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external relay driver

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Assuming you are driving a DC relay coil, remember to add a clamp diode to protect the drive transistor from the inductive kick at turn off. This also limits the radiated noise that can upset the rest of your circuit. If you drive an external relay with a small internal relay, the spike can be very large across the internal relay's contacts.
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If you drive an AC relay coil, the inductive kick will depend on where in the AC cycle you open the circuit. If opened at the peak current, it is no different than maximum DC.
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Rick Sparber

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My Web Site:
rgsparber.fifthprime.com
 

Hi all,

I want to make a board that will drive an external relay.

Problem is that I don't know what the relay will be.

I'm thinking of putting a mini relay on the board so the external
relay is isolated.

The alternate is to use either a darlington or MOSFET.

My question is of voltages.

One thing I am wondering about is the coil voltages to drive relays.
I seem to remember someone once said that you can drive a relay coil
with either AC or DC regardless of how it is labeled, but that you
have to ... this is where my memory fades... half or double the
voltage for... AC relay on DC ??.....

Can anyone shed some light ?


Dave
Manoj Cherukat
 

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hi dave,
One big pitfall in using reed relays is not using them with the desired voltage.. believe me.. i've had hell in operating a 12 V rated relay on 9 V . dc relays .. inthis case.. i haven't worked with AC relays.. the relays in this case function on 9V.. but some times.. the reed just about does not make the contact when energised.. whereas it may appear externally that the metallic strip has moved.. any how , it is better to operate them at rated voltage
Bye
Manoj
?

----- Original Message -----
From: Dave Mucha
Sent: Monday, March 01, 2004 6:55 PM
Subject: [Electronics_101] external relay driver

Hi all,

I want to make a board that will drive an external relay.

Problem is that I don't know what the relay will be.

I'm thinking of putting a mini relay on the board so the external
relay is isolated.

The alternate is to use either a darlington or MOSFET.

My question is of voltages.

One thing I am wondering about is the coil voltages to drive relays.
I seem to remember someone once said that you can drive a relay coil
with either AC or DC regardless of how it is labeled, but that you
have to ... this is where my memory fades...? half or double the
voltage for... AC relay on DC ??.....

Can anyone shed some light ?


Dave
Curtis Sakima
 

开云体育

The only experience I've have with reeds .... is them getting stuck!!?? Tap tap tap them with my finger(nails).?? Then they'd release.?? Finally got frustrated and gave up.

Curtis
?
This spring season, dazzle your special someone with flowers!
?

?

----- Original Message -----
Sent: Monday, March 01, 2004 7:56 AM
Subject: Re: [Electronics_101] external relay driver

hi dave,
One big pitfall in using reed relays is not using them with the desired voltage.. believe me.. i've had hell in operating a 12 V rated relay on 9 V . dc relays .. inthis case.. i haven't worked with AC relays.. the relays in this case function on 9V.. but some times.. the reed just about does not make the contact when energised.. whereas it may appear externally that the metallic strip has moved.. any how , it is better to operate them at rated voltage
Bye
Manoj
srinivas rao
 

please use the high quality panasonic products or the jumbo products to avoid such experience .even i got the same problems in my college labs

Curtis Sakima wrote:
The only experience I've have with reeds .... is them getting stuck!!?? Tap tap tap them with my finger(nails).?? Then they'd release.?? Finally got frustrated and gave up.

Curtis
?
This spring season, dazzle your special someone with flowers!
?

?
----- Original Message -----
Sent: Monday, March 01, 2004 7:56 AM
Subject: Re: [Electronics_101] external relay driver

hi dave,
One big pitfall in using reed relays is not using them with the desired voltage.. believe me.. i've had hell in operating a 12 V rated relay on 9 V . dc relays .. inthis case.. i haven't worked with AC relays.. the relays in this case function on 9V.. but some times.. the reed just about does not make the contact when energised.. whereas it may appear externally that the metallic strip has moved.. any how , it is better to operate them at rated voltage
Bye
Manoj

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