11.5v Electronic Transformer VS 12v

[Graham81]

Today I replaced a dead electronic transformer rated at 105vA 240v primary 12v secondary with one of identical specification except the secondary was 11.5v which seems more standard nowadays. This transformer is for three sets of small halogens & I have noticed a big difference in brightness. Would 0.5v difference on the output make that much difference?

Regards & thanks.

 

[PBC_1966]

It may well be that the new unit isn't as well regulated and that the output voltage under load drops considerably. Have you measured the voltage on load?

 

[Graham81]

I haven't tested the new one no and the old one is dead. One thing I did fail to mention is that the new one has three output connections when the old one only had one. The three lighting sets are joined to only connect to the transformer on one connections.
Not sue if that ha any impact???!

 

[stillp]

What are the markings on those 3 connections?

 

[Graham81]

It's this transformer:

http://m.screwfix.com/p/robus-electronic-transformer-35-105va/92658

 

[ban-all-sheds]

What are the markings on those 3 connections?

Ones which tell you not to put all 3 lights onto one output.

 

[Graham81]

If I split out the sets will that make a difference to the brightness then?

 

[PBC_1966]

Ones which tell you not to put all 3 lights onto one output.

I don't think the markings are really as clear as they could be. The label on the unit says "LV lamp 20-70W 6.0A max.," which taken by itself seems to contradict the 105W rating. In combination with the terminal markings it suggests 105W maximum total load but no more than 70W at any one pair of output terminals, but it really could be made clearer.

Even the manufacturer's instructions don't mention it:

http://www.ledgrouprobus.com/system/ExpressionEngine/assets/downloads/RM105DN/Instruction Leaflet for RM70DN,RM105DN(issue 1).pdf

http://www.ledgrouprobus.com/catalogue/l3/product?item_id=RM105DN

 

[stillp]

If I split out the sets will that make a difference to the brightness then?

Probably, unless you've damaged the transformer by connecting all your lights to one output.

 

[Graham81]

Thanks for the info guys. I've just doubled checked and actually the lights is one single set of 10 small halogens. Therefore the only real difference is the 0.5v. I have another set of 10 right next to this and it still has the original transformer which Is definitely brighter. Would one like the below that states 12v improve matters:

http://www.wickes.co.uk/Wickes-105VA-Electronic-Transformer/p/162383

 

[PBC_1966]

I've just doubled checked and actually the lights is one single set of 10 small halogens.

What rating are the lamps?

 

[Graham81]

They are 10W 12v

 

[ericmark]

It seems to depend where you read as to if 11.5 or 12 volt, but also there are a few points including the soft start feature, and the possibility of EMC problems with leads longer than 2 meter. But most high frequency power supplies are the same, swapping from a true transformer to a pulse width modulated power supply (electronic transformer) is only any good when the existing set-up complies with the requirements of the electronic device.

Two meters is not very long to connect 10 lamps there would only be 200 mm between each lamp. There is a huge difference between 35 kHz and 50 Hz and this includes what a coiled element inside to bulb will do with that frequency.

This

is what I call a transformer. However with a transformer what comes out is related to what goes in so in voltage 250 is going to mean brighter lights than in voltage 220 where with the electronic power supply any volt drop on the input is compensated for.

When we read the info sheets calling SELV safety extra low voltage rather than separated extra low voltage makes one think the writer did not really know what he was doing! But at least they do realise with cable length between 300 mm and 2 meters they are not suitable for any more than three lamps each.

Personally never liked SELV lighting the low voltage lamps (230v) are far safer and flexible, with less current in cables, less volt drop, bayonet connectors which will not allow the use of unsuitable lamps, and less to go wrong. Once converted to low voltage you can swap between tungsten, cold cathode and LED without problems.

 

[PBC_1966]

They are 10W 12v

10 x 10W = 100W. That's within the total rating of the supply, but apparently exceeds the 70W max. for each output (I say "apparent" because as I noted above it doesn't seem very clear from the markings or the instructions). You could try splitting the string into two groups of five lamps each and running from two of the outputs.

But I second the feelings about all this ELV lighting not being that great anyway.

 

[ban-all-sheds]

I don't think the markings are really as clear as they could be. The label on the unit says "LV lamp 20-70W 6.0A max.," which taken by itself seems to contradict the 105W rating.

Ah, hmmm...

OK - an assumption too far. I couldn't find a good image - all I could discern were 3 output pairs, each one showing one lamp connected to it, and I thought "35-105VA"..... "3 x 35 = 105"..... "Probably no one output should have more than 35W on it".....