120-277v leds on 480v (no neutral)

[ctclark1]

I'm looking at a stop-gap measure to replace some of our 400w MH parking lot light lamps with LEDs (corn cobs, 120-277v rating) as they burn out until we can get a full project in a year or two to replace them with full LED fixtures (for other reasons that will include pole replacement at that time, which is why we just want a quick and dirty fix for now).
The power to the poles is single phase 480v (2 legs of a delta system to each pole), so 277v is not available.

Someone from an electrical contractor we had in here a few months ago had told me to just leave the ballasts in place and that would be ok. While in theory this makes sense to me as part of the ballast is a transformer, I never thought about what the output voltage would be until recently. I'm finding a bunch of different information online, with regards to the open circuit voltage being much higher than what appears to be the roughly 150v that a mh lamp would use (closer to 300v open, which would be too much for the led, I don't know if the led would be enough load to bring that down to the "working" voltage). Part of me also says the capacitor should probably be removed from the circuit if the transformer theory holds up.

Is this something anyone's every heard of? If this doesn't seem right, short of buying a bunch of small 480 to 240 control transformers and replacing the ballasts anywhere were put the corn cobs, are there any other viable solutions for quick and dirty?

 

[LarryFine]

Welcome to the forum.

I would only consider it if the bulbs were labeled as suitable for use with the ballasts in the circuit.

Otherwise, you need to find some that are, or find a way to re-supply them with a lower voltage.

 

[hillbilly1]

If the ballast are multi tap, the 277 or 120 volt tap can be used. Leave the 480 volt taps connected, the ballast acts as an auto transformer. That is the quick and dirty way to do it. We did a car lot that was 480, and that’s what the manufacture sent out to make the 277 volt drivers work because they didn’t make a 480 volt driver yet.

 

[hillbilly1]

(Cap the ballast lamp and capacitor leads, they are not needed)

 

[480sparky]

So why not take one of the hot wires and make it a neutral back at the supply panel? That would give you 277v.

 

[chris kennedy]

OP stated delta system.

 

[ptonsparky]

OP stated delta system.

On top of the other existing fixtures needing 480.

 

[winnie]

Any sort of discharge lamp including MH has a widely varying voltage during different stages of operation. Once the arc (or operating current) is stable the voltage is relatively low, and current must be controlled. But for starting the voltage can be very high...in the case of MH ballasts with hot restrike capability the voltage can be many thousands of voltage with very low current limits.

A multivoltage lamp might very well work with the output of the ballast...but I agree with LarryFine, use a lamp that is specifically designed to mimic the characteristics of a MH lamp and designed to operate with the varying output voltage of the existing ballast. If the lamp is designed to work with the ballast and the ballast is designed to work with your existing supply voltage, then you should be fine. Double check that the lamp doesn't require a grounded conductor via the ballast however.

-Jon

 

[ctclark1]

So why not take one of the hot wires and make it a neutral back at the supply panel? That would give you 277v.

What chris and pton said are both absolutely true. The primary transformer from the MV distribution to the panel servicing these lights is 480 Delta, but even if we could generate a neutral, we'd only be replacing the MH lamps and ballasts with LEDs where the MH lamps have failed, intermixing the LEDs with the existing MH ballasts all currently wired for 480, so this really isn't an option. The long term plan when we pole replacement takes place would be to replace all of the fixtures with completely new 347v-480v rated fixtures, but since that involves also replacing the pole bases that's a few years out and our parking lot is quickly getting darker now.

If the ballast are multi tap, the 277 or 120 volt tap can be used. Leave the 480 volt taps connected, the ballast acts as an auto transformer. That is the quick and dirty way to do it. We did a car lot that was 480, and that’s what the manufacture sent out to make the 277 volt drivers work because they didn’t make a 480 volt driver yet.

