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Old 22nd May 2003, 03:06 PM   #11
PMiczek is offline PMiczek  United States
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This looks like a very good relay, gold and silver contact, low power coil (200mW). You could probably drive about 12-15 of these with a 1A 12V regulator and this transformer before you need a heatsink, but I find that if you have room for it, using heatsinks in d-i-y is always a good thing. Plan on 16-20mA per relay, because they will draw more than the minimum "detection" of "pick-up" current when on.

The amount of capacitance will determine how much ripple is on the unregulated side of the supply (this is the input of the 12V reg.) For the low power you probably need (assuming 3-4 relay coils at 200mW each), one 2200uF (2.2mF) cap is sufficient, although I tend to be conservative with 60/120Hz noise, so I would put two anyway, you can use cheap caps here, and add a small ceramic cap, or even better a metal film cap if you have one lying around. This will help reduce the higher frequency spikes which you can get with some rectifiers. (Your relays will not care about the noise, but your audio circuit might).

You may also need at least a small cap on the output of the regulator, and depending on what you use to drive the relays, a small diode across the coil of the relay, also to reduce spikes when the relay opens.

(It all depends on how conservative you want to be with heat, noise and filtering, and ground connections... )

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Old 22nd May 2003, 03:21 PM   #12
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If there is anything in this world that doesn't require a regulated supply to operate, certainly a relay coil is one of them. Put a diode in series with the winding, and perhaps a capacitor to ground after the diode.
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Old 22nd May 2003, 03:28 PM   #13
EC8010 is offline EC8010  United Kingdom
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Default Fap!

Quote:
Originally posted by jbateman
If there is anything in this world that doesn't require a regulated supply to operate, certainly a relay coil is one of them. Put a diode in series with the winding, and perhaps a capacitor to ground after the diode.
Absolutely. I think you mean a reverse biassed diode across the winding (to prevent the back EMF blowing up the driver transistor).
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Old 22nd May 2003, 03:40 PM   #14
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Default Re: Fap!

Quote:
Originally posted by EC8010


Absolutely. I think you mean a reverse biassed diode across the winding (to prevent the back EMF blowing up the driver transistor).

No, I mean use a diode to half-wave rectify the AC to approx 14v, with a filter cap to get rid of some of the ripple. Screw the regulator.

But, yes, an extra diode across the coil, as you recommend, would be a good idea.
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Old 22nd May 2003, 04:27 PM   #15
dhaen is offline dhaen  Europe
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Default My experience and use...

Hi,

I find a 9 volt winding is best. Bridge rectified and loaded it gives about 11 volts. (Almost) perfect for 12 volt relays.
If however, I'm passing low level signals through the relays, I'm careful that noise is filtered from the supply. Noise can intrude by coupling within the relay, and by PCB traces running parallel.
I wouldn't go so far as regulating the supply specially.

NB Relays fed with inadequately smoothed DC sometimes emit a buzzing noise.

Cheers,
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Old 22nd May 2003, 05:28 PM   #16
PMiczek is offline PMiczek  United States
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I did not mean to suggest that a relay coil REQUIRES a regulated 12V supply, obviously, at a semi-regulated 18-20 volts you would not exceed the relay coil rating.

Your ears might like it better if you do not run a couple volts of 120Hz ripple with diode switching noise on the same circuit board as switched audio signals.

With any luck that will not happen, but a 7800-series regulator and a couple caps seems cheap enough compared to the effort that goes into a typical home audio project.
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Old 23rd May 2003, 09:35 AM   #17
strulon is offline strulon  France
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thanks for all your replys, i can see there are different ways to do this

i think i am going to follow PMiczek advice, i feel more confortable with it

so the scheme is:

bridge rectifier- 2*2.2mF cheap caps - 1 metal film cap - regulator with heatsink- cap - and one diode (1N4007) across the coil of each relay (even if i have three of them on at the same time)

my last questions would be to know how much capacitance for the metal film cap and also for the cap after the regulator, i guess at least 2.2mF for the last one but for the metal film cap i am not sure

after this, i think everything will be ok and one more time, i wish to thank all of you for your help

bye

fred
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Old 23rd May 2003, 01:14 PM   #18
PMiczek is offline PMiczek  United States
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Default cap size

metal film cap: anything between 0.1 and 0.47uF will be fine
output: between 100uF and 2200uF

(I think you do not need a lot for a relay board, just so when the relays turn on, the inrush does not make a spike)

Again, this is pretty standard for a 12V linear supply, and quite conservative for your use. If you like I can send you a circuit diagram this weekend, but I don't have time to find one right now.
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Old 23rd May 2003, 02:17 PM   #19
strulon is offline strulon  France
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no no, don t send me a circuit diagram, i think everything is ok now, thanks

i ll try to post my circuit diagram, when it's finish, and a pic of the preamp too

bye

fred
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Old 23rd May 2003, 02:54 PM   #20
PMiczek is offline PMiczek  United States
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Great! Look forward to seeing a pic when it is finished.
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