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18V 5W Cree Circuit Board for Flashlights (16.8mm*5.5mm)
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Topic link: http://club.dealextreme.com/forums/Forums.dx/threadid.443649
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Subject:
2 or 3 of these in parralel
Product Forum
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I need to know if can be wired in parallel. I have read posts that say yes and posts that say no. I am trying to drive a SSC P7 C-Bin at max with 12v input.
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The answer is a definite maybe. If the PT4115 chips are all perfectly matched with respect to the on and off voltage thresholds on the hysteretic controller, then the switching transistors will be perfectly synchronized and the total current will be equally shared among all of the parallel wired regulators.
In reality, small differences in voltage thresholds may prevent perfect current sharing, and some devices will try to hog all of the current, possibly resulting in that device overheating. You'll have to just try it and see what happens. [edit] just to clarify further... let's take an example of two PT4115 regulators in parallel. Regulator one turns on at Vsense<=0.9995 and off at Vsense>=1.0005. Regulator two turns on at a slightly lower Vsense<=0.9994 and off at Vsense>=1.0005. The second regulator will only work for one cycle (a few microseconds) and then stay off! The first regulator will then carry the entire current. Because Rsense is now half (because they are paralleled), regulator one will try to run at double the current. If it exceeds the maximum rating of 1.2A, then it will overheat and shut down. At that point both switches are off and Vsense will finally drop below 0.9994V and regulator two will take over. Regulator two will then also try to deliver double the current, possibly overheat and shutdown. Eventually both chips will cool down and reactivate, starting the cycle over again. |
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Ooops, my apologies, this SKU is not using the PT4115. It uses the AX2002, which is a PWM based controller, not a hysteretic controller. This type may be a little easier to parallel since slight differences in voltage references won't result in such extreme current imbalances.
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Ok, I thought it's woth $4.00 to see how and if this works. In fact it does work to use 2 boards - paralell the inputs and output and you DO get double the current output. I asked this question elsewhere here http://www.dealextreme.com/forums/Default.dx/sku.26110~threadid.413793 but now I've done the test.
However, as Desolder predicted, one board does take the lead in current sharing and athough the combined output appears to remain steady, one board does get very much warmer than the other. To make this work as a long lasting solution, you will have to heat sink both boards to get that heat away and prevent thermal cuts. On my 10 watt rated composite LED I had the following figures that may be of interest. (SSC P7 may apply also) 12.24Volts DC feed (on load) 1 x sku.26110 board 800-900 MA 2 x in paralell boards 1.82 A (approx double!) Boards were not heat sinked in order to identify any over heating quickly. Board 2 when in paralell got too hot to touch after 40 seconds with combined O/P of 1.82 amps. So you must heat sink both boards! or you'll get thermal cutout Note I have used about 15 of these regulators and none of them have ever reached their max rated output, even driving the stated Q5s (1.2A) My feeling is that running 3 boards in paralell may be pushing the limit, especially if the current is not shared predictably as these tests indicate. If you want to run a P7 at max on a 12 V supply, you'll need a different regulator board not sold here but That OTHER LED supplier has one... cant name them because of the TOS below, but the hint 'KD' should help you a bit. More DIYers are using this kit to make 'home/ solar LED assemblies' so I wish DX would get some more 12 volt friendly regulators and LEDs in stock Hope this helps some. |
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It does not support parallell connections. One of the three coils will always get burning hot when I put them in parallell. :(
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Sorry to hear that. I've been running this configuration for several months now for at least 4 hrs a day. As stated, you must heat sink the boards well, I have a purpose built heatsink made of plate aluminium that holds the leds and boards.
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