compressor motor power

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rogerrabbitt
 

compressor motor power

Sat May 29, 2010 8:56 am

Hi
my name is roger i'm a brit living in bulgaria
i dive a da aquamaster on an italian tank with j valve,
unfortunately a fill is approximately a hundred mile round trip.
i have a dunlop major compressor with hamworthy filter towers,
i bought off ebay as damaged repairable,i've fully rebuilt it with a few extra mods
(plexiglass window on the pump to show oil level)the problem i have is that bulgarian electricity isn't very strong and it wont run the 3000 watt motor
the question i'm asking is if i run a smaller motor capable of turning the pump at a smaller rpm will it still acheive pressure ?allbeit at a slower rate ? i do hope this doesn't sound dumb.
kind regards roger.

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Bryan
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Re: compressor motor power

Sat May 29, 2010 10:53 am

I don't feel qualified to answer your question but I know that one of the features of the compressor that I have is that it runs at a lower speed and supposedly this is to give it a longer life......Here is a link to the site. I think they are made in Turkey. Don't worry, there are several others that will reply that can help you more than I can. Welcome to the forum.

http://www.airetex.com/w32m.htm
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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captain
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Re: compressor motor power

Sat May 29, 2010 11:40 am

There are two sides to this. One is the power needed to turn the compressor the necessary speed. The compressor should have a rated speed that shouldn't be exceeded. Running it slower will result in longer fill time but less wear on the compressor. The second part is the power needed to start it. Although it may need less power to run at a certain speed it will still need enough power to start it running.
Using a smaller motor will only have the motor running in a constant overloaded condition that can overheat and destroy the motor and will not result in less electrical draw and maybe will not even be able to get the compressor started.
I am sure 3000 watt motors run in your country, it may be that the motor is not the correct one for your power supply. Is It a single phase or three phase motor, is it the correct voltage and is the wiring to it correctly sized.
What is the voltage of your power.

Here in the US a 3000 watt single phase motor would pull about 13 amps using 230 volt power. This is not a very large amount.
If you can give me more information from the motor name plate and about the electricity you have I would better be able to give you possible solution.
Captain

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Bryan
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Re: compressor motor power

Sat May 29, 2010 12:40 pm

Standard AC power in Bulgaria is 230 V,50 Hz according to the net. I the motor will run slower @ 50hz but I don't remember if it is proportional to the voltage or not...I think it's something like 30% slower....And that will make it run hotter. Hope it's an air over cause you will need the cooling....
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

rogerrabbitt
 

Re: compressor motor power

Sat May 29, 2010 1:47 pm

wow thanks guys .
well it's a single phase motor and we're on 240 volts 3kw running at 1410 rpm with an 11 inch double belt pully.
but we're in a rural location most houses only have a few electrical outlets
it's a legacy of the communist era, we've had power problems since we came here
i run a small workshop but if you turn a polishing machine on the lathe will turn off
due to the load,the diving compressor has a 15 amp fuse rating it's very large for what i need as it came from a dive shop filling many tanks per day hence the large motor i have smaller motors and obtaining a smaller pully is not a problem
i just needed to know if the pump would work, slower fill time is not a problem as it normally costs us a day to go to the fill station.the other option is a 7 kva generator but i don't have the funds for one right now and i would like to get some diving in this summer.
kindest regards roger.
oh and it's great to be part of such a devoted bunch of like minded folk

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captain
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Re: compressor motor power

Sat May 29, 2010 2:03 pm

One option is to convert it to a gas engine. The gas engine will have to be a higher horsepower than the electric motor due to the compressor starting torque requirement.
An electric motor produces it's maximum torque instantly from 0 rpm to running rpm where as an internal combustion engine has to reach a higher rpm before it reaches it's maximum torque.
I converted my compressor from 3 HP electric to 5 HP gas and 5 HP is just barely enough to get the compressor started. The same compressor came from the manufacturer equiped with a 7.5 HP gas engine.
Captain

rogerrabbitt
 

Re: compressor motor power

Sat May 29, 2010 2:15 pm

Hi captain
i've allready run a 5hp gas engine and it wasn't
strong enough but i will take your advice as gas engines are cheap enough here
i would have preffered electric that way i can run it in the basement workshop.with no air contamination issues.
regards roger.

