battery voltage, 24V 48V or both?

hi,

I'm building a small boat, to be powered by an elecric motor.
For the motor the best operating voltage is 48V: more than that is dangerous, where 24V does not have enough power.
Problem is that most other equipment run on 12V or 24V (lights, cooler, etc)

I have two lifepo4 24V batteries, I can run then in series to get 48V or parallel for 24V. A simple solution is to run a step down converter so I can have native 48V for the motor and 24V from the converter for everything else... but I don't like the idea to have another device that waste a little power in the conversion, and if broken would leave me without most services.
Another solution would be to draw 24V from a single battery, which would work but would also possibly break the balance of the battery pack... I could devise a system to switch 24V from one battery to another in order to maintain pack balance, or have some balancing device do that for me...

What do you think? Anyone with the same problem and maybe a simple elegant solution I'm missing?

 

Hi Aleph.
It might be helpful to provide a few more details.
Boat size/ displacement? Motor size? Desired operating speed & range?
Regards, Tom

 

Buy a third battery, either 12V or 24V sized to run the house loads for 24h. Charging can be done by completely independent means (separate solar panel) and/or by a dc-dc charger from the drive battery (manually controlled when needed, no constant drain).
This way you achieve the desired redundancy and avoid balancing and parasitic loads problems.

 

No no no.

Do not take 24v loads from one of the batteries in a 48v series bank.

You either step down with a device or add a battery.

The other thing to perhaps avoid is using 24v at all and use only 12v for all else. This would reduce step down.

And you can always keep spare solid state step downs onboard for anything critical, although the failure state for me from one of them was a dead short which took some time to find as I did not expect it.

 

hi, thank you all for the input!

hi, this would be a small 15ft shanty boat on pontoons, designed to run mostly on solar power (should have 1.5 kw peak solar, so I would like to cruise at around 1kw motor power draw, which for a 48v is a comfortable 20A continuous draw... of course I'll design for at least double that for peak draw and contingencies). Actual speed would not be much, but I'll make do, I don't plan to do long range high speed trips with this... slow and quiet is the thing here

why would you say 12V is better than 24V? 24V should work with thinner wires and less power loss

btw the idea to have a separate small-ish lower voltage service battery to be charged from the main one is interesting, gives a nice redundancy to the system

thanks!

 

The problem with a 24v boat is some of the things you buy for a boat require a 12v supply and almost nothing requires 24v supply. So, if you want to simplify or reduce 48v conversion; I recommend, if practical to skip producing 24v.

I have about 6-8 solid state 12v transformers in my boat. 12v power is required for NEMA 2000, my VHF, iirc~the CO detection system, and a few others. If I redo it someday, I’d prefer to run a single conversion device.

But you can also run three different systems. It is inevitable you will need 12v supply is all.

 

Adding a set of 12 v batteries and their accoutrements will add considerable weight, cost and complexity.
24 volt appliances, lights, pumps, winches, and electronics and more are all readily available nowadays, as 24 volts is commonly used in the popular solar/off grid market.
The only item on my boat that requires 12v is the VHF radio, which is supplied through a small, lightweight 20 amp step down transformer, with plenty of power to spare if needed.

 

No NEMA network?

 

That’s possibly running off there as well, but isn’t much of a load.
I believe that all my Simrad electronics are powered by 24 volts with the possible exception of the network.