alternator as a generator in a car

[birt]

I have aquired an alternator from a generator and i want to use it attached to my engine to create 240v @ 50hz it claims to produce this at 3000rpm but of course of i spin it faster this will go higher can anyone suggest some easy ways of regulating this output? circuit diagrams maybe.
i intend to run power tools and lighting so a current drain of 6-10 amps should be allowed for.

TIA
Birt

 

You have to be very careful here with this one. An Alternator produces an output that is proportional to speed. This output changes in two ways frequency and voltage. But the main one being frequency, this is why you have to spin it at 3000rpm to generate the 50hz output. the voltage output is generated by the excitation present within the alternator, this can be internal or external, better generators utilise a form of external excitation dependant upon the output voltage, when you draw current the voltage drops and the excitation compensates for this and pushes the voltage up. What sort of engine are you using to drive the thing diesel or petrol ? You need to work out how to control the speed, it will be by frequency if the frequency drops then the speed govenor will cause the throttle to open to speed up the engine, or rather ensure that the frequency doesnt drop and likewise when you remove a load the engine will speed up, the govenor has to throttle back to keep this in control. So now you have excitation to control the output voltage and then you have speed control to control the frequency........
There are modules that you can buy to do this, Id go for a pulse frequency on the flywheel and use that to control the throttle so that you try to rev up if the speed drops and vice versa. hen you would have to look at the voltage, need to see what you have on your alternator to control the voltage and maintain it at 240 v...........

 

[birt]

I intend to attach this to my Landrover Discover engine, there is a space where the airconditioning pump should be. the only problemn is if i fit a mechanism to adjust the throttle on the 2.5tdi engine it must not interfere with the normal operation of the car.

 

[BrianG]

I can understand tour reluctance to make changes to the engine throttle system to control the alternator speed. If you need a stable 50Hz frequency it might be better to consider rectifying the alternator output to produce extra d.c. power and then use a solid state inverter to give you constant frequency and regulated voltage for your tools etc.

 

[birt]

The only issue with an inverter is cost, an inverter powerful enough would cost over £1000 so another solution would be great.

 

[gjones33]

Hi Birt,

Ayrboy is quite correct and throwing a 3kw load on the engine will reduce the speed and therfore speed control is essential. For saftey reasons this is definately not recommended. An alternative might be to obtain a separate small i.c engine say about 7 or 8 hp

Cheers
G

 

[BJC]

The people I buy tires (or tyres depending where you are) have such generator on there service trucks ( 3/4 ton pickup). I looked at one once but don't remember the details. The truck ran 120V tools and lights. It was real AC because the guy said he could run TVs and other thing on them. The truck had an air compressor as well. When operating tool the engine didn't seem to be running that fast ( less than 2000 RPM i would guess. It was a 5.7L chevy. I would find or look up the people who made such thing and look at there literature and find one if I could.

 

[gjones33]

Hi bjc,

The loads you mention - compressor, tv, hand tools etc are all low power less than say 500w or about 2 amps at 240 volts which is a lot less power than the 10 amps you mentioned originaly. You might get away with running the engine on a fast idle speed at these low powers but the speed and therefore frequency will vary with load. Most hand tools, drills, compressors etc are all ac/dc motors and will not be affected by frequency.

Cheers
G

 

[birt]

BJC,
Were do you get tires? perhaps i can contact them and ask who makes the generator?

 

[tmonca]

Hi

Ever thought of just buying a small AC generator? You can pick up a 2.2kVA generator from Screwfix for £350.

As far as engine regulators go, I personally would be leary of trying to fiddle too much with a 2.5TDi as they are quite a complex piece of kit. On the other hand, if you actually listen to any vehicle with an on-board generator, you can hear the engine regulator at work, changing the engine note as the power changes.

I think the suggestion to buy a small engine is prob your best bet, but obviously that isn't going to fit in where the air conditioner should be...

 

[birt]

The point is i don't want a small engine to run it, the generator needs to be discreet.

R32, Did your system have any form of voltage regulator? what stopped the voltage and frequency rising?

