Battery pack powering question

[dencar123]

I have a question that may be dumb to all of you but its my question and I hope someone can help me.

Theoretical example

The basic question is if you have a DC device that requires a minimum voltage of 7V and you use a battery pack that operates at or just above that voltage will it run longer or shorter than a battery pack that is higher, such as 11 volts or higher?

Actual example

If I use a lithium polymer battery pack (2 6600mAh cells in series for 5.6V to 8.4V) a to power a DC device that has a voltage input of 7v - 24v will I get a longer or shorter run time than if I use a 11.V (8.4V to 12.6V)?

I realize that it may depend a lot on how the device board is laid out. I also assumed that a higher voltage may be just burned off by the device and provide no value to run time.

Any information will be helpful

Dennis C.

 

[davidbeach]

It depends on many things. A high quality power supply will not "waste" higher voltage than it needs, but a low quality one will dissipate energy as heat to reduce the voltage level to what is desired. How much energy can you get out of your batteries before the terminal voltage drops below the minimum voltage necessary to keep your device functioning?

 

[itsmoked]

Yes it really depends on what your device uses to match the input voltage to its loads.

Since it seems to take in a larger range than most linear regulators can deal with this means it is probably a switching supply. If this is the case you will likely get better 'mileage' from the higher voltage. But there are a lot of contradictions to this logic too.

The best way to find out is to use a Lab/Bench-top power supply and then sweep the allowed input range and note the resulting current at the different supply voltages. This would be the final authority.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com