UKC

Hi folks,

I'm trying to wire in a USB charging hub into a leisure battery on a new vehicle of mine. I have positive and negative feeds off the battery. The device has 2 wires leading to the 12v plug, which I have cut off.

How can I tell which wire should be connected to the live battery wire? I don't want to wire it in the wrong way and it go pop!

Thanks in advance,
Knighty

In reply to knighty:
Do they have different colours or stripes?

Also, make sure you fit a fuse

If the charging hub is any good it will either work fine with the wrong polarity, or be protected against it and not work at all (but not be damaged). If it's no good it may just pop, or even worse send out the wrong polarity to whatever you want to charge

In reply to Cheese Monkey:

The wires are just sheathed in black.

What amp fuze should I use?

Also, for the sake of honesty, I will admit that I have already made one unit go pop. I am asking so I don't make the same mistake again! I assumed that the USB unit would just not work if wired backwards

In reply to knighty:

You can't tell now you've cut off the plug.

Why did you cut off the plug? Why not wire a car charger socket to the battery and then you can plug any 12V car charger into it.

In reply to knighty:

Do you still have the "cigarette lighter" plug? Can you identify which wire on the plug went to which wire on the hub at your cut? Look for writing on white printed on the side of the cables, perhaps it's just on one. If it's on both the alignment at the cut might tell you.

If the answer to all of the above questions is yes, then find which wire on the plug goes to the centre pin on the plug - that's the positive.

If not all you can do is plug it in and see what happens! Hopefully not a fire. Fuses: If it's a 2-port USB hub then a 1 amp fuse should suffice.

In reply to knighty:

Can you take it apart?

The negative / ground may be labelled on the pcb inside. If not, the negative will be the one that goes to the most obvious track on the pcb and will connect to the shields/square housings where the USB plugs go.

If you have a multimeter, test each lead for continuity to the outside rectangle of the USB ports. The lowest (0-1ohm) will be the negative

In reply to Philip:

I cut off the plug to replace a 2x12v and 1xusb unit with an equivalent unit with more usb ports.

It was already set up this way.

I also like the simplicity of having USB ports, and not having to use an adapter.

In reply to knighty:

Try this
https://goo.gl/nK4cRS

However, I agree you should fuse it. I doubt you'd need more than 2A, but you should size it by wire size and check the load is compatible.

In reply to sbc23:


Thanks for this useful nugget. Exactly what I am after. I can't open the unit, so I'll find the negative wire using the above method.

In reply to knighty:

You'll probably find that there's an inbuilt digital transformer in the plug, if you connect the wires straight from the USB lead them you'll be giving whatever you connect to it 12v.
If I understand what you've done correctly.

In reply to knighty:


well that's worked out well

Do what Steve suggested.

In reply to knighty:




So are you saying the unit you are trying to fit has two "cigarette lighter" ports on it?

If so then test the connector cable against the centre pin to find which is which. The centre pin should be positive.