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Old 30-10-2018, 06:26   #1
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Switching from 12V to 24V

I have a Perkins 4-108 installed in my yacht with 12 V alternator and starter. Right now I am installing a 24V 60A alternator (driven by a twin belts)

I have established the starter motor will have no problem handling 24V and all the instruments – tacho, water temp, oil pressure etc can work on 12 or 24V (I presume that means they can work on any voltage between 12 and 24V although I haven’t read that).

I have installed two 150AH AGM batteries as the house batteries. But what do I do now for the starting batteries? I’m inclined to install two 12V batteries in series for the engine starting so I can charge the house batteries and then manually switch to charging the engine batteries as required. Is this the way to go?

ALSO I plan to switch the yacht over to 24V completely but currently the interior lights and oscillating fans are 12V. I was planning to share the load of those items between each of the house batteries. Am I heading for trouble?

Would appreciate help.

Clive
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Old 30-10-2018, 06:36   #2
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Re: Switching from 12V to 24V

seems overly complicated,leave the engine 12v,with a 12v alternator and 12v start battery,etc and build a bracket to mount the 24v alternator as a second alternator to run your 24v house batteries
switches on the field currents to both alternators will allow you to switch one or the other off when not needed for charging
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Old 30-10-2018, 06:39   #3
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Re: Switching from 12V to 24V

Why do you want to switch to 24v? Almost 100% of the gear used on recreational boats is designed for 12v operation...
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Old 30-10-2018, 06:41   #4
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Re: Switching from 12V to 24V

I would keep the engine, start battery etc 12v.

The 12v start battery can be charged by a second 12v alternator, or a DC-DC 24/12 charger from the 24v alternator.
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Old 30-10-2018, 06:44   #5
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Re: Switching from 12V to 24V

Thanks Atoll
But I've ruled that out as I haven't sufficient room and engineering wise it would be a nightmare. Apart from that everything runs on 24V - fridge/freezer, inverter, macerator, anchor winch, mast/navigation lights so there seems little point in having 12V.

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Old 30-10-2018, 06:47   #6
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Re: Switching from 12V to 24V

Do **not** try to tap 12V circuits off a 24V bank.

For House loads, either a separate smaller bank, or a DCDC converter off the main one.

Maybe not relevant here but Yandina trollbridge 2400 is designed to power short-term 24V loads off a normally 12V "split bank", auto switches from parallel to serial.
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Old 30-10-2018, 06:49   #7
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Re: Switching from 12V to 24V

Quote:
Originally Posted by pcmm View Post
Why do you want to switch to 24v? Almost 100% of the gear used on recreational boats is designed for 12v operation...
Most gear will run on 24v or is at least available in a 24v version. The advantage of 24v is mainly the running of more powerful equipment such as anchor windlasses, inverters and bow thrusters, but there is also reduced voltage drop.
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Old 30-10-2018, 06:52   #8
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Re: Switching from 12V to 24V

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Why do you want to switch to 24v? Almost 100% of the gear used on recreational boats is designed for 12v operation...
I can get all 24V electronic navigational equipment and radios. Heavy power use (fridge/freezer, winches etc) work better on 24V.

A combination system with 12 and 24v is complicated and non redundant. Stick with a complete 12 v or 24 v system .

If your boat has powerful equipment like ac dc inverters, electric winchs, bow thrusters , 24v is the way to go.

michael pierzga, Nov 27, 201

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Old 30-10-2018, 06:55   #9
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Re: Switching from 12V to 24V

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Originally Posted by coopec43 View Post
Thanks Atoll
But I've ruled that out as I haven't sufficient room and engineering wise it would be a nightmare. Apart from that everything runs on 24V - fridge/freezer, inverter, macerator, anchor winch, mast/navigation lights so there seems little point in having 12V.

