Relay Switch-Not switching

[chunkitup]

Hello All,
One of many new builds for me and the first to incorporate relay switching. Problem is it isnt switching. I have attached a scheme.
I am using the heater taps (6.3vac) and I kept the circuit complete to itself which means I havent ran ground from this circuit to the main star point. If you see a problem please let me know. The relay part no. is:OVR-SH-205L

[Don Moose]

Bearing in mind that it's usually something simple - are you positive you have the diode the right way around?

Lessee -
(5.5V - 2.8V)/100 ohms - (about 5mA through the 1k) is about 27mA - not enough to operate a lot of relays, but 2.8V is awful high for even a cheap rectifier diode's Vf.

Things to look at -
Solder joints from Vrelay to coil, coil to switch and switch to RelayReturn.
Switch's resistance when closed.
Relay's DC resistance through the coil.
Relay's specified coil 'pickup' current.
Relay's specified coil voltage.

You may wind up with 2 diodes in series in each leg of your bridge and losing the 100R/1k divider. A bigger cap might not be a bad idea.

Hope this helps!

[chunkitup]

Bearing in mind that it's usually something simple - are you positive you have the diode the right way around?

Lessee -
(5.5V - 2.8V)/100 ohms - (about 5mA through the 1k) is about 27mA - not enough to operate a lot of relays, but 2.8V is awful high for even a cheap rectifier diode's Vf.

Things to look at -
Solder joints from Vrelay to coil, coil to switch and switch to RelayReturn.
Switch's resistance when closed.
Relay's DC resistance through the coil.
Relay's specified coil 'pickup' current.
Relay's specified coil voltage.

You may wind up with 2 diodes in series in each leg of your bridge and losing the 100R/1k divider. A bigger cap might not be a bad idea.

Hope this helps!

Yep, the diode is correct and reads .5v. I checked all the solder joints and they are rock solid. The coils resistance is 160ohms. The resistance when switch is closed is .4ohm. The coil voltage is 5vdc specified. The pickup voltage is 70% of the specified voltage, so .7x5vdc=3.5v. I couldnt find any info on the pickup current. I am leaning towards taking out the voltage divider and just adding a 50ohm1w or under resistor in series with the cap. Do you think this would be a good solution?

[defaced]

On your schem you list the switch closed voltage at 2.8v which is below the minimum pickup voltage. Your relay cares about the voltage under load, not the open circuit voltage. With the voltage divider and the coil you are drawing too much current which is causing the voltage to sag. Remove the voltage divider and record the voltage with the switch closed. If it's out of spec, then use a pot to tune a voltage divider that will work with this circuit, then replace that with resistors.

Because a relay coil is just a coil of wire, you can find the pickup current by using ohms law with the the coil resistance and pickup voltage as your inputs.

[chunkitup]

I just thought that the voltage dropped too much when switched in but I realize that the voltage divider is not set up right. Thanks for the replies.

[loudthud]

The 100 ohm in after the bridge rectifier is too high. 10 ohms will work much better. 4700uF is also way more than needed. 470uF will provide plenty of filtering.

[chunkitup]

Now back to this relay. It is still not switching. Instead of 100 and 470 ohm resistors I now have 10 and 470 ohm resistors. The voltage out of the bridge is 6.59v and the voltage across the 470/cap/coil when the switch is open is 6.45v and when the switch is closed is 5.43vdc. The coil has a resistance of 165ohms. The current thru the coil then would be 32.9mA and the power is 178mW. The relay part no. is ovr-sh-205l. I must be missing something. got guidance?

[Twist]

I've used that circuit dozens of times except you don't need the 1K resistor. The resistance of the coil will complete the voltage divider network. Do as Loudthud suggested. Swap out the values where you have the 100 ohm resistor till you have 5 volts (assuming this is a 5 volt relay) across the relay coil with the cicuit engaged. It doesn't matter what voltage you have when the circuit is disengaged. Be sure and not share that ground with the chassis ground.

[Enzo]

In the same vein I have to ask, why have the 1k or 470 or any other resistor there at all?

[chunkitup]

Ok, gone is the 1k and I now have 20ohms which gives me 5.14v across the relay but NO switching. Also, now I am getting the loud pop when switching the relay in and out. The flyback diode is in correct. This circuit is completely seperate from the rest of the amp except for what is being switched in and out. I have taken out the relay which has the socket soldered into turrets and jumpered the channel(normally open) I cant get to and that channel is quiet and sounds great.

[Don Moose]

The pops you're getting are probably from DC building up on the open switched contact. You do need to make sure there's a DC path to GND from NO and NC (and COM if convenient) on each pole - a big resistor like 2M2 or 3M3 will usually be enough to give you the pop reduction without tone suck.

Look at your schematic and see if you are DC coupled or AC coupled into or out of the relay. If AC coupled, you need the resistors.

You have:
165ohms + 20 = 185ohms

5.14v/185ohms = 27.7mA

Relay wants:
5V/165ohms = 30.3mA (magnetic fields are about current, not voltage)

That missing 3mA is 10% of what the relay wants ... just sayin'

(5.14V/30.3mA) - 165ohms = 4.65 ohms - that's less than 5% of 165 ohms.
I'd say you need to just try jumpering across that series R - at least as a test.

Hope this helps!

[defaced]

The relay coil has a tolerance the size of a swimming pool, it's -70%/+200% of the rated coil voltage. Convert that into current and you've still got a huge target to hit. Don't use a micrometer to measure framing lumber.

If the relay coil isn't open, then you should be in business because you're within the tolerance of the coil. I'd personally remove the 20 ohm resistor because it's not gaining you anything but a higher parts count.

Does the relay switch if you wire a 9v battery across the coil?

[chunkitup]

I took out the 20ohms and the same result.....BUT, I thought maybe the switch was bad so I desoldered the leads to the switch and just used a jumper and when I turned on the mains I heard the relay click, like it was switching. So with the circuit closed I played thru and it sounded like both channels were present with lots of noise and volume. But if I take the relay out and just jumper the connections (either clean or OD) there is no bleedover, they are totally seperate. Perhaps the relay is the problem. The relay is about 20 years old. I am perplexed. I really want this to work and I am getting frustrated.

[Don Moose]

So the good news is that the switch was bad(ish) and the relay switches.

Did you try checking out the contacts for continuity where you want it (relay relaxed and energized)?

--- had an interesting conversation with a vendor yesterday (my day job is as an EE for a sign company). He used to rep Omron, and got to go on a factory tour in Japan. The entire production line was staffed by physically challenged people - paraplegics, quads (this guy used a mouth-held stick to push contact assemblies into armatures) and so forth. Because of that, I'm thinking of specifying Omron products henceforth.

[chunkitup]

I did check the continuity both relaxed and energized. When relaxed there is continuity between the poles for that channel. When energized there is NO continuity between poles for either channel. It is like the switch is stuck in the middle. Although the signal does get thru but sounds really loud and lots of noise.