Author Topic: F6T5 and F8T5 to LED retrofit idea?  (Read 9051 times)
Luminaire
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F6T5 and F8T5 to LED retrofit idea? « on: December 01, 2010, 11:08:53 AM » Author: Luminaire
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I got a glass door fridge made by some Chinese company and custom branded for Red Bull.  The beauty of it is of course, in the custom decora.  This thing was apparently in constant use, but its only four years old. 

There is a F6T5 interior light inside the refrigerated compartment. The glow bottle is in the back behind a metal grill next to the compressor.  For the front panel illumination there is a F8T5 and glow starter right by the lamp. 

The irreplaceable Red Bull front panel is showing severe UV damage and the clear interior lens is toast, as you can see.

Since its been allowed to operate like this for a long time, both lamps and their corresponding starters are toast. 

I'd like to convert to LED since they are more suitable for refrigerated case application for producing less heat and I need to stop any further UV damage to the panels. 

Anyone have an idea how I should go about doing this? 
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Medved
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #1 on: December 01, 2010, 12:15:15 PM » Author: Medved
For this you would need about the same wattage of LED's (so 6 and 8W), what would need heatsinking. So generally the modification would be irreversible.
I do not see the exact configuration, so:
- Generally i would make the main lights as SELV and use a supply unit placed to some safe area (e.g. around the compressor or the control module). This would allow to not complicate the LED installation by the required safety insulation...
- Cut away the fluorescent compartment (look like a box bolted to the front panel begind the transparent cover)
- Main LED i would place on some aluminum plate overlapping the illumination window from behind. Use as large as possible, it would be the heatsink and bolt it in place of the fluorescent holder box.
- Use a chain of "3W" power LED modules (those aluminum substrate hexagonal PCB with the LED chip soldered on it): three pieces in place of the F6T5, four in place of the F8T5 (yes, one would get only ~2W, it is very bad practice to bias these on the absolute maximum power level, as the lifetime would be very limited), connect all in series.
This setup would require 0.7A current source with the output voltage range at least 19..26V, i think such LED ballast should be available on the market.
Or you may use 24V/0.7A transformer, diode bridge and a resistor in series. Resistor would be wirewound, about 6.8Ohm/10W (better check the current with the A-meter; the resistor would dissipate about 5W, so place it to some thermally robust place).
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SeanB~1
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #2 on: December 01, 2010, 02:07:05 PM » Author: SeanB~1
Try using some of those LED strings you can buy to use as accent lighting ion cars, the version that consists of a large number of 5mm led chips on a flexible base would be best, and will provide a similar amount of light. Inside the cabinet you will need to encapsulate them in clear silicone (non acetoxy cure type recommended) to keep them waterproof.
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Luminaire
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #3 on: December 01, 2010, 02:24:09 PM » Author: Luminaire
So, I look in GE catalog and these 6W and 8W T5s are only rated for 5,000 hours based on 3 hour cycle.  These miniature T5s never been great for longevity.  Given 8640 hours a year and 24/7 operation, I'm not surprised it failed during the four year period. 

Medeved,
LEDs should be much more efficacious when compared to these fluorescent.  Especially when it is used in near freezing ambient.  They can be driven at much lower power and not be adversely affected by lower temperature.

Each lamp is on its own series choke ballast with its own separate starter (WEN TAI WFS-2 4-40W/100-130v, as you can see, a very wide range general purpose, meant to cover US, Japan, Mexico from the smallest T5 to 40W T12). 

I have a box of Costa Rican made Hubbel FS-5 (made for 4,6 and 8W, so much more purpose specific) that might work better. 

Fortunately, all the wiring terminates to the rear junction box with everything on its own wires so its very easy to reconfigure wiring. I'm thinking I'll get a string of white LED Christmas light, separate out a series thread (I think they're series/parallel wired) and wire them into exterior and interior part.  I'll then wire them to be series in the back.  If I can't fit an entire series string meant for 120v, I'll just add that section into the circuit and hide it all crumpled up in the rear by the compressor. 

LEDs might degrade, but losing brightness is not a huge issue with this. 

The plastic cover for interior light as you can is completely browned.  I think I'll just cut some PETE plastic strips from some product packaging and tape it over the cavity, so it's not permanent.  I don't want to use any encapsulant that's very difficult to remove later on.   
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Medved
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #4 on: December 02, 2010, 01:50:57 AM » Author: Medved
LED's are more efficient then halophosphate, but about the same with tri-phosphor (i compared with F8T5, the with F6T5 you would be right for both phosphors), so using about 0.5A (instead of 0.7A) may compensate this.

Christmass lights would at first make not make enough light and as second, they degrade quite fast for constant use, they are expected to be used for about two weeks/year, 10hour/day (and spread over large area), so if their lifetime is about 3000hours, it mean 20years of service as christmass lights, but only a year as display light.
And if you pack them into the small fluorescent compartment, they will overheat (the compartment is originally designed to retain the heat for the fluorescent).

