering a house in emergencies), you might want to ensure that it has a 240/120 volt 60 Hz output available.

What sort of voltage does a highway-capable (65mph) EV run these days? It would be good to avoid unnecessary voltage conversions through all this, which is why I was thinking of 3-phase through the trailer connector.

360 volts (nominal) from a battery with 96 lithium cells in series (and of course some number of cells in parallel at the lowest level) is the current typical production EV practice. DIY EVs using brushed DC motors and AC induction motors sold for conversions necessarily run lower voltage. That's why existing high-rate DC charging standards allow up to 500 volts.

I was also thinking of gadget power in the vehicle, we have a ton of phone chargers and tablets and whatever crap we need for baby food. How many people run an AC wall outlet in the car? It's either that or a whole crapload of 12v or USB plugs. Or maybe all of the above.

Low-power 120 V AC outlets are common in the better-equipped trims of even non-hybrid non-EV vehicles.

Back in the day, EV builders had a high voltage battery pack and then a 12v battery for the automotive systems. Is this still the practice or do you run an inverter-pwm regulator for that sort of thing?

Current production practice, which DIY builders seem to be following, is to have a converter from high voltage to 12V, but still have a battery on the 12 volt system to smooth out peak demands and provide power before the DC-to-DC converter is powered on.

 

[brian_]

Go look at a construction site where they're putting up an apartment building, a hotel or some commercial building especially in a remote location. They have generators on wheels that have 4 cylinder automotive-sized engines or even bigger. Most of the ones I've seen are diesels, but the key here is that they are designed to run as a generator: constant speed, reasonably constant load, day in and day out. They'll be there until the power is hooked up to the site.

The problem with those is the size: for instance, a roughly 50 kW unit from Kohler weighs two tons. Automotive needs are quite different from stationary industrial needs, so although the underlying technology is the same (including sharing some base engines and using similar generator technology), the details are all different.

Constant-speed operation is a bit of an issue, too. A typical industrial unit will run a 1800 rpm all the time, to produce 60 Hz power. It might not be very efficient (and isn't quiet) at low load, but who cares on an industrial or construction site? That can be okay in a series hybrid, but it can means starting and stopping the genset often so that when it runs it only runs at high efficiency.

 

[brian_]

I've recently seen articles about opposed cylinder diesels with a common combustion chamber instead of a common crankshaft. They're reaching thermal efficiencies near 60%.

The people pushing the most recent opposed-piston diesels are great marketers, but a little short on integrity. This is old technology coming around again, and inherently has no substantial advantage.

If the pollution regulations are too tight then I'll clearly need to do something else.

... I think if diesel were ridiculously over-regulated then there would be less research on improving them right?

I doubt that anyone will ever even check the emissions of whatever you mount on a trailer, let alone regulate it.

I think that the effect of regulations is exactly the opposite. Something has to drive improvement, and if the only driver is the cost of engines and their operation, they will get ever cheaper, filthier, and less efficient. Automotive (including trucks) diesels are in an unfortunate state at the moment, much like gasoline engines of the dark days of the 1970's: they are dealing with new demands, and don't have it well sorted out yet.

Diesel fans often claim that some unreasonable demands are being placed on their engines, but in fact the nearly free ride they've had for decades is just ending as they are being regulated like gasoline engines.

 

[brian_]

Total nonsense Brian - today's diesels are several hundred times better than the 70's...

Duncan, apparently you didn't understand my post. I didn't compare the diesels of today to the diesels of the 1970's (obviously they have changed, to make them cheaper to operate and to meet regulations). I compared the situation of gasoline engines in the 1970's (struggling to meet changing regulations and not working well) to the situation of diesel engines today (struggling to meet changing regulations and not meeting them reliably).

... if anything is getting the "free ride" its the petrol engines - they are permitted to produce actual poisons! - while the diesels are not even permitted to release chemicals that in 97% of the USA are effectively fertiliser

I'll leave an uninformed deep discussion of the effects of pollutants and which emissions are regulated to another forum, since this is supposed to be about EVs... and in this case, hybrids. All that's relevant to this discucssion is

• an industrial engine will not meet automotive standards (of performance or emissions)
• an old diesel will not even come close to meeting current standards of emissions
• a current diesel may not operate both reliably and cleanly at reasonable cost (current systems are routinely bypassed or disabled)

Anyone who wants a mostly-electric vehicle and doesn't care about exhaust emissions can just run any older engine that they find reliable and cheap.

 

[brian_]

Since the EV with generator trailer thing is difficult to do well, there is another option... two vans:

1. one converted to EV for local use (maybe buy one which is cheap because it has a dead engine and/or transmission)
2. one left stock for longer trips - no trailer required

 

[brian_]

Don't buy a second van. Don't build a generator trailer. Build an EV push trailer.

