Coolmaster

[recharge]

I have recently built the silicon chip coolmaster which is currently running a chest freezer @12 deg.
I check it every day and the temp is always spot on. But this evening i could hear a clicking in the brew room and noticed it was the freezer trying to click on.
I had a look at the coolmaster controller and the led was flashing dimmly and then a little brighter when the freezer was clicking but wouldnt cycle on.
As soon as i touched the sensor to warm it up a little the freezer started up straight away.
All that said it obviously is eventually starting the freezer as temp is always spot on but should i be worried about the clicking but not starting. I thought the circuitry was designed to stop this behaviuor.

Thanks to anyone who can help.
Maybe something for others to watch out for

Cheers :beer:
Richard

 

[timmy]

sounds like the hysteresis (deadband) is too narrow. The relay is chattering until the temp gets high enough to keep the contact closed.

 

[Simon W]

Thats what I was thinking, I seem to remember the article mentioning how to adjust this, either that or it was in 'Ask Silicon Chip' a few months later.

 

[agro]

Assuming the Coolermaster is the same as the Tempmaster... VR2 (5k potentiometer) should adjust the hysterisis of the circuit. I set this to half way and have a .5 degree variance between the fridge turning on and off.

No relay in this circuit so it may be different. It uses a TRIAC (BT137F) to switch the mains.

Agro.

 

[recharge]

Not sure if the same(KC5413) but it has a triac as you mentioned.
I have posted this on jaycars forum.
May try adjusting vr2.
The instructions say it is for balancing but give no guidelines except it should be fine in the middle.

I can feel a new hobby coming on tho.

Cheers all for replies

Richard :beer:

 

[Simon W]

I'm not so sure now that a narrow band hysteresis is your problem.

Does your freezer turn off shortly after starting, maybe a second or so? or is it on for a min or so then turns of?
If the later, hysteresis is not your problem.
If its only on for a sec, then turns off, then tries to turn on again, Hysteresis could be/is your problem.

I re-read the article last night.
VR2 is for 'balance', whatever that means! I would have to get the datasheet for the LM311 and nut that one out. I dont have the time right now tho.(Rental inspection tomorrow).
I think the idea of the balance is to adjust the offset voltage between the inverting and non-inverting inputs of the comparator. So instead of the comparator conducting when both inputs are the same voltage, one can be higher/lower than the other.
This would seem to be hysteresis, but it is not. It is just changing the temperature the circuit switches at. Pin 5 of the 'balance' control on the comparator appears to control the voltage seen by the non-inverting input, therefore pin 6 must be for the inverting input. Changing these with VR2 would not give hysteresis.
However, the text says there is a feedback resistor in the circuit (the 33k) which is connected between the opto and VR2. This resistor creates the hysteresis.
It works by reducing the voltage applied to the pin 5 side of the balance control, and this only happens when the comparator is 'off' (its output is grounding) and therefore the led and opto are on, and so is the fridge/freezer. This means that the non-inverting input voltage is lowered, and the temp preset voltage is lowered.
As soon as the temp sensor reaches this voltage, the comparator turns on(output at +9v), the opto stops conducting(fridge off), so does the feedback resistor, and therefore the balance is returned and the non-inverting input is back to its original user-pre-set temp voltage waiting for the temperature to climb back up to meet it again - hysteresis.

This is confirmed in the Dec '05 issue in the 'Ask Siilicon Chip' on pg 106.
There is an answer there for chaging hysteresis, and they recommend either increasing the value of the 100R resistor to 150 or so, or reducing the value of the feedback resistor(thereby flowing more current and lowering the balance voltage further) to around 27kohm, or both.

But, if hysteresis isn't your problem, it may be that the power surge/spike from your fridge is triggering the triac. The circuit has some protection against this but maybe it is not enough? I don't know. Im leaning away from this theory tho, because you say that the fridge kicks in as soon as you warm up the sensor.

Hmmm

 

[recharge]

Sorry most of that went over my head tho i intend to read it a few more times.
Generally the led flickers for a while at the same time freezer sounds to be trying to click on then after a short time it will start. If i hadnt have heard the clicking i might never have known i had a problem as it eventually kicks in and fermenter in freezer is always spot on 12 deg.

Worse case scenario ill build another one and use this one to run a fan. Bit harder to stuff a fan i would guess.

Anyway thanks again.

 

[stephen]

I'm not so sure now that a narrow band hysteresis is your problem.

Does your freezer turn off shortly after starting, maybe a second or so? or is it on for a min or so then turns of?
If the later, hysteresis is not your problem.
If its only on for a sec, then turns off, then tries to turn on again, Hysteresis could be/is your problem.

