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Voltage regulator to get from 70vac back to 120vac? Answered

Hi all, I am using (and for strange reasons am required to use) track light outlet adapters to power some LED light strips. The LEDs use an AC adapter that requires a minimum 100vac to run properly. The problem is that the track lights are dimmed substantially, so the voltage coming from the tracks is only 70vac. Any idea what I can use to bump the voltage back up to the 100+ voltage range?

Tripp Lite has a some regulators, but they don't go down to 70vac. APC makes one that goes down to 80vac, but that's the lowest I've found. Is there an off-the-shelf regulator that goes down to 70 volts? I found this contraption that looks promising and maybe a little sketchy (alibaba style). Any other recommendations?

I guess the other question is what is the risk in running the LED strip lights if their AC adapters are getting 30v lower than they recommend? The lights appear to function fine, but will the adapter overheat? Burn out quickly? Cause a fire? If it burns out, say, once a year, I'll probably leave it, but I have no idea what the consequences are.

Thanks in advance!
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You say your LED light strips, "use an an AC adapter that requires a minimum 100vac to run properly". So what happens if you run this AC adapter on chopped-up, dimmified AC? Does the AC adapter then run improperly, and if so what constitutes improper operation?

Perhaps you have not yet found the courage to try running your LED light strips, via their AC-adapter-that-requires-a-minimun-100vac-to-run-properly, on chopped, dimmified AC?

I think it would be helpful to know more about the character of your LED light strips' AC adapter, and the reason why is that some kinds of AC adapter are more tolerant of wide variations in input supply voltage than others. Specifically I am thinking of the newer switchmode type AC adapters, versus the old style AC adapters containing a small transformer with one side connected directly to the mains (and thus running at the mains frequency). I mean some of these power supplies are so robust with respect to input voltage that they don't even care what country they're in, and the specs on the label say something like 90 to 250 VAC.

These days the new-style (switchmode) are more common than the old style (mains connected transformer), at least for new equipment. By the way, this voltage you are calling "only 70vac", that's like an RMS value, amirite? I mean the actual waveform is some sort of chopped-up, dimmified AC, like shown in this graph (Dimmed waveform is the red trace. Full waveform is the blue trace)


Anyway, if you have not already done so, you might try your LED lights and their AC adapter, on your dimmified power for a second or so, and see if anything blows up. Of course that's easy for me to say, since its not my stuff that might blow up. ;-)

If it helps give you courage, I will claim (without proof) that plugging some electronic thing into a supply with higher than expected voltage is more likely to break it than plugging it into lower that expected voltage.

Also consider, lower than expected AC voltage looks like brownout,


and brownout is not a wholly unexpected circumstance in the minds of the electrical engineers who designed your lights. If they were thoughtful, then they likely designed your lights to turn off gracefully in this condition, or to simply refuse to turn themselves on if the input voltage is much lower than what they want.

OK. So that concludes the pep talk (dare) about just plugging stuff in to see what happens.

It would be also interesting to know the total amount of power involved for powering your LED light strips. How complicated the answer, for a power converting exercise, will likely depend on how much actual power is involved. I mean you seem to be contemplating buying some 1000-watt capable regulating autotransformer,


but if the total power involved is less than a few hundred watts or so, you might just covert it to DC, around 12 volts or so, (using a switchmode power supply which does not care about its chopped, dimmified, AC input), then use an cheap inverter to convert that 12 VDC to something approximating AC mains power to run your LED whatsits.

I mean that's assuming you actually have to do any power converting, assuming there is some kind of improper operation that occurs when the LED light strips' AC adapter are just plugged into chopped-up, dimmified AC.

Thanks for the response. The AC adapter for the LED light strip is a simple wall-wart that takes 100vac-240vac and spits out (I think) 12vdc. I have run the LEDs on the "dimmified" 70vac coming from the track, and they turn on just fine. However, since the input voltage is a good 30v below what the wall-wart specifies, I doubt it's a long-term solution. If I can bump the voltage back up to at least 100vac from 70vac, I won't have to worry about them over the course of a year.

The power involved is minimal. The 1000watt regulator I linked to is just the only thing I've found that can regulate voltages lower than 80vac (it regulates voltages as low as 50vac).

It may be the case that you worry to much.

I mean if your LED lighting power supply has survived the dimmified AC fed to it so far, without releasing its magic smoke, then maybe it is happy with this condition, and perhaps you should just leave it plugged in.

You know, see who blinks first. You or the power supply.

The first stage in a typical switching power supply is a rectifier stage. The incoming AC is rectified into around 150 to 300 VDC, a number close to the peak voltage of the AC waveform. Then that capacitor feeds the next stage, which is essentially a DC-to-DC converter.

The reason I mention this is because the chopped up, dimmified AC, probably has about the same peak voltage that it did before, and as a result the big capacitor in the rectifier stage probably has about the same average voltage that it did before. There's probably more ripple voltage on it, since it is being fed by this funny, chopped-up, waveform. Also the time averaged (RMS) current in the rectifier stage has to be larger, but the currents probably aren't all that big since the total power is not that large.

Just saying, the AC adapter might be happy like it is.

Good idea, though it looks like it might be hard to find one that can deal with less than 120v input.

They all will. Just wire it backwards. That's the whole point. The supplies you have are probably not going to like having a dimmed input.

You mean because of the chopped up sine wave? I have a feeling if the voltage is in the correct range, they'll be okay, especially because they do function fine at 70v, I just don't want to leave them like that indefinitely. I ordered a couple of the voltage regulators, so I'll see if they do the trick, otherwise I'll try wiring a variac backward. If I do that, would I have to dial the input voltage to match what the track is supplying?

I'd plug it in and adjust the "output" to 120V.

Running at 70V might work in the short term, but my expectation is that the input circuit will be drawing more current than it was designed for, and the longterm life will be compromised.

Why is the voltage at the track so low ?

The lights on the track are dimmed, so there is a uniform voltage drop across the entire track.

Why not just turn the track back up then ? Many LED controllers don't like dimmed voltage waveforms

It's in a museum setting. The lights are dimmed to protect artifacts. The LED lights must get power from the light track, because the track is on a proximity sensor that switches off when no one is around, so artifacts do not get more light than necessary.

All tracks in the room turn off down when no one is in the room, and turn on when someone enters the room. All tracks are dimmed below 100v.