An update on my report above.
This PSU seems highly resilient to abuse. It's not that I'm actively trying to blow it but I've really not been trying very hard not to blow it and despite some quite bad treatment, it's still going strong.
It was briefly pumping out 2000w (at about 12.8v) today slowly dropping to about 1300w over the course of 10mins as the battery took on charge. I've had it doing >1300w for over an hour with no sign of problems - yes the fan's running full pelt but nothing seems to be getting overly hot.
My current issue though, is that there's not a perfect voltage to set it at, to cover the full range of the charge cycle. Set too high, then at the start, when the batteries are empty, we're trying to pump out 170A (or more) however, a voltage that gives a civilised output at this end, leaves us with, in effect, a trickle charge as we approach the 'full' end of the cycle.
So there is a little bit of circuitry I'd like to build but I really don't know enough to design it myself as my knowledge is basic - for example: I know, in theory how transistors work but don't have a clue how to implement them in a circuit.
Anyway...
Everyone knows pins 33+36, bridged with <500R activates the PSU.
Less well known is that pin 34, emits an 'indicator voltage' that represents the current output.
For an output >20A the indicator voltage is roughly I x 0.032 - 0.4
So 2.8v represents 100A, 2.0v is 75A
As above in this thread, I have a 'control resistance' between the trim pot and ground which, as it reduces, increases the output voltage (and hence the current) of the PSU.
What I'd like to do is to automagically manage the control resistance based on this indicator voltage.
eg. As the indicator starts to exceed 2.5v, increase the control resistance to bring the output back down.
The thing is, I can think of ways to reduce the resistance as a result of increased voltage (eg. an LDR/optoisolator) but I don't know how to do the opposite. I assume this would be childsplay for many folk on this forum but I'm afraid I am 'enthusiastic but relatively clueless'.
btw. if the answer is, "why are you even bothering? It would be much simpler to your simple solution here" please do fire away...