RG REMOTE BYPASS.- Relay Q

[QSQCaito]

Ok, as i didn't wanted to hi-jack other threads, i started my own


I was planning to build these:

http://www.geofex.com/Article_Folders/rmtswtch/rmtsw3.gif

But the only good relay, low signal i could found was the following: EA2 4.5

The questions are the following: Can that circuit be used to use a 4.5V relay, if so: i should just add a ressistance before the coil to frop voltage down to 4.5V, or should i change the whole set?

I was told TQ2-12v relay was suitable, but i'd have to change them over time. And i would prefer the EA2 4.5 because it's for low signal, has contacts that will work much better.
Which relay should i use?

Bonus question: Should i connect somehow(via resistor) the ground of this circuit with the signal ground.. or i keep the isolated and lets see what happens?


Thanks a lot lot lot from advanced

bye bye

hope this helps to someone else

dac

[oldrocker]

Radio Shack sells these 9 volt SPDT relays and they might be in stock.  You can use the Geo circuit you posted and just power both coils at the same time.  That's if you have the room for two relays.  The good thing is they are 9 volt.

Radio Shack 9 volt relay
http://www.logmonster.com/images/full/?pic=pRS1C_2110707w345_1155462600-422-13146.jpg

This is how I used them.
http://www.logmonster.com/images/full/?pic=Passthrough_1155523877-422-13153.jpg

[QSQCaito]

I live in Argentina  no radio shack, nor mauser here

That two relays posted, the EA2 4.5 and TQ2-12v, are the best ones i could find


Thanks a lot for your help anyway 

Bye bye

dac

[QSQCaito]

bump, any clues?
thank a lot!
bye bye

[cockaroacha]

Just copy an opamp power supply, like the power portion of the tubescreamer. Since the opamp requires a Vr supply (generally 1/2 the main voltage), a 9v main supply will get you a 4.5v Vr supply that you need for the relays.

[QSQCaito]

Thanks! Like that i would get 4.5 volt.
I maybe mis-expressed myself. The problem is the following, that circuit was designed to work with a 12volt relay. If im abou to use a 4.5v relay: Should i add a resistance(or trimpot, config'd as a variable resistor) near the relay, to drop voltage to 4.5volt, or should i change all resistance values to make it work for 4.5v??

thanks a lot

bye bye

dac

[QSQCaito]

shakata bump... really excuse me for being so unpatient.. got one tiniy problem.. i'll go buy parts monday.. and won't probably buy for a month or twoo 

bye

sry

dac

[oldrocker]

Two 22k resistors, one from + volts one from ground, where the two resistors meet would get you 4.5 volts with a 9 volt supply.  You might want to put a 10uf cap from the center of the two resistors to ground.

[QSQCaito]

Thanks a lot, I arrived to this:(image is copyright of rg keen, i added R4 and R5)


I couldn't understand where would the cap go.


Thanks a lot!

Bye bye

DAC!

[R.G.]

The power side of a relay is computed as though it's a resistor. That's because it is. Each relay tells you what the coil voltage and coil resistance are. From those two numbers, you know the current the relay is supposed to work on  by Ohm's law - I = Vcoil/Rcoil.

A typical 12V relay has a 1000 ohm (roughly) coil resistance and so will conduct 12 ma when connected to its designed votlage of 12V.

A typical 5V relay has the same coil power, so it has a lower resistance and a higher current: 20- 30 ma is normal for 5V mini relays. So these relays have lower coil voltages, usually in the range of 5v/20ma = 250 ohms to 5v/30ma = 167 ohms. These values are examples. Look at the data sheet for your relay.

A 5V relay working from 12V directly will burn up because it only has maybe 200 ohms of resistance and that lets 12V/200ohms = 60ma of current flow, and that's too much for the coil. It will overheat. What you need to have is some additional resistance to prevent so much current from flowing. Your R4 is in the right place in the picture you drew. Take R5 out of there. The resistor voltage divider is only good for low voltage things.

So for example if you have a 12V supply and a 5V relay with a 220ohm coil, you can make this work by
1. figuring out what current the relay needs. This is 5V/220 = 22.7ma.
2. Figuring out what resistance lets 22.7ma flow from 12V. This is 12V/0.0227 = 528.6 ohms.
3. Subtracting out the 220 ohms already in the relay, and making the additional resistance be 528.6 - 220 = 308 ohms.
4. Picking the nearest standard value. For 308 ohms, this is 300 ohms in a well stocked store, or 270 or 330 in a poorly stocked store.

My exact numbers are of course picked out of thin air; they are representative numbers, but it is unlikely that they will exactly match your relays.

[QSQCaito]

First of all, thanks a lot lot RG, this is like the fourth time you save me

The EA2 4.5:

4.5Volt
145 Ohms coil resistance.

1. figuring out what current the relay needs. This is 5V/220 = 22.7ma.

4.5/145=31.03ma

2. Figuring out what resistance lets 22.7ma flow from 12V. This is 12V/0.0227 = 528.6 ohms.

12/0.03103=386.72 Ohms.

3. Subtracting out the 220 ohms already in the relay, and making the additional resistance be 528.6 - 220 = 308 ohms.

386.72-145=241.72 Ohms

4. Picking the nearest standard value. For 308 ohms, this is 300 ohms in a well stocked store, or 270 or 330 in a poorly stocked store.

Not the least idea maybe a 250ohm .. or two 500 in parallel.. whatever i found closest.


Hope im ok

bye bye

thanks a lot once again

dac!


EDIT: PS: forgot to add, this would be the value for R4 right?? is it necessary to add a cap between + and -, as suggested by oldrocker..

do you think doing this will have any secondary effects?

[R.G.]

Good calculations. You were paying attention! 

Not the least idea Tongue maybe a 250ohm .. or two 500 in parallel.. whatever i found closest.

Actually, 240 ohms is a standard value. How much power?

P = I^2*R = (0.031)*(0.031)*240 = 0.23064 That's almost a quarter watt, and if you use a 1/4W resistor, it will be at over 100C to actually dissipate the full rating.

You need at least a 1/2W resistor there, or two 1/4W resistors.

If you use 1/4W, you can use two 510 ohm (standard value) in parallel or two 120 ohm in series.

You need a big capacitor from +V to ground. The extra resistor for dropping the voltage to the coil goes where R4 is. Actually, you could put it where R5 is, or if you use two 120 ohms resistors, you could use one for R4 and one for R5. It doesn't matter as long as there is 240 ohms of resistance somewhere in series with the coil.

[QSQCaito]

Got it with the resistors, i need total of 240ohms and total of at least 1/2watt.

You need a big capacitor from +V to ground.

Any limit with size?
I've got plenty of 2200uF caps that my dad desoldered out of his Marantz, for upgrades..
this cap has to be electrolitic, right??
any value to start with??
The cap, Between +V and ground, as you say, but: would it be wrong if i put it between the two leads of the coil, that would +V and.. -of coil(don't know how to call that)?

Thanks a lot;)

bye bye

DAC

[R.G.]

The 2200's are fine, but between your +12V and ground, not across the relay coil. 47uF or 100uF are good starters.

It would be wrong to put it across the relay coil. It's there to provide a ready reservoir of charge for when the relay coil driver needs it. If it's directly across the relay coil, turning on the relay driver will be very hard on the relay driver.

[QSQCaito]

Got it 
If we put it across the coil, the cap would suck up all the power, and until it charges it wouldnt activate. And when turned off, it would also take its time, becuase it needs to be discharged.

It's keeping energy to "filter" to ensure we always have the 4.5v.. nor les.. or something like that

bye bye

thanks a lot lot

dac

Edit: Final result pic