Building a generator...

[SuperDave456]

Just curious.
Lets say I have an old lawnmower or an old edger.

If I went and got a junkyard alternator and hooked it up on a belt driven pulley system to make a home made generator, how would I regulate the electricity so that it doesn't fry any electronics?

Lots of old alternators and engines that work well.
Just wondering how one would do this.

 

[Colt45ws]

You'd would have to find a one wire alternator, that would be best. Otherwise, find one that is internally regulated, and wire up something to kick it on.

 

[JimPghPA]

There are two basic type of generators.

The low cost ones use an engine with a governor set to a fixed speed. Usually that speed is 3600 RPM, the electrical generator-head (the part that produces the electric) is two pole,and one revolution produces one AC cycle. Some generator heads are 4 pole, and run at 1800 RPM to make 60 HZ. Some are 6 pole and run at 1200 RPM to make 60 HZ. In general the 3600 RPM gen-sets are gasoline or propane, or natural gas powered. The lower RPM units are diesel. The lower RPM units tend to run for much longer hours between major break-down.

The second type of gen-set is an inverter unit. These vary the speed of the engine and the rotation speed of the generator-head with respect to load. At a light load these systems run at low RPM. The generator-head produces DC and that is turned into AC buy a solid state circuit. There are also other ways to electrically connect up the generator-head to produce 60 HZ even though the RPMs are being varied, but those are too complicated to get into here, and probably will not be seen in a consumer model. Inverter units tend to be quieter, and are much better at being fuel efficient, thus they consume much less fuel. They usually cost much more. The smaller units of 2000 watts or less are generally very quiet, and lighter than the constant speed units. The larger inverter units are generally heavier than the constant speed units, and are also very quiet in comparison to constant speed units.

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Anyhow, in response to your interest in building a gen-set. The problem is maintaining constant frequency and voltage over the wide range of electrical loads your generator will see. The governor of the engine maintains constant speed to maintain constant frequency for the first type of gen-set. And the design of the generator-head maintains constant voltage for this type.

As for the inverter type, electronics governs the RPMs of the engine and also maintains constant output voltage. The throttle response of the engine must match the demand of the controlling electronics.

There are some generator-heads that have permanent magnets and run at low RPMs. These are best used with a diesel engine. You could add a flywheel to this to help maintain constant RPMs. You would still require a very good governor to maintain constant RPMs within a very narrow range of change.

In short there is more to the design of a gen-set than just connecting an engine to a generator.

Also you must maintain a very good flow of air to cool the engine and generator-head.

 

[JimPghPA]

One way would be to use a car or truck alternator (one that has a built in voltage regulator) to keep a 12 volt car or truck battery charged up. Then you could run an inverter from the 12 volt battery. This way you would not have to maintain a constant speed on the engine that drives the alternator. You could also use a volt meter on the battery to tell if the RPMs of the engine were high enough to maintain the battery voltage.

 

[JimPghPA]

Don't forget to have a large amount of air flow for each major component.

 

[flatlandtacoma]

And don't forget that most small lawnmower engines rely on an external flywheel (e.g. a 21" blade) to work properly. If you had a large enough pulley it would probably run ok; but that would turn your alternator way too fast.

 

[boraticus]

A lawn mower engine will be a bit harder to implement to drive a generator. Lawn mowers have vertical shafts. Most generators I've seen are horizontally mounted. It won't be impossible to vertically mount the generator, just not as easy. Chances are you'd have to build a deck to hold the engine and generator. I.e. engine bolted on top of a piece of plate with crankshaft protruding underneath. Then make a mount for the generator on the under side so that it's pulley is aligned with the pulley mounted on the engine. Pulley size will be important and as mentioned by flatlandtacoma, flywheel effect will probably be needed to assist the engine. If you have a more modern engine that allows for blade operation via a clutch, the flywheel issue won't be a problem.

If you are doing this just for something to do and will not be relying on it for power, enjoy yourself. If you really need a reliable power source, you can probably buy an inexpensive used generator for less than what it will cost to build one.

 

[meep]

been there, done this. you can make the frame from L-iron at lowes. You can use a turnbuckle to make the belt tensioner. you will either need an external regulator, an internal regulator, a homebrew regulator, or an alligator clip accross toaster heater wire for a manual regulator. you will need a 12V power source to kick it off.

A 3.5 HP engine can support a 60amp alternator, but it will have to be in its power band (3000+rpm) when the electrical loads are high. a larger engine can loaf along some.

plenty of DIY on the 'net, including pre-fabricated plate steel for mounting engine to alternator.

good, heavy, iron sheaves make good flywheels.

