I see now that the 8.2 is not the amps at max power, but in fact the amps are lower at max power because the voltage is much higher-- the max watts has a different mix of I and V. So the Ipmax is not the max amps
I also see how even with a blue sky and panel pointed, I might not see 8.2 if battery voltage is high. And this is not the same thing as the "battery acceptance rate" for amps at that voltage, which could be way more than 8.2, but has to do with the panel's IV curve.
I have seen that the controller, when controlling, starts bouncing up and down between voltages or amps--makes you dizzy to watch that on the Trimetric, and that the highest amps seen during that is not as high as 8. This fits; the battery voltage/SOC is high when that starts.
So now I will be able see all this activity and it will make sense by comparing what is going on wrt where we are on the IV curve. Love it!
* This post was
edited 07/30/12 05:02pm by BFL13 *
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The whole thing gets very complex to get optimum use from your solar.
However since you can't get optimum use due to the huge variables in solar conditions day by day and over the seasons and any changes in latitude and RV location wrt trees etc, the general idea is to just over-do it for a set-up a whole bunch and leave it alone since it is all out of your hands after that.
Some people try to get more by raising the high voltage set-point on the controller so it keeps cranking out the amps for longer in the day. However, as we see with the IV curve, the amps fall off anyway with the higher voltage. There must be an "optimum" in there somewhere that could be tested for.
I was confused in thinking the amps would flow based on how it works with normal battery charging. The batteries have a "natural acceptance rate" in amps at any SOC for a particular voltage, where at any SOC, the higher the voltage the more amps they will accept (within reason)
So I see my 4 battery bank still accepting 26 amps at 14.5v near 88% SOC so I thought using solar they would accept 8 amps to a high SOC at that or higher voltage.
Now I find that the amps will drop off due to the IV curve and it has nothing to do with the battery acceptance rate. There would be a scenario where both came into play at some high enough SOC.
The "battery voltage" in question is presumably what the panel sees. This can be the voltage per SOC or a "loaded voltage." When I ran my panel tests in May I kept a load running so the battery acceptance rate would not fall below 8.2amps the whole day.
Sure enough, the panel cranked out full amps all day when pointed and sun was high enough. However, I now learn that was because it was seeing a loaded voltage (lower on the IV curve) and had nothing to do with battery SOC type voltage and acceptance rate.
So that means without having a load, as the battery voltage rises during the solar charging over time, that you might get full amps in the morning and lower amps in the afternoon even though the panel is pointed just right etc.
So if that happens it does not mean your panel has gone bad during lunch.
The bell curve of a whole day's solar with a flat panel should be distorted by this effect where the afternoon is not a mirror image of the morning part of the curve.
But what good does it do you to try for optimum when solar is all so ropey anyway? Most here who cannot understand what all the fuss is about just slap on as much solar as the RV can take and hope for the best. Meanwhile keeping a real charger handy to run off the gen for when solar isn't getting the job done.
My OEM was 375 amp-hours of storage with 256 watts of solar. That is hardly "slapping on" as much as I could. I've always advocated between 60 and 150 watts per 100 amp-hours of storage. Others do the same, too.
> Most here who cannot understand what all the fuss is about just slap on as much solar as the RV can take and hope for the best.
Assuming they have a working reliable generator. In my case that has been a *big* if.
> Meanwhile keeping a real charger handy to run off the gen for when solar isn't getting the job done.
Full Time in a Kustom Koach Class C 28'5", 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, 2500 MSW watt inverter.
I am just surprized that with four B&D chargers to cram the batteries with every amp possible in least time.... then with solar with two panels apparently it was decided both would not max out continuously so one was sold.
Now there is a thread on solar anxiety. The priorities baffle me.
I suppose all in the fun and spirit of camping
The anxiety was from thinking there was something going wrong with my solar set-up. Now that I understand (somewhat)how the panel works I can relax about that.
No anxiety from not having enough solar to get through the day. As mentioned I still got 85AH instead of 90AH. (only need 60-70)
So I still have more solar than really needed at 130w for 458AH of battery bank.
In fact this darn solar is doing so well, I hardly ever get to play with my modified 100amp PowerMax. (which replaced three of the Vectors)
No need to be confused about priorities, which are swimming at the lake, choosing flavours for ice cream cones, reading a good book while listening to Sirius radio, and all that kind of hard work Once every day or two I pop around to the library in town (with its dog park) with my laptop for their wifi and find out what you working hands are up to