Battery Wiring

[paceman]

Recently my BIL bought a new to him fishing boat. While going through it in the garage this past weekend. We discovered that the previous owner had wires with aligator clips running from his starting battery to his trolling battery. So the BIL called the old owner and asked him what that was about. He stated that he would hook the batteries together when the big motor (40 HP) was running to charge the trolling motor. I'm not sure if that is a good idea. To me that sounds like a good way to ruin the alternator on the big motor. Thoughts?

[TruthWalleyes]

I have 3 batteries in my boat. 2 hooked up in parallel - used for TM. Another battery hooked up to the other 2 which can be disconnected with a switch. I often have all 3 batteries hooked up in parallel and the main motor of course is attached to 1 of the 3 though technically it is connected to all 3 when i have the switch thrown in that direction. All 3 are deep cycle gp27 interstates bought at the same time.

I've been told that can be bad for the main motor, i never really was given any reasoning behind that, so i'm curious if it is true.

I initially installed the switch when i did my complete boat remodel as a "Just in case" i run out of starter battery.

[BobT]

Recently my BIL bought a new to him fishing boat. While going through it in the garage this past weekend. We discovered that the previous owner had wires with aligator clips running from his starting battery to his trolling battery. So the BIL called the old owner and asked him what that was about. He stated that he would hook the batteries together when the big motor (40 HP) was running to charge the trolling motor. I'm not sure if that is a good idea. To me that sounds like a good way to ruin the alternator on the big motor. Thoughts?

The time it takes to recharge a trolling motor battery well exceeds the amount of time you would run your outboard. It really doesn't do very much.

For example, if you use a trolling motor that is pulling 20A for one hour, it will take one hour at a 20A charge rate to recharge that battery. I don't know what kind of output your boat charging system can produce but my guess is you wouldn't run it long enough to put much of a dent in the charge state of that battery.

Putting a heavy continuous load on your outboard's charging system may heat it up a bit. Heat is an electrical system's enemy.

[TruthWalleyes]

Putting a heavy continuous load on your outboard's charging system may heat it up a bit. Heat is an electrical system's enemy.

Can you elaborate please. Conditions that create heavy continuous load.

I also agree that most boat motors won't hardly charge battery, i was just concerned - as well as the OP, on whether on not it can cause damage.

[BobT]

Outputting a continuous full-load current from the charging system. For example, the alternator in my old truck was rated for 60A (going off my memory). If I put a load on the system that will draw 60A continuously for a period of time, it will cause it to get a little warm. It is rated for 60A but typically in automotive situations (like your outboard) the loads are short term as in just long enough to recharge the battery after starting your car. Those charging systems are not designed to drive at full load continuously.

Does that help?

[TruthWalleyes]

I have always stayed as far away from electricity as possilbe so i may need a little more help understanding here. Bear with me.

So i was not aware that the charging system turned on and off with the motor running. What conditions or ranges dictates when the charging system (alternator) runs and doesn't. And, is the "Full Load" created by having a battery below 12v or is it created by the charging system being connected to a battery which is presently powering a trolling motor running on High?

[delcecchi]

In cars there is a device called the voltage regulator that controls the output from the alternator to the battery to keep the voltage at the right level and not over charge the battery.

The alternator is a device that is connected to the engine and produces electricity when the engine is turning. Sometimes it is called a generator.

In the early days of outboard motors, after electric start was introduced, a low power generator was added to the motors of the day. Since it put out relatively low current, no voltage regulator was used.

Nowdays since more electrical load is encountered, the generator/alternator output was increased and a voltage regulator was added to keep from frying the battery and other electronics. Probably also when sizing the wire etc in the generator the designers made assumptions about how long a time the generator would put out its maximum rated current.

So a motor might charge the battery at 60 amps, but not be designed to do so for two hours, maybe only one hour.

[BobT]

I have always stayed as far away from electricity as possilbe so i may need a little more help understanding here. Bear with me.

