Relamping the shop

electronic ballasts in my shop fluorescent lights . I've been limping along ... Today I received via the USPS a box containing 10 four foot
LED tubes ... six of which are now installed in my fixtures and lighting my shop . Simple changes to the fixtures , hot lead to one end and neutral to the other (both pins) and bang we got light ! A lot brighter and a different color/temperature but that I can get used to . I got the clear tubes , upon reflection I might have gone diffused ... a piece of scotch tape will test that . Bottom line is for under 5 bucks a tube , they don't cost that much more than a fluorescent tube and they'll save me some bucks down the road in lower energy bills . And I used the fixtures I already had .
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On 9/19/2018 3:07 PM, Terry Coombs wrote: > A few months ago we had a power surge or something , blew out all the electronic ballasts in my shop fluorescent lights . I've been limping along ... Today I received via the USPS a box containing 10 four foot LED tubes ... six of which are now installed in my fixtures and lighting my shop . Simple changes to the fixtures , hot lead to one end and neutral to the other (both pins) and bang we got light ! A lot brighter and a different color/temperature but that I can get used to . I got the clear tubes , upon reflection I might have gone diffused ... a piece of scotch tape will test that . Bottom line is for under 5 bucks a tube , they don't cost that much more than a fluorescent tube and they'll save me some bucks down the road in lower energy bills . And I used the fixtures I already had . >
I've got 8 foot dual tube cans in my shop, and the florescent tubes work just fine. However, my last trip over to a local store found me buying what may well be the last case they will ever stock.
I expect I'll be forced to replace or rewire all my cans eventually myself, but none of the places I checked had LED tubes at anywhere near the price yours cost. Care to share your source. Also, let us know how they do after a few years. I replaced all the bulbs in my office and machine room with Leeson LED bulbs and the first one died within a few months. I think I've more than half, and I only got them a couple years ago. I originally got a lot more than I would need, and I am down to just one or two spares.
Needless to say I'll be looking for another brand of LED bulbs next time.
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On Thursday, September 20, 2018 at 6:12:51 PM UTC-4, Bob La Londe wrote:

I did a quick search on 8 foot LED tubes, and they are available from a number of sources. Did not check prices as I expect they will cost less when you need them.
Dan
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On 9/20/2018 6:57 PM, snipped-for-privacy@krl.org wrote:

Fluorescent Tube Light Bulb G13 T8 lamp fixture <https://www.ebay.com/itm/10-100-Pack-18W-48-inch-4ft-LED-Fluorescent-Tube-Light-Bulb-G13-T8-lamp-fixture/302508947434?ssPageName=STRK%3AMEBIDX%3AIT&var `1495925403&_trksid=p2057872.m2749.l2649>
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wrote:

I replaced the fluorescents in my shop with a case of 20 frosted 6500K 40W 8 footers from this guy last Feb. www.ebay.com/itm/301995907066
One half of one lamp failed within a few weeks, but that's a minor complaint compared to the increased light, decrease in the electric bill, and elimination of the magnetic ballast buzz.
The LED 8-footers available locally were drop-in replacements for the fluorescent tubes, i.e., require the ballast to operate. Stupid. The lamps I purchased connect directly across the line. It took no more than a couple hours to remove the magnetic ballasts and rewire the 10 fixtures.
Took a little longer to get used to the color change. Now the places that still have the CW fluorescents look dingy to me.
We replaced the 4 foot T8's in my wife's studio about a year ago with 10 lamps from this ebay seller. No failures to date. https://www.ebay.com/usr/minidavy?_trksid=p2057872.m2749.l2754
It seem prices have stabilized or gone up a bit since my two purchases.
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On Thursday, September 20, 2018 at 5:32:27 PM UTC-7, Ned Simmons wrote:

Maybe not so stupid. The 'require ballast' lamps get about 24V of excitation, which means seven or eight LED diodes in a series string, with other strings in parallel. The 'full voltage' get 240V, so that's seventy or eighty in series.
The failure rate for a series string of seven is 0.1 of the rate for a string of 70. And, one string failing doesn't stop the other parallel strings from making light.
Best practice for designing LED fixtures is not compatible with reusing the fluorescent fixtures unballasted OR with the original fluorescent ballasts. GE makes LED fluorescent-tube-shaped lamps labeled "Use only with General Electric LED21T8 DR/.... LED driver"
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wrote:

Where do you get 24V? A standard ballast for 8 foot F96T12 lamps outputs 750V for starting the lamp and 425mA operating. That implies about 175V across the 75W lamp once it's running. Now, in addition to the internal LED driver(s) in the lamp, you have a point of failure, the ballast, that's not doing anything useful. I'll bet I've spent as much time over the years replacing ballasts as lamps. I'd rather spend the time up-front pulling them out.
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On 9/21/2018 7:36 PM, Ned Simmons wrote:

pretty bright and tend to glare a bit . I tested it , and a strip of (frosted) scotch tape over the center of the clear side of the bulb is just about right . These are 6000K light temp LEDs , taking a bit to get used to after having less-than-enough light that was a lot more "yellow" .
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wrote:


