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Κυριακή, 12 Μαΐου 2013

DIY Handheld Radio External Battery Pack


Here is a battery bank I did for my HT.
 
My hand held radio uses a 7.4Volt Lithium-Ion battery. That means that there are batteries wired in series in the battery pack. So one can duplicate the voltage by connected two stand alone (in this case two 18650) lithium-ion batteries in series.



So this battery pack uses a 18650 battery case like this.
http://www.fasttech.com/products/1286603 
I just had to rewire it for 2series-2parallel.


Important Safety Notice…..
There is a safety issue with the way the batteries are connected in this power bank (2 series – 2 parallel). Lithium Ion batteries in series, are not a good idea without a protection circuit (either a common one like your laptop battery or an individual one in the bottom of each battery).
The theory is that dissimilar batteries put a stress on the weaker one, or the weaker gets its polarity reversed if it gets exhausted and still receives current from the other ones>Then it may ignite.
Monitoring the remaining charge and using matched batteries from the same lot will limit the possibilities of a mishap, but it still your own calling…

Following with construction, I had to work new holes in the place of the existing ones, so I added a new wall to host the plugs. It is made from a DVD case, epoxied on and soon I will be adding supporting structures in the area the original PCB screw points are

Batteries that will be used are four Samsung 2600 (Pink) in the 18650 size. This is a cheap but of good capacity battery. Alternatively one can use the Sanyo 2600 (Red) or the Panasonics NCR18650B (Green).
So with the combined capacity of 2x3400mAh* at the moment (Panasonic is expected to release a 4000mah battery in the near future) one can expect to last him almost 3.5 hours with the mike keyed ON in the 5W high mode!!!
(* Actual capacity is around 3100mAh with a 2A load)

One more pic showing the wiring in more detail.
(he black wire (ground) snakes under the fuse holder and is connected to the RCA plug case. All other wires carry the positive current.
Fuse is a 3A one, since my TH-F7 maxs at 2A.
Then the wires end in two fake batteries respectively that are placed in a Kenwood battery case.
A small notice: the batteries appear bare with no insulating shrink wrap, something dangerous. This is not the case, their orignal was replaced with new clear wrap. It is thecamera flash that made it dissapear!

It is of a good coincidence that this HT does not have an automatic battery detection feature. So I choose the lithium option from the menu and made it think it is powered by the original lithium battery (7.4V, 1550mAh).
Also it does not use 3 contacts for the OEM lithium battery, just two. This is most critical because one cannot know how this would work with the radio was using a 3rd contact to monitor battery state. Being dump proved to be helpful in this case

Addendum:

Days after this construction this was found!
this battery case has a user defined voltage output. So it will suit most of the radios in the market. But it is unknown if it can handle the supllied current steady and for how long, or how reliable its electronics are, but it is by its existence alone tempting!

Update 1/17/15

We finally updated the powerbank with a voltage meter. Lithium-Ion battery voltage directly relates to remaining capacity, so now we have a way to monitor state of chrge.

Pics:


 

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