Christmas lights transformer rating

Steve T · Dec 3, 2018

Hi

I’ve got a set of filament lamp Christmas lights, which I think is quite old.

It is a set of 80 lights, and the lamps are rated at 2.4V, 0.29W, 120mA.

The transformer is rated 24V(AC), 0.7A, 16.8VA.

It had 8 ballast lamps installed, so I assume 1 ballast lamp for a string of 9 normal lamps. However I don’t really like how the strings of 9 lamps flash on and off randomly, so I have replaced all the ballast lamps with normal lamps of the same rating as the others.

However, I thought this might overload the transformer because 80 x 0.29W = 23.2W, which is more than the rating of the transformer- 16.8VA( which I think is the same as 16.8W??).
So my question is: will this overload the transformer?

If so, would it be ok to only put in 55 lamps, to give a wattage of 15.95W, which is under the VA rating of the transformer?

Thanks for any replies!

[ElectriciansForums.net] Christmas lights transformer rating

telectrix · Dec 3, 2018

bin the lot and buy a LED set.

DPG · Dec 3, 2018

Exactly what I was going to put Tel !!

Lucien Nunes · Dec 3, 2018

But, the OP is correct. VA and Watts are the same as far as filament lamps are concerned. Having all the lamps on continuously will overload / overheat the transformer, but leaving a lamp out of some strings so that the total load is less than 17W will be OK.

I've always marvelled at how for over half a century, it was customary to celebrate winter festivals, especially Christmas. by connecting lots of small filament lamps in series, instead of the usual parallel. If they had used series-connected lighting in Judea around 4BC, you could understand wanting to keep that tradition, but there's very little surviving information on Roman electrification schemes.

DPG · Dec 3, 2018

Still seems a bit of a bodge for me. And those type of filament bulbs were never very reliable. I'd go for a nice new LED set.

Steve T · Dec 3, 2018

Fair enough, I’ll scrap the old set and just buy a new LED one.
Thanks anyway, at least I know that my theory was correct!

littlespark · Dec 3, 2018

It’s part of the Christmas tradition:- getting the old string of lights out the box, plugging them in and going along the string looking for the broken bulb/ lamp.

1984... a couple of years before leaving school I decided to rewire the family’s static tree lights by adding a 12v spotlight relay from Halfords, a flasher unit from a roadworks amber light and a few batteries to power the flasher.
So flashing tree lights before they were so popular, and quite effective, although a rather loud click sound every second or so