LED spots cuts out DAB Radio

Discussion in 'Tech/Mech General' started by Jifcom, Dec 14, 2012.

  1. Jifcom

    Jifcom Read Only Funster

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    HI All
    I'm after some advice, I have just fitted my Motor-Home out with LED bulbs in the reading spotlights, Now by DAB radio cuts out when I switch them on!!

    The original spots were 10 watt Halogens, now replaced with 2.4 watt SMD LED bulbs. I was advised by the company who supplied them that this would beok to swap.

    Has anyone come across this? how was it resolved?

    Regards

    Jon
     
  2. dave newell lvs

    dave newell lvs Trader-Vehicle Services

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    Hi Jon, I've come across a similar issue where switching the LEDs on blocked the remote control on a TV. The problem is that some LED lights, especially the cheaper ones, give off RF interference that can upset the electronics of some equipment.

    D.
     
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  3. Jifcom

    Jifcom Read Only Funster

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    Thanks Dave.

    That will teach me to buy cheap ones, will buy a better quality one to try before replacing them all,
    Strange thing is if I leave one halogen bulb in and switch that on first then switch on the LED ones all works fine???
    but if the led is switched on first, I lose the DAB signal?

    Maybe as you say, better quality ones will work.

    Jon
     
  4. Southampton

    Southampton Funster Life Member

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    This maybe answers a problem I have. My Autotrail (new) has a drop down TV in the hab area and I am experiencing interference (lines on the screen) when the LED lights are on. I have just switched them off and the lines go away. I thought it was just poor reception up here in the Lake District. A trip back to the dealers is called for when I get back. Thanks guys.
     
  5. rainbow chasers

    rainbow chasers Read Only Funster

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    Exactly as Dave says, the cheaper ones will emit a varied amount of RF signal. The more expensive lights come with drivers, which reduce power to what the LED requires and filter RF signal.

    You often find that directly powered LED will not last very long, so if you have a strip or led's that have one or two going out - you now know why! LED's should last 10,000 hours or more, they do not have an infinite lifecycle. To get the best performance, they need stepping down.
     
  6. hilldweller

    hilldweller Funster Life Member

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    Not quite right from a theoretical point of view.

    The cheapest way to limit the current through an LED is a resistor. I've got several multi-LED panels that do this. Downside is the resistor gets hot, that heat is wasted electricity, the brightness varies with battery voltage, but such a circuit cannot generate RF, it's pure DC. And as a matter of interest mine work extremely well. So the very cheapest to manufacture are the ones free from RF.

    The efficient way to limit the current is with a "Switch Mode" regulator. This switches the current on/off at very high speed. Much more efficient than a resistor, constant brightness BUT if not done properly can easily generate RF.

    All my original LEDs were expensive ones from UltraLED, all had switch mode.

    I've never noticed any RF problems.

    Bottom line is that price is not a good guide.

    In theory the EMC ( Electro Magnetic Compatability directive. CE mark ) regulations in the EU demand that ALL electrical devices are tested and do not emit RF, so much for regulations.
     
  7. hilldweller

    hilldweller Funster Life Member

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    I'm fascinated by this, if you post one to me I'll see if I can measure the problem and see if a filter on the wiring works. After the Christmas post clears up though.
     
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  8. TheBig1

    TheBig1 Funster Life Member

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    one problem that many dont realise is that the LED type bulbs have a lower resistance than conventional bulbs. this is why you need to fit a ballast resistor to cars fitted with a bulb failure circuit when converting to LED

    if your circuit works fine with all but one bulb changed, I would suspect that the supply circuit needs this resistance to work as designed. Not feeling too well today, but my thoughts are that your dab radio rellies on this circuit for power or ground. try running a feed direct from the leisure battery, using a fuse obviously
     
  9. Jifcom

    Jifcom Read Only Funster

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    Thanks for the input guys
    I must admit in a bit confused by the "Drivers" Rainbow-Chaser? When I had a look on goggle the only one's I could find were mains powered! or do certain LED bulbs have them built in? if so how do you tell?
    is this also "Switched Mode" as suggested by hilldweller or is that something else!

