Considering rebuilding my system for 48v.

[willo]

Just kicking tires on some ideas here.
My current build uses a 24v LifePO4 inverter pack along with a 12v LifePO4 house and 12v AGM engine packs. I'm plotting to add some diy hybrid power to my boat and for that I'll want to have 48v or even 96v available.

I have a few bits of 24v kit that would need to be swapped out.

• Quattro 24/5000 inverter
• 24/12 DC-DC chargers (x2)
• 24v Alternator that I'm planning to move to a single cylinder diesel as a DC genset

Much of my gear can be swapped over:

• REC Q BMS (Supports 16s, currently running 8s)
• Rec Precharge controller
• MPPT controllers (My little victrons all support 12/24/48)
• Cerbo GX
• Wakespeed 500 (setup for the 24v alt, can be used with a 48)
• Wiring would be overzied for the new lower amp draw.
• Existing battery pack is a 8s2p build, which I can convert to 16s in a couple of hours.

Now the good news imo is that I can generally recover the value of most of that gear.
The Inverter, DC chargers and even the Balmar alt should all be easy enough to sell off. I got a deal on the quattro so I think it'll offset costs pretty well.
I'll need to restructure my lifepo4 into a 16s pack, but I'm thinking of splitting up the older cells into new 12v packs (more house 12v and some winch/windlass power packs) and just replacing all the cells in the larger pack.

All that out there, I am trying to decide if it's worth doing this. This comes down to weather or not a single motor is enough for this to work. I've sized systems for the boat, and in general I'm told that I'm going to need either a single ME1616 at 96v OR a pair of ME1616s at 48v to REPLACE my 50hp diesel. That said, I don't know that I really need a full sized motor - in my limited motoring time, I didn't really need to crank the hell out of my engine. If I do need full power, I've got the diesel. If I look at it as if I'd have a spare 25HP electric... (total BS number but it'll have like half the power output of the diesel at peak) that's not too bad. I probably won't be pushing 7 knots on electric only but I don't know if I care. I suspect the electric will be truly handy for low speed things like docking.
To color that idea a bit more - the boat originally came with a Perkins 4-107 which only made 42hp at 4000rpm.

From an overall system perspective, running 48v on the inverter/traction pack is fantastic as I could regen from the diesel, charge the pack from a DC generator at 48v, generate solar at 48v, etc.

Immediate benefits:

• Individual cell monitoring
• Lower waste heat - cooler means higher efficiency
• Can power the electric motor without a huge additional investment.
• Multiplus II will take less space!
• Rewiring the pack will simply the build and might allow for re-orientation of the pack.

downsides:

• Need to buy a new inverter to have ready to swap in, so parking $1k for a month or two until I swap and sell off the old one.
• Need at least one 48-12 DC-DC to keep house pack happy for the same reason( those are cheaper tho)
• Have to re-mount those frigging DC-DC chargers (again)
• Get to rewire the pack again.
• My MPPT configuration works perfectly with a 24v system, but it does NOT work with a 48v system. I would likely end up dedicating one panel to 12v production and 2 panels to 48 production using a new MPPT or by paralleling my existing 100/20s to create a 100/40. (The wizard tells me that a 150/35 would do the job.)

 

[yabert]

a single ME1616 at 96v OR a pair of ME1616s at 48v to REPLACE my 50hp diesel

It's always the same story, high output at propeller mean fast battery discharge time. As energy in battery is limited, high power for long time is useless.
To add, high power will maybe give you 7 knot, but lower the speed by 15-20% will drop the power 50%.
So, IMHO don't hesitate to go 48V with one ME1616.
As reference, I move a 38' sailboat at 3 knot with 1 kW last summer just to test.

 

[HarryN]

In this thread, he was looking at ways to deal with a higher voltage pack goal for propulsion.

Thread 'Is it viable to charge a 72V lithium bank with Genasun Boost mppts? On a Catamaran.'

Oct 26, 2024

I was set on 48VDC for my catamaran electric conversion. But RPMs needed and amperage getting too high (BMS and genset) have gotten me back looking at 72V (and 96V).

For a boat, I have a fair bit of space on the roof. 20' wide and 12' long. (boat is 30' wide and 55' long)
I can keep building off the back a bit as well.

Its a sailboat.
So the sails and boom and angles of course will be shading.

I would like to get away with a 72V bank.
Has anyone done this without needing to put too many panels in series?
are the Genasun controllers really that effective? Hard to commit to a product...

• flatwater
• Replies: 30
• Forum: Marine

In the end, it looks like he is going with a 24 volt pack for most things, then using the inverter to boost up to the desired higher voltage.

So if you go down that path, you could just keep what you have, add a 96 volt pack, and charge it from your existing power system.

 

[yabert]

The ME1616 is given at 13 kW continuous at 48V (let say 52V LFP). With the good propeller size and pitch (or good gearbox ratio) this will move a boat quite well.
Here is Ocean volt calculator to understand nicely that drop speed by 1 knot lower power requirement a lot.

Configurator

Oceanvolt system configurator. Please fill in the specifications of your boat and we will suggest a suitable system for you. Note that this configurator is designed for sailboats and displacement boats and results are based on empirical data.

oceanvolt.com

Power to move at 4-5 knot is nothing, but can be huge at 6-7 knot.
I also use Vicprop calculator to have a good idea of power/speed ratio for a specific boat length/size.

Vicprop - Prop calculator for Displacement and semi-displacement hulls

Vicprop, marine propeller specialists.

vicprop.com

 

[Daddy Tanuki]

to the OP how do you like the REC BMS? any thing to watch out for?