Guest Posted May 15, 2011 Share Posted May 15, 2011 Hi Guys, Just a quick question about LED ballasts, I have just finished my Overland Trailer I went for LED units and although they flash at the correct speed the tell tale on my dash does not flash. I understand that to correct this I need to fit ballasts to introduce some resistance into the circuit and all should be good however as I have never used them before what type do I go for? Is there a better way of doing it? Where is best to get them from? Cheers, Jason. Quote Link to comment Share on other sites More sharing options...
nickwilliams Posted May 15, 2011 Share Posted May 15, 2011 This thread may help. Nick Quote Link to comment Share on other sites More sharing options...
Guest Posted May 15, 2011 Share Posted May 15, 2011 This thread may help. Nick Thanks Nick, I did see that thread however it seems to cover more about LED NAS lights than the trailer LED question, the lights flash at the correct speed just don't show on the tell tale hence the question about types etc I have normal bulbs in the defender so changing the relay is not an option and not needed anyway. Jason. Quote Link to comment Share on other sites More sharing options...
western Posted May 15, 2011 Share Posted May 15, 2011 you need a resistor so the existing flasher unit see's the same current draw as normal filament bulbs, have a look on http://www.ultraleds.co.uk/ Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted May 16, 2011 Share Posted May 16, 2011 They flash at the correct speed because the relay can just see the car's flashers. As sadi to get the tell-tale working you need to draw extra current. Quote Link to comment Share on other sites More sharing options...
disco_al Posted May 16, 2011 Share Posted May 16, 2011 what you need is a a smart load device - maypole do one, part number mp388b. can't find anything on the web, but it's in their catalogue here though on page 11 Quote Link to comment Share on other sites More sharing options...
A Twig Posted May 16, 2011 Share Posted May 16, 2011 Smart load device!? Jeez! Stick with western's advice, all you need is a resistor in series with the LED bulb to draw a wee bit more current. Post the numbers up and I'll even do the calculations for you! You basically need to know the difference in current between your LED set up and what would be the case with a normal set up. Your voltage is 12V (lets say 11V to add a bit of leeway). So, Ohm's Law: V = IR Original Resistance: Original Resistance = Voltage / Current Original Resistance = 11V / Whatever current the incandescent bulbs drew Find out what the resistance is now: New Resistance: = 11V / What current your LED lights are drawing (you can measure this with a multimeter/ammeter in series if you want) Therefore the resistance you need to add to get the ticker to work is: Original Resistance - New Resistance Job's a good un... Yes you'll be drawing a touch more current so your overall setup won't be quite as efficient, but short of rewiring the whole shebang that's the most cost effective way. Quote Link to comment Share on other sites More sharing options...
UdderlyOffroad Posted May 16, 2011 Share Posted May 16, 2011 I think you might have missed a few things there Twig... You basically need to know the difference in current between your LED set up and what would be the case with a normal set up To measure the current throughput - you'll either need an old-school AVO meter with a needle or a fancy digital meter with peak-hold function to determine the max current draw when the unit flashes. A £4.99 digi-meter will just flash up random numbers as it tries to keep up with the flasher relay turning on and off. Also, what a about the power rating of the resistor? It'll be more than a 0.25W standard RS-jobbie. It's worth mentioning that for this solution to work the resistors should be mounted on the trailer, not the tow vehicle itself - otherwise you might find yourself blowing fuses if you tow another trailer. When I get my truck up together I'm going to implement a smart-load device based solution to allow me to have any combination of LED lights (should I win the lottery), LED trailer lights (should I win the...etc), filament bulbs, filament trailer etc. I was going to use one of these to replace the LR flasher relay, and a smart load device such as this one (PDF, page 21) from Ryder Towing. This will give me output for the in-dash tell-tale but it doesn't have a buzzer (which drives me spare in my Eurobox). Again I can't find a supplier for this online but I'm going to try my local towbar fitting emporium. The maypole one should be available from the likes of Motaman... HTH... Matt Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted May 16, 2011 Share Posted May 16, 2011 Stick with western's advice, all you need is a resistor in series with the LED bulb to draw a wee bit more current. Parallel, dear boy In series and you make the problem worse! Regular bulbs are 21W ~ 1.5A draw @ 14V = 9.3 Ohms and a hefty resistor, couple of quid each, run one per side: Something like this will probably do the job A Link, that or an 8.2Ohm equivalent, again, 25W is fine. The reason for the difference in power and value compared to the other post is here you are just synthesising one bulb's load, and not 2. half the power and twice the resistance If you have spade connector os similar on the back of the bulb holder, cut them off and recrimp new ones on with a tail on each -solder/fix these wires to the resistor terminals and job done Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted May 16, 2011 Share Posted May 16, 2011 Just wire up a set of BULBS in parallel with the LEDS, all will be hunky-dory Quote Link to comment Share on other sites More sharing options...
simonr Posted May 16, 2011 Share Posted May 16, 2011 Why do you need a tell-tale at all? The advantage of the LED lights is that they almost always work. The tell-tale will only tell you that the ballast resistor is working but nothing about the LEDs. You still need to check the lights when you connect the trailer - but you can bet they will still be working at the end of the trip too. I would just leave the lights as they are! Si Quote Link to comment Share on other sites More sharing options...
BogMonster Posted May 17, 2011 Share Posted May 17, 2011 You still need to check the lights when you connect the trailer - but you can bet they will still be working at the end of the trip too. I wouldn't bank on that. LED lights in marine applications (used as navigation lights) are getting a lousy reputation for failing long before they should do. I ended up specifying normal nav lights on my boat last year because there seemed to be little point in paying 4x the price for something that appeared to be no more reliable. Quote Link to comment Share on other sites More sharing options...
Guest Posted May 17, 2011 Share Posted May 17, 2011 Thanks for the replies, think I sort of have the answer (fit resistance/ballasts), as originally posted I know why it is happening just wanted to get the group experience as to what was the best way of sorting it out. As to why I want it to work I believe that the tell tale is a legal requirement and although I do check my lights before setting off I do like to stay the correct side of the law as I intend to take the Landy/trailer overseas through Europe etc the last thing I want is some over official Gendarme (other European police forces are available) giving me a fine etc for not complying with the Law. Jason. Quote Link to comment Share on other sites More sharing options...
A Twig Posted May 17, 2011 Share Posted May 17, 2011 You'll either need an old-school AVO meter with a needle or a fancy digital meter with peak-hold function to determine the max current draw when the unit flashes. A £4.99 digi-meter will just flash up random numbers as it tries to keep up with the flasher relay turning on and off. I assume most people doing automotive electrics have a decent digital meter.... Also, what a about the power rating of the resistor? It'll be more than a 0.25W standard RS-jobbie. It's worth mentioning that for this solution to work the resistors should be mounted on the trailer, not the tow vehicle itself - otherwise you might find yourself blowing fuses if you tow another trailer. Quite right, as the OP has already wired up whole trailer with inverters etc I thought this was a bit grannies and eggs. But if anyone is reading this then yes, the above is VERY important! Parallel, dear boy Oops - that's what comes from trying to answer LR4x4 while at work, getting called away and forgetting what I was on about when I came back! I shall amend my original post when I get a sec... Quote Link to comment Share on other sites More sharing options...
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