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Boosting Bosch Ballast -Additional technical info by azdave

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  • Boosting Bosch Ballast -Additional technical info by azdave

    I’ve been doing a little further research into what happens when you boost the Bosch AL ballast by the method found in the very popular thread by pks485, now found in the University section.
    http://www.hidplanet.com/forums/viewtopic.php?t=21715

    Hopefully my thread here is not a duplication of another I might have missed somewhere else. I spend most of my forum time in the LED section so I'm not always up to date with HID posts but I try to keep up.

    I had a few unanswered questions about what was really going on when a potentiometer was placed across that well known little SMT resistor. I set up a small test bench and did a little data collecting for myself.

    All tests were conducted using brand new 85122+ bulbs. I used test equipment from work and from home of known good calibration status. The meter used to read the A/C voltage was a true RMS reading meter and the bulb amp draw was measured through a 10x multiplier to gain more accuracy. All readings were recorded after a 10-minute stabilization delay after each boost increase. Reading voltage and current levels of 400 Hz A/C power, generated from low voltage DC step-up inverters, has never been my strongest area but I feel these numbers are reasonably accurate.

    Some things I wanted to find:

    What is the actual bulb wattage at various resistances?
    I measured 33 watts at pure stock and a max of 68 watts at full boost.

    How linear is the boost compared to resistance changes?
    Very linear from 10K-100K.

    How closely matched are different ballasts when boosted?
    So far, they appear to be more closely matched than I expected considering that they are running well out of their intended operating range.

    How much current is carried in the added external resistor circuit?
    It is so tiny it was hard to measure. 0.004mA at lowest and 0.045mA at the highest.

    Does a longer or shorter wire running to one of the dash-mounted potentiometers affect the ballast boost level?
    Absolutely not. You could have one wire 50’ longer than the other and not notice the boost level change.

    Is a cooling fan and external heat sink required?
    In most cases yes. See more below.

    Is the 100K pot from the original thread a good choice?
    Yes. The pot is a good choice and the charts below show that while the pot does not provide for a fully linear boost curve it still works quite well (as most of you already know).

    Is there something better than the 100K pot to use?
    Yes. I think so. One thing the pot cannot do is allow you to run the original low boost level that the ballast used to have before modding. The pot, at its 100K setting, will increase the boost wattage slightly over stock by virtue of just being placed in the system. That is the nature of parallel resistance. A rotary switch will allow you to retain the original stock boost setting as well as any pre-set level you may wish. A rotary switch also allows for other options like a cooling fan at higher levels or indicator lights at any or all positions. To control both ballasts and a fan with one rotary switch you will be limited to 4 boost choices but that should be plenty.

    These photos will explain most of the setup used for testing.


    Fused output for safety.


    Charge upkeep.


    DC voltage, amps, watts monitor.




    A/C amps measuring using adapted 10X multiplier for better accuracy


    Manual resistor selection arrangement before I started using a rotary switch.


    Actual amps divide by 10 so 0.38 amps is the true reading here.




    Lots of data for time, temp, amp, voltage, etc.


    Thermocouple on top of projector for heat reference point.


    Meaured ambient, ballast and projector temps during the testing.


    Heat sink (without the cooling fan mounted). Full flush contact, lots of surface area and a thin film of heat sink adhesive between the two. There is a thermocouple in the rear center fins for recording the ballast temperature. The device seen in the foreground under the clamp (with two leads sticking out) is a thermal fuse that will reduce the boost level back to stock if it detects a temperature of over 160F on the ballast case. This is good protection if the cooling fan fails during extended high boost. It is wrapped in Kapton film for electrical isolation from the ballast case and fits very nicely under the heat sink bracket.




    This chart graphs the output wattage as compared to the actual parallel resistance in the circuit. Remember, the external resistance is being placed in parallel with the 26.1K SMT resistor on the board. The resistance listed on the x-axis is NOT the resistance of the pot alone (See next chart for that). This chart shows how linear the boost increase is (within the limits of the ballast) and also shows how closely both ballasts compare to each other.



    This next chart graphs the output wattage as compared to the external resistance added. This chart is easier for someone to determine what external resistance would be required to obtain a desired boost level. Notice how external resistance higher than 100K has less dramatic affect but does still raise the boost level above the stock 33 watts. Notice how external resistance below 10K has no affect. This also confirms my suspicions that wire length and a slight mismatching of external resistors or pots will not result in any measurable boost variances between the left and right ballast in your vehicle.



