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12V Wiring - New USB Charger


bmp

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Hi Everyone.

 

I want to add a couple of USB chargers to charge up my phone and iPad etc..  

 

Something like one of these ......   https://www.amazon.co.uk/gp/product/B07FFW919L/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Doesn't have to be that exact one - just using that as an example.

 

My boat already has a few 12V sockets for the fridge, freezer and one near the TV.

 

Being lazy ........  I was thinking of just wiring in a USB charger into the same plug as the fridge or freezer. So the actual plug would have 2 lots of cables coming out.

I will put an inline fuse before the USB charger / socket. 

Is this acceptable?  Is it a really bad idea ?  Dangerous ?

I assume the correct way to do it would be to run a few cables all the way back to the fuse board. Or could I use some sort of junction box near an existing socket?  Is that just as bad?

 

Any thoughts or advice welcome. 

 

Thanks. BMP

 

 

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You could do that. Not dangerous. Just a little bit untidy I suppose. The only thing to bear in mind is that fridges and freezers take a lot of current when starting up, which causes temporary voltage drop, and fridges and freezers tend to have a low voltage cutout. So adding extra load = current = voltage drop, might result in the fridge or freezer cutting out at a higher battery voltage than it might otherwise do. But only an issue if the fridge/feeezer wiring is marginal and/or you are in the habit of running the batteries very low.

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The one linked to looks like it's meant for panel mounting, which would be neater, provided that there is sufficent clearance behind it. No problem linking it to the back of an existing socket, although if on the fridge or freezer circuit, it might want its own fuse.

 

We, ourselves, are a bit untidy, in that our sockets are the Clipsal 2 pin ones, and we have a 4 way cigarette lighter socket adaptor on a Clipsal plug, with cigarette lighter type plug in USB adaptors.

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29 minutes ago, Alan de Enfield said:

What size wiring have you used for the fridge & freezer ?

What distance is it from the batteries to the Fridge & Freezer ?

 

These questions are relevant.

Not sure - I havent actually looked that close yet. I was just checking if it was ok to do “in theory” before delving too deep into the wiring. 

52 foot boat with batteries etc at rear. Fridge and freezer are about half way down the boat so would roughly estimate about 25 feet. 

Thanks for your reply. 

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I have a similar unit wired into the same circuit as a 5A socket with a 5A fuse. I never use both outlets together so the 5A rating is fine. I would avoid sharing with a fridge for all the above reasons.

BTW you can buy identical unit off eBay at half that price.

 

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26 minutes ago, nicknorman said:

You could do that. Not dangerous. Just a little bit untidy I suppose. The only thing to bear in mind is that fridges and freezers take a lot of current when starting up, which causes temporary voltage drop, and fridges and freezers tend to have a low voltage cutout. So adding extra load = current = voltage drop, might result in the fridge or freezer cutting out at a higher battery voltage than it might otherwise do. But only an issue if the fridge/feeezer wiring is marginal and/or you are in the habit of running the batteries very low.

Ok thanks. Will bear that in mind. Maybe just use the one by the tv. That was only used for a car radio which I don’t use anyway. 

28 minutes ago, Iain_S said:

The one linked to looks like it's meant for panel mounting, which would be neater, provided that there is sufficent clearance behind it. No problem linking it to the back of an existing socket, although if on the fridge or freezer circuit, it might want its own fuse.

 

We, ourselves, are a bit untidy, in that our sockets are the Clipsal 2 pin ones, and we have a 4 way cigarette lighter socket adaptor on a Clipsal plug, with cigarette lighter type plug in USB adaptors.

The socket near the tv has lots of space to mount the adapter I linked to and would look quite neat. Also lots of space to hide and keep the wiring tidy. 

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2 minutes ago, bmp said:

Not sure - I havent actually looked that close yet. I was just checking if it was ok to do “in theory” before delving too deep into the wiring. 

52 foot boat with batteries etc at rear. Fridge and freezer are about half way down the boat so would roughly estimate about 25 feet. 

Thanks for your reply. 