I'll admit there are parts of ballasts I don't completely understand, but my assumption had been that the MH ballasts were basically composed of a transformer to raise or lower the output voltage to the lamp to a known but stable voltage, and then the capacitor was used to create the strike voltages, so as long as the output of the transformer was within range my thought had been to just remove/cap off the capacitor leads. If that's not the case, I guess that explains why the OCV ratings on the transformer output threw me for a loop. But in your suggestion, I would leave the 480 leads on the source side, and then use the 277V or 120V primary side leads to the socket along with the common to do this?

A multivoltage lamp might very well work with the output of the ballast...but I agree with LarryFine, use a lamp that is specifically designed to mimic the characteristics of a MH lamp and designed to operate with the varying output voltage of the existing ballast. If the lamp is designed to work with the ballast and the ballast is designed to work with your existing supply voltage, then you should be fine. Double check that the lamp doesn't require a grounded conductor via the ballast however.

The LEDs I'd be using are corn cobs of the standard 120V to 277V multivolt range. They're not ballast compatible, I was just thinking that the transformer from the ballast could be used without the capacitor to drop the voltage, but I'm getting the impression it's slightly more complicated than that.

 

[hillbilly1]

I'll admit there are parts of ballasts I don't completely understand, but my assumption had been that the MH ballasts were basically composed of a transformer to raise or lower the output voltage to the lamp to a known but stable voltage, and then the capacitor was used to create the strike voltages, so as long as the output of the transformer was within range my thought had been to just remove/cap off the capacitor leads. If that's not the case, I guess that explains why the OCV ratings on the transformer output threw me for a loop. But in your suggestion, I would leave the 480 leads on the source side, and then use the 277V or 120V primary side leads to the socket along with the common to do this?


The LEDs I'd be using are corn cobs of the standard 120V to 277V multivolt range. They're not ballast compatible, I was just thinking that the transformer from the ballast could be used without the capacitor to drop the voltage, but I'm getting the impression it's slightly more complicated than that.

Yes, IF it is a multi tap ballast, if not, you will only have the 480 volt input leads, which is not doable. All wires on the output side are capped and not used. Use the common and 277, or 120 volt wire. (208 or 240 tapsmay also work, but less heat on the ballast if the 277 volt tap is used.)

 

[winnie]

I read your original post as using the normal ballast output to drive the LEDs, which I said _might_ work if you are lucky because in normal operation the ballast is there to regulate current and for the most part reduces voltage to the operating input range of the LEDs...but could also go very wrong depending upon the particular system characteristics. IMHO to use the _output_ of the normal ballast you need to use LEDs specifically designed for that use.

Hillbilly1 is suggesting a cute trick which doesn't use the ballast as a ballast. Some (many??) ballasts have a multi-tap _input_ coil. If you have this type of ballast he is suggesting capping off/cutting out all of the _ballast_ components, and using that multi-tap input coil as an autotransformer to provide 277V. IMHO this is a plausible hack which will provide the correct operating voltage to the LEDs. It has the potential problem that it doesn't provide a grounded conductor to the lamp; one supply to the lamp will be the 'hot' from the 480V delta, the other will be derived and something north of 240V to ground.

If you have the correct sort of ballast, this trick will be functional, but there are likely a bunch of unknowns which might impact safety.

-Jon

 

[LarryFine]

That's true. A multi-tapped primary will function as an auto-transformer, which is why unused taps must be insulated.

Apply a voltage to the corresponding tap (and common) and the other taps will have their voltages to the common, too.

I would disconnect and insulate all secondary conductors. I'd probably land the common on the center socket contact.

 

[hillbilly1]

Manufactures have been using the auto transformer trick for many years. In HID fixtures with integral quartz restrike lamps, they use the 120 volt tap to power a 120 volt quartz halogen lamp until the HID lamp current relay drops it out. I know at least since the 80’s.

 

[tortuga]

Manufactures have been using the auto transformer trick for many years. In HID fixtures with integral quartz restrike lamps, they use the 120 volt tap to power a 120 volt quartz halogen lamp until the HID lamp current relay drops it out. I know at least since the 80’s.

Fascinating indeed, I remember those and remember wondering how they worked.