Make my own generator 4

[Reg87]

Im researching into making my own generator as a small learning project. Ive seen alot of people getting a lawnmower engine running a car alternator which powers a inverter however thats not very efficent.

Ideally I want single phase 230V 50Hz And I want to produce between 2.3kW to 3.4kW. I believe 3 phase would be easier however there is really no need or desire for that. Ideally I see myself getting a small pump motor with a horizontal shaft so I can attach a pulley to drive my generator. Voltage regulation is a step i havnt yet decided how im going to control but ill cross that when I select a motor.

I'll start with my first hurdle. What size engine should i be looking for? What size alternator should i be looking for?

 

[itsmoked]

You should search more on the web. I've seen many builds where people, (with too much time on their hands), have crafted all sorts of interesting generators from scratch.

The professionals on this forum aren't likely to have dabbled in handmade generators. So you'll probably get better help elsewhere.

746W per horsepower.

3.4kW/746w/hp = 4.6hp

You'll want several more HP than that calculation to handle power curves, engine duty cycle, losses, etc.

Call it 6hp.

The inverter may be less efficient but it helps you avoid the very nasty hassle of speed regulation. Putting a big deep cycle battery in between a 12V alternator and the inverter provides some UPS functionality. For instance the generator can run out of fuel and die and you have a few minutes to fuel the non-running engine and restart it.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Start looking for a synchronous motor, otherwise you are going to have a lot of difficulties. Unfortunately small ones are rare, single phase ones are as common as Yeti.


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If we learn from our mistakes I'm getting a great education!

 

[Reg87]

Cheers for the reply and info. Ill continue to do some research. Quite right with the inverter and battery however im hoping to achieve something more than that.

I think ill try and find a engine around 6hp then. My air con draws 10A on start and thats probably my greatest starting load. Connect it via a belt to a 3 phase induction motor. Connect that up as 2C2.
Not sure how I will deal with speed control to maination 50hz with load flucualtions. Maybe some voltage regulator or speed control will need to be sought.

 

[waross]

Many small gasoline engines have an integral governor. It has a lot of droop but it will get you going. If you decide that you need less droop, try a cruise control system from the auto wreckers. Let us know how it works.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Before you go spending money on engines, pay heed to ScottyUK's advice. Start with the generator portion of this, it's harder to deal with. An AC motor from a pump or something is NOT going to inherently become a generator just by over speeding it. The windings must be sufficiently excited by either the grid itself or by some external means. That's what ScottyUK means by finding a Synchronous Generator (alternator) and that is why people use the ones that come from cars, because that's what they are. There are tricks to being able to modify regular motors that are not in the realm of what we as a group do, but there are plenty of "home power" websites that explain it. Suffice to say you will need more than the average laymans skill set to pull that off.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[rmw]

To itsmoked's point above, the generators we dabble in are real serious and when we finally get to get some time off, that would be about the last thing we would want to dabble with -speaking for me only, of course.

That said, were I to want to so dabble, I would be looking for a large bus alternator and then an engine that could pull it.

rmw

 

[byrdj]

While steam is my thing, I dream about a 30KW micro turbine for the house

 

[Reg87]

Thank you for the words of warning however I feel my skillset deems me capable to complete this task. Although im young to the trade, its a project I want to do because in my current line of work I feel Im loosing what I learnt at trade school and I want to challenge myself.

Waross, although ild like it to run my fridge or aircon seperatly, ill be quite happy if it accepts small loads gradually. Addressing droop will be a refinement for later I think. If I get a 6hp engine, do you think it would handle a 50% load(10A at 230V) easily?

If I look for a gen which is self excited by sliprings or an exciter...Are you aware of a really basic robust AVR out there I could retrofit?

 

[waross]

AVR SX480, $53.99 on Ebay

http://www.ebay.com/itm/Automatic-V...032?pt=LH_DefaultDomain_0&hash=item2eb9aba348

You may better prepare yourself for future trends by experimenting with homebrew invertors.
You may experiment with capacitors on a small motor for excitation but no guarantees. Success may depend on the grade of steel in the laminations and the resulting value of residual magnetism. Zapping the motor with 12 Volts DC before starting may help establish some residual magnetism.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

A series diode and resistor from a battery source pretty much guarantees field buildup. It certainly takes away the "will it / won't it" moment when relying on residual magnetism. If you want to refine it a little then add a relay to disconnect the battery source when the terminal voltage builds up to, say, 60% of nominal.

A slipring machine is perhaps not a bad starting point. You can probably make a new rotor if you have a half-decent machine shop - try to salvage the shaft and sliprings, and add a new core and windings. You'll have to make your mind up whether a salient pole design or a cylindrical design best suits the motor you're converting.



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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

You could cut to the chase:

http://www.northerntool.com/shop/tools/category_generators+generator-heads

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Nice link Keith.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Reg87]

Cheers all for your great input. Ive been looking at local wreckers to see if they have some old gens around. However ill need to borrow the megger from work before I commit.

I like your initial excitation concept scott. It keeps things simple however I dont have access to the tools for making my own gen.

Thankyou Keith for that great link. Wasnt aware you could just but them like that. Almost makes it to easy. However I cant imagine freight from the states been cheap. Might look closer to home if these wrecks dont work out.

 

[waross]

Hi Scotty. I didn't make myself clear. My bad. I was referring to an induction motor used as an induction generator.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

http://www.ebay.com.au/sch/i.html?_...1313&_nkw=generator&_sacat=See-All-Categories

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Tmoose]

"If I get a 6hp engine, do you think it would handle a 50% load(10A at 230V) easily?"

I have a Winco 110 v generator from the 1980s. It is powered by a Kawasaki FA2100 engine rated 5.0 PS. The generator/engine package is rated 3000 watts continuous, 3200 peak. They mean it. The tiniest starting surge overload, like starting an old two-tone green and white DeWalt radial arm saw with a 10" diameter blade and an induction motor, and the engine rpm gets pulled down pretty low, and the engine just labors and chugs until the breaker gets bored and pops. No amount of "bumping" with the on switch can coax it to start that saw.

I was thinking milling the (flat) cylinder head for a touch more compression and adding a 25 inch long ram tuned intake would add a few peak watts. Or maybe bolting one or two 10 inch saw blades to the crank for some extra flywheel effect.

 

[waross]

The starting surge of a 10" DeWalt radial arm saw applied to a 3200 Watt generator is a lot more than "tiny". You will need a 5KW or 6 KW set.
But, a little more power may help. I wouldn't waste the time, but I've been wrong before. If you can keep the engine from Bogging so badly it may help. Generally the minimum size generator to start a motor is 200% and that results in both the frequency and the voltage being pulled down. Also, I would not trust the rule of thumb for sizing for small sets. (Below 5 KW or so).
It depends.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

The problem is the DeWalt's start winding. That sucka is doubling the load and preventing full speed. That doubled load sucks the generator down so far that the DeWalt is then unable to reach the centrifugal switch speed so it can dump the start winding.

The whole mess just sits there malevolently on the fence. You could possibly dump the start winding yourself at that point and it would run up.

Alternatively you could probably start another motor first. One that can make it to the switch speed. Once it's running you hit the DeWalt. It then uses the kinetic energy stored in the first motor to reach the switch speed.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MikeHalloran]

Damn clever idea, Keith. Wonder if it will actually work?
Star anyway.


Mike Halloran
Pembroke Pines, FL, USA