Balancers installed

That's probably going to come down to where the charger is sensing battery voltage.

With lead acid this isn't really a problem since lead acid is held artificially high, typically 13.8v per 12v, so once the charger is no longer providing enough current the battery quickly drops about 1V.  Even with completely inappropriate wire gauge vs current there is always going to be enough voltage drop for the charger to go all-in and try to pull it back up by supplying all the current it can.

This all changes with lifepo4 and it's very flat main discharge curve.  Unless you are way up the top of SOC even 30mV of drop equates to quite a lot of energy in the battery.  If the charger is monitoring voltage at its terminals rather than the battery's all it will do is supply enough current to raise its terminals voltage by 30mV so until the battery drains enough to lower the voltage on its terminals to the point where any drop in the cabling / breakers / etc is exceeded the charger will never be in a position to supply all the current the PV permits.

9 hours ago, Sid Genetry Solar said:

MPPT current would actually go slightly negative (Morningstar Tristar, seems to be normal for them??), and the inverter/loads would run off the batteries for several minutes while the voltage slowly fell to the new "float" setting

I'll have to look closer, but I haven't noticed a negative current.  The system does seem to 'coast' for awhile as it drops slowly to float.

3 hours ago, TheButcher said:

If the charger is monitoring voltage at its terminals rather than the battery's all it will do is supply enough current to raise its terminals voltage by 30mV

I see what you are saying, but;                                                                                                                                                           Seems to me if the charger is seeing a significantly higher voltage at it's terminals than at the battery, enough that it is not correctly charging the battery, then the charger to battery cable is too long or too small or both.

3 minutes ago, dochubert said:

I'll have to look closer, but I haven't noticed a negative current.  The system does seem to 'coast' for awhile as it drops slowly to float.

So my point...just my opinion anyway...is that when the charger goes from "bulk" to "float", I didn't want to be actually discharging the batteries (microcycling) down to the lower voltage.  LFP cells will drop voltage slightly when the charge is disconnected, and I guess I just wanted to see the charge voltage drop slightly, yet without actually discharging the batteries to get there.  Of course, this is more of a personal matter; to each their own.  A lower "float" voltage might increase cell life, I dunno 😉

Negative charge current seems to be a phenomenon of the Morningstar Tristar; I don't understand the reasoning why, and didn't get a solid answer out of Morningstar--but it isn't hurting anything on a great MPPT, so I haven't pressed the question.

Not really.  Remember, we are only talking millivolts of drop.  If you have breakers odds on you are dropping at least 20mV across them at moderate amps.  Every joint, ring terminal, blah blah, it all adds up.  So long as the charger can pull the voltage at its terminals up to its regulation point, ie charger has reached the configured CV limiit, it will not provide any more current.  Grab a few meters, clamp, and observe your system in just this situation, assuming you aren't doing remote voltage sensing at the battery terminals.

You won't see it Sid.  Unless you make float = absorption you will always see some draw out of the battery until it reaches the lower voltage the charger is now targetting.  Even if you target the area with lifepo4 is in the fairly flat part of the graph 0.8V difference is 50mV.  50mV of movement at this point in the graph represents quite a lot of battery capacity.

Of course, once you load the system further unless the charger can see the battery terminal's voltage the battery will continue to provide a good proportion of the load even if solar is more than capable of fully carrying it alone.

Seems the best way to manage that is to keep the settings for bulk and float fairly close together, which you are already doing.  Can't stop the microcycling completely, so minimize it with tight settings.  Making bulk and float equal defeats the purpose of having two setpoints, so back to personal choice.  What settings do we believe provide the best performance balanced with the best preservation of cell life.  At this point, until I see some persuasive evidence to adopt different setpoints, I like the results i'm getting with my current settings.  Time will tell....

I ordered 8 more balancers on Aug 25 for my 24v bank.  The huge heatsink on the 48v bank works very well but is probably overkill.  For the 24v bank I don't have room to mount one that size so will take a different approach.  Planning to use individual heatsinks, so 8 of the type used for solid state relays should do very well in much less space.  Have 4 on hand so must run down to the electronics recycler store on friday when I'm in Boise for the other 4.  (They have a bin full of them - cheap, like me!)

Mounted in a straight line with one or two 4 inch fans for the lot.  Will put the temp sensor on the balancer that usually starts balancing first.  Tight temp settings on the big heatsink keeps it very cool.  28-26C (82-78F)  Should work about as well for the smaller setup on the 24v.

Still have to parallel all the cells and disconnect the individual active balancers on the 24v bank.  Probably take awhile to get the new balancers anyway.

Ha, yes...it seems to me that LFP are quite easy to balance.  My balancers got fairly hot the first few days--but that was it.  Now they never get even the slightest bit warm.  Probably don't even need a heatsink.

Li-Ion batteries on the other hand...they never seem to fully balance and are always running the balancers really hot.  Or else I've never had good Li-Ion batteries...