Hitachi alternator no output

[SailBelladonna]

Originally Posted by Wotname

Let us know if you can find a diode and if it works out OK - otherwise we are back to the drawing board.

I am very pleased to say the diode worked perfectly. The buzzer is now off and the alternator is working. A big thank you for all your help. Hopefully this will also help others with Yanmar engines who upgrade to LifePo4 and remove the split charge diode.

[SailBelladonna]

Originally Posted by Flod

I had the exact same problem when switching to lifepo4 and removed the charge splitter. The alarm went crazy and the alt didn’t get ignited. I couldn’t figure out how to solve this so I put the charge splitter back and made it a part of the installation. Maybe not the most elegant solution but it works

Hopefully you are able to remove your split charge diode as well now by inserting a 1 Amp diode. Removing to split charge diode is helpful in 'simplifying' the design and removing points of failure.

[Wotname]

Originally Posted by SailBelladonna

I am very pleased to say the diode worked perfectly. The buzzer is now off and the alternator is working. A big thank you for all your help. Hopefully this will also help others with Yanmar engines who upgrade to LifePo4 and remove the split charge diode.

Great news for you, good outcome!

Just to clear though, removing the split charge diode wasn't your real problem.

So far all we have done is to come up with a work around to mask the real problem and keep your buzzer quiet unless there is a oil pressure or overheat issue.

Your real problem is the modified wiring harness and alternator (probable regulator modification). That is, the linked wiring between the L and B+ terminals along with the cut red/black wire on the I terminal.

As mentioned earlier, the is zero need for these harness modifications if the alternator / regulator is serviceable in the way Hitachi designed it.

I strongly believe the internal wiring in the alternator has been modified sometime in the past or something has failed internally and whatever that is, it was "fixed" by these harness modifications.

However it is a moot point as to whether you want to chase down the 'real' problem or not.

If you like, I can post the probable internal schematics of the alternator to demonstrate why I hold this viewpoint. But I understand you might be happy to leave sleeping dogs lie.

[SailBelladonna]

I would be delighted to have the probable internal schematics so I can do a proper fix when I take the alternators out again when we have good access to parts. French Polynesia isn't the best place to do lots of work!!

[Wotname]

Attached is a likely schematic for your Hitachi alternators. This is from a 2GM20/3GM30 Yanmar service manual for the Hitachi alternators fitted around the late 1990s through to early 2000s. Of course that is no guarantee yours is the same but it is likely to be.

First thing to note there are a couple of drafting issues marked up with red circles . There isn't a connection internally between BAT and R. If there was, the ignition switched would be shorted out. Likewise the other red circle is a capacitor between BAT and E. Such smoothing caps are caps are usual. I put the errors down to sloppy drafting.

I think R1 (green circle) is about 20 ohms and you should be able to measure this between the L and R terminals on the T shaped connector when the external wiring is disconnected.

You should be able to measure the field diodes D7 to D9 (yellow circle) from the both the L and R terminals to the E terminal via the diodes D4 to D6 (blue circle) and the stator coils.

As you probably know, one of the functions of the external charge light is to provide the initial field current when the alternator first spins up. The circuit is easily seen - battery positive, master and ignition switch, charge lamp, L terminal, rotor (field) coil, darlington pair in the regulator (conducting), E terminals and battery negative.

Once the alternator spins up to operating speed, the stator coils are producing AC voltage which is rectified by the field diodes D7 to D9. This produces about 12VDC at the L terminals (regulator and alternator) and thus the alternator remains self excited. The charge lamp now has 12VDC (+ve) on both sides of it and is thus extinguished.

I wonder why your harness was modified to provide 12VDC permanently on the L terminal rather than simply initially through the charge lamp. A WAG - the alternator did not remain self excited to a failure of one or more of the field diodes (D7 to D9, yellow circle).

Another WAG - there must be some modification inside the alternator to connect R to BAT internally in order for the regulator to sense correctly. Normally the sense circuit is the voltage divider resistors (R2 & R3) plus the Zenner diode ZD (pink circle). BTW, Rn is a thermistor which derates the alternator if (when) it gets too hot.

All the above is useless information if your Hitachi has a completely different internal regulator but nevertheless, the externals functions of the wiring harness should remain the same.

Do let us know what you find if you ever delve into the reasons for the harness mods.

