diy solar

diy solar

Separate house bank from motor bank?

jdege

New Member
Joined
Dec 16, 2020
Messages
138
I have a boat that I've been thinking about converting to electric, for a number of reasons.

I've been considering ePropulsion's Pod Drives. These run at a nominal 48V, and have systems that integrate motor, controller, batteries, and AC charger. But that don't integrate solar chargers, or inverters or 12V converters for house loads.

I follow a few sailing channels on YouTube, one of which is Sailing Wisdom (The Rigging Doctor).

In a recent episode they were discussing issues they're having with their battery charging, and mentioned that they have separate banks for house and motor - 12V for the house and 48V for the motor. And that their solar panels charge the house bank, and that they can charge the motor bank from the house bank via the house bank inverter they generally rely upon the regen.

It's not something I had considered as an option. Clearly there'd be losses, charging the 48V bank through the inverter, but I can see usage patterns where that wouldn't matter much (if, for example, you were sailing a lot where regen could work, or sitting in a slip a lot, tied to shore power).

What do people think?
 
Last edited:
two independent power sources so you get some fault tolerance when (not if) things go bad seems good.
No idea of the power draw but I would expect the motor to pull a lot of current and so "maybe" its good it is by itself so as not to voltage sag every other thing on the boat?? This way all your controls/radios/devices are still happily working even if the something bad happens to the motor (locked rotor condition).
no idea really...the world of boating is even more unique than the RV world, which is vastly different than a house hehe
 
This is a sailboat right?

What’s your typical 12V draw? I’d be inclined to have a native 12V system that meets my needs- and have spare parts like controller, connectors- that I depend on for life and comfort and then do whatever’s required to supply the 48V for the non-critical, unnecessary motor.

In a boat I would want nothing of a big draw or quickly drained battery potential anywhere near my nav lights, sonar, gps, cabin lights…. But I’m funny like that.
 
Yes, this is a sailboat.

The current load for the 12v house bank is entirely theoretical. Right now, it's just the nav lights. As I build out the boat as a live-aboard, it will change - interior lighting, computer, refrigeration, microwave, induction cooktop, who knows?

The motors? I haven't decided them yet, either. ePropulsion has three models, at 1.0, 3.0, and 6.0 kW. My best guess right now is that the 3.0 would work so that'd be 60+ amps, each. (This boat was originally designed with two props driven by a pair of 5HP motors, it's currently configured with a single prop and a 27HP diesel. At low speeds it steers like a pig, with just the one prop - that's one of the reasons I'm considering converting.)
 
If I'm understanding you correctly, it would be best to have a 48 volt battery bank with any inverter attached to that and then a 48 volt DC to 12 volt DC converter, or if 12 volt loads are huge, a 48 volt DC to 12 volt DC battery charger and maintain a 12 volt battery for these loads.

Motors the size you're talking about would cause huge surges to a 12 volt inverter, and actually sounds much worst than the amp surges experienced when you run an air conditioner. I could see a battery bank pulling well in excess of 200 amps, perhaps by multiples if you stick to a 12 volt system as your main source of power. Not a good idea to have greater than a 1 kw constant draw on a 12 volt system, but with a motor, start up surge (Locked Rotor Amps?) often makes a 1 kw system undoable. IMO a 12 volt system is limited to 1 KW, unless you go to 2 kw for two minutes at a time four to six times a day.

I am doing a 24 volt upgrade and there will be a bit that I can't upgrade that needs 12 volts and I am going to install a 70 amp DC converter. That way my 12 volt 50 amp draw leveling jacks will still be occasionally powered and my 12 volt 9 amp Propane Blower fan that can run constantly will still be powered.
 
Any idea how many solar panels you can comfortably fit with out to much shade? On my 30 ft sailboat I have only 200w of panels. Just enough for compressor cooler,TV,radios, chart plotter. and fans. Using auto pilot I don't make enough power to use all night. Your boat must be fairly big if it had 2 engines. If I have to run the generator occasionally for an hour or so to help out I do it. Sailing wisdom has a small Honda generator if he needs it.
 
My boat is an odd one - 37 foot length, 8 foot beam, less than 2 foot depth, with leaboards.

boat_small.jpg

As shallow as it is, it still has 4000 pounds of keel, but the props are alongside it, meaning you get no propwalk.
 
Yes, this is a sailboat.

The current load for the 12v house bank is entirely theoretical. Right now, it's just the nav lights. As I build out the boat as a live-aboard, it will change - interior lighting, computer, refrigeration, microwave, induction cooktop, who knows?

The motors? I haven't decided them yet, either. ePropulsion has three models, at 1.0, 3.0, and 6.0 kW. My best guess right now is that the 3.0 would work so that'd be 60+ amps, each. (This boat was originally designed with two props driven by a pair of 5HP motors, it's currently configured with a single prop and a 27HP diesel. At low speeds it steers like a pig, with just the one prop - that's one of the reasons I'm considering converting.)

Do you have enough area on Deck for solar panels sufficient to run the epods longer than a few minutes to get off the beach and raise sails.
The 6 hp/3kw will require 3 cells of this size 15" L x 7.75" W x 13" H for each hour of operation. How big is your Bimini?

I lived on a Sail boat in 2001 for a few months, It had a 100 watt panel and a wind generator. The house battery served also as the starting battery. One day I made the mistake of running my computer off the battery for a few hours. I couldn't start the engine and had to sail in and out of my slip for a few days.
 
Initially I'll be mostly daysailing from a slip that provides shore power, so it'd not really be an issue.

So I could install the motors and the 48V bank, and leave the solar for later.

Wisdom seems to rely mostly on regen to charge their 48V bank. ePropulsion's 3.0kW pod is supposed to provide 300W at 7.5 knots (hull speed for this boat), which means 14 hours to a full charge, which is a lot of sailing.

There are some tradeoffs that need to be decided upon.
 
Depends on the goals of the system. If you want backup power for the motorized propulsion I would tend to build a second battery at 48 volts to connect in parallel if needed. Run the minor 12v items through a 48/12 DC-DC converter. With even a basic 15 amp 120v connection at the slip you will always be full charge at the start of the day during occasional use.

Regen will work if sailing to some other port where there is no shore power guaranteed.

Let experience guide you after the initial conversion to electric.
 
Ok. So I know more about your boat.

I’m now more of the opinion a 12V ‘house’ system separate from the 48V system to run the two 4HP electric motors is best. At 37’ there’s probably enough space to panel for 200W at 12V and have room to make 200W or more of 48V. The induction top and microwave might be asking a lot though. Maybe the microwave if it’s small; I’ve daily run a coffeemaker when I only had 200W of panels without issues.

in a tough spot I can see doing without the motors, but lights, bilge pump, and nav, gps and sonar seem important to me. And those might need 5-40A, depending.
 
I don't have plans, I have vague intentions.

I've done a fair bit of sailing, but not on this boat. I've never tried to live-aboard; my longest stay on a boat was a week.

My intent is to to spend this season sailing and motoring as-is, and to make decisions as they come. The electric motors, if I go with that, will be next winter. Solar panels perhaps the year after that.
 
Back
Top