    TheBig1, I have the DAB Radio connected directly to the positive on the leisure battery but the Negative is grounded to the MH common earth, would this make a difference if also connected straight to the battery?

    Thanks again on all comments

    Regards

    Jon
     
  10. TheBig1

    TheBig1 Funster Life Member

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    if the radio is wired direct to the battery, then this must be an RF interference issue blocking the signal
     
  11. Dubiousp

    Dubiousp Read Only Funster

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    Picking up on Dave Newells point anything that emits heat, light or sound produces a frequency its all with in a Spektrum. I think its probally more likely that the pins can some times be dirty or even slightly smaller and whilst the light may not dip a small arc may occur
     
  12. Arduino

    Arduino Read Only Funster

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    I think that having read the various posts here, I think that, because the operation of a Light Emitting Diode (LED), is not clear, a lot of conjecture has crept into the replies. I can put most of the post onto the correct footing, if people are prepared to believe what I am saying.

    The LED emits light because the current flowing through the semiconductor allows photons to be produced. Photons are what we see as light. The current flow is Direct Current (DC) and flows from the supply through the diode and back to the supply.

    By the nature of the properties of an LED, or indeed any semiconductor, the current through it is proportional to the voltage supplied, because every conductor has a known resistance. In the LED the resistance is the product of the semiconductor junction, which emits the photons that we see. Because there IS a resistance, the semiconductor will consume an amount of current at a known voltage. If the voltage is decreased, the current flowing through the semiconductor junction, decreases. If the voltage is increased, the current flowing through the semiconductor junction, will increase. These changes are proportional, because the semiconductor junction resistance is static i.e. it does not change.

    As with any current flow through a resistance, heat is generated, this heat can and will change the semiconductor resistance and therefore, if too much heat is allowed to generate, the resistance will drop to a point where the current flowing is too large for the semiconductor junction to withstand and it will break down. The LED is then knackered!

    Right, so with all this theory, how does this relate to the post presented here originally? Well, an LED, whether it be a little round 3mm, 5mm type or a Surface Mount Device (SMD), which are usually flat and rectangular, may be yellow to look at; all operate with a very small current through them. This can be anything from some 15 milliamps (0.015 of an amp), to several hundred milliamps for very large chip LEDs for use in flood lights and industrial use.

    LEDs are therefore NOT voltage dependent devices, but current. This means that it is the current passing through the LED that is critical for proper operation, best light performance and maximum life span. Most LED bulbs today contain more than one LED. So you will often see a bulb with an array of LEDs. In order to reduce the current to an LED, for optimal operation, a manufacturer will often use the cheapest method, which will be a resistor in series with one or more LEDs. This resistor limits the current through the LED, by reducing the voltage available to the resistor. So, if the voltage is measured across the LED chip, you will find it to be in the order of 1.2 to 2.2 volts, with probably 25 to 30 milliamps of current flowing. Manufacturers will also put a resistor in parallel with the LEDs i.e. across positive and negative, which will also absorb some of the current flow through the series resistor and thus diverting it away from the LEDs. This provides better operation because, if a single LED should fail, the current flow through the circuit will remain somehow constant and thus stop the remainder of the LEDs from getting an increase in current, which would shorten their life. The parallel resistor is therefore a current sink and is essential for ensuring the optimum current flow through the LEDs at all times. The resistors will emit heat though.

