Undersized low voltage transformer?

[rs1987]

I've just moved into a place that has low voltage halogen lights in the kitchen. I had a look at the installation and I see they are running 6x20w G4 halogens off a single DA-E60 transformer - specifications for the transformer shown below.

I measured the amperage draw of the light bulb at 1.8A on 11.4V AC, so the bulbs are definitely 20W bulbs. Now this transformer is rated at 60W, so running 6 of these lights off a single transformer appears to be overloading it substantially. That said, they function properly despite having a load significantly higher than the maximum rating of the transformer.

Is there a safety risk / fire hazard overloading the transformer in this way? That is to say, should I not use these lights until I've added another few transformers or installed one with a higher rating?

Thanks in advance for the advice

/rs

 

[James]

Are you sure they are all fed from that single transformer?
I would expect it to be reducing its output voltage or tripping off for protection with around double its rated load attached.

 

[rs1987]

Are you sure they are all fed from that single transformer?
I would expect it to be reducing its output voltage or tripping off for protection with around double its rated load attached.

Yes. All 6 are being fed from the single transformer.

The spec sheet for the transformer does say that it has overload protection tested at double the load. Which seems to imply that the overload protection will only trip off if exceeding double load, but it's not entirely clear from the spec sheet.

 

[James]

I wonder if it was originally designed for 10w lamps and they have been changed since installation

 

[rs1987]

I wonder if it was originally designed for 10w lamps and they have been changed since installation

Possibly yes. However, the immediate question is a safety one. I assume that if left on for a period of time this could lead to the transformer heating up substantially and being a fire hazard, right?

 

[Lucien Nunes]

This is an electronic switched-mode power supply rather than a conventional wirewound transformer. In the absence of overload protection a wirewound transformer would supply a 2x overload and overheat, but an SMPSU would tend to fail rapidly and permanently with an expired transistor or two. They are therefore designed with integral fast-acting electronic overload protection to protect themselves against failure, and hence also protect against overheating.

Like James I am skeptical whether it is feeding all the lamps. By design it is unlikely to be able to supply a 2x overload regardless of the overload protection, as that would involve using larger and more expensive electronics for no purpose. I suspect the spec sheet merely indicates a test condition, not that the protection acts at that level.

 

[rs1987]

Thanks all for the helpful replies. Since I'm 100% sure that all six bulbs are connected to the transformer, I suspect possibly my multimeter might be faulty and that the load is not as high as double the transformer rating.

I'll get hold of another multimeter and check the current draw on the bulbs to be certain they're actually 20w.

 

[Lucien Nunes]

There's probably nothing wrong with your meter, more likely is that the output frequency of the unit is too high for it (and many others) to measure correctly. I would simply check the wattage stated on the lamps. If they are indeed 20W, then it is a well over-engineered unit but is overloaded amd likely to fail, so worth replacing, or swap the lot to LED.

 

[rs1987]

There's probably nothing wrong with your meter, more likely is that the output frequency of the unit is too high for it (and many others) to measure correctly. I would simply check the wattage stated on the lamps. If they are indeed 20W, then it is a well over-engineered unit but is overloaded amd likely to fail, so worth replacing, or swap the lot to LED.

The problem is that these bulbs do not have any markings on them whatsoever, so unless I measure their current draw then I'm in the dark about their actual wattage. I plan to convert to LED anyway, but since I need to replace the dimmer modules at the same time, I need to get the landlord's permission to do so.

You're absolutely right about the output frequency being the problem. I'm using a cheap but reasonable multimeter for the price point: a Digitek / Tekpower DT-4000ZC. The output frequency of the transformer measures at 26.8 Khz and this meter is rated for ACV/ACA from 40Hz - 400Hz, so I'm almost certainly getting a nonsense reading.

It's high time I invested in a more capable multimeter.

Thanks again for all the valuable help.

 

[static zap]

In its current condition ,it may under run the lamps , and give a longer life .(but does sound dodgy !)

 

[rs1987]

I hooked up a DC voltage supply instead of the AC one to get around the limitations of my multimeter.

At an output voltage of 12.5v DC, some of the bulbs draw 0.8A of current and others draw 1.6A of current. The readings are repeatable in an accurate manner.

They seem to be a mix of 10w and 20w bulbs, although weighted 2:1 in favour of the 20w bulbs. So yes, the transformer is definitely being overloaded quite considerably.

I suspect because of the mix of bulbs that @James is absolutely correct that the installation was originally designed for 10w bulbs and subsequent tenants replaced blown bulbs with 20w versions.

Even if this is the case, I think the original installer did a poor job in fitting a 60w transformer to drive 6 G4 halogens.

 

[Taylortwocities]

Even if this is the case, I think the original installer did a poor job in fitting a 60w transformer to drive 6 G4 halogens.

You never know the circumstances. It may have been a cheap eBay kit shipped from foreign parts.
I’m guessing, as it’s working, that the SMPS is working on the edge. Before making a change, you should have a think about the future of halogen lamps.

Shedding new light on halogen bulb phase-out

Time’s nearly up for halogen lighting – with all but a few types of the gas-based bulb scheduled for phase-out on 1 September 2018.

www.energysavingtrust.org.uk

Almost all of these are being phased out. Many already discontinued. This may be the time to change the whole shebang to LED.

 

[rs1987]

You never know the circumstances. It may have been a cheap eBay kit shipped from foreign parts.
I’m guessing, as it’s working, that the SMPS is working on the edge. Before making a change, you should have a think about the future of halogen lamps.

Almost all of these are being phased out. Many already discontinued. This may be the time to change the whole shebang to LED.

Absolutely agreed. I've just got to convince the landlord as I cannot change it without his permission. This gives me good reason to advocate for the change.

 

[sunray]

So you moved into a rental property with a potentially hazardous installation.

Get the landlord/managing agent involved and let them put it right.