Driving DC relays from AC

J

jrobbo

Guest
Hi all,

I have a handful of relays with a coil rated at 24V DC. Only problem
is that the source that I want to drive them from is 24V AC....

The coil current on the relay is 15mA. I was thinking of just using a
half-wave rectifier (single diode) and a 100uF cap to drive it. Will
that work, or should I use a full-wave (4 diode) rectifier instead?

Thanks in advance for any help

Regards

John



--------------
To reply via email, remove the spam block from my email address
 
Depends, if you don't mind a small delay in operating the relay then use
half wave and accept up to a half wave delay in operating the relay.
Peter

"jrobbo" <jrobboSPAMSUCKS@jrobbo.com> wrote in message
news:tosqqvohmhvse9vn649ou9eq9kd9fk62r6@4ax.com...
Hi all,

I have a handful of relays with a coil rated at 24V DC. Only problem
is that the source that I want to drive them from is 24V AC....

The coil current on the relay is 15mA. I was thinking of just using a
half-wave rectifier (single diode) and a 100uF cap to drive it. Will
that work, or should I use a full-wave (4 diode) rectifier instead?

Thanks in advance for any help

Regards

John



--------------
To reply via email, remove the spam block from my email address
Click to expand...
 
"jrobbo" <jrobboSPAMSUCKS@jrobbo.com> wrote in message
news:tosqqvohmhvse9vn649ou9eq9kd9fk62r6@4ax.com...
Hi all,

I have a handful of relays with a coil rated at 24V DC. Only problem
is that the source that I want to drive them from is 24V AC....

The coil current on the relay is 15mA. I was thinking of just using a
half-wave rectifier (single diode) and a 100uF cap to drive it. Will
that work, or should I use a full-wave (4 diode) rectifier instead?
Click to expand...

** One diode ( half wave) rectification is fine - but use the diodes
connected alternately to the AC so the DC component in the transformer does
not build up to any large amount.



.......... Phil
 
On Sun, 09 Nov 2003 09:53:58 +1100, jrobbo
<jrobboSPAMSUCKS@jrobbo.com> wrote:

Hi all,

I have a handful of relays with a coil rated at 24V DC. Only problem
is that the source that I want to drive them from is 24V AC....

The coil current on the relay is 15mA. I was thinking of just using a
half-wave rectifier (single diode) and a 100uF cap to drive it. Will
that work, or should I use a full-wave (4 diode) rectifier instead?

Thanks in advance for any help

Regards

John



--------------
To reply via email, remove the spam block from my email address
Click to expand...

experiment with both setups and see what works best. Only takes a
minute to do.

Other thing to keep in mind is that rectified 24vac is going to
produce about 34v dc (multiply the ac x 1.414 to get the DC voltage)
which might be too much voltage for your relay's coil - specially if
its left on for any length of time. An appropriate dropping resistor
would be a good idea too;.
 
"KLR" <kreed@bigpond.net.au> wrote in message
news:rkbrqvghurjd0a3oe44i88n6nk8bls0ii6@4ax.com...

Other thing to keep in mind is that rectified 24vac is going to
produce about 34v dc (multiply the ac x 1.414 to get the DC voltage)
which might be too much voltage for your relay's coil - specially if
its left on for any length of time. An appropriate dropping resistor
would be a good idea too;.
Click to expand...


** This sort of relay is typically rated for 150 % over the nominal DC
voltage - see Farnell cat. The average voltage can be reduced buy
selecting the filter electro value - using a 22uF will allow about 10 volts
p-p ripple at 15mA and 50 Hz hence 5 volts average drop.



............ Phil
 
"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fadbb6e$0$9226$afc38c87@news.optusnet.com.au...
"KLR" <kreed@bigpond.net.au> wrote in message
news:rkbrqvghurjd0a3oe44i88n6nk8bls0ii6@4ax.com...

The best approach is to use a diode in series with the coil to the AC, and a
Click to expand...
diode in parralel with the coil, cathode to positive. This will keep some
current in the coil during the "off" half cycle and control any voltage
transients that might destroy the series diode, especially when switching
it. A DC component in the supply may not be an issue if the relay current is
small compared with the supply capacity.

All the best

Ian Macmillan
 
On Sun, 09 Nov 2003 11:19:14 GMT, "Ian Macmillan"
<iandmac@bigpond.com> wrote:

"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fadbb6e$0$9226$afc38c87@news.optusnet.com.au...

"KLR" <kreed@bigpond.net.au> wrote in message
news:rkbrqvghurjd0a3oe44i88n6nk8bls0ii6@4ax.com...

The best approach is to use a diode in series with the coil to the AC, and a
diode in parralel with the coil, cathode to positive. This will keep some
current in the coil during the "off" half cycle and control any voltage
transients that might destroy the series diode, especially when switching
it. A DC component in the supply may not be an issue if the relay current is
small compared with the supply capacity.

