Why oh why do these things happen????
I just spent a couple of hours this morning working on a relatively new mid to high $$$ six figure custom Down East style boat.
The complaint, chronically low batteries. Now keep in mind this is a power boat with a MASSIVE Cummins and a MASSIVE 200A J mount alternator and external regulator. It also has over 1000Ah's of AGM batteries on board. Sounds good, right....?
So, the batteries were at 12.2V when I got there and I went through the usual trouble shooting, checking how the system was wired and then testing for any parasitic loads. The parasitic load when the battery switch was turned on was 0.12A and when OFF was 0.008A or near perfect.. Because this is a very expensive and well built boat all the wires from the regulator and any other device immediatly disapear into wire loom. The factory wiring work was very good. It is how it was wired where the issue arose.
So we get to the part where we fire up the motor to test alt output. I have a Fluke clamp meter on the + wire to the house bank and a Fluke DVM measuring terminal on the house bank of batteries, 750Ah of AGM's. Within a few seconds of the regulator coming on we have 95A which then quickly falls to 22A of accepted current.....
Why? Because the battery terminal voltage was 13.2V and what the regulator was seeing was 14.4V due to voltage drop in the system and where the voltage was being measured by the voltage regulator.. The regulator was in absorption mode and limiting the voltage to 14.4V yet at the batteries we were only really at 13.2V.
The B+/volt sense wire for the regulator was measuring the back of the alternator. The alt output wire was also far to small for this alt. On top of that the alt B+ / feed wire picked up a bank of engine management relays along the way, pre-heater, common rail system, fuel pumps etc. etc.. This was adding even more voltage drop to the alternator charging wire. The voltage regulator was simply sensing an incorrect voltage. It was measuring the voltage ahead of any voltage drop in the wiring and should have been measuring it after the voltage drop.. The alt output did go straight to the house battery bank, but, due to poor wiring practices, it had loads pulled off it before it got there. A full face palm on this one.
I made some test jumpers and connected the regulators B+ and B- wires direct to the house battery bank. We then fired up the motor and the house bank was now taking 165A of current and was at 14.3V and climbing towards 14.4V. There is a HUGE difference in the current a battery can accept between 13.2V and 14.3V...
Multiple technicians had looked at this boat and found nothing wrong. All one had to do was put a meter on the battery bank and at the regulator to see where the problem was but no one had done so, of if they did this very simple issue still did not ring a bell.
Always measure your voltage at the regulator B+ / B- wire and then at the batteries. Low voltage at the batteries means CHRONIC undercharging no matter how big the battery bank or alternator is. Remember this was a 200A large frame alternator only capable of delivering about 22A at 13.2V yet it went right up to about 165A at 14.3V....
I will go back in a few weeks and run a 2/0 wire for the alt B+ & B- and permanently re-wire the regulator to properly senses the correct spot in the system to eliminate the charging voltage drops..
If you suspect you are not charging properly I would suggest first measuring the voltage directly at the back of the alternator and then directly at the battery posts. These voltages should be within 0.1V of each other...
I know I harp on this a lot but the vast majority of charging issues with alternators are due to voltage drop, low voltage or voltage sensing issues not necessarily what alternator or regulator you have....
I just spent a couple of hours this morning working on a relatively new mid to high $$$ six figure custom Down East style boat.
The complaint, chronically low batteries. Now keep in mind this is a power boat with a MASSIVE Cummins and a MASSIVE 200A J mount alternator and external regulator. It also has over 1000Ah's of AGM batteries on board. Sounds good, right....?
So, the batteries were at 12.2V when I got there and I went through the usual trouble shooting, checking how the system was wired and then testing for any parasitic loads. The parasitic load when the battery switch was turned on was 0.12A and when OFF was 0.008A or near perfect.. Because this is a very expensive and well built boat all the wires from the regulator and any other device immediatly disapear into wire loom. The factory wiring work was very good. It is how it was wired where the issue arose.
So we get to the part where we fire up the motor to test alt output. I have a Fluke clamp meter on the + wire to the house bank and a Fluke DVM measuring terminal on the house bank of batteries, 750Ah of AGM's. Within a few seconds of the regulator coming on we have 95A which then quickly falls to 22A of accepted current.....
Why? Because the battery terminal voltage was 13.2V and what the regulator was seeing was 14.4V due to voltage drop in the system and where the voltage was being measured by the voltage regulator.. The regulator was in absorption mode and limiting the voltage to 14.4V yet at the batteries we were only really at 13.2V.
The B+/volt sense wire for the regulator was measuring the back of the alternator. The alt output wire was also far to small for this alt. On top of that the alt B+ / feed wire picked up a bank of engine management relays along the way, pre-heater, common rail system, fuel pumps etc. etc.. This was adding even more voltage drop to the alternator charging wire. The voltage regulator was simply sensing an incorrect voltage. It was measuring the voltage ahead of any voltage drop in the wiring and should have been measuring it after the voltage drop.. The alt output did go straight to the house battery bank, but, due to poor wiring practices, it had loads pulled off it before it got there. A full face palm on this one.
I made some test jumpers and connected the regulators B+ and B- wires direct to the house battery bank. We then fired up the motor and the house bank was now taking 165A of current and was at 14.3V and climbing towards 14.4V. There is a HUGE difference in the current a battery can accept between 13.2V and 14.3V...
Multiple technicians had looked at this boat and found nothing wrong. All one had to do was put a meter on the battery bank and at the regulator to see where the problem was but no one had done so, of if they did this very simple issue still did not ring a bell.
Always measure your voltage at the regulator B+ / B- wire and then at the batteries. Low voltage at the batteries means CHRONIC undercharging no matter how big the battery bank or alternator is. Remember this was a 200A large frame alternator only capable of delivering about 22A at 13.2V yet it went right up to about 165A at 14.3V....
I will go back in a few weeks and run a 2/0 wire for the alt B+ & B- and permanently re-wire the regulator to properly senses the correct spot in the system to eliminate the charging voltage drops..
If you suspect you are not charging properly I would suggest first measuring the voltage directly at the back of the alternator and then directly at the battery posts. These voltages should be within 0.1V of each other...
I know I harp on this a lot but the vast majority of charging issues with alternators are due to voltage drop, low voltage or voltage sensing issues not necessarily what alternator or regulator you have....