Permanently energized Relay has started clicking noises

[paul8f]

There are two orange Tyco relays on this PCB. One has started making intermittent clicking noises, but I don't know which one. I'm 90% sure it's the one on the left that's actually unused in my setup, but can be used for an auxiliary pump or something.

It's an intermittent relay noise, so I'm wondering what's the best way to 'invoke' a failing episode? I'm guessing that heating and/or cooling the PCB may shed some light on the problem. (Tapping the PCB revealed nothing.)

Also.... this relay on the left has a coil that's constantly connected to a DC rail (24/7), but the relay on the right is for an ignition heating element that is only energized for about 5 minutes at a time, no more than a dozen times a day. Can a coil get weak if permanently energized like the case for the left relay?

Thanks in advance!
Paul.

[pbarton]

The right relay is used for the 5 minute start period, then it drops out.
The left relay determines if the fan is running at low speed or high speed.
The two pots at the bottom left, marked FAN HI and FAN LO on the front panel, probably sets a minimum time duration that the fan runs at a particular speed, before becoming available to change speed (lockout).
If these pots are adjusted to a minimum, then the left relay could cycle very quickly?
Try adjusting the FAN HI and FAN LO pots, to their mid-position.
Q. Can a coil get weak if permanently energized like the case for the left relay?
A. No.
Are you testing the controller with the room thermostat attached, or have you left the input to the controller open circuit?
If the input to the controller is not correctly terminated then it could be susceptible to noise, causing the left relay to cycle?

[paul8f]

The left relay determines if the fan is running at low speed or high speed.

Thanks for your ideas. I followed the traces for the left relay, and the switched contacts go to unused connections in the terminal block. I'll post back later with the main system wiring diagram, don't have it with me right now. I just figured out that the variable speed fan is connected through the Triac (Q2 in the top-right corner of the PCB).

The two pots at the bottom left, marked FAN HI and FAN LO on the front panel, probably sets a minimum time duration that the fan runs at a particular speed, before becoming available to change speed (lockout).
If these pots are adjusted to a minimum, then the left relay could cycle very quickly?

FAN HI and FAN Lo are fan speed adjustments for Full Power and Half Power modes. As the temperature approaches the cut off point, the unit will drop to half-power. After a while, if the heat demand is still significant, then it will then switch back up to full power mode. If the heat demand is not very significant, then the unit will drop from half-power mode to standby, and the flame will go out until it's needed again. This type of modulating power-modes is supposed to reduce time lag, and to improve system reliability as the heat source is prevented from switching on and off over and over again.

Are you testing the controller with the room thermostat attached, or have you left the input to the controller open circuit?

I've tried testing it with the thermostat (call-signal from the wall panel/motorized valves in my case) connected, and also tried tested it with the thermostat system bypassed so heat is constantly demanded. I didn't leave any connection un-terminated.

If the input to the controller is not correctly terminated then it could be susceptible to noise, causing the left relay to cycle?

...but I suppose a lot of ripple or momentary low voltage in the DC power rail could cause the relay contacts to drop out and start clicking. Very difficult to capture this if it is the case.

[pbarton]

Clearly my guess at how it works was incorrect.
Perhaps you could provide a little more detail on the original problem?
Is the heating system behaving correctly (responding to demand etc), and the only problem that you have observed is some spurious clicking of the controllers left relay?
Or, did you remove the controller from the heating system for a different reason and you only encountered the left relay clicking while working with it on the bench? If so, then what is the original reason that caused you to remove the controller?
I assume that the PIC is controlling both relays, but the function of the second relay remains unknown. The schematics may reveal something?

[paul8f]

No worries pbarton! Any ideas whatsoever are welcome... I've just done another small bit of investigation of the system this afternoon, and I think I've figured out what's wrong.

The original problem, was an intermittent failure to ignite the fuel. After 3 or 4 attempts, the Red fault LED would come on. One evening when the system had just switched off normally, I heard this clicking noise coming from the controller,
and thought I was on to something, but it turns out that this left relay is not needed in my setup, due to the way the electrician originally wired in the Wall-panel and the water pump.

The PCB in the picture is actually a 2nd-hand one I bought as back-up/spare, but this one turned out to have even more issues that the original board...! (When the rocker switch on the spare PCB is turned on, it brings on the red fault LED straight away. All power rails are smooth, CLK signal to uController is good, and I resoldered all pins of uController. Might be corrupt software or something??  )

The PIC only controls the Ignition element relay. The other relay is hard-wired to the main DC rail, and even continues to get power when the rocker switch is switched from the On position to Standby/Off. This relay only ever de-energizes when the power-cord is pulled.

Anyway, I used a Power-Meter to check the consumption during the ignition sequence. Then I installed a brand new ignition element, and re-measured the consumption. Even though the new element was rated 420w (v's the original at 425w), the new element used on average  3% more power than the original, so there may have been an issue with the old element. This may help explain the intermittent startups. Trouble now is that I accidentally scratched the new element against its metal mounting, and now the RCD is throwing a hissy-fit, so I must order another replacement
element.

The other issue I found was in relation to the second fan. I had already cleaned the blades of the ignition blower, but for the flue-fan I only did a really quick rough-and-ready clean. When I fully opened up the flue-fan casing I found that most of the small blades had heavy deposits on them. The negative pressure in the flue would have suffered due to this, and the air-channel back to the igniter and blast-tube area may not have had enough of a draught to facilitate ignition. I did a thorough clean of this second fan, so hopefully that will help matters.

So all in all, I think it was two separate marginal fails combining together to create an intermittent fault, all the while the unused relay clicking away randomly just to confuse matters!

I don't have the electronic schematic for the PX-21 control board, but I do have the system wiring diagram from KMP, the Swedish manufacturer of the Burner section of the system. See pic attached.

[pbarton]

Edit: your "system wiring diagram from KMP" only show one fan and you mention that your installation has two fans.

Sounds like you have resolved the problem, just in time for winter. Well done.

[paul8f]

Edit: your "system wiring diagram from KMP" only show one fan and you mention that your installation has two fans.

The wiring diagram is only for the internals of the KMP PX-21 burner unit. Not shown in this diagram is everything else (water pump, hot water cylinder thermostat, wall control panel/timer, boiler safety cut-out, motorized valves for the various zones, ... and the flue-fan).

Hopefully I can get the system working reliably for the winter. I'm sick of looking at the thing at the moment.