Best Way to Run a 7.5-hp 3-Phase Motor from Vehicle Alternator

Thanks for the reply. I'm fully aware that there's "no free lunch"...story of my life. I had the electric motor idea way before GreenSweeper.com came out with it but after much thought, decided against it. Then, when I found that someone else was doing it, I wanted to revisit the idea. Let me see if I understand what you are saying. With the greensweep system they basically built a heavy duty 8000w alternator and ran it through a varible frequency drive? So what voltage would the alternator output? As you stated and as I already figured a alternator to run a 7 1/2HP motor would be as large as a 10hp motor. So if this is the case...How are they doing it? Or am I missing something? Their alternator looks to be the same size as a regular alternator or a little larger? Thanks Dave

Here's a nearly off the shelf solution, you would need to move the controls somewhere more protected under the hood

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=45416

the electronics probably aren't set up for the highly variable speeds, still gonna have similar problems as you describe for hydraulics.

seems like there are very good reasons to use an independent power source

don't the speed of the brush & vacuum need to be nearly constant, the drivers should be able to slow down to clean more throughly clean?

I saw a similar one in Northern tool, item #165928, for about $900.00. These a 1 phase, but 3 phase must be available. -- JHF

problem with this alternator is that it has to spin at 3600 rpm to produce 60Hz Single phase. (you also need to use the 120 + 120 volts output to get this power) You better make a 1:2 conversion to have your (diesel) to spin @lower rpm. Here in the example 1800 rpm. I bought this unit for $349.00 but that is the pleasure you will get from it. To use this for continuous operation? Allow me to put a BIG ? behind it. If you want to go electrical, make sure to start from what ever alternator or dynamo, but make DC of it and go from there. This will give you one solution for the speed control independence to your main engine. That said makes me think of driving the brush with a DC motor. Industrial controllers must be to find. Depending on the size of your brush, take one with a gearbox. We can help once you make your choice. Be also aware that introducing power above 42 Volts needs special attention for your safety. Some people can get killed even with less.

Bosch used this 400Hz principle too for industrial tools from 20 years ago. Mercedes- Benz in Duesseldorf runs 400Hz throughout the plant for hand tools. Also a good solution also to not have them "removed" for home use. You'd be surprised how light the machines become.

after much searching i found these sites

http://www.nextag.com/pto-generator/products-html

http://www.generatorjoe.net/info/winco-generators/

i hope this helps

For that power range you would be better off just using a engine driven hydraulic system. Its smaller lighter and will be far cheaper plus it can carry that level of power without problems.

Hydraulic system was my original plan. Not getting off the subject but I'm putting QSB3.3 Cummins diesels in Dodge Dakota pickups. These engines should be super efficient. Then I planned on a hydraulic system to power the sweeper unit. Once I saw the electric system that GreenSweeper built, I decided to look at electrical once again. I kept thinking, no hydraulic fluid, no filters, no hoses to burst. I have to run, build, and maintain the sweeper units. Then there is the issue of keeping the hydraulic motor at speed. I've heard people in the sweeping industry complain that the operator has to keep their foot on the accelerator in order to keep the sweeping unit fan turning at the desired speed. I'm sure this is bad engineering and could be fixed. In the end I may go with hydraulics but I did want to give electric a look. Thanks

Not 3 phase, but gets you close

engine mounted, 8,000w, 10,000w peak

http://www.aurasystems.com/pages/prod_intro.html

Hi Neonfly, There is no way their alternator is smaller, lighter, less powerful than the motor that drives the sweeper. A frequency controller for 7 HP is big money too. If you want less weight, go with the alternator and motor at a higher frequency. (400 Hz- 800 Hz) Then motors and alternators need less iron and copper and are a lot lighter. Think up to 5 times gain in weight. Personally I should solve this with hydraulics-/ motors and pumps are easy to control. I should even think of powering the hydraulic pump with a diesel or propane engine and drive the vehicle also with a hydraulic motor.

I suppose you want to run a 3 phase electric motor, rated 220V 3phase, with variable speed using a frequency inverter.

If so: The Inverter can only reach to the maximum of the input voltage supplied to it. If 12V AC or DC is supplyed, then that is the limit and it will not do. If AC is available, 50 or 60Hz, then a transformer must get it up to 220V (even rectify to dc ~>220V).

On the other hand, An alternator that can produce a 3phase 220V can be any size. The problem is the power that it has to generate for the motor/inverter system. For the 7.5 HP (6kW) you need to use an alternator that can produce at least 1.5x6 = 9kW output at 220V 3phase at the used frequency, or a DC generator (can rectify the Alternator output to DC if the alternator is driven by the vehicule's motor that has no speed regulator to maintain frequency).

