Setting Up a Low-Voltage Watt Meter for a High Voltage System

From thsi thread: http://www.endless-sphere.com/forums/viewtopic.php?p=592085#p592085

You can still use the originally-linked WM for your 100V+ pack, but in a way that doesnt' monitor watts or Wh or voltage quite right (yet is simple to recalculate).

Put a tap for the watt meter to go in on 1/2 your pack, so that it is only reading the voltage from half of it, keeping it under the likely 60V max even when fully charged.

Then just multiply the W, Wh, and voltage readings by two, and you'll have the correct numbers for those, within a reasonable accuracy.

The Amps and Ah will be correct either way.

Some reasoning, from a follow-up post responding to an objection that this will not work:

Current thru the series-wired system is the same at any point in the system, so regardless of where you put it, it'll still measure current accurately.

Besides, if you are using it on the "bottom" (most negative) half of the pack, the shunt is in the ground wire of most of these meters, so it would still read the full system current, exactly as if you were measuring the full pack--the only difference is that the voltage supply to the meter is only half the pack's voltage, if it's tapped in the middle of the pack.

You could use two meters, one on each pack half, and add the watt-based readings, but multiplying a single meter's results by two is close enough for most purposes, unless you truly need to monitor actual pack voltage sag and the like. Two meters cost nearly twice as much, too (slightly less as usually shipping cost isn't doubled), so depending on price and complication of setup it might wind up easier to buy a CA or something similar.