Need help polarity of LED driver/controller connection for Christmas Tree Lights - Page 1
Forum section: electronics / repair

author: Cyclobiker
author_rank: Newbie
timestamp: February 05, 2019, 12:41:59 am
content: Hi. I am new here. Would anyone be able to direct me to a solution for this problem. I have a 30V driver for LED Christmas tree lights. The driver connects to a controller that makes the lights blink in various sequences dependng on which buttons you push.The connection between the driver and controller was intermittent. I traced the problem to a broken wire on the 29V side of the driver due to over-flexing where the wire on the 29VDC side comes out the 120VAC plug/transformer/driver unit on its way to the controller.I cut the wires in the 20VDC pair at the break and bared enough conductor to make an effective repair … but I made the mistake of not taking a picture first. Now I do not know which way to connect the dc wires.How can I determine the correct way to connect the wires so that the light controller and subsequently the lights receive the correct polarity?Is there a safe way to test before making a final connection?Is there a risk that connecting the wrong way would destroy the controller?The driver is Ting Shen Industries Model TS-8W29V rated 120VAC/29VDC at 0.28A.This connects over a pair of 20 AWG wires, one of which is "striped" with the ratings of the wire and insulation printed on it. Would this striping help identify the required polarity?I have appended a photo that shows the situation.

author: Specmaster
author_rank: Super Contributor
timestamp: February 05, 2019, 07:49:59 am
content: Quote from: Cyclobiker on February 05, 2019, 12:41:59 amYes, the way to do it is to connect a multimeter set on dc volts at around 30v, to the controller terminals. Switch on and check which way the meter probes produce a positive voltage reading. Usually it is the core that has the stripe on is the positive. Resolder the wires back on and all should be OK. If not, reverse the wires and try again. Most Christmas lights are LEDS so reversing the polarity shouldn't do any harm. They will work one way only.

author: Ian.M
author_rank: Super Contributor
timestamp: February 05, 2019, 08:40:54 am
content: Quote from: Specmaster on February 05, 2019, 07:49:59 amDON'T DO THAT *YET*! The controller is 'smart', so its not just a simple connection to a string of static LEDs. It looks like that 29V connection to the wallwart is actually a plug, normally held in by the screw on retaining ring still on the wire. If that plug's keyed to only fit one way, the odds of it being reverse polarity protected aren't that good. If however i can fit either way round, you are good to go and splice it as Specmaster suggests.If the plugs keyed, it a 50:50 gamble you'll get it right the first time. If you loose and connect it backards, there's a significant chance it will have killed it, so if it looks like the controller case can be popped open with the aid of a spudger, or it has hidden screws, it would be worth taking a look inside, as I'd bet we can identify the correct polarity if we can see photos of both sides of the board. Heck, it may even be marked on the board!If you don't or cant open it, the best chance is if you can see any trace of the writing on the remaining insulation, or if there's a ridge or stripe on the outside of the insulation of one wire (not the traces left in the middle from splitting them). Otherwise, how lucky are you feeling today?

author: Specmaster
author_rank: Super Contributor
timestamp: February 05, 2019, 09:57:31 am
content: It's going to be a polarised plug anyway, otherwise there is a danger of plugging it in the wrong way round and then the user is going to have a 50 50 chance of getting it right first time around. Get it wrong and you're more likely to think that they are broken and throw them out. The stripe wire is the most likely to be positive and by using the meter approach, you will identify the positive lead.

author: Armadillo
author_rank: Super Contributor
timestamp: February 05, 2019, 10:21:29 am
content: If the controller is a DC-DC buck, then the GND should be common, is it not?Edit: or some DC-DC boast, the GND is also common.

author: Specmaster
author_rank: Super Contributor
timestamp: February 05, 2019, 10:52:02 am
content: OK, do you have a multimeter? If yes, then check the polarity of the two wires coming from the power pack, or wallwart and identify which is the positive. Next switch the meter into the resistance range and apply the probes to the led controller, note the reading on the meter and then reverse the probes on the wires and note the reading. One way you will get a high reading or it may indicate overload if its a digital meter, the other way you will a lower reading. The wire that the red meter lead is applied to when you get a lower reading is the positive, connect that lead to the positive from the wallwart and the other lead to the other one, insulate them both and job done.

