Audi 80 1.9 TDI Generator Update

[Hilltopgrange]

Hi Guys time for an update on the Audi gen.

I left off last time having just completed the mechanical build so this is mostly the electrical side of things. It has taken a bit longer than expected as I have been tied up with other things.

First off all calculations and formula where taken from Motors as generators for micro hydo power by Nigel Smith

The Motor I used is a Dutchi 15kw from the "book" it says to de-rate the motor when run as a generator to 80% so that brings us down to 12kw max output but to be honest I don't expect to get that, anyway here is a pic of the plate

I was just about to work out the formula for calculating the required capacitance when I noticed that one of the worked examples was for a 15kw motor, what a stroke of luck! that saved a page of calculations and a whole lot of head scratching. For those that have the book it is on page 28. The recommended capacitance for excitation is 59uf I have a selection of motor run caps mostly 10 - 50 uf so the closest I could get to was 60uf.





This how the capacitance is worked out.

(NOTE TO ED If this pic causes a breach of copyright just pull it and I will repost I have no idea how to type the symbols for this lol.)

For my first test I connected the motor terminals in star and the caps where then connected across these in delta. I started the engine and started to raise the engine speed while watching a meter connected to phases. From idle at 900 rpm I see 1 volt as you raise the speed the voltage climbs steeply and at a little over 1500 rpm I am getting 400v at 50hz. If you continue to increase engine speed the voltage continues to climb

So that part seems to be working fine

Now 400v out is all very well but I need to charge batteries as well as run 3 phase tools. So I need to step this down to at least 220. There seems to be a few ways to achieve this

1. modify the windings of the motor by putting the coils of each phase in parallel (if in series)
   
2. Find a 3 phase 415 -220 transformer and then step down with another transformer set to charging voltage {48v battery)
   
   

The 2nd solution looks expensive

I was thinking this over when I had a thought, I have an old 3 phase/single phase oil cooled welder it is a Pickhill Bantam with 2 output ranges 180 amps at 50v and 130 amps at 80v. So with the motor connected star and the caps in delta I connected the welder for 3 phase 415v input and started her up I increased the engine speed but it would not excite! Hmmm time for a cup of tea and a think.

Round two

I disconnected the motor and caps had another read at the book and decided to try it again but rigged for single phase. I connected the motor in delta with the caps in C-2C for single phase and connected the load across 1C as per the book, I then connected the welder for 415v single phase and selected the 50v high current range. I started the engine and brought it up to 1500 rpm where the welder came to life and I was able to weld some hefty plate for about 10 mins. The welder and the motor remained stone cold so I think I have the direction of rotation correct for C-2C as apparently it gets hot quickly if not. I must buy a sequence tester just to check.

Now I think I am getting there!

The 50v range turns out to be 55v at 415 in, so when this is rectified we are in the ballpark for charging the 48v bank. Now for a real test, I connected the output from the welder to 2 large bridge rectifiers from a 72v forklift charger and connected to the battery via fuse and ammeter. I started her up and brought the weld current up 1 notch at a time to the max where I was getting about 40 amps(2kw) I then brought the revs up slightly to about 1600 rpm and 450v at 60hz this increased the charge to about 80 amps. I let it run for about an hour while keeping a close eye on it and it performed well the welder got warm but not hot and the motor was cool . At this point while testing with a volt meter I noticed that when I measure across the two unused phase connections on the welder I was getting 220v so as a quick experiment I connected a 24v 60A charger to charge my 24v bank at the same time. I ran it for another hour charging both banks while monitoring the temperature, both the welder and charger ran warm but not hot and the motor remains almost cold.

Now I know what I have done here is not ideal but it does seem to work with a total of about 5kw. I could easily push for more out of the welder by increasing the speed and thus the voltage as I have seen 700v output with out load but I don't know how that would affect the welder? I don't want to burn it out, I also have this picture in my mind of a fly on a zapper! Only I am the fly.

