Well, not long after the above, I did some stress testing on several aspects of the system, and in the process became rather impressed as well as very disappointed all at nearly the same moment involving the same piece of equipment...
The Chinese power supply was labeled at 40A, purported foldback overload handling, and with that, seemed the part. And then some. During load testing, I was hitting 50A with only 0.4V drop at the rails. Should have been a clue in itself. But then I added another small load and *blip*... it hiccuped.
Satisfied however that it would handle it, the next morning I went to let it push directly into the batteries, and started hearing switching chaos coming from the box, and current was a modest 23A or so... I disappeared to the garage to get my morning soda and by the time I got back, it had died. Completely.
I opened the case and as I suspected, the internal fuse had blown. So I disconnected it from everything, applied power, and bypassed the fuse. Quickly following, one of the switching transistors let all the magic smoke out with a trite bang...
So much for foldback. Chinese vendors really need to investigate the contents of the English dictionary if they're going to sell things to the English speaking public.
So I decided to go old school on it. Hard core old school. An old APC 900 BackUPS unit cleared out for the transformer was the basis, along with a couple of unipolar bridges from a triplite supply that had a bad transformer itself.
Oversize the heatsink for the bridges, and some caps to limit primary current, and I had the basics going for a robust charging solution.
It needed to be controlled however, as the caps make the transformer behave essentially as a current source, so they needed to be rearranged to change modes. A simple scratch up with a relay placed a set of three 40uF 370VAC oil caps and arrange them in series or all in parallel with each other.
The two modes provide ~1.5A and ~12.5A, plenty for the double set of batteries. When I go to double up the lead, the caps are already in the charger to be placed in parallel with the existing set. A couple jumpers and all set.
There's a manual high/manual low/auto switch that I put on the front of the unit in place of the old test/mute switch. "Auto" is a little deceptive, there are no brains inside the charger itself. It receives a relay control signal from the classic that tells it which mode to be in based on battery voltage.
All in all, I'm happier with it, and while PF isn't great (0.6 typ), the entire thing was built with parts I had on hand (I confess, only the relays and override switch were new), so it "cost" me absolutely nothing and does the job well.
That little set back slowed progress elsewhere, but things have resumed... more as it comes.
Steve