I did post this on Motorhome facts previously indirectly linked to earlier, so sorry if this would have worked for Steve but a little late for him now!

But, since the alternator only charges to 2/3rds capacity, and a Sterling is quite pricey, what if an inverter was run directly from the alternator? (How?) A smart mains charger could be plugged into this and would have put a full charge into the LB's, the inefficiency of the inverter being more than made up by the charge then acheivable by the alternator?
I am no sparky, the whole thing seems hocus pocus to me, but can anyone say if this is doable, the only drawback being switching the inverter back for hairdryer use if you wanted to?

Got this response from the manufacturer:

From what I understand, with the DC/DC converter connected straight to the battery it just shoves 15.8V at 15A into the battery, and will either over-charge and damage the battery if we leave it on for a long time (ie: drive for a long time), or if for a short period, will not charge efficiently. To achieve efficient charging of deep-cycle batteries you need to use a smart charging algorithm that alters the current and voltage sent to the battery according to battery state (ie: Steca's PWM charging system)
Yes, if the DC/DC converter is connected directly to the battery, then someone will have to make sure "manually" that the battery is not overcharged.
As you know from my last email I have already connected the DC/DC converter to the Steca regulator, and (luckily) neither were damaged! Can you tell me why they could be damaged? Can you also tell me why the Steca receives 0A from the DC/DC converter when I know the DC/DC converter is capable of producing current?

The Steca charge controllers use a regulation mode which short-circuits regularly the energy source. This is fine for solar modules, but can certainly damage any other energy source. Additionally, the mosfets inside the charge controller can heat up and get damaged irreversably, if the IV characteristic of the solar module is not recognised.

I have a solar system that is working correctly - it is the alternator charging system that I have the problem with. What I need to find is a PWM or MPPT battery-to-battery charger than can take my 24V alternator output and charge my 12V deep-cycle batteries, except this is not easy since I'm in Africa. Hence the reason I'm trying to use the Steca as an ad-hoc battery-to-battery charger. What would happen if I connected my alternator directly to the regulator? (it produces about 26V, and can produce 55A)

This will not work, because again, we can only use solar modules at the input, and secondly, the current is way too high for the PR controllers.