Charging house bank from 12v And 24v Alternators?

[Pau Amma]

My boat has one 12v 60 amp alternator and one 24v 80 amp alternator
I am about to replace the house bank (24v 360ah) and starter battery.
Currently just relying on the regulators on the alternators.
I am thinking that I would like to get more efficient charging into the batteries so am thinking that I could get an "alternator to battery charger" for the 24v alternator. Ideally I’d like to use the wasted amps from the 12v alternator as all it does is charge up the 1 x start battery for the engine. Could I use a battery to battery charger 12v to 24v to top up the charge into the house bank as well as having the 24v charger from the 24v alternator.
Should I have the 2 chargers both directly going into the house bank or should I put the output from the batttery to battery charger into the 24v alternator to battery charger?

Your assistance would be greatly appreciated.

 

[PaulRainbow]

My boat has one 12v 60 amp alternator and one 24v 80 amp alternator
I am about to replace the house bank (24v 360ah) and starter battery.
Currently just relying on the regulators on the alternators.
I am thinking that I would like to get more efficient charging into the batteries so am thinking that I could get an "alternator to battery charger" for the 24v alternator. Ideally I’d like to use the wasted amps from the 12v alternator as all it does is charge up the 1 x start battery for the engine. Could I use a battery to battery charger 12v to 24v to top up the charge into the house bank as well as having the 24v charger from the 24v alternator.
Should I have the 2 chargers both directly going into the house bank or should I put the output from the batttery to battery charger into the 24v alternator to battery charger?

Your assistance would be greatly appreciated.

Connect the battery to battery charger between the start battery and the domestic bank.

Hard to say if it would be worth fitting the alternator to battery charger without knowing a little more. What's you usage pattern for the engine ? What's the max output voltage of the alternator ?

 

[Pau Amma]

Thank you Paul
My worry with that is whether the 24v Alternator will be trying to put in 28v and will be conflicting with whatever stage of the charge process the battery to battery charger is doing?

 

[halcyon]

Thank you Paul
My worry with that is whether the 24v Alternator will be trying to put in 28v and will be conflicting with whatever stage of the charge process the battery to battery charger is doing?

That is your problem, which ever has the higher reg voltage will take precedence.

Brian

 

[William_H]

I think OP might have an absurd electrical system. 24v is preferred for high current devices like engine start. Yet it seems he has everything on 24v except the engine start. Suggest he dump the 12v system for engine start and use 24v. It seems a 12v starter is OK on 24v (but get a 24v starter if any doubts.) The engine instruments might need 12v but a simple regulator could solve that problem. (unless there is a 12v stop solenoid or 12v glow plugs) (even then a 24v to 12v converter for high current is not expensive).
For house services it is more common to have a 12v battery charged off the24v system giving that isolation of the engine start system. Again a 24 to 12v converter controlled by a VSR set to 27v.
So simplify to one alternator or if you want change to 2x 24v alternator both running in parallel.
I don't think you need or will find much benefit in the smart charge regime of the BtoB charger. If you do want then an alternator charger can be more efficient.
I reckon an ideal system would be a 24 v system for engine anchor winch thrusters etc. Charging a 2x 12v battery in parallel house system via a converter and VSR. Having 2 batteries in the house system means that in extreme of engine battery failure you could manually change wiring to convert 2x house batteries to 24 jump start. But on the other hand stick with what you have and go sailing. ol'will

 

[bristoljim]

You are heading in the right direction to increase the efficiency of the 24volt charging by fitting a smart regulator or the alternator to battery device.You have plenty of charging capacity in the 24volt alternator so my advice would be keep it simple & leave the 12volt system as is for engine starting & invest any spare cash in increasing the size of the 24volt domestic battery.
Jim

 

[PaulRainbow]

You are heading in the right direction to increase the efficiency of the 24volt charging by fitting a smart regulator or the alternator to battery device.

Without knowing what the alternator is currently doing, how can you say that ?

You have plenty of charging capacity in the 24volt alternator so my advice would be keep it simple & leave the 12volt system as is for engine starting & invest any spare cash in increasing the size of the 24volt domestic battery.
Jim

Again, without knowing his power requirements, how can you say that 360ah @ 24v is not enough ?

I have 390ah @ 12v and can stay aboard for months on end. If 360ah is not enough he'll need to be running his engine for several hours a day, or find some alternative means of charging the batteries.