The Frequency Inverters (most of the good ones) have the facility to supply them with a DC voltage. The Voltage must be >= to the electric motor's 3phase voltage required(here 220VDC). The power of the DC should also be ~ 9KW to give confort of decent operational reliability.

Cooling: Air cooling is the easiest. Since this is a project for a specific usage, a separate cooling fan (properly sized, centrifugal preferably) can be installed in such a way as to draw air from the outside, through a grill/filter and ducted to the Inverter cabinet. Do not forget to channel the outlet air to also a safe area where obstruction is not likely.

Volume: New Inverters of the size 6 kW to ~10 kW are not so big any more. their volume can be accomodate especially if you are force cooling them.

Isn't the question what is the minimum speed the alternator has to spin to provide enough output power?

all the stuff you're saying about the inverters [cooling, inputs...] is true

the overall design needs to be absolutly bullet proof

the guys using the system[s], are working all night & not always able to do troubleshooting.

I've seen allan bradley inverters mounted with the cooling fins hanging out of the enclosure, that withstood nightly cleaning with pressure washers.

this would once again require a well thought out design,

the interface/display mounted inside the cab [dash] inverter mounted external is a possibility

Absolutely right.

The Speed of the Alternator is crutial for the Power outout. That is why it must be fixed so that the driving engine will run at that speed as a minimum...

Also, The frequency of the alternator will have to be low. A higher frequency will reduce the size for a specific output.

Off the shelve frequency inverters usually need their DC voltage input to be >= to the required 3 phase output voltage. That is why you should not output at DC 12 or 24 V, but keep it higher than the 220V he requires (commenting on other inputs from contributors...)

Yeah, wasn't picking on you

you were just the last in the string

If you guys don't mind...Go to GreenSweeper.com and click on FAQ. This shows their alternator which says it produces 8000w. The alternator doesn't look much larger than a regular vehicle alternator. I think JRaef pointed me in the right direction with the aviation type alternator running at a higher HZ. Their inverter looks like a standard inverter. Somehow they are controlling the speed of the 3 phase motor and giving it soft start. Their system looks very light and compact. I have my doubt that it will be dependable over the long haul. I've been in this business for 35 years and the equipment goes through hell. I try to build everything as fail-safe as possible. If I were going to custom build this system, I would definitely make the inverter/controller liquid cooled with a external radiator. The sweepers make so much dust that it kills everything. Placing the unit behind the seat with cooling fans is a bad idea since workers with throw rain coats and other items on it. I think of all this because I have to repair them. I build the trucks for myself and if it breaks it cost me money. I don't make money by selling a product that will break and then the customer will pay me to fix it. That's why I wanted to know if a electrical type drive system would work. Electrical is attractive to me from a low cost maintenance standpoint and the fact it would be quite. But if the inverter/controller or alternator goes out every 6 months then the system is worthless. I know a hydraulic system would last for years without much trouble. But a hydraulic system also has it's bad points.

Just a thought as you want the units to be relable this is what i would do.

fit a generator that uses the same fuel as the truck.

fit the genset so it can easily be removed from the truck.

get a genset with electric start so you can turn it on and off from in the drivers cab.

then if you get a failure of the genset you simply remove faulty genset and replace with the spare one you have ready, and repair the faulty one at your leisure.

there would be no extra load etc on main engine.

very little downtime if geny fails.

more economical than using truck engine reving hi to maitain volatage stability.

what do you think?

some of the sweepers I've seen use a secondary petrol powered engine to drive the brush, cutting out the needless conversions

OP would like to increase the reliability, as much as possible...

the cheaper & more off the shelf [obtainum] the better

yes i understand the need for reliability which is why i suggested seperate geny.

if you use the main engine. It will need to reved high but forward speed of truck will be low, thus engine may overheat, this will put an extra strain on engine cooling, and all parts under the bonnet.

if drive belt breaks you loose possible both aux generator and truck alternator, so complete truck is now down.

if you rev main engine how would you drive truck slowly ? 3000 rpm equates to approx 20 mph in first gear and the only way to slow it down would be to use brakes.

a seperate gen set is by far the easiest way.

also if you go and fit extra non approved parts to truck, you may invalidate warranty.

my aim is to keep it simple

Just a thought as you want the units to be relable this is what i would do.

fit a generator that uses the same fuel as the truck.

fit the genset so it can easily be removed from the truck.

get a genset with electric start so you can turn it on and off from in the drivers cab.

then if you get a failure of the genset you simply remove faulty genset and replace with the spare one you have ready, and repair the faulty one at your leisure.

there would be no extra load etc on main engine.

very little downtime if geny fails.

more economical than using truck engine reving hi to maitain volatage stability.

what do you think?

