Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Needing to filter Capacitive Discharge feedback

  1. Mar 13, 2012 #1
    I'm trying to put some LED's on our racecar. They're 7 segment LED panels where each segment is 5 LED's with a 220 ohm resistor on the end.

    The car runs on 12 volts with engine off and 14 with engine on.

    I have power (Vin) coming off a distribution block, ground also goes to a distribution block.

    Vin then goes to a 512-KA378R12CTU 12 volt regulator, comes out, and splits off to a screw terminal and to a 511-LD29150DT50R 5 volt regulator, which sends 5 volts to an atmel 328P TQFP package. I have 47uF tantalum, 10 uF tantalum, 1 uF, and 0.33uF capacitors to clean up the input/output voltages.

    The board works as designed (querying binary coded decimal switches and sending a duplicate readout of the LED panel to an indicator display) with th engine is off (water and fuel pumps don't affect anything), however, once the engine is running, the display goes flat blank, EXCEPT some tiny, tiny pulses (1/500 sec maybe?) every so often. Shut the engine off, goes back to normal. I put my multimeter in ammeter mode, and it recorded 0.1 amps between the Vin lead and a power source. The board pulls 0.4 amps with the ignition off.

    I put my multimeter on frequency settings, and I get zero hz with nothing on or with all the pumps on. Once the engine is running, I get a 1.2 Khz wave in the system (presumably sinusoidal but without an oscilloscope I don't know...).

    I was powering the displays from a distribution block very close to the ignition box, so I made a cable going directly to the battery posts (4 ft longer cable). This made things significantly better, now only the 3rd digit (the last on the daisy chain of power) flickers on/off every second or so.

    I'm guessing I need to make some sort of filter circuit, but I'm not really sure?
     
  2. jcsd
  3. Mar 13, 2012 #2

    NascentOxygen

    User Avatar

    Staff: Mentor

    I'd guess that one of the regulator ICs is reacting badly. Try more electrolytics across their input terminals. Try 4700uF and 47uF and 0.47 uF all in parallel, 35 volt rating. Electrolytics don't like heat, so locate in a ventilated spot or they may not last long.
     
  4. Mar 14, 2012 #3
    Nascent,

    Given the decoupling caps on the power supply board and on the controller, I have no decouplers on the LED boards themselves.

    The 5 volt mcu and LED indicator don't flicker, and they run as a subset of the 12 volt circuit. This leads me to believe that the power supply board is working properly, and that I need to focus my attention on the LED panels.

    I don't know if the CD ignition box or the alternator or both are causing the 1200 hz wave (and I don't have an o'scope), but as best as I can tell, that's the only thing that changes when the engine is running.

    Not shown in these pictures is the 47uF tantalum that was added in parallel to the 0.33uF cap.

    The 1.0uF decouples the voltage before it gets to either regulator

    The 47uF tantalum decouples the output of the 12 volt regulator, while the 0.33uF decouples the input of the 5 volt regulator (they are in parallel)

    The 10uF tantalum decouples the output of the 5 volt regulator. That's really the only element that the 5 volt line sees (besides the .1uF's on the controller) that the 12 volt line doesn't- maybe that's all I need on the other side?

    On the controller (not shown), the 328P has 2 different 0.1uF decoupling caps on it, on VCC and AVCC.

    th_power_supply-front-1.png

    th_power_supply-back.png

    http://www.mouser.com/ProductDetail/Lelon/REA0R1M2ABK-0511P/?qs=sGAEpiMZZMtZ1n0r9vR22Z8b58wL7Nwv4bv%2fa21%252beXo%3d [Broken]
    http://www.mouser.com/ProductDetail/Lelon/REA010M2ABK-0511P/?qs=sGAEpiMZZMtZ1n0r9vR22YgcI%2fJYgoutoRXBBckjC2Y%3d [Broken]
    http://www.mouser.com/ProductDetail/EPCOS/B41827A6106M000/?qs=sGAEpiMZZMtZ1n0r9vR22b0Wmj03gb3uE3xfdGLFOIs%3d [Broken]
    http://www.mouser.com/ProductDetail/Nichicon/UVR1H470MED1TA/?qs=sGAEpiMZZMtZ1n0r9vR22afkwEr%252bqyzvsXww%2fp7SF0M%3d [Broken]