author: Armadillo
author_rank: Super Contributor
timestamp: February 05, 2019, 11:10:08 am
content: @Specmaster;I tried that with my DC-DC, both show charging and goes into Meg then infinity because there is a capacitor inside.

author: Ian.M
author_rank: Super Contributor
timestamp: February 05, 2019, 11:17:53 am
content: It would be most unlikely to be unpolarised as then the controller would need to have a bridge rectifier at its input. That would only be required for compatibility with legacy low voltage lighting systems using line frequency AC, but the rated voltage 29V would require a RMS voltage much greater than the 12V AC that used to be commonly used. However I didn't want to exclude the possibility without evidence.There's no reason to suspect common ground. The wallwart PSU is obviously ungrounded, and there is a slight advantage in using low side switching in the controller. However it may even use half-bridge switching for each output wire or have both high and low side switching to permit the LED string to be multiplexed or charliplexed.If it come down to a gamble, stripe + is as good a guess as any.@Specmaster,A significant number of DMMs have resistance autoranging that gets confused by diodes etc. so it would be vastly preferable to use a diode check mode.Your suggestion will work if the controller has a series reverse polarity protection diode. If its got a shunt diode and fuse it will give the wrong answer. If its not got a protection diode the results will be ambiguous - reverse biassing ICs and MOSFETs is likely to read as two diode Vf drops, but biassing them with normal polarity at low voltage may do just about anything.Edit: It looks like ambiguous wins the day.

author: Specmaster
author_rank: Super Contributor
timestamp: February 05, 2019, 01:05:24 pm
content: @Ian.M Yes the stripe being the +plus was what I posted earlier and the wallwart states that it gives out DC so the meter would show which wire from the wallwart was the +plus.I used the meter set to resistance mode on my battery powered portable oscilloscope and it worked just fine and to prove the finding was correct, I plugged the meter leads into my bench supply and fed 9V to the oscilloscope and it worked perfectly so that method does indeed work.I also tried using the diode mode as you suggested using a Fluke 25 for the test and I got OL displayed on both ways of connecting

author: Cyclobiker
author_rank: Newbie
timestamp: February 05, 2019, 07:26:23 pm
content: Problem solved: I took macro-photographs of the severed conductor coming out of the wallwart. No trace of striping on either conductor even zoomed up. Next I took a hacksaw and cut a channel into the case, not quite all the way through. I used a large screw driver to pry the case apart. Appended is a photo of the card. Testing with an ohm-meter confirms the striped conductor is connected to the circuit board terminal marked VCC. I all the work I have done on circuits VCC has been positive DC so I am confident that connecting the striped wire from the LED controller to which ever wire tests positive coming from the wallwart should be the correct connection.Appended is a photo of the controller circuit board. The input side is on the right. For the record, I connected my ohm-meter from GND to OUT2 and it read high impedance, so I assume these two terminals are not connected by copper conductor.In case anyone else is searching the internet with similar problem with this product, here are the details:LED Controller with RF Remote Control, INPUT DC 20V-32V, OUTPUT: 28V-32V 500 mA 14W-16W, MODEL YLM-4M, Silver Beauty Electronic and lighting Co.Thanks to all who replied. You advice and assistance is much appreciated.

author: Specmaster
author_rank: Super Contributor
timestamp: February 05, 2019, 08:02:02 pm
content: We're all pleased to have been of assistance to you, please come back and confirm if the lights work correctly when you have confirmed which is the positive lead from the wallwart and remade the connections again.

author: fzabkar
author_rank: Super Contributor
timestamp: February 05, 2019, 09:59:14 pm
content: Quote from: Cyclobiker on February 05, 2019, 07:26:23 pmIf there is any doubt, use the polarity of the electrolytic capacitor for confirmation.

author: Armadillo
author_rank: Super Contributor
timestamp: February 05, 2019, 10:12:14 pm
content: As a side note, the house lighting color rendering must be pretty not good, Black to Green?

author: Cyclobiker
author_rank: Newbie
timestamp: February 09, 2019, 01:17:31 am
content: I took fzabkar's suggestion. The negative end of the capacitor is connected directly to the terminal marker GND.Ok things have been reconnected treating the "striped" wire as DC positive and … the lights work. All is well.Thanks to everyone for your suggestions and advice.

author: Specmaster
author_rank: Super Contributor
timestamp: February 09, 2019, 01:49:42 am
content: The striped wire is normally in a properly organized world positive, as per my first message about this. So glad it all works OK again.