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Old 08-02-2013, 12:51   #1
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48v 36v 24v and 12v system

i dont understand the point of having anything but 12 volt on a boat.... all motor and appliances i have seen are 12 volt. what is the purpose of wiring batteries and having chargers in 24 volt or higher? what possible electrical devices could i use that isn't 12 volt?
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Old 08-02-2013, 13:11   #2
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Re: 48v 36v 24v and 12v system

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Originally Posted by drousy88 View Post
what possible electrical devices could i use that isn't 12 volt?
Just about anything. The amount of power available is a function of voltage times current. So, at 24V all other things being equal, the same equipment will use half the current. For instance, a windlass that draws 100A at 12V will draw 50A at 24V and 25A at 48V (if they all have the same power rating).

The required wire/cable size is a function of current, nothing else, so higher voltage systems can have smaller wires, lowering installation costs (especially with copper as valuable as it currently is).

Most boat items are available in 24V, but may cost you more because they are not derived from the mass-production automobile 12V market. However, as accessory power usage goes up even some autos are moving toward higher voltages.
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Old 08-02-2013, 14:09   #3
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Re: 48v 36v 24v and 12v system

During the war, US auto makers went from 6 volts to 12 to save copper for the reasons Dsanduril gave, 1/2 the current for the same work (watts) done. On my next boat I will go to 48 volts for the inverter house bank also for that same reason.
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Old 08-02-2013, 14:09   #4
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Re: 48v 36v 24v and 12v system

If you double the voltage you half the current as stated above, so you can reduce wire size by 3 AWG for the same voltage drop in the wire.

100 amp windlass at 12 V with a 40 foot round trip for the wire with a 10% voltage drop needs a 4 AWG wire. At 48 volts that becomes a 10 AWG wire.

Do much high current wiring in your boat and it adds up. Windlass, 2000 watt inverter, etc.

Rule of thumb change size of wire by 3 AWG and you half or double the resistance. 10 AWG is 1 ohm per 1000 ft.

or

American wire gauge - Wikipedia, the free encyclopedia
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Old 08-02-2013, 14:14   #5
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Re: 48v 36v 24v and 12v system

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i dont understand the point of having anything but 12 volt on a boat.... all motor and appliances i have seen are 12 volt. what is the purpose of wiring batteries and having chargers in 24 volt or higher? what possible electrical devices could i use that isn't 12 volt?
most industrial stuff is 24v dc
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Old 08-02-2013, 14:31   #6
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Re: 48v 36v 24v and 12v system

you use less amps at 48v but it also makes your battery bank have less amp hours. i.e. if i have 8x 6volt 225ah batteries wired to 12 volt i have a battery bank of 900ah. if i were to wire them at 48 volt then my battery bank would only have 225ah.......right?
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Old 08-02-2013, 14:35   #7
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Re: 48v 36v 24v and 12v system

Higher voltage is a good thing because:

1. lighter gauge wire
2. higher efficiency appliances
3. it allows you to put your batteries in series as too many in parallel has a chance of complete meltdown if one of the battery cells fails shorted and allows the other batterys to discharge thru it.


with that said I used 12 volt with 4 batteries in parallel... I am basically limited by my solar setup. In the future I would look for higher voltage panels, or several smaller ones in series that will be mounted on exact same angle next to each other as series panels do poorly in partial shade
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Old 08-02-2013, 14:40   #8
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Re: 48v 36v 24v and 12v system

Wasn't this the argument of Tesla versus Edison in which case I think Tesla should have won but was out maneuvered by Edison?
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Old 08-02-2013, 14:45   #9
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Re: 48v 36v 24v and 12v system

Most small boat electric propulsion systems are 48 volts sothere are quite a few chargers, inverters, and dcdc converters for 48v. There are also a lot of electrical appliances for 36v because most older fishing boats have 36vdc electrical systems so there are cheap heavy duty fans, reefers, etc for that voltage. A lot of high current elecrronics such as radars are 24vdc. One of my near future projects is to go 48v for my house bank because eventually when my atomic gives up the ghost i will probably go electric oe diesel electric hybrid drive. I would go 72 or 144v if inverters and chargers were cheaper. Inverters have gotten much more efficient and AC household and industrial appliances are cheaper than 12v and last longer. So I am running out of reasons to prefer a 12v bank. I dont know of any 48v starter for rhe atomic so I will keep a group 29 batt just for starting.

