Wiring a basic 12v socket? What am I doing wrong???

[James H]

Hi Everyone, 

 

Would super appreciate a real basic breakdown here of where I am going wrong. So I am trying to wire a triple 12v socket (cigarette lighter style) from my switch board to charge 2 phones and our WiFi hub. The WiFi hub says 'input 12v - 2A' on the back. I have checked online and someone as successfully wired the same Huawei 3g hub onto 12v on their boat. 

 

I intend to power the hub, and be able to charge two phones all at the same time. The hub is 2 amps max, (I assume from it saying 'input 12v - 2A') and the phones both take 2amps max as most usb phone car chargers are fitted with a 2 amp fuse etc. So that means put a 6 amp fuse in the switch board for that one?! Correct?! 

 

Then if each of the 12v USB plugs for the phones have a 2amp fuse in each then that protects the phone should more power go through.

 

So I did that, wired up the socket as above (except I had a 10amp fuse in switch board) and when I plugged in the phone it popped and I smelt burning, the fuse/USB car plug fried with too much power going in. So my question is how do you wire up a triple USB socket that can have say 6 amps minimum being supplied to the triple socket to have up to 3 devices (in this case 2 phones and a WiFi hub) without the power overloading one device and frying the fuse in the plug when only one device is plugged in???

 

I have added a pic where I show the positive line up top, that goes into the blue cable which goes into the fuse, then out to the switch and then the positive line goes out from there to the device its powering (in this case a socket), and the main negative is circled up top where I can attach the negative coming back from the socket.

 

So what am I doing wrong??? 

 

Thanks in advance for any advice, its much appreciated...

[Sea Dog]

By the look of that snakes wedding, I'd guess you're doing pretty much everything wrong, and the popping noises and the burning smells seems to back that up! 

 

I think your level of knowledge is such that you need a greater degree of help than the written word can provide considering the risks posed by misinterpretation.  You need to find someone in your area who can have a look for you. Folk here will often "pop round" in such situations - where are you?

 

[James H]

It seems pretty well wired up, the switch board has worked fine for everything on the boat since we bought it over a yr ago. Its just I've only now got round to wiring up a 12v socket so I can turn the inverter off and save some charge. 

 

I think the fuse board is wired up fine as its works well for everything else, its just something I am doing wrong with the way I have wired up the socket, must be to do with the wire or fuse, can't think what else it can be?!!!

[Alan de Enfield]

19 minutes ago, James H said:

It seems pretty well wired up

 

That is debatable - why is there a red wire going into a blue wire, disappearing out of picture and then coming back onto the switch, then a red wire on the other side of the switch 

 

Where does the blue wire go ? Is anything else connected to it ? Why does the connector where the red goes into the blue not going straight onto the switch ?

 

Someone sometime has been doing modifications and added extra wiring. It is not acceptable standards to change colours during a cable run.

Edited March 5, 2021 by Alan de Enfield

[Tony Brooks]

Total lack of knowledge I am afraid.

 

The fuses/mcbs at the distribution board are to protect the  CABLES, not what is connected to the other end.

 

The current each device you plug in is determined by what that device needs. It will not draw more than its designed draw unless there is a fault in it.

 

So IF and its a big IF your two chargers are fuse at 2 amps they will  raw less than that and with everything plugged in the 10 amp fuse at the other end of the wiring will not blow. If it does then you have a  fault, probably a short circuit.

 

Now I bet the Wi-Fi Hub is designed to be supplied from a stabilised mains wall wart, not a battery system that should spend most of its time above 12V and when charging at up to 14.5V plus voltage surges when motors turn on and off. Have you damaged the hub causing t to draw too much current?

 

I am not going to bother trying to make head or tail of your photo until you supply a diagram of what you think you have done with all the parts labelled. i think you have created a short between positive and negative somewhere or somehow even if its in a burned out hub.

 

[nicknorman]

As said, the fuse is to protect the wiring not the appliances. Looking at the wires, a 10A fuse should be OK. Everything was OK until you plugged in the phone charger, therefore it would seem likely that there is something wrong with the phone charger and/or somehow a short circuit was created with the action of inserting it. So I think the problem lies with that, not with the wiring and fusing. Just to be clear, an appliance (hub or charger) takes whatever current it needs and wants, you can't restrict that with fusing unless you want the fuse to blow and it to stop working.

[Hudds Lad]

1 hour ago, Sea Dog said:

By the look of that snakes wedding....

 

 

? thank-you for that term, not heard it before, it’s made my afternoon

[Guest]

Snakes wedding  ?

 

And you should consider buying a multimeter and checking what's coming out before plugging expensive gear in!

[Detling]

I tried a USB charger by accidentally reversing positive and negative, the results were similar to your description and the Bush charger was dead and had to be replaced, I made sure I connected the next one correctly.

 

[Richard10002]

5 minutes ago, Detling said:

I tried a USB charger by accidentally reversing positive and negative, the results were similar to your description and the Bush charger was dead and had to be replaced, I made sure I connected the next one correctly.

 

 

Like you, I have accidentally reversed +ve and -ve on a cigarette lighter type socket..... the 10A fuse in the plug blew.

 

I was wondering whether this could have been the problem with the OP situation.

[Tony Brooks]

11 hours ago, Richard10002 said:

 

Like you, I have accidentally reversed +ve and -ve on a cigarette lighter type socket..... the 10A fuse in the plug blew.

 

I was wondering whether this could have been the problem with the OP situation.

 

If the socket is fitted into a metal plate that is connected to battery negative it might be because the metal body of the socket would cause a short circuit. if its mounted on a wooden cabin lining its unlikely until something is plugged in. At that point magic smoke may be emitted from whatever is plugged in.

[Richard10002]

4 hours ago, Tony Brooks said:

 

If the socket is fitted into a metal plate that is connected to battery negative it might be because the metal body of the socket would cause a short circuit. if its mounted on a wooden cabin lining its unlikely until something is plugged in. At that point magic smoke may be emitted from whatever is plugged in.

 

Mine was the latter - mounted on the wooden cabin lining  

[Tony Brooks]

6 minutes ago, Richard10002 said:

 

Mine was the latter - mounted on the wooden cabin lining  

 

Then unless the back of the socket was touching metal nothing should have happened until you plugged something in. When you did it would be fed reverse polarity that might or might not destroy it.

[wakey_wake]

On 05/03/2021 at 21:45, Detling said:

I tried a USB charger by accidentally reversing positive and negative, the results were similar to your description and the Bush charger was dead and had to be replaced, I made sure I connected the next one correctly.

 

There are several ways to do reverse polarity protection when designing this kind of kit, and the cheaper kit does it the cheapest way.

1. a blocking diode in the supply. When it's backwards nothing happens, but when it's forward the diode steals half a volt.
2. a crowbar diode reversed across the supply. When it's forward, you get full voltage and the diode sleeps. When it's backwards there is a short circuit through the diode and hopefully the fuse blows. There may be sparks and burning smell, but most of the magic smoke should be retained so it's possible to repair the thing.
3. no protection, which saves a fraction of a penny at build time. When it's backwards, all the magic smoke is likely to escape. Any equipment connected downstream may get its own reverse polarity challenge. You buy a different brand and are more careful next time.
4. fancy stuff like the ideal diode or other active protection.
5. or it's designed to accept AC, such as those MR16 LED spotlamps. It probably has a bridge rectifier which steals a volt, but it won't care which way it is connected.

All that, and you have to know what the voltage actually is. Some vehicles run 24V but they're usually clearly marked.

 

It's still best to not trust the thing you plug the kit into until you've checked.