I ADORE the whiter LEDs and hated the piss-yellow incan color, so it was an easy swap for me. I sure like the newer pricing on LED fluor replacement strips but haven't partaken yet.
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On Friday, September 21, 2018 at 5:36:05 PM UTC-7, Ned Simmons wrote:

The LEDs are more efficient, but the ballast still chokes current at circa 425 mA. So, the voltage is lower for LEDs than for tubes. My '24V' number is only order-of-magnitude.

But, it IS buffering the LEDs from voltage spikes, without the power-wasting resistors used in some lamp-replace series strings. The starter-boost is a complex part of the ballast, but isn't required for the LEDs; if it fails, you'll never notice. The 'internal LED drivers' in the one lamp I dissected, were... only rectifiers to prevent reverse voltage.
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wrote:

Which means the LED driver in the tube has to deal with a constant current source that can deliver up to 750 volts instead of a well-behaved 120V constant voltage source. Doesn't seem advantageous to me.

The ballast is intentionally designed to develop a 750V spike.
without the power-wasting resistors

I've not seen dropping resistors in the replacement tubes. All I've seen have switching LED drivers. Look at the specs for the LED replacement tubes I pointed to. They run on 100-265VAC or 85-265VAC.

Perhaps for an electronic ballast, not so for a magnetic ballast.

I don't understand. Why would you need to protect an LED from reverse voltage?
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On Saturday, September 22, 2018 at 4:49:35 PM UTC-7, Ned Simmons wrote:

A constant current source is ideal for powering LEDs; with the right size LED (or the right multiplicity of paralleled LEDs) that's useful power.

Yes, in order to light the cold tube; but, it does that when the tube is NOT conducting, when that potential 425 mA of current isn't drawn. LEDs without a 'driver' attached will always draw that current.

Do you mean drivers built into the long tubes? I've never seen that.
Look at the specs for the LED

There's different designs, including some with heaters/neon lamps etc.

Reverse voltage can create large (surface) electric fields, and move impurities around. That causes the LED to age, dim prematurely. Forward voltage on the diode never exceeds 3V, because the diode conducts, and that means the surface fields are smaller.
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wrote:

Sure, but you can't just connect parallel strings of LED's to a constant current source and expect the current in the individual strings will be equal. And if you implement a single string connected directly to the ballast, LEDs that'll operate at 425mA are expensive, require relatively heavy heat sinks, and will present difficult-to-diffuse bright point sources. Approx 30 LED's vs. 196 in the replacement tubes I purchased.

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On Monday, September 24, 2018 at 6:12:23 PM UTC-7, Ned Simmons wrote:

Yet, it's done all the time. A 'nine-LED' flashlight with three AAA cells has nine strings of one LED each, in parallel.
Desk lamps with three or four LED strings in parallel are common, also. Sometimes resistors are added to each string, but not always.
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wrote:

So how do you insure that the current is divided equally among the strings?
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They are somewhat self-ballasting, as shown by the I-V curves. https://www.electronics-tutorials.ws/diode/diode_8.html
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On Tue, 25 Sep 2018 09:15:10 -0400, "Jim Wilkins"

Unless I'm misintrepeting the curves, or looking in the wrong place, the graph shows a potential for runaway -- the slope of the curves increases with increasing voltage.
Here's a similar curve for a tungsten filament, which is self-ballasting. https://www.quora.com/What-does-the-graph-of-the-current-vs-the-voltage-of-a-filament-lamp-look-like
This article talks about the hazards of paralleling strings of LEDs. https://www.ledsmagazine.com/articles/print/volume-6/issue-2/features/led-design-forum-avoiding-thermal-runaway-when-driving-multiple-led-strings-magazine.html
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Try this: https://www.cree.com/led-components/media/documents/CLA1BWKWMKW.pdf
The slope isn't straight like a resistor voltage divider, the reason I qualified them as "somewhat". It also shows their limited tolerance for reverse bias.
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On Tue, 25 Sep 2018 18:31:29 -0400, "Jim Wilkins"

Yeah, it's sinking in. Slowly.
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In the 1980's I designed and built a delicately balanced constant current string of LEDs, thermistors and Zeners that sensed and indicated four liquid ink levels in a rotating print head. It was a finely tuned version of the Low Fuel light in my car. At the time I understood the components' I-V curves well, but I haven't dealt as seriously with LEDs since.
The constant current limiter was a depletion mode JFET with its gate connected to the source like example 7. They were available as 2-terminal devices that looked like diodes. https://www.quora.com/What-are-Fet-application
-jsw
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