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Propex thermostat adjusting, moving the whole range downward
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jackbombay
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PostPosted: Thu Apr 25, 2013 3:16 pm    Post subject: Propex thermostat adjusting, moving the whole range downward Reply with quote

In the propex photos thread I asked about adjusting the propex thermostat so that you can set the cabin temperature to lower than 50 degrees. As it arrived, the lowest I could set my thermostat was warmer than I wanted, if its 10* out I want to be able to set it to 40* to sleep comfortably without using any more propane and battery than I need. The range of the thermostat is about 50-80* F

It turns out you can replace a resistor in the thermostat to move that entire range downward, here is what Karl posted about it,

westyventures wrote:

Ok. Thermostat adjustment folks:
"Changing R7 from a 12k resistor to a 15k resistor will lower the range slightly"
Let me know how it works out!


I decided I wanted a bit more than a slight change, so I went with a 22k resistor, it is currently 80* in my van and with the thermostat maxed out the heater won't come on, so theres that!

I imagine you guys want to see some pictures, yea?

MAKE SURE TO PULL THE FUSE TO THE PROPEX BEFORE STARTING THIS!

The resistors, $.99 for 5

Image may have been reduced in size. Click image to view fullscreen.


On the lower right you can see the resistor that needs to be changed out, the blue one right below the thermostat knob,

Image may have been reduced in size. Click image to view fullscreen.


And here is the soldering iron I used, nice sharp tip, this soldering is as bad as say adding a remote temp sensor to a Prostar charge controller, but you don't want to be messy with the solder either.

Image may have been reduced in size. Click image to view fullscreen.


And here is the resistor removed,

Image may have been reduced in size. Click image to view fullscreen.


And the new resistor with wires bent and cut to match the holes in the circuit board,

Image may have been reduced in size. Click image to view fullscreen.


And here it is soldered in,

Image may have been reduced in size. Click image to view fullscreen.


I will report back with the new temperature range with the 22k resistor installed, I also picked up a 15k resistor if this dropped the range too low.

EDIT// I ended up with a 17.2k resistor (15k + 2.2k in series) and I think it is just right, in the evening when it cools down and I'm wearing shorts and a t shirt right when I think "its a little cool in here" I can get the heater to turn on if I turn the thermostat to the max setting. This is of course an extreme example as if I were really somewhere cold I'd just have more clothes on.

Where I live it is extremely cold so I will be able to test this to "get it right" any time of year, I will also be in some ~35 weather soon so I'll have info in a couple days...
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Last edited by jackbombay on Mon Apr 29, 2013 2:53 pm; edited 1 time in total
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bluefirefly
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PostPosted: Thu Apr 25, 2013 5:48 pm    Post subject: Reply with quote

Thanks a lot for doing it.
I need to check mine first and I'll certainly do it next month.
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PostPosted: Thu Apr 25, 2013 6:30 pm    Post subject: Re: Propex thermostat adjusting, moving the whole range down Reply with quote

jackbombay wrote:
The resistors, $.99 for 5

I'm rusty - does the blue indicate 1/2 watt, and the tan indicate 1/4 watt - in which case your new resistor would be under-sized? Or is the blue/tan irrelevant in this case?
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tangojeff
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PostPosted: Thu Apr 25, 2013 7:34 pm    Post subject: an easy way to replace a resistor on a circuit board Reply with quote

The USN taught me a technique for changing components on circuit boards back in the 60's. To replace a resistor, first cut it out w/ small diagonal cutters and be sure to leave most of its two leads still soldered to the board. Next bend them straight up so they can become 'Stand Off Posts" for the replacement part. Now wrap the leads of the new resistor around these two "posts". Solder these together and trim off the surplus. Check the rear of the board. By using less heat, the original solder point probably still looks the same. And no heat damage occurs to the circuit board.
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WLD*WSTY
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PostPosted: Thu Apr 25, 2013 8:29 pm    Post subject: Reply with quote

Nice mod, thanks for the writeup! I'll be doing that upgrade soon.

