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Honeywell has a 5v supplied linear output hall effect sensor. It gives half supply (2,5V) for no magnetic flux. I've done some experimenting by cutting a gap of the same thickness of the sensor, into a small ferrite bead, using a diamond cutoff wheel from Dremmel, gluing the sendor to the bead and pass the "current carrying" wire through the bead and you can measure the current (charge or discharge) in case of a battery. It's not exacly linear output but with a microcontroller you can use a "lookup table" to correct this. Outputs 2.5V going to 0V, the current is flowing in one direction. 2.5V going to 5V, the other direction. I did not try AC current but I supose, if the ADC converter is fast enough maybe it will also work.
What current are you looking at here ? what resolution/granularity ? This will tell you what your v/v requirement is which will be a good place to start.
I am designing and eventually building an Electric Vehicle controller with capabilities to drive 1200Volts @ 800 amps max. There are a number of fellows involved in the project as an open source of information on a yahoo group called evcs. To answer your question of isolation, for current and voltage you need to use opto couplers from a comparator cirucit that is linked to a very small resistance in series with your motor drive circuit. The small resistance is in the order of .015 ohms or there abouts for my drive system and it is a very expensive resistor because it is high wattage, in and around 50$
Tom
For various ranges like 5A, 8A, 20A, 30A, 50A, 100A, 200A unipolar and bipolar, Allegromicrosystems has these hall effect current sensors:
**broken link removed**
Maybe somebody else has a simple way to detect an isolated DC voltage, because I need something like that too, but have been unable to find an inexpensive way to do it ($20 analog isolation amplifiers that need dual supplies or switched transformer setups seem too elaborate for what I realy need it for).
But you could use the analog isolation amplifiers ISO122 or ISO124 from Texas INstruments to measure an isolated DC voltage. But they are $20 and need medium voltage bipolar supplies. THe other way I know of (the much more complicated way) is to make a very very small DC-DC transformer-isolated switching converter that is very low power (since it's really passing a voltage signal and not supplying power) and produces output voltage proportional to input voltage.
EDIT:
Thomas COlins' mention of an optocoupler being used in the analog mode rather than digital got me searching. I found the HCNR200 optocoupler which with a few other parts makes an analog optoisolator whose output is proportional to the input voltage for Much less than $20 and can work with low-voltage single supplies. THanks.
MORE EDIT: IT seems THomas COlins is using the optocoupler in digital mode and not analog mode. But either way, I misinterpeted and it gave me the right idea to lead me along the right path.
The rating on the IGBT's I'm using will max out at 1200V and 800 amps.
I will be putting adjustable limiting circuits in the design and the driver will be able to have an IGBT(s) with that high a rating, myself I will be using a battery pack of probably 144Volts 500 Amps max.
I just want the controller to be generic enough for anyone who wants to use it for drag racing or any other use it can by installing larger IGBT's . The driver will be a VLA502-01 or similar from powerrex. The inline resistor will be large...no doubt... but I have checked in with a couple of people and this is how it is done. I'll probably use the heat off of it in the winter to defrost my windows...lol!
Tom
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