DIY inverter generator

[bryanb]

So the windy would need to be programed to each individual alternator so it knew what it was going to be doing at a certain output.

You would need to connect the alternator to a motor of some sort and run it  from zero to max RPM to build the reference table would you not or have one from the manufacturer of the alt with a certain specfic blade in this case.

It is my understanding that they came with a default table and then you manually "tuned" the points in the table (around 10) for your specific generator.  The MPPT algorithm then used these points to create a power curve for RPM to Current Draw calculation.

[LowGear]

SMA programming.   Sorry, I've been on a visit to the mainland.  Phone technical support at SMA USA for clear reliable advice.  My SunnyBoy was just adjusted to Line voltage parameters.  When I inquired, many years ago, I was lead to believe the WindyBoy was the same device with modified software algorithms. 

If I'm wrong I must just have WindyBoy 7000 for sale but shipping from Hawaii would not be cheap.  They weigh about 150 pounds.  We might look for a trade as well.

[bryanb]

Thanks LowGear.  I have talked to SMA before, but I just tried again, and they do not like the idea that I am doing something other that solar.  They were NOT helpful at all.  I did manage to get him to admit that the parameters can be changed.  I asked for some documentation on the parameters but all he would tell me is: read the installation manual.  I downloaded it and all it contains is paragraph on how to access the parameter menu in the unit.  It does not mention any particular parameter or what they do. 

I have also sent a query to ABB.  We will see what they say ...

Definitely let me know if that windy boy doesn't work out for you, I am interested ....

[glort]

I think I can see why this is allowed in Canada where it would not be in so many other places.
The Canadians have worked out how damn difficult and costly this can be and realised 99 out of 100 people are probably going to give up before they get started.


SMA have a reputation here  for being unhelpful, especially when it comes to warranty claims. They used to be one of the Pet/ darling brands but their recommendation has slipped substantially due to their less than outstanding customer service and their products not living up to the reputation they once had.

[LowGear]

I don't think I'd confuse SMA with details.  They were slow to tell me that they didn't want me inside the cover because of safety concerns rather than damaging the equipment.  Finally they admitted they were concerned about user safety.  Doing something not in the pamphlet might require medical attention.  The software used to be available on their website.

[bryanb]

The software used to be available on their website.

i had a pretty thorough look through the web site and all I found was two firmware updates with no info on what they were about. 

[bryanb]

So here is where I am at ...   I have figured out how to deal with the MPPT/governor conflict.  A diesel generator governor is designed to maintain the set RPM when the load changes.  Other diesel engine uses (automotive) do not have that type of governor.  For example an automotive engine governor is designed to protect against under-speed and over-speed, it doesn't care if the RPM changes with load.
My plan now is to couple a VW engine with a 3 phase IMAG, rectify the unregulated wild AC and feed a Certified grid-tie solar string inverter.  So, in effect, it will be like running the IMAG as a standalone generator.
What I am not sure about at this point is:
 will the IMAG maintain its "flash" at varying RPMs, particularly lower RPMs?  How low?
 what load will the IMAG handle before loosing its "flash"?  50% of name plate?

I am sure some of you guys know this stuff or could point me in the right direction.
Should I cross post this to the " Induction generator" category?  

[mike90045]

What is IMAG ?

A regular alternator looses it's flash magnetism if it spins down with a load connected.  Always make sure you have fuel, and cut breakers off and let genset run a few minutes to cool down before shutting down.

[bryanb]

IMAG = Induction Motor As Generator

[glort]

What I am not sure about at this point is:
 will the IMAG maintain its "flash" at varying RPMs, particularly lower RPMs?  How low?
 what load will the IMAG handle before loosing its "flash"?  50% of name plate?

I am sure some of you guys know this stuff or could point me in the right direction.

Where the IMAG will stay energized depends on how much capacitance you are running.
There is a fair amount of " Tuning" you can do with this.  If you up the Capacitance you will get more stability and the power will come in early but tends in my experience to be very peaky. Small changes is RPM make big Changes in Voltage but if you are running fixed throttle and relatively fixed load, shouldn't be all that big a deal as you can wind the throttle to give what you want.
I'd be aiming at around 300V at the RPM you want to run on the AC side which will give 430? or so DC. That will will be in the range of the GTI which are all 600V now.  This will give you plenty of head room and a margin below.
Far as I am aware the imag will loose generation at below nameplate RPM But I have gone below this using a lot of capacitance for the size motor I'm running. Slower running leads to less stability and easier to crash the field in the winding's.

I have run high and low capacitance over recommended and it all works, just has different effects. Low tends to need higher speeds to kick in which gives higher frequency ( not something you will have to worry about rectifying) and lower  give more power at lower speeds and Higher voltage which is easy to exceed the caps rating so be careful. Use the highest voltage caps you can find and not below 500V.

Don't forget with RPM you can always gear up the driving engine providing it has the grunt and run it a lot slower than the motor. I am ( still) Building my setup with the 12 KW motor and a 12 Hp Diesel. I'm going to run the diesel at about 50% RPM.  I can't pump any more than about 5kw direct down the line in the setup I'm going to use it for so the engine will have excess power I'm going to utilise in torque and lower running speed.  I have been running it a bit for testing and it is a noisy bastard.  Really need a water cooled like a little Kubota or yanmar.

AS for not running a governor, I think this will help but I'm far from sure it will fix the hunting problem.
The trackers in the inverter will be still trying to vary the load and the engine will feel that and I believe the same see sawing effect  will happen. To what extent remains to be seen.
What I would suggest is add as much flywheel weight as you can so you have more reactive power.  I picked up a couple of old truck flywheels the other day which must weigh 25Kg each.
I'm thinking to put them on a shaft  and belt drive them to the load or the engine, won't matter, to help smooth things out. It may help in this case too, bit hard to say but I think it will reduce the effect if it does not fix it.

Another thing that may help is put some caps in the DC line to the inverter. Might help smooth things that way too.

[bryanb]

I will need to run this thing from idle to full throttle for variable heat outputs so it sounds like an Induction Motor As Generator is not going to work.  The other options I can think of are:

1) Permanent magnet 3 phase generator (or motor).  I have a 23 hp low RPM (100 rpm) which is difficult to drive that slow.

2) DC generator (or motor).  Large permanent magnet motors are not common (expensive), I may be able to get a 15 - 20 hp DC motor with controllable field.

3) Standard 3 phase generator using the wild AC with the voltage regulator disabled.  Is this possible?  Do I just power the field full voltage all the time and the engine rpm determines the output?

I would like to stay as close to reproducible as possible so others can do this too, so my preference is to use a standard AC generator head (choice # 3).  Does anyone know how I would determine what the excitation voltage is for a typical generator head? 

[mike90045]

3) Standard 3 phase generator using the wild AC with the voltage regulator disabled.  Is this possible?  Do I just power the field full voltage all the time and the engine rpm determines the output?.   

Engine RPM will affect the voltage output, and at some low RPM (generator going below 40Hz) the generator will poop out.

You should look at some of the Axial Flux alternator designs, that are used on DIY wind turbines
http://www.windsine.org/2017/02/07/listeroid-backup-generator/

[bryanb]

and at some low RPM (generator going below 40Hz) the generator will poop out.

Why does it "poop out"?  Can I increase the excitation voltage at lower RPMs to maintain output?  What about a permanent magnet generator?