Hmmm. So I re-read twice. Maybe it’s the ADD but did I miss how your panels are configured? Not saying that’s the issue but in my head I can’t ‘see’ your system.
And by “bouncing” 12-15V that bothers my head. I think capacitance is the correct term, but the ‘slow’ load of the batteries should be an adequate buffer for the potential float wandering of charge controllers. So in my mind the first thing up is, “bad connection.”
On the other hand, if your meter is somehow “too responsive” I can imagine the punches of the SCC might be readable? I don’t know.
As I said and you know: the batteries should buffer or dampen the V punches from the SCC.
Do the volts on the SCC display have similar fluctuations? Or just your meter? I can see how an unweighted meter output might not be steady just like measuring a msw inverter output shows 60V-170V or just 60V instead of 110V/120V like a true-sine inverter would. With good tight connections full batteries should read a steady DC voltage even though the charge controllers might be cyclic a little, punching the charged batteries with float.
Q? Will it do the same volt fluctuations with all loads disconnected? If so you’ll know it’s not anything cyclic on the load side.
Thanks for the touch-back -- I appreciate all the help I can get!
My PV array is series all the way (chose this to reduce current between PV and SCC). I have 4 identical new 210w rated panels on the roof but started with just 2 in series at first to be sure nothing was damaged - this gave me 420W rated (328w practical - they are flat) 35Voc measured in bright sun - and well within the SCC spec. Kept getting OVD so removed one panel so now have 210w PV rated (168w practical) and it will 'hang-in-there', but no where near the power I need. With just one 210w panel I'm getting around 14-16A chg at 13.2 volts.
When I reset and start up with 2 panels in series (328wp) and monitor PV with the MT50 and Vchg with my DVM I see +/- 295wPV and chg starts at 13.5Vchg and grows quickly to 14.2V @ 20A (which is my Charge Limit) then charges at this level for 30-45 sec, then Vchg starts to jump around from current batt voltage (lets say 12.6V) on low side to higher and higher on high side till is exceeds the OVD value of 16.0V (I assume) and locks out. Fortunately the SCC keeps the highest voltage it sees until reset so I can check - and over many test runs (like - 20-30!) I have seen anything from 19V to 32V. I have tried varying different Control Parameters slightly to see if any difference - none! Unfortunately, the SCC and MT50 only appear to refresh about once per 10 seconds so don't catch instantaneous changes.
I have come up with some possibilities.
1) SCC is faulty/damaged and just does not control behavior as expected. I'm doubtful of this since I have an identical SCC and have hooked it up identically, and got the identical result.
2)The SCC's I have are 4210AN 'AUTO Voltage' versions - senses whether 12V or 24V and allegedly picks the right one from the batt lead. Thinking that the SCC might get confused at 14.2V and start jumping around, then switch to 24V - how else to record a Vmax of 28-32V?? I haven't worked with 24V systems but thinking Vboost or Vequlz could be this high?
3) As I mentioned in my original post my plan is to have 2 4210AN 40A SCC's running in parallel (with separate PV arrays) feeding directly into my batt bank. I have wired both units in (but only working on one at the moment) using about 18" of #8 fine copper to a common post on a terminal/breaker block, then from there another 24" using a common #6 copper to the main +/- terminals of my on-board Magnum Inverter/Charger, which then goes directly (about 6') to the main batt terminals via #00 batt cable. Occurred to me that there might be enough resistance in this arrangement keep the batt from clamping the SCC charge voltage steady enough to stop the SCC charging without the Vchg jumping so high. I intend to run #00 directly from the SCC's to the batt terminals soon as I get back to my shop - travelling now and not something I want to do on the road!
Thank you for the thoughts on loose connections - anything can happen on a motorhome traveling on our roads, so I will go over all connections to be sure all are tight.
Not sure what you mean by 'load side'. The only load my SCC's see is the battery - my SCC load terminals are open (not connected) and the Load function is turned off internally inside the SCC.
My next move is to completely disconnect all other loads between the SCC's and the batteries (ie the I/C'er) and use the existing #00 battery cables between the I/C'er and batteries to attempt to eliminate the I/C'er from the equation.
Please let me know what you think on all this.
Thanks
PaPaBob