DIYPNP on a 99
02-03-2010, 03:44 PM
#121
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Some items can't be ordered though, like the IRLZ44 for EBC for instance. Had to get that from Glenn's Garage.
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02-03-2010, 08:59 PM
#124
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I used 5% tolerance resistors. They come in a multi-pack. Measure across them with a DMM and use the closest ones. They're typically dead on, or nearly dead on, anyway.
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02-04-2010, 01:26 AM
#126
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Jim
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02-06-2010, 07:22 AM
#132
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Jim, if you want me to mail you a letter with a TL431 in it, gimme a shout. I'm in the neighbourhood of that shop next week so I can stop by to get you one. Last time I ordered they told me they would stock a couple.
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02-08-2010, 01:16 AM
#134
I'd only put one there if you're having problems, and it wouldn't need to be as big.
On the 12v, we have a 3300uf cap on the MSPNPs, which is really bigger than needed. Without the cap the stock electrical system (12v) gets somewhat noisy when the engine is under load. With about half that value smooths out the 12v pretty nicely, now having a nice nearly flat 12v (or 13.2 or whatever, bottom line is it stopped it from looking like a sine wave anymore) under load. The 3300uf made it pretty much perfectly flat, just a slight improvement over the smaller value. The cap was cheap, so I used the bigger one, done deal.
I discovered this a couple years ago when troublehooting the occasional misfire issue we used to see. Turns out I solved that with a much smaller cap on the 2nd input to filter the 2nd trigger, and noise on that signal had been the root cause of that. This cap on the 12v really is not required at all, but doesn't hurt, may help in some cases, so we left it in. BTW, before someone asks, there is already filtering on the DIYPNP's 2nd trigger, this little cap shouldn't be needed.
On the 12v, we have a 3300uf cap on the MSPNPs, which is really bigger than needed. Without the cap the stock electrical system (12v) gets somewhat noisy when the engine is under load. With about half that value smooths out the 12v pretty nicely, now having a nice nearly flat 12v (or 13.2 or whatever, bottom line is it stopped it from looking like a sine wave anymore) under load. The 3300uf made it pretty much perfectly flat, just a slight improvement over the smaller value. The cap was cheap, so I used the bigger one, done deal.
I discovered this a couple years ago when troublehooting the occasional misfire issue we used to see. Turns out I solved that with a much smaller cap on the 2nd input to filter the 2nd trigger, and noise on that signal had been the root cause of that. This cap on the 12v really is not required at all, but doesn't hurt, may help in some cases, so we left it in. BTW, before someone asks, there is already filtering on the DIYPNP's 2nd trigger, this little cap shouldn't be needed.
Thanks.
-Raj
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02-09-2010, 01:32 PM
#137
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That's a little high, but probably not dangerously so--as long as you're not going over 15v. You might go through headlight bulbs a little quicker.
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02-09-2010, 01:47 PM
#138
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You really should check the voltage at the battery using a DVM.
When my DVM said 12V battery voltage, MegaTune said 11.6V. Battery voltage is determined with a resistor voltage divider to bring the 12 volts down to under 5V for the MCU to convert. R3 (50K) and R6 (10K) on the Megasquirt PCB form this voltage divider. These are both 5% tolerance resistors and in my case, the ratio was 5.22 instead of 5, causing the difference between actual and MS values for battery voltage. It's best to use 1% resistors for this. It's important to have a correct reading because the MS changes certain values (injector opening time, dwell etc) depending on the input voltage.
If you find that everything is correct and you really measure 15V at the battery check if you used 1% resistors in the alternator circuit. The setpoint is determined with the formula: 2.495V*(1+ R4/R11), so it's important to use 1% resistors for R4 and R11. I used a 5% for R11 and found my setpoint to be 15.1V!
If you used 1%, you might want to replace the 48K7 resistor with a lower value like 47K5 or 46K4. Make sure your setpoint is about 14.4V. In your case, you'd have to use the 46K4 resistor to get 14.4V if you now have 15V.