So about 50 feet total length (battery to fridge back to battery) 

 

With that sort of distance your wiring for the fridge needs to be around 12mm2 (not 12mm diameter) to avoid volt drop.

 

Is it a new boat?  have you done the wiring ? has it been running a 12v fridge previously ?

 

Is the 12v freezer also run of the same cabling or does it have its own supply ?

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3 minutes ago, Floating Male said:

I have a similar unit wired into the same circuit as a 5A socket with a 5A fuse. I never use both outlets together so the 5A rating is fine. I would avoid sharing with a fridge for all the above reasons.

BTW you can buy identical unit off eBay at half that price.

 

Thanks for that. Probably use the socket I have by the tv that is not really used  

thanks for the eBay option. Was just using the amazon one for an example. 

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1 minute ago, Alan de Enfield said:

So about 50 feet total length (battery to fridge back to battery) 

 

With that sort of distance your wiring for the fridge needs to be around 12mm2 (not 12mm diameter) to avoid volt drop.

 

Is it a new boat?  have you done the wiring ? has it been running a 12v fridge previously ?

 

Is the 12v freezer also run of the same cabling or does it have its own supply ?

Yes - about 50 total. 

Boat is 3 years old. All cabling etc in place when I bought it last year. The freezer is nearer. It is in a wardrobe in the bedroom. Maybe 20 / 30 foot total. This is run on a separate cable. 

That would be my preferred location for charging my phone / iPad in the bedroom. Also can mount the adapter into the bedside cabinet. 

Thanks for the help so far.

 

 

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1 minute ago, bmp said:

Yes - about 50 total. 

Boat is 3 years old. All cabling etc in place when I bought it last year. The freezer is nearer. It is in a wardrobe in the bedroom. Maybe 20 / 30 foot total. This is run on a separate cable. 

That would be my preferred location for charging my phone / iPad in the bedroom. Also can mount the adapter into the bedside cabinet. 

Thanks for the help so far.

 

 

You should be fine running your USB charger from any of the points you have mentioned.

I was asking about the fridge cabling as I recently had a problem when I changed my fridge - the old one worked fine, but with the new fridge it would only get cold with the engine running.

The cabling was undersized and due to volt drop was running continuously and not getting cold. I re-wired the supply with the correct size and every thing works as it should.

 

If the fridge has worked previously then you should be fine.

 

Enjoy.

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1 minute ago, Alan de Enfield said:

You should be fine running your USB charger from any of the points you have mentioned.

I was asking about the fridge cabling as I recently had a problem when I changed my fridge - the old one worked fine, but with the new fridge it would only get cold with the engine running.

The cabling was undersized and due to volt drop was running continuously and not getting cold. I re-wired the supply with the correct size and every thing works as it should.

 

If the fridge has worked previously then you should be fine.

 

Enjoy.

Great - thanks for the advice. Didn’t want to do anything that might be deemed “dangerous”

Out of the 3 possible locations the bedroom / freezer one is my preferred option. The one by the TV and the freezer could be neatly done as they have a cabinet to hide it in. I will avoid the fridge as it is not as easy to mount the USB adapter anywhere. 

 

Thanks again. 

 

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11 minutes ago, bmp said:

Out of the 3 possible locations the bedroom / freezer one is my preferred option. The one by the TV and the freezer could be neatly done as they have a cabinet to hide it in. I will avoid the fridge as it is not as easy to mount the USB adapter anywhere. 

And as they are half the price on eBay, buy two and fit one in each of the "good" locations.

 

Then you can run up and down the boat and read the different voltage readings at each point!

 

@Mike the Boilerman would recommend you get three and average the readings ...

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4 minutes ago, TheBiscuits said:

And as they are half the price on eBay, buy two and fit one in each of the "good" locations.

 

Then you can run up and down the boat and read the different voltage readings at each point!

 

@Mike the Boilerman would recommend you get three and average the readings ...

Haha. Good idea. 

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  • 1 month later...

This thread could have been me!

