Short Cycle Timers, replacement for thermostat on refrigerator cooling?

Here's a little quorondrum, problem that I have run into, and maybe have a solution.

Problem:

You have done a fridge mod, and everything is working nicely, but you have the thermostat turned all the way up, which will either run the compressor full time (which will burn it up eventually) or you can not get to your coldest that you can with the fridge mod. How can you get your compressor to turn on and off on a fairly regular basis? A timer right? wrong, you want to cycle your fridge on and off every 10-30 minutes, depending on reservoir volume to keep it at the lowest temperature possible. The cheap timers that you get at home hardware stores cost 10-20$ depending on how many cycles you get per day (10$ for the 7 cycle a day, and 20-30$ for the 24 cycles a day). That means you could only cycle on and off the timer once an hour. The timers that would be perfect, that are adjustable for on and off times from 30seconds to 30 minutes are like 100+ dollars...


Answer (maybe, this is a tough logic problem, maybe the experts could help):

Is there a way to put two or more of the hour on/hour off timers in paralell or series, so that the fridge would cycle on for like 30 minutes, and off for 30 minutes? or able to get a smaller time interval between cycles by buying the cheap timers? hook them in paralell?

For example, you have timer one turn on and off every hour:

time:_____5---5:30-6---6:30--7----7:30--8
timer1:___off--------on---------off--------- on
timer2____-----off--------on----------off
combined__off-------------on---off----------------on

I realize that this would make time be off for 1:30 minutes, and on for only 30 minutes. This is kinda like an and statement, if you plugged one timer into another... only when both are on do they work... anyone interested in helping? If this was possible, it would solve alot of problems, since it's very expensive to buy the short cycle timers. Thanks, Bill

Just make yourself a dongle to plug the pump into lik in the pic using two male plugs and one female for the pump to plug into...the male ends plug into the timers, the timers plug into the wall.

Parallel:
Set timer one to turn on every even numbered hour then off a half hour later.
Set timer two to turn on every odd numbered hour then off a half hour later.

They operate independantly, so one won't know when the other one is on/off.

*edit* or are your saying that the shortest cycle time you can get is one hour on these timers?

Thanks Digggr,
I think that is basically exactly what I was looking for, and this is not just a problem for us overclockers, but it could be used say, to control my misters which water my orchids with a solenoid

http://www.efi.org/products/power/hdtimer.html

"24 on/off settings per day in 1/2 hour increments"

I believe that the timer can not go "on off on off on off" every 1/2 hour, because the distance between the on and off trip is smaller than a half hour, meaning the cycle is 1 hour between turns, even though you could make either one on a 1/2 hour setting, so that would just mean you could set all the timers to the same time and have them on different 1/2 hour settings.

The timers are 15$ so 4x15$=60$ which would still be cheaper than the 100$ short cycle timer.

There was an excellent diagram posted by Diggrr, but it seems to have disappeared? I hope it comes back, it was really awesome. Thanks so much, Bill

I took it out cause it was wrong....I knew this was too late to be thinking. I'll keep working at it though.

Once I paid closer attention, it would be on for an hour and off for an hour, the same thing you'd get with one timer.

heheh, sorry diggrr... I knew it was too late to be thinking, that's why I posted it to the forum! so hopefully somebody else would do the thinking... I know shameful, but true... I have been doing more research, and found a few timers that can switch on and off at 15 minute intervals I believe...

http://homeharvest.com/lampaccessories.htm

if you look down the page for a product called Grasslin T35 it is 22$ and to says: "48 on and 48 off, 15 minute cycles built right in. "
that's 15 minutes x 4 x 24 = 96 times per day... does that sound right?

This other product the talento 121 looks like a better solution, but haven't been able to find a place to buy it yet, still looking:

http://www.grasslin.com/pdf/talento121_oi.pdf

I will keep informed, but nobody has questioned the idea of cycling on and off refrigerators as a good way to keep the reservoir at a good temp. I think that if we had an adjustable timer, we could adjust the compressor so it would turn on just enough to keep the reservoir at the minimum temp possible, and at the same time use as little energy possible. The point is that refrigerator compressors that we use to cool our computers are way overkill for our computer cooling needs... hence the compressor should not have to run full speed all the time. Any debate on that matter would be appreciated too. Best, Bill

IF you look at the ratings of those timers you'll probably see that most of them haven't got the capacity to trun a fridge on and off, they typically say something like 3A non-inductive load, that basically means nothing with a motor in it.