I re-read the article last night.
VR2 is for 'balance', whatever that means! I would have to get the datasheet for the LM311 and nut that one out. I dont have the time right now tho.(Rental inspection tomorrow).
I think the idea of the balance is to adjust the offset voltage between the inverting and non-inverting inputs of the comparator. So instead of the comparator conducting when both inputs are the same voltage, one can be higher/lower than the other.
This would seem to be hysteresis, but it is not. It is just changing the temperature the circuit switches at. Pin 5 of the 'balance' control on the comparator appears to control the voltage seen by the non-inverting input, therefore pin 6 must be for the inverting input. Changing these with VR2 would not give hysteresis.
However, the text says there is a feedback resistor in the circuit (the 33k) which is connected between the opto and VR2. This resistor creates the hysteresis.
It works by reducing the voltage applied to the pin 5 side of the balance control, and this only happens when the comparator is 'off' (its output is grounding) and therefore the led and opto are on, and so is the fridge/freezer. This means that the non-inverting input voltage is lowered, and the temp preset voltage is lowered.
As soon as the temp sensor reaches this voltage, the comparator turns on(output at +9v), the opto stops conducting(fridge off), so does the feedback resistor, and therefore the balance is returned and the non-inverting input is back to its original user-pre-set temp voltage waiting for the temperature to climb back up to meet it again - hysteresis.

This is confirmed in the Dec '05 issue in the 'Ask Siilicon Chip' on pg 106.
There is an answer there for chaging hysteresis, and they recommend either increasing the value of the 100R resistor to 150 or so, or reducing the value of the feedback resistor(thereby flowing more current and lowering the balance voltage further) to around 27kohm, or both.

But, if hysteresis isn't your problem, it may be that the power surge/spike from your fridge is triggering the triac. The circuit has some protection against this but maybe it is not enough? I don't know. Im leaning away from this theory tho, because you say that the fridge kicks in as soon as you warm up the sensor.

Hmmm

[post="102004"][/post]​

Simon

Any chance you could post the circuit diagram or scan it and pm me. This sounds similar to a schmitt trigger type circuit operation. They can also have a serious hysteresis problem if not designed correctly.

Steve

 

[Simon W]

Recharge, try something for me: unplug the fridge while its off and before the LED starts flashing. Then sit and wait for the circuit to cut in.
See if the LED flickers with the fridge unplugged or turns on full brightness straight away. This will help me eliminate one half or the other of the circuit.
Don't forget to plug the fridge back in
If Bakers Hill wasn't so far away I'd drive up there and probe its innards!


Stephen, you are correct, thats exactly what it is. But I assume Jim Rowe(a very competent designer) has used a comparator(LM311) instead of a schmitt trigger IC because such IC's only have approx 0.8v 'backlash', whereas this circuit is adjustable.

The circuit wasn't available on the Silicon Chip website, I'll have to scan it tonight.

Simo

 

[recharge]

Will do that tomorrow.
Watched it for 5 mins today trying to start up.

Cheers guys

 

[Simon W]

Thanks Recharge.
I noticed no-one at Jaycar has replied to you yet, nice of 'em eh?
I'll see if I can track down Jim Rowe's email address.

BTW, Jim Rowe is kinda famous.....
"For the record Jim Rowe did not design the Microbee although he did join
the company for a short time around 1986. Jim did design EDUC 8 (1979 or
so) and legend has it that Jim's computer was probably the first
hobby-built PC in the world! It was published in Electronics Australia
just prior to the MITS Altair article appeared in Popular Electronics
the US. The editors of Popular Electronics did later admit, reluctantly,
that EA had published the first home PC design. " - Owen Hill.

Cool huh? Remember the Microbee? I think every school in Australia had them, and they were very popular right around the world, esp in Europe, before the IBM clones reigned supreme. Owen Hill was the designer-owner of Microbee Computers.


Stephen:

EDIT: ahhhh hello? Image?.... ahh there you are.

 

[stephen]

I'm not so sure now that a narrow band hysteresis is your problem.

Does your freezer turn off shortly after starting, maybe a second or so? or is it on for a min or so then turns of?
If the later, hysteresis is not your problem.
If its only on for a sec, then turns off, then tries to turn on again, Hysteresis could be/is your problem.

I re-read the article last night.
VR2 is for 'balance', whatever that means! I would have to get the datasheet for the LM311 and nut that one out. I dont have the time right now tho.(Rental inspection tomorrow).
I think the idea of the balance is to adjust the offset voltage between the inverting and non-inverting inputs of the comparator. So instead of the comparator conducting when both inputs are the same voltage, one can be higher/lower than the other.
This would seem to be hysteresis, but it is not. It is just changing the temperature the circuit switches at. Pin 5 of the 'balance' control on the comparator appears to control the voltage seen by the non-inverting input, therefore pin 6 must be for the inverting input. Changing these with VR2 would not give hysteresis.
However, the text says there is a feedback resistor in the circuit (the 33k) which is connected between the opto and VR2. This resistor creates the hysteresis.
It works by reducing the voltage applied to the pin 5 side of the balance control, and this only happens when the comparator is 'off' (its output is grounding) and therefore the led and opto are on, and so is the fridge/freezer. This means that the non-inverting input voltage is lowered, and the temp preset voltage is lowered.
As soon as the temp sensor reaches this voltage, the comparator turns on(output at +9v), the opto stops conducting(fridge off), so does the feedback resistor, and therefore the balance is returned and the non-inverting input is back to its original user-pre-set temp voltage waiting for the temperature to climb back up to meet it again - hysteresis.

