Guru
Joined: 25/02/2006
Location: AustraliaPosts: 495
| Posted: 02:22am 17 Jun 2011 |
Just an addendum to this.
While a 1:10 divider may appear "the fix", you need to do the calculations. A 48V bank will float at 54+ volts, so you may need even higher divider.
The problem with that is that the further you divide, the less your resolution becomes. If you have a 10-bit ADC, you have only 1024 discrete steps, and thats assuming no jitter. So a 0-60V input means your *theoretical* best resolution is 0.06V
Enough for some, but by the time you take realistic conditions into account, you'll be hard pressed to make better than 0.1V readings. Barely good enough for decent battery control.
An opamp level shifter is probably unnecessarily complex for you, but a simple and cheap way would be to "wash off" some of your volts with a zener, or some zener diodes. For example, if you got 3, 12V zeners in series you'll lose 36V right there.
You now have a battery input from (say) 40 to 60V, with an output after the zener of 4 to 24V. A span of only 20V. You still need a divider, but now a 4:1 divider will suffice, and you get resolution closer to 0.02V per bit. Much more useful.