    With reference to 12v and 24v LED bulbs, resistors are the normal method of reducing the current through the LED. There are other methods. When LED bulbs are used as replacements in the 230v mains or 110v mains circuits, a resistor is not the way to go. So electronics are used. This is where one poster mentioned 'split mode' or inverter technology. this is somehow correct, but not quite. What is actually done is that PWM (Pulse Width Modulation) is employed, which in essence turns the LED on for a short period and then off again. As the LED lights, current is drawn and when that current reaches its optimal threshold, the LED is turned off again, until the current drops below its lower threshold and the process is repeated. This is done by with the use of inductors, semiconductor chips, which are specially produced for this single task and a few discrete electronic components. My employing PWM technology, all the best conditions for the LED are met. Less heat is generated and less current is consumed.

    A side effect of PWM technology is two fold and a bit more. The LED bulbs will cost significantly more, By altering the PWM frequency (the LED is actually flashing on and off very quickly), the LED can be made to dim. It is just kept switched off longer than it is allowed to be on. A bi-product is that this on off switching creates a magnetic field around the inductor used in the PWM circuit and this generates a radiation that can be in the radio reception spectrum. Additional components are fitted to the LEDs that employ PWM, in order to reduce the effects of this. It is this radiation that is seen to affect TVs and radios.

    I have discussed PWM with mains powered LEDs, but not DC powered LEDs. The ones I have discussed here, just employ are resistor network. NO radiation can be emitted from this type of LED, period. It is quite possible to get LEDs that operate on low voltage DC that employ PWM technology as well, so the same radiation problems could be experienced. Often, several LED bulbs are coupled to a 'LED transformer', which more often than not, employs PWM technology. If you have a small auto DC bulb, then it is very very doubtful that this will have any PWM technology built into it. It is not cost effective and they are just physically too small to fit anything into.

    As to the quality of LED bulbs... I can confirm from vast experience, that a LED bulb from China on eBay or elsewhere, that only costs a quid or two, will be the same as any one else's costing ten pounds or more, BUT, and only BUT, if the more expensive bulb is not from a branded manufacturer, such as Osram, Philips, Sylvania etc. Branded bulbs are terribly expensive, because they employ good quality components that have been exhaustively tested.

    So, from my experience, if a LED bulb is just that, a bulb and NO packaging of a known manufacturer, it is the same thing you will get from eBay via china. So pay a quid, wait a month for it to turn up, use it and if it fails sometime in the future, just get another one, or buy two when you buy one. For 8 to 10 quid, you can get eight to ten bulbs from China. The guys that sell them in their tents might be doing just that!

    I hope you find this useful. It contains my views and experiences formed from many decades working with electronics. I only relate facts and not hearsay, although they are my facts.
     
  13. Jifcom

    Jifcom Read Only Funster

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    Thanks for all the reply's.
    I have no electrical in-depth knowledge, so can,t say I understand most of what has been written.
    all I know is that I have now tried 5 different bulbs?
    The only one's that worked without the DAB cutting out are theses.

    [ame="http://www.amazon.co.uk/gp/product/B004ZYJ21K/ref=oh_details_o00_s01_i00"]HQRP MR11 GU4 Base 10 LEDs SMD 5050 LED Bulb Wide Angle Cool White 6000K 12V AC / DC 2.2W 138 Lumen plus HQRP Coaster: Amazon.co.uk: Lighting[/ame]
    I have tested these just on the leisure battery and when hooked up and have had no problems at all!

    The others which effected the DAB are
    http://www.ledhut.co.uk/spot-lights/mr11-led-bulbs/mr11-2.html

    http://www.ultraleds.co.uk/12-led-mr11-150-lumen-warm-white-ac-dc-2-8w-25w.html

    http://www.simplyled.co.uk/High-Pow...iece-SMD-5050-20-watts-equivalent_A175E4.aspx

    http://www.ebay.co.uk/itm/Caravan-M...ervan_Caravan_Accessories&hash=item35becf692c

    So in my opinion, Not all LEDs are the same, dont ask what the difference is? all I know is that I now have LED lights which work and don't cut out the DAB radio so I'm happy.

    Jon
     
    Last edited: Dec 22, 2012
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