Clive
best bet is as nolex suggested,24v alternator,24v house,keep the engine 12v and start battery 12v and fit one of these or similar to charge the 12v.
cost about £100 and charges12v at 12A
Alfatronix Ltd | UK | Battery Chargers
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Old 30-10-2018, 07:06   #10
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Re: Switching from 12V to 24V

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Do **not** try to tap 12V circuits off a 24V bank.
So if I used one 12V battery to power some lights and the other 12V battery to power the rest of the lights it wouldn't be very clever?


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Old 30-10-2018, 07:13   #11
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Re: Switching from 12V to 24V

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Originally Posted by coopec43 View Post
So if I used one 12V battery to power some lights and the other 12V battery to power the rest of the lights it wouldn't be very clever?


Clive
Once you serial-join two 12V strings, you should treat it as a single 24V battery, one pos one neg point for all connections.

If the above is two separate 12V-only banks, that is OK but usually sub-optimal, because Peukert.

Simplicity rules for reliability, KISS.

Ideal IMO is two banks designed for redundancy, the norm being Starter(s) + House. I prefer Main + Reserve, but that's another topic.

If you have a **compelling need** to add a different-voltage circuit, then a DCDC converter **or** another bank + charger is the way to go.
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Old 30-10-2018, 07:29   #12
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Re: Switching from 12V to 24V

I prefer the DC to DC converter myself. There are plenty of ways to center tap a 24V bank but my experience is they tend to have more downsides then a converter. For a while a number of boat builders used Equalizers to tap 12V from 24V they work OK until they don't. Used to do a lot of work on commercial boats which would be almost all 24V, they almost always just used a converter for 12V loads.
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Old 30-10-2018, 10:44   #13
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Re: Switching from 12V to 24V

I solved a similar problem. Perkins 4.238 is all 12VDC but I replaced the alternator with a 100 Amp 24VDC version. Running a 24VDC battery bank with 8 Firefly Oasis G31 batteries. I charge the starter battery using a Victron Orion 2412 DC/DC converter, 25AMP with adjustable output voltage set to 13.8VDC. These converters are good quality and not expensive.

Most things in the boat are 24VDC, but a few things like radios, chartplotter etc require 12VDC. I parallel a couple of Victron Orion DC/DC converters for redundancy to power the small number of 12VDC loads. No big deal. Works great.
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Old 30-10-2018, 10:54   #14
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Re: Switching from 12V to 24V

Quote:
Originally Posted by coopec43 View Post
I have a Perkins 4-108 installed in my yacht with 12 V alternator and starter. Right now I am installing a 24V 60A alternator (driven by a twin belts)

I have established the starter motor will have no problem handling 24V and all the instruments – tacho, water temp, oil pressure etc can work on 12 or 24V (I presume that means they can work on any voltage between 12 and 24V although I haven’t read that).

I have installed two 150AH AGM batteries as the house batteries. But what do I do now for the starting batteries? I’m inclined to install two 12V batteries in series for the engine starting so I can charge the house batteries and then manually switch to charging the engine batteries as required. Is this the way to go?

ALSO I plan to switch the yacht over to 24V completely but currently the interior lights and oscillating fans are 12V. I was planning to share the load of those items between each of the house batteries. Am I heading for trouble?

Would appreciate help.

Clive
NOTE: Clive has stated his starter will function with 24V input.

It's only the bulbs and the fans that are a concern.

The bulbs could be replaced with 24v bulbs or possibly with LED units that are multi-voltage.

The fans, well i'd try them on 24v and see if the're ok. Most likely the'll just spin faster.
If that's not acceptable and you want to keep the fans, then you could add a small DC DC converter to each fan.
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Old 30-10-2018, 11:23   #15
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Re: Switching from 12V to 24V

I agree migrating "infrastructure" loads like lights and fans over to 24V as it becomes convenient will be best for efficiency.

But there will always be cheaper and more easily found devices in 12V, not to mention guests' needs.

Really not that much trouble to maintain that circuit long as total currents drawn are small.
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