Thermopile/millivolt Generator - HVAC - Contractor Talk

Thermopile/millivolt Generator

 
Thread Tools Search this Thread Display Modes
Old 10-28-2018, 04:56 PM   #1
Pro
 
Mike-B's Avatar
 
Trade: General Contractor
Join Date: Feb 2015
Location: Pittsburgh, PA
Posts: 370
Rewards Points: 850

Thermopile/millivolt Generator


Im working on a old Wise furnace, circa 1962. Natural gas 82K BTU. Its an old power pile system. The gas valve is a honeywell vs820a1047. It is in my mothers house.

The symptom is the pilot stays lit but the gas valve wont open and light the burner.

I disconnected the thermopile wires from the gas valve and lit the pilot. After about a minute it was producing just over 600mV with no load.

I reconnected the TP to the gas valve and checked voltage. I saw around 140mV.

The t-stat and limit switch are wired in series. I removed those wires from the gas valve and put a jumper from the TP terminal to the T-stat terminal on the gas valve. It worked just fine. Gas valve opens, burner lights.

I reconnect the limit switch and t-stat to gas valve. The valve will not open. I checked voltage and there is only around 80mV under load. Not enough to operate the valve.

I checked resistance thru the limit switch and t-stat. It was just over 2 ohms.

So the questions are:
1. Is the thermopile just too weak to provide the needed voltage? It looks original
2. Is the thermopile OK and the resistance of the limit switch and T-stat too high at 2 ohms
3. If it needs a thermopile, does anyone know where i can find one like in the photos?

One of our direct employees is an old HVAC/furnace man. He is stumped.

Our local supplier wasnt much help. They kind of looked at me funny when i started talking about a mV gas valve. One guy knew what i was talking about and said he might be able to cross something if i bring the parts in.

Ive got an account at Lennox but those folks dont seem very helpful. All they know are part numbers.







Sent from my SM-G930V using Tapatalk

Last edited by Mike-B; 10-28-2018 at 06:29 PM.
Mike-B is offline  

Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ContractorTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

   

Advertisement

 

Old 10-28-2018, 09:17 PM   #2
Pro
 
hdavis's Avatar
 
Trade: remodeling
Join Date: Feb 2012
Location: CoastalME
Posts: 22,695
Rewards Points: 7,606

Re: Thermopile/millivolt Generator


Those resistances should be well below 1 ohm.

Power from the TP is V^2/R. Get R too big, and there isn't enough power.

I'd start by cleaning the connections.

You also need to clarify where the 80 and 140 mv readings were taken

Advertisement


Last edited by hdavis; 10-28-2018 at 09:24 PM.
hdavis is online now  
The Following User Says Thank You to hdavis For This Useful Post:
Fouthgeneration (10-31-2018)
Old 10-28-2018, 11:24 PM   #3
Pro
 
Mike-B's Avatar
 
Trade: General Contractor
Join Date: Feb 2015
Location: Pittsburgh, PA
Posts: 370
Rewards Points: 850

Re: Thermopile/millivolt Generator


The 140mv reading was taken at the 2 terminals on the gas valve that the ThermoPile connects to. The T-stat and limit switch were also connected to their respective terminals but t-stat was turned off.

With the t-stat on and calling for heat, the mV dropped down to 80. I was measuring this at the gas valve. One lead on the terminal that the t-stat connects to. One lead on the + terminal that the t-pile and limit switch share.

There are only 3 terminals on the gas valve. Two are for the thermopile. The + side of the TP has a 2nd wire on the terminal which sends power up to the limit switch, thru t-stat, then back down to the 3rd terminal which operates the gas valve.

Total resistance was about 2ohm in the t-stat/limit switch circuit. Up and back thru T-stat alone was about 0.2ohms so that's good. Up and back thru limit switch was about 1.9. I pulled the wires out of the limit switch. They were shiny copper. I made sure they were well connected on both ends. No difference.

Guess i should have bypassed the limit switch to see if eliminating that resistance fixes the problem. Seems to make the most sense at this point.

The existing TP/pilot setup is a honeywell cs82A. Basically extinct. If eliminating the limit doesnt fix it, i think i will order a new pilot/TP setup. I'll throw the new TP in temporarily just to see if it fixes the problem. If so, we will retrofit a new setup in place if the old "matchbook"



Sent from my SM-G930V using Tapatalk
Mike-B is offline  
The Following 2 Users Say Thank You to Mike-B For This Useful Post:
Fouthgeneration (10-31-2018), hdavis (10-29-2018)
Sponsored Links
Advertisement
 
Old 10-29-2018, 08:36 AM   #4
Pro
 
Mike-B's Avatar
 
Trade: General Contractor
Join Date: Feb 2015
Location: Pittsburgh, PA
Posts: 370
Rewards Points: 850

Re: Thermopile/millivolt Generator


FYI for anyone working on this old shtuff.

Honeywell CS82A is the pilot assembly including thermopile.

Honeywell Q302A 1025 is the thermopile/powerpile/millivolt generator only.

I was able to dig up a Q302A on ebay.

