48 V Relays - source needed

Suggestion Use 24VDC 3-legged regulator 7824 off the 48V and then you can run 24v DC relays with suitable contacts via 1n2001 diodes. Protect supply with an anti back-EMF diode 1n2001 or 1n4148 across each coil. Jim

In article , Rick Hughes writes

Two things spring to mind here:

(1) Use a 12v or 24v relay and drop the energising voltage.

(2) Use the 1A 48v relays but parallel-up the contacts to increase the current rating.

What sort of size and type of relay are you looking for? Is the 48 V for the coil AC or DC?

If it's of any use, RS do octal plug-in style relays (10 A DPCO contacts) with 48 V coils:

- 349-535 for 48 V DC

- 349-406 for 48 V AC

You might just as well use a power resistor, as the load is constant. Also, I don't think the 7824 is specced to take 48V in.

What load is 3A in a CH system?

ac or dc?

I'd probably use a series resistor and a 24v ac relay, if its a 50v ac supply. Resistor will need to be same resistance and power rating as the relay coil.

I wouldn't parallel lesser rated relays, the contacts wont open or bounce simultaneously..

NT

Rick Hughes formulated on Wednesday :

Several ways around the problem (you didn't specify 48v AC or DC)...

1. Put a suitable resistor in series with the coil of a 24v relay.
2. Put 2x 24v relay coils in series.

1. If AC use a 2:1 ratio transformer to drop the voltage down to 24v

2. If dc use a 24v DC series regulator to drop the 48v to 24v. You may need to include a dropper resistor before the regulator.

Hi Rick.

Try this link

Bob

Rick Hughes said the following on 07/12/2005 17:21:

A zenner diode works too and is smaller and cheaper then a three terminal regulator.

Regards, Dan.

Oops!, didn't check max i/p volts allowed to regulator. Sorry. Agreed, use dropper resistors at 25% more than correct wattage and anti backsplash diodes. Jim

Nonsense! The guy just needs to get a 48vdc or ac relay from RS or Farnel

..and you could use two 24V SPCO relays to give yo the DPCO....

But probably not as cheap as a resistor.

This is for a Heat Recovery control unit ... it has 48V DC fans and the relays are to handle the switching of these - fan speed is a 3 speed option .. depending on which pin you apply 48V to on the PSU. (via a 3 way switch) So I want to use this 48V DC control for the relay coils as well as switching 48V DC

Rick

Rick

There are DC fans in the system are 48V 90W ... now I know that give me under 2A, but to allow for any start surge the 3A would be nice to have.

In article , Rick Hughes writes

As it's a motor start application Andy Wade's 8A ones from CPC sound best, most inductive ratings are heavily derated so that'll give you more headroom. Ones I have around show 8(2)A for resistive vs inductive so 3A would be a bit lightweight.

The CPC ones seem ideal, have access to 48V Telecom relays form Strowger switchgear .. but the current rating is too low.

Rick