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Old 19-03-2012, 14:33   #1
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12volt/24 volt alternator

Hi
I need to mount a 12 volt and a 24 volt alternator on my engine. Any one
now how to wirring these. Perhaps a having a diagram

thanks in advance
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Old 19-03-2012, 14:51   #2
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Re: 12volt/24 volt alternator

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Originally Posted by Kastrup View Post
Hi
I need to mount a 12 volt and a 24 volt alternator on my engine. Any one
now how to wirring these. Perhaps a having a diagram

thanks in advance
Rather than actually running two alternators why not just run one and route output through a transformer?
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Old 19-03-2012, 14:55   #3
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Re: 12volt/24 volt alternator

If you mean you will have two separate alternators, one 12 V the other 24 V, then the only way to wire them is to have each system completely separate from the other. If your boat has a common negative ground to the engine block or electric panel then you will wire the ground from both alternators together.

How to connect the positive side, 12V and 24V will depend on your boat and what systems you are running with each voltage.

One common example, a boat that has most things 12V like the lights, water pump, bilge pump and engine starter but uses 24 V for the anchor windlass or for a bow thruster.

In that case the 12V alternator is connected to the main battery and DC electrical system in the boat. Then you will have a separate 24V battery system for the windlass and the 24V alternator will go only to that battery.

Might help if you can give more details of your boat, why you have 12 and 24V systems and what you will power with them
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Old 19-03-2012, 14:56   #4
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Re: 12volt/24 volt alternator

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Originally Posted by belizesailor View Post
Rather than actually running two alternators why not just run one and route output through a transformer?
Well transformers only convert AC voltage. You would need a DC voltage converter to get 12 and 24 V from one source.
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Old 19-03-2012, 16:14   #5
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Re: 12volt/24 volt alternator

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Well transformers only convert AC voltage. You would need a DC voltage converter to get 12 and 24 V from one source.
Yes, "converter" would have been the more technically correct term to use, but, semantics aside, there are plenty of 12V/24V converters available on the market.
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Old 19-03-2012, 16:25   #6
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Re: 12volt/24 volt alternator

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Originally Posted by belizesailor View Post
Yes, "converter" would have been the more technically correct term to use, but, semantics aside, there are plenty of 12V/24V converters available on the market.
Yes, sorry. Maybe nitpicking here but would not want to send the OP out looking for a transformer. Very different beast.

There are certainly many DC/DC converters available. But if you are talking about handling the max output of an average alternator say 80 amps at 24 V you would need something like a 2000 Watt converter. Never dealt with one this large but guessing it might be somewhat costly.

But compared to dual alternators and all the associated bits and pieces the converter might make sense.

Really comes down to what the OP is trying to accomplish.
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Old 19-03-2012, 16:33   #7
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Re: 12volt/24 volt alternator

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Originally Posted by skipmac View Post
Yes, sorry. Maybe nitpicking here but would not want to send the OP out looking for a transformer. Very different beast.

There are certainly many DC/DC converters available. But if you are talking about handling the max output of an average alternator say 80 amps at 24 V you would need something like a 2000 Watt converter. Never dealt with one this large but guessing it might be somewhat costly.

But compared to dual alternators and all the associated bits and pieces the converter might make sense.

Really comes down to what the OP is trying to accomplish.
Agreed, now if the OP could just post the 12V and 24V amp requirements?
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Old 20-03-2012, 00:16   #8
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Re: 12volt/24 volt alternator

Hi
Thanks for you input
The story is that i have bought a GRP boat where the
engine reguires 12 volt and my domestic sysstem reguires 24 volt. My problems is, that the only way i can charg my 24 volt system is by landpower. The alternator
on the engine is 12 volt.
I'm planing to mount a 24 alternator. So i have a 12 and 24 volt alternator on the engine. The one for charging the 12 volt battery and one for charging the two battery 12 volt batteri for 24 volt.
But what about the wirring of the charglamp for 24 volt, can it be placed, together whit the wirring from 12 volt
on the ignition switch, or what do i do their ?

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Old 20-03-2012, 04:07   #9
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Re: 12volt/24 volt alternator

Hi Kastrup,

Just to make sure I understand your system correctly. The engine starter is 12V but all the systems in the boat: lights, bilge pump, electronics and navigation are all 24V? Not impossible but is an unusual arrangement. Are you sure that the two 12V batteries for your domestic systems are wired in series for 24V and not wired parallel which will still be 12V but give more battery hours?

