BG Doorbell Transformer

ITGURU · 11 Aug 2020

Hi.
I purchased 2 x BG Doorbell Transformers both of which I am unable to get any DC output out of any of the terminals.
I took them back for another and the same issue.
I can't believe that I have 3 faulty transformers but can't see I'm doing anything daft.
I can check with multimeter and get 240v input however when I probe the 0v terminal and 12 volt terminal I get no reading. if I probe 0v and 24 v I get nothing.
if I check with a laptoo power supply the meter reads the 19v.
can anyone help with what I might be doing wrong or do I have 3 from a faulty batch?!
Thanks in advance.

plugwash · 11 Aug 2020

If it's just a transformer then the output will be AC not DC, have you tried measuring with your meter in both modes?

ITGURU · 11 Aug 2020

Yes I've set the meter to 200v ac and 20v dc and can't get a steady output reading on either just returns 0. jumps to some random numbers when probe it thrn settles on 0.
Transformers are usually DC as per the specs I've read?

Taylortwocities · 11 Aug 2020

ITGURU said:
Transformers are usually DC as per the specs I've read?

Wrong
A true transformer is AC in and AC out. Power supplies, on the other hand may be AC In and something else out. They can be DC out, it depends.

standard doorbell transformers are AC out. I see the BG2 doorbell spec does state DC out.
https://www.bgelectrical.uk/public/downloads/data-sheets/devices/CUB1.pdf

Between what terminals are you testing for the DC voltage?
Does your meter measure the voltage from a battery correctly?

DetlefSchmitz · 11 Aug 2020

Well. The data sheet claims they output dc. The data sheet was also written by someone with no technical training so is complete nonsense. (It apparently has a constant power output - I don't think so!) It sounds like you may be doing something wrong though. Maybe a picture of you testing it would help?

AndyPRK · 11 Aug 2020

Try 20v AC

ITGURU · 11 Aug 2020

DetlefSchmitz said:
Well. The data sheet claims they output dc. The data sheet was also written by someone with no technical training so is complete nonsense. (It apparently has a constant power output - I don't think so!) It sounds like you may be doing something wrong though. Maybe a picture of you testing it would help?

AndyPRK · 11 Aug 2020

You meter only goes down to 200 vac.
Wonder if it would detect 20

DetlefSchmitz · 11 Aug 2020

Interesting; the transformer output is uses a symbol indicating an ac output. This would be traditionally what a bell transformer would output. So try testing as a.c. output - as Andy suggested.

plugwash · 11 Aug 2020

The 200V AC range on a typical meter should detect 20V fine.

Another thing, always tighten screws before probing them.

On some styles of terminal if the screw is loose then it doesn't make reliable electrical contact with the electrical parts of the terminal.

ITGURU · 11 Aug 2020

plugwash said:
The 200V AC range on a typical meter should detect 20V fine.

Another thing, always tighten screws before probing them.

On some styles of terminal if the screw is loose then it doesn't make reliable electrical contact with the electrical parts of the terminal.

well i only resorted to testing with a multimeter because I installed the first 2 I had straight off and the doorbell wouldn't power up! I have tested with the probes as shown and Directly in the terminals where the cables would go!

ITGURU · 11 Aug 2020

OK - so with the meter set to 200V AC i get the following readings :
across 0v and 12v - Meter Read 16V AC
across 0v and 24v - Meter read 28.8V AC
the doorbells requires 16 to 24v so which terminals would be recommended?

bernardgreen · 11 Aug 2020

Or does the meter have a Hold function and the 243 display is held from a test when the mains lead was connected ?

echoes · 11 Aug 2020

ITGURU said:
OK - so with the meter set to 200V AC i get the following readings :
across 0v and 12v - Meter Read 16V AC
across 0v and 24v - Meter read 28.8V AC
the doorbells requires 16 to 24v so which terminals would be recommended?

The voltage will drop when current is drawn, so use the 24V terminals. Is it a mechanical door bell?

ITGURU · 11 Aug 2020

echoes said:
The voltage will drop when current is drawn, so use the 24V terminals. Is it a mechanical door bell?

Nope, it's an IP video doorbell

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BG Doorbell Transformer

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