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24v-12v dropper install


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Hi there,

 

New fit out. 24v system. Installing a voltage dropper for 12v outlets on the boat (largely for computer chargers which are not available in 24v). Victron Orion 24/12-40, will provide 40A continuous @ 12v with a 55A peak. I will install 7 cigarette lighter outlets, each rated at 10A. Obviously not all of these outlets can be used to full capacity, but on a 4 berth vessel I figure 40A should be plenty.

 

I am interested in the installation of the device at the power end.

 

My proposal:

 

24v input wired via a suitable fuse direct to battery bank (downstream of master switch). Distance from bank less than 1m. Thick cable.

 

Remote on/off connector wired to main DC distribution panel. Distance from bank, 2-3m. Thinner cable.

 

12v output fused at 50A split and run to various outlets.

 

Thoughts welcome

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I would suggest that the cable between the unit and the distribution board should be as thick or thicker than that between the battery and the unit for a coupe of reasons,

1 it will be carrying twice the current

2 its twice as long

3 volt drop between battery and unit will still result in a 12 volt output, volts dropped between unit and appliance are lost for ever.

 

see bonus, I found 3

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Also consider some USB outlets. These days all my crew ever want is to charge a smartphone.

 

Our boat is 24v but I have not replaced around half the outlets with USB ones.

 

Not super future proof, and they do have a parasitic load, but will run off 24v Carly which not all cigarette lighter USB units will.

 

 

Daniel

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...

 

My proposal:

...

12v output fused at 50A split and run to various outlets.

 

Thoughts welcome

I would suggest that each 10 amp socket has it's own fuse, 10 or even 15 amp, but with a master fuse of say 50 Amp.

Cable on supply and return both of suitable current carrying capacity.

 

The reason being, most cigar lighter plugs are not fused, so you would need to blow a 50 amp fuse with low amp cables.

Look at extension leads, some with USB outlets, input wiring barely capable of carrying 5-10 amps let alone 50 amps.

Also the connectors on cigar type sockets are not designed for two cables on each terminal, each carrying 50 amps.

Also there is reliability, if one socket is taken out by a faulty appliance, it only takes out one 10 or 15 amp fuse, the other sockets should still remain intact.

 

Hope it makes sense.

Richard

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There is a fundamental problem with 24v to 12v droppers. They deliver 12v which is not a proxy for the 12.5 to 15v usually found in a nominally 12v system. In my experience, a number of devices can throw a bit if a strop when fed with perhaps 11.8v (or even lower when the boat cabling is less than massive). To overcome this effect I use a 24v to 13.4v dropper.

 

I'm sure the OP will be installing suitable fat 12v cabling but I suggest bearing this in mind in the fit-out, as might anyone considering a 24v domestic battery bank and nominally 12v domestic electrics.

  • Greenie 1
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The cigarette lighter plugs here ARE fused. 8A or 16Aand are well made and rewirable. They also have 12/24V flush mount sockets rated 20A/

 

https://www.roadpro.co.uk/catalogue/02g03-procar-universal-plugs

But that doesn't preclude someone plugging in their own faulty cable. Hence the suggestion that the feeds need to be individually fused.

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Hi all, 

Thanks for the comments. Really helpful stuff. 

Yes, I will also have USB outlets (in even more places than 12v outlets in fact) run direct on 24V.

Fusing the individual outlets is a good idea, and one I will muse upon. My plan at present is to run 4 rings, each one wired in 6mm cable, and each with two or three outlets on. The max distance on any ring is 9m (one way). The effective CSA of the cable feeding an outlet will be 12mm (albeit over a slightly longer distance if it is taking the long way round). I was then proposing to put a 15A breaker on each of these rings, as the voltage drop if one ring is pulling 20A+ is too great. 

As I said, these outlets are largely going to be used for computer charging, the two we currently have (mac and pc) draw 7.5A and 5.6A each, and specify a minimum voltage of 11.5 and 11. I have tried to make my system capable of having both of these chargers plugged in at the same time, drawing their full current, in any of the outlets. Obviously the sockets may end up being used for other things in the future, but this seems like a good starting point. 

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Seems best to me to run a 24V 'bus' along the boat, otherwise you're starting to negate the advantages of 24v.

Then have say a few 24V to 12V 10A droppers near the ciggy sockets, each feeding pair of sockets? The converters should have some sort of foldback over current protection, so a 10A coverter would just need a simple fuse on the input.

A modern lappie should run 10 to 20W once the internal batt is charged. These type converters look OK, worth checking out idle current, though it should be small.

http://www.ebay.co.uk/itm/DC-DC-Converter-Regulator-12V-Waterproof-StepUP-StepDown-Car-Power-Supply-Module-/291672497098

 

Edited by smileypete
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