Another Another Compressor Thread

[normspanners]

Well OK then, if that is what you believe.
I am going by my experience and electrical and mechanical knowledge that a motor can burn its coils out in seconds----- if overloaded and also fed too large a supply bearing in mind
a 13A mains plug fuse can pass 25A for about 30 minutes before it blows, and can also pass a LOT higher amps if timed in seconds.
also 16A type b mcb can pass 80Aish for up to 5sec before it blows

 

[the snooper]

the 3hp motor has been used to fill the 4hp compressor once.... and as the original compressor with the same motor on it was blowing fuses this stands to reason that the problem with the motor/caps was present on the old compressor, so i cannot see how filling the 4hp one once would of done so much damage

restarting a compressor that already has pressure in it takes more power to get the pump running again then it does filling when empty, so had you tried from empty again it may well have filled it again no problem, using an underpowered motor will only damage the motor by creating excessive heat in the windings of the motor leading to a breakdown in insulation and total burn out in the end leaving you with no compressor at all

 

[Wallace]

Might be worth checking the non return valve is functioning correctly, if the 4hp motor has died that and the cold weather may have contributed to it.

 

[normspanners]

Might be worth checking the non return valve is functioning correctly, if the 4hp motor has died that and the cold weather may have contributed to it.

Thanks but:-
Has been suggested on previous threads, re this machine, in fact this motor WAS starting a previous compressor with NO--- NRV.

 

[dannyp]

from how i read it, the motor unloaded, ( belt off nothing to drive ) is instantly poping fuses and barely driveing. ( even with bad caps they normaly spin up under no load they just won't do any work )

iirc you say you've done the caps so the only thing left is wireing. disconnect the electrics from the motor, put a FRESH wire into the motor and directly onto a plug. plug it in and turn it on with the belt off. if it instantly blows the fuse recheck the caps and repeat, if you get the same result the motor is dead.

if the motor runs, keeps runing for say 5 minutes unloaded and dosent get hot. it's worth looking at, as in put the belt back on and let it spin the pump with air outlet on tank open to atmosphere

 

[Wallace]

Thanks but:-
Has been suggested on previous threads, re this machine, in fact this motor WAS starting a previous compressor with NO--- NRV.

Ah, only part of the mystery in this thread then!

For those who wish to read the previous thread here. (Mind you don't get caught in a perpetual thread loop!)

 

[normspanners]

iirc you say you've done the caps

No danny the original 4hp had new caps fitted, this is a S/H 3hp motor that was blowing fuses on another compressor, that had been running with no NRV fitted. that repeatedly blew several 13A fuses, so the motor has had some serious Amperage through it .
The 3hp was put in place of a complete 4hp machine that had problems but the caps on the 3hp are original AFAIK.
THis 3hp has pumped up the compressor once or twice then has blown fuses again,
Chances are the 3hp's caps / motor have taken a beating starting the original comp with no NRV.
then was fitted in place of a 4hp on the second machine and expected to do that job. Obviously overloading it.
But with the weather being cold ie sub 5* the pumps are going to be harder to start anyway.

 

[the snooper]

as norm says above
2 machines.
original machine blowing fuses, 3hp motor, no NRV or or unloader valve connected putting strain on 3hp motor
new machine 4hp bought with faulty motor original owner renewed the capacitors

then the op stuck the 3hp motor on the (new to him) 4hp machine filled it once from empty then tried again with 80psi already in the receiver blowing the fuse which could be down to needing extra Hp and as norm states the low temp also adding to problems

 

[jasongtr]

last 2 posts are correct, i have wired the 'old' 3hp direct to the connections on the junction box attached to the motor without the caps and then with (both with no belt on) motor was fine, connected the belt back up and wired it through the capacitors again and it will fill the tank, it seemed to slightly dim the lights a very small amount when it started getting full, this is all with the old caps on the 3hp motor and wired direct bypassing the main compressor push button switch.

Ill try it again tomorrow, i have also emailed clarke to get a price on a new 4hp motor as this is obviously the best thing to do, i just wanted to make sure the pump and anything else other than the motor or caps were good, as i dont see the point in buying a new motor and a new pump (triggers broom springs to mind) when for not a lot more i could get a brand new compressor

 

[dannyp]

i dought clarke will have left much if any head room on the motor sizeing, 3hp would proably carry the pump to a lower pressure say 120 psi instead of 150 psi.
new caps will help the 3hp as has been said they do go off.

personaly my advice if your going to be useing it lots, is just face upto the fact compressed air is expensive flog both compressors as what they are and put whatever you get for them to something that'll do the job. i'm a bugger for ******* about with old kit determined to get it working and save money but i even gave up with my old compressors.

in the end i gave up bought a used but good condion 250ltr clarke with 2x3hp pumps on it and air dryer. bit of an ouch at £700 but wish i'd done it sooner now. it just works and i can crack on with what i'm meant to be doing

 

[jasongtr]

not sure what that means

'i dought clarke will have left much if any head room on the motor sizing'

but i hear you on buying a new one, i dont use it all the time to be honest, yes i have a unit with a ramp etc and use it for air tools, but i dont spray or air sand/DA when i do use it, say once or twice a week it might fill up 5 or 6 times.

 

[dannyp]

The 4HP clarke proably needs all 4 HP . some kit will say have a 4 hp motor but will only really need 3hp they allow a bit extra sometimes when it's desinged genearaly in the more expensive kit. the compressor a mate has in his unit has a motor rated at 7.5 KW but put it on a power meter it'll only be pulling 6KW so there is 1.5 KW of grunt in the motor left in reserve proably for a cold stiff pump or motor going off a bit or low voltage. thats all i meant

 

[jasongtr]

ah ok that makes sense, ill wait to see what they come back with regards a 4hp motor price.

thanks

 

[normspanners]

'i dought clarke will have left much if any head room on the motor sizing'

To explain 'overhead' or 'head room' a 40ton truck travels down a flat level motorway at 60mph and it takes 200hp to do that, the truck has 300hp maximum power
therefore it has 100hp 'overhead' or 'head room' to deal with hills/ head wind etc to keep the truck doing 60mph
If it didnt have any overheads when it hit a hill it would slow down and you would have to drop gears to get up the hill. it would make it up the hill but slower.
So putting that example to your compressor because they don't have any overheads built in and you have fitted an even smaller 'engine' you need to change down a gear to a lower ratio. IE fit a smaller pulley. to keep the compressor running .

 

[jasongtr]

like the explanation, thanks

 

[Rig Pig]

If your giving this compressor a bit of stick then a Clark motor probably isn't the best choice, we use Brook motors at work and they take a beating and keep on running.

 

[jasongtr]

the compressor i am looking to replace the 4hp motor on is a clarke and has the NRV fitted so won't be giving it any 'stick' as it goes the 3hp motor off the old compressor is a brook hansen one

 

[Rig Pig]

My point is that there are motors and there are motors, a quality motor will out perform and outlive a cheap import motor.

 

[jasongtr]

quite agree, do you know where to buy them, done a quick search and didn't find much, did find some TEC ones for sale, uk built so that could be good

 

[Rig Pig]

A quick google search of electric motors Oxfordshire brings up Alger electric motors ltd - Brook agents and a load of other company's who stock motors.