This is confirmed in the Dec '05 issue in the 'Ask Siilicon Chip' on pg 106.
There is an answer there for chaging hysteresis, and they recommend either increasing the value of the 100R resistor to 150 or so, or reducing the value of the feedback resistor(thereby flowing more current and lowering the balance voltage further) to around 27kohm, or both.

But, if hysteresis isn't your problem, it may be that the power surge/spike from your fridge is triggering the triac. The circuit has some protection against this but maybe it is not enough? I don't know. Im leaning away from this theory tho, because you say that the fridge kicks in as soon as you warm up the sensor.

Hmmm

[post="102004"][/post]​

Simon

Any chance you could post the circuit diagram or scan it and pm me. This sounds similar to a schmitt trigger type circuit operation. They can also have a serious hysteresis problem if not designed correctly.

Steve

[post="102074"][/post]​

Just had a good look at the circuit. the LM311 is basically an OPAMP being run pretty well in saturation mode, ie. If one was to feed an audio signal into the input, the output would only switch between a high state and a low state or vice versa with no amplification of the original signal. VR2, the balance resistor sets the "gain" of the OPAMP which, in effect sets the hysteresis - the difference between the switch/switch off voltage or in this case when the temperatures when the fridge/freezer should be turning on and off. VR1 purely sets the voltage to be compared by the LM311 from the temp sensor through TS1 and the 10k resistor. So the area I would be looking at would be VR2 that sets the difference between the switch on/switch off temps.

If you have any further questions feel free to pm me or just place in the forum so we all can learn.

Regards

Steve

Disclaimer - I am relying knowledge I was taught in my technician course almost 25 years ago.

 

[recharge]

Ok i had the plug out today and waited hours for it to turn led on (ambient temp in brew room currently 15 freezer set at 12) so decided to do a brew while waiting. What else !!
Anyway back to the point. I didnt see it turn on but it was off one sec and on about 10 secs later when i looked, it doesnt do this when freezer is plugged in.
I also tried holding sensor in the air by the wire so as not to put any rapid heat into sensor, definately cycled in properly with or without plug in on these occasions.
Any idea which way to turn vr2 and by how much or will this just be a trial and error jobby.

Thanks again

Richard

 

[stephen]

Ok i had the plug out today and waited hours for it to turn led on (ambient temp in brew room currently 15 freezer set at 12) so decided to do a brew while waiting. What else !!
Anyway back to the point. I didnt see it turn on but it was off one sec and on about 10 secs later when i looked, it doesnt do this when freezer is plugged in.
I also tried holding sensor in the air by the wire so as not to put any rapid heat into sensor, definately cycled in properly with or without plug in on these occasions.
Any idea which way to turn vr2 and by how much or will this just be a trial and error jobby.

Thanks again

Richard

[post="102506"][/post]​

Richard

Unfortunately the next couple of days/weeks are going to drive you insane. Not knowing the qualities of all the componants in the circuit I can't calculate an answer - and I no longer have my study notes to refer to. My suggestion to you is to set it mid way, make sure you fridge is full of cold beers and watch what happens and then make minor (approx one clock hour adjustment) and see what happens from there. If it is still having fun and games I'd probably start looking also at IC2 - the MOC3021 - it looks like an opto coupled Diac to switch on the Triac - BT137F.

Any questions please feel free to ask. If it all gets to hard take it back to where you got it from - there may have been a defective componant supplied with the kit.

Have fun

Steve

 

[recharge]

Im gonna buy another one tomorrow as i want one to run a cooling fan anyway.
In the mean time i will have a play with vr2 see if i can settle it down. I

I was more concerned really with whether it would damage my freezer compressor, hate to wreck a good freebie.

Cheers :beer:

Richard

 

[stephen]

Hey Recharge

How much are these kits worth?

Steve

 

[recharge]

$39.00

 

[agro]

Don't underestimate the value of a lump of ice and your hand. I used some ice in a cooler, a thermometer and the head from my hand to test the one I built and to calibrate an external knob so I could more easily adjust the temperature.

Makes it real easy to vary the temp quickly, and you should see the LED turn on and off reliably at the threshold temp. Just don't leave the AC plugged while your playing...

Jason.

 

[recharge]

Agro
It definately has no probs with rapid temp change as you describe i was just holding it against the cooling coil of freezer or in my hand, works fine. Seems to be a prob at the very slow rate my chest freezer increses in temp.

No biggie cuts in eventually

Cheers
Richard

 

[2es]

I've been fiddling now for a week.Blown 4 triacs and solved the problem with a exhaust fan.Must be working as a spike control.Now have the problem of cutting in and out over 1/2 degree.Have had 3 new lm311s still the same .Pin5 voltage 8.79v pin6 8.91v .Will try tomorrow 150 ohm resistor.Jaycar only sells the produce but has no service after.