48 V Relays - source needed

[Rick Hughes]

I have a Heating System project that needs 2 relays, with double pole changeover contacts rated at around 2A (3A pref) ... The problem is that I need 48V operating coils.

Great majority of relays I have found are 12V or 24V coils (and of course

240V AC)

I have found some 48V relays (BT type 47) but these are only rated at 1A.

Anybody come across relays that would suit.

Rick

[Jim Gregory]

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

[Mr X]

In article , Rick Hughes writes

48v DC is a "telephone system" type voltage.

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.

[Andy Wade]

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

[Mike Harrison]

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.

[meow2222]

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

[Harry Bloomfield]

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.

[Bob Watkinson]

Hi Rick.

Try this link

RS do a range of 48v reays in both AC and DC

Bob

[Rumble]

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

with DIN rail base:

d.c. coil

8A @ 240V contacts

[Dan Mills]

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

Regards, Dan.

[Jim Gregory]

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

[Bob Watkinson]

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

[Mike Harrison]

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

[Mike Harrison]

But probably not as cheap as a resistor.

[Rick Hughes]

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

[Rick Hughes]

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.

[Rick Hughes]

2 x 24V SPCO in series seems a neat solution ... thanks

[fred]

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.

[Rick Hughes]

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

Rick