Thursday, August 15, 2013

Upgrading the MTR: We need more power!

It's been a while since I updated the blog so here's a post on the latest development in the life of my MTR.  As you've seen already, its been outfitted with a really slick touch keyer, BNC connector, and an on board 9v battery.  Unfortunately it seems my 9v is dying so I decided I'd give this LiPo battery tech a chance.  I meandered over to the favorite Chinese location: HobbyKing.com.  They have a ton of options for batteries and many other things.  I went looking for a 3S battery - they have 3 cells and have a nominal voltage of 11.1v, perfect for 5w output from the MTR.  You can get 3S batteries pretty small but I was hoping to max out the capacity while maintaining the ability to stick it to the side of the MTR case, just like my 9v.  The ideal capacity ended up being 850mAh, just a bit less than the 1Ah capacity of a lithium 9v, but obviously with a lot more juice at 11.1v.  Here's the one I picked:

After picking one of their cheapest chargers and applying shipping, for $21 I had a full setup.

The battery comes with a male JST type connector but I decided to go the more permanent way and just solder the wires directly to the switch I've already got wired up in my MTR.

Here's the battery compared to the 9v its replacing:


The DC-4S is the charger for the LiPo, also very small!
 Remember when cutting leads off of a battery like this that you should cut them ONE AT A TIME!  Don't ask how I know that.

Anyway, I ground down the one corner of the top case on the MTR (not pictured) and passed the wires into the MTR that way.  Unfortunately with these batteries, there's also a balanced lead that you plug into the charger to control the cell balancing.  In my case, the charger I got actually charges through the balance wires so it works out OK, I don't have to remove the battery from the MTR in order to charge it!

I am getting 5w on 20m and 4.5w on 40m with the battery at 11.7v, which is about what I would expect since that was roughly what I got with my 8 cell NiMH pack which tops out at about 11.2v.  I made a few QSOs on 20m and went outside for a glamour shot.  That yellow really looks nice next to the blue!
There's still testing to do as far as how long this is going to last, hopefully I'll get out to the park on Saturday and put it through its paces.