FX Radar Chronograph - LOVE IT, KInda'

I've tried regular NiMH batteries and what I've found is they don't hold a high enough voltage long enough. 3xAAA alkaline new will give you ~4.5v. 2xAAA NiMH will give you a nominal 1.2v per cell for ~3.6v which is below the FX radars low voltage threshold. So you don't get much runtime from NiMH.

I am currently using Energizer AAA Lithium batteries and get a lot more runtime. They have a higher nominal voltage of around 1.65v out of the package and can sustain their voltage longer with the higher current the FX radar draws. 

@Jason - how are you plugging the radar into a power bank? A USB 5.0v input would be perfect for the radar - they really should have put a USB port on it.

Ah okay, I thought we were talking about lithium rechargeables. Yes the non-rechargeable lithiums are electrically compatible and have something like 2x the capacity of alkalines but boy are they pricey.

Regarding the use of an external USB battery pack, you just have to locate the first and last contacts in the battery bay and apply the 5V to them. Some level of DIY is required. For example, cut two pieces of dowel at the length of a AAA battery to make fake stand-ins. Add a copper tack to one end of each and solder a wire to it (or if you don’t want to bother with buying copper tacks, just bring the wire out through the end of the dowel and flow a generous blob of solder on the end). Then chop the end off of a USB cable and tie the red and black conductors to your fake batteries.

The middle position in the battery bay is just left empty. Not needed to complete the circuit.

Ahh - ok so you're simply wiring into the battery contacts. A USB power pack is definitely the way to go - I'm gonna see if I can maybe wire a USB port into the battery cover. 

Ah okay, I thought we were talking about lithium rechargeables. Yes the non-rechargeable lithiums are electrically compatible and have something like 2x the capacity of alkalines but boy are they pricey.

Regarding the use of an external USB battery pack, you just have to locate the first and last contacts in the battery bay and apply the 5V to them. Some level of DIY is required. For example, cut two pieces of dowel at the length of a AAA battery to make fake stand-ins. Add a copper tack to one end of each and solder a wire to it (or if you don’t want to bother with buying copper tacks, just bring the wire out through the end of the dowel and flow a generous blob of solder on the end). Then chop the end off of a USB cable and tie the red and black conductors to your fake batteries.

The middle position in the battery bay is just left empty. Not needed to complete the circuit.

Click to expand...

There is a (+) and (- ) connection (marked) on the circuit board. It's not used.

EDIT: But connecting 4.5V-5V to the last and first will work. Just tested. So just need to run two wires out to a regular 5V phone charger. Or you can place a sub-mini power socket inside the case in the sidewall of the enclosure. There is already a hole inside the sidewall of the enclosure and right where it is there is the (+) and (-) labeled connection on the circuit board. Either solder two wires and run them outside the case to a plug, etc. or install a sub-mini two-prong power socket inside the case over the existing hole.

Make sure when you solder do not mix up the two connections and do not bridge them together or there maybe smoke! Also, DO NOT, DO NOT USE the external power supply at the same time when also using batteries! Will destroy the batteries and start a fire. And make sure that if you are using batteries that external power connections (even if already disconnected) cannot short to each other or to the ground. 

Better to install a sub-micro plug inside the case for a removable external connection instead of a permanent hard-wired cable running to a charger.

Also, I am pretty sure this will void your warranty. 

Nicely done! Thanks for taking the time to give us a rundown and pictures.

When I get around to it, I'm going to see if its minimum operating voltage would make an 18650 cell a good candidate, that way it could still use it uncabled.

An 18650 won't cut it. LVC seems to kick in around 4 volts and an 18650 will only be above that for a short period of time with its 3.7 nominal voltage. 

A USB power bank seems to really be the cheapest option for the right voltage output. You'd need two LiIon cells in series and a voltage regulator to bring it down to 4.5-5volts. 

Thanks for checking the LV cutout.

Wow, 4V is a poor design spec. Three alkalines won't hold that level for anything approaching their design capacity. The usual design practice is to operate down to ~3.0V (1.0V per cell). That's a massive part of its reputation for eating batteries, it's because only a portion of the batteries' capacity is useable with such a high cutout. It's like a gas tank with a feed tube going only half way down.

Not ideal at all. It's like someone designed it for a USB connection and at the last minute someone said let's use poopty AAA batteries with zero capacity and almost no ability to hold voltage under load.

Another quick and simple idea. I did this to a couple radios I have on my bike handle bars. I have a pedal assist bike that has a usb socket. Hated replacing batteries in the radio. Take a usb cable, cut off one end, strip the wire ends back. Cut 2 wooden dowels just a hair shorter then the length of an AAA battery. Take 4 small but large headed screws ( to touch the battery springs) and screw these into the ends of the dowels. Using a screw on (one) end of each dowel to secure 1 + and 1 - wire. Just like batteries, make sure your + and - are inserted correctly. Notch the battery cover to route your wire. Can always switch back to regular batteries too. If you use the existing hole in the side, remember to run your wires before connecting to the dowels. You can now plug the usb cable into a usb tap. Or if you need a longer cord, you can use a standard usb cable as an extension cord. 

Make sure you cut the right end off the usb cord!

Thank you for sharing and inspired. 

Hello, I also did something with mine. An old phone charger, I'm fine taking the batteries to the field.
a greeting

I tried out with the phone battery back up, the FX chrono doesn't like that set up, shut itself off. (battery pack has smart circuit, may not let the chrono stay on)

Working well with phone charger plugged in though.

Here is one more. I can share the files if anyone wants to make these but it is quite expensive to make just one if you don't have the parts (shipping)