Electric boat conversion - the VCS

This picture shows:

On the left, a 72:12 (volt) DC:DC 400W converter which allows the "start" and "domestic" batteries (both 12V) to be recharged from the 72V drive batteries - powered or not by the 72V generator. In our case - at least for now - this recharging is done by manual choice via switches on the control panel, where one can asses the need from battery level meters on that panel (one for each of the 12V batteries.)

(In fact our wiring - by error - has a snag.. the manual switches do not actually connect the (12V) re-charging current, but cause relays to do this... powered by the (12V) "start" battery. So if the latter is flat the relay doesn't click over to recharge the battery!! In our case the start battery has nearly been that flat... but luckily not so flat a flick of a fingernail on the relay casing didn't cause it to operate! Clearly, though, the relays should be powered by the charging source - the output of the convertor... and I must change this!!)

On the right is the "VCS" - "Voltage Control System". This box of electronics regulates the speed of the generator so that its voltage ouptut (the charging voltage for the drive batteries) never exceeds 90V (>15V per drive unit) as its main function - although it has the secondary function that it always sets the generator speed to minimum after switch-off so that the generator starts with near zero load and then speeds up appropriately. Equally, via a switch I fitted, it can slow the generator before it is switched off so that the load reduces to near zero, which allows the generator to cool for about 5 minutes... which (usually) means the generator doesn't register "ghost" overheated condition when you next try to start (see under generator problems!)

The VCS unit comes with the Fischer-Panda unit - but in our case it was either faulty or Alan (our engineer) blew something or mis-wired it (or I blew something trying to find out was wrong, later!)... so the electronics inside the box in the picture is actually mine - I simply re-used the box and connectors!!

To explain, the speed of the generator is controlled by an automated "accelerator"... called the "regulator". This is a simple (but neat!) system on the generator where when a small 12V motor turns the one way, via a screw thread, the regulator moves to increase fuel flow, or, turning the other way, decreases....

The motor is driven by short pulses of about 0.1 sec every second, so that when the regulator meets mechanical end stops (one can set) either up or down, the motor simply tries to move the regulator further but can't - because it is only trying with brief pulses it doesn't overheat for having the mechanical movement thwarted!!

So, after "turn on" of the generator the VCS "issues" "Accelerate" pulses until the generator has either accelerated to full speed (as set by the mechanical stop) or until the voltage output has reached a preset value - as set via the volume-control knob visible in the photo....

From battery data, this should be in the range 85.2 - 88.2V.

So, normally, one starts the generator (batteries down from near full re-charge) and it speeds up because the VCS is emitting "speed up" pulses - indicated (in my case) on the VCS box by the dual-colour LED on the right at the top of the box (as in the photo) flashing green as each pulse is sent. This goes on flashing continuously... unless and until the drive batteries' plate voltage is in the range above (in my case, about 87.5V)... once this voltage goes above 87.5, the VCS emits a "slow down" pulse (LED flashes red) and the generator is slowed slightly.... reducing the voltage output.

With such a slight change being crucial - only about 0.4 V in 87V or 0.6% - the detecting circuit has to be very sensitive... and with changes being definite pulses of 0.1s per 1s... the system "hunts"... but very slowly and smoothed out by the generator not reacting instantly... the effect is that the generator slows in pulses (but sometimes speeds a bit in between!) as the batteries come up to full bulk recharge.... and as the charging voltage decreases, the re-charging current falls (in time, all the way to zero - although in practice 20A is low enough and the solar cells will do the rest.. only some tiny % of full recharge, less than 1%.)

When the generator is turned off at any time the VCS detects this action and then emits about 20 "slow down" pulses so the regulator is always back to min before next starting the generator.

(My switch to slow the generator before actually turning it off merely "tells" the VCS the generator has been turned off (when in fact it hasn't been) so the VCS issues the 20 "slow down" pulses whilst the generator is in fact still running... if one reverses this switch before actually turning the generator off it speeds back up again!)

Without issuing an actual circuit diagram of the electronics, people may be interested that it contains (1) a slow (electronic) oscillator creates a 0.1s pulse per 1 sec all the time which (2) is switched on to drive the regulator motor via a relay if conditions are suitable, with the polarity of the output controlled via another relay, direction being "increase" for battery voltage less than 87.5v,or "decrease" for battery voltage greater than 87.5V OR for 20s (seconds) after "generator off" signal.

Detecting the voltage o/p so accurately is done by dropping the battery voltage through zener diodes to lose 80V and then the remainder (about 7V) is compared with 7V set by another zener in the otherwise 12V circuitry....

Anyway, point is, you MUST have something to accelerate up-to and then limit the generator output to max about 87.5V and to set the regulator to minimum after turning off.