Feature Request - Current monitoring
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Usual apologies if this has already been raised but searching for a term like "current" returns a LOT of hits.
Is there any possibility of including a current monitor on at least the main power input (the heater outputs would be nice but not essential)
Measuring the voltage difference across a 10 milliohm series resistor resistor would achieve it without dropping more than 0.2V even with a full 20A load
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You already measure the input voltage so adding this could simply be a case of adding the resistor and a second identical voltage monitor on the other end of it. (a differential op-amp across it would be better but more complicated)Current monitoring would be useful during the initial build process to confirm that board and power supply limits aren't being exceeded - Cheap imported heaters don't always match their specs (and builders like me don't always read them).
I know you can measure currents with a multi-meter but voltage drops across cheap ones in current mode can be quite large and many only go up to 10A. Besides poking around with cables capable of delivering up to 500W of power is asking for trouble.
In normal operation, in addition to providing status information, current monitoring could help to spot intermittent shorts and heaters that are starting to break down as well as providing an additional fan trigger source.
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Aren't most of the heaters just simple resistive ones anyway? So you could just measure the resistance with a decent multimeter and approximate the current draw. Heaters consume the majority of power in a 3D printer, then you just add some overhead for the motors and whatnot and you're good to go.
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It's certainly possible to do that, using a high-side current sense IC such as http://www.farnell.com/datasheets/1631320.pdf. However, I doubt that the additional cost would be worth the utility for most users.
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When you’re dealing with high currents “simple” is a bit of a relative term. Resistance has a nasty habit of changing as things heat up. Admittedly it goes up for cheap copper heaters so a cold measurement would suffice for a safety check.
Having said that, insulation is a bit of a relative term when dealing with cheap imports.
DC is, of course, right though - current measurement is definitely a nice to have and almost certainly not worth the additional cost.
