Charging 24v Bank from 12v Alternator

[Dockhead]

Originally Posted by Kenomac

So.... If you swap out your 12v alternator for a 24v alternator plus add a few bits so it can charge the 12v batteries, and assuming you don't bin your perfectly good 12v alternator and choose to include it in the spares inventory....

How has that saved you any weight over obtaining a 24v spare alternator in the first place? Does 30 pounds of alternator really make any difference on a 25 ton cruising boat? Why not just empty out 12 liters of water from the tank, it's the same weight? Come to think of it... why do you carry around a full water tank weighing thousands of pounds, instead of having a watermaker to produce water as needed... if weight is so important to you?

Well, these are all valid arguments.

Where weight is concerned -- it all adds up, and if you don't think about weight every time you start to add another 50 pounds of something, pretty soon even a 25 ton boat is overweight. I guess I have close to a ton of tools and parts on board as it is, and am really loathe to keep adding to the mass.

Concerning watermakers -- you are absolutely right about hauling around a ton of water. But this is another tradeoff -- one more system requiring a lot of maintenance, and needing to be used regularly, which I don't need where I sail (there is free fresh water EVERYWHERE). I do think about the weight and often don't fill my tanks more than half full.

[CaptNemoO2]

Originally Posted by Dockhead

And the carb tends to gum up with disuse.

A propane powered one would actually be more practical -- easier to get rid of the fuel, and no gumming up. But still a lot of space and weight for something which is theoretically never used.

I'll just leave this here...

https://hutchmountain.com/products.h...235/category=0

Let's you switch back and forth between gas and propane. Can apparently also use the propane to run the carb dry. (FYI, No affiliation and never used it).

[Dockhead]

Originally Posted by CaptNemoO2

I'll just leave this here...

https://hutchmountain.com/products.h...235/category=0

Let's you switch back and forth between gas and propane. Can apparently also use the propane to run the carb dry. (FYI, No affiliation and never used it).

I like it.

You wouldn't even need that much propane since you could switch to your dinghy gasoline supply for sustained use.

You could maybe get rid of the internal fuel tank altogether, or just block it off. Would make it much easier to make the generator free of gasoline for storage inside the main hull volume.

My next boat will have a special locker for outboards, fuel cans, and if necessary, gasoline/petrol generators, to eliminate this storage problem.

[Ahmet Erkan]

Another option might be to charge the 24V battery in two steps. Connect the lower 12V battery to the starter battery, let it charge and then do the same for the upper 12V.

[atoll]

Originally Posted by Dockhead

Hmmm. So I guess you wouldn't approve of the convection oven, induction cooker, and dishwasher I plan to have in my next boat?

what no sauna,gym and microbiotic garden

[Catalysis]

Originally Posted by Dockhead

Electrical power on board most cruising boats is mission-critical. I think I've even heard of boats being abandoned because of loss of power.

I have two fully redundant means of producing bulk quantities of electrical power -- a heavy duty externally regulated school bus alternator on the main engine, and a heavy duty low speed generator (6.5kW Kohler), both devices very reliable. I have backup inverters and battery chargers to provide redundancy in the AC-DC conversions.

I was so paranoid about electrical power that for years I even carried a Honda suitcase generator as a backup to the backups. It was in the way, however, and I finally got rid of it last year.

Well, last week I suffered failures of BOTH systems within about a week of each other. What are the odds?! It was quite disturbing. There was a thread on my travails with the generator. I did get it running within a few days (with a lot of help from knowledgeable people on here -- thanks), and with parts and tools I had on board, but the whole incident has left me dissatisfied with my setup.

An easy fix would be to carry a spare alternator. It's not that expensive, but the large frame device is a bulky, heavy beast. I'm debating whether to bite the bullet on the storage issue, or just carry a full set of bearings, brushes, etc.

But as someone on the other thread pointed out -- I have TWO alternators on the main engine -- what about the other one?

Well what indeed? The problem is that the other alternator, used exclusively to charge the engine start battery, is 12v, and my system is 24v.

I looked for a battery-to-battery charger which would let me charge a 24v bank from a 12v one, and couldn't find anything.

This is not electrically complex. I suppose I could just get a large DC-DC converter and run a B2B charger from that.

Anyone have any tips?

Power systems for our cat with twin 80 hp yanmars:
- 24v (2.5 kw) and 12v (1.3kw) alternators per engine
- 2 kw (24v) solar panels
- 9 kw genset
- 20 kw lifepo 24v house bank
- individual agm (12v) start batteries
Pretty flexible system
Paul

[Dockhead]

Originally Posted by Catalysis

Power systems for our cat with twin 80 hp yanmars:
- 24v (2.5 kw) and 12v (1.3kw) alternators per engine
- 2 kw (24v) solar panels
- 9 kw genset
- 20 kw lifepo 24v house bank
- individual agm (12v) start batteries
Pretty flexible system
Paul

Lovely system!

Redundant propulsion has so many advantages, and this is yet another one.

If I had a boat with two propulsion engines, I would have two separate fuel tanks with possibility of pumping fuel between them through a polishing system. Then never fill both tanks from the same source, and you are practically fail-proof.

[Catalysis]

Agreed we have two polishing systems (60 gph each)per hull and the ability to cross feed if required.

[Juho]

How about making the new boat an all diesel boat, with diesel generator, diesel stove, and maybe also diesel outboard for the dinghy (if you can find one). Diesel generator and outboard could be heavier than some other motors, but you could save in fuel storage, since you would not need to extra reserve for all fuel types, just one. (Disclaimer: I haven't done any calculations .)

[Colin A]

Well I think this was mentioned but swapping in a 24V starter and alternator onto your engine may be possible. But you would have to check on some modern diesels you also have to swap the computer and wiring harness. Or as said you could go down to 12V from 24.

I used to work on Bass boats many years ago lots of them run 24V trolling motors with 12V everything else. I know Minn Kota used to make a setup for charging from 12V. There was also a company out of TN called stealth as I recall. The Sterling look like a good setup.

Then you get into things like Vanner equalizers but I have seen too many issues with those on boats (many wiring design related but still).

For you next boat maybe twin gens a little 6KW and a 12KW, balance the loads.

[Dockhead]

Originally Posted by atoll

what no sauna,gym and microbiotic garden

I actually spent some time on a big Swan with a sauna. This is actually not a stupid thing to have on a boat sailed in cold latitudes.

Cheap and takes up no space -- just insulate one shower cabin. Yeah, next boat might have that.

[john61ct]

Yandina Trollbridge lets you use 24V for loads, but then charge 12V.

[Juho]

Originally Posted by Dockhead

I actually spent some time on a big Swan with a sauna. This is actually not a stupid thing to have on a boat sailed in cold latitudes.

Cheap and takes up no space -- just insulate one shower cabin. Yeah, next boat might have that.

Obviously too much time spent in Finland. The heat is getting in your head.

[Catalysis]

Perhaps time to "Finish" this thread ?

[Dockhead]

Originally Posted by Juho

Obviously too much time spent in Finland. The heat is getting in your head. [emoji3]

Once you experience Finnish-style bathing, you never go back.. .