    http://www.mouser.com/ProductDetail/AVX/TAP104K035SRW/?qs=sGAEpiMZZMtZ1n0r9vR22SKv3nCGDP6cmjwZVaWgu7k%3d [Broken]
    http://www.mouser.com/ProductDetail/AVX/TAP105K035CCS/?qs=sGAEpiMZZMtZ1n0r9vR22X84dCiTW0OjwZB4uN8T5Aw%3d [Broken]
    http://www.mouser.com/ProductDetail/AVX/TAP106K035SCS/?qs=sGAEpiMZZMtZ1n0r9vR22Xu88swJg3nY7eBNkT2YtbA%3d [Broken]
     
    Last edited by a moderator: May 5, 2017
  5. Mar 14, 2012 #4

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    would it be worth disconnecting alternator belt (or field wire) and running for a few seconds?
     
  6. Mar 14, 2012 #5

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Ferrite chokes do a good job of tidying up waveforms, too. This applies to the signal lines as well as the power lines to your electronics.
     
  7. Mar 14, 2012 #6
    going to stack the electrolytic capacitors on the connections and put a choke on the power wire. the .1uF has a 3milliAmp ripple current spec so I'm debating to put it on there, 1uF has a 22mAmp, 10 is 50 something, 47 is well over 100.
     
  8. Mar 14, 2012 #7

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Did you think of buying a suitable filter unit? You can get them as bulkhead fittings instead of a simple feed-thru and the cost may not be all that high for the 'right thing'.
     
  9. Mar 14, 2012 #8

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Most car radios have a filter in power line to keep out "alternator whine"
    and most junkshops have junk car radios.

    It's just a simple LC filter, probably the inductor from a speaker crossover would do.

    We're pullin for ya !
     
  10. Mar 14, 2012 #9
    I'm 2 blocks from mouser headquarters, I can get anything at the will-call office within an hour of ordering.

    So here's what I came up with today. Notices i said our car...I should have said a friend's car. Our car already has one.

    Using regular 18 gauge doesn't work at all. I have to use my 6x22guage wire bundle. It's not shielded, but I think the 4 unused wires are acting as a shield.

    The ignition box gets power from the barrier strip, which is 4 feet of 14 gauge from the battery. The charging posts on the back of the car go directly to the battery via 4 gauge cable.

    single 18 or 6x22 don't work at the barrier strip
    single 18 or 6x22 don't work directly at the battery terminals
    single 18 doesn't work at the charging posts, 6x22 does.

    I stacked 2 47uF, 2 10uF, 2 1.0uF, and 2 0.1uF all together on the input line, slowed down the flashing just a bit, maybe from a couple thous of a second to maybe a hundredth or so per second (.01 on .99 off).

    What we did for testing, was relay the board off the charging posts, switching with the ignition switch. I still get 1200 hz at the input terminals of the power supply board, but the LED's stay steady.

    Something to think on- the ferrites are making a HIGH pitched hum/whine- around 15kHz or so. If I unsnap them, it goes away. I have one on the power lead for the power supply and one on the power lead for the ignition box.

    We're gonna do a quick test rig on his second car tomorrow, so see if it's roadster or if it's something I need to make a design compensation for. He has 4 cars and bought a display for each one. Just makes me really nervous not being able to start the other car I've already put one on.

    on his car:

    https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/417024_10150856967159606_771454605_12582084_408841564_n.jpg [Broken]

    on another car (couldn't start it, may or may not work?!):

    https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-ash4/417181_10150849242164606_771454605_12558482_690369463_n.jpg [Broken]

    on our car (works perfectly fine):

    https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc7/431409_10150829834529606_771454605_12489056_227043297_n.jpg [Broken]
     
    Last edited by a moderator: May 5, 2017
  11. Mar 15, 2012 #10
    So we hooked up his second car today, and it works just fine, we tested it with the LED boards sitting on the ignition box with the car running. I didn't get a frequency measurement though. The roadster has an older msd 6-AL box in it, the others have a slightly (maybe 1 year) newer 7AL2 box.


    So it's something with that specific ignition box.
     
