Ian Barrett Posted September 1, 2011 Share Posted September 1, 2011 My old compressor motor burnt out, and like a berk I binned it without taking any details from it, though I seem to recall 1400rpm and 1hp. The only thing I have for certain are the motor pulley dimensions (shaft is 19mm, keyway is 9.5mm, pulley size is 4.3/4 inches) and details of the compressor motor are that its a 60's Ingersoll Rand v-twin Type B Does anyone on here know enough about compressors to tell me what size replacement motor I should get? I'm considering one which is 1.5hp, single phase, 1400rpm Does anyone know a good source for motors? I've heard the ones from Machine Mart are made from chocolate but still expensive. Quote Link to comment Share on other sites More sharing options...
stuck Posted September 1, 2011 Share Posted September 1, 2011 Ian, Motor frame sizes (metric ones at least) are usualy dictatetd by the height to the centre line of the shaft from the base plate. I.E. a D160L motor's shaft centre line will be 160mm from the base plate. Can you estimate the shaft height from the guard or something? If you have the frame size, power rating and speed thats all you need really. HTH's, Mick. Edit: 1440 RPM is a 4 pole motor or bog standard in other words. Quote Link to comment Share on other sites More sharing options...
Team Idris Posted September 2, 2011 Share Posted September 2, 2011 Or work it back from the hole spacing. A D71 has one standard foot, and so on up the range. We currently use Rotor-Motor at work. Beatsons arn't far up the road from you and have always been helpfull when I've asked for stuff Its the maker you want, rather than the supplier, who often sell a range of qualities! I know I should be able to tell you what a V twin piston compressor power is, given the CFM and pressure But I note the motors seem to be a little oversize to get the thing started. Unlike the screw's that start off-load. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 2, 2011 Share Posted September 2, 2011 Loads of 2nd hand motors on eBlag, no harm in going for more powerful than you need, it'll only draw as much power as it needs. Quote Link to comment Share on other sites More sharing options...
nickwilliams Posted September 2, 2011 Share Posted September 2, 2011 You'll need to take a few measurements and do a little maths so you can work out what the displacement is. Calculate the swept volume of the cylinder(s) and then how fast the compressor rotates (from the pulley diameter ratios and the fact that the original motor speed was about 1450 rpm). This gives you a number for the unpressurised volume of air the compressor will shift (otherwise known as the 'free air delivery' rate). The magic figure you then need to know is that you will need about 1hp of motor power for every 3 cubic feet per minute of free air delivery. Nick. Quote Link to comment Share on other sites More sharing options...
simonr Posted September 2, 2011 Share Posted September 2, 2011 Well done Nick - that's good tech! Si Quote Link to comment Share on other sites More sharing options...
cackshifter Posted September 2, 2011 Share Posted September 2, 2011 Ok, a couple of things. Compressors are difficult to start, the type of motor is crucial to give good starting torque. The best is capacitor start, capacitor run. If not that, capacitor start, but it'll use more current. Machine Mart motors aren't suitable for compressors. No harm in going for a little more horsepower but, the pulley may have to be bored out (and keyway filed out) to fit a bigger shaft, and although it will only use the same power ie watts (ish) it WILL draw more current (amps) but at a lower power factor, in other words your wiring, starter switches may need to be uprated. If you're sure about size I'd say look for a good quality single phase 1hp (1440rpm) 4pole motor. They are standard sizes, so will probably fit without a fight.The full load current is a good indication of how efficient it is, the lower the better. Beware of American or European 220v motors, as the voltage goes above nominal (we are usually over 240 here), the motor reaches magnetic saturation and the current climbs drastically (I had a 220v motor on a compressor, 15A at 220v, 40A at 240V, no wonder it got hot) TBH 1hp sounds too small, Ingersoll Rand kit is normally pretty beefy. 19mm shaft sounds more like 3hp so I'd check before you buy. SeeMy link Nigel Quote Link to comment Share on other sites More sharing options...
nickwilliams Posted September 2, 2011 Share Posted September 2, 2011 A compressor should not be particularly difficult to start if the unloader valve is working properly. Anything with a V-twin compressor head is likely to need at least 2 Hp, and more likely 3. 3 Hp is generally accepted as being the largest motor it is possible to run off a single phase supply (you can go bigger, but not on a 13A socket or a 16A spur). As FridgeFreezer says, the motor will only use what the compressor demands and an over-specced motor will run cooler and last longer so you can't go far wrong with a 3Hp motor if you can find one which will fit. However, you will need to check that the switchgear is rated for a 3Hp (2.2kW) motor load or the start-up current will knacker the contactor in fairly short order. Nick. Quote Link to comment Share on other sites More sharing options...
