The link should help with the "why".

Some brands of fixtures (Contrast) can be ordered with either magnetic or electronic transformers so be certain what you are dealing with.

Here is a link that might be useful: LV dimming

Dim

Thanks for the info - very helpful.

I have contacted the manufacturer of the LV lights as well as the dimmer company. Once I hear back, I will post the results.

After reading the Lutron info - it appears that trace DC voltages and surges appear to be the issues that can destroy the transformers in magnetic/inductive lights.

The special magnetic dimmers eliminate any trace DC voltages on the load side and provide either a fuse or some other surge protection to protect the transformers against surges.

I have asked Insteon if their dimmers protect against these issues. I know they have integrated surge protection - but I am not sure if that is to protect the dimmer or the load from surges.

Thanks for the help

I spoke with technical support at Sea Gull Lighting - the vendor of one of the low voltage transformers I would like to dim.

They said that I could use either a magnetic dimmer or a regular dimmer for incandescent lights - as long as it is on the supply (110 V) side. They mentioned that the magnetic dimmers might reduce some of the hum that these transformers produce. I asked why - and they could not give me a reason. I wonder if the louder hum they experience with the regular dimmers is related to any low level DC voltages that may be present of the load side of the dimmer that would be feeding the transformer?

Sea Gull also mentioned that their devices are "potted" - does anyone know what that means and what it does? I have heard of a potentiometer - an adjustable resistance - is it possible that they use the pots to protect the transformer from DC voltages? Any idea of how that works?

Given this information , the Sea Gull indoor low voltage transformers should work with my Insteon dimmers. But I am still waiting to hear back from Insteon to double check and will post that info when I get it.

The hum (or "singing") is caused by the distored waveform that triac dimmers produce. A higher quality dimmer with more electronic filtering will produce a smoother waveform.

"Potted" means that the device's electronic components are buried in some kind of protective material, such as an epoxy of some sort. This helps keep the device from being bothered by moisture. It also makes reverse engineering it more difficult, and makes it almost impossible to repair.

I got the following response from SmartHome :

"Both the Dimmer and Relay switches will function in conjunction with Magnetic transformers. The Dimmer switches are not fond of electronic transformers though. You would be looking for Item# 2476DH (INSTEON SwitchLinc Dimmer 1000W). These switches do not carry a surge protector. "

Looks like I can dim all of my low voltage lights with Insteon dimmers.

Update - always check 2 sources!

I contacted SmartLabs - the engineers who designed the product (SmartHome is just a re-seller of Insteon products). The tell me:

"the Insteon dimmers are triac dimmers on the output and as such would be unpredictable on the low voltage loads. Many people still use them but we do not recommend doing this. You should go with a relay version of the product to be safe"

Great - except that contradicts what the SmartHomes website says "This dimmer switch can control incandescent bulbs, low-voltage halogen (e.g. track), and other low-voltage lights with magnetic or dimmable electronic transformers."

So I will use the non-dimming Insteon relay switches for my low voltage lights. Hopefully they will come out with a true low voltage dimmer someday.

In case you did not read the posts above - the issue is trace amounts of DC voltage that may be present on the load side of the dimmer. Magnetic dimmers remove this DC voltage - incandescent dimmers do not. These small DC voltages will not harm incandescent lights, but eill over time destroy magnetic transformers.

Case closed - I think.

I'm coming to this thread a little late, but I have a couple of comments.

1) Potting is used primarily to eliminate vibration & transfer heat. The other issues the poster above mentioned are side effects but not the main reason.

2) The statement by SmartLabs "unpredictable on the low voltage loads" was clearly a misunderstanding. They assumed you wanted to dim the low voltage side. As Seagull correctly states, you have to dim the high voltage side so the Insteon dimmers should work fine.

Sunil

"After reading the Lutron info - it appears that trace DC voltages and surges appear to be the issues that can destroy the transformers in magnetic/inductive lights. "

It is the distorted waveform that causes the problem.

While normal AC power is a very smooth sine wave shape with a single frequency (60 Hz in the US) when the waveform becomes distorted higher frequencies are produced (120 Hz, 180 Hz, 240 Hz, etc) and these can cause heating on transformers or coils used in the 'electronic' transformers.

Since most of these things are sold based on price the manufacturer is not going to design for dimming if it costs extra money (and it always does).