  12. Mar 16, 2012 #11
    Also, on the roadster with the issue, I put a piece of sheet metal between the MSD and the power supply, and that didn't help any. So I don't think it's something coming as magnetic waves, but since I'm getting the same 1200hz signal at the charging posts with it working, I don't think it's anything in the electrical signal, either.

    I'd wonder if it's a ground loop or something of the sort, but it doesn't even work when tied directly to the battery.

    Based on a calculator I found:

    4 gauge spaced 50mm apart:
    9pF/m
    1.3uH/m DC
    1.2uH/m HF
    355 ohm HF

    x 2/3 meter = 6pF, .8uH DC, .72uH HF, 250 ohm HF


    22 gauge spaced 1mm apart:
    24pF/m
    .57uH/m DC
    .46uH/m HF
    141 ohm HF

    x2 meters= 48pF, 1.14 uH DC, 0.92 uH HF, 282 ohm HF

    18 gauge 1.5mm apart:

    26pF/m
    .53uH/m DC
    .43uH/m HF
    129 ohm HF

    x 2/3 meter = 18pF, 36uH DC, 28 uH HF, 76 ohm HF

    x 2 meter = 52pF, 1.06 uH DC, .86 uH HF, 258 ohm HF

    The only working combination is 2 meters of the 22 gauge with 2/3 meter of the 4 gauge..

    6pF, .8uH DC, .72uH HF, 250 ohm HF
    48pF, 1.14 uH DC, 0.92 uH HF, 282 ohm HF

    check my math:

    5.3333 pF, 1.94 uH DC, 1.64 uH HF, 532 ohm HF
     
  13. Mar 16, 2012 #12

    NascentOxygen

    User Avatar

    Staff: Mentor

    That shows they are working! :smile: It also confirms that there is high frequency current in that cable. Did you just clamp the ferrite cores onto the cable? The use of ferrites I've seen had the cables looped through the cores 3 or 4 times, to increase the inductance. Try that.

    Ferrite is magnetostrictive, it expands and contracts slightly in time-varying magnetic fields.
     
  14. Mar 16, 2012 #13
    The multiconductor I had just going through it once since the jacket OD matched the ferrite ID. The 22 gauge I had looped 3 times.
     
  15. Mar 16, 2012 #14

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    That tells me they BOTH are passing HF current.
    Which suggests that the ignition box takes huge gulps of current at that frequency
    and it is easier for Mr Ignition (who's a sorta brute force guy) to get them from your LED's filter caps than out of Mr Battery.
    That's because Mr Battery's wires are spaced wide so have considerable inductance.
    That makes it easier for the HF current to come right out of Mr LED's filter cap, it has lower impedance
    so feeds backward into what looks to it like an external fault.
    Proverbial candy from a baby?


    I had a similar situation once on a huge 130 volt battery bus. It was modulated by 3 inverters(~65 amps each) making over 100 volt peaks at 120 hz. They wouldn't run if not in synchronization.

    I would bet a beer that if you open Mr Ignition you'll find his electrolytic filter cap on input has developed extreme ESR which lets him modulate your battery voltage to point Mr LED can't run on it.
    Tack a huge electrolytic right across Mr Ignition's terminals, and if both ferrites quiet
    down you have established probable cause to open him up.

    old jim
     
    Last edited: Mar 16, 2012
  16. Mar 16, 2012 #15

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

  17. Mar 16, 2012 #16
    So I went back to that dragster's shop so we could start it. Did the same thing as the roadster- blinked (has a Mallory ignition box, completely different). So I stacked a 1000 uF and a 470uF in parallel at the LED board itself, and it took the frequency down to 20 Hz, and slowed down the blinking rate to about 3 tenths of a second on and 7 tenths off.

    So you're saying I need to tack inductors and make an LC filter?

    On this one, I'd say there's probably 14 feet of the 22 gauge multiconductor. And the box mounts right above the coil and distributor, probably doesn't help but I have to make it work.

    On this dragster:

    no caps- 230-330 Hz flunctuating
    58uF of stacked caps- 86-98 Hz flunctuating
    1470 uF of caps- 20Hz fairly steady

    22 gauge spaced 1mm apart:
    24pF/m
    .57uH/m DC
    .46uH/m HF
    141 ohm HF

    x4.25 meters= 102pF, 2.42 uH DC, 1.955 uH HF, 599.25 ohm HF

    but I don't know if the waveform is triangular, square, or sinusoidal since I don't have a scope.
     
