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Eliminating RF interference from HID(xenon) ballasts

Discussion in 'Radio and Wireless' started by fkon, Dec 6, 2012.

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  1. fkon

    fkon

    4
    0
    Dec 6, 2012
    Greetings!

    (I hope this is the correct forum, otherwise some kind mod could move the thread?)

    Some background:
    I have installed after-market(chinese) Xenon HID High-beams in my car. These have a ballast which transforms 12VDC from the car battery to 23kV AC required to ignite the lamps. The problem is that every time i turn on the HID:s the car stutters and warning lights inside the car(ABS, EPS etc)turn on.

    I work with R&D for a car company so I've conducted measurements both on the car itself and on separate HID-kits and a spare car battery. Unfortunately my area of expertise is combustion engines so i have only a rudimentary knowledge of electronics. My conclusion so far is that there is high frequency interference returned from the ballasts which propagate through the DC-cables(the error disappears when i use an external battery so airborne interference is not the cause) to the battery which in turn cause a reset of some node on the CAN.

    On the battery, oscillations with and amplitude of of ~150V and a frequency of 15-50MHz occur when the HID:s are turned on. I don't know if they are common mode or differential mode, it is difficult to get repeatable measurements with the oscilloscope since it picks up the airborne noise also.

    The ballasts use approximately 70A each in peak current during the first ms after the lamps are turned on but it appears(also a bit uncertain) that the disturbances occur before the large current peak.

    I've tried filtering the current cables from the battery to the ballasts close to the ballasts with capacitors, 1, 10, 100 nF(which should have low impedance in this frequency range) and ferrite chokes scavenged from computer cables. These help to some extent but don't eliminate the problem completely. The error still occurs from time to time.

    My next step would be to order ferrite cores with correct permeability from an electronics supplier. However, if the EMI is not common mode i will have to pass the + and - cables from different directions and the ferrite cores will become saturated(because of the 70A current) and will not be effective against the EMI, right?

    Some questions:
    1 Do you know if EMI from these types of transformers is usually common mode or differential?
    2 How should I wind the cables around the cores?
    3 Should I even use ferrites or something else entirely? Inductors?
    4 If the EMI is differential mode and i cannot find ferrite cores which do not saturate, how should I go about in adressing the problem?

    As I said, this is not my field of expertise so maybe I'm asking the wrong questions and maybe I'm not providing sufficient background information, in that case comment and I'll try to be more clear!

    I'm in a bit over my head here so I'm extremely grateful for any assistance!

    Regards
    F
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,070
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    Nov 17, 2011
  3. fkon

    fkon

    4
    0
    Dec 6, 2012
    Thank you Harald. That looks promising, unfortunately noone seems to have tried the proposed solution. The inductor for instance is rated for 10A but measurements show that the ballasts use approximately 70A peak current for 1ms. Is this acceptable, i e is 10A for steady state but higher peak currents are OK for short durations?

    Will the inductor not saturate from the high DC-current?
     
  4. fkon

    fkon

    4
    0
    Dec 6, 2012
    What I meant was that no one had replied in the thread and confirmed that it works.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    10,070
    2,151
    Nov 17, 2011
    You could be the first to try and respond :)

    Yes, the inductor will saturate, but an inductor normally tolerates a short overcurrent and can recover from saturation. How much, how long and with which consequences depends on the material and the construction of the inductor. I cannot help you with a general answer. Go ahead and try it.
     
  6. fkon

    fkon

    4
    0
    Dec 6, 2012
    OK, now I have a more specific question:

    The person who suggested the filter in the forum thread Harald linked to also suggests 2200uF Aluminium Electrolyte capacitors. From what I understand electrolytic capacitors are not suitable for eliminating RF, they are too slow.

    Will this filter really be effective for EMI in the 10-50MHz range?

    However finding ceramic or other 'fast' capacitors with the capacitance he has suggested for this lowpass filter is not a trivial task.

    Suggestions?
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    10,070
    2,151
    Nov 17, 2011
    Right, electrolytic capcitors are generally nit the right toll for EMI suppression.

    You will not find 2200µF ceramic capacitors - not at a manageable price.

    The 2200µF caps are there for buffering the voltage and delivering the high inrush current. The EMI you experience may be a result from the current spike that induces voltage sags in the wires and creates strong magnetic fields. By placing the large caps near the lamp, the capacitors are able to deliver the inrush current over a short distance, thus minimizing the effect of the inrush current on the rest of the car's electronic. If you are concerned about continuous EMI during operation of the lamp (not at switch-on), place a few 100nF film capacitors in parallel to the big ones.

    Harald
     
  8. JMW

    JMW

    90
    3
    Jan 30, 2012
    The 2200ufd capacitor is not for the EMI issue, it is for the 70Amp surge that is causing the engine to stutter, the gauges to flash etc. You might be able to rewire them and solve this by supplying the ballast directly from the battery using 4 or 6 gauge wire and a large relay.
    As for the EMI, once the car is running, you will have to track down and isolate the cause. Is the ballast leaking (shield the ballast and make certain it is grounded). As for the power leads, I would not use stainless braid, as suggested in the other post. Go to the local 2 Way radio shop and ask for a suitable length of RG 213. This has a tinned copper braid. It is much easier to cut and can be soldered (one end only) and grounded at a single point.Tape the ungrounded end to prevent unraveling. All three leads (1 for each lamp and the black and red power) should be grounded at the same point. Place the 4 or 6 gauge red and black leads in a variable speed drill and twist them together, leaving only sufficient exposed to make connections to your battery, relay, and ballast.
    Hopefully, you have also purchased the proper lenses, otherwise you will see no improvement, blind oncoming drivers as well as any you are following.
     
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