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Open for any sort of non-technical discussion regarding EVs
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EV2Go
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Post by EV2Go » Thu, 30 Jul 2009, 19:20

Just curious but would it be physically possible for a genset to provide sufficient power for an EV to do a long distance drive. I know GM are planning on releasing such a car with it built in, but I am think more along the lines of something trailer mounted for those who have already converted.

I guess my question is more around the logistics of such a device, would it be possible to bypass the battery pack altogether and have it powered straight from the generator? would you want to do this? What about in conjunction with some kind of capacitor bank so you could get off the road if the genset stalled? Guess I am thinking if you were to constantly pumping electricity into the battery pack the whole time, you are driving and that voltage is going up and down would this shorten the battery pack life?

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Post by Carv'n Marv'n » Thu, 30 Jul 2009, 20:18

...A compressed air driven generator would be good.
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Post by antiscab » Thu, 30 Jul 2009, 21:19

Carv'n Marv'n wrote: ...A compressed air driven generator would be good.


pity the energy density of compressed air is so low (much worse than lead)

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Post by Tim » Thu, 30 Jul 2009, 21:34

Carv'n Marv'n wrote: ...A compressed air driven generator would be good.


... and pity the ears of any bystanders   Image
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Post by woody » Thu, 30 Jul 2009, 22:16

EV2Go wrote: Just curious but would it be physically possible for a genset to provide sufficient power for an EV to do a long distance drive.
Definitely. Been done. AC Propulsion Long Ranger
EV2Go wrote: I know GM are planning on releasing such a car with it built in, but I am think more along the lines of something trailer mounted for those who have already converted.
I'd like one too.
EV2Go wrote: I guess my question is more around the logistics of such a device, would it be possible to bypass the battery pack altogether and have it powered straight from the generator? would you want to do this?What about in conjunction with some kind of capacitor bank so you could get off the road if the genset stalled?
You could, this is how diesel-electric trains and the big mining dump trucks work.

I don't think you'd want to bypass the battery pack.
Some caps to reduce/eliminate the ripple would be very nice.

I guess you'd size the genset to be capable of continuously generating the power required for 110kph speed. i.e. 15-25kW depending on the vehicle.

The battery would pick up the slack if you were climbing, out of fuel, accellerating etc.

A big enough capacitor bank would be enough to be able to disconnect the batteries, but you'd want to be able to plug in the batteries automatically when you put your foot down.
EV2Go wrote:Guess I am thinking if you were to constantly pumping electricity into the battery pack the whole time, you are driving and that voltage is going up and down would this shorten the battery pack life?
I'm thinking the caps and a decent control system on the Genset would take care of that. Maybe diodes / precharge resistors too?

If you disconnect the batteries, you'd want a genset as powerful as your motor/controller, which could be an option - drop out the pack and shove in a 80kW peak 20kW continuous generator in the space.

Being an AC-head, I was thinking an 11ish kW 3 phase motor + VFD with a small, efficient, proven engine, or even the ICE I rip out of the cortina. This could:
a) start the ICE
b) control the throttle based on the bus voltage
c) provide 11ish kW continuous
d) provide 30ish kW peak.
e) have a largish capacitor bank in it anyway
f) drive the car without the batteries for everything except steep fast climbs or accelerations.
g) match the DC voltage of the AC VFD for the car (i.e. no transformer/charger)
h) provide engine braking by closing the ICE's throttle and reving the AC motor.
i) be made from ebay parts.
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Post by EV2Go » Thu, 30 Jul 2009, 23:32

Large caps fitted on the trailer, so as not to take up space in the car?

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Post by coulomb » Fri, 31 Jul 2009, 01:37

I don't see the need or want for the capacitors; you have the pack (even of it is discharged by definition, i.e. you only use the trailer when the SOC on the pack is low).

So the generator can be running at its optimum efficiency, even when going downhill or slowing down for built-up areas (I'm assuming mainly country or highway driving if you need the trailer).