    Last edited: Mar 16, 2012
  18. Mar 18, 2012 #17
    reading this: http://www.allaboutcircuits.com/vol_2/chpt_8/2.html

    and this: http://linuxcar.sone.jp/reg.en.html

    and this: http://www.play-hookey.com/ac_theory/ps_filters.html [Broken]

    I am borrowing a spare of the offending units, an MSD 6AL, to bench test with. It is rated at 1 amp draw per 1,000 RPM. I will hand-turn a spare distributor to fire off the ignition, running off a small 12V gelcel, to replicate the issue. I can then use a drill to gain speed. The issue shows up at a measly 500 RPM, which is only 250 RPM of the distributor, or about 4 rotations per second.

    Things I see on the second to last image: 150uH inductor, 20V 600W Zener (is that really necessary?), 1000uF decoupling cap before regulator, 2200 decoupling cap after regulator.

    seeing as 1470uF brought it down to 20Hz, The next step of 2000+uF and an inductor is all I need?

    02300.png

    02301.png

    reg.png

    rectifier_full_wave_lc_filter.gif

    ----------------

    http://www.mouser.com/ProductDetail/Fastron/HBCC-101J-02/?qs=sGAEpiMZZMueR%252blcXtRMwTF%2fyJ2D16pKJ2Kbgoo7HPU%3d [Broken]
    http://www.mouser.com/ProductDetail/Bourns/5800-151-RC/?qs=sGAEpiMZZMueR%252blcXtRMwXbDwFg%252bO9QWnKibw9JhM6M%3d [Broken]
    http://www.mouser.com/ProductDetail/Bourns/5800-221-RC/?qs=sGAEpiMZZMueR%252blcXtRMweTvlE%2fCoLxyD6jdE9zdVC8%3d [Broken]

    http://www.mouser.com/ProductDetail/Vishay-BC-Components/MAL202117102E3/?qs=sGAEpiMZZMtZ1n0r9vR22ciSY6ngmHpL2xflyuHcHrs%3d [Broken]
    http://www.mouser.com/ProductDetail/Vishay-BC-Components/MAL202117152E3/?qs=sGAEpiMZZMtZ1n0r9vR22ciSY6ngmHpLrF%252bfbmNQIFU%3d [Broken]
    http://www.mouser.com/ProductDetail/Panasonic-Electronic-Components/EEU-TP1V202/?qs=sGAEpiMZZMtZ1n0r9vR22RLWfCw%2fHjMd4a0byORSsPc%3d [Broken]
    http://www.mouser.com/ProductDetail/United-Chemi-Con/ELXZ350ELL392MM40S/?qs=sGAEpiMZZMtZ1n0r9vR22fqp084l1X3esgjl60Q7HGo%3d [Broken]
     
    Last edited by a moderator: May 5, 2017
  19. Mar 18, 2012 #18
  20. Mar 21, 2012 #19
    So I have an MSD going to a gelcell battery, ect.

    the 12 volt LED's flicker as expected when I spin the distributor, but the whites don't...asterick.

    If I turn the booster down on the white LED's, then they'll start flickering. I know the spot I have marked is 17.5 volts.

    I have the filter configured as a pi filter, 3900 uF input, 470uH inductance, 3500uF output.

    on a related note: This would make a fun halloween project with 40,000 volts floating around from the coil firing... FYI that's what is causing the flicker. The MSD is eating all the juice from the battery and screwing with the supply for the LED's.



    https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-ash3/548085_10150875048389606_771454605_12643308_1791448242_n.jpg [Broken]
     
    Last edited by a moderator: May 5, 2017
  21. Mar 22, 2012 #20
    So the guy with the roadster went from an electric fuel pump to a belt drive fuel pump, and now the LED boards are displaying random segments, like the shift registers are getting some sort or crap signal. But I don't know if it's coming from the controller or from the power line. The shift registers are just getting the signal at 5 volts and using the signal to switch the 12 volt transistor loads, more or less.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Needing to filter Capacitive Discharge feedback
Loading...