    Supplies?
    I am using 2, 3 or 4-pole rotary switches with fixed value resistors for better versatility than the 100K pot. If you want to turn the cooling fan on and off with the rotary switch you will need at least a 3-pole switch. The resistors can be any wattage you find since the current through them is insignificant. The tolerance is not an issue either. Some cheap 1/8 watt 10% will work just fine. With the rotary switch choice I like the fact that I can quickly select known pre-set boost levels and that I can have the cooling fans turn on using the same switch at any boost level I choose. I also plan to have a few LED dash indicators tied to the switch to remind me when I’m running the higher levels of boost. For cooling I found a great fan/heat sink package that fits nicely on the back. It comes with a mounting bracket and a 12V fan ready to go. It is very quiet and kept the ballasts a few degrees above ambient during the longer tests. It should be all the cooling I’ll ever need, even in Phoenix this summer.

    More about cooling.
    My initial concern here was restoring the heat transfer that needs to occur between the circuit board components and the rear case. When the circuit board is removed to access the SMT resistor there are two heat sinks that are pulled apart. Between the actual board and the case is a thin wafer that electrically isolates the board from the case. One side of this isolator has a pressure-sensitive adhesive and the other uses a permanent heat sink adhesive caulk. When the board is lifted up, one or both of the adhesives are pulled apart. Restoring the heat transfer properties of these joints can be critical to getting rid of heat efficiently. I made sure to apply new heat sink adhesive to the disturbed surfaces before reassembling the ballast. During testing I found that the ballast can easily take short periods of boosting without significant heat buildup. For extended use or by the time summer heat has arrived you will want at least a large external heat sink and since it is quite easy to find computer fans and heat sinks it’s a wise choice to have them. I’ll be running a thermocouple for a few months to see how hot my ballasts get when no fan is used just for curiosity. Speaking of heat, one component inside the case that also gets quite hot is the inductor coil. I measured in at just over 200F after a standard test session of about 45 minutes with the last 10 minutes at full 68W boost. That was causing some noticeable heat inside the case but I don’t feel this heat would lead to a failure of the coil as the windings are insulated with a very high temperature coating for such reasons.


    Here is a simple video (featuring my garage door at center stage). I had trouble finding a video camera that would allow full manual exposure lock. This was taken with an old Sony and I could step the exposure down but it still was adjusting somewhat. The faster I switched between wattage settings the better it look in the video. It looks much more dramatic in person. I guess the next time I should just shoot a series of animated stills where I know I can fully lock the exposure settings. Anyway, the video shows the startup and 6 steps of wattage up and down a few times. It also has a few bursts from lowest to highest wattage like if you set up a flash-to-pass switch too.

    http://www.youtube.com/watch?v=vU7IbG6bwgk

  • #2
    =D> =D> =D> Do you plan to pot them when all your testing is done? I am sure it will help with heat transfer.
    1933 Chrysler co-6 convertible coupe
    1933 Dodge commercial sedan
    1933 DeSoto 3 window coupe
    1933 Dodge commercial canopy

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    • #3
      Originally posted by russgvrs
      =D> =D> =D> Do you plan to pot them when all your testing is done? I am sure it will help with heat transfer.
      I don't think it's worth the trouble to me since the fans work good and I don't plan on long periods of high boost.

      Comment


      • #4
        Very good and detailed write up. Amazing work! I guess the only open ended question is, the long term affects of a boosted ballast. For instance, running at 55W at all times for a year. The effects it has on the lifespan of the ballasts and bulbs.

        Comment


        • #5
          Great work as always Dave =D>
          BST Rules

          00 GS300
          06 TL
          06 RL
          00 S2000

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          • #6
            Great post Dave!

            I'm still trying to digest all the info,so forgive me if the answer is already posted. I have boosted Bosch ballasts,there's no pot wired to them yet,I just have a switch connected to my test ballast so I can go from normal output to full boost.

            Since I'm using DL50 bulbs,I'd like "regular" output to be @ 50w,what external resistor value should I use? I see 100K ohms is almost 40w.

            My initial concern here was restoring the heat transfer that needs to occur between the circuit board components and the rear case. When the circuit board is removed to access the SMT resistor there are two heat sinks that are pulled apart. Between the actual board and the case is a thin wafer that electrically isolates the board from the case. One side of this isolator has a pressure-sensitive adhesive and the other uses a permanent heat sink adhesive caulk. When the board is lifted up, one or both of the adhesives are pulled apart. Restoring the heat transfer properties of these joints can be critical to getting rid of heat efficiently. I made sure to apply new heat sink adhesive to the disturbed surfaces before reassembling the ballast.
            Do you think potting the area between the circuit board and rear case with a thermally-conductive epoxy (I used it on Densos in this thread) would improve heat transfer or will those original spots do the job?
            Originally posted by HK45
            I don't even look to see what Eddie writes anymore. I'm too busy staring at his avatar.

