Easily Measure 1S Battery Voltage

 If you've ever measured 1S battery voltage with a voltmeter, you know it's kind of hard to squeeze the voltmeter probes into the 1S connector.  I worried that (a) I might munch up the plastic on the connector and (b) short the battery out, since the's about 1mm or less between the leads.

So, I made a quick measuring jig, soldering an male XT-60 onto a pair of banana clips.

I then soldered a female XT-60 to a 1S connector, making it easy to plug in the battery and check the voltage.  Of course, the XT-60 plug gives me an easy way to check most of my other batteries, although as a practical thing I'll probably still use my little meter that plugs into the balance plug.

Thanks again to Crash, who's having a hints-and-tips contest over at the CrashCast.  I don't think this gives me any advantage in the drawing, but it did give me the kick to put up some of my small ideas for managing small batteries.

Using a LiPo in a Turnigy 9X radio

Here's how I replaced the battery pack on my Turnigy 9X radio.  Andreas did it first... I just copied what he did.

It's pretty simple: cut the connector off of the original battery pack (the one that holds 8 AA cells) and solder on your favorite connector to the just-cut wire.  I picked JST because it was small and didn't take up much room in the case.

I used an old 3S 1800 mAh battery that I wasn't using for anything else.  A 2S battery will also work.  RC Model reviews has a popular article on swapping out the battery.  It's a comprehensive solution, and involves resoldering the motherboard.

The method presented here is a lot simpler.  You don't have to touch the main board, but you lose the low voltage beeper.  That means it's possible to discharge the LiPo battery below 3V/cell.  You just have to be careful at the start of the day to have the battery charged to 10V or more.

The discharge rate is about 0.1V/hour, so if you're charged to 10V or above, you will probably be OK.

Be careful when soldering your connector not to reverse the polarity.  There's no polarity protection on the motherboard, so if you get it wrong you'll fry your unit!

That being said, it's working well for me.





Update: the old battery I was using started having problems with one of the cells.  I didn't have another conveniently sized LiPo, so I replaced it with a LiFe battery from HobbyKing.  Notes on that are here:

http://eastbay-rc.blogspot.com/2011/10/life-battery-in-turnigy-9x.html

Update: Javio left me a great comment on diydrones that goes into detail on how the LM7805 voltage regulator works:

There is a little confusion about the best 2S vs 3S better battery for the 9X. If conceptually it is true that a bigger dropout voltage between input and output leads in a bigger heat dissipation, the 7805 regulator has been designed to give the best performances with a differential voltage between input and output of about 5 to 10V. With the 7,5V (from 6V depending on the model) minimum input required voltage (2,5V of differential dropout voltage between input and output for 7805) the output peak current can not be achieved (the regulator can´t work at full dynamic range). In fact the factory testings of the LM7805 are done with a typical input voltage of 10V. Following this lines, and assuming that the input regulator is a 78xx, a 3S Lipo battery should be a better candidate than 2S to power the turnigy 9X. You can check the Peak Output Current Vs differential input-output voltage characteristic in the figure of page 21 of the attached datasheet or the Droupout voltage characteristic googleing "7805".

This explanation does not means that a 2S is a bad option, but in this case the regulator won´t work at full dynamic range of its output current. By the way, looking the datasheets a dropout of 5 to 7V between input and output (corresponding to an input voltage between 10 and 12V) doesn´t lead in a significative amount of heat increase.

Cheers from Spain.

Javio

LM7805 data sheet

Giant Cod guides

Here's the battery guide.  There's some others that look like they might be interesting.

Connector Mania: JST-XH

The small connector on most batteries is called  a JST-XH and is used for balancing.  A 2S pack will have a 3-wire connector, a 3S pack will have a 4-wire connector, etc.

Two adjacent wires will connect to one cell.  The first and last wires will be connected through all the cells.

Batteries can be charged through this connector up to a current of 3A.

The crimper seems to be $480 (!!?!?!??)  Some possible replacements are mentioned here.  Magic search keyword seems to be "D-SUB/DOUBLE-D SERVICE TOOL".