power for bell over cat5?

[measureitonce]

Hi,

not sure if this is more of an electricians question or not.

I need to connect a loud bell to a gate entry system. I have timed relay switched contacts (volt free) available on the entry system.

i'm looking at the 12v dc version of this and using a bog standard 12v plugin transformer to power it via the switch contacts for the pos side.
http://www.discount-electrical.co.u...2-masterbell-grey-6-inch-security-bell-12v-ac

I already have a run of cat5 to the location where I want the bell to go (next to an existing phone bell). Can I safely run the 12v 4W bell power over this? There should be 3xpairs available if it helps.

thanks muchly!

 

[pcaouolte]

How long is the cable run?

 

[measureitonce]

less than 50ft I should think

 

[pcaouolte]

Should be ok using two pairs of conductors.

You are drawing one third of an amp. Each conductor is rated for half an amp.

Volt drop over 50ft will be about 3.5% using two pairs, leaving you about 11.6v at the bell if you start with 12v at the PSU.

 

[measureitonce]

great thanks. I assume a 12v bell should be ok at 11.6V?
Woudl there be a benefit going for the 24vdc option instead? obviously with a 24vdc transformer.

Also is there a preffered way to wire it? a pair for (+) and a pair for (-), or solid colour (+) and white/col (-) or does it really not matter?

 

[pcaouolte]

Yes a 12v bell should be ok at 11.6v.

24v would reduce the current to one sixth of an amp and also reduce the volt drop so should be ok using a single pair in the cat5 cable rather than two pairs.

Your choice of wire colours, it wont make any difference which ones you pick.

 

[measureitonce]

I've just realised there is a spare telephone bell up there, wonder if I might be able to use that somehow?

 

[OwainDIYer]

I've just realised there is a spare telephone bell up there, wonder if I might be able to use that somehow?

Telephone bells are designed to work on about 70 V ac at about 20 Hz; they're often unresponsive on 50 Hz.

 

[bernardgreen]

If the voltage drop is problem over a very long cable then the following is a useful "trick"

Use one pair to trickle charge a battery close to the bell and a second pair to operate a relay to connect the bell to the battery when needed.

With a couple diodes it can be achieved with a single pair, one polarity charges the battery and reversed polarity operates the relay.

 

[josh451]

I suggest you look at the link again, that's a 12v AC bell

 

[OwainDIYer]

I suggest you look at the link again, that's a 12v AC bell

That'll be why measureitonce is

looking at the 12v dc version of this

 

[josh451]

I suggest you look at the link again, that's a 12v AC bell

That'll be why measureitonce is

looking at the 12v dc version of this

Why did he not post the 12v DC link then?

 

[measureitonce]

because they hadn't got the 12vdc version listed and I hadn't found stock of it or equivalant anywhere at the time. Figured the description was clear enough for most people

I've opted for 24vdc in the end to be safe on the cat5 and volt drop stuff.

I've rejigged it slightly to link to cctv too . Cat5 from 2 pairs of volt free relay contacts on gate entry to alarm inputs 1&2 on cctv system. The first pair will trigger camera snapsnot of the gate to be emailed to remote user on alarm input1. Second pair on alarm input2 will activate alarm output1, which will be wired to the 24v bell, and plug in 24v transformer.
Alarm output2 will then be wired back to the "open gate" contacts on the entry system.

Alarm outputs on the cctv system can be triggered remotely by web interface (which is constantly monitor at remote office) and smartphone app in case its out of hours. so we can ring the bell to get peoples attention, and/or open the gate remotely.