Battery Life, Part II

I previously posted about monitoring how long my vx8-dr would last on different types of batteries. One of the things that I noticed was that there is a relationship between battery voltage level and the output power but I had no way of watching what was happening. So I invested in a Diamond SX-600 SWR & power meter along with an MFJ-261 dummy load and re-ran parts of the battery test.

2,000 mAh lithium ion w/ power

vx8-dr 2000mAh power

relative time voltage wattage
0:00:00 8.2 4.2
1:35:31 8.0 4.2
3:59:07 7.7 4.1
5:50:41 7.6 4.1
7:16:26 7.5 4.1
8:21:35 7.5 4.1
9:19:13 7.4 4.0
11:04:18 7.4 4.1
12:33:02 7.3 4.0
13:56:41 7.2 3.9
14:37:08 7.0 3.8
15:10:24 6.9 3.0

This is pretty much what I would expect. As the power available from the battery goes down, the output power on the radio goes down.

AA alkaline w/ power

vx8-dr aa alkaline power

relative time voltage wattage
0:00:00 4.2 0.90
1:48:19 3.7 0.15
2:40:05 3.7 0.10

This, ladies and gentlemen, is utterly ridiculous! Starting with fresh AA alkaline batteries, the output is less than 1 watt and it quickly deteriorates from there.

I swapped out the AA alkaline for AA lithium ion and found a similar output power level. Since it started with less than 1 watt output power, I didn’t bother running through the whole test. This was not at all what I expected, The input power voltage level is critical for the vx8-dr to perform well.

My original intention was to use AA lithium ion and / or AA alkaline batteries as a backup power source for the vx8-dr in the event of an emergency. This now looks like a bad plan. Running on anything less than the lithium ion battery packs has a detrimental effect on output power. It might do as a backup to the backup power but I don’t think it’s a good idea to count on it.

Right now, I’m thinking multiple 2,000 mAh lithium ion battery packs, a charging dock and perhaps a solar panel to charge it all. Plus an automotive plug adapter. And a plug w/ anderson powerpole connectors.

This was an interesting experiment!


 

Update:

I was asked about the discrepancy between the maximum measured power out of 4.2 watts with the battery voltage of 8.2 and the published maximum of 5.0 watts. I have a couple thoughts on that though they’re not based in much more that aether.

  1. The published specs may be coming from theoretical maximums.
  2. The published specs may be coming from values measured in a lab under ideal conditions.
  3. Maybe the battery’s just not quite fully charged.
  4. The SX-600 power meter may be off calibration.

I did plug the radio into the wall wart that comes w/ the charger. The voltage showed at 10.8v and the output power at 4.3 watts. Using the automotive cigarette plug, the voltage shows at 12.8v and the output power was measured at 4.5 watts.

BTW, the manual for the vx8-dr has specs for the supply voltage maxing out at 12v.

From all this, I take the maximum output wattage as being 4.5 with a more typical of 4.0 to 4.2.

Battery Life

I had an experience a few weeks ago whereby I couldn’t join the ORCA net on my vx8-dr because of a low battery. From that, I thought I’d run a test to look at how long different types of batteries run in the vx8-dr. The basic protocol is to setup the vx8-dr to transmit APRS location messages on a regular basis and measure the battery voltage over time. The voltage measurement comes from the vx8-dr itself. Yes I’m trusting that it was accurate but with the test running the same way across all the types of batteries, I think it’ll be a valid test. Besides, the reading from the vx8-dr is what I’ll be using in the field.

The vx8-dr can use 4 different types of batteries: 2,000 mAh lithium ion, 1,100 mAh lithium ion, AA alkaline and AA lithium ion. I ran a set of tests over the course of 8 days.

2,000 mAh lithium ion

vx8-dr 2000mAh

relative time voltage
0:00:00 8.2
1:04:28 8.1
2:05:27 8.0
3:14:07 7.8
4:58:20 7.7
6:04:41 7.6
6:46:38 7.6
7:43:17 7.5
8:34:24 7.5
9:30:31 7.4
11:21:29 7.3
12:22:51 7.3

1,100 mAh lithium ion

vx8-dr 1100mAh

relative time voltage
0:00:00 8.2
0:00:00 8.2
2:15:51 7.8
3:06:14 7.7
3:58:57 7.5
6:27:44 7.4
8:01:43 7.1

AA alkaline

vx8-dr aa alkaline

relative time voltage
0:00:00 4.2
0:43:23 3.9
1:26:23 3.8
2:02:19 3.7
2:46:57 3.6
3:43:42 3.6
5:02:25 3.5
8:15:51 3.3

AA lithium ion

vx8-dr aa lithium ion

relative time voltage
0:00:00 4.5
1:23:24 4.3
3:33:47 4.1
5:19:44 4.1
9:04:00 3.9
9:55:36 3.9
20:56:06 3.7

I unintentionally left the vx8-dr running over night and the battery level only dropped 0.2 volts. That was very unexpected.

Conclusion

I came to a few conclusions from this test:

  1. Measuring the voltage will most likely be a good way to keep track of when to change batteries.
  2. Just measuring the voltage doesn’t provide any data on how well the transmitter is working with the available voltage / power.
  3. Judging by the AA lithium ion battery test, I need to re-run the 2,000 mhA and 1,100 mHa test. It looks like the voltage level of the lithium ion batteries may not be linear. That may put a kink in the use of the battery voltage to determine remaining power.

I’ll re-run the 2,000 mHa and 1,100 mHa tests over the next few days to see how long the batteries last. Perhaps lithium ion batteries don’t have a linear voltage level over regular usage.

More importantly, I need to expand the tests to determine the output power level as the batteries are used. I’m not yet sure how to do that. Maybe it’s time to invest in an RF power meter.

 

Portable APRS Server

I had a thought yesterday, in the event of an emergency the internet connections will be down. Wouldn’t it be useful to have a localized APRS display to show the location of various people. Set up a radio to listen for APRS transmissions, send them to a small computer, run a webserver on the computer w/ OpenStreetMaps on it, have a wifi connection and power connections. Drop it all into a portable case of some sort and it can be made available to a local group of people who need access to the data.

There’s a bunch of unknowns here but it could be an interesting project. Would it be useful? Reliable? What else is needed?

Net Troubles

I wasn’t able to get on the ORCA net last Thursday. It’s worked before and I haven’t changed anything on my radio. Very strange.

In talking things through with Peter (KO6R), we realized that the batteries ran low. Without enough power, the VX8-DR wasn’t able to transmit far enough to be heard by anyone. I was running with the AA battery pack instead of the lithium ion battery pack. It looks like AA batteries just don’t have very much power in them and they ran out of power much faster than I expected. I’ll need to experiment a bit to see how the various battery options last w/ the HT.

First Radio – VX8-DR

I’m now the happy owner of my first radio, a Yaesu VX8-DR. It’s a lovely handheld that I’m looking forward to using and getting on the air.

It’s actually not my first, I have a Micro-Trak RTG tracker that I used on K9 for Burning Man last year. I was able to use it because Phil (K6CQU) was gracious enough to let me run it under his call sign. Now I’ll be able to use it under my own call sign. Simple pleasures!

I chose the VX8-DR because it has a GPS receiver and can receive and transmit on APRS, just like the Micro-Trak RTG. I’m a bit enamored with the idea of tracking locations via ham radio operations.