Help fixing car battery charger cord

[headmotty]

Hi - this may an easy question, but I need some help here. I'm putting a new plug on a severed car battery charger cord, and can't figure out which wire should be hot / which wire should be neutral. There are 3 wires - green is the ground, and two black wires. One of them has some ribbing along the side vs. the other being smooth, but then the smooth one is the one with the lettering, etc. stamped into the insulation, so that isn't helping much with identification.

I can see that inside the unit, the wire with the lettering is the one that hooks up to the transformer, and that the other goes to the volt/amp selector switch.

If someone could tell me whether the hot or the neutral should go to the transformer, then I would be able to connect the new plug end correctly.

Thanks!!

 

[Resqueline]

Not that I believe it really matters, but if I had to make a choice/guess it would be that the hot goes through the switch.

 

[LTX71CM]

Not that I believe it really matters, but if I had to make a choice/guess it would be that the hot goes through the switch.

That would have been my guess too. Is there not a scrap of wire still attached to the old plug? If so inspect it very closely to find a ridge, writing or some other distinctive marking.

 

[headmotty]

Thanks both of you for your replies. I forgot about the "does it even matter?" option.

I can't examine the old plug. Somebody had just hastily spliced and taped a new plug to the old cord, so I'm trying to do it right.

Electronics isn't my strong point, but I was actually leaning towards the opposite - that the incoming full current would go to the transformer first to be stepped down, but after your replies and examining the insides again, going to the switch first looks more correct. Let me describe what I'm imagining based on what I see...the current goes to the switch via the black hot wire. There are 3 volt/amp settings, and three wires (orange, brown, yellow - I assume one for each setting) go from the switch to the transformer. Then the current can come out the other side of the transformer and out to the +/- terminals of the battery. The second black wire going from the wall outlet to the transformer would be the neutral to carry any free current back to the wall outlet. Does that sound correct?

If the incoming full current went to the transformer first, then the only way for it to get to the volt/amp selector switch would be via those 3 colored wires, and then the only way for it to get back to the transformer and out to the car battery would be via the black wire hooked to the switch - but that doesn't lead to the transformer, it leads back to the wall outlet. So that wouldn't make sense, would it? You both must be right in that the hot wire would go to the selector switch first.

Does this sound correct? I'm just trying to get the actual flow of current straight in my mind. (Sorry, I'm not satisfied with just getting the right answer - I like to understand stuff!)

Thanks again!

 

[Resqueline]

I couldn't agree more on you last statement, it's how I work too.

The only difference between Neutral & Live (hot) is that the Neutral is at (almost) the same voltage level as Ground while Live is at full mains potential and "hot" to the touch.
The wire having the greatest risk of being shorted to ground during a fault condition should be connected to Neutral. If there's a ground break too you wouldn't get a shock.

To understand the flow of current; don't introduce the secondary battery circuit into the reasoning of the primary mains circuit. They're separate, although inductively coupled.
If the primary side has AC mains across its winding the there will be (a lower voltage) AC at the secondary side, being rectified before being fed to the battery.
What (current) "comes out of" the Live must return to the Neutral.
The three taps can be compared to a lever system that jacks up the output voltage the closer to the "hinge point" (Neutral) you apply the "movement" (mains voltage).
Hth.

 

[headmotty]

OK, I think I got that. I put it together and it seems to be working fine, so all is good.

Thank you again for your guidance. Much appreciated!