Using 3 cell Li-poly pack on a MicroStar

The MicroStar Encoder will operate with a voltage supply from a 3 cell Li-poly pack. These pack will provide a higher nominal voltage (around 11.1 volts) than you get with conventional 8 cell NiCd packs (9.6 volts). This higher voltage will actual help a little on achieving full ADC range. Please read the 10 bit vs 12 bit ADC article to get a better understanding of this issue.

The place where the higher supply voltage may cause a problem is the RF deck. There are a lot of RF deck options and I can’t speak to all of them but I can provide a little guidance. First; my RF deck will work fine with the 3 cell Li-poly packs with no modifications. If you have concerns you can lower the voltage going to the RF deck by placing rectifier diodes (1N4001) in series with the power lead going to the RF deck. You will get about a 0.7 volt drop across the diode so putting two in series should do the job.

I have heard of one case where a 3 cell Li-poly pack resulted in a RF deck failing but I have heard of many cases with no problems. So, I am not sure if the diode trick is really needed. You could also go to the trouble of using a voltage regulator but you would have to use a low drop out (LDO) regulator. These are regulators designed to operate with a very low voltage across the regulator.