Wayne Burdick <[email protected]> writes: > I finally installed a single 50 W, 12 V solar panel on the roof for > light backup purposes -- phone/pad/laptop/flashlight charging, > natural-power use of the KX2/KX3, etc. Connecting the panel directly > to automotive-style USB chargers works great when the sun is shining. > > My 15 year old thinks it's cool. He wants me to turn the mains breaker > off for a whole day so we can get the full off-grid experience :) > > To facilitate that more rigorous purpose, I'd like to add a modest > battery pack, say 10 to 20 AH, that is charged by the PV panel without > intervention. The charger has to be compatible with simultaneous > charge/discharge, i.e. we may need charge USB devices at the same time > the PV panel is charging the battery. The battery voltage should be 11 > to 12 V minimum after any controller drops so it'll work with the > radios.
You said "12V" panel, so I am assuming that the V_oc is about 20V. You have basically a few decisions: MPPT controller vs PWM vs on-off equipment directly on the battery (well, fused) vs a controller that has low-voltage disconnect (LVD) battery size Lead acid vs LiFEPO4 For me, the hard part is finding a place to mount panels and mounting them, so paying a bit more for a good controller is cost effective. I have a 55W panel with a Genasun GV5 and a 100W panel with a sunforce on/off controller, and about 200Ah of lead acid batteries, and no low voltage disconect. For years I charged solar only, and now I supplement with a power supply and diode (soon to be better) this time of year (sun is often shining, but angle is low and behind those pesky trees). Given that you mention operating and not just phone charging, and you have only a 55W panel, I recommend an MPPT controller, and basically I recommend that anyway. You'll get more power out of the same panel, and this will be even more noticeable on marginal-sun days. The Genasun GV5 is big enough for your panel. The sunforce controller is interesting; it's <$20 and just passes the panel to the battery until the battery reaches 14.2V, and then opens until the battery drops to 13V (aimed at lead acid). This is sort of ok, but with a panel that's large compared to the battery, the high current will cause the 14.2 to be hit and you won't fully charge the battery. (I'm using it on my 100W panel because I had one handy, and really I only need that panel when the system sags over the november low-sun bleak weeks, and then I don't see 14.2V -- but I have 200 Ah to absorb maybe 6A. But I should get a GV-10.) I don't use the LVD, because some of my loads are > 5A occasionally, and because I have batteries in two places to avoid drop under load (but all connected). But the GV5 has output terminals I think with almost no drop, that will open up at 11.4V or similar. You might as well use it, if using lead acid. With LiFePO4 that has BMS that does that already, I don't see that it matters and it is probably just complexity you don't need. With batteries, unless you are buying new LiFePO4, you should actually test them. I have found used batteries to vary from useless to almost as good as new, and new batteries to be mostly ok but some of them have been troubled from day one. I use a West Mountain CBA2. 10 Ah sounds low for using a KX2/3. Here we have multiple days of clouds sometimes. If you can get free lead acid batteries in good shape used (wheelchair pulls), that's a good plan. Otherwise you should think hard about LiFEPO4. I would recommend that you either get: a bunch of 7Ah batteries that were free to good home one 33 Ah or more sealed lead acid (almost all are AGM, $60ish each?) one or more 73 Ah sealed lead acid if free to good home (often GEL) one 20 Ah LiFePO4 (e.g. bioenno), or maybe 12Ah ($200, $100 very ish) The charge controller needs to match the battery chemistry. Genasun configures the GV-5 for LiFePO4. Probably it makes the most sense to go with LiFEPO4 for the scale of system you are planning, especially when you consider the voltage on transmit will be better matched for >5W operation on the KX2/3. While the battery is more money, the controller and panel are the same, and I expect the system to work better and last longer. Plus you can get away with not doing tests on incoming batteries. I also like to have a voltmeter on the battery at all times, visible (7 mA draw LCD intended for cars). Or an ADC into Home Assistant with alarms. Not sure how that relates to "cobbling", but if you just wire the panel to the GV5, and put a powerpole cable on the battery terminals of the GV-5 and plug in to a LiFePO4, you're basically done. 73 de n1dam ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