I would like to be able to run it as 3 phase rather than the C-2C single phase setup but it just refuses to excite with all 3 phases connected, if I remove 1 phase it excites and generates on 2, should I add more capacitance or should I add capacitance to the load?

If I can get a 3 phase transformer 415v 220v would it cause the same problem or does the welder have a large inductor in it that is causing the collapse or is it simply to large  of a load

Any suggestions on the best way forward would be most welcome!

Since the last diary entry I have also managed to get the chassis painted and looking a bit prettier, it is now bolted down in its new home and connected to a decent size fuel tank. I have also been playing with different fuels and blends. When running on diesel starting is instant, with no need for the glow plugs to preheat. Next up was waste engine oil filtered to one micron and preheated to about 90c just before the injector pump. Starting from cold takes about 3 seconds with a little bit of smoke on starting but clears very quickly and no visible smoke at working temp of 80c. Next was the waste veggie oil again filtered to 1 micron and preheated the same as the waste eng oil with the same results. No doubt if this was repeated on a car with straight oil there would probably be some smoke or hesitation on acceleration but as the generator will run at a constant speed I don't think it will be an issue. It will be interesting to see how well it starts when winter sets in. Fuel consumption so far is about 1.5 litres per hour, not that it matters as my fuel is free and the noise level is way down compared to the little Lister Petter I used previously.

To sum up

Have I achieved my goal.. well it sort of works if I could over come the collapse of excitation current and run 3 phase I think it would be better but 5kw isn't to bad. The multi fuel engine has worked a treat and although I haven't started with the recovery of heat yet, I don't foresee to many problems. So all in all I am pleased with the results and think it was well worth the effort. Total cost of build so far is under £75 ($150) Total value of sticking two fingers up at the Electricity Company... Priceless

So that's it so far warts and all! Any ideas or suggestions would be very welcome, is there a better way to do this?

Many thanks in advance

Russell

[wdyasq]

Russell,

Looks real nice. I may copy that formula down and put it in a spreadsheet so mathematical morons could enter the needed numbers and get an output.

Ron

[electrondady1]

congratulations .

that is a whole lot of generator for $150.

[tdmack]

Good work Russell

Not sure if you are switching in the load after excitation or not but I've had better luck getting them  started by switching off inductive loads until I have voltage.  Also switching off loads prior to shut down prevents loss of the small residual magnetism required for the next start up.  

Tim

[Flux]

Don't take those capacitor calculations as anything precise. If it excited you are near but adding inductive loads will require more capacitors. You may have to build up off load and then switch the welder transformer in.

You can run it delta connected and use 230v loads balanced round the phases but you will need lots more capacitance, start with about 3 times the star value but expect to have to increase.

These self excited induction generators are very unstable, you are relying on saturation for voltage regulation. They work fairly well on constant load and constant speed ( mainly hydro with load control circuits) They will not have the stability of a decent synchronous alternator with AVR. Expect lights to flicker all over the place if you are switching loads.

Don't try to take power from the other phases in the C/2C connection

If you are a bit short of capacitance you can always raise the speed a bit to increase the excitation.

Similarly if you have plenty of capacitance to take inductive loads then it may be over excited and run hot on no load, you can drop the speed a bit to bring the excitation back to a reasonable value.

You seem to be doing reasonably well, don't expect miracles with battery charging. If you mainly want it for battery charging then look for a 3 phase transformer. Single phase battery chargers are a pain on small alternators.

Fortunately most loads are not very voltage or frequency critical. Sensitive electronic things now mainly have built in regulators, not like the earlier TVs that used to be very fussy.

Flux

[Hilltopgrange]

Hi Ron, yes that would be very handy as I am one of those mathematical morons! I can do the math ok, just cant remember it.

Russell

[Hilltopgrange]

Hi electrondady1 thanks, I was lucky to have most of the parts at hand. I tend to be a bit of a horder when it comes to engines etc. I just cant stand to part with good "pruck" as they say in these parts, every now and then it pulls you out of a hole!

