[Elecraft] OT: Solar Panel Tests with K1 and A123 Battery

[k3ndm at comcast.net]

Eric, 
Don't put a solar panel on a battery without a charge controller! I fried a few batteries on a boat I had by going without a charge controller, and all I had was a good 10 W panel. 

I have been using 45-60 Watts of solar panels for the last few Field Days with 2 K2s, an FT-817, and a K1. The battery has been a size 24, ~85 Ah. On this operation, we have had charge controllers, and our battery has been useful for the entire time. 

The company that I would have suggested for a charge controller is belly up, but there are a number of sources for marine and RV controller that will work. Additionally, you might try Harbor Freight. They are the folk we got the 45 W worth of panels from. 

73, 
Barry 
K3NDM 

----- Original Message -----
From: "eric norris" <gliderboy1955 at yahoo.com> 
To: elecraft at mailman.qth.net 
Sent: Sunday, June 10, 2012 7:18:24 PM 
Subject: [Elecraft] OT: Solar Panel Tests with K1 and A123 Battery 

Dear Gang: 

I'm a newbie to solar power, but I ran some tests today that I think might be of interest to those thinking of solar operation in the field. 

The story so far: I converted to Buddipole A123 packs for portable operation more than a year ago and have been deliriously happy with them. However, to my knowledge there were no solar charge controllers available for them when I bought them, and so last year, when I first used a solar panel for Field Day, I tried a using a small 5-watt, ancient glass panel I got at a flea market for $10 and plugged it directly into a gel cell. Though it could not keep up with the K2's power demands, it extended the discharge of the battery. 

To the best of my knowledge, an undersized panel can be used directly with a gel cell. I have read that you do not want to try this with an A123 pack, and I was not going to risk it. 

Buddipole now offers a solar charge controller for the A123 packs. However, it is currently sold out. I went with a Genasun GV-5 Li 14.2v controller (NOTE: these are offered at different cut-off voltages so make sure you order the correct one-- Li 14.2v for A123 packs). The Genasun controller has the added feature of dropping the battery out from the load when it reaches 12v so you don't damage the expensive A123 pack. I much prefer fail-safe features like this that prevent me from doing stoopid (sic) things. 

Today I hooked up my K1 (as a pre-test for the K2) to a dummy load, and had it calling CQ from its memory constantly. Using a 5w PowerFilm panel (these fold up small and are great for QRP operations in the field), it would not keep up with the K1's power drain at full tilt, about 7W out,as expected. I then hooked up a 10w PowerFilm panel, and it did keep up with the power drain, essentially keeping the 4s2P pack fully charged as indicated by the Genasun's LED. I disconnected the panel, and drained the battery a bit, then hooked it up again and it reached full charge as indicated by the LED, while still calling CQ. I confirmed this after the test by hooking up the battery pack to a Cellpro 10s charger which indicated the pack was at full charge. 

I further crash tested the Genasun by disconnecting it from the battery, panel, and load in random order to see if I could destroy it. I repeated this in every different order I could think of, and still it soldiered on. Better it get destroyed now than in the heat of the moment on Field Day. 

The 5w panel showed about 300ma of charging current. The 10w panel showed about 600ma of charging current. Put in parallel, for 15w, they showed about 850ma of current. Note: If you connect multiple panels in parallel you must use blocking diodes. PowerFilm panels supposedly have these built-in. 

The Genasun did its job, showing no current from the panel to the pack when the pack was fully charged. 

This was an "ideal" test, with the panels flat on the ground and near noon. However, I won't be calling CQ continuously during Field Day, either, and so I think this setup with 15W of panel power may be able to keep up with the K2 at 10 watts, given time talking to visitors, eating, and goofing off. Time will tell! Ultimately, having a fully-charged battery near the end of the day means night operations, too, but the need for enough excess panel capacity so that the pack will charge during the day even with the radio drawing power. You'd need more capacity for something other than casual operation. 

If I had it to do over again, I would have bought a 20w panel for use with the K2 (and eventually a KX3), though they are expensive. A 5w panel might be adequate for a KX1 in the field, but cloud cover, tree cover, limited charging time, and less-than-optimal angle between the sun and the panel all translate into the need for a bigger panel than you might think. 

PowerFilm sells a daisy-chain cable for hooking two panels together. It is expensive, but it does use their water-resistant connectors. 

I'd appreciate hearing from others with more experience with portable solar power for the Elecraft rigs. 

I have no financial relationship with any of the companies listed, though I am still seriously in love with Elecraft :-) 

73, 

Eric WD6DBM 
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