WOuldn't the capacitor do the same as the parallel diode? my
Click to expand...
experience using relays on 50 hz half wave rectified without a cap is
that they buzz, so a cap is needed.

All the best

Ian Macmillan
Click to expand...
 
"Arpit" <DONTSPAMMEF00Lneko4@dodo.com.au> wrote in message
news:8ml3rvomht2264jp8ah9vijovab5vhtpr3@4ax.com...
On Sun, 09 Nov 2003 11:19:14 GMT, "Ian Macmillan"
iandmac@bigpond.com> wrote:


"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fadbb6e$0$9226$afc38c87@news.optusnet.com.au...

"KLR" <kreed@bigpond.net.au> wrote in message
news:rkbrqvghurjd0a3oe44i88n6nk8bls0ii6@4ax.com...

The best approach is to use a diode in series with the coil to the AC,
and a
diode in parallel with the coil, cathode to positive. This will keep some
current in the coil during the "off" half cycle and control any voltage
transients that might destroy the series diode, especially when switching
it. A DC component in the supply may not be an issue if the relay current
is
small compared with the supply capacity.

WOuldn't the capacitor do the same as the parallel diode? my
experience using relays on 50 hz half wave rectified without a cap is
that they buzz, so a cap is needed.
Click to expand...


** Correct - the extra diode in parallel is not enough to stop severe
relay oscillation at 50 Hz.

A 10 uF or greater cap will however do both jobs.



.............. Phil
 
Phil Allison wrote:

"jrobbo" <jrobboSPAMSUCKS@jrobbo.com> wrote in message
news:tosqqvohmhvse9vn649ou9eq9kd9fk62r6@4ax.com...


Hi all,

I have a handful of relays with a coil rated at 24V DC. Only problem
is that the source that I want to drive them from is 24V AC....

The coil current on the relay is 15mA. I was thinking of just using a
half-wave rectifier (single diode) and a 100uF cap to drive it. Will
that work, or should I use a full-wave (4 diode) rectifier instead?




** One diode ( half wave) rectification is fine - but use the diodes
connected alternately to the AC so the DC component in the transformer does
not build up to any large amount.



......... Phil
Click to expand...
DC component in a transformer? UH?
Dave

 
Phil Allison wrote:

"KLR" <kreed@bigpond.net.au> wrote in message
news:rkbrqvghurjd0a3oe44i88n6nk8bls0ii6@4ax.com...



Other thing to keep in mind is that rectified 24vac is going to
produce about 34v dc (multiply the ac x 1.414 to get the DC voltage)
which might be too much voltage for your relay's coil - specially if
its left on for any length of time. An appropriate dropping resistor
would be a good idea too;.





** This sort of relay is typically rated for 150 % over the nominal DC
voltage - see Farnell cat. The average voltage can be reduced buy
selecting the filter electro value - using a 22uF will allow about 10 volts
p-p ripple at 15mA and 50 Hz hence 5 volts average drop.



........... Phil

Adding a Cap changes the Average Voltage...UH?

Dave
Click to expand...

 
"D.Castles" <d.castles@latrobe.edu.au> wrote in message news:3FB2D642.1010707@latrobe.edu.au...


Phil Allison wrote:

"jrobbo" <jrobboSPAMSUCKS@jrobbo.com> wrote in message
news:tosqqvohmhvse9vn649ou9eq9kd9fk62r6@4ax.com...

Hi all,

I have a handful of relays with a coil rated at 24V DC. Only problem
is that the source that I want to drive them from is 24V AC....

The coil current on the relay is 15mA. I was thinking of just using a
half-wave rectifier (single diode) and a 100uF cap to drive it. Will
that work, or should I use a full-wave (4 diode) rectifier instead?



** One diode ( half wave) rectification is fine - but use the diodes
connected alternately to the AC so the DC component in the transformer does
not build up to any large amount.



.......... Phil

DC component in a transformer? UH?


** Transformers have always been a big problem for Dave's dinosaur brain.





............ Phil
 
Phil Allison wrote:

"KLR" <kreed@bigpond.net.au> wrote in message
news:rkbrqvghurjd0a3oe44i88n6nk8bls0ii6@4ax.com...



Other thing to keep in mind is that rectified 24vac is going to
produce about 34v dc (multiply the ac x 1.414 to get the DC voltage)
which might be too much voltage for your relay's coil - specially if
its left on for any length of time. An appropriate dropping resistor
would be a good idea too;.





** This sort of relay is typically rated for 150 % over the nominal DC
voltage - see Farnell cat. The average voltage can be reduced buy
selecting the filter electro value - using a 22uF will allow about 10 volts
p-p ripple at 15mA and 50 Hz hence 5 volts average drop.



