relay buzzes while energizing

I followed the wonderful directions on this site to change the polarity of my door switch from a negarive to positive output in order to install an overhead DVD player (with lights) using the wiring to the dome light.

The installation went great and the lights on the DVD player now function properly, however the relay seems to be misbehaving.

I'm using a 30A, 5 prong automotive style relay and when I open the door, the relay takes a second to activate and it does so with an buzz which increases in tone and volume until the switch is activated.  When the key is in the ignition and the relay deactivates, it does so much more quickly, but is also quite noisy with what can only be described as a short BZZRT. (very descriptive and helpful I'm sure . . .:oops: )

I tried swapping other automotive relays into the socket and all of them exhibited this behaviour.

What could be causing this behaviour in the relay? Where do I start troubleshooting? Is it likely a voltage problem? not enough current? Not enough lode (couple of LED lights on the DVD player)  

Thanks in advance!

Does your dome light fade on and fade off with the door?  It sounds like your voltage is slowly ramping up down which will cause some chatter.

The easiest solution would probably be to replace the relay with a reed relay - they are silent.  I'm sure there are other ways to fix it as well.

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Kevin Pierson

I haven't observed the lights that closely but It certainly sounds worthwhile trying a reed switch.

I never considered a reed because I was not familiar with them (I thought they were only used on circuit boards, and I thought soldering directly on to their tabs can overheat them?)

Is it safe to solder directly of the pins, or is there some sort of socket I can solder the wires to which will fit on the pins of a Reed relay?

Thanks for helping out an ignorant newbie such as myself!

I always get a prototype circuit board and solder them to that - that gives you a little more meet to solder. They should have proto boards where you buy the reed relay. I have never seen one in a socket, but that doesn't meant they don't exist.

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Kevin Pierson

Have you dioded across the coil of the relay?

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

howie ll wrote:

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Have you dioded across the coil of the relay?

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No I haven't - Should I have? How would a diode affect the relay? I thought a diode only helped for deenergizing the coil?

Please humour me, try it and let me know. 1N4004, band side to either 85 or 86 whichever is at the voltage rather than ground.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Thanks and will do! I should have some time to try this over the weekend. I'll report back Monday!

<5 posts vs >6000 means "humour" the expert!  

Well, here are the results!

The place where I bought the relay was out of 1N4004 Diodes, so I went with the 1N4007 ones (I assumed a higher voltage rating could only be better?) I ran the diode across the coil, and it did not cure everything, but it somewhat improved the noise, especially on denergizing. It still took a while to activate and had quite an audible (from outside the vehicle too) buzz.  Pulling magical nubers out of the air, I'd say the energizing noise / delay was improved by 30% whereas the de-engergizing was probaly 50% quieter and faster. (still a quick buzz and not the "click" you would expect)

So, with that part of the experiment out of the way, I proceeded to cut up a prototpye PCB, solder a Reed Relay to it, and attached the appropriate wires. Worked like a charm! Now I have practically silent switching. Thanks for the advice howie II and KPierson. If you ever find yourselves in Edmonton, I owe you a drink!

Glad you got a good result.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

It may be worthwhile checking to see if your control signal is actually a fancy dimming setup that works by changing the pulse width.
If it is, you may no longer hear the buzzing, but it would tend to stress the relay contacts by rapidly opening and closing during the transition between open and closed. Depending on how big a load you're putting on the relay vs. its rating, it might cause a premature failure because that's hard on the relay contacts.

Assuming you don't have something like an oscilloscope available, you could try hooking up an LED to the signal, and watch it as you open and close the doors.
Does it just turn on and off in one shot, or does it flicker during the transition, like LED taillights on some of the newer cars? You have to kinda sweep your eyes around nervously to see the flicker depending on how fast it is due to the persistence of vision phenomenon.

Changing the duty cycle is one way to get reduced brightness with better efficiency than using resistors, but if that's how your domelight is set up, you may need a circuit to handle it cleanly.