So i was not aware that the charging system turned on and off with the motor running. What conditions or ranges dictates when the charging system (alternator) runs and doesn't. And, is the "Full Load" created by having a battery below 12v or is it created by the charging system being connected to a battery which is presently powering a trolling motor running on High?

When you connect an electronic device to a battery and turn it on, the device draws power from the battery in the form of electric current. The battery has a limited supply of power available. The longer you leave that device connected the more power it draws from the battery until it uses all of the available power the battery can deliver.

When a battery is low on charge and you connect a charger to it, the battery will try to recharge itself as fast as it can and so it will put a heavy load on the charging system. Most charging systems have special circuitry built in to limit the charge rate to the battery. The reason for this is because if you let a battery draw current too fast, it can damage the charger or over heat and damage the battery.

Charging systems are not designed to be used as power supplies but only for recharging a battery. A power supply is designed to deliver power for longer periods of time continously.

Here's an example. A 14ga. wire is rated for about 15A. You can connect it to a 15A load and leave it on for extended periods of time without risk of damage. It is also possible to use it on a 20A load but only for short periods. If you put a 20A load on a 14ga wire for an extended period of time it will begin to heat up, melt the insulation, and probably break down. Put an even higher current load on that 14ga. wire and it will break down even faster.

The charging system in your boat or car is capable of delivering relatively high current for short periods of time but if you use them to deliver high current loads for long time periods, they will not like it for very long.

Hope this didn't get too long.

[merkman]

I'm not sure if that is a good idea. To me that sounds like a good way to ruin the alternator on the big motor. Thoughts?

[TruthWalleyes]

Right on. Mine has been going for 2 years no problems. I have ran the motor for upwards of 8+ hours at a time.

[redneckdan]

Most outboards actually use a stator and a shunt type voltage regulator. The stator produces the same amount of energy at a given flux no matter if the accessories are demanding that amount of energy. The excess is shunted to ground through the voltage regulator, any deficit is made up with battery energy. So by having enough energy demand at a given flux level you are actually putting less strain on the regulator. Everything else doesn't see any difference no load versus full load, it still makes the same amount of energy for a given flux.

Of course Evinrude has to go and be the exception to the rule with E Tec. Those motors use a multi coil stator that the regulator can chose how many coils to utilize based on load. The stator and regulator are still designed to handle the full energy production of the stator.

Neither system operates like a car where the field strength is varied based on input from the voltage regulator based on electrical load. This system is much more complex, requires brushes and is not really suited to outboards. I/Os and inboards use an alternator.

[bobbymalone]

I have ran the motor for upwards of 8+ hours at a time.

Hold up, 8 hours? Did you make it to St. Louis?

[TruthWalleyes]

Honestly i've gone longer, typically trolling combined with long runs at WOT. Don't have enough licenses to fish all the way to st louis though.

[BobT]

In the grand scheme of things, using the charging system of your outboard to recharge the trolling motor battery does very little. Using the charging system in this way is not what it was designed for and it will have an affect on the life of the charging system. Maybe it won't matter that much in the time you own the outboard, maybe it will but with so little to gain it might not be worth it in the long haul.

At idle the output from the charging system is not likely to be enough to recharge much if anything at all so idling for 8 hours or 8 days may not matter.

Here's something else to consider. If you have your starting battery connected in parallel with your trolling motor battery, your trolling motor is drawing power from your starting battery. After a few hours of use, you could find yourself unable to start your outboard because that battery has been cycled too deep.

For me, its not worth it.

[delcecchi]

If one were to want to charge trolling battery from outboard, one could install a device made for that purpose that controls the flow of current. For example, consider "Minn Kota® On-Board DC Alternator Charger"

[TruthWalleyes]

I don't have all 3 in parallel so they can all be charged, it is to have more capacity available for my accessories on long trips.

I could care less if the motor charges then or not. Just wanted to make sure like the op that it wouldn't cause damage