alternator question

[supersteve2181]

i have recently purchased my first boat,,but i have noticed that after each outing i need to put my battery on charge,do johnson outboards (model n.o bj90tlcos) its a v4 90hp have alternators?
the battery i have has been checked and is mine,,its a exide maxxima 900dc deep cycle battery,is this battery powerfull enough for my engine,,im scared to switch the engine off when im on the water incase it doesnt start again,,also the previous owner had recently had an "engine overheat alarm" installed on the boat,,i have no idea how much battery that will be wasting,but i dont want to disable it as knowing my luck as soon as i did the thing will overheat!!

cheers
steve

 

[jtexas]

Re: alternator question

What's the CCA of your exide battery?

Yes you have an alternator.
How to tell if the charging system is working:
1. It probably isn't if the battery needs charging after every outing.
2. Measure the battery voltage with the engine off (fully charged battery is at least 12.65 volts). Then measure it with the engine running at a fast idle, should be higher. If it's not, then replace the rectifier.

This "overheat alarm"...it's some kind of aftermarket device? Shouldn't affect the battery at all. Anyway the engine comes with a factory overtemp horn already.

 

[supersteve2181]

Re: alternator question

its says on the battery that the cca is 750a-900a

thanks

 

[F_R]

Re: alternator question

The battery should be adequate. As previously stated, check the voltage at the battery, then after it has run awhile. Should go up to around 14.5 volts or so if the alternator is working. But also consider a possible short circuit somewhere that is draining the battery faster than the alternator can recharge it. But my money is on a bad rectifier. Rectifiers can be blown by loose or dirty battery terminals, disconnecting the battery while the engine is running, or connecting the battery backwards. Even for an instant in any of these cases will blow it.