I understand what you want to do, and why you want to do it. I use CR123As everyday, and they're great! I 'll confess to lining up three 123's in front of my FNB-23 and trying to dream up some way of doing this.
There are some important things you need to be VERY AWARE of regarding CR123A Lithium primary cells.
First, CR123As will not tolerate ANY form of charging. There are documented cases of mixed CR123As exploding when a new cell is installed with a discharged cell. You will need to take measures to ensure that it would be absolutely impossible for reverse current to be applied to the cells should the radio be accidentally plugged into external power while the 123 pack was on the radio.
I was thinking about putting a 2-3 amp ,25v diode in series with the cells, but it would be a very snug fit. I toyed with the idea of using two or three smaller 1A diodes in parallel, but unless they were carefully matched and each had a low value series resistor, the one with the least forward resistance would be carriying most of the current. At least until it overheated and failed.
The voltage with two cells would only be 6V, which really isn't enough for full 5W output. The radio's going to be ramping the PA down, I'm guessing the around 3W. Three cells would be 9V, and the forward drop across the diode would bring this down to around 8.4V; the same as a fully charged OEM Yaesu battery.
There's no problem with putting 12V-16V into the battery contacts in the battery compartment of the radio. The EXTPWR circuit feeds the radio along the same pathway, and when charging the OEM batteries on the radio, pulses of up to 12V are present there.
The last thing I'd recommend is a picofuse in series with the cells and the diode. The 123's can deliver an awesome amount of current, and though they are allegedly equipped with internal thermal fuses, I definately wouldn't want to risk finding out how well they work. I'd go for a 3A picofuse (either Digikey or from Radio$haft) They're only about the size of a 1/4W resistor and would need to be soldered in, but could save you from a lot of grief.
I just looked at the PDF for the battery cell holders you got from Digikey; wow, three of those will be a very tight fit. I'm not even sure if it's possible. The height of the cells in the cellholders looks like it'll be more than what will fit inside the radio. I don't have my FNB-23 handy, but I do recall that the back side is flat with the back of the radio case, rather than protruding like the FNB-80LI does. Here's a thought. Instead of starting with an FNB-23, why not use a dead FNB-80 od FNB-58 instead? Take a dremel tool, and carefully cut the outside rear surface (where the drop-in charger contacts are...)
That'll give you a nice flat inner surface to mount the cellholders to, though the cells thamselves might protrude out the back of the radio a tad. We could call that a "design feature" that serves as a visual reminder NOT to plug in the EXTPWR.
Let me know if you decide to do this, and how well it works out for you. I've got an OEM battery that is due to be taken out of service in a few months, and I but CR123A's by the dozen for my SureFire flashlights. Since the price came down to $15/dozen, there's no reason to be shy about using them.
8.4V at 3000mAH... That's a battery...
Gary N[...]
I'd like a (small, lightweight) "full power" non-rechargable emergency battery pack.
I've schemed to do this by gutting a FBA-23 (removing the regulator) and supplying power with 123A batteries.
I've purchased a spare FBA-23 and some battery battery holders (
http://www.batteryholders.com/BC2-3AE.pdf ) from Digikey.
But then I run into a stupid question.
I recall seeing that the external DC will allow 12V DC, but I noticed that the normal battery pack is 7.2V. And, IIRC the FBA-23 outputs about 4.5V.
Sooo... What voltage range is acceptable using the internal battery contacts? Is more than 7.2V allowed?
My preference would be to 9V or 12V but obviously I don't want to kill the radio.
Thanks for your help,
-john
