How long will it take my outboard to charge my batteries?

[climb29028]

Hello everyone. I'm currently running dual batteries in my 16 foot fiberglass boat and wanted to know roughly how long it will take my outboard motor to charge the batteries while cruising. My outboard is a 2001 60 HP Yamaha four stroke. If I was cruising at approximately 3000rpm how fast does the motor charge the batteries? Any help would be greatly appreciated. Thanks.

 

[fhhuber]

Look up your engine's magneto output (amps) rating.

figure a typical marine "deep cycle/starting" dual use battery about 100 amp-hr. (or look on the battery label) divide battery capacity by the output and multiply by 2 to account for operating loads and losses in the process plus not operating at the magneto's best rpm. That should be a realistic estimate.

I would expect around 10 hr...
It might add enough for a restart to a battery that required you to jump-start the boat in 10 to 15 min, but I wouldn't count on it.

You don't have a high power alternator system expecting headlights, a bunch of fans and other loads as a typical car would have.
Your typical car alternator will charge the battery from needing to jump-start to full in about an hour if you are driving on the freeway and not using lights.

Your outboard has close to the surplus charge capacity of a large sized lawn tractor. If you have a lot of add-ons pulling electricity it may not keep up.

Best to keep the batteries on a float charger when the boat is parked.

 

[steelespike]

A trolling motor battery will require a shore charger to recover a days use.If I recall correctly 1 hour trolling requires 2 hours of charging at say 10 amps.
Trolling battery should be charged as soon as possible after use. A float charger is a great idea but will only keep a charged battery up.

 

[climb29028]

Thank you for the help, it was greatly appreciated. I don't have a lot of things drawing power in my boat, I basically just have a garmin chartplotter, vhf radio and depth sounder. I'll check my motors magneto rating and go from there. Thanks again !

 

[thumpar]

I wouldn't rely on an outboard to charge a battery. They are usually 6-10 amps total so you have to deduct the power for the ignition and devices onboard. That is why bass boats usually run a lot of batteries if they have a bigger trolling motor. The shore power charger is probably the best idea. If you need longer run times off the batteries just get more of them.

 

[H20Rat]

To add to all the above, if you are running a stator based system at 100% for too long, you will end up cooking something. They generally don't do well with lots of heat.

Some outboards have alternator kits that can be added, I know merc has them for various models, not sure of yamaha though.

 

[robert graham]

I generally remove my battery from the boat and put it on a slow charge(2 amps) overnight to sorta "top it off" before launching....full battery, full gas tank....and keep the kids/grandkids out of the boat, as they love to mess with accessory switches and leave a light or something on.....very dead battery in the morning!

 

[NYBo]

It won't take much time to make up for what was used to start the motor if the motor is in good shape and starts quickly.

 

[fhhuber]

Its all about input vs output...

If you are demanding more from the batteries than the motor's charging system is supplying... you'll never charge the batteries.

Modern fish finder with huge screen and back-light so you can see it with the sun directly on the screen and a few lights and a high power stereo... you can be WAY past demanding what the outboard is supplying.

Baseline I'd expect the nominal output of the magneto to be a bit more than double what the engine requires to run. That outboard doesn't need much to run.
Running your accessories and expecting the system to charge the batteries may be expecting too much. Turn all of the unnecessary stuff off and it will take a while to charge up from a near dead battery to full.

This is why they make the double and triple battery chargers for boats. The good ones will charge at a higher rate if they detect the battery is low and then go to float charge to maintain a full battery. Plug the boat in while its parked and the batteries will be full when you go out. (unless the battery is worn out...)
Even a low rate automotive float charger would EVENTUALLY charge up the battery... It might take a couple of weeks.

Since the electrical loads on our boats keep growing... I expect the engine makers to eventually put on a higher power magneto or alternator (especially the 100hp and larger engines)

Older engines... I don't expect them to do a lot more than keep up with the daytime operation loads. Add a couple of bright spotlights and you might be draining the battery while running at full speed.

 

[H20Rat]

Since the electrical loads on our boats keep growing... I expect the engine makers to eventually put on a higher power magneto or alternator (especially the 100hp and larger engines)

Most EFI 4 strokes have already started doing this, often with belt driven alternators. The computer(s), injectors, and high pressure fuel pump all take a fair amount of power, more than what a stator can easily deliver.