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Thread: VSD power tests

  1. #61
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    Quote Originally Posted by Stustoys View Post
    Well after a little postage stuff up my scales have turned up. I've tested the first one against Rays and it pretty damn good. Now assuming things go smoothly tomorrow I'm going to start running some tests. A the 240V VSD has a current display I figure I would start there.
    The motor is rated 0.6kW at 1375rpm so thats an easy starting point. But what slip should I use for the other tests? the same rpm drop or the same % of max as the Hz, something else? I'm thinking same %.
    5Hz steps?

    Stuart
    Good question, I think you should load it until it stalls, at each voltage. Joe has some shoes you can borrow...

    What will happen is that as the load increases the slip increases and hence the current will increase. So the torque will stay pretty much the same, but the horsepower will decrease. ( because the rpm decreases with frequency)

    When you get the half frequency the voltage will be around half and I think the horsepower will be about half, but the torque will be the same.. ( that's the prediction anyway.. )


    Ray

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  3. #62
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    lol

    So you want power v rpm at each Hz setting? I guess thats unlikely to hurt anything on the 240V VSD.
    Will have to see how well the "dyno" behaves, getting accurate numbers below maximum might be a little tricky.
    Then again there might be so little power, who knows.

    I might try test at spec rpm on the 415V VSD just to get a baseline.

    Stuart

  4. #63
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    Quote Originally Posted by Stustoys View Post
    lol

    So you want power v rpm at each Hz setting? I guess thats unlikely to hurt anything on the 240V VSD.
    Will have to see how well the "dyno" behaves, getting accurate numbers below maximum might be a little tricky.
    Then again there might be so little power, who knows.
    I might try test at spec rpm on the 415V VSD just to get a baseline.

    Stuart
    I waiting to see what, if any, bugs you find because I want to set up something similar.
    Testing at 415 would be interesting

  5. #64
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    Wow,,,,,,,,havent been out into my shed for a few weeks...... dam its a mess!!!!!!
    Only got time for two roughish numbers today before my dyno melted. Who would have thought you cant use Telsta rope as a brake
    Its not looking good 700g at 240V, 3.5kg at 415V. Thats 20%.

    Stuart

  6. #65
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    Dam!

    I'm sure I read somewhere that telstra rope is good for everything!

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  7. #66
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    Quote Originally Posted by simonl View Post
    I'm sure I read somewhere that telstra rope is good for everything!
    Well I saw a car on a tandem with one piece of telstra rope around the back bupper I figured it would be right

    Really I knew it wouldn't last on 1hp, but the leather I was using was working to well. I changed to the rope as a test to increase the "weight needed". The leather also "self energized" which didnt do much for the ease of measurement.

    Stuart

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    The problem with leather or nylon is that they are good insulators so the heat won't move away from the friction zone all that well and local temps will build up rapidly.

    Maybe a spring steel strap and an ally disc would be be better?
    Plus a fan to cool the disc?

    I'm getting more and more tempted to make something as well.

  9. #68
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    Sounds like a small prony brake is the go.

    Phil

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    Phil, you know the rules...

    Michael

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    Hi Bob,
    The leather has done ok just is works to well... if I cut it to half the width it might work ok but then get to hot. I have some steel strip but that might need to much weight ........ and I I doubt the noise will be all that pretty. I'll have a look around the shed and see what I can come up with. Maybe I should have built a real brake.


    Quote Originally Posted by Steamwhisperer View Post
    Sounds like a small prony brake is the go.
    Hi Phil
    That's pretty much what it is.

    Stuart

  12. #71
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    Go to the wreckers and find an old rear drum brake. I know at least the holdens used the main shoes for the hand brake. Then you have a cable activated brake that will never fail...

    Ew
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

  13. #72
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    Quote Originally Posted by Ueee View Post
    Go to the wreckers and find an old rear drum brake. I know at least the holdens used the main shoes for the hand brake. Then you have a cable activated brake that will never fail...
    yes. That may have to be the next model......thought how well a car brake will work at these loads I dont know. I guess I could just keep cutting away pieces of shoe until it was working badly enough to be useful. Remember we are only replacing a shoe
    It also makes it a bigger build. but. if it has to be it has to be.
    I could likely get my hands on brake shoe lining but havent bothered as yet for the same reasons....I only need something that can live with 750W for a few minutes at a time.


    Stuart

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    Quote Originally Posted by Michael G View Post
    Phil, you know the rules...

    Michael
    oops,
    Hi Michael,
    I thought I took a heap of pics just recently but can't find them.
    I do have some though.
    The last one is a scan of the exact same engine with the prony set up.

    Phil
    Davey Paxman (26).jpg Davey Paxman (25).jpgScan 3.jpg

  15. #74
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    Thanks Phil. Always interesting to see how someone else does things. The water bath is a nice touch - I wouldn't have thought of including one but to get steady state conditions it's probably necessary.

    Stuart, can you manage a waterbath or even just a pond pump running water over the brake wheel?

    Michael

  16. #75
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    Stu, some ideas for a diy dynamometer. How about you buy a DC motor next time one comes up cheaply on ebay. Then make a variable load for it. You measure current and voltage and know exactly how much energy you are dissipating. A variable can be made with a large power transistor and a heatsink. Another idea would be to use a car or truck alternator, feed its output into a fixed load like a bank of 12V lamps, and use an adjustable power supply to feed the rotor excitation in order to adjust the power taken up. Again by measuring voltage and current going into the load you know the power taken up.

    Another idea to make a cheap high power variable load for a dyno generator was used long time ago to regulate speed on early Italian electric locomotives: a tank filled with saltwater with a plunger electrode, by adjusting how deep the electrode goes into the bath you can adjust the load. That is probably the simplest and cheapest high power electric load that can be built.

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