Re: Power options
Hi,<br /><br />I do not know if Your Johnson 20 hp 1992 has an alternator so it can charge a 12 volt marine battery but if it has electric start it for sure will have the ability to charge a battery (higher Amp at higher RPM usually).<br />Maybe the alternator output then can produce around 5-10 amp at higher RPM (guessing here, You have to look in Your outboard Users guide).<br /><br />Without the ability to charge the battery while using the outboard You will drain the battery rather quick, quicker the more you load it with electrical accessories.<br /><br /><br />Fish finders usually do not draw that much current (Ampere). <br />Example: Garmin Fishfinder 250 C (Color) will draw about 1.2 Amp at 12 volt.<br />If You have a 75 Amp. hour (Ah) marine battery the fish finder can be used rather many hours before it is drained to a critical level as You can calculate.<br /><br />Navigation lights will draw more but You can replace them with the new LED navigation lights now that draw almost no current (abot 1/10 of regular nav ligts).<br />For example Hella marine has such navigation lights.<br /> <br />You will probably have a consumption of about 1-2 amp with a top and left+right navigation LED light.<br /><br /><br />If you by "lights" mean search lights, that will draw rather much current. A 55 Watt search light will draw about 4.5 Amp.<br /><br />If Your outboard has no alternator today I would guess it can be added as an option (I do not know the cost). Or You could buy two 12 volt marine batteries and always have one charged at home ready for use while using the other. That way You should always have a battery ready to be used even if you need much current same day (just bring with you two batteries then, but I doubth You will drain a battery in one day/evening). You could also select to have two batteries in the boat regardless if you have an alternator or not (and regardless if Your outboard use electrical start or not).<br />If it has electrical start and you want to have two batteries onboard you can use a battery selector switch to only use the second battery for accessories so the startbattery is not drained and always able to start the outboard.<br />For example Blue Sea System has such 4-way (1, 2, both, off) battery selector switch, like this:<br /><br />Bluesea.com<br /><br />(this switch also allow both batteries to be on if you want, for example while outboard is charging)<br /><br />If Your outboard has an alternator (or if You decide to add one if it is possible ), or if it has no alternator and use it without alternator, I would select a marine battery at around 75 Ah (will weight around 20 kg/44 lb).<br /><br />As for the electrical scheme You should add one main switch near the battery on the plus cable (red) that goes from battery to plus terminal, like this:<br /> <br />Bluesea.com <br />Or use the 4-way battery switch (link above)<br /><br />And after the switch also a main circuit breaker (preferably an automatic) at 15-20 Amp or so in your case, like this:<br /> <br />Bluesea.com <br /><br />From the start motor on the outboard (if it has electric start) a plus cable will go to main switch. <br /><br />From battery minus pole you will use a cable (black) to connect to the minus terminal. Also a minus cable will be connected from outboard start motor to battery minus pole.<br /><br />To organize electrical accessories you should add them on something like this (it has both plus and minus terminals and fuses in one and same box):<br /> <br />Bluesea.com <br /><br />(it use ATO/ATC Fuse, no other fuses will work)<br /><br />To this box You connect the nav lights and fish finder and other electrical accessories You need to use. <br />This way You will have everything nice organized.<br />Remember to use thicker plus and minus main cables to avoid voltage drops and to avoid risk of overload.
