# DC test equipment to see voltage extremes? [closed]

I want to experiment with magnets and coils to produce voltage. I need test equipment to find the highest positive voltages and the lowest negative voltages obtained during tests.

My needle driven testers move too quickly for me to accurately gauge them. And my digital meter does not refresh fast enough to see the extremes. I can't afford an expensive oscilloscope.

Is there an inexpensive software type oscilloscope or other test equipment you can recommend that will record the entire voltage wave form in order to see where the extremes fell? .

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• Can you breadboard a peak detector?with Op Amps , diodes & film cap or Analog switch with comparators? bipolar supplies or single? Cost $1 – Sunnyskyguy EE75 Feb 27 at 17:38 • Look for a USB DSO oscilloscope. Benefit: together with a laptop (on battery) you can measure kind of isolated. – Huisman Feb 27 at 18:37 • Detector is the word I must have needed. I've seen some of the software packages for oscilloscope on laptops and cell phones... My budget is limited so I don't want to put my laptop in peril. – John Muggins Mar 7 at 20:42 ## 2 Answers There exist many DMMs with peak detecting capabilities, some for less than$50. Just look for those that have a Min/Max setting or button.

These are not as fast or versatile as a more expensive oscilloscope, and you should check the specifications to learn how small of a peak these can measure, but these should be much more than enough to satisfy your needs.

The more expensive ones advertise Fast Min/Max which can detect peaks shorter than 300µs.

• I'll look for peak detection capabilities. Thank you. – John Muggins Mar 7 at 20:42

# Simple circuit

simulate this circuit – Schematic created using CircuitLab

Note difference when Magnet moves inside coil vs outside with fringe effects. Fleming's Rule with coil orientation determines polarity.

## More sophisticated

Using a precision full-wave peak detector with a dual Op Amp and 2 diodes + R's, you can measure Voc ( open-cct) or no-load voltage with a DMM. Or you can measure each polarity independently. This is just voltage potential from Faraday's Law of Induction and not power from Joule–Lenz's law. P=I²R ( sometimes linked to Ohm's Law )

Then you can use a load shunt R to measure near short circuit current , Isc using the same cct to measure Ipp current.

• The power it can generate will be about 1/2 to 2/3 of the VI product.
• recall that generators like motors have a no load voltage kV/RPM and a short circuit current and the max Power can be 1/2 to 3/4 of no load max speed

There are various Full wave and Half wave precision rectifiers circuits which have a low frequency cutoff determined by input RC=T1 value and peak and hold decay time by output RC=T2 decay time.

There are many other variations with comparator, analog switch and only 1 diode (half) 2 diodes (full) with some limitations

• Thank you for your help. This looks like a good possibility. I don't need extreme accuracy for my experiment. Just an indication if different stator elements will produce more or less voltage. – John Muggins Mar 7 at 20:39