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Portable Generators

Discussion in 'The Pub' at netrider.net.au started by vic, Jul 15, 2007.

  1. Hi Folks,

    Are there any bright "sparks" out there that can assist.

    I am contemplating buying a portable petrol generator.

    I have a mug press and a flat press that need to be powered portably.
    Only problem is that I have no idea how much power they need to, well, power them.

    They are both 240v. The mug press gets from 0 to 180c in about a minute and there are no dramas with that one.

    The big flat press (30x30cm heating plate) takes a good 10 minutes to get up to temperature and occasionally trips the power board that it's plugged into. So either there is a fault with the unit or it draws more than 10amps.

    I think the latter as it was recently moved and has only started to trip the circuit that it's plugged into.

    What I would like to know is how big a generator will I need to power these things.
    How long is a piece of string I hear you say.........and rightfully so.
    I don't have a "doovie" that can measure current drain/draw whatever it is you call it.

    The presses are from China so there are no markings on them.



    Do I need to put a "doovie" on the thing or is say an 1100 watt generator going to do the job?

    Me not know :)
     
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  2. Hey Vic,

    1st up your going to have to get someone in to work out the 'startup' and running watts of both machines so we can then start to match you up with a suitable gen set. I take it your going to want a silenced gen set? :p
    If so once you get above 5kva your getting into serious dollars as well as weight / size.
    Also your going to need one that uses an inbuilt inverter, they give steady outputs... non inverted can be erratic in there power delivery and cause damage etc.

    This site has got a good rough calculator, I'd use the household scenario and then the hairdryer / heaters as a guide.

    Don't worry about their $$$ though, I can get access to Gen Sets up here @ very good prices, if you get that far and still decide you want/need one. :)
     
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  3. It'll need to be a big one - anything heat generating is normally a couple of thousand watts, even a hairdryer uses a minimum of about 1200 W and most are 2400W.

    2400W is normally about the maximum a 10A point can run.


    Best bet would be look at the specs for the two presses and work from there.

    Do they both need to be running simultaneously or one on standby and one running?
     
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  4. If the big press is drawing 10amps then you're going to need something capable of producing at least 2400w continuous power - a lot of generators sold tend to quote the peak power, or the power of the engine rather than the actual output of the generator. I'd be thinking you'd probably be needing something around the 5kW mark to be safe. Most tool rental places have generators of various sizes for rent which might be a good way of trying out a few different size units to find out just how small (and cheap) you can go before forking out for a new one.
     
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  5. Cheers folks.

    There are no markings at all on the presses on what they draw etc etc.

    A silenced one would be great but not too essential. I'm thinking of taking my equipment to the local markets and offering mugs and mousepads etc done on the spot.

    They don't need to be both running at once. The large press takes ages to cool down. The mug press takes 1 minute to heat up. I suppose I could keep the flat press running and then turning it off when I needed the mug press. By the time the mug press has done it's thing the flat press would have been off for approximately 5 minutes. It would have only lost about 10-20c.

    I suppose the other thing that I need to think about is powering the laptop and printer as well.
     
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  6. Do you have model numbers at least so you can check out the power use on the web?
     
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  7. Carefull of some of those cheap chinese Gensets Vic :? There is some absolute junk out there-samesame-but still the bloody same-like in Chinese bikes.
    I have a truckload of literature somewhere on gensets if your interested that I may be able to dig up.
     
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  8. Cheers Ken,

    The actual equipment that I need to power are from China not the generators.

    I've done some searching on the net and there are a million and 4 different Chinese presses, most flat presses seem to be around the 1750watt mark.

    The mug press seems to be around the 450watt mark.

    Will I need an inverter?
     
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  9. Vic keep an eye out for an alternator (AC generator) of about 3kva. And NO you wont need an inverter unless you intend to run all this stuff off batteries. An inverter turns low voltage DC into 240V AC.
     
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  10. I understand the presses are Chinese Vic,fun gin eveything is made in China. As I seem to recall,but I would have to reread my notes and please =; ,Netrider boffins,correct me if Im wrong-as Im sure all they will-The generator normally has an inverter in built. It produces 12Vdc and the inverter "inverts"( -gee,with a name like that,what are the odds) 1 half of the DC sign wave to give AC power at 240v AC.
    Im presumming your press runs on 240 Volts AC Vic?
    Another possibilty may be whats called a softstarter, that slowly ramps up the current to the press so you dont trip out the circuit breaker. Though if you are trippin it- albeit occassionaly, means your running close to the circuits capacity to supply current.

