Best electrical design for solar and 115amp alternator

[seafox67]

Over the last few years I have been adding to my electrical system and this winter I want to review the layout and make sure that I have the best design.

Being a small boat, I'm using just three batteries... A starter, a AGM house and another battery up at the bow for my windlass.

With a recent new Volvo Penta engine I got included a 115 amp alternator which I would like to get the most charging power out of as possible.

I also have 180 watts of solar with a Victron bluetooth MPPT and a shore charger with two battery outputs.

After reading up on the internet, my feeling is keep the solar MPPT wired up to the house battery, Wire the alternator to just the starter and then put a Victron Orion dc to dc charger (I like that this also has bluetooth for a phone app) from the starter to the house battery. Finally keep the current VSR that connects the house to the windlass battery up at the bow. The shore power charge with two outputs would be connected to both the starter and house batteries.

I am hoping this design would get the most charge out of my 115amp alternator and solar.

Could anyone with a similar setup advise if I've thought this out correctly or even point to somewhere on web that shows a better solution.

Many thanks
Paul

 

[PaulRainbow]

Nothing wrong with your proposed arrangement. You should be aware that your alternator will never output the 115A max current, as the batteries should never accept that much current, no matter what you do.

As an alternative to the Orion, you could fit a 2nd VSR, which would allow the solar to keep the engine battery topped up, but, as i said, nothing wrong with using the Orion if you want.

 

[ghostlymoron]

I don't think you'll get the most out of your large alternator with that arrangement. If you connect it directly to the engine battery, it will be very lightly used. The engine battery uses say 200 amps but only for a few minutes each time you start. This is easily replenished in about 4x the start time. The rest of the time it'll be idling.
Mr Rainbow is the expert on this kind of thing I'm only an amateur.

 

[PaulRainbow]

I don't think you'll get the most out of your large alternator with that arrangement. If you connect it directly to the engine battery, it will be very lightly used. The engine battery uses say 200 amps but only for a few minutes each time you start. This is easily replenished in about 4x the start time. The rest of the time it'll be idling.
Mr Rainbow is the expert on this kind of thing I'm only an amateur.

The B2B charger will allow current from the engine battery to the domestic battery, which will close the VSR and allow current to flow to the bow battery. The limiting factor will be the amount of chare the batteries can accept. As you say, the engine battery will be charged pretty quickly, leaving just two batteries to charge, assuming 200AH or so between them, they won't accept anywhere near 115A, ever.

 

[seafox67]

Nothing wrong with your proposed arrangement. You should be aware that your alternator will never output the 115A max current, as the batteries should never accept that much current, no matter what you do.

As an alternative to the Orion, you could fit a 2nd VSR, which would allow the solar to keep the engine battery topped up, but, as i said, nothing wrong with using the Orion if you want.

Thanks for your quick response Paul... My thinking around buying the Orion was that the starter battery would be fully charged most of the time and so the battery charging management in the Orion would charge the house and windlass more efficiently than maybe the VSR option... However, this is my very amateur understanding! lol... If you think there would be no charging benefit using the Orion over a second VSR, The VSR is a cheaper option?

Also, I think the alternator that came with the Penta might be a 'smart'! Can this be effected by the solar MPPT or if the starter battery is fully charge (when the house battery may not be fully charged). The alternator is only connected to starter battery.

 

[PaulRainbow]

Thanks for your quick response Paul... My thinking around buying the Orion was that the starter battery would be fully charged most of the time and so the battery charging management in the Orion would charge the house and windlass more efficiently than maybe the VSR option... However, this is my very amateur understanding! lol... If you think there would be no charging benefit using the Orion over a second VSR, The VSR is a cheaper option?

I don't think there will be any measurable difference between the Orion and the VSR. Within a very short time both VSRs will close and all three batteries will be in parallel, each will accept a different charge current, depending on its state of charge. So, if the engine battery is fully charged (for instance) it will accept very little current, but a partially depleted domestic battery will take more current. If you wanted different charging regimes for the engine and domestic banks or you don't want the solar to charge the engine battery, the Orion is a better choice.

Also, I think the alternator that came with the Penta might be a 'smart'! Can this be effected by the solar MPPT or if the starter battery is fully charge (when the house battery may not be fully charged). The alternator is only connected to starter battery.

The alternator will sense the battery to which it is connected or the terminal voltage at the alternator B+ connection (depending where it's connected). As the batteries would all be in parallel, if using 2 VSRs, the battery voltages would quickly balance out.

The alternator will be affected by the solar controller, in varying degrees. When you arrive at the boat the batteries will all be fully charged, the alternator will sense this and ]the output will be limited. If you were sat at anchor for a few hours and partially depleted the domestic battery and the Sun was shining brightly, when you start the engine the alternator might see the solar controller voltage and behave as if the batteries were all charged, you'll need to keep an eye on this and see how it works for you, results can vary but are not usually a big issue.

A similar thing can happen when you connect to shore power. The solar controller can sense the mains charger, "think" the batteries are fully charged and put out little to no current.

 

[seafox67]

I don't think there will be any measurable difference between the Orion and the VSR. Within a very short time both VSRs will close and all three batteries will be in parallel, each will accept a different charge current, depending on its state of charge. So, if the engine battery is fully charged (for instance) it will accept very little current, but a partially depleted domestic battery will take more current. If you wanted different charging regimes for the engine and domestic banks or you don't want the solar to charge the engine battery, the Orion is a better choice.



The alternator will sense the battery to which it is connected or the terminal voltage at the alternator B+ connection (depending where it's connected). As the batteries would all be in parallel, if using 2 VSRs, the battery voltages would quickly balance out.

The alternator will be affected by the solar controller, in varying degrees. When you arrive at the boat the batteries will all be fully charged, the alternator will sense this and ]the output will be limited. If you were sat at anchor for a few hours and partially depleted the domestic battery and the Sun was shining brightly, when you start the engine the alternator might see the solar controller voltage and behave as if the batteries were all charged, you'll need to keep an eye on this and see how it works for you, results can vary but are not usually a big issue.

A similar thing can happen when you connect to shore power. The solar controller can sense the mains charger, "think" the batteries are fully charged and put out little to no current.

Thanks for the detailed feedback... very clear, cheers.
I think maybe using all VSR's sounds more simply and cost effective. The solar MPPT is bluetooth to an app which I think has an option to switch off the solar so I could use this if it does cause an issue during motoring or shore power connection.

Many thanks, Paul

 

[PaulRainbow]

Thanks for the detailed feedback... very clear, cheers.
I think maybe using all VSR's sounds more simply and cost effective. The solar MPPT is bluetooth to an app which I think has an option to switch off the solar so I could use this if it does cause an issue during motoring or shore power connection.

Many thanks, Paul

You're welcome. If it's a Victron controller it does have an option to turn the charging off. Unlikely to be a problem with shore power be a problem with shore power and likely OK with alternator charging too, just watch it a couple of times to make sure.

 

[Alex_Blackwood]

The B2B charger will allow current from the engine battery to the domestic battery, which will close the VSR and allow current to flow to the bow battery. The limiting factor will be the amount of chare the batteries can accept. As you say, the engine battery will be charged pretty quickly, leaving just two batteries to charge, assuming 200AH or so between them, they won't accept anywhere near 115A, ever.

He could always stick in great big batteries to use up the max rated output of his alternator!