measure the power usage of your portable battery powered radio

[wenzeslaus]

in another thread it was mentioned that a particular emergency radio eats batteries. most people don't take that into account and while some manufacturers might list specs like sensitivity or even selectivity, they never mention battery efficiency. nobody does. but it should be a huge consideration when selecting a radio that will be running only on battery power, or to know the efficiency of the radio you have.

cut a piece of flat thin plastic to fit in the battery compartment between battery contacts. put marks on it so you don't lose it. krazy glue 2 pieces of metal on both sides, with tabs that stick out for the clip leads of a multimeter.

put it between the batteries. use a very small screwdriver to pry the batteries apart to insert the shim, or put the shim in at the same time as the batteries. connect leads to the multimeter. put it on mA, high scale to prevent fluctuation. turn on the radio and put it on a station.

this reading is 10.8 mA.

then check voltage of the batteries. added together, they were 2.94V.

multiply to get mW. this was 2.94 * 10.8 = 31.8 mW.

batteries run down. so it's a problem when you measure the mA of a radio at different stages of battery life. what you do is standardize to 1.500 volts. that is the mW it should use at 1.500 volts. note, a brand new battery will be around 1.614, that should be standardied also.

to standardize, take the mW and either

a) divide by average voltage of the batteries, then multiply by 1.500

b) divide by the sum voltage of all batteries, then multiply by multiples of 1.5

31.8 / 1.470 * 1.500 = 32.4 mW

31.8 / 2.94 * 3.0 = 32.4 mW

I have measured several radios and for an analog radio, 20 mW is typical, some got down to 16 mW, the worst were 50-60 mW. I haven't measured many digital radios but a Tecsun PL-606 was 66 mW and a Kaito KA-500 was 164 mW.

then you can estimate battery life. a Sony SRF-59 (1AA) was measured at 24.3 mW (standardized). the manual says it lasts 140 hours on its 1 AA battery. battery life vs mW is not specific to any one radio; if it uses twice as much mW it will last half as long, and so on. therefore, hours = X/mW.

according to the Sony manual, it gets 140 hours per 1 AA battery, and mW= 24.3, so X= 3400, which you will notice is about the mAh of charge a battery holds.

but I think that is optimistic. the manual says that figure is valid for their Sony alkaline battery. the best batteries I know of are Energizer Max alkalines, which according to their data sheet, AA produces 3000 mAh at 25 mA or 2500 mAh at 100 mA. so to standardize I will assume using an Energizer Max alkaline battery at their 25 mA rating (typical analog radio is around 20 mA) so mAh = 3000.

divide 3000 by the standardized mW of your radio, then multiply by the number of AA batteries.
(for a digital radio use 2500 instead of 3000)

from the example above, 3000 mAh / 32.4 mW and it used 2AA batteries so the answer is 185 hours.

SUMMARY

1. make a shim

2. measure mA used, voltage of batteries

3. calculate mW with mA * (total voltage)

4. standardize with mW / (total voltage) * (ideal voltage)

5. calculate battery life with 3000 / (standardized mW) * (# batts)
(for a digital radio use 2500 instead of 3000)

you will have a standardized rating for the power usage of your radio, and an estimate of battery life when using a standardized battery model.

check your radios. they are different. compared to the best analog radios, the worst analogs can use more than 3x as much battery, and the worst digital radios can use 10x as much.

 

[TAC4]

Very interesting ! I only have grade 12 public education so I have take your word (math) for it.
I can tell my 4 D cells last forever in my Eton Elite Field radio with the back light set to low. So based on that observation my radio sips power and is energy efficient lol.

Skippy 🇨🇦

 

[wenzeslaus]

nah. D cells hold 5.3 times as much energy as an AA, so even if your digital oinker lasted as long as another radio that uses 4AA, it's sucking 5.3 times as much power, you're just using bigger batteries.

and I really doubt it does. digital radios use 3 to 10 times as much power as analog. they all suck. with rare exceptions.

 

[TAC4]

They may be "pigs" but I am still a DSP fanboy lol

Skippy 🇨🇦

 

[Boombox]

You know, it's all relative. You get the spare batteries you need for a power outage, and use whichever radio will get the job done. And if you're not sure when the power's coming on again, you use headphones, or turn down the volume if using the speaker, and increase the life of the batteries in the radio that way.

Very interesting way of testing a radio's battery drain, however. Looks easy enough to do.

Thanks for posting this.

 

[wenzeslaus]

yep. true. it doesn't matter a whole lot when you can just throw in batteries and it works.

this was meant to help select a battery-efficient radio if that's important.

just the other day I tested my SRF-59 with 1 almost-dead AA battery (1.1V) vs my R-606 with 2 fully charged AA's. equal reception on both.

 

[Boombox]

yep. true. it doesn't matter a whole lot when you can just throw in batteries and it works.

this was meant to help select a battery-efficient radio if that's important.

just the other day I tested my SRF-59 with 1 almost-dead AA battery (1.1V) vs my R-606 with 2 fully charged AA's. equal reception on both.

My SRF-59 still has the battery I put in it when I got it in 2012. Still works. I never have used it all that much, though. Not since 2014 or so. But it's amazing how a headset-only radio can conserve battery life.