However, I think it would be simple to rig up a vibrating flip flop circuit, a multivibrator, with a big honking capacitor that turns a big honking relay on an off, at regular intervals. You should be able to put a couple of pots on it so you can vary the timing and the duty cycle. Most basic electronics books will tell you how to do this.

regards,

Road Warrior

My system runs 12hours a day. According to an appliance site I visited recently refrigerators have an average life span of 14 years. Another quote was from a HVAC tech that said that they had a compressor returned as faulty and subjected it to testing. Someone forgot about it and the compressor ran non stop for 20 years before someone decided to switch it off and it was still working.
It is important to bear in mind that a compressor is designed to run at a specific temperature. When it is designed by the manufacturer the cooling is deemed to be satisfactory. A compressor will probably reach its operational temp within 5 minutes and whether it runs for 1 hour or 20 hours it will stay within the manufacturer specifications. Cycling will have no short term benefit for the compressor life. The most likely cause of compressor failure is the brushes on the commutator will wear out long before it burns any field coils. A compressor is only likely to burn out when it is run at condenser pressures over its designed maxima.

Re:

I know this is a very old post, however, it is still found by search engines.

The main problem with this is temperature control. Since this is the main purpose of a refrigerator, it is a big problem. Only a temperature sensing solution is viable. All timing solutions are best guess... frozen beer or warm beer. Cycling the fridge with a timer cuts the fan that circulates the air between the freezer compartment and the food compartment. Also, the fridge will normally go into a defrost cycle, where heaters are activated and the compressor will not run at any temp. When you are cycling the fridge and it is in this cycle it will dramatically affect the temp. As for the twenty year continuously running compressor... I'll believe it when Elvis shows me. Believable statement, `I forgot and left the compressor on all night and it's still running`. Obama statement, `I forgot and left the compressor on for twenty years, and it's still running`. First of all, who's shop is so large as to forget a running compressor for 20 years, and second who's minding the shop? I do know however, that an ac compressor can be used to compress air at atmospheric pressure into a tank at over 125 psi. I have one that has worked for over five years.

Funny what a redneck will engineer to keep his beer cold vs buying a $20 dollar part. And, I'm with you all the way... been there, done that!

My first and probably last post...A search about timers for refrigerators brought me here and I signed up just so I could reply.
I have a 1948 era GE refrigerator that came with my 1948 house. (I bought the house 20 years ago from the original owner's estate). This refrigerator has been in continuous service since 1948. The problem: In early 2012, the compressor stopped cycling and just stayed on. I Really hate to admit this but the compressor has been running continuously for 4 years. It's more of a freezer now. I have finally gotten around to searching for a solution which brought me here. I've located a possible source for a replacement thermostat. Search 'retrofit thermostat for 1948 GE fridge' and you will find there are people out there who really like fixing old appliances. Apparently, these compressors don't give up easily. It made me sad to see the identical fridge at the transfer station shortly after moving in - probably just a bad thermostat. Just had to let you know!

Use the replacement thermostat (should be commonly available at HVAC parts stores) to switch a 40A contactor. Adds a $10 part but it will last almost forever with the load. Also check the cap(s) since it's very likely it will fail if it hasn't been replaced in a long time. (If you want it to last, use a replacement with the same uF but a higher voltage rating.) That said, ancient refrigerators are so inefficient that a modern one will pay for itself in a pretty short time.

I have worked at a shop (just doing a little IT work for a family member) that uses an old A/C compressor for the compressed air supply. The story was that the compressor rusted and started to leak years ago, so it was replaced. The repair tech didn't want to take back the old one, so one of the mechanical engineers who ran the shop back then repurposed it into an air compressor to replace the clunker that was on its way out. Just put a little filter on the intake to keep out dust and it was one of those really old compressors with a sight glass so topping up the oil to the proper level was trivial.