The BATTERY capacity of the auxiliary will be a function of how long you think you will need the bow thruster in one session, and how often sessions will occur. Refer to the bow thruster current requirements to determine this figure. For example, if the bow thruster draws 50 amps (about 1.5 horsepower) and you need to be able to run it for up to 30 minutes, that comes to 50 x 0.5hr = 25 amp hours. You should double this figure to provide a safety factor and reduce cycling the battery below the 50% charge level. So a 100 amp-hour automobile battery for about $35 would be ideal. You should match the chemistry of the battery to that of the starting battery - don't mix an AGM or GELL battery with a WET lead acid. Otherwise the batteries can be of different ages, manufacturers or style. You don't need a deep cycle battery here - the usage is more like that of a starter motor battery in an automobile.
Charging time after a typical use can be calculated by dividing the amp-hours used, say 25 in a 30 minute period, by the charging current, say 4 amps = 6 hours, or 12 times the discharge time.
The HEADLAMPS should usually be the highest wattage you can find. In fact I use a high/low beam headlamp and wire the high and low terminals together so both filaments are in parallel. The high temperature will reduce life but since they are only going to be on for a few minutes a day maximum, who cares? A major advantage of using headlamps to limit the current is that the resistance is non linear. As they cool down the resistance goes down dramatically and they tend to draw a constant current for charging even though they are not brightly lit. You should consider placing the headlamps so the light is visible from the bow thruster control panel location so you don't forget to switch back to CHARGING when the bow thruster is no longer needed, otherwise the headlamps will eventually discharge the auxiliary battery.
The SWITCH should be sized for the maximum current of the bow thruster plus a safety margin. For an economical installation, a simple battery disconnect switch is ideal. If you want a remote control, then you should use a simple single pole, normally open relay instead of the switch. We have a 130 amp relay in our Parts and Kits catalog that will handle many thrusters.
Just wire one side of the coil to a remote on-off switch connected to +12 on your control panel, and the other side of the coil goes to the normal negative 12 volts.
The CABLES should be sized as recommended by the bow thruster manufacturer with regard to the length of the run. Note that only the cables to the switch have to be this size. The cables to the headlamps only have to carry a few amps so a 12 or 14 gauge wire would be adequate.
Charge your 24 volt trolling battery from a 12 volt supply.
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|The Trollbridge24 will only support 24 volt loads up to 85 amps.|
Contact firstname.lastname@example.org for availability of the Trollbridge24-500 that can supply 500 amps for anchor winches or bow thrusters up to 16 horsepower.