DC to DC charger size

[Stu Jackson]

But the Hitachi will sort of let you know if it’s getting too hot by how low its’ output voltage gets.

Here's why:

Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. Any battery at any state of charge simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

http://forums.sbo.sailboatowners.com/showthread.php?t=125392

and these, too:

Hitachi Alternator and Smart Regulator Instal Question - Cruisers & Sailing Forums

Most practical way to upgrade Yanmar alternator? - Cruisers & Sailing Forums

 

[Davidasailor26]

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

All true, but if I remember right the guidance is generally from the era of lead batteries being charged either directly from alternators or through ACR’s. A lithium battery being charged by a DC-DC charger doesn’t care at all about the alternator’s output voltage. If the DC-DC is set to 40A and the alternator can push that much current in the low 13 volt range without overheating that’s fine for the batteries. You won’t get the charging as fast as a higher output better regulated alternator, but it won’t damage the lithium sitting longer at a low PSOC like lead.

 

[Johann]

Here's why:

Hitachi/Yanmar Alternators: (by Maine Sail)
…

Yes those are great articles, and the Hitachi is a super dumb way to charge a lead house bank. But charging LFP through a smart DC-DC the Hitachi does a pretty good job. It will put out 40A all day and the DC-DC will make sure the LFP gets the right charging profile. If you wanted to push it higher (with the 50A XS) you could set an input voltage lockout so if the Hitachi dropped below say 13.5V the Orion would stop charging. Since the Hitachi output is also going to the start AGM there is no risk of a damaging voltage spike.