Circuit tester confusion!

[petercharlesfagg]

Friends,
This is the circuit tester that I purchased 20 years ago for setting up my first model railway and it did the job intended as regards electrical connectivity!


I also built my own transformer with (2) outlets for 16 V AC.


After I had built the transformer there was some speculation amongst the members of the Isle of Wight "N" gauge society as to whether the transformer was actually producing the current needed because the point motors were slow and the locomotive (Jinty) was slow in operation.


The components were supplied by a reputable company who recommended them as being compatible and trustworthy!


Therefore, can anyone instruct me, gently, as to how I can use the tester to test the outputs on the transformer and what am I looking for on the scale?

PLEASE keep technical jargon to a minimum!

[edwin_m]

Set it to "ACV 50" and put the two probes on the outputs of the transformer.  You should get a reading of 16 on the black scale that runs from 0 to 50.  Repeat with a few locos running at the same time, to see if the voltage drops.  If it does then the transformer is struggling to supply the current. 

If your point motors are Peco or SEEP then they will use up to 4 amps or so, but only for a very short time so you wouldn't see this on the meter even if it had a suitable current setting (which it doesn't). 

[petercharlesfagg]

Set it to "ACV 50" and put the two probes on the outputs of the transformer.  You should get a reading of 16 on the black scale that runs from 0 to 50.  Repeat with a few locos running at the same time, to see if the voltage drops.  If it does then the transformer is struggling to supply the current. 

If your point motors are Peco or SEEP then they will use up to 4 amps or so, but only for a very short time so you wouldn't see this on the meter even if it had a suitable current setting (which it doesn't).

Thankyou for your prompt reply, it is easy when you know how!
I will eventually own a locomotive for testing!

I will try your suggestion on Thursday and let you know if anything blows up!

Regards Peter.

[Lawrence]

Peter, I think what you are trying to measure is the current output from your transformer and I am not sure your meter will do that as it requires a meter with a dedicated Ampere socket.  If you can borrow such a meter you can check the current output from your transformer, watch this video for a how too (replacing their battery for your transformer)

measuring current

Voltage is measured in parallel - so your meter provides a load across the output terminals and is "in parallel" with the circuit
Current is measured in series - so your meter goes in the supply line and is part of the circuit and is "in series"

[petercharlesfagg]

Peter, I think what you are trying to measure is the current output from your transformer and I am not sure your meter will do that as it requires a meter with a dedicated Ampere socket.  If you can borrow such a meter you can check the current output from your transformer, watch this video for a how too (replacing their battery for your transformer)

measuring current

Voltage is measured in parallel - so your meter provides a load across the output terminals and is "in parallel" with the circuit
Current is measured in series - so your meter goes in the supply line and is part of the circuit and is "in series"

Lawrence, are you saying that if I couple my meter up as suggested I will do some serious damage to the tester and/or the transformer?

Regards Peter.

[Lawrence]

Hi Peter
there is no way I can tell how the meter is wired internally or whether or not switching to Amps switches the meter internally to a similar mode as described in the video.  Frankly I would be more concerned about damaging you 
I really would recommend purchasing a basic modern meter which have built in fail safes and will provide you with more accurate metering, perhaps something like this
http://www.amazon.co.uk/Draper-60792-Digital-Multimeter-Backlight/dp/B0001K9XKW/ref=sr_1_3?s=diy&ie=UTF8&qid=1361302158&sr=1-3

[edwin_m]

To measure current you would have to remove one wire from the transformer and put one probe of the meter on the detached wire and the other on the terminal you detached it from.   

However you would need a meter with an AC current setting to do this, "which in our case we have not got".  You may also cause damage if you connect up as I suggested above with the meter set to a current setting rather than voltage, so select the voltage range before you connect it up. 

You could get a better multimeter for about £10 from Maplins but I don't think you actually want to measure the current drawn.  The transformer is supplying enough current to move the loco and the points, otherwise they would not move.  But if they are going too slowly it could be that the voltage is dropping too much when it does so, which is why I suggested measuring voltage.  If it helps, think of a garden hose with the current being the flow of water and the voltage being the pressure. 

Be aware also that you might be overloading the transformer.  Model transformers normally have overload protection to shut off the power if the current is enough to cause damage, but a home made transformer might not have this.  I would also suggest extreme caution if you are considering home-building a transformer, as dangerous mains voltages are involved. 

[petercharlesfagg]

Friends,
Thankyou to everyone for all the information.

Well I tried but I did not meet with success, I connected up my tester as described by others, switched on the transformer and "Kapow!" the tester needle wavered, shot over to the other side of the scale and died!

It is not entirely deceased?

An electrician tested my transformer with his digital gizmo and it gave a reading of 16.47 AC at each ternminal so it is OK!  ( I clap myself on the back for constructing that bit at least, correctly!)

The electrician then turned his attention to my defunct tester and explained in words ONLY another electrician would understand, (I nodded sagely!) and informed me that I now have reduced capabilities (the tester that is!) but I could use it for checking DC circuits only!

So at least the MOST important function is still working!

Thought you might appreciate knowing?

Regards Peter.

[Lawrence]

Peter, I would refer you to my reply #5
whilst your initial construction is commendable I would suggest self preservation should be your priority  and you make a small investment in some equipment that meets current safety standards, gives you more flexibility and, more importantly, keeps you safe 

[petercharlesfagg]

Peter, I would refer you to my reply #5
whilst your initial construction is commendable I would suggest self preservation should be your priority  and you make a small investment in some equipment that meets current safety standards, gives you more flexibility and, more importantly, keeps you safe 

Lawrence,
Thankyou, but to allay your fears and anyone else.

The transformer is built into an authorised and acceptable housing, it is double insulated.
 
In the event of catastrophic failure it has an in-built cut off that isolates mains power.

The (2) outlets are also separately fused with 1.5 amp fuses and the electrician has also PAT tested the unit.

I feel quite safe with the unit but I thank you for your concern for my continuing good health!

Regards Peter.

[Lawrence]

I was thinking more about your meter Peter

[petercharlesfagg]

I was thinking more about your meter Peter

Nice thought, I appreciate that!

I doubt if I will purchase another, it was basically for trains years ago and I can still check a 3 pin plug and cable if need be!

Thanks again for the thought, Peter.