    PS-Ducfreak I was thinking DC output straight after rectification,before an R-C network to smooth out ripple
     
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  11. Sorry to shoot you down in flames "movin" , but , DC is "flat" AC (from the mains or a good alternator) is a Sine wave.
    Soft starters are used on motors to reduce starting current AND inertial shock on the load os the motor on startup. Resistive loads (heaters) have no real "inrush" at switch on.
     
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  12. Yeah, both presses are 240v 10 amp.

    The flat press takes ages to heat up to 200c
    the mug press only a minute.

    I might find a sparky that can test the equipment under load and see what happens
     
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  13. if you do a quick google you will find a power conversion of
    watts= amps x volts so each press needs 2400 watts

    those small GMC generators are 750 watt but I think have an average of 500 watts, I guess you could try to hook 5 of them together LOL
     
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  14. Sorry but your thinking of the 12/24 DC inverters that run off battery power and convert DC to 240AC to run small TV's etc.
    The inverters in Gen Sets 'smooth' out the power flow to stop power spiking as the governor kicks in and out.
    If you ran for example : a TV of a non inverted Gen Set, and where also running a thermo controlled heater on the same Gen. The TV would suffer a huge power drop as the heater kicked in followed by a surge as the governor cut in to bring the load back to 'normal'.
    Most elect equipment cant take the huge drops and spikes of a non inverted type Gen Set.

    To get technical : they smooth out the sinusoidal output wave and the harmonic distortion to 5% or less at full load, they also incorporate the short circuit / thermal overload and earth safety switches.

    For me to fix em I gota know how they work :LOL:
    They get real nasty when you get up to the 3 phase stuff :? :LOL:
     
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  15. look for a data plate on the equip
     
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  16. Cheers for that, why didn't I think of it........

    Oh yeah, that's right, I did, and I mentioned that there is nothing on the chinese equipment :(
     
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  17. AAHHH OK Bob. Gen sets now run variable speed drive type "inverters" on the outputs :shock: . I suppose they are so cheap now it doesn't really add to the cost of the "good" ones too much. :oops: I now do contract work where a 240v single phase in 240v 3 phase out ""inverter"" is used for speed control on a motor :oops: , I really wish people would call them VF drives instead of inverters.
    BTW VTRBOB it wasn't you heading south the Sunday after the Ulysses AGM (trying to keep up with an old DUCATI :grin: ) was it???
     
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  18. The thing to remember is

    P = VI

    That is Power (Watts) = Volts (V) x Current in Amps (I)

    and kva is 1000 Watts.

    A standard 10 Amp power point is (in theory) 2400Watts.

    As for the heater thing tripping the breaker you might need to change the CB for what's referred to as a C curve breaker, C curve breakers are designed to absorb the initial start up surge of current and not trip (we use them on circuits with air conditioners which have a start up surge of just over 20 Amps).
     
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  19. Generators have what's called a "power factor". Typically it's 0.85pf. So, if it has an output of 6kw, then its kva is calculated by multiplying power output by the power factor. The above figures would relate to around 5kva. I dunno why they measure portable generators in this way.

    Vic, probably best to hire one for the day and see how it goes. When we had the crap weather here recently, we were without power over 2 days, so I hired a 5kva unit. It barely ran one fridge, with us swapping between its matching freezer. I fired up the toaster while the freezer was running. It barely glowed. It might've been the generator itself. Dunno. I couldn't find my multimeter so I couldn't check the volts. The motor was able to handle the load, so it wasn't being overly worked.

    Anyway the hire cost me $50. CGE Hire had them for around $80 a day.
     
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  20. What's the difference between the two (engine output v generator output)?

    All generators that I've seen all quote "kva" as their rated output. Why, I dunno. Never really asked about it. Only needed to recently when we were without power during the Gippsland storms. (most of the rest of the street was fine. Only a few houses on two phases such as us that were stuffed)
     
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