Hitachi alternator question

[Captain Bill]

I'm in the middle of moving my house bank to LiFePO4 and leaving my start bank as AGM. I have completed the isolation of my start bank from the house bank or at least I think I have. Mainly this consisted of moving my alternator outputs from the house bank to the start bank, removing the ACR and replacing it with a DC-DC charger. I started testing everything on the start bank side and noticed that the alternator outputs from my Yanmar 55A alternators were running at almost 14.6 volts. I've owned these things for 16 years and have never seen them above 14.2 when they were connected to the house bank. These are standard Hitachi alternators with their dumb regulators. Does anyone have any idea why they would now be putting out 14.6?

[Bill O]

Colder temps? In the winter (up north), my solar can hit 15.0 when its very cold out.

Is the 14.6 a true read out (amp meter at alt) or your panel reading of the battery bank?

[Captain Bill]

I've run these alternators in every temperature from 19F to 100f and have never seen the output vary more than .1V when the batteries were full. Of course the voltages were lower on depleted batteries. I'm in Florida and the temperature was 78f when I tested them yesterday. This was the panel voltage which is the same one I have always used so there has been no change there. The panel is connected to a rotary switch and can show voltages on the house bank or the start bank. I used this same switch/meter combination to check for proper functioning of my ACR and would see the same voltages on the house and start bank when the ACR was tripped. Of course these dumb regulators are operating at engine compartment temperatures when the engines have had time to warmup and they get much warmer than the 100F maximum ambient temperature I've ever seen in the boat.

[HeywoodJ]

Have you accounted for voltage drop? If the cables to the house batteries were a lot longer then voltage drop while charging could result in the alternator regulator "seeing" less voltage. If you now have short cables only within the engine room....

Same for possibly all connections getting cleaned up while re-configuring the system.

[Pete7]

Originally Posted by HeywoodJ

Have you accounted for voltage drop? If the cables to the house batteries were a lot longer then voltage drop while charging could result in the alternator regulator "seeing" less voltage. If you now have short cables only within the engine room....

Same for possibly all connections getting cleaned up while re-configuring the system.

Agreed, makes a huge difference, also the alternator may not be working so hard charging just the engine start AGM and a limited amount of power for the DC>DC charger so running cooler.

Bill, good idea to move the house bank though, no battery likes heat although difficult to move the engine battery and keep the wiring short. We have also left the AGM start in the engine bay and accept a slightly shorter life. That said, its only one battery and if it lasts 5 years well that's okay.

Pete

[Captain Bill]

Actually the run to the start bank is longer than the run to the house bank and the voltage sense wires are connected to the battery posts. If anything I would have expected to see a slightly lower voltage. The start bank is for all practical purposes at 100% so I would not expect to see any voltage drop at all since almost no current is flowing.

[Bill O]

Maybe I missed this part, did you recently move all the batteries out of the engine room and now seeing the higher voltage? If so, would think seeing a higher V would be normal w/the volt sensor/batteries now at a much lower temp.

Do you know which internal regulator (voltage) you have in your Hitachi? Maybe need to take it apart to confirm which one is in there. Had the same alternator in another boat and changed it over to a heavy duty external regulator from a Lincoln Continental. Wasn't as dumb then.

14.6 should be fine for the AGMs.

[Captain Bill]

Originally Posted by Bill O

Maybe I missed this part, did you recently move all the batteries out of the engine room and now seeing the higher voltage? If so, would think seeing a higher V would be normal w/the volt sensor/batteries now at a much lower temp.

Do you know which internal regulator (voltage) you have in your Hitachi? Maybe need to take it apart to confirm which one is in there. Had the same alternator in another boat and changed it over to a heavy duty external regulator from a Lincoln Continental. Wasn't as dumb then.

14.6 should be fine for the AGMs.

The AGM's (start Batteries)have not moved, they are still in the engine rooms. The house bank is not in the engine rooms.



The Hitachi alternators are the same ones I have always had. I did have them rebuilt about 8 years ago but they acted exactly like they did before the rebuild. So even if the rebuilder had changed something, I have an 8 year history of them putting out 14.2V. I don't know which model regulators are actually in the alternators.



I simply moved the alternator outputs from directly charging the house bank to directly charging the start bank. Previously the start bank was charged only through an ACR. Because I am moving the house bank to LiFePO4 I did not want the alternators with their dumb regulators charging the LiFePO4 and decided to have them charge the start bank only(which remains AGM) and use a DC-DC charger to charge the LiFePO4 bank from the alternators. Solar is my primary method of charging the house bank when off the dock, backed up by a genset and Inverter/charger if needed. The purpose of the dc-dc charger is only to carry house loads when motoring at night. If somehow I should badly deplete the start bank, It would seem that all I have to do is reverse the input and output leads to the DC-DC charger and I could let the solar/LiFePO4 bank put some charge in the start bank.