Electronics wiring question

[beezwax]

Hello TRF,

I don't have much electronics background so I'm hoping someone here can tell me if I'm on the right path or about to do something stupid. I have a Garmin Astro that I'm thinking about swapping batteries on. The stock battery is pictured below (actually it's a photo of a generic replacement battery that I just pulled from eBay but it's the same as the original). The stock battery is much bigger than necessary for rocketry purposes, so a lot of size/weight could be saved by going with one of the little LiPo batteries used by many rocketry altimeters, I have several from both Featherweight and AltusMetrum.

The voltage is the same so it would seem to be simply a matter of getting it wired up correctly. In the photo you can see the battery connected to a 6-pin connector. This is what mates with the circuit board. I'm *assuming* that the first two (red/black) wires are the actual positive/negative wires from the battery. The last two (red/green) wires leading to the 2-pin connector mate to the exterior case, this is what sits in the charging cradle and is how the battery is recharged. I have no idea what the middle (white/blue) wires do.

Can I simply substitute the positive/negative leads from one of these smaller LiPo batteries for the red/black positions on the 6-pin connector and leave the other four spots empty? I was going to just hook it up and see if it works but I thought I'd ask here first, not sure if that cold damage it somehow. Any help is appreciated

 

[botscott08]

I take it you have the new DC50 collar? The DC40s are still available with everything integrated into one package. That's easiest.

Do you have a multimeter? I'd like to know whether the two red wires on the 6 pin connector have continuity when the battery is connected to the rest of the collar. Usually the electronics built into a lithium battery like that is a low voltage cut off. Pictures of the rest of the collar electronics and whatever's under the heat shrink would be helpful. Replacing the battery with a smaller one is as simple as you're suggesting but I want to be sure of the connections first. I wouldn't imagine you'll save much weight on the battery though. Those little 160mAh cells won't last very long. If you really need to save weight I'd just use an RF tracker.

 

[beezwax]

Thank you for the quick reply! I do have the DC40, not the newer DC50 so yes everything is contained in one unit and very convenient for medium to large airframes. But you can get a pretty significant size/weight improvement if you pull the circuit board from the case, it becomes small enough to fly in 38mm airframes even, and the size/weight benefit would make another noticeable gain if you swap the stock battery. I do have a little RF tracker, but it's pretty Stone Age compared to GPS tracking so I'd love to see how much I can shrink the Garmin.

I also do have a cheap multimeter, but my knowledge of how to use it is basically to see if my AA batteries are dead (I told you I had very little background in electronics ) I'm going to pull it out and see if I can muddle through the rest of what you suggested.....

 

[beezwax]

Okay a few more pics-- the circuit board, plus the battery without the wrapper. The OEM battery wire colors vary slightly from that generic one I posted from eBay. They are red, black, yellow (instead of white), blue, orange (instead of second red), green. The first two definitely seem to be the battery +/- judging from what is printed on the little board on the battery. Also, I tried to check for continuity between the two red (or rather the red and orange) wires. If I understood what you we asking....I poked the #1 and #5 pin on the circuit board with my multimeter leads and did not get any continuity beep. Did I do that correctly?

So it would seem I could safely swap a smaller LiPo battery in for the stock 18650, I just need to get the right connector. Any idea how to figure out exactly what connector that is and where to get it? Do I need some kind of special tool for those tiny little crimp pins on the wire ends? I was going to run down to RadioShack tomorrow but I don't know if they stock such things.

For comparison, the stock battery is 2400mAh and weighs 46.7g. The tiny 130mAh battery pictured next to it weighs only 3.6g. If that doesn't allow enough run time I also have a 400mAh battery which weighs in at 9.2g.