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Gilldiver
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Re: compressor motor power

Sat May 29, 2010 4:49 pm

It sounds like a 8 HP (6 Kw) or 10 Hp (7.45 kw) Honda engine would do nicely. They start easy and should be imported into your area.

Or, you might go with a larger natural gas generator set that can be used to run some of your machines when not powering the compressor.
Double Hose Regulators, It not just a Hobby, it’s a Disease

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antique diver
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Re: compressor motor power

Sat May 29, 2010 8:59 pm

I would have to know a lot more about your compressor and the current motor horsepower, rated amp draw at full load (FLA) etc... BUT, you could use a smaller motor by going to a smaller drive pulley, as that will turn the machine slower and use less amperage at the same voltage. The correct size depends upon several factors which I need to know first.

Can you provide all the info on brand, model number and rated volume output, outside diameter of the pulley that is on the compressor, etc. Also all the info off the motor plate, specifically the horsepower or other equivalent rating, full load amps, pulley outside diameter and any other info you can come up with. We could probably decide on a suitable smaller motor once you also determine the amperage available at your power supply. Lot's of stuff to find out, but that's the only way I might come up with a suggestion for you.

Also a good photo of the unit might be a big help along with close ups of the motor info plate and compressor plate if any.

rogerrabbitt
 

Re: compressor motor power

Sun May 30, 2010 3:22 am

thank you all.
antique diver i will get all relevant information and post as soon as i can
i'm a bit busy right now but will push the envelope as i need this pump working.
and again many thanks for all the helpfull replies.
kindest regards roger.

rogerrabbitt
 

Re: compressor motor power

Sun May 30, 2010 8:55 am

ok here's what i got.
dunlop model 9 ic460/1
1100 rpm
delivery 4.5 cfm
max working pressure 4000 psi
16 inch diameter pulley
photos of compressor and motor ident plate.
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antique diver
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Re: compressor motor power

Sun May 30, 2010 9:30 am

That info helps. Also need to know specifically what happens when you try to run it now. Does it trip a circuit breaker or blow a fuse in your main power box? Does it start off running ok, then slow down as pressure builds? Any additional info will be helpful. Also what motor sizes and amp ratings are on your motors that work on other equipment you have? Have you checked the actual voltage available to the motor, and what the voltage is to the motor when it its running?
Sorry to make this complicated, but it might help us to figure out a solution.

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captain
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Re: compressor motor power

Sun May 30, 2010 11:23 am

3 KW converts to 4 HP. My compressor is 3.5 cfm, 3000 psi @ 1500 RPM and came with a 3 HP 3600 RPM motor. Your motor is 1100 RPM so you maybe could go to a slightly smaller higher speed motor with a smaller motor pulley. What size is you present motor pulley? With that info we can determine what speed the compressor is running.

All in all, compared to my compressor the motor size seems reasonable. You maybe could go down to 3.5 or maybe 3 hp at a higher motor speed but it is hard to say if it will reduce the current draw enough to solve your problem. What about dedicated wiring direct from the distribution panel with a separate circuit breaker just for the compressor or a second service feed just for the compressor. If that is doable it might be the easiest and most cost effective way. When I was running mine on electric power I had a dedicated circuit just for the compressor coming off my distribution panel.
Antique Diver is asking good questions, keep sending the info.
Captain

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Bryan
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Re: compressor motor power

Sun May 30, 2010 11:51 am

I have used step up transformers in areas we were not getting clean power at a consistent voltage. Motors are driving 1hp water pumps that run 24/7. Due to low voltage they were overheating the service life was very short. I agree that a dedicated line/breaker and correct wire size will solve a lot of problems right away.
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

rogerrabbitt
 

Re: compressor motor power

Sun May 30, 2010 11:54 am

ok the biggest equipment i run is a low pressure vtwin compressor
it's 3kw but it has to start with an open valve until it kicks in properly.
the diving compressor turns over maybe five times then labours and blows a fuse.
and it's huge i'm no big feller but i have trouble lifting it.its about 25 percent bigger physically than the other 3kw motor i have
11 inch pully.
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