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Old 08-02-2017, 03:27   #31
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Re: 12v to 24v conversion

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Originally Posted by Dockhead View Post
This is an old post, so the OP has maybe already made all these decisions.

But I agree with his arguments above. 24v is better than 12v and brings similar benefits as going from 6v to 12v in cars -- remember that? Everything just works better and lasts longer with 24v.

As others have written above -- it is trivial to power the few things you can't get in 24v, using droppers, and droppers give the additional serious benefit of stabilizing voltage. Only significant issue may be SSB.
No, actually i haven't made the final decision yet. The boat that i was referring to in the initial post was finally bought by someone else. i am currently looking at another Hughes 38 - a 1978 version, but many of the same issues apply - she also doesn't have a windlass so the Lofrans Tigre windlass is a distinct possibility.

And, yes, the SSB is an issue. i can't find them in 24volt, and the power drain is substantial when transmitting. i'm also not heading to sea without the ability to get weather maps from NOAA - and that means SSB - or HF ham. ideas?

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Originally Posted by Pizzazz View Post
Having two battery banks on the boat ends does not make much sense. Better put them amidships.
On the Hughes 38 the batteries are under the forward end of the quarterberth - where the navigator sits. There is a possibility of putting them under the port saloon settee, as i plan on removing the holding tank and using a composting toilet. (i can see no reason to carry a bunch of smelly water around with me just so i can flush the toilet - does EVERYTHING on a boat have to be like the dirt version?)

thanks y'all (even tho she's a sloop)
jon
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Old 08-02-2017, 03:57   #32
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Re: 12v to 24v conversion

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Originally Posted by longjonsilver View Post
And, yes, the SSB is an issue. i can't find them in 24volt, and the power drain is substantial when transmitting. i'm also not heading to sea without the ability to get weather maps from NOAA - and that means SSB - or HF ham. ideas?
I think the best way would be a seperate small 12v battery, possibly lithium. A seperate battery mounted high above the bilge powering communication is not a bad safety feature anyway. I have that on my current boat.

This could be charged with one of the 24v to 12v chargers. Some of these have a program for lithium and have outputs of 20A. This means the battery won't do much work, as the charger will supply most of the power even during transmit. The battery is more a buffer to stabilise voltage (the stable high voltage of lithium batteries during discharge would make them a good choice for this application).

Another option would be a large 24v to 12v converter. You would need to check the size. My guess is you would need a unit capable of 40 Amps or more.

You also need to check the RF interference from the switch mode supply. This may be an issue. If so you would need a large enough 12v battery to supply all the power and charge the 12v battery when not using the SSB.

However, this is a lot of complication and expense for a 38 foot boat. At this size I would definitely stay with an all 12v system.
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Old 08-02-2017, 06:15   #33
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Re: 12v to 24v conversion

Quote:
Originally Posted by longjonsilver View Post
No, actually i haven't made the final decision yet. The boat that i was referring to in the initial post was finally bought by someone else. i am currently looking at another Hughes 38 - a 1978 version, but many of the same issues apply - she also doesn't have a windlass so the Lofrans Tigre windlass is a distinct possibility.

And, yes, the SSB is an issue. i can't find them in 24volt, and the power drain is substantial when transmitting. i'm also not heading to sea without the ability to get weather maps from NOAA - and that means SSB - or HF ham. ideas?



On the Hughes 38 the batteries are under the forward end of the quarterberth - where the navigator sits. There is a possibility of putting them under the port saloon settee, as i plan on removing the holding tank and using a composting toilet. (i can see no reason to carry a bunch of smelly water around with me just so i can flush the toilet - does EVERYTHING on a boat have to be like the dirt version?)

thanks y'all (even tho she's a sloop)
jon
For the SSB, there are a couple of good solutions:

The best is to power it with a separate battery charged from the main system with an echo charger. You can power your main VHF and maybe other key electronics from this as well, and then as a bonus, you have an extra safe separate power supply for these life-safety critical devices. This is actually required for SOLAS vessels.

If you go this route, make sure the echo charger has enough capacity to support the voltage when you're transmitting. The battery itself should have enough capacity to maintain reasonable voltage, but the charger should be capable of keeping it at least 12.5v or so. A small LiFePo4 battery unit might be ideal for this as they have less voltage sag than lead acid.

I would have done this but just didn't quite have the right space for the battery.

So what I did was simply to use a jumbo Victron dropper. I was concerned about possibly electronic noise, but it works fine. Also has a pretty big advantage (like other dropper situations) that it provides stabilized output at 13.6 volts, which is ideal for the radio and will significantly improve the radio performance compared to sagging normal 12v supply.

So in my view there is some extra complication, but not really a fatal issue.


Edit: I wrote this this morning but didn't post it until just now. I see that Noelex has pretty much covered this points. I'll leave this post up as there may be one or two useful details.
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Old 08-02-2017, 12:35   #34
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Re: 12v to 24v conversion

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Originally Posted by Dockhead View Post

The best is to power it with a separate battery charged from the main system with an echo charger.
While there are solutions to this - DC-DC converters such as those from Victron - an Echo Charge is not one of them. It requires both battery banks to be the same voltage.

I agree with Noelex - over-complicated and illogical for a 38' boat. For a boat over 50' it can make sense.
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Old 15-05-2017, 05:28   #35
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Re: 12v to 24v conversion

i asked this question on another thread, and i'll ask it again here since i didn't get and answer. As far as fire hazard is concerned, which is safer 12v or 24 volt?
jon
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Old 15-05-2017, 06:25   #36
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Re: 12v to 24v conversion

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Originally Posted by longjonsilver View Post
i asked this question on another thread, and i'll ask it again here since i didn't get and answer. As far as fire hazard is concerned, which is safer 12v or 24 volt?
jon
Doubt it makes much difference. Each can start a good fire.
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Old 15-05-2017, 07:06   #37
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Re: 12v to 24v conversion

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Doubt it makes much difference. Each can start a good fire.
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