Now, who has the mod to allow the circulation fan to run for a couple of minutes AFTER the burner shuts down? My home furnace does that, moving the residual heat out of the furnace into the house. I've found that the Propex has that heat left over too, and I can manually flip on the fan as soon as the burner shuts down and get warm air for 2-3 minutes. Now to find a way to do that automatically. I figure that should improve efficiency by at least 10%.
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jackbombay
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PostPosted: Fri Apr 26, 2013 6:53 am    Post subject: Re: Propex thermostat adjusting, moving the whole range down Reply with quote

luVWagn wrote:
jackbombay wrote:
The resistors, $.99 for 5

I'm rusty - does the blue indicate 1/2 watt, and the tan indicate 1/4 watt - in which case your new resistor would be under-sized? Or is the blue/tan irrelevant in this case?


the color bands, according to the radio shack package, indicate the resistance of the resistor and the last band indicates its tolerance. according to the radio shack guy the size of the resistor was the only indication of its wattage.
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jackbombay
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PostPosted: Fri Apr 26, 2013 6:56 am    Post subject: Re: an easy way to replace a resistor on a circuit board Reply with quote

tangojeff wrote:
The USN taught me a technique for changing components on circuit boards back in the 60's. To replace a resistor, first cut it out w/ small diagonal cutters and be sure to leave most of its two leads still soldered to the board. Next bend them straight up so they can become 'Stand Off Posts" for the replacement part. Now wrap the leads of the new resistor around these two "posts". Solder these together and trim off the surplus. Check the rear of the board. By using less heat, the original solder point probably still looks the same. And no heat damage occurs to the circuit board.


There is plenty of space behind the propex thermostat cover so this technique would work!
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jackbombay
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PostPosted: Fri Apr 26, 2013 6:57 am    Post subject: Reply with quote

WLD*WSTY wrote:
Nice mod, thanks for the writeup! I'll be doing that upgrade soon.

Now, who has the mod to allow the circulation fan to run for a couple of minutes AFTER the burner shuts down? My home furnace does that, moving the residual heat out of the furnace into the house. I've found that the Propex has that heat left over too, and I can manually flip on the fan as soon as the burner shuts down and get warm air for 2-3 minutes. Now to find a way to do that automatically. I figure that should improve efficiency by at least 10%.


My propex is new, and it does just that, 3 minutes of "after run", maybe a new thermostat would make yours run like this?
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jackbombay
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PostPosted: Fri Apr 26, 2013 7:06 am    Post subject: Reply with quote

Results from last night, the 22k ohm resistor lowered the whole temp range about 30*, with the thermostat maxed out, the heater clicked on when it got down to 50* F, normally at the max setting the heater should kick on at 80*.

So, for every 1k ohms of resistance added to 12k, the whole range will drop 3*, a 15k resistor should drop the range to 41*-71*.

I have done some reading around about resistors and you can get virtually any resistance you want by running them in series, so if you was a 15* temp drop you can run a 15k and a 2k ohm in series for a total of 17k ohms.
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westyventures
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PostPosted: Fri Apr 26, 2013 8:31 pm    Post subject: Reply with quote

WLD*WSTY wrote:
Nice mod, thanks for the writeup! I'll be doing that upgrade soon.

Now, who has the mod to allow the circulation fan to run for a couple of minutes AFTER the burner shuts down? My home furnace does that, moving the residual heat out of the furnace into the house. I've found that the Propex has that heat left over too, and I can manually flip on the fan as soon as the burner shuts down and get warm air for 2-3 minutes. Now to find a way to do that automatically. I figure that should improve efficiency by at least 10%.


What vintage is your heater? Only the really old EX1800 series and prior don't after-run. If yours doesn't, then it may have a circuitry issue.
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WLD*WSTY
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PostPosted: Fri Apr 26, 2013 10:04 pm    Post subject: Reply with quote

Karl, I've got an older 1600, which works fine but I guess I need to find a schematic of the newer thermostats and retro the circuitry into mine. If you might know where I can find that circuitry online, please let me know.
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westyventures
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PostPosted: Sat Apr 27, 2013 8:16 am    Post subject: Reply with quote

WLD*WSTY wrote:
Karl, I've got an older 1600, which works fine but I guess I need to find a schematic of the newer thermostats and retro the circuitry into mine. If you might know where I can find that circuitry online, please let me know.


