Time delay relay

[Eric H]

I am looking for some time delay relays to stagger start the motors on my SS air dryers. The ones I normally use (24 volt)are up to nearly $60 each. I need 8 = $480. I did buy some from grainger for $16 each but they are 120V and the motors are over the 1/3-1/2 hp rating on the relay. I already burned out two of them.
I have been searching the net for a 24V delay but have not had much luck. I know there are guys here that are using delays on vac motors. Can someone help me out here?

 

[Randy]

Why don't you use 30 amp Mercury Relay to take the load off the time delay relay. That's what I use on my vac motor to take the load off the timer. They cost about $20 a piece.

 

[Ghetto Wash]

I just ordered one today from McMaster Carr. It was about $75. $60 sounds good to me.

 

[Eric H]

Found this one:
http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1941243&PMT4NO=0
picture shows as 120V but description is 24VAC. $22.67 isn't a bad price
Does anyone happen to have anything bad to say about using this to operate this contactor:
http://www.grainger.com/Grainger/items/1YCZ4?Pid=search
BTW: thanks for the help so far

 

[MEP001]

You shouldn't need to stagger the motors starting unless you're exceeding the circuit with them all starting at once. I definitely recommend a delay just to prevent unnecessary starting/stopping of the motors, but as already suggested a mercury relay will handle that load and last for many years. You can get them from Kleen-Rite for about $40.

I don't recommend the Grainger relay you listed. They have a tendency to stick closed. If you do use it be sure to add a varistor to minimize arcing across the contacts.

 

[Eric H]

You shouldn't need to stagger the motors starting unless you're exceeding the circuit with them all starting at once. I definitely recommend a delay just to prevent unnecessary starting/stopping of the motors, but as already suggested a mercury relay will handle that load and last for many years. You can get them from Kleen-Rite for about $40.

I don't recommend the Grainger relay you listed. They have a tendency to stick closed. If you do use it be sure to add a varistor to minimize arcing across the contacts.

I am delaying one motor 1 second and the second motor for 2 seconds to keep the motors from starting unnecessarily when the rotary switch is moved past the dryer and to lower the inrush.
I have been using 12 of the grainger relays for over 2 years without any problems. I'll switch over to the mercury relays if they begin failing. I have 8 already installed in the new equipment I am building now.

 

[pitzerwm]

You are right to delay the start, to reduce the "power demand" which can raise your electric "power demand multiplier" . Those are the one that I used, you're just controling the contactor, which doesn't draw much amps.

 

[Eric H]

Thanks guys. I am ordering the delay now but MEP has me worried about the contactor now.

 

[Randy]

I?ve been using and installing the mercury relays on vacuums for almost 20 years and haven?t replaced one yet. I use them to take the load off the vac timer so the timer will last almost forever. If a motor shorts out the timer will not be ruined. There are no contacts inside the relay to burn and fail like in a motor contactor. They are in the Kleen-rite book, #RLM24 for 24 volt or #RLM120 for 120 volt. They cost $21.50.

 

[cantbreak80]

ICM makes some inexpensive cube timers...if you can deal with a 1.8 second delay

I've found 'em here for less than $10:

http://www.southsidecontrol.com/acatalog/Products_ICM_ICM102_Delay_On_Make_Timer_ICM102_3657.html

Grainger also has them...for more money.

Or, for less than $220, another option would be an Idec Smartrelay or Siemans LOGO with an expansion module. You can program them without software with 2 on-delay timers for each input and 2 outputs for each input...wired to your power relays.

If you didn't require the initial on-delay you could get by without the expansion module...as they have only 4 outputs.

 

[MEP001]

Thanks guys. I am ordering the delay now but MEP has me worried about the contactor now.

When I've had issues with them sticking closed it was always on a bay selection that would cause it to get briefly closed and opened again while the motor was pulling full current during startup. If you have a delay on all three motors (An OFF delay as well, so it can never "shock" the relay) they should last well, but I'd still go for mercury relays. You're talking less than $20 per bay for something rated much higher than needed instead of something that's just adequate.

I use the Siemens LOGO for all sorts of things - you can get them from awc-inc.com for $130 each, but you'll still need relays for each motor. It seems like overkill for this application.

 

[cantbreak80]

I use the Siemens LOGO for all sorts of things - you can get them from awc-inc.com for $130 each, but you'll still need relays for each motor. It seems like overkill for this application.

Yeah?LOGO may be a bit extreme, but Eric H was asking for a less costly option than the timers he found at $480.

On the other hand, one LOGO and one expansion module can do everything?

On-Delay for each motor AND Off-Delay for each motor.

16 timers in one device
Easy/simple I/O wiring
Simple programming

One LOGO $130 + one expansion module $58 = total $188

$160 for mercury relays

$132 left over for BEER!