generator head variable load

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guy stuller
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generator head variable load

Post by guy stuller » Fri Jan 30, 2004 12:54 pm

I wan to use a 10,000 watt belt driven generator head to place a measurable, variable load on small, single cylinder racing engines that I'll be testing and breaking in. The generator I imagine won't put much load on the race engine unless there's something plugged into the generator's outlet(s) creating load. I'm trying to figure out load device I could plug in that would be variable to a somewhat fine degree. I was thinking of a hot plate but then I'd have to put the heat to work in order to keep up the demand on the generator. Plus how big of a hot plate would be need to create enough load? Is there a better way to put a variable/measurable load on this generator? My whole objective is to be able to test small racing engines at finely measured increments of load. I know squat about electricity so I can use any ideas out there. Thanks

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Crowbar
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Re: generator head variable load

Post by Crowbar » Fri Jan 30, 2004 1:46 pm

I initially thought of a variac connected to a surplus mill-type resistor, however that would be a huge resistor and variac to handle the full rated load of the generator. What is the input horsepower rating of the generator and how much do you want to load it? If your driving engine is small enough you could get away with a much smaller load resistor and variac.
Keep Prying...

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Bernius1
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Re: generator head variable load

Post by Bernius1 » Fri Jan 30, 2004 2:00 pm

We use a board with clips holding an array of quartz 1000W tube lamps. Each one is individually switched. 5 bulbs gives up to 5KW loading, & if you switch several on at once, you get a surge load. Maybe you can put a dimmer control and 250W incandescent as a last lamp, to make it adjustable. BTW, what type of engines ??
Can't we end all posts with a comical quip?

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Edd
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Re: generator head variable load

Post by Edd » Fri Jan 30, 2004 2:34 pm

A <<small, single cylinder racing engines>>??? small like ~3.5-12hp for like…like…maybe…go karts..or model UFW’s (Unidentified Flying Watercraft).
Your direct driven generator should mechanically load down around 13 hp. You’d probably have all the hot plates in the neighborhood , using them,
Hi wattage lamps have such a resistive shift from off to on states. Of common things that you might use for different decades of electrical load, with out excessive expense, the Calrod replacement heating elements utilized in electrical water heaters come to mind. There are quite a few different wattage ratings as well as using a 240v unit at only 120v input with its corresponding halved wattage consumption. The progressive switching in units as generator loading would scale up the load. Mounting them in the top of a 55gal metal drum of oil should equalize out and balance their thermal/temperature/vs resistance shift.
For the controlled minute vernier loading of one decade/section; that could be accomplished via the utilization of electronic PWM switching of that one section into circuit….however that’s another story if you’re not electrical/electronic savvy…and not too many dimmer switches I know of carry more than ~600W. unless you were to use multiples switched in.<p>Addenda: If mechanics tends to be more of your forte....you definitely might take that 55 gal drum I loaned you and make a recirculating pump with its reservoir as suggested by Sir JOSMITH.. :D <p>73's de Edd
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;) ;)<p>[ January 30, 2004: Message edited by: Edd Whatley ]</p>

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Chris Smith
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Re: generator head variable load

Post by Chris Smith » Fri Jan 30, 2004 2:57 pm

Light bulbs would be your best countable and scalable way to place a reliable load on the generator. <p>13 or 14 HP worth would be 10,000 devided by say 500 watts = only 20 bulbs! <p>But they do make resistive carbon loads, like in the old days of amp testing for Batteries.<p>However the last time I priced them out they cost 200 bucks. <p>So 20 X 500W bulbs sound better again. <p>Three for five bucks at the major hardware store and you can make the sockets your self out of two fixed alligator clips on a foil coverd board.<p> Just don’t stare at the board when it all lit up!

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Re: generator head variable load

Post by josmith » Fri Jan 30, 2004 2:59 pm

Appliances like hot plates usually vary load by cycling the power on and off. This would not be good for your purpose. You need a variable source of resistance that can dissapate 10kw. As you can see from the above posts it's possible but not easy.<p>Pumps are usually a better choice for loading a motor since they are cheaper and easy to load with a simple valve.

Dean Huster
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Re: generator head variable load

Post by Dean Huster » Fri Jan 30, 2004 10:19 pm

When I was last teaching, the auto mechanics instructor's kid raced go karts, 5 hp, lots of rules and regs on the engines. It was to the point that he was wanting me to design an electronic measuring wheel (like cops used to measure tire skids) so that he could accurately measure the difference in track length between the inside and the outside wheels so that he could shave the tire diameter to give a bit more edge.<p>Anyway, he had a setup for measuring horsepower output of the engine, developed by a guy in Moberly (I think), Missouri. It consisted of a flywheel (he got his from an old hay baler), a tach, a brake (just to kill wheel rotation after the test) and a computer interface and program. The horsepower was calculated by providing all the flywheel dimensions initially, and then the system would measure how long it took the engine to "accelerate" from low rpms to high rpms. From what I gather, the system was pretty accurate and didn't depend upon a lossy and questionable generator/load dynometer system.<p>Beyond that, remember that one horsepower is 746 watts. <p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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Carl Pugh
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Re: generator head variable load

Post by Carl Pugh » Sat Jan 31, 2004 9:52 am

Light bulbs sound like a good idea. If you can get to the generator field, then using a separate variable power supply for the field could be the way to go.
The separate variable power supply should not be operated off the generator output.

