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Old 27-03-2016, 11:42   #1
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24V Alternator, 12V System. Simple Question?

I am absolutely sure this simple question has been asked before, but I cannot seem to find the answer.

My engine data states it has a 24V Alternator. I would like to run a 12V system however. Will it cause any problems if I have my two batteries in parallel (still 12v) or do I have to put them in series to make them 24v, or even change the alternator?

Also, is there a thread anybody knows of to compare the difference?

Thanks, James
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Old 27-03-2016, 12:50   #2
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Re: 24V Alternator, 12V System. Simple Question?

If your Starter is 24V your opions are limited, you will need two batteries in series to start your Engine, and another battery for your 12V consumers. You can use a battery to battery charger to charge your house battery off the alternator.

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Old 27-03-2016, 13:03   #3
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Re: 24V Alternator, 12V System. Simple Question?

Hi - and thank you for replying. the starter has recently been rebuilt and it is a 12V starter. It is an old engine and I am not sure what may have been altered on it.
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Old 27-03-2016, 13:07   #4
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Re: 24V Alternator, 12V System. Simple Question?

If your Starter is 12V, replace the alternator with 12V one.

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Old 27-03-2016, 13:09   #5
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Re: 24V Alternator, 12V System. Simple Question?

Thank for saving me much time, I will look into doing so. James.
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Old 27-03-2016, 14:37   #6
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Re: 24V Alternator, 12V System. Simple Question?

24v allows the builder to use smaller gauge cable for the same length of run needed for the same 12v consumer (motor/ lights/compressor etc) , so you need to.clarify what voltage your consumers are rated for?

It is not unusual for larger boats to have Both 12v and 24v systems, with 12v being popular for navigation electronics
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Old 28-03-2016, 09:19   #7
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Re: 24V Alternator, 12V System. Simple Question?

I'm building a simple system from scratch. Have engine/alternator, batteries, and no consumers (other than the starter motor) so far. I will check out the alternator - although it is a bigger boat, I don't have heavy electrical needs.
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Old 28-03-2016, 10:03   #8
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Re: 24V Alternator, 12V System. Simple Question?

Many boats use 24 (and 32) volts for engines, thrusters, windlasses, heads, etc. If you have a 24v boat and wish to run 12v items we usually install voltage converters (24 >> 12). Newmar makes great ones; the one we usually use can take 20 to 50 VDC and convert it to regulated 13.8v. Our most common model handles 30amps constant (temp surge to 35). This would handle almost all the common 12 loads; many larger motoryachts end up with 2 of them. This means no additional batteries, etc.
Newmar |DC-DC Converters | Standard Series | 12, 24, 32 and 48 VDC In | 12 and 24 VDC Out | 3 to 50 Amps
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Old 28-03-2016, 13:19   #9
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Re: 24V Alternator, 12V System. Simple Question?

Okay that makes a lot of sense, I am enlightened! stand by for many, many more electrical questions... ;-)
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Old 28-03-2016, 13:57   #10
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Re: 24V Alternator, 12V System. Simple Question?

Quote:
Originally Posted by BlackWind View Post
Okay that makes a lot of sense, I am enlightened! stand by for many, many more electrical questions... ;-)
It's a bit sad to switch from 24V to 12v when most would be happy to do the other way around. But you say you don't have heavy electrical needs and everything else including the starter is 12V so buying a 12V alternator seems to be the most cost effective and simple solution.
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Old 28-03-2016, 14:50   #11
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Re: 24V Alternator, 12V System. Simple Question?

Thanks Rom, I will work on my design further and keep you posted... I do understand what you are saying so I will do some proper calculations.
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Old 28-03-2016, 21:50   #12
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Re: 24V Alternator, 12V System. Simple Question?

did you only change the starter to 12v?? all your gauges, fuel pump, stop solinoids etc are probably still 24v?...


everything else on the boat? bilge pumps etc? you can't just convert a 24v boat to 12v.
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Old 29-03-2016, 09:05   #13
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Re: 24V Alternator, 12V System. Simple Question?

Hi Smac,

There is nothing else electrical on the boat, and the starter motor was already bolted to the engine. I suspect somebody has changed the alternator from the one in the engine spec but I will measure it tomorrow and find out for sure...
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