2
\$\begingroup\$

I'm repairing my stove. The control board has a relay (G2RL-1A-E-HA DC12) for the oven element. When turning the bake function on, the element heats, but it won't turn off when bake is turned off.

My question is, is it possible for a relay to switch on/off properly when no load is attached, but fail (latch on) when a load is present?

The board is hard to get to, and operate the controls when it's live - so to enable testing I desoldered the relay and connected it to 2 wires running to the board. This enabled me to test continuity on the load side of the relay, without any load attached. The relay worked properly.

I'm reluctant to solder it back on, and try to test it live, because moving the control around exposes high voltage/current terminals.

Should I just assume the relay is a dud and order a new one? The $ cost is minimal but I have to wait for it to get here, which would be less than ideal if it isn't the problem.

EDIT: Pictures, please forgive the goofy wiring, the red and white wires are just parallel because I didn't have more suitable wire for the task.

I don't know if there's a flyback diode because I don't know what a surface mount diode looks like.

enter image description here enter image description here enter image description here

EDIT: More pictures as requested enter image description here enter image description here enter image description here enter image description here

I found that relay P11 (P1 is the relay I've been talking about) is a DLB for the element. DLB means double line break, so I believe the heating element circuit goes through P11 and P1 in series, both can turn the element off. Which is more baffling because it means they'd both have to fail. That would make you think that the logic coming from the chips is wrong, but remember when I tested the relay it was opening and closing properly when the oven was turned on/off by me, but I didn't have load on it at the time. Can I test a relay for continuity while there is load on it?

\$\endgroup\$
  • \$\begingroup\$ Can you post a picture of the relay? \$\endgroup\$ – Marcelo Espinoza Vargas May 10 '17 at 0:36
  • \$\begingroup\$ This sounds like a lack of pullout force due to circulating currents coupled to a marginal relay...is there a flyback diode anti-parallel to the the relay coil on the control board? Also, did you have a flyback diode on the coil when you were testing the relay? \$\endgroup\$ – ThreePhaseEel May 10 '17 at 0:48
  • \$\begingroup\$ @ThreePhaseEel thanks - unsure about the flyback diode, can't tell from looking at the board because it's surface mount. I didn't wire up any extra diodes. \$\endgroup\$ – Jim W says reinstate Monica May 10 '17 at 2:11
  • \$\begingroup\$ K2 is the relay in question right? \$\endgroup\$ – ThreePhaseEel May 10 '17 at 2:14
  • 2
    \$\begingroup\$ You can test a relay for its state while it is loaded -- simply measure the voltage across the contacts. A closed contact will drop barely any voltage, while an open contact should drop the full voltage (or at least half of it in your double line break scenario) \$\endgroup\$ – ThreePhaseEel May 10 '17 at 4:16
2
\$\begingroup\$

THermal regulating Relays get a lot of cycling and inrush currents at random phase voltage . When they cycle a few times a minute they can wear out prematurely from arccing and pitting on the contacts which of course causes them to be partially welded and stay on.

The problem may be some engineers overlook the fact that the rated current is less than the surge current due to the PTC resistance coefficient and if switched at peak voltage at random with a low cold resistance to the heater element instead of 10A it might be 25A peak before it settles to 10A. This naturally erodes the contact plating faster.

SMD diodes come in dozens of case sizes incl. SOT023 shown in your photo enter image description here

Read and understand this Consider a better replacement if it fits.

Time to replace the Relay with an equivalent or better rated relay from OMRON or Panasonic. Many disti's carry these and ship same day https://www.digikey.com/products/en/relays/power-relays-over-2-amps/188?k=&pkeyword=&pv69=80&FV=1200002%2Ca8c0007%2C16040020%2C160c0027%2C160c002c%2C160c0036%2C160c0039%2C160c003f%2C160c0041%2C160c004f%2C160c0052%2C1f140000%2Cffe000bc%2Cfffc00ec%2Cfffc00ff%2Cfffc0027&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=500

\$\endgroup\$
  • \$\begingroup\$ Makes sense and what I was hoping would be true, thanks. \$\endgroup\$ – Jim W says reinstate Monica May 10 '17 at 16:38
1
\$\begingroup\$

I suggest measuring the relay coil voltage when it is meant to be off (or at least when you are commanding it to turn off). If there is still voltage (12VDC) on the coil, then it is nothing to do with the relay, it's doing what it should be doing and remaining closed. If however the drive voltage disappears, however you still have closed relay contacts, then it is a faulty relay.

\$\endgroup\$
0
\$\begingroup\$

Maybe your oven has a connection like this one, the normally open button is the one that powers your relay, once it's powered the contact is closed and starts to feed both the load and the relay, until a NC switch (maybe a thermal relay) is opened to stop the current flowingh trough the coil.

enter image description here

\$\endgroup\$
  • 1
    \$\begingroup\$ I don't think so. The oven is sophisticated enough to have a self diagnostic test, and it fails saying there's a comm. error. My feeling would be that the thermostat is digitally controlled, since it has the facility to digitally monitor the temperature and show it on the display. \$\endgroup\$ – Jim W says reinstate Monica May 10 '17 at 2:13
  • \$\begingroup\$ So the oven is not working at all? Since it has a self diagnostic test then anything could be wrong with it. The answer goes more towards your question about if it's a dud relay or not, so if it's working without load but when you connect it to the board it remains on, then what I showed you in the picture might be what's going on and the relay is OK \$\endgroup\$ – Marcelo Espinoza Vargas May 10 '17 at 2:19
  • \$\begingroup\$ It works in that, if you press bake it turns the element on - it just never turns off, not if you press bake again, nor if it reaches the desired temperature. I saw some posts on the net about relays causing problems like that, which is what lead me in that direction. I expected the relay to just stay stuck on, whether load was present, or not - which is why I've asked the question, because it doesn't quite make sense to me. \$\endgroup\$ – Jim W says reinstate Monica May 10 '17 at 2:22
  • \$\begingroup\$ There are two relays, let's call Relay A to the relay you took appart and Relay B to the other relay that's still in your board. Maybe Relay B is supposed to cut the energy to Relay A (like Relay B is the second button in my diagram), if Relay B is not working then Relay A will always be closed until power is taken apart. \$\endgroup\$ – Marcelo Espinoza Vargas May 10 '17 at 2:25
  • \$\begingroup\$ Yes, I wondered that - I will double check the technician sheet, but the odd thing is that Relay A does switch off when I tested it (no load). So I suppose maybe if another relay can send current to the element, but... not clear how that could be. I'll recheck wiring. \$\endgroup\$ – Jim W says reinstate Monica May 10 '17 at 2:37

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.