Alternating Relay Circuit

[herefishy]

I have 4 condensing units serving a chiller circuit. I want to alternate the lead / lag C.U. operation via the four stage temperature controller. I can find 2 switch and 3 switch alternating relays ( ref. http://www.macromatic.com/products/custom.html ), however is anyone aware of a 4 switch alternating relay?

Any ideas?



the chiller manufacturer will do it, but the price ain't too good.

I know I can do it, but looking for the one-component answer. searching the web, I found a three switch alternating relay. I don't mind using it, leaving one C.U. as the perpetual "lead".

Do you think that is the best answer?

Later,

[RogGoetsch]

I know when alternating two compressors on an industrial system, it was not considered good practice to run them the same number of hours per year (alternating lead-lag equally) because of the possibility, though small, of service problems related to service life. (e.g.: one compressor shut down to address a problem occurring at 3000 hours as the second compressor hits 3000 hrs.)

With four units, this precaution is probably not important, but I would be comfortable with reassigning lead-lag-lag-lag status on an annual basis.

Rog

[Andy]

Hi, Herefishy. Try the following site. www.thermofrostcryo.co.uk
They sell Eliwell and Dixell pack controllers which can take a NTC temperature probe for contol. I have fitted four dixells recently to replace a PLC on a water chilling plant, using the main water tank stage controller to rotate the lead lag, and three other pack controllers to load and unload the compressors. So far they have worked better than the PLC cutting out a lot of the hot gas loading that was previously used to trim control at low ambients.
Regards. Andy.

[herefishy]

thanx all. It took me some time, but I found a 5-switch 4-load alternating controller by (ATC) Diversified Electronics.

I determined it was not a "relay" that I needed, but a "controller", whose main function is rotary switching. The ARM-120/24-AGE can be selected with SOSO or FOFO logic. I decided the SOSO was the way to go. All I will be controlling are the (24V) solenoid valve coils (4).

see ya'