Horsepower motor question

Hello guys.

I know I am sounding a little strange to be asking this simple question, but I really have no idea on the following problem I faced.

The countable number of projects I have done all have starter to kickstart the motor. But I would like to know if it is possible to start a motor without a starter? I'm pretty sure it is possible but I do not know what is the capacity of the motor that would not require a starter.

Can anyone shed some light on this?

Thank you!:nodi:

regards
Sherine T.

this will depend on the rating of the output card u are using
i think max 2A but no one would recommend that

I mean what is the maximum size of motor that would not require a starter (size as in horsepower..etc)

Any MOTOR, single or 3 phase should be on a relay/contactor/starter.

Sherine,

Its a matter of termonoligy; A "starter" is a "contactor" (which is just a large relay) with an overload attached to it. A "relay" is usually refering to a small signal relay, usually used for logic, or isolation. Some relays like a KUP style may be able to handle up to 10 amps @ 240 volts, smaller relays like a KH style usually have 5 amp rated contacts. Inductive loads such as motors will require de-rating of the relay to account for arching/contact wear.

If you have a small fractional HP motor (1/6 or less) you might be able to use a KUP relay. Anything larger you need to consider a contactor, or starter.

To expand on what Mike said, a starter doesn't "kick-start". It is basically a switch with an overload. Just on/off.

The main variation is just the opposite of what you said. The term is "soft-start" or similar which is to lower the "kick" of the start.

motor

Sherine T.
You can start a motor just about any way breaker, disconnect, cord with a plug on it. Just about any way you can get juice to it will start the motor. The problem comes when stopping a motor. By this I mean if the motor is not loaded and you stop it all is well, but if this motor is hung up or has a serious overload on it and you and lets say you have started it with a disconnect and now you are going to stop it with this under a heavy load it may blow the disconnect up. Because the arks will follow the blades out so for and then may go together and BANG! A starter is designed to interurpt this heavy current and not explode or go BANG. We have started and stopped motors up to 250 hp with only a breaker, but this is diffenantly not a safe way to start and stop any motor.

Any MOTOR, single or 3 phase should be on a relay/contactor/starter.

Click to expand...

This is very good advice.

when is a relay not a relay

Just to confuse matters, not all starters are relays or contactors. As Rick said, the "soft start" is totally electronic in nature and has NO contacts in it (at least the SMC3 that I use). As a matter of fact, if you have the "starter" off and the motor not running, you can still measure 480 VAC at the motor (just not enough current to cause it to run). It still has OL capability and I use them often. One thing for me though is I do put an isolation contactor on the input of the soft start only because I don't like having 480 VAC at the motor with the motor off.

Soft starters:

Bruce is correct. We also install an isolation contactor. However the motor is wired open delta with the isolaton contacts oposite the soft starter scrs. (each winding has a SCR on one end an contact on the other end). The isolation contactor is brought in before the soft start is activated, and dropped out after the soft start is deactavated. This allows for a smaller sized soft start & contactor. However the Siemens soft starts fault out when the isolation contactor is cycled. I tried to get Siemans to change the firmware but after much discuession it didnt work out, so we now use a different brand.

Mike it would be good to see a diagram of this hookup?

:site:

Bruce, the SMC-3 actually incorporates an SCR bypass contactor inside the soft starter. This is how AB manages to make the unit as compact as it is. The SCRs manage the current delivered to the motor during starting and stopping, once the motor is up to speed the bypass contactor engages. This way smaller SCRs can be employed, a large heat sink is not required, and a large contactor is not required to handle inrush.

I use the SMC3 and SMCFlex startes almost exclusively now. They are price competitive with a NEMA starter and I haven't had any problems with them.

With soft starters, even with isolation contactors, its still good practice to put hazard warnings on the motor peckerheads and make sure all your maintenance people understand why hazardous voltages can be present even if the motor is off and that those voltages can become more hazardous if the motor circuit is opened. Follow lock-out-tag-out policies. I was in one plant once where 50 hp motors in a critical pumping station were wired with plugs so that they could be swapped quickly. The motors were on SMC Plus soft starters. I noticed in the MCC that at one point an isolation contactor had failed so it was bypassed. There would be lethal voltages on the plug should it ever be disconnected from the motor without shutting off the MCC disconnect. I keep a stack of engraved warning labels to be screwed to the peckerhead for just that reason, you never know what some in-a-hurry tech will do to what was originally a good design.

guest said:

Mike it would be good to see a diagram of this hookup?

Click to expand...

jolio ST said:

Hello guys.

I know I am sounding a little strange to be asking this simple question, but I really have no idea on the following problem I faced.

The countable number of projects I have done all have starter to kickstart the motor. But I would like to know if it is possible to start a motor without a starter? I'm pretty sure it is possible but I do not know what is the capacity of the motor that would not require a starter.

Can anyone shed some light on this?

Thank you!:nodi:

regards
Sherine T.

Click to expand...

I read this countless times and what i think Sherine is refering to is a "capacitor start or start switch" hence the "Kick start"

Now to answer that i must say most of the single phase motors i have hooked up all have them..the 3 phase ones however did not..I am sure there are others who would have a better idea..

D

I believe that darrenj is correct. He is asking about a capacitor start motor.

Sherine,

There are several styles of motors that use a capacitor or starter. The capacitor is used to give the motor a little extra kick when trying to start. After reaching a predetermined speed the centripetal switch (inside the motor) takes the capacitor out of the motor circuit.

Some motors like a Capacitor Start/Capacitor Run use a capacitor to start the motor then another one to help keep it running (air compressor).

Some motors like the shaded pole may not have a capacitor at all.

The type of motor determines the use of a capacitor(s) not necessarily the horsepower.

Someone please correct me if I am wrong.

Steve

In these kinds of motors the capacitor does not give the motor a kick to get it going. Simply put, the capacitor determines what direction the motor will turn because one pole lags. Without a capacitor or a shaded pole a single phase AC motor's rotation direction will be random.

Usually a heavily loaded induction motor, provided it is still poperly sized, will draw the extra current it needs to get the load moving form the line without any extra device. If its undersized, it will still draw extra current from the line to try and get the load moving until something trips or burns.