Wallace
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Sorry my fault, meant to ask zzr1200.
- Thread starter Psychosaffa
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Sorry my fault, meant to ask zzr1200.
zzr1200
Working at 650 ft on open steel work.
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- 5,809
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- Glapwell, Chesterfield, Derbyshire, UK
My large compressor is an old school 3hp motor 14cfm 200 ltr tank, its not one of these new soft start jobbies has to have a 30amp supply, even then the lights dim a bit.
I purchased it new from an industrial compressor manufacturer in East London years ago, its been a brilliant compressor.
My small compressor needs time to refill the tank, but I expect that...
Psychosaffa
The Angry African.
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- 237
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- Glasgow, Scotland
Would a direct on line starter not make life a bit easier?
zzr1200
Working at 650 ft on open steel work.
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- 5,809
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- Glapwell, Chesterfield, Derbyshire, UK
To be quiet honest I have no idea, it has the usual pressure on/off pressure switch on the tank and the cable has a 30 amp plug on it. I've never ever considered wiring it any other way, the plug just allows it to be connected/disconnected quickly in case it needs moving for any reason.
brightspark
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- yarm stockton on tees
the only reason a dol starter would be needed is if he requires the motor to be protected from overload if its left unatended
Sidewinder
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& NVR...
daleyd
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- Wrexham, North Wales
DOL is effectively the same as a switch, there is nothing to smooth out the starting. Star/Delta is the usual contactor arrangement for a smoother start.
zzr1200
Working at 650 ft on open steel work.
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- 5,809
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- Glapwell, Chesterfield, Derbyshire, UK
Not on 240 single phase as far as I know, simply on or off...
Psychosaffa
The Angry African.
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- 237
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- Glasgow, Scotland
So is a DOL starter really necessary then for a 3hp motor if it's not left unattended? I'm building another compressor and it would be handy if I didn't really need a DOL starter as they are about £50
Sidewinder
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Depends on what if anything you need to comply with, legally, morally, or insurance wise?
Psychosaffa
The Angry African.
- Messages
- 237
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- Glasgow, Scotland
So it will work without one, but it's not recommended then. £50 is a small price to pay for safety I guess..
zzr1200
Working at 650 ft on open steel work.
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- Glapwell, Chesterfield, Derbyshire, UK
Put it on a dedicated spur with the correctly rated RCD in the consumer unit...and use the on/off switch on the pressure switch unit...
Sidewinder
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How is that going to give you NVR unless you use an active RCD?
zzr1200
Working at 650 ft on open steel work.
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- 5,809
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- Glapwell, Chesterfield, Derbyshire, UK
Why would you leave it turned on, when your not in the workshop using the compressor, ???
I just turn the thing off, when its not being used... simples...
Plus why do you need a NVR on a compressor with no unguarded open moving parts, I can see the possible need on an open blade, ie: saw table, but again why leave equipment powered up/switched on while not being used?
Surely that is just bad workshop practice...
Last edited:
daleyd
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Yes, you are right but DOL is not really used as a term for 240v motors either. Single phase usually have a capacitor to smooth out the starting
zzr1200
Working at 650 ft on open steel work.
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- 5,809
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- Glapwell, Chesterfield, Derbyshire, UK
Totally agree.
My old style 3hp motor has 1 capacitor, I believe you can now get soft start 3hp motors that will run off a 13 amp plug, how many capacitors do they have and how are they wired/switched???
Sidewinder
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Not correct, the capacitor on a single phase motor is not to smooth, out the starting, it is there to generate a second "supply" out of phase to generate the rotating field to make the motor turn, if it is a start cap.
Sidewinder
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The number of caps will either be one, if it is a start cap, one, if it a pcap, or 2 if it has separate start & run caps
daleyd
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As it reduces the start up current and increases the start up torque compared to a split phase type (for example), I'd say yes it does smooth out the starting, though you are of course correct in the way that it does it.
daleyd
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As sidewinder said above, if it's a start capacitor it'll probably be 1 which is switched out as the motor gets up to speed, usually but not always by a centrifugal switch.
3hp is close to a 13 amp supply limit, and during start up the current draw will be many times this (up to 4-500%, maybe more depending on load). You can buy dedicated soft starters which use clever electronic trickery to limit the start up current which helps immensely.
