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Old 07-01-2009, 02:26 PM   #11
CodeRage
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Originally Posted by lamarguy View Post
Ha...I can see it now - Guys, I installed a PID on my converted fridge and the compressor burnt up a week later.

Using a PID to control a compressor is a bad idea...
Heh, thats not true.

I've been running my fermenter from a PID for well over a year with no problems. Have to set a dead band +- 2 degrees or so and a min on and off time, think mine is set to 5 minutes.

But yes, You certainly don't want to cycle the compressor excessively.


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Old 07-01-2009, 02:57 PM   #12
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Originally Posted by Virtuous View Post
I've been running my fermenter from a PID for well over a year with no problems. Have to set a dead band +- 2 degrees or so and a min on and off time, think mine is set to 5 minutes..
What brand PID are you using? I don't believe the Auberin PIDs have a min off time setting, which was the basis for my advice.


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Old 07-01-2009, 02:59 PM   #13
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Virtuous wrote:Heh, thats not true.

I've been running my fermenter from a PID for well over a year with no problems. Have to set a dead band +- 2 degrees or so and a min on and off time, think mine is set to 5 minutes.

But yes, You certainly don't want to cycle the compressor excessively.
lamarguye is correct too, it's all in the setup.
What are your parameter settings?
Compressors are not designed to run on low voltage.
If your controller calls for less than 90% of power the compressor sure will suffer.
At a very low voltage won't start at all, just heats up.
It's not like a heating element which can run from 0-100%

My edit:
One thing I forgot to mention is the compressor starting circuit.
Depending on the circuit, relay, PTC. etc. the compressor will not turn on at all if the voltage for the starting circuit is too low or the duty cycle is very short.
In this case no harm is done.


Cheers,
ClaudiusB

Last edited by ClaudiusB; 07-01-2009 at 04:04 PM.
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Old 07-01-2009, 03:47 PM   #14
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Originally Posted by ClaudiusB View Post
lamarguye is correct too, it's all in the setup.
What are your parameter settings?
Compressors are not designed to run on low voltage.
If your controller calls for less than 90% of power the compressor sure will suffer.
At a very low voltage won't start at all, just heats up.
It's not like a heating element which can run from 0-100%


Cheers,
ClaudiusB
I see this thread going off on a wild tangent

SSRs, at least to my knowledge, can not be throttled. It is either off or on. This is because the internal resistance across the junction changes while it is in transition. Any measurable amount of resistance across that junction for an extended period of time (micro seconds) will cause so much heat it will burn up. That why you need a heat sink on these guys, between the switching and the minuscule amount of resistance when the junction is closed still creates heat.

the point is you are not varying the voltage going through the SSR to the load. You are switching it on and off. the rate of cycling determines the 0-100 % out put. For example 2 seconds on and 2 seconds off could be considered 50%. For our intents and purposes an SSR behaves just like a mechanical relay but it can be switched faster and makes less noise.
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Old 07-01-2009, 08:07 PM   #15
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so are you guys basically saying to run a 9v dc inverter between the pid and the SSR? and from the SSR to the element? and if so how many amps for the inverter? are we talking cell phone size of computer size? thanks for all the help so far

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Old 07-01-2009, 08:18 PM   #16
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Very small, the wall wort transformer variety.

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So as I am walking out the door this morning I think to my self:
"self, going to work on Monday is like knowing you're going to get kicked in the nuts. You just don't know when or by who"
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Old 07-01-2009, 09:17 PM   #17
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SSRs, at least to my knowledge, can not be throttled. It is either off or on.
Correct, I don't think I sad it that way.
I was only talking about PID output and lamarguy compressor problem..

Like I sad from the beginning it depends all on the parameter settings how a connected devices will behave.
Long cycle time and large duty cycle sure is better for a compressor.

Quote:
For example 2 seconds on and 2 seconds off could be considered 50%.
Same applies to 10 seconds.

The PID output is a PWM signal (for my units), the average voltage is what my load sees for the given duty cycle.
Low effective voltage can be damaging to pumps, compressors if driven directly.
If 120 V is required and the effective voltage is 70 V for non resistive devices,
like motors, etc., can create starting problems or even excess heat.

If you have the equipment you can measure the effective voltage at the load.

The cycle time we can program (not the same as duty cycle) is the time the controller can use to make adjustments to the required duty cycle.
The duty cycle On & OFF time has to equal the cycle time.

If we set the cycle time to 5 seconds and the controller calls for 20% duty cycle, the output will be ON for 1 sec and off for 4 sec.
If we set the cycle time now to 50 seconds the output will be on 10 sec and off for 40 sec, it is a lot better for my load device.
40 second at 100% operating voltage.
Imagine a motor, pump, etc. to run for 1 sec and coasting for 4 sec and starting all over for a long period of time at a 20% duty cycle.

I hope we are talking about the same thing.

Cheers,
ClaudiusB
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Old 07-01-2009, 09:26 PM   #18
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Yes, we are. Previously you said 0-100% power with out mentioning PWM which had me head scratching and put me on the SSRs do not behave like a rheostat tangent.
and yes, I agree with you
No worries.
I dont know what kind of PID controller is on my fridge, some Chinese knock off that did PID and hysteresis controls.

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Brutus 20e build | Electrical Primer for Brewers | Auber SYL-2362A2 PID Install & Config
So as I am walking out the door this morning I think to my self:
"self, going to work on Monday is like knowing you're going to get kicked in the nuts. You just don't know when or by who"
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Old 07-01-2009, 09:39 PM   #19
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Originally Posted by ClaudiusB View Post
I was only talking about PID output and lamarguy compressor problem.
Sweet! I got something named after me..."Dude, watch out for the lamarguy compressor problem."
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Old 07-02-2009, 06:27 AM   #20
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can anyome still help me with the inverter?



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