Russell

[Hilltopgrange]

Hi Tim

       Thanks, I have tried switching them without success. I can get it to excite with any 2 phases connected I could try switching the last one, i will try that tomorrow and see what happens. I always switch off the loads prior to shut down as I had read that in the book. I will let you know how it goes.

Russell

[Hilltopgrange]

Hi Flux

       Thanks for the detailed reply, it is very helpful. I have some more of the caps so I will try them and see if it helps.

I won't be running lights from this it will mainly be for charging. If I can get it to run the welder it would be very handy for the new tower I am planning, the only other load would be a 3 ph 5hp radial arm saw.

I am well pleased with it even as it is but it would be nice to have the option of 3 phase. I may be able to get a 3ph 415 - 220v transformer or I was thinking if I could get a 3 phase 48v forklift charger. It's hard to know the best route, I may also be able to get my hands on a larger welder I think it is 220amp.

The best bet I think is to try the extra caps and switches to get this welder going first and then take it from there.

If I run up the speed/voltage to about 1700rpm and 475v I get about 80-90amps at 48v about 4.5kw plus 60A at 24v on the other charger so about 5-6kw total isn't to bad, but I am afraid of damaging the welder with the higher voltage and frequency (about 70hz)

I will try all your suggestions and see what happens.

Thanks again Russell

[Flux]

Russell

I am not sure I follow what you said. Did you imply that it will not excite 3 phase star connected with delta capacitors, but it will do so if you remove one phase or did you mean that it will excite as 3 phase but not with the welder connected.

The magnetising current of that welder will be very high at 415v and you may need to at least double the capacitance.

As long as there is no phasing problems with the winding ( star point correctly connected) then it should excite on 3 phase if you have enough capacitance. To run reasonable loads I would expect you to have to well over excite it on no load ( 460 volts perhaps) and the thing may overheat on no load ( not a useful way to run it so it doesn't matter).

I think you are being a bit too theoretical about the capacitors, just throw more at it. No two manufacturers are likely to end up with similar magnetising currents, its mostly trial and error.

Flux

[Hilltopgrange]

Hi Flux

        it will excite in 3 phase with the motor in star and the caps delta and no load, if you connect the load the excitation colapses, how ever if you disconect 1 of the phases on the load it will excite but will colapse if you try to connect the 3rd phase again, I hope you can follow that I am starting to confuse myself!

I have a pile more caps so I will try them tomorrow.

Thanks again

Russell

[Flux]

Transformers rated for a given voltage and frequency will not bother about volts and frequency being raised in the same ratio. A 50 Hz 400v transformer will be happy with 480v at 60 HZ so in that respect you need not worry.

Welders tend to have a high magnetising current as the magnetising loss is small compared with the severe copper loss during welding. Those oil filled beasts will probably not be too bothered about a bit more magnetising current.

I am not sure what current rating they can stand long term, welding duty is often as low as 20%. The insulation inside is class A so probably a container temperature of 60C is about your reasonable limit for long term survival.

Welding duty is likely to be the worst duty possible for a self excited induction generator and you may really have to add much more capacitance on a short term basis than it could stand continuously.

For single phase loads you can run them from line to neutral on the star winding without needing a 415/230v transformer. Just try to keep them balanced. Keep the capacitors delta to keep the size down.

Flux

[alibro]

Hi Russell

I just read your diary entries and am well impressed with everything you have achieved. I thought I was the only one to have built a wind turbine from scratch in our wee country but mine is more for fun than serious off grid living. We did that for a while and the boss was not impressed   I live just outside Moira, Co. Armagh.  and with the current cost of diesel I love the idea of using wvo but I am not a mechanic so I am worried about the implications. My wife drives an old Landrover Freelander (the model before the BMW TD4 engine) do you know if it would be suitable for conversion? I agree that the hassle (and cost) of making Bio diesel means it is hardly worth it. To be honest I would be scared to try as If I did anything to harm her beloved Freelander I would never hear the end of it.

Sorry this is a wee bit off topic but I wanted to let you know there are at least two of us here.

You can read about some of my antics in my diaries.

Cheers

Alibro