mini-phil

As I want something that will last all day while out in the field and a rechargeable batter pack would seem to be an economic solution that was all. Phil

I am looking at making an external battery pack to plug into the DC-in on the NH900. Measuring the voltage of the NH900 power supply I get 3.49 volts under no load. I have seen a design for an external battery supply that uses 4 rechargeable AA cells, which are supposed to have a voltage of 1.2 volts, this would make 4.8 volts! But actually the reacheable cells measure as 1.49 volts each freshly charged and falling to around 1.41 volts some 15 minutes after coming off charge. Now 4 of these cells would give you an initial voltage, freshly charged, of 5.96 volts, this seems rather high for an input that takes 3.49 volts from a mains power supply? Some 70% over value! To make up the correct voltage using the rechargeable cells would seem to be almost impossible, as using 2 rechargeable cells would appear not to be enough getting either 2.4 volts 'nominal' or nearly 3 volts when freshly charged then falling. Three cells would again appear to be too much as they would be OK at their 3.6 volts 'nominal but would be around 4.7 volts freshly charged, and as for the design using 4 cells this would appear to be way too much at either 4.8 volts 'nominal' or 5.96 volts freshly charged! Unless there is some substantial tolerance on the input. Does anyone know what the 'maximum' voltage you can safely apply to the DC input of the NH900, without causing any damage to it? Thanks