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Old 20-03-2012, 14:53   #16
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Re: 12volt/24 volt alternator

I have a very similar electrical system and it's not that difficult to mount two alternators if you have space for them. I have a smaller 12v alternator that came mounted on the engine for the start battery, along with the navigation lights and some smaller electronics.

I have a larger pulley where I mounted the 24V alternator in front of the engine (there's also a refrigeration compressor running off that larger pulley with a hp draw of about 3) which powers my house bank for lights, blowers, pumps, etc.

I have a DC/DC converter just for redundancy on my nav lights, electronics etc.

It's nice running wires etc because the voltage is lower and thus lower wire gauge size but expensive for the 24V options.
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Old 20-03-2012, 15:43   #17
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Re: 12volt/24 volt alternator

If the OP needs to run separate systems then probably common ground and two battery banks. I suggest two Balmar charge controllers - one on each alternator. They will self regulate each system as required by each battery bank. This is a bit odd but totally can be done.
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Old 21-03-2012, 00:14   #18
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Re: 12volt/24 volt alternator

hi all
First thanks for all your inputs, it have been very helpfull.
I have found a wirring diagram for mounting an ekstra 24 volt alternator, so i have decide that, that is the way i'm going.
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Old 21-03-2012, 08:11   #19
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Re: 12volt/24 volt alternator

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hi all
First thanks for all your inputs, it have been very helpfull.
I have found a wirring diagram for mounting an ekstra 24 volt alternator, so i have decide that, that is the way i'm going.
Going with single 24v or 24v + 12v alternators?
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Old 21-03-2012, 09:25   #20
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Re: 12volt/24 volt alternator

All you have to do is get a single 24 volt alternator. Then put two 12 volt batteries in series. Then connect your 12 volt system to one of those 12 volt batteries.

Then what you have is a 24 volt system and a 12 volt system being powered by a single alternator. Trust me on this, your 12 volt system will only be sensing 12 volts across one 12 volt battery.
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Old 21-03-2012, 23:12   #21
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Re: 12volt/24 volt alternator

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Going with single 24v or 24v + 12v alternators?
Hi
It will be a twin system, comprised of a 12 volt and a 24 volt alternator. If you need a wiring diagram you can pm mail me.
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Old 21-03-2012, 23:16   #22
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Re: 12volt/24 volt alternator

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All you have to do is get a single 24 volt alternator. Then put two 12 volt batteries in series. Then connect your 12 volt system to one of those 12 volt batteries.

Then what you have is a 24 volt system and a 12 volt system being powered by a single alternator. Trust me on this, your 12 volt system will only be sensing 12 volts across one 12 volt battery.
What about the startengine and the instrument panel, they are all 12 volt ?
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Old 22-03-2012, 05:39   #23

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Re: 12volt/24 volt alternator

Kastrup, I don't think you mentioned what type the engine is, or what needs 12v besides the starter.

It is very possible that you could run just a 24v alternator, no need for extra brackets and machine work and belts and complications, by using two 12-volt batteries for your starter. EIther manually or with an automatic relay, shift them into parallel to use as a starting battery, and then shift then back into 24-volt series configuration to let them recharge fro mthe main alternator. The switching is fairly easy, the drain from starting fairly small and recharged.

You can of course also use a 24-to-12-volt regulator, easily built if not available off the shelf, which would charge and maintain your 12v starter. All solid state, effortless to use.

But if you've got lots of room to install extra alternators and access them...by all means.
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Old 06-08-2016, 09:09   #24
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Re: 12volt/24 volt alternator

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Hi
It will be a twin system, comprised of a 12 volt and a 24 volt alternator. If you need a wiring diagram you can pm mail me.
Can you please send it to me?
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Old 06-08-2016, 16:12   #25
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Re: 12volt/24 volt alternator

Battery Management System

This may help.
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Old 06-08-2016, 17:30   #26
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Re: 12volt/24 volt alternator

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All you have to do is get a single 24 volt alternator. Then put two 12 volt batteries in series. Then connect your 12 volt system to one of those 12 volt batteries. Then what you have is a 24 volt system and a 12 volt system being powered by a single alternator. Trust me on this, your 12 volt system will only be sensing 12 volts across one 12 volt battery.
Very well put. Often it's the other way around, you just want 24v for the starter.
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Old 06-08-2016, 19:12   #27
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Re: 12volt/24 volt alternator

Do they really have to be separate? I thought GND can be common?

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Old 06-08-2016, 19:54   #28
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Re: 12volt/24 volt alternator

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If the OP needs to run separate systems then probably common ground and two battery banks. I suggest two Balmar charge controllers - one on each alternator. They will self regulate each system as required by each battery bank. This is a bit odd but totally can be done.
I'm a bit baffled by all of the responses that this is an 'odd' setup. I'll admit it's not usual on a 37' boat, but it's actually quite common on 50'+ boats as the electric motor sizes increase on windlasses, furlers and bowthrusters. It also reduces wire size requirements. We've never found availability of common items such as lights, bilgepumps, washdown pumps, fridges, etc, etc, etc, are all readily available in 24v versions and many small electrical items are often dual voltage. Where items like radios or instruments are only available in 12v small 24/12v converters are cheap and easy to install. I certainly recommend keeping any 'house' loads off the 12v system as the possibility of draining your start battery inadvertently increases dramatically.

See if you can find a wiring diagram for an Oyster online as I believe they use 24v for the house and 12v for the engine and generator start system. I'd recommend our boats, but most Amel's have a floating ground system, so that's probably not applicable to the OP's situation.

Regarding the recommendation of dual Balmars and external controllers. That's fine for the 24v house bank, but unnecessary for the 12v start system. A cheap internally regulated alternator is typically all that's installed.
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Old 07-08-2016, 06:42   #29
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Re: 12volt/24 volt alternator

Yep.

I would simply run one system and up or down step the voltage for the lighter loads. This often implies a 24V system with 24 to 12 down step via V converter.

In a converted set-up the 12V subsystem can still have its own 12V backup/float/emgncy battery; but in this case this is just one small battery rather than a big heavy and expensive bank.

Voltage converters tend to be less expensive than separate alternators, batteries and cables ...

This is often achieved on 24 Volt boats that run some amt of 12 Volt systems.

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Old 07-08-2016, 06:56   #30
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Re: 12volt/24 volt alternator

There are devices available that will take 24vdc input and produce a regulated 12vdc battery charger output (rather than a straight dc-dc converter). Probably cheaper than doing a two alternator system too. You'd still need to change the existing alternator to 24vdc and rewire to feed the house batts.

Pulling 12v from a series 12/24 battery system is not a good solution because inevitably one battery will become unbalanced relative to the other. Again there are devices you can add on to mitigate the problem, but why add complexity'
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