I have a 40 W panel and a charge controller on the way to me, I have a 110Ah AGM battery for use at home and will eventfully buy a 24Ah AGM for my portable set up. Here's my question, whilst waiting to build up funds to purchase a battery can I run a charger and other devices directly for the output of the controller?
Hi Norm! Bear with me here as I throw things out quickly to save time....
A solar charge controller will not work unless a battery is attached to it. Some get returned when users try to measure operation without it. Also, attach the battery to the charge controller first to allow the controller to get a reference, and *then* attach the panel. Cheap on/off ping/pong mosfet switching types from the 70's don't count. We're talking modern solar controllers.
For batteries we are assuming that they are NOT SLI starters, but at the very least hybrid, dual-purpose faux-deep-cycle marine types. Dedicated RE is the best choice.
Watch out for the classic "deficit charge" scenario where the panel is not realistically large enough to support the battery. This involves meeting a minimum current from your panels...
Flooded charge rates are C/12 to C/8, where C=20 hour rate in ah. If you go below C/12, the battery suffers acid stratification. Larger than C/8 usually exceeds the manufacturer's maximum inrush rating. See manufacturer's specs for max rate.
AGM - high quality lead-calcium types like Deka/East-Penn can accept a maximum inrush of 0.3C. East Penn recommends charging at close to this rate as long as you don't go overtemp for longest life. Small ups-style lead-calcium's like Powersonic can also handle this, but my preference for these smaller types is about 0.25C max. Minimum current? Agm's can accept lower current than flooded but the problem is that you can walk-down the capacity if they are not charged up to at least 75% SOC within about 72 hours max, otherwise hard sulfation takes place. So you may not be able to do that from a deep discharge with your 40w panel setup. Even Schumacher warns against using "maintainer" currents typical of 1-2A chargers with their very own chargers on large batteries like your 110ah after a deep discharge. You'll walk down the capacity. While getting up to 75% SOC slows down sulfation, it does not mean it stops. By far the best thing to do is finish the charge.
For lead-calcium agm's, shoot for at least 0.1C, 0.2C even better, and close to 0.3C recommended by East Penn. I trust them. As always, check the manufacturer's docs. Again, we're dealing with recharging them faster than they sulfate, so extremely low currents can actually be harmful, but may not be noticeable if you are only doing a one-off low-current charge here and there.
Pure-Lead option: pure-lead batteries like Optima, Odyssey, Hawker can accept HUGE amounts of inrush current if you have the solar panel power to adequately charge them, and are an advantage in areas with very limited solar insolation. Typically 0.4C is the minimum for Odyssey's if you don't want to walk down the capacity from deep discharge (50% DOD or more). But don't tickle these - they want to see some beefy current. Don't overlook small Hawker monoblocks.
Quick SOC voltage determination chart for agm's - measured after 4 hours or more of no-charge, no-load)
12.8v + 100%
12.5v 75%
12.2v 50%
12.0v 25%
Best bang for the buck is usually running no more than 50% DOD.
Solar-insolation hours vs sunrise-to-sunset hours are very different! Find the solar-insolation charts for your area, although I imagine in Gippsland it is probably very good. Use the "winter" hours to give you some headroom when calculating how long it will take to recharge. A lot of solar projects fail when they use the sunrise-sunset hours instead of the published solar-insolation hours. Typically, these hours are between 10a - 2pm. Sunlight before and after this are too weak to be incorporated into charge calculations. Solar insolation will change these hours depending on geographical location.
Many use PVWATTS, and another useful chart for north american users can be seen here:
http://www.bigfrogmountain.com/SunHoursPerDay.html
If ground mounting, watch out for long-shadows. Mono's cut their power output very fast when even a small leaf, shadow, or other debris lands on them. Amorphous deals with shadows and debris much better, but you do not want to do that on purpose and are bigger than mono since they are less efficient. I've seen plenty of ground mounted panels with grass over the bottom edge - not good!
A general guide to recharging is (AH used / A charge current) * 1.7 = hours needed to allow for efficiency compensation during charge. Not exact, but ballpark. Your geographical solar-insolation will help determine this. Stay under 72 hours if at all possible, the less the better. This will help guide your selection of panel wattage needed obviously.
The key point here is to get at least up to the absorb voltage within 72 hours time. If not, the batteries sulfate, even while charging (albeit a bit slower than no charge at all). Sooner is better. If you take into account your discharge level, solar-insolation for time, and the power output of your panels, you can see if you are going to meet the 72 hour time limit.
There are plenty of deficit-charge setups out there that seem to work for a short time while the op is interested and the battery is new, but come to find they don't hold their load 6 months down the road when a real load other than a cellphone charger is placed upon it.
There is plenty of stuff available here. I'll be buying an AGM battery, I currently have a 110Ah that cost me nothing, I bought a 110Ah originally for our caravan, it wasn't until after the truck had delivered it I realized one of the end cells was cracked and the company replace the battery leaving me with the cracked one, a friend suggested I get it plastic welded which I did, I then opened the cell and topped it up with acid with the help of the local battery wholesaler, I was very pleased to see the battery come up as OK on his test meter. That battery is amazing it sits outside of my radio shack and I check the charge every so often and put the ctek on it never charges for more than about 15 minutes, even after three months standing it never drops below 13V.
