Charging 24v Bank from 12v Alternator

[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?

[Kenomac]

I left a helpful tip and solution to your dilemma on your other thread, but you were dismissive to the obvious solution. Install some solar panels and never worry again. Now I look at a Smartgauge reading looking something like this everyday without touching the generator or engine.

Make some room for solar.

[Dockhead]

Originally Posted by Kenomac

I left a helpful tip and solution to your dilemma on your other thread, but you were dismissive to the obvious solution. Install some solar panels and never worry again. Now I look at a Smartgauge reading looking something like this everyday without touching the generator or engine.

Make some room for solar.

Not dismissive at all, and I specifically answered this suggestion.

We had solar on the last boat and loved it.

But as I said -- there is no room for solar on this boat! There is no bimini, and there will never be an arch (ugh!) on this boat, which needs to be able to eat up miles upwind and can't afford the windage.

As I mentioned, the next boat will have solar built into the pilothouse roof.

Also -- solar is not really a backup to other power sources, as it only works when the sun is shining and only works at a relatively low rate. It might not help in an emergency, at night say.

[Kenomac]

A 54ft boat with "no room for solar?" You can't be serious....

Solar works all day to keep your batteries fully charged, so you won't get caught again with your pants down like last week.

[Dockhead]

Originally Posted by Kenomac

A 54ft boat with "no room for solar?" You can't be serious....

Not a "54 ft boat" but a "54 foot sailing machine without a scrap of unnecessary windage"

[Kenomac]

Originally Posted by Dockhead

Not a "54 ft boat" but a "54 foot sailing machine without a scrap of unnecessary windage"

The last I heard, you owned a 25 ton Moody 54 cruising yacht. Add some solar panels to prevent future emergencies.

"Those who cannot remember the past are condemned to repeat it." George Santayana

[Dockhead]

Originally Posted by Kenomac

The last I heard, you owned a 25 ton Moody 54 cruising yacht. Add some solar panels to prevent future emergencies.

"Those who cannot remember the past are condemned to repeat it." George Santayana

Yes, a Moody 54 with D/L of 188 and with carbon laminate sails, which regularly does 200 mile days. Sailed 1500 miles upwind every year. I have systematically removed everything dragging us down upwind, and there's no way I'm putting a couple of square meters of solar panels on her anywhere. It would be like putting the dinghy back in davits, or even worse than that.

Also, like I said, I don't think anything other than a gigantic solar array coupled to a gigantic battery bank would "prevent future emergencies". We need quite a bit of power to run the boat during long night passages up here (16 hours of darkness in the winter).

[conachair]

What about going the other way?

Ditch the 12v alternator for another 24v and fit a sterling battery to battery to charge the 12v start battery, looks like they do 24v in, 12v out.
https://sterling-power.com/products/...ttery-chargers

[edmundsteele]

Only cheap and nasty way is to get a 12 volt inverter to 110 volt A/C and run it from your engine battery (it doesn’t matter what your house A/C system is, 12 v / 110 v will be the cheapest option, ditto the extension cord). Run a 110v extension to either your house battery charger or buy a 24 volt battery charger from NAPA (or any place that sells 24v truck parts) and charge up the house batteries. Not an ideal solution but a cheap work-around.
Ed

[Privilege]

Just a thought, if the alternator is externally regulated to 12v, the chances are that in fact it puts out much more than 12v. If this is the case, a 24v external regulator might work?

[john61ct]

Big amp converter, back flow blocking diodes for isolation, if it is just for rare usage babysit it yourself, if for regular usage get a 24-24 B2B.

[Kenomac]

It was me who reminded you on your other thread that you have two alternators on your engine. Now I'd like to remind you (since you don't have a fuel polishing system or solar panels) that if something goes wrong with your diesel fuel or fuel delivery system, it won't matter how many alternators you have on board, you still won't be able to charge up even your flashlight (torch) with your generator and engine not working.

[Dockhead]

Originally Posted by conachair

What about going the other way?

Ditch the 12v alternator for another 24v and fit a sterling battery to battery to charge the 12v start battery, looks like they do 24v in, 12v out.
https://sterling-power.com/products/...ttery-chargers

I hadn't thought of that. Thanks.

[Dockhead]

Originally Posted by Kenomac

It was me who reminded you on your other thread that you have two alternators on your engine. Now I'd like to remind you (since you don't have a fuel polishing system or solar panels) that if something goes wrong with your diesel fuel or fuel delivery system, it won't matter how many alternators you have on board, you still won't be able to charge up even your flashlight (torch) with your generator and engine not working.

Yes, I've thought of that, and think about it all the time. The fuel tank is a single point of failure so I concentrate on it.

I open, inspect, and clean my tank every other year, have dual Racors, and two cases of spare filters on board.

I actually run a 2 micron filter in one side of the Racor as an "early warning device" -- if anything starts to happen, there will be an instant vacuum with that inappropriately fine filter. I check the vacuum every time I start the engine and sometimes in the middle of a long motoring passage.

I also keep an emergency jerry can at the ready.

I think fuel polishing is a good thing and I will have it on my next boat. My starting point will be Jedi's excellent fuel system design.

[Jetx]

Would something like this Sterling B2B charger (12v in, 24v out) connected between the start battery and house bank, do the trick?