paralleling relay coils

[[email protected]]

I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.

-bhavj

 

[Uwe Hercksen]

I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.

Hello,

the current through one coil is 40 mA, the five coils take 200 mA. A
1N400x is good for 1 A. If these five relays are not far away from each
other, only diode will do in my opinion. The current flowing through the
diode should not be much larger than the current flowing through all
coils together.

Bye

 

[[email protected]]

[email protected] schrieb:





Hello,



the current through one coil is 40 mA, the five coils take 200 mA. A

1N400x is good for 1 A. If these five relays are not far away from each

other, only diode will do in my opinion. The current flowing through the

diode should not be much larger than the current flowing through all

coils together.



Bye

The relays stacked together and trace length is approx 70 mm from 1st relay coil to the 5th relay coil. So, do you think it would be a better option to place the diode across the coil of the middle (3rd) relay?

 

[[email protected]]

Make sure you use the low-voltage one, 1N4001. Higher-voltage diodes of

that series have long turn-on delays, so they aren't much good for

suppressing inductive kicks.



Cheers



Phil Hobbs



--

Dr Philip C D Hobbs

Principal Consultant

ElectroOptical Innovations LLC

Optics, Electro-optics, Photonics, Analog Electronics



160 North State Road #203

Briarcliff Manor NY 10510 USA

+1 845 480 2058



hobbs at electrooptical dot net

http://electrooptical.net

Thanks. Would it be better to use 1A schottky than normal diodes like 1N400x?

 

[[email protected]]

The 1N4001 should be fine, but do use at least a 60V transistor to drive

the relays.



Cheers



Phil Hobbs



--

Dr Philip C D Hobbs

Principal Consultant

ElectroOptical Innovations LLC

Optics, Electro-optics, Photonics, Analog Electronics



160 North State Road #203

Briarcliff Manor NY 10510 USA

+1 845 480 2058



hobbs at electrooptical dot net

http://electrooptical.net

BCX56 is the transistor. Relay coils are connected between emitter and ground. 12V is applied at the collector.

 

[Nico Coesel]

I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.

I always use a transistor or MOSFET with internal diode. No need for
an external diode.

 

[bud--]

I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.

-bhavj

may be of interest
http://web.archive.org/web/20110104...electronics.com/appnotes/app_pdfs/13c3264.pdf

 

[[email protected]]

I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.



-bhavj

Here is the schematic I quickly drafted. All the 5 coils and fly back diode are in parallel and will be connected to 12V_RLY_COIL.

https://picasaweb.google.com/106331...vh_NXi3AE&feat=directlink#5912784366042056882

 

[Harry Dellamano]

Here is the schematic I quickly drafted. All the 5 coils and fly back
diode are in parallel and will be connected to 12V_RLY_COIL.

https://picasaweb.google.com/106331...vh_NXi3AE&feat=directlink#5912784366042056882

Sorry, you have just been demoted to SCI Electronics Basic!
Harry

 

[Martin Riddle]

The OP should post his schematic. I've seen interesting things, like
putting TTL levels into a base and expecting 12 volt swing at the
emitter.

I was thinking the same thing with a NPN and the collector tied to the
12v rail,
you'd need to take the Base above the 12v rail to turn it on.

Cheers

 

[[email protected]]

https://picasaweb.google.com/106331...vh_NXi3AE&feat=directlink#5912784366042056882

Is that supposed to be funny?

 

[Spehro Pefhany]

Sorry, you have just been demoted to SCI Electronics Basic!
Harry

Harry is right.. there are multiple issues.

1) Can we assume you're trying to drive the relays with a
3.3V CMOS output, and 3.3V in should turn the relays "on"?

1a) If so, is the common for the 3.3V supply same as the ground
shown?

2) Any particular reason you want a high-side driver
(so one side of the relays is grounded)?

3) Is this an automotive 12V system with the associated
transient issues?

