Thread: 15 amp power lines

Bob,


I don't think the cupboard is the problem. As you know I placed mine in a cupboard in order to soundproof it and my cupboard is smaller and I don't have any problems.

I think it is either the compressor or your new wiring. Do you have any other 15 amp plugs on a different circuit? If so try running the compressor from that for a while and thus ascertain if it is the plug and associated wiring or the compressor.



Peter.

I would have expected that capacitor to be 400V, not the 220 you stated.

It is only overvoltage which kills capacitors.

Ed T

OK
I measured the voltage at the outlet and got 237 volts. That is OK, 240 is only a nominal voltage anyway.
Plugged the new condenser in and turned on the power switch for the compressor. It ran for about 10 seconds while I was getting the probes in place for the voltage readings and then the condenser spat electrolyte and started smoking.
If , as ED T says the condenser is meant to be 400 volts then that would explain it. Would it make a difference if there were two condensers sharing the same load? Can they split the voltage between them and get 400 volts that way?

Just phoned Qld Trade Tools and they assure me that the 200volt condenser is correct for this machine. It is beginning to look like I may need a new motor, or at least this one rewound.

Bob,

Another thought, perhaps the start switch on the motor has stuck, leaving the start capacitor in circuit after it should have been switched off. Still, ten seconds is not all that long, it should handle that.

Did the compressor sound normal during the ten seconds?

regards,

John

Originally Posted by Bob Willson

If it does, then it will cost me $30 to find this out.

If the voltage drop test doesn't work then I will try it outside again.

I will test about 1 or 2 pm (when I wake up )

OOPPS

Bob,
Just a quick thought, is this a real compressor - one with a belt and possibly 2 stages or one of those direct drive things?

I had one of those horrible direct drive things first and wouldn't give you 2 cents for it. It too blew up (condensor) but was caused by the motor being overloaded by a gauling compressor piston. Shound't have bought crap - new compressor is 2 stage belt drive - cost a s##t load but was worth it.

Johnno is on the right track I think. CHECK THE SWITCH.

If you parallel up two identical capacitors, the resultant will take same voltage with twice the capacitance.

Put them in series and you get twice the rated voltage, but half the capacitance.

Ed T

First off, two things:
The capacitors are not equal. The first one is marked a 16 uf 500 volts and the other is 108 - 140 MFD and is 200 volts.
Next, this is a "proper" compressor. twin cylinders, belt driven.

OK, I took off the belt guard and removed the belts to see what the condition of everthing was like. I next removed the top of the switch. This allowed the switch to pop up into the 'ON' position. (Knocking it down turns it off.)
I then ran the motor by pluging into the 15 amp line and using the 15 amp socket switch to turn the motor on/off.
I ran it for 10 seconds and tested the heat build up in the capacitors. NIL
I ran it for 60 seconds and tested again. NIL
VERY slight heating of the motor itself, well within specs I should think.
These tests were done with the belt OFF.
So, where do I go from here?
PS even though the capacitor had leaked electrolyte it still seemed to work fine. Maybe I won't need to spend that extra $30.

Johnno was not talking about the on/off switch, but the one which brings in the capacitor during the start up.

You probably have a capacitor start, induction run motor. These are the most common in the 2 to 3hp single phase range of motors.

Single phase motors develop b all torque until they get up near their design operating speed. So starting a compressor is tough. So the capacitor is designed to boost the torque until it gets up to speed. Then it is supposed to cut out. The switch which does this is a centrifugal one on older motors, attached to the shaft. Newer motors may have an electronic one.

Johnno is suggesting that this switch may not be working.

Your no load test proves nothing, because the motor is not loaded.

See following for lecture on motors


http://www.iprocessmart.com/leeson/l...se_article.htm


Ed T

This may be resereceting the dead a bit, but as Bob hasn't yet posted his latest findings, may I very humbly ask if the replacemet capacitors are the correct type, that is start or run types, in the correct place?

One thing has occured to me.
Is the dump valve working. This is the valve that dumps the head preasure when the motor stops. It should be part of the presure cut out switch.
If it isnt the motor may be trying to start under load and failing to properly start causing excess load on the capicitor.
Did you say the motor ran OK with the belts off?
A compressor motor should be at its lowest load at the beginning of the run and the highest load at the end.
Can you measure the current drawn with a clamp meter?
There are a variety of motor types It is probably a good thing to find out what type the motor is.
I have a trade tools compressor & I don't think it has on speed contacts I think its just a simple phase shift induction motor, ie capacitor in circuit all the time.

I'd also be enclined to trace the path of the existing wiring.
If It was me I'd be running 4sq mm all the way bach to the board. With recent changes in the regs a lot of sparkies would be inclined that way too.

Afterall this is realy sparkies work.

cheers

Hey guys I've got 6sq mm cable X 25m run to my shed, what would be the max safe amp loading, would it handle a 35amp load conituosly?(3hpTS/3hpdusty/2hp comp/2hp evap aircon + 9 fluro lights could all be running at the same time)

Harry

6mm² cable will carry 38amps. You would need to calculate the amperage of each machine to see what your maximum load would be. Just check what the compliance plates say on each motor bearing in mind that if the dusty, airconditioner and the saw all started at the same time there will be a significant load on it at once.

A 6mm² circuit should be protected by a 32amp circuit breaker or HRC fuse or a 25 amp rewireable fuse.

There are so many factors involved in this such as where the cable is running either in free air or in conduit or in insulation how long the run is, if it is buried underground, how many sub-circuits off it which will have derating factors applied to it.

To calculate the maximum demand is as follows.

Lights - 75% of the connected load
GPO's - 1000w for the first out let and 400w for each additional outlet
Airconditioners - Full connected load
Motors - Full load of the highest rated motor and 50% of the full load of the remainder.

This is only a very tiny bit of how the load is to be calculated and probably the average electriction would not sit down and calculate it out accurately.

Originally Posted by B_W

6mm² cable will carry 38amps. You would need to calculate the amperage of each machine to see what your maximum load would be. Just check what the compliance plates say on each motor bearing in mind that if the dusty, airconditioner and the saw all started at the same time there will be a significant load on it at once.

Yeah thats what I thought, I calculated by adding up the watts of each, 3hp TS is 2250w,3hp dusty 2250w, comp is 2hp 1500w, aircon is 1.5hp but I allowed 1500w, the 9 lights are 18w ea unsure on lights? so I allowed 500w.
So that adds to 8000w /by 240= 33.3amp would that be correct(or near).

Am I right in thinking the dusty/aircon is a continous draw, the TS would be a cascading draw(changing draw between cuts etc)and the comp is a ramping draw?
This condition would only ever happen in summer(aircon), but the TS/dusty will be on a regular basis together, the comp will only run occasionly as I use it to remove saw dust from the machines as Im machining.

I intend to have 3x 15amp PO(1 ts,1 dusty, 1 spare), 5 GPO's, dual circuit on the lights 3 center and 6 outer lights.
If this draw is too much for continous work, would it be advisable to run a second 4sqmm supply for the 5 GPO's(3 will be doubles)?