MPPT regulator connected to alternator?

[Isola]

Hi,

I bought a Bavaria Ocean 40 last year and I’m going to equip it with LifePo4 domestic batteries, and five 100W solar panels to keep them charged. The charge will be regulated with a Victron SmartSolar MPPT 100/30 regulator, and I wonder if this unit also could solve another problem? The MD22 engine has a traditional alternator that I believe can deliver 70 A. Initially, I planned to get an isolated DC to DC charger and let the engine battery charge the lithium batteries – but couldn’t the MPPT regulator be used instead?

I’m planning to use a relay to switch between solar power and alternator power for the regulator. When the engine is turned off the solar panels are charging and when it’s on the alternator is charging. This way I can charge the lithium batteries exactly the way they should be charged and at the same time I will limit the current from the alternator so it won’t burn up from overheating. The alternator will always be connected to the AGM engine battery so it can’t be destroyed if the regulator shuts off.

The only disadvantage I can see is that I wont be able to use both the alternator and the solar panels to charge at the same time …

Anyone out there with some skills?

[tiger79]

I bought a Bavaria Ocean 40 last year and I’m going to equip it with LifePo4 domestic batteries, and five 100W solar panels to keep them charged. The charge will be regulated with a Victron SmartSolar MPPT 100/30 regulator, and I wonder if this unit also could solve another problem? The MD22 engine has a traditional alternator that I believe can deliver 70 A. Initially, I planned to get an isolated DC to DC charger and let the engine battery charge the lithium batteries – but couldn’t the MPPT regulator be used instead?

You have an MPPT controller which can handle 30A max, and you're planning to connect your 70A max alternator to it?

[Isola]

That's not a problem. You can connect a 200 A alternator to a smal lightbulb without any problems – that's how electricity works ... 30 A is how much the regulator can deliver, not how much it can be connected to.

[elias]

I would suggest motor battery only be charged by alternator , nothing else . I think is safer to be isolated. The service battery can be connected parralel to alternator and solar charger . My only concern is I don’t have any knowledge if the lithium batteries can charge directly from the alternator . The solar charger is for solar power I guess not mess with alternator

[tiger79]

That's not a problem. You can connect a 200 A alternator to a smal lightbulb without any problems – that's how electricity works ... 30 A is how much the regulator can deliver, not how much it can be connected to.

If that's true, and I don't know whether it is, why would you want to restrict the ability of your alternator to recharge your batteries?

[Isola]

If you look att my electrical drawing you will see that the solar panels can only charge the domestic battery. The batteries are totally isolated from each other, both by the relay and the battery separator. If you charge the 540 A lithium batteries I will have the alternator will burn up since the batteries will absorb all it can deliver. It's simply not made for it. And when the lithium batteries are fully charged the BSM will shut them off with the result that the alternator doesn't have any load, and that will also kill it. So the current must be regulated, otherwise it overheats, and it must always have a load (that's why the engine battery is connected the way it is. The solar regulator doesn't care where the electricity come from – as long as it isn't more than 100 volt. The beauty of a MPPT regulator is that it transform any voltage to whatever is best for the batteries.

[Isola]

Tiger 79, look at it this way – do you dare charging your electrical toothbrush at home with 220 volt and a 10 A fuse? The reason I want to limit the current to the batteries is to protect the alternator – see my previous post.

[tiger79]

Tiger 79, look at it this way – do you dare charging your electrical toothbrush at home with 220 volt and a 10 A fuse? The reason I want to limit the current to the batteries is to protect the alternator – see my previous post.

That's not an appropriate analogy.

I think you need to ask a marine electrician for advice.  Your diagram shows a "battery separator" but it's unclear whether it's correctly wired.  If it is correctly wired, then your alternator will always have the load of the start battery, so it'll never be in danger.

[Isola]

Well, I'm actually educated in this field ... I'm just wondering if there is anyone out there who have more knowledge and experience regarding lithium batteries, and have used MPPT regulators this way?

[Markus]

I think this looks like a brilliant approach to efficient charging with minimal equipment. The only thing in my mind is to double-check how the Victron MPPT algorithm work and to make sure it does not cause anything unwanted with the alternator. I think you could also send your query to Victron to check what they have to say.

Perhaps it would make sense to add a cheap manual switch to by-pass the victron (from alternator to house bank) so in case of it's failure you can still charge without re-wiring.

[elias]

If you look att my electrical drawing you will see that the solar panels can only charge the domestic battery. The batteries are totally isolated from each other, both by the relay and the battery separator. If you charge the 540 A lithium batteries I will have the alternator will burn up since the batteries will absorb all it can deliver. It's simply not made for it. And when the lithium batteries are fully charged the BSM will shut them off with the result that the alternator doesn't have any load, and that will also kill it. So the current must be regulated, otherwise it overheats, and it must always have a load (that's why the engine battery is connected the way it is. The solar regulator doesn't care where the electricity come from – as long as it isn't more than 100 volt. The beauty of a MPPT regulator is that it transform any voltage to whatever is best for the batteries.

Sorry i was checking it from my mobile and i didnt see the diagramm well. As about the alternator burning i think professional advice should be asked. In my mind i have this, when i use my anchor windlass it uses around 90-100 amps i guess (1200w/12.5V ), with my engine on so alternator on around 1500 revs. So this load stresses the batteries and the alternator that are cooperating . I m not sure in your case that the alternator will burn out, maybe it just wont be enough?Actually pv array and alternator will share the demand, so if you have certaintity that the MPPT can hadle any current given and limit it to 30amps, there is no need for that relay ?

[Yngmar]

Well, I'm actually educated in this field ... I'm just wondering if there is anyone out there who have more knowledge and experience regarding lithium batteries, and have used MPPT regulators this way?

It won't work, because if you read the fine print of your MPPT regulator, you will find that it needs an input voltage 5V above the battery voltage to begin charging. Your alternator is unlikely to deliver this. You could switch to a 24V alternator, but then you can no longer charge the 12V starter battery from that directly or use a battery bridge switch, so I wouldn't recommend that either.

What you actually want for this job is an A2B (alternator to battery) charger, which will buck/boost as needed. Sterling makes one that supports LiFePO4 batteries (leaving temperature control to the battery BMS). Or just generate AC (something like the Integrel things) and use your shorepower charger if you don't want to fit another box. That's a pretty cool solution, at least until you look at the Integrel pricing

https://integrelsolutions.com/estimator/

[semaphore]

Yeah, I don't follow why you'd want to disconnect your solar panels.

I would put an automatic charge relay ACR, between the two batteries.
And use an alternator with an external regulator which is Lithium aware.