Yanmar/Hitachi alternator with battery isolator?

My boat has twin Yanmar diesels. Each engine has a stock Yanmar/Hitachi alternator connected to a start battery and a house battery via a Sure Power multi-battery isolator. I discovered this week that the starboard alternator was not charging its batteries.

1. All connections are clean, tight and correct.

2. The alternator is receiving 12.5 volts from the start switch.

3. The isolator passed all the manufacturer's tests (multimeter on diode setting) with flying colors.

4. I removed the isolator and connected the alternator directly to the start battery. No charge - multimeter reads 12.5 volts across battery terminals with engine at 1,500 rpm.

Subsequent Googling suggests that Hitachi alternators with internal voltage sensing do not work with Sure Power battery isolators. For an alternator to work, it needs a separate battery sensor wire that connects directly to the battery.

I suspect that the alternator never did charge its batteries and that I have been living in blissful ignorance of this because the other charging systems (solar, s/power etc) take care of battery drain. I shall be investigating the port engine this weekend and expect to find the same thing.

Does my assessment make sense?

Did the isolator cause the alternator to fail - like reportedly happens if you disconnect battery from alternator while engine is running?

Mike
I chased a similar charge system problem on my Mainship and finally rewired it.
Here's a link to my post re: Charging System Mods & website w/ a summary of what I did.

I purchased the MS and suspect the boat never charged - owner only ran a few hrs on a small lake and didn't anchor out - shore charger recovered the batt'ys when returned to dock.

Diode isolators are a problem and I took the isolator out and connected Alt output directly to start batt'y (via starter wire in my case) and still no output.
Removed alt & had an auto electrical shop test it - they found the alt OK w/ good 14.2V output starting to put out at approx 800-900 RPM's
He told me the Hitachi's won't work w/ diode isolators (others have also confirmed this) and that you need 3 good connections to make the Hitachi work - Batt'y +, Good Ground and 12V "ignition" to either the R or L terminal - I forget which - it's one of the small wire terminals at 90 degrees.

When I checked my wiring I was not getting the 12V ignition which energize the rotor until the alt output & V Reg takes over.
I traced my wiring and found it was connected incorrectly through an eng rm fire system controller - after correcting this connection my alt worked fine.

Diode isolators have an inherent voltage drop at reduce the effectiveness of the charging... best to remove them - you may want to consider something like the ProMariner ProIsoCharge Controllers - or

Sterling ProSplit R

both are available for several multi eng & batt'y bank configurations - other TFers have reported good luck w/ them - my situation was a little tricky and I chose the Sterling CVSR per my linked write-up.

The Sailing Today article on my website is also available for download in the TF Library - Misc section - pretty good review of the options available to replace diode isolators

I have wiring diagrams for the Hitachi Alt / Reg that explains how they work if you are interested.

I'd suggest:

1. Making sure you have direct 12V batt'y connection to the Bat Terminal - Good Ground and do have 12V to either the Ror L terminal
2. If still no output - remove alt & have an auto elec shop test it - possible one or more of the internal diodes are not working properly
3. Consider one of the alternative combiners / charge controllers to replace the diode isolator

Let me know if the Hitachi schematic would be of help I can post or email it

I too have read that you should not use a Hitachi or similar alternators with a battery isolator. But I don't think it is because they won't work. They will work, but because the isolator causes a half volt or so voltage drop, the battery is always seeing a half volt less than the alternator puts out. With a half a volt less, the battery will charge very slowly.


But that is just a digression, because your alternator is not putting out anything when directly connected to the battery. Do a couple of checks. Is the voltage from the key switch, 12.5 at the alternator terminals. That indicates the alternator is turned on and getting field current (if it is not otherwise bad). If it is not getting 12.5 then there is something wrong with that circuit to the key switch.


The diodes could be blown or the regulator is toast or a coil is fried. Take it to an automotive electric shop and they can quickly check it out and maybe rebuild it. I doubt seriously if the isolator caused it to fail.


So, unless you need lots of amphours to recharge house batteries after on the hook use, this is what I would do. Replace each of the isolators with a battery combiner or ACR. Yandina (yandina.com) makes their Combiner 100 which is on sale (always) for $65 each. You will need two for the port and starboard engines. These have no voltage drop so that the battery will see the full alternator output voltage.


Rebuild the bad alternator and switch to a couple of combiners and you should be fine.


David

djmarchand said:

I too have read that you should not use a Hitachi or similar alternators with a battery isolator. But I don't think it is because they won't work. They will work, but because the isolator causes a half volt or so voltage drop, the battery is always seeing a half volt less than the alternator puts out. With a half a volt less, the battery will charge very slowly....

David

Click to expand...

David...
I wonder why SurePower and others would single out Hitachi (and few others) to recommend against using diode isolators.
Are they the only internally regulated alts that you can't adjust regulators?
I've looked at the schematics and can't figure why it shouldn't work???

Don:


I don't know. Maybe they single out Hitachi because it is the most popular marine alternator that has no external voltage sense connection to the regulator. I think all Delcos have one.


David

Thanks David and Don for your swift and insightful responses.

As noted, the starboard alternator is getting 12.5 volts from the key switch. Everything is as it should be except that it isn't charging. That unit is confirmed defective and has to go visit the alternator shop.

I ran the port engine today with the port isolator still in the circuit:

Voltage across battery posts - engine OFF 12.5 volts
Voltage across battery posts - engine ON 13.6 volts

Then with isolator removed:
Voltage across battery posts - engine OFF 12.5 volts
Voltage across battery posts - engine ON 14.0 volts

So the isolator does work after a fashion with this type of alternator, but the voltage drop will make for slow charging and no adjustment is possible.

The port alternator is not damaged, so it would appear that the isolator did not cause the other alternator to fail. I wonder what did.

I shall now investigate battery combiners.


BTW: Thanks for the offer of the Hitachi schematic Don, but I already have one in the Yanmar service manual.

Shoalwaters said:

I shall now investigate battery combiners.
.

Click to expand...

Thanks for the update.
The Sailing Today article is a worthwhile start. Some good write-ups here on TF as well.