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Forum Index : Other Stuff : Apliance burn outs*
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Rastus Guru  Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi all, Over time,I've had a number of electric air compressors,domestic pressure pumps ect,fail.They are being powered by a 5kw petrol alternator.Has anyone else exsperienced this problem? I'm wondering if it is caused by frequency fluctuations and if there is anything that can be done to smooth it out? The appliances are single phase.Cheers Rastus see Rastus graduate advise generously |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Rastus When the compressor starts up, does the generator RPM take a dive? Also, is it an inverter type generator? Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Glenn, Had a 5kw briggs and stratton for 40yrs,with one motor change,had no problems.Inheritted a 5kw gift horse so didn't look in it's mouth,I'll get back to you with the details but it certainly takes a dive when the compressor or pump start up.It seems to work pretty hard compared to the unit it replaced.The compressors,one came from repco's the other supercheap auto's so I exspect they are chinese manufactured.Burned a couple out within minutes. Water pump was European 1.5kw start up and would only be used in conjunction with a couple of lights.Hope there's a clue in there somewhere.Cheers Rastus see Rastus graduate advise generously |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Rastus I have found that the new alternators being made now have a different regulation system than the old ones and have difficulty starting inductive loads that start under load such as compressors, also there is not enough flywheel weight in the new motors to apply inertia to maintain rotation speed during starts. My 5KVA generator will not start the supercheap 2.5 HP compressor Chinese direct drive thing. Engine sags and volts die utterly useless needs a 12 KVA to start it. It is flat out starting a 1 HP motor without load, only good for the battery charger electric drills and emergency frodge power during blackouts. The old ONAN 5 KVA starts it no worries. (Big Flywheel and stone age regulation) new aint always better. Bob Foolin Around |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi fellas, its the capacitor excitation that is the problem, as the generator loads and slows, the current flowing through the exciter winding drops of very quickly and this means the power output will slump badly. Some well designed generators hang on a lot better than the rest but its the downside of this excitation system. The old style magnetic amplifier exciter is not as robust or cheap to make but under load it throws everything, including the kitchen sink at an electric motor to try and start it, the limit is the capacity of the generator itself. I have a genny sitting in my workshop now that is very fickle about speed, the exciter winding stops making power at 49.2 Hz, that's only 50 rpm down. If the governor doesn't catch up quick enough it gets stuck at about a quarter of its rated output, running a little overspeed helps. Anyone use a large inverter style generator? I would be interested to see how they go with compressors , pumps and washing machines. I'm confused, no wait... maybe I'm not... |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Thanks Bob and Yahoo2, The details you've provided line up exactly with what's happening.So it looks like I've got a satisfactory supply for battery charging(exspensive) elecric drills ect.and the lights.When possible I'll have to pull the Briggs/Stratton to bits and see if it can handle a "hip replacement" to last another leg of the marrathon.Cheers Rastus see Rastus graduate advise generously |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Sometimes replacing the capacitor with a fresh one helps, if the voltage is low while its running under a normal load. Sneaking the set speed just above 50 Hz at an unloaded idle is worth a go. 250 volts is OK for unloaded voltage on a cheap cap style genny. One of the more unusual faults I have seen is the neutral cable going high resistance under heavy load, very hard to pick with a generator that is permanently wired, if there is no ground to earth. Some single phase motors are just complete dogs, one of my small air compressors has a 2.5 HP motor that takes 50 to 60 amps under load to start it, if I fitted an electric clutch or perhaps a fluid drive to make it soft start it would work fine on a small generator. I have been asked to look at another compressor that is not starting easily and I am thinking from the symptoms, that there is a poor connection in the switching mechanism, maybe dirt or water or ants have got in there and damaged the contacts. 'sigh!' seems like more stuff means more problems  I'm confused, no wait... maybe I'm not... |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Yahoo2, Increasing the set speed should be straight forward,so I'll give that a go first.Is the slightly higher voltage detremental to smaller appliances long term?Thanks for the advise,Cheers Rastus see Rastus graduate advise generously |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
hi Rastus, Some of the older switchmode power supplies in appliances have disc capacitors rated to 250 Volts but they are pretty rare nowdays. I would be more worried about running at higher Hz, having said that, I have had a look at my gear and I have not spotted anything that would be affected...yet. Have a play with your genny by hand before you adjust anything permanently. Plug a couple of extension cords in so you can probe the positive and neutral on one cord with a multimeter and apply a load to the other. Your multimeter should let you leave the setting on AC volts and press a button to read the Hz. Check the linkages and springs from the governor arm to the carby's butterfly, elongated holes, worn linkages and loose or broken springs will let the generator drop revs under load. I make replacement linkages out of high tensile wire. you can sit your finger on the throttle buterfly linkage right at the carby and push the revs slightly higher and lower and see what that does on the meter with no load. hook up a small load (a light or something similar)and see how much the revs drop and play with it again. Do the same thing with a large inductive load, like a heater then lastly run the air compressor through a few cycles. if the voltage drops down to 175 volts or higher then picks up in less than a couple of seconds its not great but OK. If it gets lower than that ( I have seen them drop to 135 volts) or stays down in volts for more than 4 seconds then your looking at motor damage i would think. yahoo I'm confused, no wait... maybe I'm not... |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Yahoo, Thanks for the step by step analysis procedure.It will help me and others too I exspect,Cheers Rastus see Rastus graduate advise generously |
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mac46 Guru Joined: 07/02/2008 Location: United StatesPosts: 412 |
Hi Rastis, A new spark plug, and even a new plug wire may also help. Pull the tinwork off and check for accumulation of debree/ and clean it out. As long as the engine has good compression it should respond as if it were new...provideing everything in the govenor is tight with no slop in the linkages. There should also be alternate holes in the adjustment plate on the carb. to allow for a quicker/slower response.(might just be a weak or streached spring). Reset the idel and run mixtures to assure proper settings and use only regular gasoline, not ethinol. Check for tight fuel line connections/ not sucking air,ect. anywhere, esspecially around the carb. to the engine. Good luck with it. Mac46 I'm just a farmer |
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| Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301 |
Hi Mac46, Even though the unit is relatively new(only used half a dozen times)its worth checking it out thoroughly.So I will follow up with that.Like most of us I have to much on my plate at the moment and the indegestion that goes with it,lol,so I'll post a follow up as soon as I can.All the posts have been very helpfull.Cheers Rastus see Rastus graduate advise generously |
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