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[Articles Home]  [Add Article]  

Batteries That Bamboozle

Jordan Scott Reaser (K6TAR) on September 18, 2017
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Bamboozled By Your Handheld Radio Battery Pack
Scott Reaser, K6TAR

This story starts with a FT-60R the owner told me was going to be pitched because even with a charged battery the unit would receive fine, but the screen blanked out on transmit. Actually the radio was just fine. The battery had high internal resistance. How do you readily tell this plus identify other battery ailments?

Consider a shell game of three battery packs: A, B, and C. All are “charged up”. One will provide expected service life, one will fade quickly, and one will not transmit at all. Which is which? How can you tell with minimal equipment?



Figure 1 (About The Batteries) shows that an equivalent battery series resistance limits the battery current to your load.

Parallel resistance saps the charged energy. All batteries age and lose storage capacity. This happens both from calendar age, and from number of charge-discharge cycles.

The simple test gear you need to sort out A, B, and C is shown in:


Figure 2 (Things You Will Need).

Items:

* A DVM or VOM with an amp scale
* A pair of alligator clip leads. (Make up some of these handy shack items if you don’t already have some)
* Test resistor for transmit load. A 4 ohm, 10 watt unit is shown which gives about a 1.5 amp load.


Figure 3 (High Internal Resistance, Voltage) shows identifying a battery “C” by output voltage without and with transmit load. Without a load (left) the output voltage is great. With a transmit load, right image, the output voltage drops below the handheld 6 volt cutoff voltage.


Figure 4 (High Internal Resistance, Current) shows the clip leads reconnected to read load current. Low output voltage is reflected in low output current.

In comparison is a good battery, “A”, with the output voltage check done in:


Figure 5 (Good Battery, Voltage).

The open circuit output voltage, left image, holds up under transmit load, right image.


Figure 6 (Good Battery, Current) shows that current to the load is correct.

The last case is battery “B” which is still working, but is very tired. Transmit time is minutes, not hours.


Figure 7 (Worn Out Battery, Voltage) shows that open circuit voltage on the left is ok, but loaded voltage on the right tails off even as you watch. Similarly, the output current drifts down in minutes:


Figure 8 (Worn Out Battery, Current).

There are good programmable battery test units on the market, and they do a great job giving battery performance metrics. The quick and simple testing I have described here sorts out the good, bad and worn out status of handheld batteries.

Member Comments:
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Batteries That Bamboozle  
by AB9TA on September 18, 2017 Mail this to a friend!
Very nicely done!
This is an excellent article, especially since you are showing a low-cost way to test batteries. The only suggestion I would make is that it would be a good idea to run the test on a brand-new battery when purchased as a baseline.
And, this method could be applied to any battery, you would just need to calculate the desired load current and use the proper sized load resistor for testing.
Care would have to be taken if testing is done on larger batteries, all that stored energy plus a mistake in connections would be very exciting.
The only nit I can find to pick is that it's "lose", not "loose".
Otherwise, an easy to understand article with diagrams and photos that illustrate the point.

73!
Bill AB9TA
 
RE: Batteries That Bamboozle  
by W3TTT on September 19, 2017 Mail this to a friend!
It appears that the 10 ohm resistor is in parallel with the battery under test.
 
RE: Batteries That Bamboozle  
by AF6AU on September 19, 2017 Mail this to a friend!
A good basic article, well done.

NEVER short a battery pack. Most do have fuses inside, but I have found some without. A fully charged AA Nickel cell can deliver 20 amps and cause a fire pretty fast if shorted with no fuse.

I have to mention, be careful with nickel metal hydride and Lithium packs when test discharging them. In all packs the cells are several connected in series. No cells are ever exactly the same, and if discharged down to where the weak cell is depleted, the current flow from the others passing through it is in reverse. Reverse current on Ni-Mh and Lithium cells is damaging and why newer packs have fancy circuits inside to monitor this. Never discharge these below ~85% their full voltage or the least cell will be wrecked quickly. I ruined a rebuilt 10 AA Ni-Mh cell pack (new Maha 2100Mah cells)in only 5 cycle-tests using a small light bulb and discharging 100% then full recharge.

Old school Nickel Cadmium cells tolerate the weakest cell reverse current abuse farily well. Ni-Cads also charge with low current, 1 reason they are still used with solar charged yard LED lights. Nickel Hydride cells take a different and beefier charger than Ni-Cads, and when full they get warm, a sign to stop charging.

If you have an older hanheld and the pack uses AA Ni-cads, the 800MaH AA Ni-Cad cells Home Depot sells for yard LED lights will work if you want to rebuild a pack with Ni-Cads available locally. They actually work as well as the more expensive Tenma brand cells.

1 more thing, Nickel batteries going into long term stroage (a year +) store best with a low charge, 10-20%. This a point where the voltage no-load will be 1.2V X #of cells, but the current out will be low. This is how store bought Ni-Cads are. Full charge long term storing will shorten the life. I learned this lesson the expensive way as well.
 
RE: Batteries That Bamboozle  
by N2MG on September 25, 2017 Mail this to a friend!
@AB9TA

I spotted the lose/loose error as well. Fixed it.

73 Mike N2MG
 
Batteries That Bamboozle  
by WD9IDV on November 11, 2017 Mail this to a friend!
Good article. Obviously you would know a bad pack for an HT by simply charging the pack and see if it worked in your radio. I like to take apart the packs. On occassion, maybe one individual cell is bad and can be readily replaced. When posibble, I will rebuild or buy a Li-ion or Li-Fe pack to replace NiMH packs.
 
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