Long interval timer ideas

You guys helped a lot with my watermaker control so I am coming back with a little simpler problem. This time it is the refrigerator and freezer. 12V Danfoss hermetic compressors are capable of running at any speed from 2000 to 3500 RPM. Speed is controlled by a resistance of from 0 to 1523 ohms in the thermostat circuit. Conservation of battery power is important but while these compressors are most efficient at the slower speeds getting the beer cold as fast as possible is equally important so the compressor needs to run at close to maximum speed for about 3 hours to cool a case of brew. When a fresh case is added I want to push a button to switch in an additional resistance for about 3 hours. Here is a proposed soultion and a question.

First I will set the "normal" speed with a 1K trimmer pot so that the compressor has a duty cycle of about 85%. A one shot timer driving a SPDT relay will switch in another 1K trimmer in series with a 510 Ohm resistor. I don't think I would trust a 555 for 3 hours so I am considering a CD4541 and a 4017 decade counter. The button push would start the 4541 and a trigger a 4013 flipflop to set the relay. The 4541 would be set to pulse very 20 minutes or so and Q0 to Q7 of the 4017 could drive an LED array to display the relative progress. Q8 would set off the 4013 and end high speed operation.

I have this breadboarded pretty well but I still have one more question. How do you stop the D&$#ed 4541. It keeps running so the system goes back to high speed 3 hours later!.

Take the mode control pin (10) to 0V (?).

Best regards, Spehro Pefhany

Tried that but I only get one cycle. I need 8 cycles to complete a cool down period.

Wait a minute! Are you saying to mring the MODE low AFTER the 8th cycle? Now that might work. Lemme see, it could be connected to the extra half of the 4013. The start button could bring it high and the 9th pulse take it low.

MCs are out because they are to hard to fix in Bora Bora. Likewise it is hard to find beer already cold there too. :-)

The problem there is that the compressor will cut off several times before the beer gets cold.

That is the backup system.

I'm not buying that argument. As a practical matter, you can't get discrete logic there either. And you probably don't have tools handy to replace parts. No reason for a MC to be any less reliable.

That sounds like a fundamental problem. Your beer is not getting cold "as fast as possible" if the compressor shuts off. Stated another way, if the compressor is shutting off, you'd be more efficient to run it at the lower speed initially. Or stick a fan inside so it doesn't shut off.

When you did the math, how much energy did you save with the two-step speed optimally implemented vs running low speed all the time? How much clock time did you save getting to drinking temperature (BTUs removed) given that the high speed mode ain't running all the time?

To make this work optimally, you're gonna have to do a LOT of experimenting. I volunteer as a beer consumer.

Another practical matter about booze: I've empirically determined that after the first one, I'm much less picky about the quality of the second. By the third, it don't matter much at all ;-) mike

Something like this: View in a fixed-width font such as Courier.

"Fred Bloggs" wrote

Exactly! That's two I owe you and Spero. You guys are now on the launching party guest list.

Thanks!