The reasons for higher voltages are already well stated above, as are the reasons for 12v so I wont restate the obvious but these days 48v is looking more attractive to me.
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Old 08-02-2013, 15:00   #10
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Re: 48v 36v 24v and 12v system

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Originally Posted by drousy88 View Post
you use less amps at 48v but it also makes your battery bank have less amp hours. i.e. if i have 8x 6volt 225ah batteries wired to 12 volt i have a battery bank of 900ah. if i were to wire them at 48 volt then my battery bank would only have 225ah.......right?
Yes. So? 1/4 the current at 4x the voltage is the same amount of energy and accomplishes the same amount of work.
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Old 08-02-2013, 15:20   #11
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Re: 48v 36v 24v and 12v system

Yes, but the wires are finer, lighter and cheaper. Big factor in any big boat.

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Old 08-02-2013, 16:02   #12
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Re: 48v 36v 24v and 12v system

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Originally Posted by drousy88 View Post
you use less amps at 48v but it also makes your battery bank have less amp hours. i.e. if i have 8x 6volt 225ah batteries wired to 12 volt i have a battery bank of 900ah. if i were to wire them at 48 volt then my battery bank would only have 225ah.......right?
More detail than the last post, but basically the same info.

Power is what you use to accomplish the task. Power = voltage times current.

A 12 volt windlass that draws 100 amps consumes 1200 watts of power.

To be able to pull up the same size anchor at the same rate with a different windlass would require it to use 1200 watts of power.

48 volts x 25 amps = 1200 watts.

You can only compare amp-hrs for the same voltage. If you are going to compare different voltages you want to look at your battery capacity in watt-hours.

900 amp-hrs times 12 volts is 10800 watt-hrs

225 amp-hrs times 48 volts is 10800 watt-hrs.

The amount of work you're able to do is the same.

power is work/time.
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Old 08-02-2013, 18:00   #13
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Re: 48v 36v 24v and 12v system

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Originally Posted by cal40john View Post
More detail than the last post, but basically the same info.

Power is what you use to accomplish the task. Power = voltage times current.

A 12 volt windlass that draws 100 amps consumes 1200 watts of power.

To be able to pull up the same size anchor at the same rate with a different windlass would require it to use 1200 watts of power.

48 volts x 25 amps = 1200 watts.

You can only compare amp-hrs for the same voltage. If you are going to compare different voltages you want to look at your battery capacity in watt-hours.

900 amp-hrs times 12 volts is 10800 watt-hrs

225 amp-hrs times 48 volts is 10800 watt-hrs.

The amount of work you're able to do is the same.

power is work/time.


i understand now, so what's the safest daily discharge out of my 900 ah bank?
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Old 08-02-2013, 18:14   #14
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Re: 48v 36v 24v and 12v system

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Originally Posted by drousy88 View Post
you use less amps at 48v but it also makes your battery bank have less amp hours. i.e. if i have 8x 6volt 225ah batteries wired to 12 volt i have a battery bank of 900ah. if i were to wire them at 48 volt then my battery bank would only have 225ah.......right?
What matters are the total number of watt-hours that can be stored. Comparing amp-hours is fine as long as you are also comparing the same voltage. This way you are comparing apples to apples.
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Old 08-02-2013, 19:12   #15
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Re: 48v 36v 24v and 12v system

The one issue with drawing down batteries is that lead acid prefer to be discharged slowly, particularly with the deep cycles we use on boats. This does result in an efficiency gain, so by drawing 6 amps at 24v you do actually get more usable power from the same batteries than if you draw 12amps at 12v.
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