The voltage on the pack is going up and down all the time anyway, with regen and rests.

There are also pusher trailers, where the trailer is the front end of a car with a remote throttle connection. Like this one:

http://www.evalbum.com/753

Looks all arse backwards, but if it works, it at least avoids two energy conversions: mechanical to electrical, and electrical to mechanical. Both are reasonably efficient, but it's got to be better without them, unless the speed is changing enough to make a constant speed and power generator better.

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Post by EV2Go » Fri, 31 Jul 2009, 03:07

coulomb are they legal for use in Australia?

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Post by coulomb » Fri, 31 Jul 2009, 03:55

Legal in Australia? Uh, I don't know, I haven't looked into that, sorry. USA is the land of minimal regulation...
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Post by Tim » Fri, 31 Jul 2009, 03:57

EV2Go wrote: coulomb are they legal for use in Australia?


I can say with a fair amount of confidence that they would not be acceptable for road use in any State in Australia... even WA   Image
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Post by woody » Fri, 31 Jul 2009, 04:35

Are you sure about WA? They're pretty permissive - they let you have extra letters on your number plate even.

The volvo B12B "bendy bus" is a similar configuration (powered trailer pushing a glider). There are some differences, granted, but you could argue it's the same dynamics. I think a bendy-bus licence is the grand-daddy of all licenses, too.
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Post by Tim » Fri, 31 Jul 2009, 05:19

The first problem with the 'pusher trailer' is that by definition it isn't a trailer. It is a motor vehicle, and a non-complying one. And from there it only gets worse! Image   

The WA comment it a bit of a local joke really, taking a light-hearted dig at the fact that they have only recently started using the same rules that the rest of Australia adopted 10 years ago... and also that they have allowed all sorts of wierd and wonderful (?) vehicles to be used on the roads that can't be driven anywhere else in the country.

A 'bendy bus' isn't really the same. It is a single vehicle, not a motor vehicle towing a trailer. It doesn't come apart, and is also fully complying and recognised vehicle in both the ADRs and Regulations.

If the back part of the bus was considered a trailer... no passengers could travel in it either   Image
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Post by woody » Fri, 31 Jul 2009, 05:54

Tim, we've had this discussion before. Was it on the Zeva forum? I couldn't find it on this forum.
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Post by Thalass » Fri, 31 Jul 2009, 09:40

Woody you're a genius. I have been thinking about this for a while, and the main problem is how do you feed the power in? Do you have a 600v generator and put the power across the whole pack? Or could you have a 48v generator, and somehow charge the batteries in parallel sub-packs while discharging the pack in series?

I figured the latter wouldn't be possible - or at least not practical. So how do you get 600v at the 30 or 40 amps (guestimated) you need to keep the car going at 110km/h. It hadn't occured to me to use another 3PIM to generate the power. I know they have been used as the generators in wind turbines, effectively using regenerative braking to produce the power from the wind.

Something similar with a motor driving a motor in regen mode would work great! You could pair up the induction motor controller with the driving engine (petrol, diesel, stirling, steam, whatever) controller to maintain the optimum efficiency. I like it!

Of course that means I would need three induction motors, and two or three induction motor controllers.... hahaha
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Post by Electrocycle » Fri, 31 Jul 2009, 15:48

if you're only using the ICE for relatively constant speed cruising, it would be more efficient just to have it drive the wheels directly (could be a smallish engine connected to the main electric motor shaft)

Adding the extra generator stage means a lot more weight and less efficiency, but it is a lot more flexible in what you can do with it (charging while stationary, etc)

If you're using an industrial VFD you could easily feed another induction motor (in generator mode) into the original 3 phase AC input.
A 2 pole motor running at 3100rpm or so would give you 50Hz, but if the VFD can handle it, a 4 pole motor running at the same sort of rpm will give 100Hz and double the power to weight.