 

[beezwax]

Well after a lot of time spent googling I can answer my own questions here. So in case anyone ever stumbles across this thread and wishes to try the same thing:

The connector on the Garmin is made by JST, it’s their ZH series (6-pin, 1.5mm pitch). You are not going to find these at Radio Shack, unless your local is much better than mine, I did go in and ask. I ordered the mating connection housing from DigiKey (part no. 455-1129-ND) as well as the female terminals (part no. 455-1130-1-ND). You also definitely need a special tool for these tiny crimp terminals, which you can spend an awful lot of money on (in the hundreds of dollars). The best solution for the non-professional seems to be the Engineer PA-09 Micro Connector Crimper, which still is going to run you about $45. Order extra terminals (they cost just pennies) as you’ll likely mess up the first few times until you get the hang of working with these tiny things. An alternative is to simply buy some connections that are already wired up, do a search on ebay for “JST ZH 1.5 6-pin” you can find a bunch for a few dollars, though usually shipping from China. This will save you the cost and difficulty of the special crimping tool, but you’ll then have to splice these wired terminals to your existing battery leads (less clean) or re-solder the new leads directly to your battery. I was experimenting with various batteries and multiple types of micro crimp terminals so I just went ahead and got the PA-09 crimper from Amazon.

First I tried using the 130mAh LiPo that I got with my Raven altimeter. This battery uses a Molex PicoBlade connector (2-pin, 1.25mm pitch). The mating connection housing from DigiKey (part no. WM9724-ND) and male terminals (part no. WM4560CT-ND). The good news? It works! I did all the crimping and wired up the Raven battery in place of the stock battery (leaving the other 4 pins in the 6-pin connection empty) and it powered up just fine. Be careful with the polarity from the Raven battery, use a multimeter to confirm that you have it correct before you plug it in. It’s not possible to tell just by looking at the Raven battery which is +\- since the connection terminal is mounted directly to the battery. The not so great news, it only had enough juice to power the GPS unit for a little over an hour, not quite as much as I’d like.

So next I wired up a 400mAh battery that I got from the folks at Altus Metrum with my TeleMini altimeter. I cut the existing leads and crimped JST ZH 6-pin to the battery. I also soldered the mating JST 6-pin connector (DigiKey part no. 455-1661-ND) to the other end of the original battery leads. That way I can reconnect the battery to its original connector terminal (which is yet another variety, a JST PH series I believe, 2-pin 2.0mm pitch) for the purpose of recharging it with my Altus Metrum charging unit. The good news? I powered the GPS unit for 3hours20minutes before running out of juice. Enough of a cushion for me to feel comfortable flying it, and still very small and light.

I’m now in the process of building this Garmin tracker into a 38mm nose cone. Perhaps I will do a more detailed thread with pics at some point if people are interested. The unit will easily fit inside a 38mm coupler, even while still attached to the bottom half of the stock case. If you wish to remove the circuit board from the hard shell case entirely, the circuit board itself is small enough to fit inside a 29mm airframe! But in order to remove the board from the case you do need to de-solder one connection, the antenna connection which is an M3 screw (metric, M3-0.5 pitch x 5mm) that passes through the hard case and terminates in a pin that is soldered to the board. I did this in order to do a bit more experimenting. I removed the circuit board and in place of the big thick stock antenna I soldered in a length of 18awg stranded wire. This new much smaller wire antenna did work, I was able to power up the collar unit and communicate with the Garmin hand-held tracking unit as normal (tip: the Astro did not recognize the collar unit at first until I went into the menu for that collar and selected “Upgrade Dog Unit”…that seemed to reboot the unit somehow and re-establish the link). The length of the wire should be between 18.5 and 19.5 inches for a 1/4 wave, depending on the frequency the collar is on. The Garmin units transmit on one of five frequencies (in the US) depending on the collar ID:

151.82 Mhz ( ID code:0-9)
151.88 Mhz ( ID code:10-19)
151.94 Mhz ( ID code:20-29)
154.57 Mhz ( ID code 30-39)
154.60 Mhz ( ID code 40-49)

You can see the ID code for each paired collar unit by navigating to that unit on the Astro hand-held. You can also choose to use a different ID from the menu screen for that unit. Antenna wavelength calculators can be found online.

Completely removing the circuit board from its case and replacing the stock battery and stock antenna turns this Garmin tracker into a very small unit. But, after establishing that this was possible, I decided to reattach the board to the bottom half-case and reattach the bigger beefier antenna. I really don’t fly any 29mm airframes so 38mm is plenty small for me, and the bottom half of the stock case actually makes a perfect sled for the unit, no need to screw it to anything else. I am definitely going to use it with the new smaller battery though. Feel free to ask for more info if any of this is useful to you.