 

[Dockhead]

You are heading in the right direction to increase the efficiency of the 24volt charging by fitting a smart regulator or the alternator to battery device.You have plenty of charging capacity in the 24volt alternator so my advice would be keep it simple & leave the 12volt system as is for engine starting & invest any spare cash in increasing the size of the 24volt domestic battery.
Jim

I agree completely with this.

I would strongly discourage you from messing with the intentional simplicity of your system with its entirely separate starting and house electrical systems!! This is a very good thing!

The 12v alternator on your main engine is NOT designed for bulk power production. You don't need it for charging the house bank -- that's what your large frame 24v alternator is for and what it does well.

A starting battery needs very little charging because only a very small amount of power is used when starting an engine. Replacing this lost power and powering the very low power draw engine systems, is what the 12v alternator is designed for. Even with upgraded regulation, it won't do a good job at producing bulk power, and you will be risking compromising your starting system.

So I would LEAVE IT ALONE! Adding good external regulation to the 24v alternator will not indeed result in greater power production (read MaineSail's articles on this on his site, links to which you can find on Cruisers Forum). However, it will put a much better finishing charge on your batteries, if you are relying on running the engine for charging through the whole cycle.

 

[PaulRainbow]

I agree completely with this.

I would strongly discourage you from messing with the intentional simplicity of your system with its entirely separate starting and house electrical systems!! This is a very good thing!

The 12v alternator on your main engine is NOT designed for bulk power production. You don't need it for charging the house bank -- that's what your large frame 24v alternator is for and what it does well.

A starting battery needs very little charging because only a very small amount of power is used when starting an engine. Replacing this lost power and powering the very low power draw engine systems, is what the 12v alternator is designed for. Even with upgraded regulation, it won't do a good job at producing bulk power, and you will be risking compromising your starting system.

So I would LEAVE IT ALONE! Adding good external regulation to the 24v alternator will not indeed result in greater power production (read MaineSail's articles on this on his site, links to which you can find on Cruisers Forum). However, it will put a much better finishing charge on your batteries, if you are relying on running the engine for charging through the whole cycle.

What a load of nonsense. If the 12v alternator isn't for battery charging, how do you suppose all of the boats with 12v alternators get their batteries charged ?

 

[pvb]

What a load of nonsense. If the 12v alternator isn't for battery charging, how do you suppose all of the boats with 12v alternators get their batteries charged ?

No point trying to apply logic...

 

[Dockhead]

What a load of nonsense. If the 12v alternator isn't for battery charging, how do you suppose all of the boats with 12v alternators get their batteries charged ?

I didn't say it's not for battery charging. I said it's not for bulk power production.

It has nothing to do with voltage. It has to do with the TYPE of alternator -- car type, versus bus type.

Car-type small frame alternators suck at charging large house battery banks, and external regulation doesn't solve this problem. They are not designed to produce their rated output continuously. They are progressively derated as they warm up (to keep them from melting down). You will be lucky to get 30 amps continuous, average, out of a 65 amp small frame alternator.

Mark Grasser and Balmar do make specially customized small frame alternators which do better than this.

Large frame alternators designed for school buses and emergency vehicles are designed according to completely different parameters, for a different purpose. These WILL produce their rated power continuously even at high temperatures.

Therefore, a boat like the OP's with one of each gains nothing by adding the puny practical output of his car-type small frame alternator, to the abundant power of his large frame alternator. That was my point, and it is based on facts.

 

[lw395]

Surely the main point is that unless the whole setup is really struggling, the 24V alternator will spend most of its time voltage regulated, so the batteries will be taking whatever charge they take at 28.6V or whatever.
Paralleling in another charge source will simply mean the second source provides a share of that current and the '24V' alternator does less work.
You might reach voltage regulation slightly quicker shaving a few seconds from the charge time.

 

[PaulRainbow]

I didn't say it's not for battery charging. I said it's not for bulk power production.

It has nothing to do with voltage. It has to do with the TYPE of alternator -- car type, versus bus type.

Car-type small frame alternators suck at charging large house battery banks, and external regulation doesn't solve this problem. They are not designed to produce their rated output continuously. They are progressively derated as they warm up (to keep them from melting down). You will be lucky to get 30 amps continuous, average, out of a 65 amp small frame alternator.

Mark Grasser and Balmar do make specially customized small frame alternators which do better than this.

Large frame alternators designed for school buses and emergency vehicles are designed according to completely different parameters, for a different purpose. These WILL produce their rated power continuously even at high temperatures.