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Post by Johny » Fri, 31 Jul 2009, 15:55

Thalass wrote:Of course that means I would need three induction motors, and two or three induction motor controllers.... hahaha
Can't see that - only one more ACIM and one more controller.

It's not that expensive either. The difference being that the VFD (controller) would only have to be rated at 12kW or whatever your generator was. Unlike the traction motor controller which is called on to provide 4 to 5 times this power. Controllers in this power range are a lot cheaper and far more readily available.

Likewise the generator ACIM only needs to be 11kW and can be a stock standard voltage. There are heaps of 132 frame 7.5kW ACIMs for low cost - they should handle 10-12kW with good cooling. The ICE running the system would be tuned to optimum power at a certain speed which makes it more fuel efficient. A small diesel would be as great choice.

You would really have to do sums to see if just buying an off-the-shelf genset might be cheaper - certainly easier.

Of course for the Industial ACIM folk, the genset 3 phase output is just linked straight to the 3 phase input on the VFD. Some thought to protecting the batteries here, but high power Lithium should be fine as they are.

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Post by Thalass » Fri, 31 Jul 2009, 16:08

I'm going to have two induction motors anyway, one for the front wheels and one for the back. So a third to act as a generator. :P

But that is a point. A 12 or 15kw induction motor controller would at least be cheaper as it wouldn't need high rated components. And that should be plenty of power to start a 500cc or 1l diesel.

There's a motor rewind company not far from me (I'm not sure if they're still in business, though), so an alternator rewound for 600vdc output is a possibility. I don't know if they make custom motors/generators from scratch, though, so if the output isn't enough I'd have to find something else to modify. I might wander down there when I start my conversion, maybe they'll have some motors lying around they don't want...

Electrocycle: I'd argue that a geneset would be more efficient in more situations, as the genset could be at a constant 1000rpm no matter what, and if you were going up hill you'd be discharging the batteries, but downhill would see you charging your batteries. Whereas an ICE directly driving the car would be less efficient as it struggles uphill.
Last edited by Thalass on Fri, 31 Jul 2009, 06:14, edited 1 time in total.
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Post by EV2Go » Fri, 31 Jul 2009, 16:21

Electrocycle wrote: if you're only using the ICE for relatively constant speed cruising, it would be more efficient just to have it drive the wheels directly (could be a smallish engine connected to the main electric motor shaft)

Adding the extra generator stage means a lot more weight and less efficiency, but it is a lot more flexible in what you can do with it (charging while stationary, etc)


So you suggesting a reverse formula 1 setup, use the motor as the primary source and the engine as the back up?

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Post by Electrocycle » Fri, 31 Jul 2009, 16:28

yeah pretty much..

This is really just for a highway cruise type application, whereas a full generator setup will be able to charge the batteries, work around town, etc.

My main concern is the amount of weight you add with a generator, etc.


Say if you had a small petrol engine that makes just enough power to maintain highway cruise speeds (~30kg or so) connected to the main motor shaft by an electric clutch, it could operate over a speed range of say 80-110km/h, with the electric motor adding power when needed, or regenerating it when there's an excess.
As soon as the car is out of the ICE's efficiency range the engine can be disconnected and turned off.
Last edited by Electrocycle on Fri, 31 Jul 2009, 06:30, edited 1 time in total.
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Post by Johny » Fri, 31 Jul 2009, 16:32

Electrocycle wrote:My main concern is the amount of weight you add with a generator
If it's for highway cruising wouldn't the main concern be air drag and rolling resistance? Since this is a build-from-scratch you could have a lot of fun building a reverse teardrop near-perfect aero trailer. With a lot of thought you might even be able to improve the car's aero shape in the process.