The newer thermostats won't work with your model. I'll ask Propex if there is a way to make it after-run without too much trouble. Usually those older models would only after-run if it detected the heat chamber was too hot, and would come back on briefly.
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westyventures
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PostPosted: Sat Apr 27, 2013 8:22 am    Post subject: Reply with quote

jackbombay wrote:
Results from last night, the 22k ohm resistor lowered the whole temp range about 30*, with the thermostat maxed out, the heater clicked on when it got down to 50* F, normally at the max setting the heater should kick on at 80*.

So, for every 1k ohms of resistance added to 12k, the whole range will drop 3*, a 15k resistor should drop the range to 41*-71*.

I have done some reading around about resistors and you can get virtually any resistance you want by running them in series, so if you was a 15* temp drop you can run a 15k and a 2k ohm in series for a total of 17k ohms.


Great work, thanks for the detailed experiment - this should help out tremendously! Maybe we can get Propex to install a slightly higher resistor standard. Seems like a 45-75 range would be better suited to most folks. I've alerted them to this thread. Wink
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jackbombay
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PostPosted: Sat Apr 27, 2013 8:39 am    Post subject: Reply with quote

westyventures wrote:

Great work, thanks for the detailed experiment - this should help out tremendously! Maybe we can get Propex to install a slightly higher resistor standard. Seems like a 45-75 range would be better suited to most folks. I've alerted them to this thread. Wink


You're welcome Smile


I installed a 17k resistor yesterday and I think its just about perfect for me. When the thermometer by my thermostat read 67* I had to have the thermostat knob about 1/8" of rotation (measured at the edge of the knob) from full blast to get the heater to come on. I don't have "lowest setting" info available yet, but once I get home in may we should should still have some nights in the 20's so I should have info on that soon.
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PostPosted: Sat Apr 27, 2013 9:52 am    Post subject: Reply with quote

great job!

Im left wondering what the range of the thermostat is, once it is set.

iow, lets say it comes on at 50F, how high does it go before it shuts off.. 60F? That would be a 10 degree swing between off and on..

just curious how big the temperature swing is between thermostat on and off trigger points, for example, if set to shut off at 50, does it actually drop to 40, or less, before it comes on again?
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PostPosted: Sat Apr 27, 2013 6:40 pm    Post subject: Reply with quote

I'll throw a high low thermometer in the van witht the proper running when I get home and let you know.
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PostPosted: Sun Apr 28, 2013 10:27 am    Post subject: Reply with quote

jackbombay wrote:
the van

Is this on the Sprinter, or did you get another Vanagon?
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PostPosted: Sun Apr 28, 2013 8:15 pm    Post subject: Reply with quote

Witless Joe wrote:
jackbombay wrote:
the van

Is this on the Sprinter, or did you get another Vanagon?


El sprinter.


Currently down south enjoying some warm weather, the Detroit coozie was given to me years ago and I always try to get pics with it in unique locations and I send the pics to the guy who gave it to me...

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westyventures
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PostPosted: Mon Apr 29, 2013 9:30 am    Post subject: Reply with quote

jackbombay wrote:
Witless Joe wrote:
jackbombay wrote:
the van

Is this on the Sprinter, or did you get another Vanagon?


El sprinter.




I know that is no Vanagon, but inquiring/interested minds would like to see what you've done with the interior. My 'next' camper is going to be a custom Sprinter also. Cool
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PostPosted: Mon Apr 29, 2013 9:36 am    Post subject: Reply with quote

More from Propex UK:

In the older Compact 1600 the post purge cycle is controlled by a 60 degree n/o thermostat in the heater, but of course under normal running that temperature would not be reached unless the heater was forced to run hot.
If that thermistor was changed for a 50 degree thermostat it may persuade it to come on more readily.
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