You'd need a junkyard diff, probably a single big motor, and minimal batteries. And a trailer skeleton. Done. Mount it however you want, super easy.

Why would the batteries be "minimal"? It would need the same capacity as any EV for vehicle of this mass... no, more because it is so heavy and has so much drag.

The tradeoff being that now when you're tootling around town every day, you've got the trailer with you.

That tradeoff is a huge handicap. I can't imagine wanting to be stuck with a trailer for every trip, even short local errands.

And it's much safer than a gasoline push trailer regening the van up front.

Pushing the van with a trailer to keep the van moving is not much different from pushing the van with a trailer for through-the-road battery charging (which is not regenerative braking). Pushing the van with a trailer hard enough to accelerate the van is downright scary.

No push trailer, period. I've pulled trailers for a lot of miles. Enough crap goes wrong with them that I will absolutely not make a push trailer.

I'm with Ken on this one!

Well, that was a gasoline push trailer that you'd use to recharge batteries by regen braking on the lead vehicle.

This is just an electric push trailer. No braking, no charging. Unless you want to charge the batteries from the engine, in which case it's just like pulling a slightly heavier trailer.

It is simpler, but it is still a trailer pushing the van. This truly is putting the cart before the horse, in a physical sense rather than as the usual metaphor for lack of planning.

 

[brian_]

The van as it is has an automatic transmission. You can't tow a vehicle with an automatic transmission unless you disconnect the drive line or you risk damage to the transmission. Something about the rear shaft turning and flinging all the oil off and messing up the gears.

The problem is actually that pressure and flow of the transmission's fluid is normally provided by a pump driven by the input shaft, and so if you push the vehicle with the engine not running the transmission isn't properly lubricated or cooled, so it is eventually destroyed. There are ways around this, but it is situation to be avoided.

 

[brian_]

... I found some manufacturers for AC induction motors for automotive use, and a single motor costs as much as I expected the entire van conversion to be. 2 of them would be plenty, but I'm not spending $70k USD on just 2 motors for a van conversion, not counting anything else. I'll go buy a house or something instead. Hopefully something can be found used or maybe not gold plated.

A single quantity of an expensive-to-build and obscure component is going to be expensive... EV-related or not. I assume that this is a high-voltage motor; if so it is comparable to motors used in production EVs, although $35K each is wildly high even for premium motors. One problem is that they are sold as premium products in small volumes by retailers which get them from distributors who only carry small volumes of them, and get them from manufacturers who have no interest in quantities in less than the tens of thousands and price small volumes accordingly.

Very few DIY projects use a motor like this (or even half the price), unless they are salvaged from a wrecked production EV. The Tesla Model S or X is the most common source of these, with the most common source of permanent magnet motors of this class being the Nissan Leaf. Both Tesla and Leaf motors are usually used complete with the car's transaxle (for reduction gearing and differential).

Induction motors have fallen out of favour for production EVs and state-of-the-art custom EVs (and few production EVs ever had them); AC synchronous (normally with permanent magnets) motors are usually used instead. Even Tesla has switched to PM motors for the Model 3 and both planned models (new Roadster, Semi). Who is selling an induction motor at this price level?

 

[brian_]

Pretty sure my van won't have that problem.

Well, no, since you're not going to push it, with or without the automatic.

 

[brian_]

I wasn't arguing for PMAC over induction motors, just pointing out that it would be surprising for the most expensive motors to be induction. As the Tesla blog item explains, PMAC is typically more expensive due to the magnets.

The linked motor is, of course, from Tesla's original motor supplier. I haven't seen a motor advertised as high as "180 kW" available for retail purchase, although at 75 kW continuous it's not really more powerful than the motors found in common current production EVs of just about every brand. This is the sort of thing that few people buy new for DIY projects, using salvaged production EV motors instead; an alternative is to get one of the leftover Siemens motors from the Azure Dynamics bankruptcy... that's US$2,800 for a motor (albeit with no manufacturer support and no warranty) plus perhaps $US5,200 for a Rinehart PM100DX/DZ controller, rather than US$35K for a motor with controller.

The lack of economical availability of larger motors is a challenge for anyone wanting brisk performance with a larger vehicle. Two motors can be combined, but that doubles the price and bulk. Much larger motors are certainly available - TM4 seems to make some good stuff - but I have no idea where you could buy one individually, or what it would cost. TM4 has just been acquired by Dana, and something like Dana's Spicer Electrified eS5700r e-Axle would be a nice direct replacement for the van's rear axle. Back in the real world, perhaps the idea would be to salvage a motor from a light- to medium-duty truck that had been EV converted by one of the conversion companies.

If using two motors just to get enough power, they could be used to separately drive the front and rear axles, which would at least gain 4WD as well as the extra power. Full-size vans of course are rare in 4WD, but it's a common aftermarket conversion using parts from mechanically similar pickup trucks.