Will probably buy a limit switch too and see what fixes it...hopefully.



Sent from my SM-G930V using Tapatalk
Mike-B is offline  
The Following User Says Thank You to Mike-B For This Useful Post:
hdavis (10-29-2018)
Old 10-29-2018, 02:25 PM   #5
Contractor of the Month
 
Inner10's Avatar
 
Trade: Control Systems
Join Date: Mar 2009
Location: Ottawa, ON
Posts: 25,502
Rewards Points: 3,718

Re: Thermopile/millivolt Generator


Sand the probe, she will put out a few more volts.
__________________
The Following User Says Thank You to Inner10 For This Useful Post: Leo G
Inner10 is online now  
The Following User Says Thank You to Inner10 For This Useful Post:
Fouthgeneration (10-31-2018)
Old 10-31-2018, 07:32 PM   #6
Pro
 
Fouthgeneration's Avatar
 
Trade: Masonry
Join Date: Jan 2014
Location: Mid west
Posts: 2,221
Rewards Points: 7,939

Re: Thermopile/millivolt Generator


Buy your Mom a New furnace or at least a 90%+ efficiency used one.

Seriously, that furnace is older than I am...

ALL parts have past their design lifetimes, especially the firebox plenum/ heat exchanger= CO and CO2 poisoning = No Momma.

Lower gas bills = More inherited money....

If you are stubborn, try a couple of added ground straps to make sure the electrons can complete the circuit.

A little low pressure canned air & a gentle vacumning wouldn't hurt.

Make sure the thermocouple well is wholely in the hot spot, maybe try turning up the Pilot gas flow for one more year's heat if you can't replace it now.

Your limit switch is out of tolerance According to web consensus...Replace and post again please.
__________________
I might be an Idiot, but I know things that You don't: Please wait till after you get my know-how to insult me....
Fouthgeneration is offline  
Old 11-01-2018, 06:50 PM   #7
Pro
 
Mike-B's Avatar
 
Trade: General Contractor
Join Date: Feb 2015
Location: Pittsburgh, PA
Posts: 370
Rewards Points: 850

Re: Thermopile/millivolt Generator


We have ignition!
New limit switch and new millivolt generator installed today.
She runs like a champ.







Sent from my SM-G930V using Tapatalk
Mike-B is offline  
The Following 2 Users Say Thank You to Mike-B For This Useful Post:
Fouthgeneration (11-03-2018), hdavis (11-01-2018)
Old 11-12-2018, 07:34 PM   #8
Pro
 
daffysplumbing's Avatar
 
Trade: plumber
Join Date: Oct 2017
Location: California
Posts: 202
Rewards Points: 862

Re: Thermopile/millivolt Generator


Funny!!! I've been doing heating for more than 50 years and never called a thermocouple a thermopile. I had to look it up.

Regardless, a good thermocouple generated 750 millivolts (3/4 of a volt) and the only place I can find a 750 mv thermocouple is at Johnstone supply. Every thermocouple we purchase at supply houses generates about 350 millivolts or only 1/3 of a volt.

Test the thermopile with an volt meter and set to millivolts. If you are not getting 320 millivolts then that is the first thing you need to change.

We also test valves by wiring a 1.5 volt battery across the thermostat wires and this will tell you whether or not the valve is functioning. If the valve does not work flip the positive to the opposite wire.

I always disconnect the thermostat wires to test the voltage. This helps to tell when wires are corroded, or are twisted together somewhere and have bad connections.

Last edited by daffysplumbing; 11-12-2018 at 07:42 PM.
daffysplumbing is offline  
Old 11-14-2018, 04:13 AM   #9
Pro
 
beenthere's Avatar
 
Trade: HVAC
Join Date: Mar 2009
Posts: 2,436
Rewards Points: 1,178

Re: Thermopile/millivolt Generator


Quote:
Originally Posted by daffysplumbing View Post
Funny!!! I've been doing heating for more than 50 years and never called a thermocouple a thermopile.
Well thats good. Cause a thermocouple is not a thermopile.

Advertisement

beenthere is offline  
The Following User Says Thank You to beenthere For This Useful Post:
hdavis (11-14-2018)


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to properly hook a generator up to a plug to run sump pump reweb Electrical 4 01-19-2017 11:50 PM
Generator caught on fire today Burns-Built Tools & Equipment 11 10-13-2014 07:05 PM
generator sizing te12c02w Electrical 1 06-28-2012 07:56 AM
wiring a generator powered hunting shack CNC General Discussion 2 08-18-2009 10:31 PM

Join Now... It's Fast and FREE!

I am a professional contractor
I am a DIY Homeowner
Drywall Talk is for
PROFESSIONAL CONTRACTORS ONLY!

At DrywallTalk.com we cater exlusivly to professional contractors who make their living as a contractor. Knowing that many homeowners and DIYers are looking for a community to call home, we've created www.DIYChatroom.com DIY Chatroom is full of helpful advices and perfect for DIY homeowners.

Redirecing in 10 seconds
No Thanks
terms of service

Already Have an Account?