Power relay from rectifier winding?

[daz]

Dammit, just hit a mouse button accidentally and lost a long post. Anyways, i'll make this short. I don't mean to dismiss you guys and your ideas, as you are all much more knowledgeable than me. But i had to try what i have done in the past successfully and it worked. I know probably not the right way to do it but i paralleled 4 LED's and put them in series with the coil. The LED's stayed cool for approx 5 minutes i kept it on and the coil triggers both audibly and the contacts do close and the coil now sees 7vdc. I don't think the wart will meltdown because like i said i have done this many times and used it like this for years. The only reason i asked in the first place was I initially was using the amp's unused winding and had never done it that way b4. But now that i'm going external with a wall wart i just figured since it;s worked like this b4 i should work now and it seems fine. Also note it is only powered for short durations, mostly solos. So normally it;s off.

By the way, i tried a 47 ohm R in seies with the coil but it only dropped a fraction of a volt. Doesn't matter now that i've got it working but i found that odd. Definately a 47R (Y/P/B) and the coil does measure 100 ohms and is a 5v relay.

[SoulFetish]

Dammit, just hit a mouse button accidentally and lost a long post.

That'll break your heart

[daz]

That'll break your heart

I hate it, happens all the time. Some forums have auto save tho so you don't lose it unless you close the browser, and even then i think if younhave cookies set for the site it's there when you go back.

[olddawg]

As far as the OP goes. I've been reading this thread. It don't see an issue running a 5vdc relay off of a 5vac tap. A piece of perf board with a small bridge rectifier, a 1000uf cap, and a 5v TIP regulator would probably do the trick. If you want an LED indicator in your foot pedal just use a DPDT switch to provide a different circuit path for the LED. Or not. Many times I have just wired an LED and a resistor across the SPST switch contact. It doesn't draw enough current to activate the relay when the switch is open. The LED will light when the relay is NOT engage with the footswitch open.

[Dave H]

Dammit, just hit a mouse button accidentally and lost a long post.

If you are writing War and Peace hit <Ctrl> A then <Ctrl> C from time to time to copy it to the clipboard, then when the forum takes a dump you can hit <Ctrl> V to paste it back in.

[Dave H]

By the way, i tried a 47 ohm R in seies with the coil but it only dropped a fraction of a volt. Doesn't matter now that i've got it working but i found that odd. Definately a 47R (Y/P/B) and the coil does measure 100 ohms and is a 5v relay.

Well there is definitely something wrong there. If the resistor is half the resistance of the coil it must drop half the voltage of the coil not a fraction of a volt. Did you measure the resistor?

[Steve A.]

Dammit, just hit a mouse button accidentally and lost a long post.

That'll break your heart

After starting a reply here if it looks like it'll be longer than a few sentences I'll copy and paste what I have into Evernote (a multi-platform app) and finish it there. Windows users might paste it into Notepad or Notepad+.

https://evernote.com/

Another tip: you can copy your text to the Clipboard periodically as you compose a reply here... especially right before you save your post just in case the BBS software screws up.

BTW we do have auto-save here but I've never figured out how it works...

Steve Ahola

[daz]

Well there is definitely something wrong there. If the resistor is half the resistance of the coil it must drop half the voltage of the coil not a fraction of a volt. Did you measure the resistor?

Yeah. I am 100% positive that 1-the resistor was 47 ohms, 2-the coil is 100 ohms. Not sure what i couldn't done wrong but in any case no matter.

[SoulFetish]

Yeah. I am 100% positive that 1-the resistor was 47 ohms, 2-the coil is 100 ohms. Not sure what i couldn't done wrong but in any case no matter.

A divider of 47 ohms and 100 ohms gives you an output voltage of 6.12V (on the coil).

[daz]

A divider of 47 ohms and 100 ohms gives you an output voltage of 6.12V (on the coil).

I'm not saying he's wrong. i'm just saying what i saw. Maybe theres something i'm missing but like i said, no matter anymore.

[Chuck H]

Was that with the coils energized or off switch? If the coils aren't switched in they cant shunt.

[daz]

Was that with the coils energized or off switch? If the coils aren't switched in they cant shunt.

With the 9v applied of course. It read about the same as it did w/o the resistor. Like i said, maybe i spaced but again it doesn't matter anymore.

[Steve A.]

By the way, i tried a 47 ohm R in seies with the coil but it only dropped a fraction of a volt. Doesn't matter now that i've got it working but i found that odd. Definately a 47R (Y/P/B) and the coil does measure 100 ohms and is a 5v relay.

I will the trust the readings on my DMM more than predictions based on a mathematical formula and also more than my eyesight in reading color codes (I check all resistors I use with a DMM just to be sure.)

I will go with empirical results every day of the week and if 4 LEDs and a wall wart are what work for you, go for it! So did you already post the specs of your wall wart?

BTW what can get tricky about powering a relay from a DC voltage as supplied by the drawing I posted is that the ( - ) terminal is not at chassis ground so if you are going to use a Switchcraft-style 1/4" jack going to the footswitch you must use insulating bushings.

Also in getting one to three relays to work properly with an unregulated voltage supply I had to fine-tune it using fractional ohm resistors.

Just some tips in case you decide to try for an internally powered relay some time in the future (it really is a more elegant solution) it's probably better to use voltage-doubling rectification with a 5V voltage regulator than screw around with dropping resistors (or diodes) to bring the voltage down to an acceptable level for multiple relays (why just stop at one?)

Steve "Damn the theory, where's my DMM?" Ahola

[Rob's Radio-Active]

Steve "Damn the theory, where's my DMM?" Ahola

The calculator is for the first iteration of any new circuit. Gotta tweak and debug almost all of them once built or breadboarded.
Actual testing and measurement is as much a part of engineering as calculation.
Rob

[daz]

Was that with the coils energized or off switch? If the coils aren't switched in they cant shunt.

Energized of course. Wouldn't get ANY voltage otherwise and i didn't say i got a fraction of a volt, what i said was it only LOST a fraction. So instead of lets say 6.5v it would have been 6.3.

BTW what can get tricky about powering a relay from a DC voltage as supplied by the drawing I posted is that the ( - ) terminal is not at chassis ground so if you are going to use a Switchcraft-style 1/4" jack going to the footswitch you must use insulating bushings.

Already did that. Made the power jack isolated by using heat shrink on the threads and made plastic washers out of a guitar pick.