PCB Relays - General questions replacing a bad relay

Thread Starter

jfeazell

Joined Oct 26, 2022
1
For a quick bit of background, I'm a software engineer and a ham radio operator, not an electrical engineer. So, while I can certainly find my way around all things electronic, I would not assume that I know anything that is "common knowledge" in the field. Having said that, I'm working a little project and need some direction. :)

I have a HarvestRight freeze dryer, and the unit isn't working. I've diagnosed the problem down to a relay mounted on the relay board in the unit. The relay seems to have failed and while the coil energizes, there is no high voltage coming from the contacts to energize the heater inside the machine. HR is replacing the whole relay borad, but I'm keeping the old one and I intend to replace the bad relay on it so that I have a backup. I would actually like to make an "improved" version, which is why I'm here. That brings to mind two general questions...

1) Is the pinning / shape / size (what I would call the "form factor" in the vernacular of computer components) the same for relays within a certain family / style of relay?

2) In keeping with #1, do other components (like a socket, for example, or a solid-state relay versus an electromechanical relay) share the same form-factor / pinout?

The reasons I ask this quesion might make sense with a bit of background on the issue... The relay that failed on this board is a relay that activates a heater that cycles on and off during the freeze-drying process. The coil on the relay seems to energize (it "clicks" when activated), but no high voltage comes off of the contacts, e.g. no heater. The manufacturer of the machine says this is a common problem because the relay goes on and off quite a bit, and therefore its contacts wear out (seems peculiar ot me, as it's only a few months old and not THAT heavily used, and I would certainly expect a higher MTBF on a component like this, but I digress). As an engineer, my thoughts here were twofold: First, if the relay is expected to fail well within the reasonable lifetime of the board, why not choose a socket-mounted version, thus being able to simply pop out a $2 relay instead of tossing a $50 board? Second, if the cycling of that electromechanical relay is so apparently detrimental to its lifespan, why not use a solid-state relay instead? From what I have read about these (from Mouser and other places), they are quite reliable and are suitable for applications such as this (based on my estimate of the current draw used by this thing).

For reference, the relays on this board are FT K1CK012W, and looking for it on Mouser, this appears to be a Fujitsu relay. Interestingly, the relays on my board say "Japan" on them, while everything I find on the web says "China". :(

Since I don't have the means to entirely remake their IC, what I'd like to do is remove that relay, then replace it with some type of generic socket that would allow me to plug the same or a compatible relay into it (I assume a socket-mountable device doesn't use the same type pins as a soldered one, hence I say "compatible" one). This would allow me to have an easily replaceable relay for the next time it fails.

Alternately (and really the more "improved" version of the board), I would like to simply replace that electromagnetic relay with a solid-state one. Howeer, as I look at different solid-state relays, none of them appear to have the same pinning / form-factor, so retrofitting it onto this board might be difficult (or perhaps even impractical if they are for some other reason not electrically compatible with the circuit design for the current relay.)

Any thoughts or advice on this would be greatly appreciated!
 

dl324

Joined Mar 30, 2015
15,439
Welcome to AAC!
1) Is the pinning / shape / size (what I would call the "form factor" in the vernacular of computer components) the same for relays within a certain family / style of relay?
Multiple relays can have the same form factor with different pin functionality. For example, an SPST and SPDT relay can be in the same form factor.
2) In keeping with #1, do other components (like a socket, for example, or a solid-state relay versus an electromechanical relay) share the same form-factor / pinout?
Without knowing about the specific relay you're referring to, I'd say it's possible.
 

MisterBill2

Joined Jan 23, 2018
13,709
The first question is how many poles/contacts on the relay. and what is the coil voltage. Solid state relays are available but I am not aware of a common form factor for small ones except for those intended to plug in to circuit boards. Those are almost all single pole devices.
The only common form factor that I am aware of for small relay sockets that is shared between manufacturers id the 4-pole double throw arrangement with 12 + 2 positions. (4 contact sets by three connections+2 coil connections.)
 

MaxHeadRoom

Joined Jul 18, 2013
26,263
For reference, the relays on this board are FT K1CK012W, and looking for it on Mouser, this appears to be a Fujitsu relay.
For starters, any of those PCT board relays, have a vent 'pip' (see the one in the top corner) that is used to seal the relay while the board is defluxed etc. It is wise to open this pip, which manuf rarely do, this prevents ionization of the interior, especially for a relay that operates repeatedly with a high current.
This prevents arc over and burning of the contacts.
 

Attachments

twohats

Joined Oct 28, 2015
362
You said, 'the coil on the relay seems to energize (it "clicks" when activated), but no high voltage comes off of the contacts, e.g. no heater'. My question, is there high voltage on any of the pins? Apologies if I have got it wrong.
Good luck.......
 

MaxHeadRoom

Joined Jul 18, 2013
26,263
One other common problem I have found with these PCT relays that switch hi current, is often it is the board trace to the relay power pins that burn open, I have replaced the relay and repaired the board with dry-wick/copper braid.
 

MisterBill2

Joined Jan 23, 2018
13,709
Certainly a close examination of the power traces would be in order, no question there. I had presumed that the TS had done that already.
 

MaxHeadRoom

Joined Jul 18, 2013
26,263
What I would do initially is replace the relay with the original type and try the vent option first, if that fails in a short operation time, then look for other off-board options.
 

MisterBill2

Joined Jan 23, 2018
13,709
If the failure is common enough that the company admits that it is a problem, then it seems that the relay is an incorrect choice for the application. Of course it may be that the relay contacts open slowly because of the transient prevention circuitry. That is another possibility, especially if the relays have weak springs.
Amazingly enough, there are some rather poor quality products marketed. Some companies produce junk.
 

MaxHeadRoom

Joined Jul 18, 2013
26,263
Fujitsu have a good quality reputation and although they have factories throughout Asia, the products carry ISO 9002 or ISO 9001 standards certification.
If a spare replacement relay is at hand, I would try the vent method first.
 
Top