You might want to look into these brushless DC motors. (they are about 4.5 kW continuous output, peaking at close to 15)

I am using, for a prototype vehicle, a couple of motors very similar to these (although in brushed versions for the prototype). A gasoline engine powers one such, used as a generator. Voltage control is via rpm control. In my application (a plug-in hybrid) when current drops to a point where the engine is no longer heavily loaded, the engine shuts off. Two more motors like these drive the front wheels independently.

Controllers are readily available and inexpensive (because they are basically golf car stuff).

As generators or motors, they are about 90% efficient.

PMG in Germany makes some highly regarded PM DC motors of similar size. The brushed versions have good brush life (unlike the brushed Etek motors in my prototype) but you may have reasons to avoiding brushes, and may want water cooling rather than air cooling. PMG also makes brushless versions of ample hp for your needs, but they tend to be pricey -- but perhaps for your application that is ok. They are available air or water cooled.

A battery bank could have some advantages for control -- not the least being that typical golf car controllers look for voltage within a range... and you wouldn't want to have to reset the controller all the time if voltage dropped off with the engine at idle, for example. Having a vehicle alternator keep a battery pack at 48V would be quite simple: a DCDC boost converter could be used. Then the vehicles engine and the electric drive system would be effectively decoupled, without the need to run the engine fast for peak power. Depending on how you use the system, perhaps the truck could recharge the battery pack in driving between parking lots, by using a production heavy duty alternator.

Just random thoughts.

Also check out hiperformance golf cars, who make ac motors for golf car use (and can supply matching controllers).

And then there's hydraulics... probably simpler, lighter, and cheaper.

Thanks, I appreciate the help. Found this site following your advice. Manta PMG Permanent Magnet Generator MAKE BUILD ELECTRIC CARS VEHICLES PANCAKE ELECTRIC MOTORS etek ELECTRIC MOTORCYCLE PMG P... From the description the motors look to be very dependable. If I were to go with a battery pack, what would be the best option for heavy duty use? Lead Acid, Lithium? I could go to autozone and purchase lead acid batteries with 7 year warrantee but I would imagine with auto batteries the cycle life would be limited. Of course, they would last longer if they were not allowed to run very low and kept charged. As you stated the batteries could be recharged while driving from job to job. What kind of management system could I use to extend battery life. The RPM of the motor shaft could be 4 speed instead of variable. I need to turn my fan at around 3000 rpm max. I'll try to post some photos of the fan. I could use either a belt system or a overhung load adapter.

Here's a couple of links you may find interesting. Tesla Motors - Engineering

http://www.metricmind.com/data/man_w.pdf

In this configuration you can oversize your alternator that charges the batteries and use less batteries (weight!!) What are all the loads on your engine together? 7 kw for the brush? If one golf cart motor is too small, you can put 2 / one on each side of the shaft and spin one in reverse. When you synchronize the controls it will work. Lead Acid, preferably deep cycle - if the budget is there even deep cycle gel. ( $700 for 200Ah ) - need to match your working voltage - these batteries come most with wires. If your alternator matches up the losses, regular automotive batteries can work also but last only a few years.Your vehicle engine has a lot more power available at your sweeping speed and can drive a super alternator or higher frequency type/p]

PMG is not, as far as I know, a trademark of Perm in Germany, but is often associated with their motors... so I am a little skeptical of a company using that designation to promote rebuilt Etek motors (which were a product of Briggs and Stratton). The Eteks have very good performance characteristics... but pretty short brush life -- dropping below 100 hours if you operate at near peak power. As I said, I have a couple Etek motors and am happy with them, but I am expecting to have to replace brushes, if I put a lot of miles on the proof-of-concept prototype (and will almost certainly use brushless in the production vehicle).

The 275,000 hours brush life claimed in the link you provided --- I seriously doubt it. Also I doubt their efficiency claim (94%) because I have the actual (motor by motor) dyno curves from both of mine, and the peak is 89%, and varies only slightly from motor to motor. Some time ago, I looked into the Manta motors, and did not conclude, at that time, that they are doing anything to improve efficiency substantially. (In the motor world, the difference between 89% and 94% is very large, in the sense that you pay a lot extra for that increment, usually). I've planned to order their replacement brushes, and once I install those, (if) I may find that they work exceptionally well... but 1000 times longer than expected brush life??

The Perm motors have a reputation for being much easier than the Eteks on brushes, (and their brushless DC motors [they call them synchronous] avoid the issue entirely.) The Mars motors are designed by the same guy who designed the Etek, and are a fraction of the price of the Perm brushless motors (and in fact, less than half the price of the Perm brushed motors, which have varied in price in the US, around $1000).

With reasonable precautions, you can probably use air-cooled motors (like the Mars brushless). (See designs for "Dorade" boxes used on boats) Kelly Controls make a controller (actually a bunch of controllers) for the Mars brushless motor.

