Date: Sun, 21 Jul 2002 23:52:38 -0400 From: "Alan Barrow" Subject: Regulators rarely needed for solar portable ops (was: Portable Operation From Norway) Long post. Short version: It's hard to get enough solar output to require/justify a regulator on typical portable ops. Art writes: > Use an adjustable LM317 to build a regulator for your solar panel, adjust to > 13.8 or 14.2. Will handle up to 1.5 amps, at least 10 watts if > heatsinked. Schematics on Internet and in handbook. 5 parts. Personally I rarely bother with the regulator. If you are using batteries larger than AA's like a 3 AH Sealed Lead Acid (or LCR), you can use the solar panel to float charge the battery, and you are in good shape for most portable configs. (Not permanent unmonitored installations) The only reason to regulate is if your peak panel charge (Isc) current exceeds comfortable battery max charge, which is usually .4C for SLA's and modern nicads. So for any SLA larger than 1.5AH, the solarex panel could be used in float mode for typical portable operation durations. Realistically, the radio's current drain is usually offsetting the charge current as well, thus lowering the peak charge current even more. (Our friend Kirchoff) Most people don't realize that solar panels operate as current devices, delivering relatively constant current across a wide range of voltages. Isc (Short circuit) is usually your peak current, and it drops from there. Try it with your ammeter sometime. Measure panel current output direct into an ammeter, then into a 12v battery. It will be within a few percent. For extra credit, explore Thévenin and Norton equivalents to determine the internal resistance of the linear range or panel operation. (Hint: Voc /Isc) On the MSX-10, and most similar panels, current is almost constant from 2-12 volts load. So you can float it direct across the battery and radio and the battery will "regulate" the panel voltage. Battery voltage will go up as it charges, but it will stay within normal charge voltage range. Most SLA's handle a constant current charge with no problem as long as you do not overcharge, which is hard to achieve in most portable ops. Between radio current drain, panel angle, and typical light variation during a day, you'd be hard pressed to over charge. Additionally, constant voltage charging has some serious issues unless combined with current limiting. A tenth of a volt change in charge voltage can make the difference between undercharge and overcharge. Temperature also has a significant impact on cell voltage, and thus required charge voltage. That's why constant current is often advised for steady state trickle charge, set slightly higher than the battery's self discharge current. For most folks a panel like the MSX-10 is a good size for 3AH SLA's. Larger panels get unwieldy unless you go to expensive flexible panels, which are less efficient. Even assuming full .6A MSX-10 current output, it would take 9 hours to charge a completely discharged 3AH SLA. And it's rare to even approach 70-80% of that on a typical sunny day of typical portable solar operation. Unless you are planning on leaving a battery to charge unattended for more than one day with no radio operation, I consider regulation unneeded, and don't bother with my MSX-10. Larger panels I play it by ear. Even unattended for an entire day with larger panels it's hard to overcharge due to reduced output from the solar angle changes during the day. Even for as small as C nicads you can get away with no regulation. Max Charge for cycle use on Panasonic standard C's is 800 mA for 4.5 hours. You would need 6 hours at 600mA for a full charge, again hard to achieve in realistic portable radio operation conditions. If for some reason you still feel the need to regulate, I'd use a current limiting constant voltage source. You can make one out of two 317's, one as constant voltage feeding another in constant current mode. It will have a higher "dropout" voltage (2 * 2v +1.25v) due to the two regulators in series. Many panels have enough headroom on sunny days to do this, but there are other ways to achieve current limited constant voltage if they don't. As others have pointed out, the MSX-10 is a great panel, and I wish I had a 2nd. I'm trimming 1/4" off mine to fit in the lid of my $18 Lowes aluminum hardcase for my portable kit. OK, probably more than you ever wanted to know about solar charging. But the subject of regulating small panels pops up here and in NVIS quite a bit, so maybe this will save some folks time and money. Have fun! Alan km4ba ============================================================================ Date: Sun, 11 Dec 2005 09:23:12 -0800 (PST) From: Shawn Upton Subject: Re: How much loss is there when using the back panel DC connector? While I don't have the schematic handy, what they most likely have is something on the order of like a 100mA constant current source to charge the battery; chances are, it won't work if the input voltage is less than 11V. Give or take, that is--don't have it in front of me and I haven't measured it. However, on a soler panel, you may want to run it through something to prevent any over-voltage conditions. Haven't tried it yet, but perhaps something like an NPN with a base resistor and a zener to GND (something around 14V) would do it (resistor and collector to panel, emitter out to radio). Under voltage passes through, while overvoltage turns on the zener and causes the NPN to drop voltage. Haven't tried it, I'd have to think about it some more, but first thoughts seem to me that it would work. Anyhow... You could make a simple mod to the radio, to bring out a direct connection to the battery. [I think the W4RT batteries do that, been too long.] Then, make a simple C/10 charger and run it directly to the battery. You could put the charger in the panel, or in the radio, your choice; and add all the protection ideas you want. Shawn KB1CKT --- nwrebel wrote: > I am setting up a solar charger for use on wilderness back packing > trips. I will be using a solar cell for battery charging. I am trying > to decide if I should charge through the rear DC connector or connect > directly to the battery pack. I think that there is at least a little > loss throught he rear DC connector when charging because it is > powering the CPU at least enough to calculate the remaining charge > time and display it. > > Since weight is a big factor, and I need to take a small solar panel, > and need to avoid any significant power loss. Does anybody know what > operations run while charging through he rear connector, and what the > power loss/usage is other then what goes into the battery? > > Using the rear connector would be handy too, because I could use the > solar panel to help power the radio during the day time. > > Your experiences and thoughts would be helpful! > > Thanks, Dean KG7MZ ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ====================================================================== ======================================================================