slipstick:
There are plenty of non-invasive ways of measuring current that don't require a shunt. Have a look for "non-invasive current sensors". Since many of them are designed for automotive use 200A DC is not a problem.
Like this?
slipstick:
But I wouldn't have anything to do with that "instructables" thing. There are many better ways of making a speedometer.
Do you have any links to point me in the right direction?
raschemmel:
Do you have any filter caps or flyback diodes across the motor ?
No, the motor is a DC brushed industrial permanent magnet motor. It connects tho the battery and controller like this:
DVDdoug:
And hopefully, you know how to calculate power dissipation in the shunt.
LOL, not yet, but that's what Google is for! (sigh, What happened to the old days when you could stop learning as soon as you left university? 
)
DVDdoug:
For voltage, the [u]Analog Read Voltage Example[/u] will get you started. You'll need a voltage divider (2 resistors) and you'll have to scale the readings appropriately. And, I'd recommend a couple of [u]over voltage/reverse voltage protection diodes[/u] in case of unexpected spikes from the motor or charger.
Thanks for the links and pointing me in the right direction! I'll be sure to post my results when I get everything sorted out.
Thanks everyone!