If you do have the batteries in series to give 24 V for domestic power I would consider another plan instead of a 24 V alternator and all the additional complications. You could change the two 12V batteries for your domestic power into parallel wiring and keep the voltage at 12V. Then connect a DC/DC converter to these batteries that converts 12V to 24V. Connect that output to your domestic system. Now you can charge all the batteries from one 12V alternator.

If you do use this system it would be best to connect the alternator output directly to the domestic batteries and use a device like the Xantrex Echo Charge to maintain the engine starting battery. This is the best option since normally you use very little power to start the engine so less recharging is needed.
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Old 20-03-2012, 04:32   #10
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Re: 12volt/24 volt alternator

Hi skipmac
You have understand the system correct. I think it's unusual to. But that is how the previous owener had build the system. And it's not possible to get i contact with him for an explanation. All the power system is really thought out and professional build. But on this specific point, i can't find out, what he have had in mind.(charge til 24 volt bank)
And yes i'm sure that the two 12V batteries for my domestic systems are wired in series for 24V, i have done my self.

Your suggestion, sound interesting, i have to think it over.

Thanks
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Old 20-03-2012, 13:48   #11
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Re: 12volt/24 volt alternator

Odd system indeed. One idea: might be easier to install a single 24V output alternator to charge your house system and have a 12V converter to charge start battery (not many amps required for charging a start batt and running engine controls).
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Old 20-03-2012, 14:20   #12
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Re: 12volt/24 volt alternator

Hi belizesailor
You are right. But what do i do, with my start engine, then it reguires 12 volt
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Old 20-03-2012, 15:09   #13
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Re: 12volt/24 volt alternator

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Originally Posted by Kastrup View Post
Hi belizesailor
You are right. But what do i do, with my start engine, then it reguires 12 volt
Do you have a separate start battery? If so, you should able to drive the starter, and all other engine related electronics, directly from the start battery. Just using the 12V output to charge. Will need some kind of regulator set-up for the 12v charge control.

Also, how's your tachometer set up? Most are driven by a signal from the alternator so will probably have to make some changes related to this too.
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Old 20-03-2012, 15:24   #14

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Re: 12volt/24 volt alternator

Kastrup-
You say your engine requires 12 volts. Do you mean that you have a gasoline engine with a 12-volt ignition system? Or is it a diesel engine, which actually requires no DC power other than for the injectors and fuel pump?

I suspect that depending on what you have and what is actually 'required' it may be simpler to just mount a 24-volt alternator, 24-volt battery bank, and then do something fairly simple to either convert the engine systems, or make it happy. For instance, if the engine doesn't require a lot of power (even a gasoline automobile engine can often be run from flashlight batteries!) it may be simple enough to add a 12-volt regulated power supply and a 12-volt SLI (starter) battery without spending a fortune OR getting complicated. Or putting in a 24-volt starter as well and making things even more reliable.

What exactly do you have?
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Old 20-03-2012, 15:38   #15
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Re: 12volt/24 volt alternator

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Originally Posted by hellosailor View Post
Kastrup-
You say your engine requires 12 volts. Do you mean that you have a gasoline engine with a 12-volt ignition system? Or is it a diesel engine, which actually requires no DC power other than for the injectors and fuel pump?

I suspect that depending on what you have and what is actually 'required' it may be simpler to just mount a 24-volt alternator, 24-volt battery bank, and then do something fairly simple to either convert the engine systems, or make it happy. For instance, if the engine doesn't require a lot of power (even a gasoline automobile engine can often be run from flashlight batteries!) it may be simple enough to add a 12-volt regulated power supply and a 12-volt SLI (starter) battery without spending a fortune OR getting complicated. Or putting in a 24-volt starter as well and making things even more reliable.

What exactly do you have?
One problem may be the engine starter which, from the information by the OP, is 12V. The cost for a new starter IF a 24V version is even available, could be very expensive. Also, many diesels have mechanical injector and fuel pumps and would need no power at all to run once it's cranked.

Certainly would be a simpler system if the engine ran on the same DC voltage as the rest of the boat but converting one side or the other could be expensive.

I think the cheapest, simplest, most reliable would be to have one alternator and one voltage for engine and house batteries, either 12V or 24V all around. Then install a DC/DC converter to supply the missing voltage.

Using a DC/DC converter to make 12V from a 24V battery system introduces issues with how to regulate the voltage to charge the 12V starting battery. With a fixed 12V supply to charge the battery you run the risk of undercharging or overcharging and cooking the starting battery.

If you make all the batteries, house and starting into 12V systems then add a 12V DC to 24V DC converter you can supply a nice stable 24V to all the house systems from the 12V house bank, plus with appropriate smart charging system, make sure all batteries are getting the best 12V charging regimen.
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