Wiring modifications

I have now carried out wiring modifications - mostly as outlined in entry "Q" - and been able to observe effects (all seems good!)

A.
As a main outline, ALL domestic and ancilliary functions (except as below) are now powered by a 400W 72:14.7 (DC:DC, volts) converter from the drive battery stack. An output of 14.7V was selected because this is (said to be) the "ideal" recharging voltage for Odyssey -type batteries (our drive battery type.) The converter is powered from the stack of six drive batteries, turned on by the main "on" switch by the steering position. This does mean this must be "on" for any electrical activity (including lights, pumps, etc.)... but since you would be on the boat to use anything, this is all to the good! Note that we no longer use any batteries other than the drive batteries.

The only exceptions to this arrangement are that:
(1) the gen-set satrter motor and its solenoid are powered by the "first" of the drive batteries (in the stack) - call it 'A'.
(2) the bilge pump auto-switch-on is powered similarly. Not that for manual use, it is powered by the converter.

Note that this means (virtually) all 12V power comes from ALL the drive batteries - charge returned by running the generator.

I was advised/warned that the asymmetric extra use of 'A' would cause a minefield of problems. I myself assumed 'A' would need "extra" recharging and wired so that it can be recharged at 14.7V from the converter, at will, with a manual switch. The charge state of 'A' (in fact, just the voltage across its plates!) is metered (using the meter that previously measured the state of the 'start' battery) and the charge state of the "next battery up" (call it 'B') in the series chain of drive batteries is also metered, using the meter that previously measured the state of the 'domestic' battery - these meters are side by side (see "control panel" posting) so it is easy to compare battery states.

In fact it turns out that when 'A' and 'B' are in near-fully-recharged state the last 0.5V or so does not represent much charge, and one can see that 'A' reads lower after using it "extra" to start the generator. However, once 'A' and 'B' are used more heavily (driving the boat) the difference of state is not really measurable and over a cycle of use (20/30% discharge and recharge), 'A' ends up as much recharged as 'B' and doesn't need extra recharge - the batteries self-equilibrate.

In fact if one guestimates the amount of charge used for a start, this is less than 0.1 A-hr - less than 0.1% discharge, so it isn't crazy the re-charge self-equibrates - if unequal charge states of this kind of order didn't self-equilibrate, no rechargeable battery made of more than one cell would last long - the "weaker" (slightly less re-charged) cell (and there will be one) would quite rapidly become weaker and weaker - an unstable equilibrium effect - and the battery become useless quite rapidly. This doesn't happen (thank goodness!)

Simple current theory precludes a process of self-equilibration, but batteries aren't simple conductors! In fact the re-charging process will be (at low level) a wave-type process of currents (ions) overall flowing the one way, yes, but with back ripples, so there is certainly room for an unequal recharging process as the ions settle down for full re-charge state - and, waves or no, the current flowing in the more re-charged batteries will have less recharging effect than in the less-charged battery, so it can "catch up". OK, not exactly exactly but the last 0.1% really doesn't matter... and I only USE 0.1% to start the generator!

Even more to the point, the theory doesn't matter, simple observation is that 'A' and 'B' self-equilibrate over a cycle of use. It may be that 'A' will wear out slightly sooner although I doubt the effect would be really significant. If I detect signs that 'A' is "tireder" later on I will simply swap batteries so that which actual battery is 'A' is rotated. However, I won't bother to do this unless there are any signs 'A' is suffering!
Incidentally, at one point I switched 'A' to have extra recharge only to find it was now MORE recharged than 'B'... luckily this effect self-equilibrated for another cycle of charge and discharge!

