Control of the hatches needed to be simple, battery operated and adaptable to any possible future upgrades and Ascom mediated synchronization. The schematic below seemed to offer this and required a minimum of circuitry to control both motors, namely the Main Hatch control motor and the Front Hatch servo that both were chosen to operate off 12 Volts.
A lead acid gel accumulator of the type used in UPSes and burglar alarms is cheap and gives a sterling service for many years provided it is kept charged at an ideal dwell voltage. So it is very important to choose your charger well and make sure it hovers on or around 13.7 V under trickle conditions.
The workings of the schematic are simple but at the same time cunning :), making use of diode switches to stop the travel of the hatch at both ends. Normally OFF (NO) magnetic reed switches sited at the upper and lower extremities of the hatch window opening on the right are turned on at the arrival of the magnet that is bolted to the side of the hatch in front on the right close to the anchoring point of the chain.
When this happens, relays are actuated that open up a normally closed (NC) contact that was shorting out a diode rectifier wired to oppose the current flow to the motor. This causes the motor to stop. A red LED lights up to alert you that the fully open position has been reached and a green LED when fully closed. These also indicate that the relay is still activated. The battery can handle several hours with the relays’ current flowing but the switches were purposely chosen with a centre-zero state to allow manual shut down of current to the relays once the open /closed state is reached thus conserving the juice.
I added bipolar LEDs to indicate the direction of travel of the hatches. These light up red or green depending on the polarity applied to them. This is obviously an optional but I thought they looked “cool” .
SW3 allows operation of the hatch from an external supply and the wiring also permits the battery to be charged from a separate supply while the dome is in the parked position. This charging is best left on 24/7 when the dome is not in use.
The three double pole switches have to be capable of handling at least 10A. Most car type switches easily manage this and they sell cheaply (usually in quantities of 5 or ten!) on ebay or such. A digital voltmeter was added at the front end to ensure proper monitoring of the all important charging state of the accumulator.
The external ‘cigarette lighter’ output socket is wired in parallel with the external power socket. This allows hatch control by an external 12v source in case of battery failure. I have a small 12V portable camping type supply that I keep for such eventualities and it also serves to start my car if that battery goes dead! The 7amp 13.7v bench type power supply I use to run my AVX would also manage the hatch if the need arises. Conversely 12v can be tapped off from the external supply to feed the AVX via the extra socket.
The panel was made from scrap aluminum sheet and screwed to two short lengths of timber and made to fit neatly between the two arched risers to the right of the front window. The small accumulator cell also fitted well in the space behind the panel. A cardboard template of the space at the top of the panel allowed me to make a roof for it out of plywood. This was just push fitted over the top to allow for easy access to the battery should the need arise. The charger was placed underneath at the spot where it is usually parked but its output cable gave it substantial leeway.