FYI the shunts on the 20A controllers are about 1.6 mOhm, and the 35-40A controllers are around 1.2 mOhm, so that should tell you what shunt voltages you'd be seeing and what your A/D resolution will be like without any amplification.wtf wrote:I was browsing the "Crystalyte Controllers - Repair and Modification information" thread and saw the information on the shunt for measuring current. Are there any issues with using it to directly interface to an A/D port on a microcontroller (or through an A/D chip to a microcontroller port)? I am thinking about using a Rabbit 4000 series chip for data sampling/display, gps, web interface, etc.
The bulk capacitors do well to filter a shunt placed on the battery leads before the controller, but they don't have any filtering effect for the onboard shunt. When the mosfets are in the OFF state, there is zero current through the controller shunt, and when the PWM is in the ON state then the full motor current passes through the shunt.maxwell wrote:"The shunt sees the PWM waveform"
It is smoothed (quite a lot) by the bulk capacitors, a small filter after the shunt is still a good idea.
Sure, in conjunction with a shunt. I clamped a cheap analog voltmeter and ammeter to my handlebars.monster wrote:can you measure current with a multimeter in series with the batteries? i don't want to spend Ãƒâ€šÂ£50 on a drainbrain or wattsup when i just want to know the limits of my batteries.
The shunt is so simple even a cave-xyster can explain it. The shunt is a piece of metal of known resistance, in this case 50mv at 50 amps. The shunt is in series with a main battery wire. The wires to the ammeter connect to each side of the shunt. The ammeter itself is just a voltmeter with a 50mv scale, measuring the voltage drop across the shunt, thereby measuring the current running through the main battery wires.monster wrote:i dont really understand how the ampmeter shunt works. something to do with not having the full power running through your meter and back?
could you give me a circuit diagram?