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Post by Electrocycle » Fri, 31 Jul 2009, 16:59

what I mean is that the generator would be mainly useful for highway cruising, but would be a fair bit of dead weight to carry around the rest of the time (unless it was removable or on a trailer)

For most cars an onboard generator would be harder to do than a small mechanically coupled "boost" engine, but obviously if it's a trailer it has to be a generator.
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Post by EV2Go » Fri, 31 Jul 2009, 17:21

Since the whole premise of starting the thread was to explore different ways of extending range I think both ideas are valid. I was primarily thinking about the odd trip out into the country as opposed to something permanent. So both ideas could be just as feasible... space permitting drop in a smallish motor in temporarily to provide cruise speed or if you planned to do a number of trip maybe something trailer based.

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Post by woody » Fri, 31 Jul 2009, 17:24

Johny wrote:
Electrocycle wrote:My main concern is the amount of weight you add with a generator
If it's for highway cruising wouldn't the main concern be air drag and rolling resistance? Since this is a build-from-scratch you could have a lot of fun building a reverse teardrop near-perfect aero trailer. With a lot of thought you might even be able to improve the car's aero shape in the process.


For a sedan you should be able to reverse teardrop from the boot downwards.

I was thinking why a gen trailer?
a) easy to attach / detach
b) fits into RTA world view - they exist already

But the aero idea gives me another idea - a trailer without wheels. e.g. a bike rack or a continental kit.

I.E. a detachable aeromod which encloses a generator.

You have some sort of removable cart which enables you to attach the aeromod quickly + easily.

Another idea I had was a generator mounted under the bonnet - the cortina will have heaps of room in there. Maybe a car turbo based gas turbine? I know a guy...

Weights?
5.5kW ABB 112.102 4 pole, 34kg.
Will be 400V Star, 230V delta.
So should peak at 28kW mechanical @ 2500rpm.

Efficiency?
ACIMs under 50kg are only about 80% efficient, over 60kg about 90%
VFD's about 95% efficient, possibly different for regen.
ICE is up to 40% efficient (Diesel).
Rolling resistance is proportional to weight. Weight in the car or trailer doesn't really matter.
Drivetrain efficiency (FWD) is maybe 85% total in a 1:1 gear.
Air resistance is more of a concern than normal as you're probably going to use this for freeway speeds.
ICE efficiency is dominated by constant running cars get best efficiency at 80kph or so, overdrive helps despite being less gearbox efficient, so maybe 2000rpm is best.
You could get the car computer bits to work out the fuel consumption and compare it to the generator output...

Efficiency Chain:
Gen ACIM x GEN VFD x Wiring x Drive VFD x Drive ACIM x EV drivetrain
90% x 95% x 99% x 95% x 90% x 93% = 70% :-(
1/2 car trailer ~ 85%.

Weight of EValbum 773 style = 560kg
Weight of ACIM + diesel gen trailer = 160kg?
Weight of ACIM + removed car ICE = 260kg?

Extra 400kg is only an extra 20Wh/km rolling resistance, not a big deal
The drag calc is going to be tricky because you're not in clean air.
The closer the trailer to the car, the better I would think, and you could actually improve the drag.

If you had a drawbar mounted generator (Maybe you're driving your EV 400km for a holiday?) you get a trailer to carry all your holiday crap too.
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Post by Johny » Fri, 31 Jul 2009, 17:37

woody wrote:But the aero idea gives me another idea - a trailer without wheels. e.g. a bike rack or a continental kit.
That may add too much weight to the back of the car - but - remember a while back seeing an article that showed a small trailery thing that had a high speed caster wheel that took the weight of extra luggage. It let the car reverse without any of the normal trailer aware skills required.

It was somehow mounted hard on the back of the car using a modified tow hitch and some extra hardware. It sounds perfect to me and lends itself to changing the shape of the back of the car which would be really helpful and back it's addition an advantage.
I'll try to find it.

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Post by woody » Fri, 31 Jul 2009, 17:40

Another idea is a small genset which you carry in the boot which is big enough to charge your pack in say 2-4 hours (1-2kW), so you can charge while parked where you can't get a power point. (hopefully not in an underground carpark)
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