Although 15V is still within spec, I don't feel comfortable with it. Your bulbs as well as your battery will live longer at 14.4V
When my DVM said 12V battery voltage, MegaTune said 11.6V. Battery voltage is determined with a resistor voltage divider to bring the 12 volts down to under 5V for the MCU to convert. R3 (50K) and R6 (10K) on the Megasquirt PCB form this voltage divider. These are both 5% tolerance resistors and in my case, the ratio was 5.22 instead of 5, causing the difference between actual and MS values for battery voltage. It's best to use 1% resistors for this. It's important to have a correct reading because the MS changes certain values (injector opening time, dwell etc) depending on the input voltage.
If you find that everything is correct and you really measure 15V at the battery check if you used 1% resistors in the alternator circuit. The setpoint is determined with the formula: 2.495V*(1+ R4/R11), so it's important to use 1% resistors for R4 and R11. I used a 5% for R11 and found my setpoint to be 15.1V!
If you used 1%, you might want to replace the 48K7 resistor with a lower value like 47K5 or 46K4. Make sure your setpoint is about 14.4V. In your case, you'd have to use the 46K4 resistor to get 14.4V if you now have 15V.
Although 15V is still within spec, I don't feel comfortable with it. Your bulbs as well as your battery will live longer at 14.4V
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02-10-2010, 03:42 PM
#140
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You really should check the voltage at the battery using a DVM.
When my DVM said 12V battery voltage, MegaTune said 11.6V. Battery voltage is determined with a resistor voltage divider to bring the 12 volts down to under 5V for the MCU to convert. R3 (50K) and R6 (10K) on the Megasquirt PCB form this voltage divider. These are both 5% tolerance resistors and in my case, the ratio was 5.22 instead of 5, causing the difference between actual and MS values for battery voltage. It's best to use 1% resistors for this. It's important to have a correct reading because the MS changes certain values (injector opening time, dwell etc) depending on the input voltage.
If you find that everything is correct and you really measure 15V at the battery check if you used 1% resistors in the alternator circuit. The setpoint is determined with the formula: 2.495V*(1+ R4/R11), so it's important to use 1% resistors for R4 and R11. I used a 5% for R11 and found my setpoint to be 15.1V!
If you used 1%, you might want to replace the 48K7 resistor with a lower value like 47K5 or 46K4. Make sure your setpoint is about 14.4V. In your case, you'd have to use the 46K4 resistor to get 14.4V if you now have 15V.
Although 15V is still within spec, I don't feel comfortable with it. Your bulbs as well as your battery will live longer at 14.4V
When my DVM said 12V battery voltage, MegaTune said 11.6V. Battery voltage is determined with a resistor voltage divider to bring the 12 volts down to under 5V for the MCU to convert. R3 (50K) and R6 (10K) on the Megasquirt PCB form this voltage divider. These are both 5% tolerance resistors and in my case, the ratio was 5.22 instead of 5, causing the difference between actual and MS values for battery voltage. It's best to use 1% resistors for this. It's important to have a correct reading because the MS changes certain values (injector opening time, dwell etc) depending on the input voltage.
If you find that everything is correct and you really measure 15V at the battery check if you used 1% resistors in the alternator circuit. The setpoint is determined with the formula: 2.495V*(1+ R4/R11), so it's important to use 1% resistors for R4 and R11. I used a 5% for R11 and found my setpoint to be 15.1V!
If you used 1%, you might want to replace the 48K7 resistor with a lower value like 47K5 or 46K4. Make sure your setpoint is about 14.4V. In your case, you'd have to use the 46K4 resistor to get 14.4V if you now have 15V.
Although 15V is still within spec, I don't feel comfortable with it. Your bulbs as well as your battery will live longer at 14.4V
We did use a 1% resistor but we did not test it, I'll look at it again tonight. Thanks for your help.
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