With modern high capacity and high current capability batteries it is very important to install the proper fuse in the battery circuit. So I did, but....
I installed six 2000 mAh NiMh AA batteries in a holder for my ham radio hand held radio. I put a fuse between the battery pack and the power source. What I failed to consider is that there was a possible current path from the battery prior to the fuse. The jumper leads I used to connect to a charging stand accidently shorted and the fuse did no good since it was between the power source and this connection. The batteries discharged into the short circuit and resulted in a melted battery holder. Should have placed the fuse between the battery and everything else!
Lesson is to fuse the battery lead between the battery and EVERYTHING else in the Universe.
Neil
Hope the battery holder was separate from the radio so you can replace it.
Yes we all have done things and overlooked something.
Mark
Looking at the microphone interface circuit I built for my Alpmic experimental microphone I see NO BATTERY FUSE!
The battery in use is a 9-Volter, and we've read warnings that 9-Volt batteries can ignite fires!
Alright. We shall install the appropriate fuse.
How much do we owe you for the consultancy?
In bygone years the zinc/carbon chemistry was used in common household batteries.the short circuit current was limited to maybe a few amps. While it was possible to cause damage with such cells, the relatively low current was generally an intrinsic safety factor.
With the advent on modern batteries, NiCad, NiMh and Lithium Ion, the dangers of shorts are much higher since these cells produce short circuit currents an order of magnitude higher than the old cells. This is why fusing is so important for any power source which can produce many tens of amps of current.
Those of us who grew up not worrying about battery shorting due to the old technology and lack of experiencing damage from small battery shorts need to realize that modern batteries are different and can be dangerous.
Neil
Even alkaline batteries.....technically carbon zinc as only the electrolyte is alkaline based instead of acid based, have a lot more short circuit current than "regular" batteries did.
Hope you could replace the battery holder!
Mark
Mark,
Fortunately, the damage was mostly internal to the battery case. The case is split and 3 batteries are installed in each half and then the halves are snapped together. Electrical contact is made between the halves via small metal tangs. One such contact point is what overheated and melted the plastic. I was able to remove the damaged clips and hard wire the connection so the pack is still usable. There is slight sagging on one side of the case visible on the outside and there was no damage to the radio. This radio is 40 years old and the pack is no longer available, even on the internet auction sites but since I can still use it and the radio is only for backup, all is well. Thanks for your concern.
I caught the problem when I smelled the melting/burning plastic. Glad I was present the whole time and was able to shut it down to prevent further damage.
Neil