Ian Barrett Posted September 3, 2011 Author Share Posted September 3, 2011 Thanks for all the replies guys. It will be interesting trying to work out the free air delivery rate. Another question - sorry. As I need to ensure the switch gear is rated for the 3hp motor, will the rating of the switch gear I currently have give me an idea of what the motor was. In all this, there is obviously no guarantee the motor was original anyway. I've certainly only had the unit for the last few of its nearly 50 years. Quote Link to comment Share on other sites More sharing options...
zardos Posted September 3, 2011 Share Posted September 3, 2011 You'll need to take a few measurements and do a little maths so you can work out what the displacement is. Calculate the swept volume of the cylinder(s) and then how fast the compressor rotates (from the pulley diameter ratios and the fact that the original motor speed was about 1450 rpm). This gives you a number for the unpressurised volume of air the compressor will shift (otherwise known as the 'free air delivery' rate). The magic figure you then need to know is that you will need about 1hp of motor power for every 3 cubic feet per minute of free air delivery. Nick. Sorry to deflate you :-) But what you have described calculating is the displacement volume not free air delivery. See linky for FAD calculation, FAD is measured at the compressor outlet. Most piston compressors quote the displacement volume not the FAD as the FAD is much lower e.g. as a rough guide 12CFM displacement will be about 8CFM FAD Vane compressors quote FAD as displacement volume does not make sense for their design. Quote Link to comment Share on other sites More sharing options...
nickwilliams Posted September 6, 2011 Share Posted September 6, 2011 You are, of course, correct. Thank you for the clarification. Nevertheless, the basic principle (which is that it is fairly easy to calculate the power you are likely to need) still stands Nick. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted September 8, 2011 Share Posted September 8, 2011 Electric motors online supplied me a 3hp 1400 motor a short while ago for about 90quid, they're an ebay trader, but have a hotmail email at onlinelectricmotors@hotmail.co.uk also very helpful people. Quote Link to comment Share on other sites More sharing options...
Ian Barrett Posted October 19, 2011 Author Share Posted October 19, 2011 Oh. Wish I'd read your reply yesterday ejparrott - before I bought the motor I've got. Anyway, lets see if we can get this thing working. So more questions for you guys if you'll be so kind. I have the biggest damned motor I've seen. Its old but looks to be a quality unit but the plate is missing. I was told it is 2-3hp and 1400rpm. Today I fired it up and it starts and runs fine. BUT when I hook it up to the compressor it wont spin unless its given a turn after which it runs OK. But this kind of defeats the object for a compressor motor so I thought it might be the capacitor which is at fault. It looks very Heath Robinson in its big square tin and has no writing on it at all. So I wired in the capacitor off my old motor, which worked fabulously - for a minute before the capacitor blew its guts all over the garage. The (now dead) capacitor has written on it AC Motor Starting 90/120UF (its not actually a U but similar) 275v.RMS/Surge 439/1/90232/90 Can anyone advise me If the problem is likely to be the capacitor What capacitor I should have if it is the problem Where to get them? With any luck I might one day get my compressor running before winter so I can get all this Dinitrol I've got into the chassis. Cheers chaps IanB Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted October 19, 2011 Share Posted October 19, 2011 Try this: http://www.wikihow.com/Check-a-Start-Capacitor Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 19, 2011 Share Posted October 19, 2011 Some motors have start capacitors, some have run capacitors. http://en.wikipedia.org/wiki/Motor_capacitor Sounds like you put a start capacitor on instead of a run capacitor. Quote Link to comment Share on other sites More sharing options...
Ian Barrett Posted October 19, 2011 Author Share Posted October 19, 2011 Thanks CwazyWabbit and Bowie69, the links were very useful. It certainly seems I replaced the Heath Robinson capacitor with a Starter capacitor. The problem I now have is the motor won't start when hooked up to the compressor with the original capacitor And the Starter capacitor makes it work but gets blown up. What do I do? Quote Link to comment Share on other sites More sharing options...
Ian Barrett Posted October 19, 2011 Author Share Posted October 19, 2011 I've found this information which suggests the 90/120uf capacitor wasn't correct for my 3hp motor Motor Rating........Motor start Capacitor (HP)........(MFD) 1/6 HP......20-25MF 1/5 HP......30-40MF 1/4 HP......40-60MF 1/3 HP......60-80MF 1/2 HP......80-100MF 3/4HP.....100-120MF 1HP........120-150MF 1.5HP.....150-200MF 2HP........200-250MF 3HP........250-350MF However, what I don't understand is whether I need a start capacitor to give the motor a kick initially, and what switches it off when the motor is running. Is it possible to tell by the way the motor/capacitor is wired? Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 19, 2011 Share Posted October 19, 2011 Start capacitors are sometimes switched out of the circuit using a centrifugal switch which is built into the motor. You hear a click once the motor is up to speed. I have seen others that use a current sensitive switch instead. Quote Link to comment Share on other sites More sharing options...
Ian Barrett Posted October 20, 2011 Author Share Posted October 20, 2011 I gave up trying to figure this out and today took the motor to a local company who rewinds motors. They are going to figure out what capacitor it needs and I'll buy it from them. Once nice thing which also happened today was that I took the motor to them in the Landy, and the guy there interrupted me talking about the motor to give the Landy a good once-over and ask me all about it. I was quietly really chuffed when he was shocked at how old it is. I'll let you know how I get on with the motor/compressor. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted October 20, 2011 Share Posted October 20, 2011 To be honest that would have been my next suggestion, probably be the cheapest place to get the right capacitor as well Nice when you find another Landy fan when you least expect it Quote Link to comment Share on other sites More sharing options...
landroversforever Posted October 20, 2011 Share Posted October 20, 2011 To be honest that would have been my next suggestion, probably be the cheapest place to get the right capacitor as well Nice when you find another Landy fan when you least expect it I keep finding people at work who are LR people... always someone to 'waste' an hour of my day nattering too!! . Quote Link to comment Share on other sites More sharing options...
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