[Oldmanandhistoy]

Hi all,

I have a problem with a couple of BOB’s that I bought a while back and have just got around to using them.

In the doc that came with the board it says once power is supplied you should hear the relays click. What I am getting from both boards is a loud buzzing noise from the relays. If you look at the pictures; when I touch any of the points marked in red with a finger the buzzing stops and when power is switched on and off the relays click as they should. I can get the buzzing to stop also when I move the boards about but this is hit and miss.

Any ideas or solutions will be very much appreciated.

John

[Al_The_Man]

It sounds like armature noise (the moving part of the relay that is attracted by the coil).
Normally there are two reasons, too low a voltage or bad seating of the armature, but this is usually prevalent in AC relays.
Do you have 24vdc on them?
As even raw DC (unsmoothed) does not cause this, unless maybe 1/2 wave rectified DC.
Just for kicks you could put a 100 to 500µfd across the coil to see if it stops , observing polarity, but make sure it is DC!.
Al.

[Oldmanandhistoy]

Hi Al Thanks for your input.

The boards come with a 6Vdc switch mode psu. There is a 470uF cap across the terminals of the psu connecting blocks. If I touch ever wide of the cap the buzzing stops also.

[spark-el]

Could be a cold solder joint or a crack in the foil path within the board.
If you're pressing on those points and the relays come in, then I would suspect the negative common not making good connection somewhere on the board. If you can isolate the point you may be able to solder a small
guage wire across it at the nearest two terminal points. Usually when a relay or starter vibrates like that, it is due to one side or the other not passing enough current to bring it all the way in and hold.

[Oldmanandhistoy]

Could be a cold solder joint or a crack in the foil path within the board.
If you're pressing on those points and the relays come in, then I would suspect the negative common not making good connection somewhere on the board. If you can isolate the point you may be able to solder a small
guage wire across it at the nearest two terminal points. Usually when a relay or starter vibrates like that, it is due to one side or the other not passing enough current to bring it all the way in and hold.

Hi spark-el,

This problem is the same on both the boards I have; would that still imply a cold solder joint?

John

[sailandoar]

Do you have a schematic as part of the documentation and if so have you done any basic meter testing to see if voltages are present and proper as specified. Unlikely but possible that you have or can get test point data for the board. (i.e. go to this place and look for that voltage and/or signal)

[Oldmanandhistoy]

Do you have a schematic as part of the documentation and if so have you done any basic meter testing to see if voltages are present and proper as specified. Unlikely but possible that you have or can get test point data for the board. (i.e. go to this place and look for that voltage and/or signal)

Hi sailandoar,

Please keep in mind I am at best a beginner in electronic and would not know where to start.

John

[spark-el]

Could be, if they've seen some abuse or excessive vibration. Follow what
oar and sail says and you may be able to isolate the problem. Check your
voltage across each coil, use an analog meter if possible, the needle will
show vibration if the voltage is fluctuating.

[Oldmanandhistoy]

Could be, if they've seen some abuse or excessive vibration. Follow what
oar and sail says and you may be able to isolate the problem. Check your
voltage across each coil, use an analog meter if possible, the needle will
show vibration if the voltage is fluctuating.

Unfortunately I only have a digital meter; would I still be able to isolate the problem? I have to say it sounds to me that all the relays are vibrating.

As stated this problem is affecting both boards, does that imply they both have a cold solder joint?

John

[Oldmanandhistoy]

Another thing to consider is that if I touch the ground point on the parallel cable connection plug it also stops the vibration.

[spark-el]

It could also be a low voltage problem. See what you read across the coils of the relays with your digital meter. The fact that it stops when you press on those locations is what points to a bad connection. Check across each
relay. Are they all chattering? Who is the mfr of the boards, and what are
they for?

[spark-el]

Yes, could be a bad cable also. Kind of hard to help you over the internet, I just think it is a low voltage problem caused by a bad connection somewhere.
Only time I've ever seen a relay buzz is due to either a bad holding contact or the voltage driving them fluctuating. Good luck!

[Oldmanandhistoy]

It could also be a low voltage problem. See what you read across the coils of the relays with your digital meter. The fact that it stops when you press on those locations is what points to a bad connection. Check across each
relay. Are they all chattering? Who is the mfr of the boards, and what are
they for?

I got the board via Ebay from brenthub, there is no indication of a manufacturer and I want to use the boards for my CNC routers.

I will just go and see what I get on my meter; could I damage anything if I test wrong points on the relays?

John

[spark-el]

You'll probably be alright, just make sure that each probe is only touching one terminal point (not shorting another that may be close to it). Before doing that, see if you can ring out your cable, i.e. test each conductor from one end to the other with the ohmmeter. If the female connector has small holes, you may have to use a paper clip or something smaller to get into it.
is this a 120V supply cable, or do you have another power supply?

[Al_The_Man]

You want to make the tests without the switched load disconnected, you do not need that to test the coil side.
It almost sounds like a stray leakage or ground currents, ( which could be of an AC nature) that is getting into the board.
A pretty sure way of testing is to eliminate the switching power supply altogether by feeding the board with a 6v battery supply, I thought they were 24vdc but it looks like they are 5vdc relays, according to the part number.
Al.

[Oldmanandhistoy]

I have put my meter across the 6 relays on 5 of them I’m getting about 3.3V and on one I am only getting around 1.3V.

The parallel cable is not attached.

[Al_The_Man]

Thats probabally part of your problem, especially if the DC has any kind of ripple on it.
Al.

[Oldmanandhistoy]

The actual board is mark for +5V but in the instruction it say use a 6v supply?

[Oldmanandhistoy]

I have the psu connected through a drop down transformer (250V to 110V) would that make a difference?

[Al_The_Man]

It should not make any difference, If a DC relay is fed from clean non-ripple DC once it has energized or pulled in, it has something called hysterises, which holds it in until the voltage drops well below the pull in voltage.
If there is any kind of large ripple at a voltage below the pull in voltage, you can get buzzing that way.
It sounds like your 6vdc is not very 'clean' or the relays are not being switched on sufficiently, what energises them, hopefully not the the printer port directly?
Al.