B.
Whilst rewiring to avoid the need for separate ancilliary batteries, I also "tidied up" some inconsistencies in the original system - for example, it was possible to start and run the generator (and therefore the boat, for as long as you liked) without having to turn on the key!!
I have now rationalised all this so that the key must be on to run/start the generator, or work the bilge pump manually or for the drive motor's cooling fan to operate (or work the horn, front light.) The boat cannot now, therefore, accidentally run down battery 'A' whilst you aren't there or aware of what you've set - unless the bilge pump switches automatically and jams "on". Ah well, in that (terribly unlikely) event I'd have to use my switch to bring 'A' back in line!
I incidentally used the now "spare" switch previously used to recharge the 'domestic' battery so one can choose to turn off the motor-cooling fan. This may sound silly - surely the fan must come on automatically if the drive motor is "too hot"?
Well, for a start this fan was only fitted to upgrade the motor from 10kW to 12kW. We never normally actually use more than 6kW except briefly - so the fan isn't really needed! However, possibly just as well to have it because air-flow around the motor is fairly restricted... but it isn't essential it is on every second if the motor is a bit hot. And, in fact, its (the fan's) noise is quite distracting if you are doing quiet manouevres. Even better, now we have the choice - yes, the fan might is possibly better run IF the motor is a bit warm and the noise isn't intrusive, but, if it is, you can switch it off.
C.
My (home-made) VCS (the unit that controls generator speed and so output so the recharge voltage never goes over 88.2V) started playing up recently. Very startling because it had been so fail-safe reliable. It was an intermittent fault. Opening up the box I discovered a fine wire checking "common earth" between the 72V drive batteries and the previous 'start' battery had actually melted at some point... without going into every detail of my deductive process and discoveries, basically I have to be sure that as previously wired the 'start' battery had only had "common earth" with the drive batteries because the voltage across it and the 'domestic' battery were (very nearly) the same... which went wrong when the 'domestic' battery had a cell fail last Christmas!!!... all in all a whole lot of strange observations were explained - I hadn't realised the earths hadn't been wired solid from the outset!...
Clearly, with a wire melted, my circuit had suffered some most peculiar voltages... anyway, hopeless to try and trace which semiconductor was damaged, easier to re-build... which also caused me to re-think what I actually wanted. Thing is, the previous circuit, built to mimic the original Fischer-Panda unit (but better!) had a silly property it continually tried to accelerate the generator unless its voltage was in the 85.2 - 88.2 V "ideal" recharging range even though most of the time when boating (as opposed to topping up the batteries) the voltage is necessarily way below this. And when running the generator for that top up, yes, the unit cut the speed as the voltage rose but also "hunted" - put in a speed-up burst to be cut again - whereas the process you want is that the speed is cut when the voltage rises over the limit... generator runs at the slower speed, voltage on the batteries rises as they recharge more - takes as much as five minutes - then the generator needs to slow another (single) pulse.... not a continuous checking operation! There had also been a problem when the VCS did go funny that I had an indicator on the box, yes, but not showing on the control panel...
Anyway, so the whole system revamped. For one thing, you can see what the unit is "telling" the generator to do - a LED flashes green if it's telling the gen-set to speed up, red if telling it to slow down. And a three-position switch allows you to tell it to do the (hopefully) most sensible thing for different situations, as follows:
(1) "Down": the VCS issues "slow down" pulses indefinitely. This is used to slow the generator to minimum speed and zero output - if there's time this is the ideal thing to do before actually turning the generator off - run it about 5 minutes at this speed before actually turning it off and it cools enough not to "claim" to be too hot when you next go to restart it. (Where the illogic is that it needs to start to pump the water to cool itself!) See other postings about this rather annoying problem! Once the generator is at min. revs, you return the switch to "neutral" mid-position.
(2) "Up": the VCS issues "speed up"pulses idefinitely unless you are nearly recharged, in which case these stop when the voltage is over settable level - our case, about 87.5V. IF the voltage goes even higher (as it can since the system can take a time to adjust), the VCS issues a "slow down" signal. In normal usage this will never happen whilst cruising because the voltage never gets near 87.5V and this position is actually used to simply speed up the generator after starting to get max. output. Once this is achieved, you return the switch to mid "neutral" position.
(3) Mid position: I've called this "neutral, but in fact it isn't! In this position the VCS issues no pulses unless the voltage rises above 87.5V, in which case it issues a "slow down" pulse but never a speed-up pulse. This position ensures the voltage never goes above 87.5V for any cause. It's use is when you leave the generator running for final top-up - the generator will slow as recharge is obtained. You can leave the boat doing final top-up knowing it will "look after itself".
Please note, compared to people running their motors forever to "keep the batteries happy" our system only takes about 40 minutes for full recharge from quite severe discharge.
D.
If you are and wonder why I bothered with eliminating auxilliary batteries to use only the drive batteries, there was good practical cause. I had minor havoc last winter when the 'domestic' battery refused to recharge - and I had to be careful to keep the 'start' battery recharged. The Odyssey - type batteries simply don't require this much attention, and they don't self-discharge if left reasonably fully recharged - not only as the sales people say but as observed fact, by me!
I also suddenly realised that if our domestic 12V power came from the drive battery stack the effective capacity was 600 A-hr - quite enormous. And simply no point in having a separate set of batteries for this if we didn't need them. By using the drive batteries directly, this also meant the power-source had this astonishing property you could recharge in amazingly short times... even if we slobbed all evening in front of our very cheap but current-eating TV it only means running the generator an extra ten minutes in the morning - not exactly a problem whilst you decide to have another cup of coffee or not.
Overall, be clear the system works. Very well.