Thundersky lithium ferophosphate batteries are reasonably-priced and much lighter and far longer-lived than lead acid. In general, I've found the Chinese companies far easier to deal with than A123 -- a US-based company. Chinese and Korean companies have contacted me out of the blue, whereas A 123 does not respond at all to direct inquiries, typically -- they cannot be bothered with small entrepreneurial companies, from as far as I can tell.

Thundersky batteries have a longer vehicle-installed history here in the US than any other (Lithium) , I would say, and they started out with quality "issues" but seem to be really pretty good now. For my own prototype I may use Headway batteries, which have the advantage of greater power density (but no better energy density than the Thundersky batteries.)

The tried-and-true way to go would be Trojan lead acid batteries (deep cycle, 8 or 12 V). They are somewhat expensive but good quality, and much lower in initial cost than any of the Lithium chemistries. There are other good LA batteries, but the Trojans are the standard that every EV converter has heard about.

Poke around EValbum, and look through the archives. You will find 48V systems mainly in the motorcycles.

Re the Tesla link, I think the conclusions are right on the money: Induction motors in large high hp electrics, brushless DC in smaller vehicles and hybrids. The lower the HP, the lower efficiency of ac induction motors goes... and there just has not been a large installed base of AC motor vehicles, outside of the fork truck market, (There, I looked for a motor and controller, and darn near suffered a fatal heart attack when told the price of the motor alone, let alone the controller. An AC fork truck motor of about the size needed for my small vehicle (to serve as an alternative for $900 worth of Mars motors) would be $12,000.)

Poke around the EV discussion list archives (see EValbum) for recomendations on battery management systems. These can range from very simple (a zener diode across each cell, disipating over-voltage power to a light bulb) to complex. Usually, undervoltage is sensed by the controller, and if the cells are pretty close (via the zeners) it is unlikely that on e cell will be very far below the low limit when the controller says: stop. You could be conservative on the low limit to help ensure that no cell goes below the point of no return. (This, in itself, extends battery life: 2000 50 AH cyles are better than trying for 1000 100 AH cycles.)

Four speed control, as outlined on the Manta site would be far more effort than it is worth, I think. The ordinary switches for motors like thes are contactors, (of a size that bang rather than click) not manual slider switches. This system also completely screws up any attempt to keep the batteries balanced. (And with brusless motors, it is useless.)

Vicor has a good reputation in the DC DC converter world. (Using a DC DC boost converter -- albeit expensive in high amperage sizes -- would be simpler and more reiable, I think than switching the batteries from series to parallel for operation/charging.

Also, a 48 V alternator would be simple, if there is space for it. A 12 V alternator can be easily made to produce 48 V, without even needing to rewind it -- its just a matter of changing the voltage regulation -- the diodes are already rated at 100V or more, typically. All sorts of possibilities: speed up the drive ratio, and provide an AC clutch to prevent overspeed; only plan for adequate voltage when the truck is opearating at over 2000 rpm... of rewind or find a real 48V alternator.

But again, weigh all this stuff, and the potential benefits of stored power. If there is not great need for power storage, then hydraulics would probably be cheaper and easier, I'd think. Once you start to add hydraulic accumulators, the advanrtages can tip in favor of electrics....

And then there is another possibility -- makes your trucks electric.

Just to throw out an idea outside of the box, look into portable welders and the potential of using one of them as your power supply. You can either adapt the drive to run off of your pto or use it driven independantly. Lots of power and just about as bulletproof as you are going to find. You also could adapt dc drive for your motors too with very little difficulty as most of your welders are in the 36 volt range and that is also the same range of most of your electric fork lifts. So it becomes just a matter of adapting of the shelf equipment that has a very proven track record of dependability.

Good luck

Rich Hurd

Everyone is addrssing the running power - how about start up power? Is this 7-1/2 hp motor under a load when starting? You are taking about 8000w + running BUT maybe 16000w starting and maybe even more if the motor is under a heavy startup load.

The people you are talking about may be using a bank of batteries and getting 3-phase from that?

Have fun!

No they are not using a battery bank. Yes, the motor is starting under load although not a huge load. This is probably why they use soft start. Once the fan is spinning it doesn't take as much torque to keep it running. They slowly bring it up to speed. If it were to start up at 2500rpm then that would be a huge initial load. At least I think I'm correct about this.

My inclination would be to go hydraulic using a variable volume pump (compensated). If you specify a pump capable of providing the required volume of oil at the lowest expected operating engine speed, it should be good to go as long as the maximum engine speed does not over speed the pump.

If electrical is the chosen answer, why not use a 3 phase alternator rectified to DC. Then use variable frequency/speed drives that run off the DC to power the brush and vacuum. One really does not care about the frequency of the 3 phase alternator or the voltage output so long as the DC derived from that output is appropriate to the VFD inputs powering the fan and brush drives.

My response is probably useless noise but I feel better for having typed it, so that is enough!

Have FUN!
TT3