Sizing a Charger for My Bow Thruster?

Question:

Hi Jeff, I want to move my (2) 12V bow thruster batteries (starter batteries in series) under the V-birth to reduce the voltage drop. The current cables are about 60' in total going back to the engine bay.  Someone suggested I put a 24V 20A charger up front and wire it to a breaker in the salon. What would you recommend for the charger and the breaker size to buy? The thruster is a 10 yr old EXtern.  - Rich

Answer:

When sizing a battery charger, make sure it’s at least 10% of your battery bank capacity. For instance, two 8D batteries in series would be 250 amp-hours at 24 volts, hence the charger should be at least 25 amps. Sizing the wire and the breaker to feed this charger, should follow the charger’s recommendation, for instance a 20 amp 24 volt charger will probably require a 14/3 AC wiring and probably a 10 amp AC circuit breaker.