BE CAREFUL. weak mounts, sloppy builds, fingers in belts.... **** happens.

NOTE: when you look at weight, operability, simplicity, unless you source EVERYTHING used, thr $400 robin-powered coleman at home depot is a MUCH better deal.

M

 

[SuperDave456]

I'm just thinking about it.
Not actually considering it.
I have an old briggs edger (It was my grandfather's, then my Father's, and now mine.) That runs without a flywheel and sits vertically.

 

[punisher]

Best alternators for these projects are the old generic GM alternators from the mid 70s (10SI). Cheap, plentiful, and easy to get single wire regulators for.

 

[JimPghPA]

One of the things that becomes a problem with gen-sets is the efficiency, or lack there-of.

A 9, 10, or 11 HP gasoline engine running a 5000 Watt (6250 Watt Peak) generator at 3600 RPMs all the time is a gas hog. A 5 gallon tank will last something like 6 to 9 hours at 1/2 load depending on the brand of engine, and the shape it is in. And these gen-sets are VERY NOISY.

Larger gen-sets are even more of a gas-hog.

Many people get something around 5000 watts and then end up buying something smaller like 3250 or smaller so they consume less gas.

People pay the high price of the inverter models like the Honda 2000 or Yamaha 2000 because they sip gas. Something like 5 hours or more on one gallon. And they are quiet. Inverter models produce the cleanest electric output.

If you have a long power outage such as a major weather hit, gen-sets that drink gas can be a real pain to keep supplied with fuel.

Also the constant speed gen-sets require you to change the oil more often. Such as every 25 hours with a dino or every 50 hours with a synthetic. The inverter models are good for 50 or 100 hours.

Also there are some small low cost gen-sets with 2-cycle engines. The advantage of a 2-cycle is you do not have to change oil in winter temperatures. 2-cycle carbs are very touchy and tend to gum up quickly.

A good reliable gen-set would be a Generac 3250 watt 3600 RPM model, with a 4-cycle engine, like the kind you can pick up at Lowes.

After break in, a great oil would be GC, and if you wanted to run lower cost oils Rotella, or Delvac. Generac models make relatively clean electric. The cleaner the electric the better the chance of it running TVs and computers without a problem.

You have to keep spare spark-plugs, air-filter, and oil.

You also have to keep enough gas that has been pre-treated with something like Sta-Bil, or Sea-Foam. And you have to rotate out the old gas and then store new. I have 2 and 1/2 gasoline jugs, and store 55 gallons of gas in 22 of them. Just the cost of 22 2.5 gallon jugs is over one hundred dollars.

Generators require you to run them on a regular basic to keep them reliable. You can not store them away for years and expect them to run when you need them. There is a residual magnetism that gets the generator-head going. If you do not run them every few months, this will be lost and the generator-head will not produce power until you zap it with a 6 or 12 volt battery. The carb can gun up on generator engines.

Also you must NEVER exceed the peak power output or you will fry the generator-head. Do not expect the circuit breaker to be fast enough to protect the generator from an over-load.

There is also the questions of 120 or 240? And how will you connect it to what it will power? Will you run cords, or install a transfer switch?

 

[boraticus]

Interesting stuff Jim but from my experience with thirty years of generator ownership, I cannot agree with a few things.

Such as..


"Also the constant speed gen-sets require you to change the oil more often. Such as every 25 hours with a dino or every 50 hours with a synthetic. The inverter models are good for 50 or 100 hours."

My Kubota diesel generator requires an oil change every 250 hours. Some genset builders using the same engine recommend oil changes every 500 hours.

My cheap Champion 3000 watt, home back up generator manual says to change the oil every 100 hours under normal load/operating conditions and every 50 hours if under constant heavy load and/or dusty conditons with conventional oil.


"2-cycle carbs are very touchy and tend to gum up quickly."

From my experience, two cycle carbs are no worse than four cycle carbs. Be it carb design or the fact that they use mixed fuel. Good fuel management/engine maintenance is all that's required to prevent carb problems.


"Generators require you to run them on a regular basis to keep them reliable. You can not store them away for years and expect them to run when you need them."

Over winter, I leave my Kubota diesel unused for five to six months at a spell. Every spring, when I fire it up, I have electricity. I've read that certain types of generators have "exciters" to establish the flow of electricity. Not sure how prominent they are these days.

Nowhere in the data provided with either of my generators does it say that I must use the genset within a certain period of time. Long term storage instructions say nothing about using the generator to prevent loss of establishing electrical flow when I take it out of storage.

I know people who have had generators stored away for years at a time. They had trouble getting the engine started but never had a problem getting the electricity going.


