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Battery charging question

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doehunter

New member
I have a BF8A.
It has an alternator/generator output plug on it, that I have never hooked up.
My motor is on a 26 ft sailboat, and I plan on doing some camping trips on it, so I need to be able to charge my batteries.
I have a big trolling motor battery that I use for lights, stereo, GPS, etc.
Can I just connect the motor charging output to my battery? Does it regulate the charge current? Is there any chance it will over charge my battery?
I also plan on adding a smallish solar panel (5 watt) that is sold as a trickle charger. It supposed to have built in overcharge protection.
If I have the solar panel hooked up in parallel, will it damage my motor's charging circuit?
Jim
 
Most of the 8A's have a regulator/rectifier. It depends on your serial number. The first of the 8A's only have a rectifier. If you lift your hood and see in the front of the engine, the charge wires leading to a square piece (about an inch or so square) that looks like it has several layers with air spacing. Then it has only a rectifier and it will not regulate the charging and can overcharge your battery. If you have a large battery, you will probably have to run the engine a long time to overcharge, since the charging amperage is still pretty low.

It can put out up to 5 amps. However, the motor has to be running at about 6000 rpms. At a normal cruising speed, it will probably put out about 2 to 3 amps.

It normally is not a good idea to connect two charging systems to the same battery. Your 5 watt solar cell is only putting out about 0.4 of an amp. Most likely they will not harm each other. However, to be absolutely safe, you could always connect each one through one switch. It could be a double pole double throw. That way, only one is connected at any one time. That switch can be a simple panel switch. You do not need a huge battery switch. Just find one rated at 10 to 15 amps. It should only be a few bucks.

If you want to connect both of them for a combined charging, then you could connect each of the positive sides to the battery through a diode. Radio Shack has a diode that would work. They come in a set of four. http://www.radioshack.com/product/index.jsp?productId=2062591. The diodes would isolate each charging system from the other.

I think the best is the switch.

Mike
 
Thanks for the info. It almost sounds like I wasted my money on the solar panel. In the box, they label it as a trickle charge. .4 amp is a pretty small trickle!
I never run the motor wide open for more than a minute or so. I usually run about half throttle getting in and out of the bay, so it's really 10 or 15 minutes at a time really unless I have to go straight up wind which is rare.
It might not be worth bothering with wiring in the motor. I have been charging with a 6 amp AC charger, and it takes overnight. Longer if the battery was real low. I don't see myself running the motor wide open for 8 hours at a time! I guess I can see now why all the sailboaters, have those huge solar panels, and wind generators. HMMM.
Today I'll try to check the amperage output on me solar. It sounds like it;s low enough I could check it through a multimeter. I hope it's higher than .4!
See Ya!
 
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Unfortunately, 5 watts divided by 12v equals .4166 amps. Using the formula watts = current x voltage.

Even though your charging will be limited, it would be better than nothing at all. If you get in a pinch and the battery dies, the motor should give it enough charge to at least run the nav lights if your battery dies at night.

Mike
 
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