Relay problems

[radiance]

What is the problem when a relay is making a soft buzzing noize?
It's my third relay in a row that stats doing this (other similar ones are death quiet).
I'm using relays for bypassing on the ssl clone.
I power them with a separate bridge rectefier and a regulator (7815) so I'm not using the power from the ssl.
I also have put a diode across the coil to prevent switching noise.

 

[owel]

Mechanical problem?

 

[CJ]

Sounds like low voltage.
How do you have the diode hooked up?
What are you using to pull in the relay?
Maybe it wants dc and you are feeding it ac, although most relays have a built in bridge to make them ac/dc compatibale.

 

[radiance]

well, these relays are for use with dc and that's what I'm giving them.
On the relay it sais 12v and what I'm getting from the regulator is +/- 13v.
I do believe these relays have some margin in the voltage you're giving them right?

 

[mcs]

9-15V should be fine for a 12V relay. If it's just one relay acting up try replacing it - perhaps with a different type. Omron G5V-2-H1 should be a good choice for audio switching.

Best regards,

Mikkel C. Simonsen

 

[Svart]

what's the relay model? I bet you have a small degree of ripple on the dc. Vregs can do that sometimes, I see it on pro video cameras all the time. the noise is terrible until you put a cap on it so put a cap (.1uf 35v) across the gnd and output and see if it goes away or not. this can change from one manufacturer to another!

 

[PRR]

What is this, Relay Week???

> What is the problem when a relay is making a soft buzzing noize?

You aren't feeding it clean DC. You may think you are, but....

Do you have an ample filter capacitor on the rectifier? Relays need more current than chips. Use at least 1,000μFd per Amp of current, and more is better.

Is your regulator oscillating? If the only load is an inductive relay, it probably is. Put 470Ω 0.5Watt across the output to give it a steady DC load. Use the maker-suggested output cap: 0.1μFd or 22μFd, whatever they say is best.

> believe these relays have some margin in the voltage you're giving them

Yes. A "12V" relay will usually pull-in at 9V, and usually won't burn-out at 17V. Read the spec sheet. And I would not fool with regulators: build your raw transformer rectifier and capacitor power supply, add a resistor to drop the voltage and another capacitor to smooth it more, and use that to drive the relay. If your transformer AC voltage is similar to your relay DC voltage, the dropping resistor can be about half the relay resistance. This won't work with several relays: voltage varies too much depending how many relays are on. But for one or two relays, a little cut-and-try with the resistor value soon gives a workable compromise.

 

[radiance]

This is the power suply I use for powering the relays.

 

[radiance]

Also, the power suply is powering two 12v relays and three 24v lamps (in the pushbuttons) max.

 

[gyraf]

that 0.33uF is way too small.

Use minimum 470-1000uF rated the DC voltage you have (1.41x the transformer AC voltage)

Jakob E.

 

[radiance]

Thanks Jakob and all of you.
I really did not know why all these relays died on me. Looks they're not death after all.
I tried a bigger cap and the buzz was gone.
@Jakob: What exactly do you mean by: Use minimum 470-1000uF RATED the DC voltage you have.
does it mean:Use minimum 470-1000uF ACCORDING TO the DC voltage you have?
I use a 2 x 15v toroid (from the ssl) transformer and tapped the + and - to create the separate relay power. I meassure 32,5v AC and 28,2v DC (after the bridge rectifier but before the regulator). After the regulator I meassure 12,8 v DC.


Thanks!

 

[gyraf]

With 28,2v DC you should use the next larger voltage capacitor - in this case a 35V type.

Make it 470uF/35V or 1000uF/35V..

Jakob E.

 

[matthias]

I also want to build some relais for input output switching in my ssl comp

can I grab the 15V from the 7815 regulator that powers the comp..??

which type of diode do I need??

thanks
mat

 

[Svart]

i would build a separate supply for the relays or you'll drag your rail down and your ICs won't like that, neither will your ears.. :green:

 

[NewYorkDave]

Here's a handy general-purpose relay driver circuit. It has high current capacity and can handle up to 440mA including the optional LED indicator. I recommend keeping the total load under 400mA just to be on the safe side.

 

[matthias]

to power the relais of my ssl comp: if I use an extra 15V regluator for the relais, can i grab the dc input voltage from the in of the 7815 regulator from the comp section, or do I have to build an extra "powersupply path" for the relais with bridge rectifier and caps like "radiance" did ??

 

[gyraf]

Matthias,

There should be no reason to regulate power to the relay circuit. Simply use a resistor to reduce the voltage to approximately what you need. But a regulator would work too.

Yes, you can take power from existing 7815 regulator input.

(A more elegant solution would be to use a 48V relay, and use power between '7815 and '7915 regulator inputs - there's 40-45V here. This way you load symmetrically, draw less current, and loose less power in the circuit.)

Jakob E.

 

[radiance]

OK, here is what I did:
.

I replaced the 0.33 uf cap with a 470uF 35V cap.
Where I first meassured 32,5v AC and 28,2v DC (after the bridge rectifier but before the regulator) and after the regulator 12,8 v DC now it has become 41,5v (after the bridge rectifier but before the regulator) and after the regulator 14,9 v DC . This looks more like it and the relay buzz is also gone.
Obviously the 35V cap has to be replaced with a 50V one right?

Also one other thing: this power suply is powering three 12v relays and three 24v lamps (inside the pushbuttons) max.
I noticed that when I powered all the relays and lamps that the regulator sometimes stops working (it's not giving 14,8V but 0,01 V). When I shut the power down and start it back up with only one lamp powered everything is back to normal. Is this because the regulator is becoming to hot?
Do regulators have some kind of safety shut down meganism inside where it resets itself after a short period?

 

[PRR]

> Is this because the regulator is becoming too hot?

If it sizzles when you spit on it, it is too hot.

> Do regulators have some kind of safety shut down meganism inside where it resets itself after a short period?

All living monolithic regulators have "thermal protection".

Yes, 42VDC on a 35V cap will blow-up the cap after a while, minutes or years, hard to predict.

Also note that 42V is technically over the rating of those regulators, which are 35V or 40V.

And you are wasting 15/42= 2/3rds of your power as heat in the regulator.

Find a 15VAC or 18VAC transformer, a much better match for a 15VDC supply.

 

[radiance]

Thanks PRR.
I'm taking power from the transformer in my ssl clone wich is 2 x 15V.
Maybe I should put a 7824 regulator in front of the 7815? So that the 7815 does not have to bring the power down from 41V but only from 24V?