Quick terminology question on AD-20 powering

[Diamond_D]

So I looked up the info sheet online, and it says "Power: 5.5V to 25V at 50ma." So am I correct that that means it will operate until the battery (9V) gets down to 5.5V and the low batt light will come on somewhere around there?

I know how to get run time from mAH capacity, but not from voltage. What do you think is a "safe" voltage to put in there before a standard 3 hour run time? I.E., I picked up a multimeter today, and some of my used batts are at 8.5V, and some at 7.5V. Are the 7.5V ones still good enough for another show you think? Comments appreciated, thanks!!

[Lil Kim Jong-Il]

So I looked up the info sheet online, and it says "Power: 5.5V to 25V at 50ma." So am I correct that that means it will operate until the battery (9V) gets down to 5.5V and the low batt light will come on somewhere around there?

That should be correct.

I know how to get run time from mAH capacity, but not from voltage. What do you think is a "safe" voltage to put in there before a standard 3 hour run time? I.E., I picked up a multimeter today, and some of my used batts are at 8.5V, and some at 7.5V. Are the 7.5V ones still good enough for another show you think? Comments appreciated, thanks!!

The short answer:
No one can really answer this question accurately.  You need to measure some battery starting voltages and then run them down until the AD-20 shuts off.  If you record the values of starting voltage and time to failure, you'll eventually get a reasonable idea from the data points you collect for that particular make and model of battery.  Then you should publish your results.

The long answer:
It depends on what type of batteries you are using - the chemisty type and the capacity of the cell.  Each cell chemistry has a unique characteristic discharge curve.  Some of them fall off in a sort of gradual slope (alkaline for example) and others maintain a voltage near the rated voltage far out the curve and then drop off rapidly (NiMH for example) at around 80% discharge.  So a battery showing 7.5V could have "some" or "very little" charge remaining depending on it's type, but in either case it's weak. 

If the battery is a type that has a nearly linear sloped discharge curve, then theoretically you can calculate the remaining charge based on a voltage measurement and using the manufacturers published discharge curve.  But these are all slightly different between manufacturers and the actual behavior is dependent on operating temperature and discharge rate among other things.  So, your calculations could easily be off by as much as 10-15 minutes.  Also, sometimes you just get a bad battery. 


I wouldn't trust the batteries at 7.5 for a show.  I'd use them in a noncritical appliance like the remote for a garage door opener or use them to run the above test.  I used to run an MV100 and it ran on two 9V cells.  It would indicate low voltage when the supply rail hit around 15V or 7.5 per cell.

[Diamond_D]

perfect, thank you sir! +T