I'm curious why you would use a gasoline powered generator and store that much gasoline rather than use a diesel generator? Diesels are very easy to live with once you get past the initial cost. Diesel fuel can be stored for years without the degradation that may occur with gasoline. Many diesel gensets run at 1800 and are very fuel efficient. My 6000 watt unit, sips one liter of fuel per hour at half load and it's twenty eight years old!

I'd never buy a large capacity gasoline powered generator. The fuel cost and maintenance cost savings of owning a diesel genset would pay for the additional cost of the price of a diesel of equivalent size in short order.

 

[tig1]

A friend built his own, but never could get the RPM regulated to maintain 60 Cycles. Finally gave up on it.

 

[JimPghPA]

Regarding the portable 2000 watt inverter gasoline models. One of the advantages is that these units weigh just under 50 pounds dry, and can be moved by one person. Generac makes a 2000 watt inverter model that sells for $550, Yamaha 2000 watt cost $1000 , and Honda 2000 watt cost $1150. The Honda shuts off the fuel to the carb when you shut off the engine. This is nice for contractors who use it often, but makes it hard to run the carb dry.

Regarding OCI, the time intervals I talked about are for 3600 RPM gasoline models.

The engines used for the gasoline 3600 RPM units, and also the inverter engines do not hold a lot of oil, and the ones I have seen recommended those OCI.

Regarding residual magnetism, the manual for some of these gen-sets shows how to apply a battery across the brushes to get the generator to produce power if the residual magnetism is lost. The loss of residual magnetism is related to the amount of time that the generator is not used.

The Diesel engines in general run at lower RPMs. I would suspect they also hold more oil.

The gen-set I have is a very good fit for my application because it is light enough to transport the way it has to be moved, and has enough power to run what I have to run.

 

[Chris142]

I have a Pressure washer thats dead but has a good 270 Honda engine. I was going to put an internally regulated GM alternator on it like your describing and make a portable battery charger.

I couldn't find the pullys I wanted so I just bought some long extension cords and a battery charger that will reach to my truck.

 

[MolaKule]

Quote:
Inverter models produce the cleanest electric output.


Clean? Not in my experience. My Honda 3000i engine is very quiet but the electrical output is very noisy due to the switching transistors in the inverter. And they don't filter the output.

 

[Texan4Life]

http://www.theepicenter.com/tow082099.html

 

[Cujet]

I regularly get 1 year old, 24v, 44AH lead acid aircraft batteries. So, I built a little diesel 3HP, belt driven alternator like the link above. I cobbled it up to the array of batteries and the 2ea, 2000 watt inverters provides 115v power.

The Chinese diesel engine failed due to horrible bearing quality and improper crankshaft balance. However, as a system, it worked very well and could produce way more peak-starting and short term power than a 3HP conventional or inverter generator could ever hope to.

Given some time and a reliable engine, I would have fabricated a variable speed control for the engine. 28V would result in idle speed and less than 24v would result in full rack (throttle).

While the neat little Honda gensets (I have the 1000 watt unit)(and an older 500 watt unit), are very efficient, they cannot compare to a 3HP diesel-battery-4000w inverter setup. Heck, that little diesel will run 2ea, 10,000 BTU window units. And, that's enough to keep my house cool.

 

[boraticus]

Yo Cujet:

I bet the home made rig wasn't quite as portable nor quiet as the Hondas was it?

 

[meep]

yea... that's what I'm saying. My home rig was 14" by 24" weighed ~60lbs, held only 1 gallon of gas, and needed an auxiliary battery to smooth things out and excite the alternator. But, mine ran at 1800rpm, so it was way less racket. But then ya gotta add in the inverter.

I've read of folks rewiring the alt and running them at 440hz (maybe it was 400) which most electronics will actually accept, but A/C motors will not. Too outside the norm for me.

I started it as a project, actually made a 60hz-output 0-24V regulator, and I was going to feed the Alt output to a 1:5 stepup transformer. DC side was great but I forgot about magetic hysterisis. Figured that out, looked at the amount of additional circutry I'd need, and stopped. After all that time and $, I saved and bought a 2000i.

It's quiet, thrifty on fuel, runs medium power tools, consumes zero oil. I wouldn't run it at a jobsite--- seems like real-world power tool use would kill the transistors, but for my regular home use (garage has one circuit, aluminum wired, no ground, shared with kitchen...) it's great. Quiet enuf that I've run small PA off of it for music work.

oh, and agree with above, some models DO rely on resident magnetism to self-excite. They, if ignored for long periods, needed the 12v field to kick them off.

M