Remove choke when switching fom T8 flurecent to LED? - Page 1
Forum section: electronics / general

author: Grottenolm85
author_rank: Newbie
timestamp: May 29, 2015, 10:34:33 am
content: @ Dave and all other interested ones:You mentioned in one of the Videos, that you are using LED-retrofit-tubes in your lab.Did you remove the choke? If not ,why? Isn't it kind of useless with LEDs? Just sitting there getting warm...I am wondering, because i am about to change 13 tubes to LEDs soon and i am wondering whether i should take the time to bridge the choke....Thanks

author: amyk
author_rank: Super Contributor
timestamp: May 29, 2015, 01:58:14 pm
content: It's there to limit the current. LEDs are constant-current devices, just like fluoro tubes.

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2015, 03:57:44 pm
content: This is a typical read the manual case. I'd check the datasheet of the replacement tubes to see how they have to be powered.

author: SeanB
author_rank: Super Contributor
timestamp: May 29, 2015, 05:01:32 pm
content: Leave the choke in. While the LED lamps do not need the choke for operation, the extra supply impedance will do wonders to increase lamp life, as it limits the voltage spikes that destroy the SMPS inside the tubes. The small power loss across the choke ( under 10V will not be a worry) is more than compensated by the increased reliability of the whole unit.However if doing a lighting upgrade it probably would be better to simply replace the entire fitting with a LED one, as then you get a light which hopefully is designed with the aim of keeping the LED chips cool, and the electronics as well. The tube refits are both expensive and have issues with hot running leading to light output degrading with time as they run very hot internally, with the glass tube increasing internal temperature.

author: djQUAN
author_rank: Frequent Contributor
timestamp: May 29, 2015, 05:30:18 pm
content: Quote from: amyk on May 29, 2015, 01:58:14 pmLED tube retrofits already have built in driver supplies. So, no. That is not the case here.I cannot find where I read that leaving the ballast in improves the power factor as it smooths the high peak input currents of a capacitor input SMPS of an LED driver and causes the input current to be more sinusoidal. Although a particular LED tube replacement did not work when I tried it at home. Worked fine when I removed the ballast.

author: tom66
author_rank: Super Contributor
timestamp: May 29, 2015, 07:58:12 pm
content: Wouldn't the inductor create a potentially large voltage when the switch to the fluro is turned off, esp if it is turned off near a mains peak?This spike could damage a sensitive LED driver.

author: Zero999
author_rank: Super Contributor
timestamp: May 29, 2015, 09:48:38 pm
content: Generally you should disconnect the inductor if the LEDs come with their own SMPS (always the case, as far as I'm aware). Of course you don't have to throw the old ballast out. You could just leave it there disconnected and unused.

author: amyk
author_rank: Super Contributor
timestamp: May 30, 2015, 10:13:05 am
content: The ones I'm familiar with use the existing ballast to do current limiting and don't have much more than a rectifier and smoothing capacitors:http://www.edn.com/design/power-management/4425599/Product-How-to--Drive-LEDs-with-fluorescent-ballasts--part-1-http://www.designingwithleds.com/inside-cree-t8-led-fluorescent-lamp/?PageSpeed=noscript

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 31, 2015, 10:08:35 am
content: When I replaced some fluros with LEDs I measured the difference in power consumption when the choke was bypassed - I don't recall the figures but concluded it wasn't worth bothering as the difference was minimal.With the LED tubes, the choke doesn't get noiceably warm.It probably is worth removing the PFC cap though.

author: djQUAN
author_rank: Frequent Contributor
timestamp: May 31, 2015, 12:37:36 pm
content: Quote from: amyk on May 30, 2015, 10:13:05 amThat's interesting. I have never come across those. I always encounter LED tubes with built in offline SMPS drivers but the smaller ones use the capacitor dropper, though I must admit I don't have a lot of experience with them

author: Zero999
author_rank: Super Contributor
timestamp: May 31, 2015, 12:55:39 pm
content: Quote from: djQUAN on May 31, 2015, 12:37:36 pmSame here, also note if it's a capacitive dropper, then connecting an inductor in series could cause smoke, as it might lower the impedance, causing more current to flow.

author: Grottenolm85
author_rank: Newbie
timestamp: May 31, 2015, 06:06:48 pm
content: I bought one LED-Tube for testing.There is only a small hole in the Lamp where i can see the choke, so i could not bridge it easily. After 2x4 min of running time the choke was not even noticeable warm to the touch, so assume the losses are minimal.Sadly there is no easy way to measure the power...