Hi.
I'm a volunteer committee of management member for a local hall near where I live. The people using the hall have told me that the gas heater is a bit on the blink. It's turn on via a coin box.


At this stage I'm looking at the coin box first to be faulty. The only "wearing" part that I can see in it, is a mechanical relay (OMRON GP8-1A4P, 12VDC, 30A, 250VAC, 4 pin - through hole type). I can't find one cheap enough and locally, so the first thing is, can I use a different type locally? Does anyone have a suggestion. Second question is, can I replace it with a solid state relay instead so as to minimise a faulty contacts problem? Again if so, any suggestion. Thanks in advance.

 

Are you sure its the relay? How old is the controller? Looks to me at least 30 years.

I would avoid changing the designed relay to a solid state one. If you are confident its the relay, then change it to at least one with at least the same specs (12V coil, 250V 30A contacts). Any reputable relay (eg Omron) should have sufficiently reliable contact life for another long spell of operation.

 

Since (presumably) you don't know whether the relay is switching AC or DC, and the voltage and current being switched, changing to an SSR is a bad idea.

 

AT89C35?

 

Don't forget that a SSR will dissipate 1W for each amp of current through it. It doesn't look as though that enclosure has any facility for dissipating heat.

 

As it is controlling a gas heater I think the current that it controls will be quite small. (It will probably just drive a solenoid valve and a spark igniter.) I suggest that you start by diagnosing the fault rather than guessing. I would do this by adding an LED idicator in parallel with the relay coil and a neon indictor (Assuming it is switching mains voltage.) to monitor the switched output. I would susspect the coin detector more than the relay but that is a guess as I don't know how the coin detector works.

Les.

 

Don't forget that a SSR will dissipate 1W for each amp of current....

They can get unexpected very hot, needing effective heatsinking which a mechanical relay doesn't.

 

Hi.
I'm a volunteer committee of management member for a local hall near where I live. The people using the hall have told me that the gas heater is a bit on the blink. It's turn on via a coin box.
View attachment 327939 View attachment 327940

At this stage I'm looking at the coin box first to be faulty. The only "wearing" part that I can see in it, is a mechanical relay (OMRON GP8-1A4P, 12VDC, 30A, 250VAC, 4 pin - through hole type). I can't find one cheap enough and locally, so the first thing is, can I use a different type locally? Does anyone have a suggestion. Second question is, can I replace it with a solid state relay instead so as to minimise a faulty contacts problem? Again if so, any suggestion. Thanks in advance.

Hi,

As others have said, it's probably not a good idea and may even involve some other circuit rework to get it to work right. Too many unknowns.

If you are not sure if it is the relay, you can usually hear a distinct 'click' when the relay closes and a more mild click when it opens, more like a soft 'clunk' sound. You can listen for each of those when you activate the unit.
If you do not hear both of those or at least the click when it closes, then something is probably wrong. Unfortunately, it could be the relay or what drives it.
In my experience I've seen relays fail by sticking in the closed position. That means they will never open. If that's the case, you can sometimes get them to work by tapping them with some tool like a rubber hammer or just tapping with the end of a wrench. OF course you do not want to tap too hard or the case may break open.
This can work, but there is of course the chance that it will happen again.
The reason for this is relay applications are not that well understood by circuit designers. They are often placed in circuits that require a higher current rating than the relay can handle for a long time. Relays really should be overrated when selected for a given design if they have to handle current, and there is more to consider than that too. If that unit really is 30 years old, count your blessings and move on because that's a good design.

Replacing a relay is a heck of a lot simpler than trying to retrofit a SSR into a mechanical relay application.

 

What does “a bit on the blink” mean? What is it doing wrong?

Why do you think it is the coin box? Did you rule out the possibility that the heater itself is malfunctioning? You could do that by simply shorting the wires from the coin box relay to see if the heater operates normally.

 

Before replacing parts based on a guess, it is useful to understand the problem. A "Gas Heater" system has quite a few parts that can fail. But without any better description than " a bit on the blink" there is no suspect part in particular. But based on logic, there is a sequence of suspects:
1. Gas supply manual shutoff valve.
2. Electrical mains power connection.
3. safety interlocks on the blower compartment access points.
4. The blower motor control thermostat
5 Combustion air supply and exhaust ducting.
6. External thermostat and it's connections.
7. Pilot light and it's ignition and sensing arrangement.
8. Main burner gas control valve.
9. wiring between control box and gas valve.
10. Blower motor to blower drive belt.
11. Coin control box power and internal coin sensor hardware.
12. Coin box security switches.

So those are the initial suspects based on what most gas-fired heating systems are built from.
And that broad description of failure is fairly useless.
For selecting a replacement relay, the first specifications would be contact current and voltage ratings, and then the coil operating voltage.
I have only once had to replace a PCB mounted relay, and that was one that physically broke, on the control board of a commercial ice-cream machine. Those relays seldom fail.

 

The coin box may not be faulty. Have you tried operating the heater without the coin box?
If the heater then works, you can conclude the coin box is faulty.

 

We do not even have a hint as to just what the failure is. Consider the possible complaints: #1Does nothing at all, #2 heats too hot,
#3 The blower comes on but no heat #4 the heat comes on but no blower , #5 it runs but makes a noise. #6 It does not heat warm enough.
And each of those complaints would have a different cause. So we really need a more detailed description of the problem.

 

My first suspect on the list would be the relay, especially one will that age of service.
They are obsolete AFA Omron is concerned.
Often a SS solution is not easy due to the relay offering isolation.
BTW, as far as those sealed relays are concerned, it pays to open the vent 'Pip'. in the corner, these are left sealed when flux is applied to the board at assembly time. But shortens the life of the relay if left closed.

