Alternator output questions

[Dantodd]

I have a Hitachi 80A alternator on my Yanmar 4JH2E

At idle it puts out less than 5 amps and at cruise (2500) it only puts out about 25A.

This was measured via a BMV600 into a 675ah bank at ~50% SOC.

On the AC charger the bank was taking in a measured 43A from a 40A charger so I know the batteries were not the limiting factor.

I rarely ever run the engine over 2800. Is there anything I can/should do to get more from the alternator at cruise speed?

Thanks in advance.

 

[JohnShannon]

Check the output voltage of the alternator, if the voltage is OK (say 14.something), compare for example to the Vout of your AC charger. The the issue is most likely connection resistance, somewhere between the alternator and the battery you have a bad connection.

If the voltage is not OK then maybe a blown diode inside the alternator or a loose/slipping belt. Does this have external or internal regulation?

 

[Dantodd]

Internal regulation. I'll check the resistance between the output and the battery. I think the voltage was similar to the AC charger which was in the mod 13's IIRC. How do I check the diodes?

 

[Don12364]

You are probably only looking for another 0.2 volts at the battery so, at 25 amps you are looking to reduce the circuit resistance by 8 milliohms. This is normally beyond the capability of a normal meter to detect.
If the charger is on the same battery posts as the alternator (some batteries have wing nuts as well as lead posts) then it is not likely to be these.

If it has always been thus then perhaps the cabling was not upgraded when the 55 amp Hitachi was changed for an 80 amp version.

 

[Bill Roosa]

Internal regulators are auto regulators. they are designed under the assumption that the engine will always be on when you are in the car and the alternator will power ALL the electrical devices. they are not deep cycle battery charging devices. So they keep the voltage at 14.0 or less to keep from boiling the water out and killing the battery.
External regulators come in both flavors, deep cycle charging and auto.

 

[flynfol]

Removed.....in my haste didn't didn't see it was Maine's forum. Best reading in the entire SBO.

 

[Maine Sail]

I have a Hitachi 80A alternator on my Yanmar 4JH2E

At idle it puts out less than 5 amps and at cruise (2500) it only puts out about 25A.

This was measured via a BMV600 into a 675ah bank at ~50% SOC.

On the AC charger the bank was taking in a measured 43A from a 40A charger so I know the batteries were not the limiting factor.

I rarely ever run the engine over 2800. Is there anything I can/should do to get more from the alternator at cruise speed?

Thanks in advance.

Something is not right. The LR-180 is regulated to 14.5V +/- 0.3V. So at a minimum it should be putting out 14.2V. You could have voltage drop in the wiring, undersized wiring, a bad ground or other terminations that are bad. I really dislike case grounds and usually add an additional ground wire the same size as the + wire connected directly to the alt case and the batt - post or dist bus. You may also have a blown diode.

The LR-180 should easily be able to develop 60A at just 2000 alternator RPM. This means it can produce about 60A, at close to idle, with a 2:1 pulley ratio.

One thing to consider is that the LR-180 has built in temp compensation which is designed to be protective of the alt. It cuts the voltage, which in turn cuts the output when the alt gets too hot. Compare the output when the engine is cold and when it is hot. Also when you conduct these tests it is best to not have any other DC devices running and be charging just the one bank. It could also be a mis-wired shunt...

I am uploading a video of a 60A Hitachi pumping out about 47A at dead idle then up to 64+ amps when I bump the RPM. These alts are pretty decent units if wired appropriately and working as they should. The bank it was feeding was a 210 Ah bank of wet batteries and was right up against bank "acceptance" so it quickly settled back down from 64A to about 25% acceptance or 50A +/-..... But this is a 60A Hitachi pumping out 47A at idle and held at acceptance for a long while..... I will add the video when it is uploaded..

I'd take it to an alternator repair shop and have it tested something is clearly not working right....

 

[Bill Roosa]

could this be a measurment issue?
how confident are you that the BMV600 is accurate at high amp levels?
I'm thinking a quick voltage check at the battery terminals when charging would be helpfull in diagnosing the problem. Not the BMV600 readout but across the batts with a multimeter.

 

[Bill Roosa]

also repeat with the charger engaged for comparison.

 

[Dantodd]

OK, I suspect the alternator may need some real attention.

I'm pretty confident in the measurements I am taking.

The ALT is terminated to the battery side of the house bank's on/off switch. This is the same place that the AC charger/inverter terminates.

The shunt is installed between the DC common switch and the house bank. The starter battery is charged via an echo charger. The echo charger and the starter battery are both terminated on the load side of the shunt. The DC common switch has the house load on the switched side, the echo, AC charger, shunt, and starter battery lead on the unswitched side and the house bank negative on the "other" side of the shunt. The BMV is giving accurate V readings compared to my FLUKE DMM and the amperage readings are reasonable for the load, I've been messing about a bit with different loads just for fun and the monitor is showing draw measurements in line with expectations.

The test I did in the OP was with a stone cold engine in about 65* ambient so I doubt that is an issue.

I didn't head down to the boat today but tomorrow I'll go replace the alternator wiring. What gauge wire should I use? It is a 8-10 ft. run around the engine and to the terminator. Is 4 overkill or just about right?

 

[mitiempo]

4 is not overkill - it's too small. If you figure 20' total there and back and 80 amps @ 2% voltage drop calls for 1 awg. 15' there and back calls for 2 awg @ 2% drop. I would use 1 awg for the lowest drop even if it is not that far.

14.5 volts at the alternator less 2% gives you 14.2 volts at the battery.

You estimate of 8 - 10 feet - is that to the battery or the switch?

 

[Dantodd]

To the switch, from there it is a 5' run of 2/0

 

[Stu Jackson]

Please don't forget the (-) length.

 

[mitiempo]

Dan

How close is the house bank to the alternator?

It makes more sense to go from the alt to the house bank positive if it is closer than the run to the switch and then to the house bank.

And how close is the negative bus or the shunt to the alternator?

As it sits with almost 10' to the switch and then on to the batteries and likely a negative wire of the same length I would use 1 awg. I would still use a large wire but if you can create a shorter route it would be better.

If you had an external regulator with battery voltage sensing it would be less of an issue.

 

[Dantodd]

Direct run to the positive terminal would be about the same 5' as going to the switch so I'll just run direct. The negative run is about the same but running to the battery would defeat the shunt so I can't really run direct there.