One more relay/power supply question-resolved

[John]

First, does the polarity matter on the 5V relays Doug sells? Naturally, it was only after I have everything wired up that I see the "bottom view" marked on the relay.   I'm thinking polarity shouldn't matter, since I'm just making or breaking a circuit, basically. I do have the cathode (banded) end of the diode pointing towards the positive wire.

Second, how on earth am I getting 15Vdc off the power supply I built (following Doug's example). I've got 3.4 Vac going to each pole on the bridge rectifier (coming off heater wires) but I'm getting 15 Vdc coming off the positive at the 4700uf cap. I know something's wrong somewhere, but even after quadrupling checking everything, darned if I can find it.

Any help is appreciated! I swear, this relay thing is just kicking my butt!

[Boots Deville]

regarding the 15VDC, are your heaters elevated?

[John]

I'm using the 100R resistors to ground instead of the CT, if that's what you mean. :) And of course, after more thought I'm thinking that if polarity didn't matter on the relay, they wouldn't have bothered marking it + and -. 

[phsyconoodler]

When the relays are engaged the voltage will drop.It's like a wall wart that puts out 12v with no load and settles down to 9v when loaded.
   2 relays draw say 35ma each so it sucks that voltage down.The relays are indeed polarized.They will only activate if they are wired the right way.
  The diode orientation is right but I can't see what you've done so it's hard to say if you have it right.I'm assuming you have two relays?
When using DC voltage supplies remember they do drop when a load like a relay is added and activated.Same as your tube amp power supply.It may be 525v unloaded and settle down to 450v with a load.Same principle applies here.

[John]

Well then, I'll switch the wire and diodes around so everything is right, and perhaps use a slightly higher resistor across the 4700uf caps, since these are only 5 volt relays. I'm sure it's not critical, but I'm afraid 15 (or even 12 after engaging) might burn them out? Oh, and yes I'm using 2 relays.

Thanks for the replies!

[stratele52]

Yes 6.3 volt heater supply if you rectified with a bridge and a high value cap you can have 15 volts DC and if you have a very low current load relay . Tooooo much for a 5 volt relay it will burn. Use a half wave rectifier and if need a lower 'lytic cap value.

You can also purt a resistor on your relay coil ,  in parallele.

Where is the schematic of this mod  ?

[stingray_65]

Second, how on earth am I getting 15Vdc off the power supply I built

Is the 4700uf cap rated at 15WVDC?

Under even a small load it will drop to around its expected 5-6V

Also be sure to use a flyback diode across the coils of the relays

Ray

[John]

Ray, yes, the 4700s are the 16V Doug sells, as outlined on this page:
http://www.el34world.com/projects/relay_switch5.htm
In the photo he used 25V because that's what he had, but he now stocks the 16V for this. Otherwise, the power supply is that one exactly.

Good to know about when the relays actually engage ... you know, when I finally get them wired right  the load may very well drop that low. I do have the diodes across the relay coils, and I will even! remember to reverse them when I reverse the + and - wires.

Funny, I was going over this in my head last night, and planning pretty much this course of action - switching the wires and stuff - but it really helps me to talk things out with other, much more knowledgeable guys. I have twitches thinking about blowing something because of one stupid mis-wire.

Thanks again!

[stingray_65]

Ok what is likely happening then is the capacitors are charging fully with no load.

I freaked out building one of my first amps and fired it up after I ran all the HT stuff, recto,e caps and dropping resistors.

With a 330-0-330 PT I was measuring 450VDC every where.

the 450 was the WVDC of the caps.

As soon as I added a bleed resistor (now the current was flowing) everything dropped where it was supposed to be.

Ray

[stratele52]

You have to adjust the 180 ohms resistor for have close to 7 volts . That is write on the EL34wold project.

If you lower it the voltage will drop.

[John]

Thank you both! And after reading about the working voltage, I'll wait to tinker with that 180R till I see what the voltage does with relays engaged. Somehow I never realized that that is how they work. One more  moment! The funny thing is that in most areas I'm of average intelligence (God, I hope so!) but this stuff makes me feel like an idiot sometimes!

[John]

And, they work! Thanks for the help!!

[stratele52]

Congratulation John. Don't forget, it takes few year in school to learn electronic and many many years for have good experience.