Changes by last author:
Deleted:
|
I'm afraid that you simplify this too much, it took a long time for us to find the actual problem with the PWM solution and your powerflyback variant doesn't address the main problem at all. It's pretty much identical to the prototype I built a few years ago (also without knowing what caused the random problems we sometimes saw). As you are obviously willing to experiment and have access to a number of cars to test on you should do some modifications that will address the problem. You need to replace a few diodes in the ECU with faster units. As it is VERY possible that the diode modification can cause other problems we decided to use the safe and in many ways better resistor solution instead. The current diodes we have are about as fast as a common diode will get, this "ultra fast" diode is however sluggish compared to a Schottky diode. The Schottky type diodes will not survive as much voltage as the standard diodes but they are a lot quicker and they will prevent the very high inrush current that is the cause of most of the noise and that kills the FET when you PWM them. You should start replacing these diodes on all boxes you plan to PWM: D7,D8,D10,D16,D17,D25,D28 and D29. For added safety you should leave the original diodes in the D79,D169,D259,D289,D299,D179 and D89 positions, that way the box will pretty much go back to normal if the schottky diode would fail. You will need to examine the Schottky diodes on the test cars periodically to see how well they survive the beating they get. The behavior of the car will not change if the Schottky fails but the FET's will start to take a severe beating again. I must say that I'm suprised that you used a FET for this, even if the part you use is fairly rugged I find that most FET's are much more fragile then an IGBT or NPN. Note that any tests done with the 1600cc Bosch injectors are not likely to test how rugged the box is after it's modified. The 1600cc injector hardly put any load on the electronics and it's always used without a resistor. - Jörgen Karlsson, Gothenburg,Sweden. |
| * Interesting. With my parameters (13.3Vbatt, 36V flyback, 2Ohm injectors) 77% duty gives 1A injector current, however 75% is 0.48A, and 73% is -0,0055A ?? Weird. I managed to fry at least one of my injectors, BTW :-0 |
|
* Interesting. With my parameters (13.3Vbatt, 36V flyback, 2Ohm injectors) 77% duty gives 1A injector current, however 75% is 0.48A, and 73% is -0,0055A ?? Weird. I managed to fry at least one of my injectors, BTW :-0
---- I'm afraid that you simplify this too much, it took a long time for us to find the actual problem with the PWM solution and your powerflyback variant doesn't address the main problem at all. It's pretty much identical to the prototype I built a few years ago (also without knowing what caused the random problems we sometimes saw). As you are obviously willing to experiment and have access to a number of cars to test on you should do some modifications that will address the problem. You need to replace a few diodes in the ECU with faster units. As it is VERY possible that the diode modification can cause other problems we decided to use the safe and in many ways better resistor solution instead. The current diodes we have are about as fast as a common diode will get, this "ultra fast" diode is however sluggish compared to a Schottky diode. The Schottky type diodes will not survive as much voltage as the standard diodes but they are a lot quicker and they will prevent the very high inrush current that is the cause of most of the noise and that kills the FET when you PWM them. You should start replacing these diodes on all boxes you plan to PWM: D7,D8,D10,D16,D17,D25,D28 and D29. For added safety you should leave the original diodes in the D79,D169,D259,D289,D299,D179 and D89 positions, that way the box will pretty much go back to normal if the schottky diode would fail. You will need to examine the Schottky diodes on the test cars periodically to see how well they survive the beating they get. The behavior of the car will not change if the Schottky fails but the FET's will start to take a severe beating again. I must say that I'm suprised that you used a FET for this, even if the part you use is fairly rugged I find that most FET's are much more fragile then an IGBT or NPN. Note that any tests done with the 1600cc Bosch injectors are not likely to test how rugged the box is after it's modified. The 1600cc injector hardly put any load on the electronics and it's always used without a resistor. - Jörgen Karlsson, Gothenburg,Sweden. Thanks, Jörgen, for this comment. This information must be in wiki long time ago. Some words for defence: It is not single spike what kills FET. needs spike AND time = energy. Current diodes protect INJFETS from this energy, although those are "slow". If you want I can make high resolution scope shots on injector output! For statistics: I have two-three fried FETs on ~30 boards. All with clear cause. No single FET fried on 3 boards where described limiter are used. More detailed history you can read here: http://195.159.109.134/vemsuk/forum/index.php/topic,189.0.html including why FET in device. In short: using PWMing injectors have significant better linearity and predictability at idle and low loads than with resistors. There is some unsolved problem with hardware anyway. Lot of users claims about fried FETs using simple High-Z. What protects FETs from -20V spikes on gate? MembersPage/GintsK ---- |