Will
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Re: generator head variable load

Post by Will » Sat Jan 31, 2004 9:57 am

A long time ago (Beginning of WWII) I remember examining a variable resistor at a dog racing track. It consisted of a water container (With salt water or saline solution (Conductive) in it and it had a circular segment shaped blade actuated by a handle. When the opersator moved the handle the segment was eithjer immersed further into the water (Reducing the resistance) or pulled out (Increasing the resistance) The device was driving the fake rabbit which the greyhounds chased around the track and the operator altered the speed to keep it just ahead of the hounds. I also saw a similar arrangement (With about a 10 foot square blade) being used to test a 500 kW Merlin Geraun ?generator on the offshore oil platform we were building. I don't have saltwater resistivity info at hand but I'm sure you could find a steel plate to insert into your 55 gal drum. According to my 'off the top of the head math' 10 kW would produce about 34,000 Btu/hr approx = to 570 Btu/min so, if you were boiling the water off (Which is what happened in the greyhound track machine) then you would be boiling off, at 10 kW, little over 0.5 lbf/min i.e. about one gallon per 15 minutes.
BB

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Re: generator head variable load

Post by amuron » Sat Jan 31, 2004 11:50 pm

Hearers work quite well. Check out Watlow and Chromalox for cartridge heaters. Stick them in a block of aluminum with a few pipes so serve as a crude heat exchanger. The nice thing about heaters is that the loading is fairly constant unlike a incandescent lamp.<p>Ron

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Chris Smith
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Re: generator head variable load

Post by Chris Smith » Sun Feb 01, 2004 12:44 pm

Heater elements work exactly like light bulbs. Low resistance when cold, higher when hot. <p>Light bulbs are much cheaper however, and more scalable in 100, 200, 250, and 500 watt ranges. <p>Most heaters only come in 800, 1000 and 1500 watt ranges for the most part and cost as much as 20 bulbs for just one.

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Re: generator head variable load

Post by amuron » Mon Feb 02, 2004 5:12 pm

Most nichrome wire heaters can be assumed to be resistive, with a very small temp co unles of course you run then beyond 700 deg F, where in the resistance temp co changes fairly dramatically. If you continue to go on up in temperature then the curve dramatically again changes yet again. Take a look at Nichrome 60 resistance vs temp curves to get an idea. <p>Now if you switch to Balco, or someother materials instead of nichrome the temp coefs again are quite dramatic. You can also take a look at moly-disilicide heaters, and they take on the a light bulbs resistance vs temp curve to an extreme. They are a real pain to control due to their almost zero ohm resistance until they start to glow. However, they are one of the best ways to electrically heat materials to high temperatures.<p>I have built hundreds of load systems over the years. I always used heaters, and would size them and the heat exchanger so the max temp would not exceed 200 deg F. In large loads, water cooling becomes ciritical.<p>You can get cartridge heaters from http://www.watlow.com/products/heaters/ht_cart.cfm<p>These are pretty stable and long life, but as one poster said, a lot more expensive than a light bulb. However if you need a resistive load that is fairly constant, they are a good solution. Just be sure to size things to keep the heater temp fairly low. <p>An aluminum block with water tubes works well, otherwise you can use some aluminum extrusions and forced air. Just be sure your plumbing does not leak...<p>The big load testers we built years ago used our corporate pond as a reservoir. Then again we were testing large power controllers where in a 480V 600 amp unit was considered small.<p>Lastly a cheaper solution, albeit a little scary is to create a sandwich of range elements, aluminum blocks, and copper water coils. Coat everything with a good dieletric barrier to prevent corrosion. Be sure to keep all of the electrical elements isolated. I actually serviced a commercial fog machine that used this combination back in the early nineties. It did not have UL approval and was pretty scarey, but it sure filled up a place with fog in short order.<p>Good luck
Ron

Bernius1
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Re: generator head variable load

Post by Bernius1 » Tue Feb 03, 2004 6:01 am

So, the options are; resistive heat elements, for higher power; resistive lamps for lower power. My dad (mechanic extraordinaire) suggested a water or hydraulic pump, where you close the bypass valve slowly, and note the highest pressure. I had wanted ( 3 or 4 HP range) to use a lever-type torque wrench, bolted to a plate, with the head driven by the centrifugal clutch. Short, open-throttled burst, & note max torque-wrench deflection. (Wrench max is 150 ft-lbs. That's more than most Japanese cars put out !)
FYI, I was 'hot-rodding' a Briggs 4HP on a 20" Snapper. Anyone who's seen the 'cloud-factory' science fair project knows that the thickest vapor is at the bottom, away fromm the evac. port. I perceive this as a pressure-gradient.So, I drilled 3) 1/16" holes thru the block, between the fins, just above Bottom Dead Center (top-of-piston). Viola, the muffler glows cherry red. Dad says "it's running too lean" (i.e., MORE air @ the same fuel). So I de-burr the ports, re-profile the cam, smoothe the head, & richen the mixture. A 12" 3/4" pipe as exh. header, & it SPINS THE WHEELS ON ASPHALT, WITH A FOOT ON THE DECK ,HOLDING IT FROM MOVING !! A small success, but fun. Then an old-timer told me that they did that to flat-head L6's in the 50's ( side-drilling the block). What's old is new again.
Can't we end all posts with a comical quip?

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