Replacing generator with inverter on 330 Express

[Automated14]

I’d like to do this to my 330 but I want the AC to run off it. I’m thinking I need about 600 ah of batteries and a proper inverter/charger. I’d love to hear any input you guys may have on specifics like inverter size/model, etc

 

[everwhom]

I’d like to do this to my 330 but I want the AC to run off it. I’m thinking I need about 600 ah of batteries and a proper inverter/charger. I’d love to hear any input you guys may have on specifics like inverter size/model, etc

I tried running my AC off my setup and I was observing about 1100 watts steady state (as I recall). My 2000 watt Mastervolt inverter seemed to run it just fine. If you assume 90% efficiency then the actual DC amperage for 1100 watts should be about 100 amps. With my motors running they were supplying about 60 amps, so the battery draw is about 40 amps when the compressor is running.

 

[doug228]

I dont think this is an issue because Alternator output is still connected to the cranking batteries. Issues would occur if there was no place for the output to go.

The issues is the low resistance in the lithium battery will suck the current out of the alternator at a rate it cannot handle. DC to DC is a must for lithium unless you can install a different voltage regulator (inboards have this option)

 

[kees.barfield]

The issues is the low resistance in the lithium battery will suck the current out of the alternator at a rate it cannot handle. DC to DC is a must for lithium unless you can install a different voltage regulator (inboards have this option)

That makes no sense. The Lifepo battery isn't sucking the current. It is accepting the current. And doing it efficiently without resistance. It has been my understanding folks use DC/DC chargers in RV setups where the RV's alternator puts out a lot of current (i.e. one might be capable of 120amps) and the Lifepo battery can only be charged at 100amps. DC/DC charger would regulate that down to a level acceptable for the BMS.

 

[everwhom]

So I did a ton of research on this, and the issue is twofold: (1) some (but not all alternators) can burn out when supplying too much current. The issue is that they were designed to charge a lead-acid battery which will not accept the high level of current an lithium battery will. More sophisticated alternators don't have this problem however. (2) Lithium batteries typically come with a built-in battery management system which can instantly disconnect the battery in certain error conditions, such as overheating. Apparently the sudden disconnect of the load can also damage alternators.

For these reasons, both the battery manufacturers and inverter makers strongly recommend using a DC-DC charger in between an alternator and a lithium battery. I spoke directly to tech-support at Victron and they confirmed this recommendation.

But just to complicate matters further, some outboards, in particular Yamaha, do not use automotive-style alternators at all. On my motors (4.2L F250's), DC current is created by fixed magnets on the fly-wheel rotating past "lighting" coils. My understanding is that the Yamaha systems generating a constant amount of current depending on the RPM of the engine and they simply sink any unused current to ground through a water cooled shunt. So I don't believe there's anything that can be burned out. As for what can happen if the battery is suddenly disconnected, I'm a lot less certain. I'm definitely unwilling to risk damage to the engine, though, since I do some pretty far offshore trips and engine reliability is the most important thing to me.

 

[everwhom]

Minor Update: I rewired the system last season so that inverter/charger is no longer in-line with the shore power system. Instead it's output goes to where the generator output used to go (see diagram). The reason is that my particular unit had this annoying feature that even if the unit was on standby, as soon as AC power was available it turned itself on and if power then went out, it would begin inverting running down the battery bank. So if someone disconnected my shore power, I'd end up fully depleting the battery bank which would be bad for it.