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Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?
2

Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

(OP)
I've got to install pilot light on a indicating panel. 125VDC, LED. Amber colored. It just goes through a contact and lights up. The Vendor or choice is putting a two week lead time on the full voltage type. That's too long.

I never considered the "transformer" type, as they make one in full voltage. Why would you use that type? Is it better?

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

DC transformer??

Try the GE ET-16 or ET-16 LED. A resistor on the lampholder body determines the voltage.

old field guy

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

LED lamps use DC, very low voltage. If you get a "full voltage" version, there must be a tiny little SMPS embedded in it that is specifically designed to take that voltage. It's more expensive and there is a different version for every line voltage possible (or a small range thereof). So it's more expensive for the mfr to maintain them in inventory.

"Transformer type" just means YOU have to tell them the voltage you are giving to the primary side of a tiny transformer (via selection) but for the LED driver, it is ALWAYS coming off of a consistent secondary voltage of that transformer. That way EVERY one of the LED driver boards is exactly the same, more volume, less carrying cost, lower overall price (or more profit). So mfrs are "driving" our buying habits in that direction by making the full voltage concept distasteful using longer lead times and/or higher prices.

"Will work for (the memory of) salami"

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

Be careful using resistor droppers with LED indicators. I'm not saying it doesn't ever work, just that sometimes this method doesn't have the expected result. Unless you expected a firework show of course. wink

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

I haven't researched the cost/reliability factors of pilot lights. But for small power supplies in general, I'd go with the SMPS design. As have most power supply manufacturers.

These can be made to work over a wide input voltage range. 100 to 240 Vac is a common wall wart spec. and that could be expanded without too much trouble. DC operation is also possible (full wave bridge input before the inverter stage). And size/efficiency is not an issue. 5V USB supplies are made in an enclosure little larger than a standard US plug (could probably fit a single board Linux computer in a British plug wink).

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

(OP)
So Scotty you seem to be disagreeing with Old Field guy. I called a local vendor and he gave me a part number: for a Lovato Electric, 22mm oiltight lamp holder(8LP2TIL225) and LEDs part no. 36942ATR. Not familiar with this company. They sell lots of them he says.

It's on the order of 1/10 the price of the Allen-Bradley 800 series.

What does SMPS mean?

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

I don't think the internal electronics liked the high impedance supply, and it caused the lamp to fail with smoke and blown indication fuses. Can't remember the brand, but likely Telemecanique or A-B. I ended up using a miniature bayonet LED lamp designed for 110V DC in a standard direct voltage lampholder. I think the lamps were by MARL.

Lovato seem to be gaining market in the bottom end industrial / commercial market where price is a big factor. Never really used their products so can't comment objectively. Interested in feedback though if you do use them.

SMPS = switched mode power supply, high efficiency power conversion.

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

I use both 24v and 120v LED indicators all the time. The 120v indicators have nothing more than an appropriately sized resistor to drop the voltage to the LEDs. There is no SMPS in theses indicators.

Transformer-based indicators are a throwback to the days of incandescent indicator lights; higher voltage incandescent filaments were mechanically fragile and had low lifetimes, so transformers were placed ahead of the low voltage (typically 6-12v) lamp at each indicator. With the advent LED indicators, these are now obsolete.

Buy yourself an LED indicator for the voltage you require and you'll never have to replace it in your lifetime, or that of your grandchildren. Lower current draw, no appreciable heat, and they last forever. What's not to love?


SceneryDriver

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

My experience is very similar to SceneryDriver's. Just buy the LED version for the voltage you have.

Best to you,

Goober Dave

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RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

I might also mention that the LED versions can be powered from either AC or DC (of the appropriate voltage, of course). I believe they have little bridge rectifiers built right in. Transformer-based indicators can not be used with DC supplies.

SceneryDriver

RE: Two types of pilot lights: Full Voltage vs. Transformer - why choose one over the other?

Transformers also provided some isolation between the bulb and the main control power. This prevents blowing the control power fuse when someone is changing the bulb and causes a short. They also present a much lower voltage in the lamp housing which removes the shock hazard so operators can change the bulbs with power applied. Not much need for transformers when using LED pilot lights and transformers are no use on a DC circuit.

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