Altenator upgrade

[CaptRich]

Hello, has anyone upgrade from the oem 55 amp to a higher out put 65 or 70 amp and how do you get from the 4 wire to two upgrade. 1996 23 sr , 5.7 l 260. the old one is not charging as it should. two batteries.

[shrew]

What size boat? I doubt you have enough load to need a higher amp alternator. If you want to charge the start and house bank while underway, install a BlueSea Automatic Charging Relay (ACR)

An ACR will draw from the start bank at start. Will draw from the house bank at rest, and will isolate the starting bank to protect it from being drawn down.

A higher amp alternator will introduce heat. If you have a large draw you'd be looking at an external charge controller.

Likely you're fine replacing the alternator with the same setup, using the internal charge controller on the alternator and installing a ACR if you want to charge the house and start bank while underway.

[CaptRich]

Thanks For the Info, its a 23 Sr , have ACR installed, just seems like a need a replacement because it does not look like its charging right, low amps at start up and not much better running at higher rpms, looking at a mando 65 amp replacment.

[shrew]

Don't read the amps. Read the voltage. Most alternators won't send a charge at idle. They usually need an increased RPM. The internal charge controller is likely dialing back as the battery reaches full. Are you getting 14+ volts with the engine rpm's increased?

[yahoo82]

Also keep in mind that a battery’s charging amps slows down as it approaches full capacity. I installed the victron battery monitor on my house bank (highly recommended!) and even when down to 50%, it was only charging at 14 amps max. Above 80% it was around 4-6A. These were also dual group 31’s so for a single battery it would be half the current. Lead acid battery chemistry just doesn’t charge quickly. Plus if you’re starting with full batteries, starting the motor isn’t going to drain much so you're still in the “slow charge” region. If my math is right, 600 cranking amps for 30 sec is like 5Ah … only like 5% or so of most starting batteries. If you really want to improve your power management in the boat, I would recommend a victron or equivalent battery monitor first, which will tell you a lot about what’s happening and what you could improve.

[shrew]

Originally Posted by yahoo82

Also keep in mind that a battery’s charging amps slows down as it approaches full capacity. I installed the victron battery monitor on my house bank (highly recommended!) and even when down to 50%, it was only charging at 14 amps max. Above 80% it was around 4-6A. These were also dual group 31’s so for a single battery it would be half the current. Lead acid battery chemistry just doesn’t charge quickly. Plus if you’re starting with full batteries, starting the motor isn’t going to drain much so you're still in the “slow charge” region. If my math is right, 600 cranking amps for 30 sec is like 5Ah … only like 5% or so of most starting batteries. If you really want to improve your power management in the boat, I would recommend a victron or equivalent battery monitor first, which will tell you a lot about what’s happening and what you could improve.

Agree 100%. Balmar is also nice. Victron and Balmar work on slightly different technologies so read both and decide.

For basic volt-meter analysis, first take a read on the battery voltage at rest. 12.8-12.9 will be Full. Then start the engine, and take another read. Now advance the throttle in neutral again and keep taking a read. Eventually, the alternator should jump in voltage. Anything above 13 would indicate a charge is being sent. 14.2-14.4 will be a full battery. Once completely full the voltage will drop. In my case it's around 13.6 for float.

If you're still reading 12.8 - 12.9 with increased RPM's then there is an issue with the either the alternator or the circuit from the exciter wire. You can read the input at the exciter wire to see if the battery is sending voltage to the alternator to being with.