 

I used to have a 12V socket about 16m away from the switch. It worked with the 12V USB chargers that I use (which I highly recommend - https://www.amazon.co.uk/gp/product/B075WQQG7C), but every now and then the switch would trip. It has since stopped working entirely. I'm not sure how thick the wires are, they look like about 3mm in diameter including the insulation.

I want to install 12V cigarette lighter sockets in three locations. I'm trying to figure out what gauge of wire I need. The locations are 8m, 11m and 16m from the 12V trip switch board (one way wire run). The chargers that I use are 3.75A max.

 

Should I:

    A. Run these all to the same fuse and select a gauge appropriate for a 3.75A*3=11.25A over 16m? This I worked out to need 16mm^2 (5 AWG), which results in a voltage drop of 3.17%.

 

    B. Run these to their own separate fuses, with the largest required cable being 3.75A over 16m? This I worked out to need 6mm^2 (9 AWG), which results in a voltage drop of 2.83%.

 

I also have four other very nooby questions regarding 12V wiring:

    1. Do you wire the negative directly to the hull, like a car? Or run a negative cable back to the battery?

    2. The switches on the fuse board have very skinny little wires connecting them to the main supply. I would have thought that the whole circuit would have to be in large gauge - the weakest link essentially limiting the whole circuit. Or doesn't it work like that?

    3. The switches have some kind of built in trip with a little reset button. They don't seem to be fused.

    4. Where is a good vendor to buy electrical wiring? Online shop?

Edited by ivan&alice
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2 hours ago, ivan&alice said:

Do you wire the negative directly to the hull, like a car? Or run a negative cable back to the battery?

Never ever ever. Avoid any -ve connections to the hull at all costs. 

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1 minute ago, WotEver said:

Never ever ever. Avoid any -ve connections to the hull at all costs.  

Noted, will run cable there and back.

I'm pretty sure the hull or at least engine block is connected to the -ve terminal in the engine bay, or am I mistaken?

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2 hours ago, ivan&alice said:

The switches on the fuse board have very skinny little wires connecting them to the main supply. I would have thought that the whole circuit would have to be in large gauge - the weakest link essentially limiting the whole circuit. Or doesn't it work like that?

If a circuit requires a fat cable to avoid voltage drop then the wiring behind the fuseboard for that circuit doesn’t need to be the same size (because it’s only very short) but it does need to be sized correctly for the fuse in that circuit. Having said that, 1.5mm2 is good for up to 20A so it really doesn’t need to be very heavy. 

4 minutes ago, ivan&alice said:

I'm pretty sure the hull or at least engine block is connected to the -ve terminal in the engine bay, or am I mistaken?

That is correct and how it should be. That is the only hull connection that should exist on your boat. 

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Thank you. I must admit I'm surprised that the circuit can have short thin sections without causing major voltage drop. I suppose that short section will act like a resistor and perhaps get a little warm.

I also suppose I will have to have a nut&bolt and crimped lugs to convert the small fuseboard wire to the large gauge wiring.

 

Any thoughts on 3x 6mm^2 cable seperately switched or 1x 16mm cable that connects the three sockets in parallel, with only one switch?

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11 hours ago, ivan&alice said:

I must admit I'm surprised that the circuit can have short thin sections without causing major voltage drop. I suppose that short section will act like a resistor and perhaps get a little warm.

All cables have resistance. The thicker the cable the lower the resistance, and the shorter the cable the lower the resistance. So a short length of 1.5mm at the end of a long length of 16mm (for instance) will have no effect on voltage drop. So as long as the thin cable is comfortably within its current rating there’s no problem. 

 

11 hours ago, ivan&alice said:

I also suppose I will have to have a nut&bolt and crimped lugs to convert the small fuseboard wire to the large gauge wiring.

Sounds good. 

 

11 hours ago, ivan&alice said:

Any thoughts on 3x 6mm^2 cable seperately switched or 1x 16mm cable that connects the three sockets in parallel, with only one switch?

Individual cables is arguably more elegant but if the likelihood is that you’ll rarely have all three feeds simultaneously fully loaded then the single feed will give a lower voltage drop. 

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