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Discussion Starter · #1 ·
350kw Generator with Transfer Switch with 16 units on timers. Anyone install one these setups lately? Since the owner is on the cheap side, were talking about installing a transfer switch with some sort of load management system (timers) to disperse the load of 16 commercial freezers. We might be able to decrease the size of the generator (hence <$$) that way. Facts via owner 3phase delta, 240 volts, fla 380amps (all 16 freezers), locked rotor amps ?? 600 amp service in bldg, 20-35Hspower motors per freezer,

That's all I know for the moment. I'll report back when I look at the job and get the real story.

Any thoughts? Rent, Own, Lease Generator ?? Timer system ??
 

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ampman
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this is very easy to do you first must know how many of the 16 they want to run at one time and for how long. say 2 at a time size gen for that then set timer for 1hour for 1-2 then one hour for 3-4 use timer to activate/deactivate freezer controls with interlocks to prevent more than two units from starting,also time delays to allow one unit to get up to speed then start next unit . it depends on what the owner needs , my times were just examples i do this stuff for commercial greenhouses all the time
 

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Discussion Starter · #3 ·
Freezers

Nice. You have a diagram of that setup?? Initially, I was just thinking of setting up 8 timers with 2 units per and a contactor setup (like parking lot lights) but, it sounds like your talking 1 timer with controls. I'm curious to see that setup diagram/photo style (picture learner here). A diagram would be nice for me and maybe others. We would have to have about a 50kw generator min to be safe and room for some expansion if needed. I'm not sure yet of Locked rotor amps but I usually assume about 600%ish. Their running amps for 2 would only be about 16kw

Thanks
 

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Electrical Contractor
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37 Posts
I would suggest a programmable relay or plc for this application.

I've used these for a similar application. You can enable the program to run only when the generator is running(however you choose to do this), using temperature controls/alarms(basically the thermostat) to decide which would be able to run,how many and the starting sequence by just controlling the liquid solenoid valve (and hope they don't leak:whistling)

For example, with just using a series of timers, you may enable a compressor to run but, it may be at temperature or at least not in an "alarm" condition and not need to run whereas a "box" whose temperature is up that needs to run is disabled. Once the temperature is out of the alarm range, it can enable another one to run instead of waiting for a timer to time out. You may have a 30 minute run time but the temp is able to be reached in 10 minutes so, you have to wait 20 minutes before another is able to start.

Also, something to consider with freezers, is defrost, door and vent heaters, and condensate line heaters that will need to be allowed to run.

These are very inexpensive, usually have a free software download or can be programmed at the keypad, and are expandable. You can start with the basics and add features as you go without rewiring.
 

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ampman
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783 Posts
I would suggest a programmable relay or plc for this application.

I've used these for a similar application. You can enable the program to run only when the generator is running(however you choose to do this), using temperature controls/alarms(basically the thermostat) to decide which would be able to run,how many and the starting sequence by just controlling the liquid solenoid valve (and hope they don't leak:whistling)

For example, with just using a series of timers, you may enable a compressor to run but, it may be at temperature or at least not in an "alarm" condition and not need to run whereas a "box" whose temperature is up that needs to run is disabled. Once the temperature is out of the alarm range, it can enable another one to run instead of waiting for a timer to time out. You may have a 30 minute run time but the temp is able to be reached in 10 minutes so, you have to wait 20 minutes before another is able to start.

Also, something to consider with freezers, is defrost, door and vent heaters, and condensate line heaters that will need to be allowed to run.

These are very inexpensive, usually have a free software download or can be programmed at the keypad, and are expandable. You can start with the basics and add features as you go without rewiring.
this would be alot better i dont know much about them (i should) but here electronics seem to get "struck" by lightning often
 

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ampman
Joined
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783 Posts
Nice. You have a diagram of that setup?? Initially, I was just thinking of setting up 8 timers with 2 units per and a contactor setup (like parking lot lights) but, it sounds like your talking 1 timer with controls. I'm curious to see that setup diagram/photo style (picture learner here). A diagram would be nice for me and maybe others. We would have to have about a 50kw generator min to be safe and room for some expansion if needed. I'm not sure yet of Locked rotor amps but I usually assume about 600%ish. Their running amps for 2 would only be about 16kw

Thanks
i don't know how to size a gen but i do know someone who does and he said a good rule of thumb is 2kw of gen for every h.p. of motor so a 35 h.p. motor would mean 70 kw gen(start up) let the gen supplier size the gen.
 
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