........... Phil







What about the average voltage one Phil? (see below)
Click to expand...
I can't wait for your explanation and next insult. I love them, they
make me stronger.
Dave
 
"D.Castles" <d.castles@latrobe.edu.au> wrote in message news:3FB2E783.6000206@latrobe.edu.au...



What about the average voltage one Phil? (see below)
I can't wait for your explanation and next insult. I love them, they make me stronger.
Dave



** What's to explain ??

Only a complete moron would even ask the question.


BTW STOP POSTING IN FUCKING HTML !!!!!!!!!


............ Phil
 
** One diode ( half wave) rectification is fine - but use the diodes
connected alternately to the AC so the DC component in the transformer does
not build up to any large amount.



......... Phil
Click to expand...
I'm not sure what you had in mind here Phil, were you thinking of a
CT with a diode to each end?
 
"Michael" <michael@clift.com.au> wrote in message
news:ec96e13a.0311121910.79fb8ea7@posting.google.com...
** One diode ( half wave) rectification is fine - but use the diodes
connected alternately to the AC so the DC component in the transformer
does
not build up to any large amount.



......... Phil

I'm not sure what you had in mind here Phil, were you thinking of a
CT with a diode to each end?
Click to expand...

** No.

My post is VERY clear - do not have all the diodes rectifying the
same. Alternate them.



......... Phil
 
Phil Allison wrote:

"D.Castles" <d.castles@latrobe.edu.au
mailto:d.castles@latrobe.edu.au>> wrote in message
news:3FB2E783.6000206@latrobe.edu.au...



What about the average voltage one Phil? (see below)
I can't wait for your explanation and next insult. I love them,
they make me stronger.
Dave



** What's to explain ??

Only a complete moron would even ask the question.


BTW STOP POSTING IN FUCKING HTML !!!!!!!!!


............ Phil

Do you have an anger problem Phil?.
Click to expand...
I believe there are anger management councillers that may help.
As for average voltage.... I re-ask my question because I am possibly,
as you say, a complete moron and don't understand.
If you half wave rectify a sine wave then how is it that a capacitor
lowers the average voltage of that waveform?
This is a genuine question Phil, please don't get upset.
As for posting HTML my Netscape tells me that this is the preferred way
of posting to this newsgroup. Is this not correct? Would you be happier
with plain text or that I don't post at all?
Thanks Phil for your kind attention to these matters
Dave
 
"D.Castles" <d.castles@latrobe.edu.au> wrote in message news:<3FB30B8E.6020101@latrobe.edu.au>...
Phil Allison wrote:



"D.Castles" <d.castles@latrobe.edu.au
mailto:d.castles@latrobe.edu.au>> wrote in message
news:3FB2E783.6000206@latrobe.edu.au...



What about the average voltage one Phil? (see below)
I can't wait for your explanation and next insult. I love them,
they make me stronger.
Dave



** What's to explain ??

Only a complete moron would even ask the question.


BTW STOP POSTING IN FUCKING HTML !!!!!!!!!


............ Phil

Do you have an anger problem Phil?.
I believe there are anger management councillers that may help.
As for average voltage.... I re-ask my question because I am possibly,
as you say, a complete moron and don't understand.
If you half wave rectify a sine wave then how is it that a capacitor
lowers the average voltage of that waveform?
This is a genuine question Phil, please don't get upset.
As for posting HTML my Netscape tells me that this is the preferred way
of posting to this newsgroup. Is this not correct? Would you be happier
with plain text or that I don't post at all?
Thanks Phil for your kind attention to these matters
Dave

--
Click to expand...
Dave, by selecting a lower capacitance, the voltage across the cap
discharges more between cycles. Hence the average voltage across the
relay coil is lower. What is your argument?
 
"Michael" <michael@clift.com.au>
"D.Castles" <d.castles@latrobe.edu.au

Dave, by selecting a lower capacitance, the voltage across the cap
discharges more between cycles. Hence the average voltage across the
relay coil is lower. What is your argument?
Click to expand...

** Dave is a highly qualified mental cripple - see:

http://www.latrobe.edu.au/ee/people/profiles/Castles.html


He gets his jollies by baiting naive Christians on their newsgroups -
and pulling the wings off flies.




............ Phil
 
On Thu, 13 Nov 2003 04:39:47 GMT, "D.Castles"
<d.castles@latrobe.edu.au> wrote:

As for posting HTML my Netscape tells me that this is the preferred way of
posting to this newsgroup. Is this not correct?
Click to expand...
Dunno, I'm braindead but I'm considerate enough to others who have
text based readers to NOT post in html.
As for running relays from AC, I'd use a bridge rectifier with a
decent sized electro taking note of the pull in and hold in voltages,
maybe even use a variable supply to test the relays I want to power so
I could choose a suitable voltage transformer but I'm just a mechanic,
not a farkin electronic genius. Ask Phil.

Al

2003 insult page awaits your contribution
http://kwakakid.cjb.net/insult.html
 
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