Suppose i could have a throttle adjuster and just only switch it on when i want to generate AC, how difficult would that be to make? any good ideas?

 

[BJC]

Here's one. These work well enough for tools and lights. The people use use them are not emotionally attached to there vehicles. The truck is usually a tool used and rebuilt as needed. They don't mind running the engine 1200 RPMs for 6 or 8 hrs.

http://www.tendaire.com/b_Ser.htm

 

[Lewish]

Check the duty rating on your alternator. If it is not rated for varying speeds and no load conditions, it is going to fail from spinning while you are driving down the lane. I would recommend fitting an A/C clutch to the shaft, so that you can stop the alternator from spinning when you don't need to use it.

 

[birt]

Lewish,
excuse my ignorence, A/C clutch? what is that when it is at home?

 

[Lewish]

birt, an air conditioner compressor in an automobile has a clutch on it to prevent over-compression of the cooling gas. That is an A/C clutch. All cars with A/C have a clutch on the compressor. Just pick one up off a wrecked car and adapt it to your needs.

The clutch is engaged by electric current. So, you will have a switch some where to engage it when you want to use the alternator. The one side of the switch goes to your +12V supply and the other to the wire on the clutch. Current return is thru the frame in most units, but some have a ground wire.

 

[birt]

Thanks, i'm away on bussiness at the mo but i will be trying a few things when i get home, the idle speed is fairly constant and if i calculate the correct fly wheel size i can get 3000 rpm when the engine is idling.
we will see how it goes

 

[peebee]

Maybe you could adapt a cruise control device (either aftermarket or existing in your truck) to provide engine speed control. You might want to run the neutral safety switch through the controller to make sure the device is defeated whenever the car is not in neutral.

 

[birt]

Next idea, how about a hydraulic constant speed drive thingy, aparently they have them on Airplanes but i know nothing about them. ideas gentelmen please or an explination/website with a diagram etc thanx

 

[evelrod]

birt, Since you seem to be having a great deal more difficulty than you should be, let me add my two cents (2p) worth here. Every generator I have ever used, AC or DC output have had some sort of throttle control to keep a constant output voltage. Welding machine mounted (Miller, Lincoln etc.) to my Onan 3.5kw in the motorhome, all use throttle control. You do not have to disrupt your normal throttle to accomplish this. Try not to reinvent the wheel and just look around at what the portable generators are using and just copy one. If it works for them, it'll work for you! I am not an electrical engineer and I now monitor this forum because y'all have lots of helpful ideas I can use. Let me return the favor and direct your inquiry to the automotive forums. I'll just bet you will find someone there who has already done what you are attempting.
I have used AC output systems on work trucks many times and I don't recall any particular difficulty aside normal maintenance!

Rod

 

[don01]

brt
If I assume you only want to run some pretty rough gear ~ say lights drills etc and not your prize tv or stereo or such that will worry about some frequency or volts change (not lots of change) heres a suggestion which should be at the low end of the cost spectrum, (and you can worry about the details)
If you have the alternator permenately connected to the drive pulley (crankshaft or harmonic balancer ) then 2 things will happen. It will spin a hell of a lot while you go to the beach and wear the brushes bearings etc etc, AND if you put the foot down and get the revs up, It may well self excite and with no load or open circuit the volts will go very high and you wont have to worry about using it.
my suggestion runs along these lines. I assume the ac pulley on the crank is the outer pulley if not it's probably an accessory at the off road shop to get one that will put the belt outside. Now a discovery shop have a tacho so you can get the rpm at warm idle and calulate the pulley(s) to get the right rpm.
Make up a quick fit bracket with say wing nuts (say 6mm rod welded to the nut) where you would adjust the belt tension.
Now If you want to use it loosen the wing nut and fit the belt tension and start up. Finnished? stop motor and remove belt.

I reckon you might almost get away with it- provided your load can tolerate a bit of variation in Hz - suggestion use light globes to test it at various loads and make a note of Hz and volts V amp

Good luck
Don