Thursday, Oct 10, 2024 at 03:41
The are a few ways chargers could know a Li is full, a smart charger knows a Li is full simply by watching the amps flow out of it at a given voltage for a given duration aided by some absorption master set time determined by the batteries voltage on start, aswell the charger might stop charging every few mins to monitor the batteries voltage-more so with dc-dc, dumb buck boost chargers just stop when the voltage rises to the set point dropping down to a float voltage, solar complicates things with clouds and the algorithms are pretty generic.
If the Li is hungry and the two chargers can be maxed out in amps then the battery will just pull all the amps (assuming the Voltage regulator set point is high enough and there is minimal vdrop in cables)
If the Voltage regulator set point on a constant voltage source isnt high enough and there is some other source of charging say in the latter part of the cycle then the former might just contribute a rather poor amount of amps. if its v set point is high enough then overcharge can occur, overcharge arises as the voltage is too high for too long, so 13.9ish volts for an alternator is the sweet spot, ,may have to raise that as the Li IR increases overtime.
The reason a flooded cranker "laps" up current quickly is due to; it has a higher internal resistance than a good agm, it has a very poor coulombic efficiency overall, the asymptotic reduction comes earlier and is more aggressive. thus it requires a rather high voltage that many alternators cant muster up and limits current badly. instead of getting 10years out one you might get 4-5. the voltage curve doesnt have anything to do with it, some li-ion have very steep curves and pull every amp they can take.
I dont think you can say a Li has a flat voltage curve. On empty under a 0.3C charge rate they typically start out at ~12.8-13V, then that rises to up to 14.6, at least 14ish, which is on average a whole 1.25v to play with. As long as the Li never exceeds 0.5C charge rates and the charger drops down to float ~13.5v once its full (trail amps 0.05% of C), never charges over 0.3C when cell temps are below 5deg C, 0.05C below zero, they are pretty foolproof.
"This has lots of benefits including redundancy and partial shade situations."
then please mention them all, otherwise its just a baseless assertion as per usual.
The redundancy claim is problematic as this greatly increases the foot print, charge bus/
infrastructure and raises the odds of appliances failing more which in your careless generalization failed to take into consideration, a problem for many. sometimes a single failure is better to deal with. the odds of a single mppt failing is rather slim and a once in a while event.
When two panels are in parallel to the mppt and one is shaded, for the most part it gets knocked out with minimal leakage current to it from unshaded panel, but the single mppt is hunting for a single Vmp point as its assuming a single IV curve, so the shaded panel could bring down the good panel's Vmp some what, so the good sunny panel will be loaded more but now at less voltage and so less power. again on a flat roof plenty diffuse light will keep the shaded panel's OCV high enough it should be minimal.
More controllers means more conversion losses, assuming mppt, conversion losses can be lousy due to a wide voltage delta between battery and panel or from being feed small power relative to its size.
mppts consume power as they continually track the optimum power point, some worse than others.
Multiply mppts may consume enough standby power to negate the gains of max power extraction from individual mppts per panel.
On a flat roof exposed to consistent irradiance multi controller is easy and by the same token a single controller would work
well, but in west vs east type facing arrays they can be bad, as you wanna make sure the controller with the shaded or no light panels doesn't have the task of finishing the charge.
a good reason to use multi mppt is the single unit might have poor heat dissipation due to how awful passive cooling is, victron gear leaves something to be desired for, dunno how those engineers thought plastic body around 5 sides of the charger was a good idea LOL. needs massive heat sink fins with massive surface area that isnt practical, for above reason and made worse by the power density and heat flux considerations at the matting faces of the cooled components are slowed right down by the slow passive dissipation of the heatsink.
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