[SailBelladonna]

I have been running the new wiring but the starter battery has died despite charging it every couple of days (not a concern since I was temporarily using old service batteries to start the engine). I bought a new battery and tested where the current was going. I measured 3 amps between the battery positive and the alternator. Disconnecting the "red" wire between "B" and "L" removed the drain.

So I tested the diodes thinking that they may be broken by disconnected all the wires from the alternator and measuring between "B" and "E" in diode test function. This gave 0.93v in one direction and overlimit in the other direction. This implies that the diodes D1 to D6 are working since the voltage is less than 2v?

I then tested from "E" to "L" which gave 0.576v in one direction and 0.857v in the other direction. I think this would imply the diodes D7 to D9 are faulty as per your analysis.

I have also done some tests as per your previous comments.

Originally Posted by Wotname

I think R1 (green circle) is about 20 ohms and you should be able to measure this between the L and R terminals on the T shaped connector when the external wiring is disconnected.

I measured 211 ohms with the external wiring disconnected.

Originally Posted by Wotname

You should be able to measure the field diodes D7 to D9 (yellow circle) from the both the L and R terminals to the E terminal via the diodes D4 to D6 (blue circle) and the stator coils.

2524 ohms between R and E
2304 ohms between L and E

Originally Posted by Wotname

I wonder why your harness was modified to provide 12VDC permanently on the L terminal rather than simply initially through the charge lamp. A WAG - the alternator did not remain self excited to a failure of one or more of the field diodes (D7 to D9, yellow circle).

It sounds like this "WAG" is correct. When we had a split charge diode installed it stopped the parasitic drain on the batteries AND stopped the flow through the yellow circuit you highlighted earlier causing the buzzer to go off (now surpressed with the 1amp diode).

Both engines have been modified. Could this be caused by the previous owner turning off the engine switches without stopping the engine? We now have alternator protection devices fitted which would presumably stop this issue.

I imagine the company I took the alternator to get repaired did not check the diodes. They said the regulator was faulty and needed replacing and the diodes were working.

[Wotname]

Originally Posted by SailBelladonna

I have been running the new wiring but the starter battery has died despite charging it every couple of days (not a concern since I was temporarily using old service batteries to start the engine). I bought a new battery and tested where the current was going. I measured 3 amps between the battery positive and the alternator. Disconnecting the "red" wire between "B" and "L" removed the drain.

So I tested the diodes thinking that they may be broken by disconnected all the wires from the alternator and measuring between "B" and "E" in diode test function. This gave 0.93v in one direction and overlimit in the other direction. This implies that the diodes D1 to D6 are working since the voltage is less than 2v?

^^ I agree.

I then tested from "E" to "L" which gave 0.576v in one direction and 0.857v in the other direction. I think this would imply the diodes D7 to D9 are faulty as per your analysis.
^^ On second thoughts, I believe I have lead you astray. After having a closer look at the circuit, I note the resistor voltage divider (R2 & R3) are in parallel with the field diodes D7 to D9. This makes it difficult to test D7 to D9 externally.


I have also done some tests as per your previous comments.


I measured 211 ohms with the external wiring disconnected.



2524 ohms between R and E
2304 ohms between L and E



It sounds like this "WAG" is correct. When we had a split charge diode installed it stopped the parasitic drain on the batteries AND stopped the flow through the yellow circuit you highlighted earlier causing the buzzer to go off (now surpressed with the 1amp diode).

Both engines have been modified. Could this be caused by the previous owner turning off the engine switches without stopping the engine? We now have alternator protection devices fitted which would presumably stop this issue.
^^ Possibly

I imagine the company I took the alternator to get repaired did not check the diodes. They said the regulator was faulty and needed replacing and the diodes were working.

The faults are intriguing to say the least. The fact the alternator does not work as intended by Yanmar strongly suggests there is an internal fault or a previous internal modification. Yanmar expects the charge light to be connected as well as the R terminal.

Perhaps a different internal regulator has been fitted sometime in the past and the local guy simply replaced it with a similar one. I guess the mystery will remain until the internals of the alternator can be 'forensically' analysed.

In order to stop the 24/7 3 amp drain, you could interrupt it with a switch or use the key switch so it is only connected when the engine is operating.

[SailBelladonna]

I think I may put the isolating diode back in between the alternator and battery and buy another one for £34 for the other engine. THe batteries won't fully charge, but we haven't used the alternators for 6 months now since we just turn the battery charger on from the LifePo4 (but having alternators gives us useful backup). Perhaps replacing the alternators when they need re-winding (replacements are so expensive out here).

Thank you so much for all your time and help.