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Thread: [Gauging Interest] LED Side Marker Blinker Mod Fix

  1. #1

    .

    I'm sure many of you have thought about putting LED's in your side markers, but didn't want to give up the benefits of the incompatible blinker mod. Or maybe you upgraded, but miss the way the blinker mod worked. LED's are directional by default, they will only light when current goes though them one direction, which is counter to the blinker mod's reliance on the incandescent bulbs not caring which way current goes.

    Sadly, my source for bi-directional BA9s LED's has discontinued their units, and after scouring the internet ever since, there are no other units built that are compatible with the blinker mod. So, what's a guy to do?

    It yourself. DIY a circuit to allow current both ways on input, while always sending output one way only. Traditionally this has been done via a diode bridge, which is inherently limited by design -- the current always goes through two diodes, dropping voltage by around 2V while simultaneously limiting current to around 1A (assuming a 1N00... guy is used, which is incredibly common). After research, there is not only a chip designed to do this with minimal extra parts, but it is extremely efficient compared to previous approaches. Behold, the LT4320-1!

    It only requires four MOSFET's and two capacitors, and built with the MOSFET's I've selected, appear to allow 10A at something like 100mV drop. This means that you could potentially use this with far more powerful equipment than a simple LED (bear in mind, the incandescent BA9s bulb uses less than 0.5A, LED's are far more efficient!)

    Now here's the catch: with one-car quantities, the LT4320-1 itself costs $9.12, however this drops to $6.10 if a quantity of 25 to 99 is purchased, and drops again at 100 units per order. The other components have savings too, but not quite as drastic.

    In order to get that lower price, I would need at least SIX individuals to express serious interest. Once they are built, I can start selling them. I have already ordered enough for four boards for my own car as a "test run". Price for that guy is about $15 to $20 per board (I will get a complete rundown once I've finished the board design itself), however with the batch buy, I am suspecting $15 per board may be overall cost. This would mean $90 (plus shipping) per car, assuming four per car.

    So the question becomes: how many of you guys are willing to plop $100 on a set of boards that let you pick whatever damn LED you want in the side markers?

    (Note: for those of you also interested in my completely-rebuilt side marker project, I will allow returns of the LT4320-1 boards for a full refund up to whatever quantity of side markers you purchase later, as a "Thank you" for early support! So if you buy 8 LT4320-1 boards now, and 4 side markers later, I will refund four of the LT4320-1 on a functional return. Buy four more side markers, I'll refund the final four LT4320-1 boards in your inventory. Simple stuff!)
    Last edited by Shep; 03-04-2017 at 05:57 PM.

  2. #2

  3. #3
    Quote Originally Posted by Bitsyncmaster View Post
    Damn I wish I saw that before I went through all the hassle of building my boards...

    Voltage drop might be higher than mine, and amperage might be more limited too, but price point alone is very attractive compared to mine.

    That said, I will still install the ones I'm building on my own car. Might as well since I'm already this close.

  4. #4
    I'm always concerned about voltage drop with LED power. But I used diodes only dropping 0.2 volts with LED loads. But if you want zero drop, just provide constant 12 volt to the + side of the lights. That is how my car is wired. I did not think of getting light power using diodes when I prototyped these a few years ago.

    I will probably increase the price someday. I kept it at $30 just to get enough sold to break even.
    Last edited by Bitsyncmaster; 02-27-2017 at 02:59 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #5
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    I don't remember much about the turn signals, and not quite keeping up.

    Do the side markers not normally flash with the turn signal indicators?

    When I upgraded to LED's on my first DeLorean, I recall swapping out the OEM flasher with a unit specifically for the LED's but I don't remember the behavior of the side markers.

    Can someone give me the cliff notes version?

    Thanks!

  6. #6
    In stock form the side marker don't flash with blinkers.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
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    Quote Originally Posted by Bitsyncmaster View Post
    In stock form the side marker don't flash with blinkers.
    For the [side marker] blinker mod, does it matter what LED's I get, and do I still swap out the OEM flasher?

  8. #8
    Quote Originally Posted by Bitsyncmaster View Post
    I'm always concerned about voltage drop with LED power. But I used diodes only dropping 0.2 volts with LED loads. But if you want zero drop, just provide constant 12 volt to the + side of the lights. That is how my car is wired. I did not think of getting light power using diodes when I prototyped these a few years ago.

    I will probably increase the price someday. I kept it at $30 just to get enough sold to break even.
    I think mine's somewhere in between there. I mated the LT4320-1 with 3 mOhm MOSFET's. The LT4320-1's datasheet seems to suggest the IC's voltage drop is 55mV, and the MOSFET's voltage drop is (mOhm * A), for an overall formula of:

    (3 mOhms * Amps) + 55 mV = drop in mV

    So, stretching this out across the operating range (theoretical 50A if I'm reading the MOSFET specs right), I arrived at:
    0.5 amps = (3 * 0.5) + 55 = 56.5 mV
    5 amps = (3 * 5) + 55 = 70 mV
    50 amps = (3 * 50) + 55 = 205 mV

    I am not fully convinced those numbers are wholly accurate though, that seems extraordinarily low for something like this.

    Worked up the price to be $16 per board (minus the board itself), so we may be close!

    Quote Originally Posted by Rich_NYS View Post
    Do the side markers not normally flash with the turn signal indicators?
    From the factory, no. That said, many owners have done what's called a "blinker mod" (Bill posted a schematic in this thread). I'm working up a simple-to-understand diagram for that in the interim.

  9. #9
    Quote Originally Posted by Shep View Post
    (3 mOhms * Amps) + 55 mV = drop in mV

    So, stretching this out across the operating range (theoretical 50A if I'm reading the MOSFET specs right), I arrived at:
    0.5 amps = (3 * 0.5) + 55 = 56.5 mV
    5 amps = (3 * 5) + 55 = 70 mV
    50 amps = (3 * 50) + 55 = 205 mV
    Your numbers are correct but you don't need to be using those high current samples. I fight with those numbers with my fan relay and fan fail units because the OEM cooling fans can draw 30 to 40 amps for both. You care about voltage drop because voltage times current equal the heat (watts) the parts produce and have to dissipate.

    Typical side marker LED current is 30 to 60 ma. for each marker. Even incandescent bulbs are less than one amp.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #10
    Quote Originally Posted by Rich_NYS View Post
    For the [side marker] blinker mod, does it matter what LED's I get, and do I still swap out the OEM flasher?
    It does mater if your just doing the original mod intended for incandescent bulbs. And yes with all LEDs in the OEM flasher circuit, you need the LED flasher.

    The bulb type does not matter for the side markers using my side marker flasher. My unit is limited to 3 amps so powering both side markers your limit is 1.5 amps for each marker.

    Don't confuse the OEM flasher with the "side marker flasher". They are different functions. The OEM flasher powers the front and rear "blinker" lights.
    Last edited by Bitsyncmaster; 02-28-2017 at 05:40 AM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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