 

My first guess is the igniter element, if the heater does not have a standing pilot flame. Or the thermocouple that monitors the standing pilot.
BUT we can only guess until we get more information.

 

Thanks everyone for you suggestions. Sorry I wasn't clearer about the fault (a bit on the blink). Here's a bit more info (and using some suggestions above):

1. When a coin is inserted, I can hear a distinct click, and then when I turn the heater on, the gas fires up and it works. I haven't listened for the softer "release" click - not to say it doesn't do it.
2. A hall user tells me that when she puts in a $2 coin, the heater turns on as expected for the 30 minute duration, then turns off as it should. Other times, she has to put in a 2nd coin to get it working.
3. Some times she puts in 5 coins and it works for 5 x 30 minutes. Other times, the 5 coins only go for say 1 hour. Maybe the relay isn't "detatching" after she's put in the 2nd coin (as MrAI noted above).
4. The circuit breaker for this heater is 40A, however I think that's because it's driving other stuff in the hall. The relay is rated at 30A. However, given the circuit feeds back to the heater somewhere, and the heater is getting it's main power from a GPO on the wall, I can't image this wire has a big load.
5. This heater is quite old and during winter, I'm guessing there are about 500 to 1000 coins inserted. On an Omron website, I read that a mechanical relay is good for up to 50 million operations. I doubt it! But this seems like the most likely suspect given sometimes it registers and other times it only partially registers.

Taking eetech00's advice above, I've just disconnected the wiring to the coin box and fed the active wire directy to the single active wire that leads back to the heat. I turned on the heater and it worked. I only tested it for 5 minutes. I'm going to leave it bypassing the coin box for a day and ask the same hall user tomorrow if the heater worked without issues. Elimination.

 

Not so clear that it is the relay, tbh. Given you can't just get another relay and swap it out as a preemptive first step, a bit more diagnosis will be productive.

 

Is this the one?
https://uk.rs-online.com/web/p/power-relays/6831412
https://www.rapidonline.com/hongfa-hf165fd-12-hy1tf-pcb-relay-12vdc-spst-no-30a-71-4673

 

Thanks everyone for you suggestions. Sorry I wasn't clearer about the fault (a bit on the blink). Here's a bit more info (and using some suggestions above):

1. When a coin is inserted, I can hear a distinct click, and then when I turn the heater on, the gas fires up and it works. I haven't listened for the softer "release" click - not to say it doesn't do it.
2. A hall user tells me that when she puts in a $2 coin, the heater turns on as expected for the 30 minute duration, then turns off as it should. Other times, she has to put in a 2nd coin to get it working.
3. Some times she puts in 5 coins and it works for 5 x 30 minutes. Other times, the 5 coins only go for say 1 hour. Maybe the relay isn't "detatching" after she's put in the 2nd coin (as MrAI noted above).
4. The circuit breaker for this heater is 40A, however I think that's because it's driving other stuff in the hall. The relay is rated at 30A. However, given the circuit feeds back to the heater somewhere, and the heater is getting it's main power from a GPO on the wall, I can't image this wire has a big load.
5. This heater is quite old and during winter, I'm guessing there are about 500 to 1000 coins inserted. On an Omron website, I read that a mechanical relay is good for up to 50 million operations. I doubt it! But this seems like the most likely suspect given sometimes it registers and other times it only partially registers.

Taking eetech00's advice above, I've just disconnected the wiring to the coin box and fed the active wire directy to the single active wire that leads back to the heat. I turned on the heater and it worked. I only tested it for 5 minutes. I'm going to leave it bypassing the coin box for a day and ask the same hall user tomorrow if the heater worked without issues. Elimination.

Hi,

I can not be certain it is the relay either, but because it's a 30 amp relay it could be handling a lot of current. And that rating of 50M operations that could be under more ideal circumstances. If you run a 30 amp relay at 30 amps it's not going to like it. That's partly because of surges that can cause the current to go up much higher momentarily. It worked for so long though maybe that's a moot point.
If it really is the relay and if you can't get an exact replacement, then you are in for a little rework. It is possible to run wires to an external box that holds the relay. That opens the door to relays that have a much different foot pattern and shape and all that. Of course the wires have to be rated for the full current, and you can even get away with using a relay socket for the relay.

If you can fit it inside the case it has to be mechanically stable as well as electrically wired right. Unfortunately wiring outside of the original case may come with some safety laws too.

I just have to wonder now, how much is it to purchase a whole new controller unit, complete with new relay and all that stuff, and would work right out of the box. With something like this that is probably what I would do even though I've fixed thousands of devices large and small in the past. Sometimes you just have to, as they say, "bite the bullet".

 

1. A hall user tells me that when she puts in a $2 coin, the heater turns on as expected for the 30 minute duration, then turns off as it should. Other times, she has to put in a 2nd coin to get it working.
2. Some times she puts in 5 coins and it works for 5 x 30 minutes. Other times, the 5 coins only go for say 1 hour.

These are strong evidence against the relay being the culprit. It sounds more like it is either the coin sensing circuit or the counting / timing circuit.

 

If there is a variability in the time and sometimes it appears to not recognize multiple coins, that points a finger at the coin box system rather than the output relay. Perhaps the coin box coin mechanism has switch contacts that need to be cleaned, given that coin sensing mechanisms are often mechanically complex.

IT does not make sense that a relay would be released and then operated again after each paid-for time increment, and certainly a heater does not need to stop and restart.

One more thought is that if the ICs in the coin box plug in to TI brand sockets, those sockets were notorious for poor connections at one time, in which case simply unplugging the ICs partly and then re-inserting them fully may provide a quick fix. I found that to be a quick fix for one brand of electrical testers in an auto plant about 25 years ago.