78 Johnson 70hp: Does the motor charge the batt?

Does the motor on my 78 Johnson 70hp charge the battery?

Im asking b/c I want to install a radio, depthfinder, and trolling motor to my boat. I have two large marine batts. One is currently hooked to the starter,lights,bildge,horn (horn doesnt work, any ideas? everything is connected).

my question: should i hook both batts together (does that change the voltage,both 12V) or should I leave them seperate (i can run the radio/trolling motor dead and the boat will still start w/ all legal needs)

any advice is great!

thanks guys, to all those who have helped me! gimme 10yrs and maybe I can answers some ?s instead of asking

Re: 78 Johnson 70hp: Does the motor charge the batt?

The drawings show it with a 6 amp stator coil and a non regulated rectifier so yes potentially it will charge the battery. But how large is large?

Clip a volt meter to the battery and see what reading you get. If it is charging then you will see the volts rise above 12 to around 14 and even to 16 when the battery is charged.

If they don't rise then it is not charging due to some defect.

You can connect both batteries in parallel but permanent connection of two batteries has the disadvantage that if one goes bad it can discharge the other.

Use of a voltage sensitive relay (VSR) is a good way of automatically charging a second battery without then being permanently connected together.

Don't discharge any battery, other than a deep cycle traction battery, below 50% of its capacity regularly.

Always recharge a battery, even if only slightly discharged, as soon as possible after use.

Re: 78 Johnson 70hp: Does the motor charge the batt?

Thanks for the advice! I will look into the VSR system.

When I use my batt charger in my garage if i hook it to the 1st batt in the VST system it should also charge the second batt?

If the motor is sending out less than 12V is it draining the motor? (how much power does a standard spark plug use?) just curious

Re: 78 Johnson 70hp: Does the motor charge the batt?

McBoatin said:

If the motor is sending out less than 12V is it draining the motor? (how much power does a standard spark plug use?) just curious

Click to expand...

Charging system uses separate coils in the stator than does the ignition system. Battery power to engine is only used for starter motor, choke solenoid, and Tilt & Trim if you have it. In the controller it is used to power the over-temp warning horn and can be used to power gauges when the key is on if desired.

Ignition system sends 300vdc to the ignition coils which then produce somewhere around 30,000 volts to the spark plugs, I think. Enough voltage to have a bright blue spark jump a 7/16" to 1/2" gap. Not a good idea to grab a spark plug wire with bare fingers while the engine is running, I can personally tell you.

-- Jeff

Re: 78 Johnson 70hp: Does the motor charge the batt?

thanks Jeff,

I hope i learn from your mistakes! but learning the hard way is sometimes the best, but not always.

but that makes sense about the batt and motor have diff power supply.