Power relay from rectifier winding?

[daz]

Any reason that i can't use the rectifier winding to power a relay? I'm concerned about noise issues like pops and such if i tapped off of any supply thats being used, and since i am using a SS rectifier i figure the unused rectifier windings would be a good source. No reason to think not, but i'm asking to be sure theres not something i'm missing. It has plenty of power at 2A for 5v or 1A for the 6.3v tap.

[Leo_Gnardo]

Sure, why not? And if you rectify & filter that 5V to run relay coils, very little chance any pops & ticks will find their way into the audio. BTW it is good practice to put a rectifier/cap parallel on each relay's coil to further reduce noise when the coils are switched on or off. Doesn't take much, a cheap 1N4001 plus 22 uF 25V cap combo works fine.

Good to see you back daz, now we don't have to wonder "whatever became of ..."

[daz]

Thanks. Thats what i figured. Using a full wave rectifier the circuit will be isolated from the audio circuit but i just wanted to be sure i wasn't missing anything because.....well, as you will recall as i have always said, i dunno what the hell i'm doing ! Do you think using a cap across the coil is necassary since it will be isolated supply?

[Leo_Gnardo]

Do you think using a cap across the coil is necassary since it will be isolated supply?

Every little bit helps. In the case of the rectifier/cap coil snubbers, you're not only knocking down the noise reflected to the power supply, but minimizing the electromagnetic field noise at the relay's physical location, that can put clicks & pops into nearby audio circuits. Cheap insurance, the parts cost pennies.

[daz]

Every little bit helps. In the case of the rectifier/cap coil snubbers, you're not only knocking down the noise reflected to the power supply, but minimizing the electromagnetic field noise at the relay's physical location, that can put clicks & pops into nearby audio circuits. Cheap insurance, the parts cost pennies.

Ok, then what the heck. Any thought on the value? If it matters it'll be a 5v coil well under an amp.

[Chuck H]

It's not expensive and it's good insurance for the relay as well. There can still be spikes on the lower voltage windings that lower voltage devices will be subject to. The cap will help with that. The diode prevents any inverse voltage from the coil charging and discharging which can cause a pseudo AC condition you MAY hear induced on the signal as a POP.

I think

[Chuck H]

...

a cheap 1N4001 (diode) plus 22 uF 25V cap combo (wired parallel across the relay coil) works fine

[daz]

Oops, missed that, thanks.

[daz]

Hmmmm...this is odd. Just to test it i connected the relay to the 5v supplied by the full wave rec i put on the 5v PT rectifier winding and it reads about 5v, but the 5v relay starts buzzing like the contacts are intermittently going on and off very fast like a hummingbird's wings. So it's just a fast buzzing. Any idea why thats happening? i could maybe see it is the voltage is low but it's like 4.6v which has got to be in range. Maybe this coil draws more than 2A? I wouldn't think so, as it's one of those tiny relays about 1/2" long.

EDIT: tried the 6.3v tap too, also tried the cap/diode. Tried several relays and the contacts buzz on/off constantly. One didn't, but i think it;s a 12v one so it wouldn't probably latch reliably.

[daz]

I just thought to measure AC and sure enough it is showing about 1/2 the amount of AC as it shows DC ! If i read DC it shows about 5vdc and if i read AC it shows about 2.5vac. WTF? What would cause it to allow AC thru? Diodes test fine. I'm an idiot to be sure, so maybe i'm doing something wrong but i can't figure out what that might be.

[J M Fahey]

WAIT: I EXPECT you are NOT using a rectifier tube so the 5VAC winding is an UNUSED winding,floating and away from anything else.

I see somebody reading this thread and feeding a switching relay fom the rectifier winding in his JTM45 or any amp (tons around there) which DO use a tube rectifier ... so his relay coil and the switching jack, which are connected to the Outside Worls through a jack and footswitch is sitting on DEADLY 400VDC.

If at all possible, edit your post and make it very clear that you refer to an UNUSED 5VAC RECTIFIER WINDING, NO RECTIFIER TUBE.

As of chatter, you have non smoothed DC with horrendous ripple.

Add a filter cap, say 1000uF x 16 or 25V and youŽll both have real DC and a couple extra Volts, that will help your 12V relay.

[daz]

I said in the first post "since i am using a SS rectifier i figure the unused rectifier windings would be a good source". So no, it's not being used. I'll try the cap but it;s a 5v relay not 12v.

[Chuck H]

I've never wired up relays in any of my builds, so I looked up some example circuits in *oogle images (NOTE-You must open and read the actual article to be sure the circuit you're looking at works ) Anyway... Most use a smoothing cap after the rectifier and a single diode (without the cap) across the relay coil (some relays have a diode built in, so be aware of that). About half use a zener or zeners for some crude regulation. This is probably a good idea since the rectified DC will probably be greater than 5V and you don't need extra stress on any part. So the circuits getting a little more complex now.

But wait! There's more! Act now and you can also trouble with an LED indicator circuit while your at it. Requiring a bit of a peripheral circuit of it's own

It really shouldn't be that tough. A little research will reveal example circuits that already cover all the bases. Any questions about specifics can always be asked here. And when it's done you'll have something really pro that you did yourself

[daz]

I've never wired up relays in any of my builds, so I looked up some example circuits in *oogle images (NOTE-You must open and read the actual article to be sure the circuit you're looking at works ) Anyway... Most use a smoothing cap after the rectifier and a single diode (without the cap) across the relay coil (some relays have a diode built in, so be aware of that). About half use a zener or zeners for some crude regulation. This is probably a good idea since the rectified DC will probably be greater than 5V and you don't need extra stress on any part. So the circuits getting a little more complex now.

But wait! There's more! Act now and you can also trouble with an LED indicator circuit while your at it. Requiring a bit of a peripheral circuit of it's own

It really shouldn't be that tough. A little research will reveal example circuits that already cover all the bases. Any questions about specifics can always be asked here. And when it's done you'll have something really pro that you did yourself

I've usually had no problem doing this but i always used a wall wart for power. I usually just wire up a couple LED's together to keep em from burning out and the relay has never had an issue triggering reliably. Just hack work w/o knowing much of the theory but it's always worked. Today nothing worked because i only had one relay within a reasonable voltage range and either i somehow arc'd the contacts or somehow screwed it up because the contacts i needed (common and normally closed) were showing a fluctuating resistance. Didn't have time to run around looking for one with all the electronics shops 1/2 hr away. But at least i have a clean 6v now.

[Enzo]

Relays come in two flavors, AC and DC. You can usually run anay type on DC, but if you have a DC relay and power it with AC, it will buzz. Even if you rectify the 5vAC, you still need to filter it, at least a little, did you?

Re: pops and stuff. The main reason we get pops in guitar amps when relays switch is the unterminated switch contacts in the audio path, not the coil circuit.