Therefore, a boat like the OP's with one of each gains nothing by adding the puny practical output of his car-type small frame alternator, to the abundant power of his large frame alternator. That was my point, and it is based on facts.

Where on Earth do you get this from ? It's just utter nonsense.

Car type, bus type, huh ?

How do you imagine my puny 12v alternator charges my domestic bank, which is larger than the OPs ?

How do you imagine all of the other boats, also fitted with normal everyday 12v alternators do the same ?

Further words fail me

 

[noelex]

Many standard alternators fitted to marine engines are poor performers, with a low sustained output.

When outfitting a boat with a 24v house system a common practice is to maintain the 12v starting system. In this case the simplest, and arguably the best system, is to keep the the engines existing 12v alternator suppling the house bank and install a second, good quality 24v alternator, capable of sustained high output. This supplies the the 24v house bank, keeping the two battery systems seperate.

If there is room, this second alternator is ideally a large frame (or bus) alternator. This is the cheapest, most reliable, alternative. If there is not room, there are some high quality, small frame alternators, but they are more expensive (often a lot more expensive) and still have less output than the large frame alternative.

So rather than trying to harness the output of the 12v alternator, I agree with Dockhead that the best way forward would be to concentate on the 24v alternator, rather than trying to harness the relatively small output from standard 12v alternator.

If the output of the 24v alternator is inadequate it may need external regulation, or perhaps replacment. It is difficult to say without more details.

 

[moomba]

Where on Earth do you get this from ? It's just utter nonsense.

Car type, bus type, huh ?

How do you imagine my puny 12v alternator charges my domestic bank, which is larger than the OPs ?

How do you imagine all of the other boats, also fitted with normal everyday 12v alternators do the same ?

Further words fail me

they do so with inefficiency , a car alternator is not designed to charge efficiently (the key word here ) a large house bank but a single vehicle battery which really only needs a good burst of power when starting , therefore the alternator can charge without to much load
other boats with so called car alternators may take longer and therefore you will have to run your engine longer , all combining in extra load , fuel , and possibly damage

 

[PaulRainbow]

Not one of you knows the OPs engine running routine, how power use or any details of his alternator, other than it's 24v. You don't have the faintest idea of its make, model, type or regulator settings, yet some of you see fit to advise on how the OP should make changes to it or its regulator, or to fit external controllers.

Amazing, would one of you be kind enough to PM me next Fridays Euro Millions lottery numbers please ?

 

[PaulRainbow]

they do so with inefficiency , a car alternator is not designed to charge efficiently (the key word here ) a large house bank but a single vehicle battery which really only needs a good burst of power when starting , therefore the alternator can charge without to much load

More nonsense. A modern car, with all of its electronics and electrical equipment will use a hell of a lot more power than the average sail boat.

other boats with so called car alternators may take longer and therefore you will have to run your engine longer , all combining in extra load , fuel , and possibly damage

What ? You can fit a massive, highly efficient, alternator, but in most cases it won't charge the batteries a great deal quicker, the batteries just won't accept the charge.

 

[PaulRainbow]

No point trying to apply logic...

I was going to say "you can't make it up", but it seems you can

 

[lw395]

More nonsense. A modern car, with all of its electronics and electrical equipment will use a hell of a lot more power than the average sail boat.

.....

A modern car will use maybe 30A for extended periods when lights, heated seats, demist etc is on. Plus maybe the same again intermittently for power steering.

But the OP's 12V alternator does not sound like a 'modern car alternator', not even 1990s 'modern'.

Some sailing boats are running microwaves through inverters, plus charging big house banks at initially high currents.
Cars and boats both vary a lot. Generalising doesn't help much. It would be useful if people gave more info about how they use their boat electrics, and why they find what they have isn't good enough, otherwise we can only give vague opinions.

 

[PaulRainbow]

A modern car will use maybe 30A for extended periods when lights, heated seats, demist etc is on. Plus maybe the same again intermittently for power steering.

You'd be surprised, i've seen cars with dead alternators flatten a brand new battery, to the point the light are going dim and warning lights are coming on the dash, in a few miles.

Some sailing boats are running microwaves through inverters, plus charging big house banks at initially high currents.
Cars and boats both vary a lot. Generalising doesn't help much.

My point was, to say that a "standard" 12v alternator can't put out useful power is nonsense.

It would be useful if people gave more info about how they use their boat electrics, and why they find what they have isn't good enough, otherwise we can only give vague opinions.

Indeed, i asked this back in post #2