4) What's with the 100uF cap across the relays, and the
0.1uF cap, for that matter?

--sp

 

[amdx]

Is that supposed to be funny?

Why is it that nobody helps the guy, rather than just letting him
know you're all smarter than him.

The more common method to drive a relay is;
+12v to one side of relay, other side of relay goes to the collector of
an NPN transistor, emitter of transistor goes to ground. Put a 1k
resistor in series with base of transistor and apply your 3.3v the 1K
resistor.
Install diode across relay.
Is there a reason you don't want to do it that way?

Mikek

*1K value can be adjusted.

 

[[email protected]]

Why is it that nobody helps the guy, rather than just letting him

know you're all smarter than him.



The more common method to drive a relay is;

+12v to one side of relay, other side of relay goes to the collector of

an NPN transistor, emitter of transistor goes to ground. Put a 1k

resistor in series with base of transistor and apply your 3.3v the 1K

resistor.

Install diode across relay.

Is there a reason you don't want to do it that way?



Mikek



*1K value can be adjusted.

Could be automotive relays with one terminal at frame ground, then he needs a high side switch.

 

[[email protected]]

Nah, your average 12V relay will pull in around 9V. 11.3ish is fat city.

Not at max operating temperature...and depending on relay design, you could be looking at 40oC core temp rise in steady state.

 

[Spehro Pefhany]

Looks like he wants to switch the coils and regulate the coil voltage
down to 12. 18V is a bit much, 2.2x the normal coil dissipation.

He could use this as a $2 one-chip solution: TL751M12QKVURQ1
(active low input).

It's possible to modify the given circuit a bit and make it work okay
too.. eliminate the caps, connect R68 to the input voltage (and make
it 10K), reduce R67 to 330 ohms, add Q1 same type as Q3, E to ground,
C to base of Q3, base to input through 2K. It will have a higher
dropout voltage than the regulator solution so examine carefully the
high ambient temperature (at the relay)/low input voltage condition.
(this is also active low input).


Best regards,
Spehro Pefhany

 

[[email protected]]

I scribbled a few circuits, until I ran out of paper.



https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Relay_Drivers.pdf



Oh, 1117s need an output cap.









--



John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com



Precision electronic instrumentation

Picosecond-resolution Digital Delay and Pulse generators

Custom timing and laser controllers

Photonics and fiberoptic TTL data links

VME analog, thermocouple, LVDT, synchro, tachometer

Multichannel arbitrary waveform generators

Thanks for taking time to draw them. Yes, as you said I am trying to regulate as well as switch the power to the coils. In the fig-1, why is that pnp needed instead of resisting to limit current?

 

[Spehro Pefhany]

I scribbled a few circuits, until I ran out of paper.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Relay_Drivers.pdf

Oh, 1117s need an output cap.

I really like (4). Short and to the point.


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

I've obviously led a sheltered life, since I've never seen a 12V relay
datasheet where pull-in wasn't guaranteed at well below 11.3V. Do you
have an example?

Cheers

Phil Hobbs

Hi, Phil:-

Consider a relay such as this one:-

http://media.digikey.com/pdf/Data Sheets/Tyco Electronics P B PDFs/ORWH.pdf

Pull in voltage is rated at 8.4V for the 12V nominal relay. That's
specified "without pre-energization at ambient temperature 23°C" (fine
print).

If you require the type F insulation (155°C) they offer, then the coil
resistance could then be more than 50% higher than at 23°C, so the
guaranteed minimum pull-in voltage would actually be more than 12VDC!

Somewhat less than nominal voltage is normally okay if the input
voltage is regulated and/or the environment is fairly benign, but
that's not always true. Probably sluggish turn-on doesn't help relay
life either. I don't like unnecessarily to give away voltage in a
relay driver (eg. by using darlingtons).


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

I like 7, assuming the firmware cooperates.

Possible pattern-sensitive relay operation frightens and confuses me.


Best regards,
Spehro Pefhany