            Comment


            • #7
              ^^ The idea isnt to just hold it together with the back plate, it indeed is to make sure that the heat from the board gets transfered to the back aluminum cover. When people take the board off it actually breaks that bond between the aluminum cover and the board, thats why thermal epoxy is needed.
              BST Rules

              00 GS300
              06 TL
              06 RL
              00 S2000

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              • #8
                great post, i had a feeling the boosted setups were reaching over 50w. i wonder how the results would look pushing 50w dl50 bulbs at full boost.

                Comment


                • #9
                  Originally posted by JnC
                  ^^ The idea isnt to just hold it together with the back plate, it indeed is to make sure that the heat from the board gets transfered to the back aluminum cover. When people take the board off it actually breaks that bond between the aluminum cover and the board, thats why thermal epoxy is needed.
                  Yes I understand a caulk/adhesive is needed between the board and case for a good thermal bond. That wasn't my question,maybe I wasn't clear about that.


                  The brownish/yellowish pads are where the board bonds to the case,notice how those areas are raised. There's maybe a 1/8" air gap between the board the the sunken areas of the case.

                  My question was would filling that gap with thermal epoxy improve heat transfer at all or it the effect negligible?
                  Originally posted by HK45
                  I don't even look to see what Eddie writes anymore. I'm too busy staring at his avatar.

                  Comment


                  • #10
                    Not really since most of the heat would be generated by components around that raised area.
                    BST Rules

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                    06 TL
                    06 RL
                    00 S2000

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                    • #11
                      Originally posted by JnC
                      Not really since most of the heat would be generated by components around that raised area.
                      Actually air has a lower thermal conductivity value than the popular thermally conductive epoxy, MG 832TC, meaning it does a lot worse job of transferring heat.

                      Air Thermal Conductivity: 0.025 W/m*K
                      MG 832TC Thermal Conductivity 0.682 W/m*K

                      So, yes, filling that gap with thermally conductive epoxy, such as the MG 832TC, would improve heat transfer from that side of the board.

                      BTW, awesome work, azdave! I love these kinds of write-ups.

                      Comment


                      • #12
                        I think the oem thermal design was designed as such to pull heat only from specific high heat producing components. Like for example the coil. If you pot it you are going to pull the heat out of the coil and into the other electronic components. This could be bad for some of the low current temperature sensitive components. I think it would improve the thermal tranferance to the heatsink but at what cost?
                        1933 Chrysler co-6 convertible coupe
                        1933 Dodge commercial sedan
                        1933 DeSoto 3 window coupe
                        1933 Dodge commercial canopy

                        Comment


                        • #13
                          Originally posted by russgvrs
                          If you pot it you are going to pull the heat out of the coil and into the other electronic components.
                          I don't know about that theory, because if it did, wouldn't that cause the same problem with potting almost any ballast (or basically any circuit board for that matter)? My fully-potted Denso ballasts are still going strong and each has two coils.

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                          • #14
                            Originally posted by Eddie
                            Since I'm using DL50 bulbs,I'd like to "regular" output to be @ 50w,what external resistor value should I use? I see 100K ohms is almost 40w.
                            I expanded the chart so you can see it easier. Looks like 35K would be very close to 50 watts. I used a 30K in one test and measured 52 watts.

                            Comment


                            • #15
                              Originally posted by Eddie
                              My question was would filling that gap with thermal epoxy improve heat transfer at all or it the effect negligible?
                              It would help but I don't feel it is worth it unless we start getting reports of properly heat sinked ballasts going into overheat conditions regularly. I don't like to pot anything unless I have to.

                              Eddie,
                              Do you realize the brown pads in your photos are the insulating wafers that got pulled off the boards when you opened up the ballast? Wasn't sure you realized that those normally would stay attached to the boards.


                              Here is what one of my ballasts looked like after taking it apart. One of the two wafers stayed on the board but the other stayed in the case. I removed all the old glue/adhesive and replaced it with new heat sink glue. Those tiny holes are just additional vias used to tranfer the heat through the board into the insulating wafers. The wafers were attached to the board with a special heat-conductive clear pressure-sensitive adhesive and then the wafer was attached to the case with a heat sink adhesive.



                              In this pic I have cleaned off all the old white adhesive from the bottom thermal pad. The top wafer was later removed and re-attached to the board before putting it all back together with more heat sink adhesive on the thermal pads.

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