Can I spur from doorbell wiring?

[TheMiddle36]

Hi, I’m wanting to power my alarm hub from the same place that the doorbell is wired in to.

The hub is powered by a plug, rated 12v, 2a.

Can I use one of these from a spur at the doorbell (before the doorbell) to provide power to the hub: https://cpc.farnell.com/carel/tra12un100/transformer-240vac-12vac/dp/MC01881?st=240v transformer 12v

wire transformer in, chop off the connector from the existing hub power supply and wire it to the out put from the transformer?

Thanks,
TM

 

[ipf]

No tranny with the hub?

 

[TheMiddle36]

I’ve not looked yet to be honest, I reckon so, but not sure the tranny in the doorbell will power the doorbell and the alarm hub... will check though.

Good idea!

 

[telectrix]

does your hub require 12V a.c. or 12V d.c.? a pic of the hub and it's plug, showing the spec. on the plug would help.

 

[ipf]

I’ve not looked yet to be honest, I reckon so, but not sure the tranny in the doorbell will power the doorbell and the alarm hub... will check though.

Good idea!

They should be fed separately. If you have a mains supply for the bell, there you go.

 

[TheMiddle36]

Thanks, the linked transformer is up to the job I need it for, would you say?

 

[Mike Johnson]

Alarm panels normally use mains power and have a transformer built in to power the internal battery, so they are still operational during a power cut.

 

[TheMiddle36]

Alarm panels normally use mains power and have a transformer built in to power the internal battery, so they are still operational during a power cut.

It does have a back up battery.
I’m want to power it from the mains, wired in, instead of using the plug and transformer that it was supplied with

 

[Mike Johnson]

Alarm panels do not usually have an external transformer and plug lead, inside the panel there should be a terminal block with fuse holder?

 

[telectrix]

Alarm panels do not usually have an external transformer and plug lead, inside the panel there should be a terminal block with fuse holder?

xome even come with fused fitted. ??

 

[TheMiddle36]

Cheers everyone, this isn’t a hardwired alarm system.

It’s a wireless type alarm with a hub which plugs in to the mains, and has its own internal battery too.

I’m looking to do away with the plug and provide the power directly from a spur.

I’ll add a picture of the existing plug shortly and am just looking for confirmation that the linked transformer will do the trick ?

 

[Lucien Nunes]

No. The transformer linked is just that - a transformer - which produces AC output, but the alarm will almost certainly need a stable 12V DC from an electronically regulated power supply which is what is inside most normal 'wall warts'. That transformer is also only 3VA output so probably too small for the doorbell (less than 0.3A available from the output).

Some doorbells work on either AC or DC, some are AC only, so it is quite possible that you can't power them both from one source at all. Doorbells are typically highly inductive and produce vicious voltage spikes, so regardless of the voltage regulation and whether it is AC or DC, sharing a supply between doorbell and alarm would run the risk of the doorbell interfering with (e.g. crashing) the alarm.

As stated above, use separate power supplies. You can get inline regulated DC power supplies in a little flat plastic case that can be wired into an FCU. We should look at the spec of the original one before recommending a replacement.

 

[TheMiddle36]

OK, thanks. Had probably overlooked the conversion from AC to DC.

In regards to the doorbell, I'm only wanting to use the supply to the doorbell (because it's handy where it's located) not actually any part of the doorbell wiring.

So I'm assuming (until I can get to it and check) that the doorbell is supplied with 240v AC, in which case I'd like to spur from this supply and convert to 12V DC at 2A. Is there something I can wire in to do this?

Thanks very much for all your help!

 

[Lucien Nunes]

Something like this?
12V 2A inline PSU

 

[TheMiddle36]

Something like this?
12V 2A inline PSU

If i can wire the side of that with the 3 pin plug directly to mains spur then yeah? via FCU?