MX Battery Block/Battery Disassembly

[njh621]

Hello all,

So now that I'm into the MX series of radios, need a little assistance in the area of batteries. In terms of tearing them opening, getting the bottom plate off is an issue/pain in the rear. I've read that if you freeze the pack in question, it causes the glue to fail (assuming it's an older pack) and the bottom should fall off after whacking it on the ground. Well, I tried this and I managed to get the plate off, but broke off all of the corners in the process. Is there another method to cracking open the batteries that will leave the bottom piece intact so that it could be glued right back on? (Besides using a Dremel!)

Next part. Picture below is the MX battery block, essentially a hollowed out battery with two banana plug jacks to bench-power a radio using a variable power supply. Tech data says it has over-voltage and polarity reversal protection, along with a fuse. Does anyone have a schematic for this battery block, or an idea how I could go about building one inside of a battery case? I was thinking a couple of rectifier diodes for the polarity protection and I can figure out the fuse, but I couldn't think of how to do over-voltage protection, or what size/type of fuse to use/etc. Input appreciated!

[PETNRDX]

Look up LM317 single IC voltage regulator.
I find those to be the easiest to make as specific voltage.
With just a couple of components you can set it to to the voltage you need.
You might even google homebrew battery eliminators using that IC or other single voltage IC's.

[Tom in D.C.]

The exact output voltage on any three-terminal regulator (Fairchild, etc.) is set by putting
a variable resistor between the middle terminal and the output terminal. I've built many of
them with a nominal 12VDC output that is adjustable to 13.8VDC using this connection. You
would need one with a rating/set point of 7.5VDC. There are tons of cookbooks out there
about how to build, adjust, regulate and protect these things, many provided by the chip
manufacturers.

[Will]

DANGER!!! Some /\/\ battery blocks did not have a regulator in them.

[Tom in D.C.]

Will,

I don't understand your comment. We're talking about building a power supply fed by 12 to 13VDC that internally
limits the output voltage to something around 7.2 to 8VDC, with enough current capacity to run the MX on
transmit, that's all.

Regards,

[wazzzzzzzzup]

i recently cracked open a W&W Associates MX battery pack, the front side was barely glued on, i went in and ran wires to the power pins on top to a maxtrac style power plug, then to a 7.5 volt HT1250 battery that i soldered the leads to. this allows me to make adapter batterys for any 7.5 volt battery operated radio and the good HT1250 battery can clip on the belt wile providing power to whatever radio you have conneced to it. this setup works great for alot of my radios, i used to keep a good battery of about 4 styles on hand for Fest use, but it just got expensive.
heres a picture of the HT1250 ULTRA HI Cap battery with wires soldered to it (i think im going to cover the exposed leads to prevent accidental short.) also pictured is the SABER battery eliminator, oddly enough both of these batterys were former W&W Associates, thier cases are easy to crack open at the seams. aside from the looks you may get at Fests, you can smile all the way to the bank knowing you are saving lots of cash on battery buying.

[njh621]

The LM317 is looking like a winner, I'll just have to figure out the specs of what all to use. In terms of amperage, for the fuse and the diodes, what should I be thinking of in terms of limits? I was thinking something between 0.5A and 1A. Following the basic circuit from http://www.electronics-lab.com/articles/LM317/ and using the calculator, R1 will be a 10 Ohm resistor and R2 would be a 50 Ohm resistor. This is the design I'm picturing so far (didn't have room to include the diodes):



Already I read somewhere that using rectifier diodes might create an excessive current draw? Didn't make much sense to me, but then again I've dealt with relatively simply circuits until recently.

So can anyone else confirm the freezing process for cracking open the pack? WAZUP, when you cracked open your MX back, you said the front wasn't glued? I was under the impression the battery shell was two pieces; the main body (which was a single, solid-cast part) and the bottom plate which was glued on. Regarding the money saving bit; in my book if you can break it down and saving pieces part or build something else out of it, do it. I managed to assemble a working Xbox-1 that way, using a busted motherboard.

[wazzzzzzzzup]

congrats on building the XBOX! Well the W&W Associates battery's had minimal glue around the sealing points, their battery's may come apart differently that genuine Motorola versions. it is a testament to the quality of Motorola made battery's compared to aftermarket versions. im holding a genuine Motorola version at the moment and it appears it is sealed from the bottom.
you might try using a hack saw or dremel and make a cut 1/2 inch below the top on all sides just far enough to contact the internal cells, that will give you the access you need to pop the top off by wedging a screwdriver into the cut area, and enough battery area to grab with pliers and rip those puppies out of the case. when you are done making your connections and have made an exit for the wires out of the pack, i would recommend filling the top half and bottom half with silicone sealant leaving a 1/2 inch gap on each half in the area to be super glued and let it dry, then super glue the halves back together. when the super glue is all dry, drill a 1/2 inch hole in the back of the pack along the super glued line, then squirt a bunch of silicone filling up the center area, fill the silicone to be flush with the 1/2 inch hole. that will provide extra vibration and sturdiness support. i find the silicone keeps things from vibrating loose and provides similar regular pack weight. i find brown, black and clear GE silicone II work well for this, i think the best for sturdiness is clear, but clear has a bluish tint to the backdrop of a brown pack, but if the hole is behind, few will see.

many years ago i did some projects with the LM317 regulator, you will need a nice size heat sink if you plan on driving a load much above 1.5 amps. and i think the radio transmitting will consume about that. the little multi fin heat sink radio shack sells is NOT enough heat dissipation in my opinion. be sure to use some dilectric grease between the 317 and the heat sink. i dont recommend hiding the regulator and heatsink in the battery pack unless you never plan on transmitting due to the heat dissipation needs.