And with these modifications, i would be afraid to use anything not isolated from mains and not using safe voltage, inside the box is usually lot of condensed water...
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DieselNut
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #5 on: December 02, 2010, 10:30:26 AM » Author: DieselNut
I would put the fluorescent lights back in place and put them on a switch, then turn them on only when you need them.  That is what I did on my little Red Bull refrigerator.
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SeanB~1
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #6 on: December 02, 2010, 12:43:33 PM » Author: SeanB~1
I am looking at doing a LED conversion for my fridge, as I am trying to reduce the heating in the top cavity, which houses the 2 chokes for the 18W and 36W lamps it uses. I also need some room to fit the PID controller and the relay inside the cover, and do not want to toast the nice BTC 9090 controller that I am using, and to have the display somewhat visible to see behind the perspex cover. I am looking into buying some car accent LED lights, and will use them as interior lights ( they should be waterproof enough to use there, and the cold ambient will help with LED life) to show the interior ( Pity I just bought a new GE food colour lamp, it has a nice red colour that accents meat product displays - R80/$11 sitting around now looking for a use somewhere) and probably will look to get a string for each side to illuminate evenly. Power for the LED units will probably be a SMPS from an old one arm bandit, I have a few of them around somewhere that probably will fit the cavity, otherwise one modified fax power supply coming up ( change output from 24V to 12V which will be OK as it is constantly loaded and should be happy at the lower end of the regulation range - just add a resistor across the sensing string to the TL431 regulator should do it.
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Medved
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #7 on: December 02, 2010, 11:59:25 PM » Author: Medved
@SeanB:
With these car light strings i would be suspicious about their life: Passenger cars are designed only for about 5..10k hours drivng (alone, without major overhaul; it correspond to about 200..400x1000 miles) and i suspect these LED's would last way shorter (they are usually of the ElCheapo products, same as the cheapest LED "retrofits"), so the lifetime would not be too long....

And do not overestimate the temperature effects: Temperature is by far not the only degradation factor, so once you are below certain die temperature (i would guess below 60..70degC), other aging factors (phosphor aging by high intensity light itself,...) would be dominant. And if the reason for the high junction temperature is high thermal resistance, it is way better to first tackle this, as it offer way higher temperature reduction (then ~20..30degC inside the freezer versus normal ambient) so cooling it further down by the ambient does not make as big difference.
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SeanB~1
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #8 on: December 03, 2010, 11:41:54 AM » Author: SeanB~1
I bought 2m today, made up of a flexi board with the diode units being surface mount ones bonded to the board, with the whole string being sleeved in a shrink tube with a adhesive backing. The display ones have been on and lit for the last year, and are not appreciably degraded, unlike the one next to them which uses 5mm LED units, which are 2 years old with significant phosphor degradation and a marked blue output.

The 2m unit can be cut to size, but the 2m string uses 1A at 12V. I even got the whole box of sleeves for them, as I bought the remainder of the package.

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Medved
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #9 on: December 03, 2010, 03:12:06 PM » Author: Medved
The 3mm and 5mm "classic" LED shape is the worst for anything other then low intensity indicators. The plastic degrade very quickly and make quite large stress on the die and bonding (mainly at cold temperatures - as the plastic hardened when hot).
SMD LED's offer way better thermal properties, assuming the PCB copper layer pads they are soldered to are large enough to spread the heat. Mainly because of way shorter distance between the die and the copper plate heatsink (those pads on the PCB).
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Luminaire
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #10 on: December 03, 2010, 04:21:29 PM » Author: Luminaire
By the way, many of super market display cases have gone LEDs.  LED is recognized as highly efficacious compared to fluorescent both in lumens per watt as well as lower load on refrigeration system, as such government incentive picks up a good bit of the tab.
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Medved
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #11 on: December 03, 2010, 06:42:40 PM » Author: Medved
For refrigerator's use you are absolutely right due to two reasons:
At first the cold environment does not cause them to loose their efficacy.
And at second, the small lumen packages fridges need are hard to reach in efficient way with "classic" sources (both incandescent and fluorescents)
The 3'rd advantage of LED's is their low operating voltage, what allow the internal lighting to be made using SELV, so not face safety problems in humid and accessible area.

But what is the problem with many cheaper, low output LED's is their very poor thermal design and generally power handling capability. So poor, then even 60mW (20mA) drive per chip frequently cause it's very quick wear.
This is the reason, why i always better use decent "power" LED's, even if they seems to be more expensive - they simply have no issues with lifetime, even when stressed at AbsMax rating (however still by far not recommended practice, good compromise is to use about 2/3 of the current or power rating)
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #12 on: December 04, 2010, 02:16:12 AM » Author: SeanB~1
I intend to use some 5mm LED units for the top, running at 20mA, as I will have a few spare after doing some conversions of LED torches to UV. A little Veroboard, some resistors and a little used Cat5 cable will do it easily.
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Zelandeth
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #13 on: February 18, 2011, 08:50:07 PM » Author: Zelandeth
Here's a thought.

The single issue here is the UV emission from the tubes isn't it?

Why not just shroud the tubes in one of those anti-shatter sleeves?  Sure I've seen them listed somewhere in the dim and distant past with UV-blocking as one of their characteristics.  Wouldn't that - coupled with a switch to turn the tubes off when not needed - be a more sensible approach than a complicated retrofitted lighting setup?

Given that these are relatively rare items, I'd be hesitant to make any modifications that aren't easily reversible.
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DieselNut
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Re: F6T5 and F8T5 to LED retrofit idea? « Reply #14 on: February 18, 2011, 09:33:23 PM » Author: DieselNut
I agree. I would keep it fluorescent, especially since yours is preheat. Mine is HF electronic. I added the switch to turn the lamp on/off. I have seen these with very yellowed out lenses. It looks like a piece of glass or plexiglass could be fitted in mine if needed. If the HF ballast croaks in mine, it will get converted to preheat.
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