Litch
New Member
Building a power monitor for my car.
The following is a "probe" for the power monitor (which will talk to this probe via I2C). I'll build a few of these, one to monitor the feed into the audio amps (0 - 600A) another to measure the batteries (-50 to 600A) and one more for the alternator feed (0A - 400A). From this I'll be able to graph and analyse the power-performance of my (significant) car audio install, the charge rate of the batteries and other interesting stuff like RPM to Alternator output performance. The below (as a start/template for the rest) will be for the amp power feed (0 - 600A)
Theory:
Thanks in advance.
-KB
The following is a "probe" for the power monitor (which will talk to this probe via I2C). I'll build a few of these, one to monitor the feed into the audio amps (0 - 600A) another to measure the batteries (-50 to 600A) and one more for the alternator feed (0A - 400A). From this I'll be able to graph and analyse the power-performance of my (significant) car audio install, the charge rate of the batteries and other interesting stuff like RPM to Alternator output performance. The below (as a start/template for the rest) will be for the amp power feed (0 - 600A)
Theory:
- Tolerance: Assume all resistors are 1%, all caps are 10% and everything else is of standard/popular values.
- [POWERIN]/[POWEROUT] is the zero-gauge wire to the audio amps running through a current transducer (LEM HTFS series).
- [OUT] is 50% of Vcc at 0A, 100% Vcc at +600A and 0% Vcc at -600A
- [REF] is 50% of Vcc (reference for 0A)
- [OUT] is fed into ACD's CH2, then grounded via a 5K resistor. (V=IR, I=V/R, I=5/5K, I=1mA drain, P=VI, P=5mW drain)
- [+12v IN] is a direct feed from the car's +12v (which will be more like 12.6V when engine off, and 14.8v when engine is running)
- This feeds a low noise DC-DC switching reg (that, in turn, powers the ADC and the current transducer via [+5V1A])
- Power draw is likely < 50mA for the circuit, it's overkill but meh - room for expansion.
- The [+12v IN] also goes to ACD CH1 via a 33% voltage divider (33% of 15V = 5V = ADC's max input voltage) and smoothed a little more via a 100nF cap.
- The ADC is capable of 200kS/s
- Ignore the +5v feed into the I2C connector - superfluous, won't be used.
- With 12bit accuracy - do I need better smoothing of the analogue inputs?
- Is that 100nF on CH1 sufficient or should I be looking at an RLF filter?
- But at what point of smoothing do I lose the degree of accuracy I'm looking for calculating power draw of the amps - it would be nice to sample all this at 10kS/s and graph it out.
- Do you see any red flags? Comments? Advice?
Thanks in advance.
-KB