search

jbruce12000 / kiln-controller

Turns a Raspberry Pi into an inexpensive, web-enabled kiln controller.
191 stars 105 forks source link

Defective MAX31855 modules and potential fix. #93

Closed dsilfvast closed 2 years ago

dsilfvast commented 2 years ago

I've had several defective MAX31855 modules. If you’re having problems, do a quick check to see if “T-” (pin 2) is shorted to “GND” (pin 1). The datasheet explicitly states “Thermocouple Input. See Table 1. Do not connect to GND”.

It’s not a pretty fix, but I’ve been able to scrape a needle between those IC pins to break the copper connection. It cleared up some real funny problems.

jbruce12000 commented 2 years ago

cool. thx for sharing.

tonymoon61 commented 1 year ago

I've run into this one 4 modules now - two 31855, and two 38156. I wonder if there is some application for them that this is beneficial, because it's awfully common, and always the same spots.

rondoc commented 1 year ago

I think it's that both modules need the tc to be isolated. So often one lead will be grounded or has a leaky electrical pathway. Could be worse at high temps as some glazes and clays become electrically conductive then.. use porcelain or better alumina insulators. To check disconnect tc from anything. Then using high range ohmeter VOM OK. Measure either lead to ground..IT MUST BE OPEN TO GROUND . A few hundred Kohms is not always high enough. I found the 31855 to be perfectly OK for the pi using K type tc. K is ok for less than cone 12. Over that temp S type. I keep a Fluke thermocouple thermometer connected at all times to keep a check on kiln and also to compare with the pi kiln system. Usually tracking is within a degree. Ronald.

On Fri, Sep 30, 2022, 11:04 PM Tony Moon @.***> wrote:

I've run into this one 4 modules now - two 31855, and two 38156. I wonder if there is some application for them that this is beneficial, because it's awfully common, and always the same spots.

— Reply to this email directly, view it on GitHub https://github.com/jbruce12000/kiln-controller/issues/93#issuecomment-1264257024, or unsubscribe https://github.com/notifications/unsubscribe-auth/AXA65GZVJSP5L6ERPGKQU6LWA7H5XANCNFSM5WVUBNTQ . You are receiving this because you are subscribed to this thread.Message ID: @.***>