Interesting AA M11 Battery issue

[nvradtec]

I had a perplexing problem with an Airtronics M11 that I aquired, The radio would
work great when I filled the AA battery tray with Energizer alkilines, but would have power issues when I used my 3000Mah Nimh rechargables.

This was driving me bonkers, so being that I'm an old ham radio guy
I set out to find out why, I tested and recharged all my rechargables,
no "bad" batteries, voltage and capacity were all fine, (still scratching
my head) Till something caught my eye, the button on the top (+) side
of the battery, so I dug out my measuring calipers, here is what I found.

measurements I come up with
across the button, Energizer 5.36 MM Nimh 4.8
top of button to top of battery case, Energizer 1.57 mm, Nimh 1.4 mm
overall battery length Energizer 50.44 mm Nimh 50.32

The M11 AA battery tray uses U shaped spring wires instead of metal
spring tabs on the battery + side, here is what I found in my case.

With the Nimh's installed the top of the battery case was resting on the plastic that retains the spring wires, with the button being smaller in diameter and .17 mm shorter the button of the Nimh would fall in the middle of the U shape or barely make contact thus making your battery meter dance all over the place and getting the low voltage alarm.

I only had 2 different brands of rechargeable Nimh's to play with
but the measurements were about the same.

So if you've had issues with rechargeable Nimh AA batteries in your M11
this may be the reason as it was in my case, a little tweaking of the U shaped wires helped me out as it might yours

Or just replace the poorly designed AA case with a soldered together or store bought battery pack

These are just my findings in my case, yours may be different, just something to ponder

[reden]

I've seen this on other types of equipment too.
Dove me crazy to find the problem but in the end it was the battery button on top.
Altered the the plastic devider(made it thinner) and all types od batteries worked.

[nvradtec]

Originally Posted by reden

I've seen this on other types of equipment too.
Dove me crazy to find the problem but in the end it was the battery button on top.
Altered the the plastic devider(made it thinner) and all types od batteries worked.

I'm recovering from an emergency appendectomy and in recovering mode and I got bored so I measured batteries...hehehe

Just thought it may help some others out if they were having issues
as I was

[rdcobra]

If you run Lipo already... Invest in a 3-cell lipo, you can crawl all week on a charge. I went lipo in mime, and have not looked back. I keep the AA tray as an emergency backup, but have yet to use it.

[Charlie-III]

Be careful measuring overall length with a caliper that is metal, you WILL create a direct short!!

As to rechargeables vs. alkalines, rechargeables (most of them) are nominally 1.2VPC vs. 1.5VPC (VPC = Volts Per Cell).
A set of fully charged rechargeables starts at about what a set of alkalines are near end of life voltage wise.

[nvradtec]

Charlie

I used my plastic one...hehehe

And I'm aware of the differences in voltage

Originally Posted by Charlie-III

Be careful measuring overall length with a caliper that is metal, you WILL create a direct short!!

As to rechargeables vs. alkalines, rechargeables (most of them) are nominally 1.2VPC vs. 1.5VPC (VPC = Volts Per Cell).
A set of fully charged rechargeables starts at about what a set of alkalines are near end of life voltage wise.

[Charlie-III]

Originally Posted by nvradtec

Charlie

I used my plastic one...hehehe

And I'm aware of the differences in voltage

Cool..........just looking out for the other 95%.........

Since I work with ~545VDC battery systems (UPS applications) I NEVER assume anything......Hope you understand....

[Manning]

Originally Posted by Charlie-III

Be careful measuring overall length with a caliper that is metal, you WILL create a direct short!!

As to rechargeables vs. alkalines, rechargeables (most of them) are nominally 1.2VPC vs. 1.5VPC (VPC = Volts Per Cell).
A set of fully charged rechargeables starts at about what a set of alkalines are near end of life voltage wise.

And since lots of radios use 8 cells, that difference adds up.

Back in the day when oval racing was all the rage, I added a 2 cell tray to the bottom of my radio to make up that voltage difference. Some people were convinced it was an unfair advantage. Funny stuff.

[Rok Krawl]

Just run a lipo 11.1V. AA recharge cells dont last that long and duracell or any other just get expensive. I run a 900 lipo on my m11.

Any of you found a larger lipo pack to run that will fit in the bottom of the TX? I could prolly build wire harness to run 2 of these packs in bottom of my TX.

[nvradtec]

I also work with 48 volt battery strings myself and larger ups backups in radio sites, and yes I understand

Originally Posted by Charlie-III

Cool..........just looking out for the other 95%.........

Since I work with ~545VDC battery systems (UPS applications) I NEVER assume anything......Hope you understand....