Sorry - Another Hitachi Alternator Question

[Rick486]

I have read all the existing Hitachi alternator threads looking for this answer and I couldn't find it so I'd appreciate if a knowledgeable person could help me with this.

I have a Yanmar 4JH4E with a Hitachi 80 amp alternator. After a friend of mine with the same engine installed a new identical alternator, I was prompted to look into the Hitachi and this question came up.

In motoring yesterday for 4 hours I was watching the voltage readings on my house bank (3 6D Gels) and my start bank (1 Group 34 Gel). The voltage on the start bank was a consistent 14.2 V and the voltage on the house bank was a consistent 13.4 Volts. These were read from a calibrated analog VM. I've read the posts so I expected both readings to be 13.4 Volts. I have a generator and use it when on the hook so this issue has never really come up before as I use the generator to manage the house bank. I'd appreciate anyone helping me understand the difference in charging voltages. How can the start bank see 14.2 V and the house bank see 13.4 Volts from the same Hitachi alternator? Also, I didn't notice any voltage drop when the engine came up to temp and stayed there for almost 4 hours??
Thanks
Rick

 

[Stu Jackson]

How is your reserve bank wired into the Alternator Output?

 

[Rich Stidger]

If the Hitachi alternator has an internal regulator like I think it does, it is probably regulating the alternator terminal output at 14.2V. I also imagine that your starting battery is much closer to the alternator than the house bank. Since the house bank is certainly drawing more recharge current, there is a greater voltage drop in the wiring to the house bank. Additionally, the house bank may be connected through a relay that routes charge current to the house when the engine is running but disconnects the house when the engine is at rest. Any of these conditions can easily account for the 0.8V difference.

 

[Maine Sail]

This is really not a Hitachi alternator question but rather a question of how the battery charging circuit is physically wired. Many Hunters did feed the start battery first which is a bass ackwards way of doing it. Only you can determine wire gauges, circuit path to house bank from alt & whether you have a diode isolator, ACR, key on excited el-cheapo relay etc. etc.. ...

 

[Miles Hutchinson]

Could you please explain more fully:
"Many Hunters did feed the start battery first which is a bass ackwards way of doing it."?

 

[DaveJ]

Depending on how the system is wired, the ~.7V difference could be due to the diode isolator (if you have one).

 

[Davidasailor26]

+1 for what DaveJ said. What Maine Sail means is that the starting battery really has very low charging needs, so it should not be the priority of the charging system. Ideally the engine should charge the house bank directly, and then charge the start bank through an echo charger or voltage drop free combiner. You probably have the order of charging backwards and the old style diode isolator is causing the voltage drop. That's a very inefficient way to charge the house bank and will probably shorten its lifetime.

 

[Rick486]

Thanks all for your ideas. Seems like what I need to do is dig out the schematics and study how my system is wired. I would imagine any Hunter owners may be interested this as well. Might want to check your house and start charge voltages under way.
Thanks again
Rick

 

[Rick486]

Well, first thanks for the help guys.
I went to the schematic and it appears as suggested above that the charging voltage from the alternator goes directly to the Start bank and then in parallel to the House bank except that it goes through the combiner solenoid. So the two banks are in parallel except the solenoid is in series with the House bank on that leg. The combiner solenoid is normally open but closes when the engine panel key is in the "on" position, presumably to use the full voltage of the combined banks. The schematic notes that the "Alternator charges back through the starter", which I imagine means that the output of the alternator goes directly to the positive pole on the starter and back through a heavy gauge wire to the barrel switches. So the charge voltage drop to the house bank is probably due to the presence of the combiner solenoid, as suggested by Rich and Main above.
Now for solutions:
1. Leave it alone. Has worked fine for 10 years.
2. It could be as simple as reversing the leads on the combiner solenoid such that the house bank is on the upstream side of the combiner and thus places the combiner on the Start bank leg of the charging circuit. Why do this? Well, we do motor a lot and it may save on generator hours as the House bank should be charged up after a few hours of motoring.
3. Look for others?
Thoughts?
Thanks
Rick

 

[Maine Sail]

Well, first thanks for the help guys.
I went to the schematic and it appears as suggested above that the charging voltage from the alternator goes directly to the Start bank and then in parallel to the House bank except that it goes through the combiner solenoid. So the two banks are in parallel except the solenoid is in series with the House bank on that leg. The combiner solenoid is normally open but closes when the engine panel key is in the "on" position, presumably to use the full voltage of the combined banks. The schematic notes that the "Alternator charges back through the starter", which I imagine means that the output of the alternator goes directly to the positive pole on the starter and back through a heavy gauge wire to the barrel switches. So the charge voltage drop to the house bank is probably due to the presence of the combiner solenoid, as suggested by Rich and Main above.
Now for solutions:
1. Leave it alone. Has worked fine for 10 years.
2. It could be as simple as reversing the leads on the combiner solenoid such that the house bank is on the downstream side of the combiner and thus places the combiner on the Start bank leg of the charging circuit. Why do this? Well, we do motor a lot and it may save on generator hours as the House bank should be charged up after a few hours of motoring.
3. Look for others?
Thoughts?
Thanks
Rick

#1 Get rid of the key activated solenoid/relay. It is not built for that duty cycle to begin with.

#2 Route alt power to house bank, or it's very close by house bank positive busbar, using sufficient sized positive and negative wire plus a fuse within 7" of the bank at 150% of alternator output rating.

#3 Install a real combiner or voltage sensing relay (VSR) such as a Blue Sea ACR (120SI / 7610 model) or an Echo Charger or other DC to DC charger such as a Sterling battery to battery charger to charge the start bank. In theory a solenoid should have zero volt drop but the contacts are likely burned and it's now creating a high resistance spot and dropping voltage because it was never really intended for that type of work...