Hi BLF
I will "attempt" to answer your questions without adding additional confusion
1. The panel instructions warn that it can go over its ratings at times (such as cloud effect or cold temps, etc) and advises choosing the components (controller size, fuses, etc) to account for that by 20% (at least Sharp does)
Yes indeed good panels can and do exceed their nominal ratings – Sharp is a good panel. I started with Kyocera panels many years and have stuck with them over the years. As with your Sharp panels the K panels easily exceed their nominal ratings under the right circumstances.
2. The US NEC requires a 20% margin above panel amps rating for homes and (not sure if required or advised) RVs.
Not sure either if it applies to RV’s but is a good thing to keep in mind when designing PV systems for the RVs
3. Some (all?) PWM controllers will allow amps higher than their amps ratings to go through to the battery. The word is that the controller can then overheat and eventually fry but is ok for short times like cloud effect.
I believe some do allow excessive current, however to me that’s a poor system design and will lead to early component failure
4. Some (all?) MPPT controllers limit their amps output to their ratings. Either:
Can’t speak for all the MPPT controllers available – might be some of the Cheap units do not and simply self destruct if over driven. All quality MPPT controller attempt to protect themselves some do a better job than others
a. That allows for panels going over their ratings so the controller won't overheat, or
If the system was designed at its limits in the first place – for me I would put a 60 amp control if I had 500 watts or more – they run cooler and thus last longer at lower current ratings
b. It will run warm at rating which will shorten its lifespan, or
Heat is a bad thing for the semiconductor junctions – as I remember a 10 degree rise in the junction temp results in ½ the expected life duration (there is something else to it as well I Have a case of CRS)
c. It will overheat if you strap it to too much panel so the incoming is way over its built-in overhead allowance
Overheat and or die
5. Incoming voltage rating not to be exceeded at all or controller will fry instantly.
This is true from even many quality MPPT controllers – sure there is some headroom but not much. Designing a system that gets with 20% of the controllers rating is never a good thing to do
"Overhead" here is to allow for incoming voltage to be above the panel rating Voc taken at 25C such as in cold temps. Total array Voc (series or parallel) is what counts to the controller when figuring that.
Yup – the array is to the controller the “panel”
6. Expected max voltage or amps depends on the "voltage" of the system 12/24/36/48
Don’t understand your statement – The RV market is only one of many markets the controller manufacturers target their offerings – Let’s talk Telecom remote sites which are powered by a 48 VDC supply with a POSITIVE ground. Thus the 48 volt operational mode, everything is the same except the battery voltage is 48 as compared to 12 allowing the array max power (45 amp controller) to be (45 amps X 48 Volts = 2,160 watts) with the same max inout voltage limitation of 150 VDC – the controller will then be able to put 45 amps (it's 45 amp rating) into the 48 volt battery bank. I believe 2oldman has a 24Volt battery bank which is great because it Greatly reduces the wire size needed for a high wattage inverter. A 45 amp controller could have up to a (45amps X 24 volts = 1080 watt array) and then supply 45 amps to the 24 volt battery.
For most of us with RV’s all we ever need to consider is the basic 12 VDC system operation
I can't follow what happens to the ratings and their max limits when going from 12 to 24 to 48 and series parallel unless it is spelt out slowly not using any big words.
Clear?
