Low voltage from alternator

[Hhew]

Need some opinions from the group. I recently upgraded house and start batteries from AGM to LFP. Volvo D2-55 in a Bene 42. In the old setup, alternator B+ went to a Surepower battery isolator, which then fed each battery bank with charging voltage. Alternator output was nominally something like 12.8V. In the new setup, I added a Victron Orion isolated DC-DC charger between the alternator and the Surepower isolator. Now, with the engine running, the alternator output at B+ is 9.0 V. The Orion seems to be taking this and turning it into ~14.8V and both banks appear to be charging, although they are both up around 100% so there is not a lot of charging demand. So questions:
1. Why is the alternator only putting out 9V?
2. Is alternator output dependent on charging demand? Ie if SOC is down around 50% and the charger was in bulk cycle, would I see 12.8V at the alternator?
3. Is this a problem?
4. Is the isolator creating a problem? Should I replace it with a simple bus bar?

[Kettlewell]

Not sure exactly what is going on, but you shouldn't need the Surepower isolator when using the Orion unit, which isolates the batteries.

[wholybee]

Originally Posted by Hhew

Need some opinions from the group. I recently upgraded house and start batteries from AGM to LFP. Volvo D2-55 in a Bene 42. In the old setup, alternator B+ went to a Surepower battery isolator, which then fed each battery bank with charging voltage. Alternator output was nominally something like 12.8V. In the new setup, I added a Victron Orion isolated DC-DC charger between the alternator and the Surepower isolator. Now, with the engine running, the alternator output at B+ is 9.0 V. The Orion seems to be taking this and turning it into ~14.8V and both banks appear to be charging, although they are both up around 100% so there is not a lot of charging demand. So questions:
1. Why is the alternator only putting out 9V?
2. Is alternator output dependent on charging demand? Ie if SOC is down around 50% and the charger was in bulk cycle, would I see 12.8V at the alternator?
3. Is this a problem?
4. Is the isolator creating a problem? Should I replace it with a simple bus bar?

Almost certainly what is going on is that the alternator has a voltage sense on the battery. The Orion is boosting the voltage to 14.8V, and the Orion is lowering its own voltage because that is higher than what it wants the battery to charge at.

The Orion needs to go between 2 batteries, to charge one battery from another. It doesn't go between an alternator and a battery. That doesn't allow the alternator to work properly(and is your problem). The normal setup (assuming the Orion is meant to protect the alternator from the LFP.) is for the alternator to be connected to an AGM , then an Orion between the AGM to the LFP, to charge the LFP. There is no reason to convert a start battery to LFP, AGM actually works better for that purpose. Perhaps the easiest fix is to put your AGM back in service as a start battery, and use your extra LFP to yield a larger house bank.

What kind of alternator do you have? Internal or External regulation? A quality alternator with external regulator can be connected to the LFP without a DCDC. You could then just go back to using the isolator and skip the Orion.

[Hhew]

Warren, the alternator is a new-ish Prestolite 70A with a V belt pulley. I’d rather not convert the engine to serpentine pulleys for a more powerful alternator. I’m also sticking with LFP for engine start. Would an external smart regulator like a Wakespeed WS500 work in between the alternator and the isolator/battery banks? And get rid of the Orion. The goal here is to provide proper charging profile while protecting the alternator from over-stress.
Harry

[wholybee]

If your alternator will work with a Wakespeed, then yes, and that is why I was asking the question about what you have. The wakespeed will provide the correct profile, and will use a temp sensor to protect the alternator and dial it back and keep it within safe operating temperature. Then get rid of the Orion.