Mongrel Shark
- Jun 6, 2012
- 260
- Joined
- Jun 6, 2012
- Messages
- 260
I suspect many of the Joule thief circuits I am working with lately are fluctuating the amps at a high speed, equal to the fluctuations in voltage (Sometimes up to 300v).
I have tried my best multimeter, which has TRMS designed for AC mains work, it has a TRMS AC+DC mode that is more accurate than anything else I have tried, but I think the the sample rate is to slow. Also I would like to see max, min, p to p amps etc.
I have tried shunt resistors with my scope. Every time I connect the negative probe it kills the oscillation.
So I tried using two pos probes and the add subtract Chanel a & b function. It does not show the waveform well, the peak is about 10x smaller and shorter, and there is a ton of noise from mains power etc. Also I'm not sure exactly where to put the probes, and whether I want to add A+B or Subtract A-B.... Will this work? If so how do I apply ohms law to my waveform?
The scope is a DSO Quad 203. It's battery powered. The noise is a lot less with the usb charging cable disconnected. I do know the scope is interfering with the circuit in other ways too. Because the LED often light with only one leg attached to the circuit, when I touch the other leg with my finger, when this happens I do not need to be touching any other part of the circuit. Not sure exactly whats going on here, but wireless transmission is part of it as I can light the led from my 300v JT with just one leg connected, and no measuring kit attached, only if there are high enough voltages present. it gets a little brighter if I touch the disconnected leg. I only mention this in case someone knows how to alleviate the interference...
Mostly I just want to be able to measure and record (with a pen if I have to) real time amps fluctuations up to around 1mhz. 500khz would still be useful. amp measurement needs no me in uA and able to read up to around an amp, maybe 10?
I am prepared to by some new kit to do this, but budget is probably around $200 (AU/US) unless it's going to be good for other stuff as well...
I can also do maths pretty well if I have all the right formulas.
Any suggestions?
I have tried my best multimeter, which has TRMS designed for AC mains work, it has a TRMS AC+DC mode that is more accurate than anything else I have tried, but I think the the sample rate is to slow. Also I would like to see max, min, p to p amps etc.
I have tried shunt resistors with my scope. Every time I connect the negative probe it kills the oscillation.
So I tried using two pos probes and the add subtract Chanel a & b function. It does not show the waveform well, the peak is about 10x smaller and shorter, and there is a ton of noise from mains power etc. Also I'm not sure exactly where to put the probes, and whether I want to add A+B or Subtract A-B.... Will this work? If so how do I apply ohms law to my waveform?
The scope is a DSO Quad 203. It's battery powered. The noise is a lot less with the usb charging cable disconnected. I do know the scope is interfering with the circuit in other ways too. Because the LED often light with only one leg attached to the circuit, when I touch the other leg with my finger, when this happens I do not need to be touching any other part of the circuit. Not sure exactly whats going on here, but wireless transmission is part of it as I can light the led from my 300v JT with just one leg connected, and no measuring kit attached, only if there are high enough voltages present. it gets a little brighter if I touch the disconnected leg. I only mention this in case someone knows how to alleviate the interference...
Mostly I just want to be able to measure and record (with a pen if I have to) real time amps fluctuations up to around 1mhz. 500khz would still be useful. amp measurement needs no me in uA and able to read up to around an amp, maybe 10?
I am prepared to by some new kit to do this, but budget is probably around $200 (AU/US) unless it's going to be good for other stuff as well...
I can also do maths pretty well if I have all the right formulas.
Any suggestions?