Ryan,
How much house power do you need, and what is the relative balance of motor power vs. house power?
If the house requirements are tiny, then running a converter to regulate the 48V down to 12V may be a good answer. On my small boat, this is what I have done - at least for now.
If your house requirements are large, then getting a sufficient regulator becomes more of an issue.
You might also consider how "critical" each supply is. One reason house banks are kept separate from starting battery banks on many boats is to prevent the owner from accidentally running down the battery so far that he/she is no longer able to start the main engine. In your case - would you want separation of the banks so that you didn't accidentally run down the power so much that you couldn't get home?
If you have a backup generator - then that is much less of a problem.
One other option is that if your house needs are small enough, you could consider a separate house bank - but keep it at 48V and use a regulator anyway. That would allow you to have the house bank and the motor bank both at 48V, so that your house bank could be a "backup" for your motor, if anything bad happened to your main motor bank (i.e. if you ran it down unexpectedly).
Ultimately, it's a judgement call for you. As with so many engineering problems - there are many answers. Some less efficient, and often no single obvious perfect answer.
John
On Thursday, June 25, 2020, 12:46:09 AM CDT, Ryan Sweet <ryan@ryansweet.org> wrote:
Wow, I apologize for not editing for autocorrect typos. Hopefully the ones below make sense in context.
> On Jun 24, 2020, at 22:42, Ryan Sweet via groups.io <ryan=ryansweet.org@groups.io> wrote:
>
> I am at the beginning of a conversion for a 32' ketch, and I have the 10kw thunderstruck kit, charger, reduction, and battery bank all working on my bench under artificial load. She will be at a dock soon where I can pull the diesel and begin refitting with the EV drive.
>
> The boat has an existing house system with four 6v golf cart batteries in 2p2s for both the 12v house loads and the starting motor, along with two 50w solar panels and a charge controller. During the summer in the Pacific NW the solar keeps up with the house loads at anchor all summer, she is usually at a dock plugged in for much of the winter.
>
> I originally intended to leave all the existing 12v system in place, and keep the 48v ev system separate, but I'm realizing that once the old motor comes out, it's really prime time to simplify as many things as possible, so I'm wondering about the necessary equipment and pros/cons of running the house load off of the same battery bank as the EV (right now I am working the EV with 4x 12v 200ah AGM in 4s).
>
> What becomes complicated or inefficient about running them together (with a 48v to 12v step down) vs having separate systems?
>
> I halfway thought that I would try leaving the existing house system as-is, adding the EV with the AGM bank separately, and if it is all working well, then switching the EV drove to a m bank of lifepo4 and rewiring the AGM bank in 4p at 12v, replacing the older system which is nearing end of life in the next few years anyway. But I also am drawn to the simplicity of only having one set of batteries to worry about for all loads.
>
> What are the practical considerations that you guys have encountered for each scenario?
> My boat will mostly be used for crushing near shore, likely with power though most winters, and at anchor or underway in summers.
>
>
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