Positive ground lesson

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289Glenn
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Joined: Wed Jun 10, 2015 6:49 pm
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Positive ground lesson

Post by 289Glenn »

Greetings Gents!

I made an interesting observation last night...................

As we all know, but may not think about it every day, almost all AC cars are positive ground. I think they all are as are many early British cars. I'm not sure when the POS ground era ended. I'm sure someone here knows.

If one installs a regular battery charger with the standard SAE plug on the battery for a smart battery charger, one needs to be mindful of the fact that the exposed terminal on the battery side of the harness is now negative and if it touches the chassis (positive), you will have a big spark and possibly a melted wire and in a bad stroke of luck, a fire!

AND this "negative" side of the harness is NOT protected by a fuse. So, you must remember to replace the included rubber cover when not in use. OR I fully suggest that you cut off the supplied terminal ring on the negative side and install an inline fuse holder and a fuse. So, you will have (2) fuses on your battery charger harness. POS and NEG. Remember, a fuse is not intended to protect the device, its purpose is to protect the section of wire between the device and the fuse/battery. That is why fuses should be as close to the battery as possible.

If anyone needs such a modification to their battery charger harness and cannot make this modification, just let me know. I'd be glad to send you a "safe" charger harness.


Picture attached;

Note the "black" ring terminal is intended for the "NEG" terminal post on the battery. If you follow that to the other side of the harness, it ends in an exposed unprotected terminal. This terminal can easily short to the "POS" chassis or body or any other exposed metal item connected to the "POS" ground of the car.

Maybe somebody makes a "POS" ground battery charger/harness combo. I don't know. But that would be a problem if used on a standard SAE pigtail. Possibly Gerry at Hawk cars can weigh in on this topic. Or, maybe this is commonly known amongst the AC community. If not, I'm just here to help. I'd hate to see a fire in a car due to this situation. This cannot be the first time this has come up.

This is my first POS ground car (newbie) and it got my head all messed up. Stay tuned for my LED headlight installation tutorial. I am a fan of the new Holley Retrobright LED headlights. As you know, on POS ground cars, the three-pin connector for the H4 headlight has the polarity reversed, so while a regular incandescent headlight bulb will work, it does not care about polarity, an LED does need the correct polarity. I am designing a simple polarity reversing circuit that will simply plug into any POS ground car and give you real-world nighttime lighting. These Retrobrite headlights come in an original-looking "warm" white color too. Even the front "glass" cover looks period correct. They are not cheap, but I like them a lot.

Even though I am a lighting engineer and I now work for Holley, I had nothing to do with the design of these lights. I wish I did. They will not work in POS ground cars without a special wiring harness. I can supply one to you if you want to upgrade your lighting.

Of course, these are intended for LHD cars in the US. So, they will not be useful in the UK and other RHD countries. I hope this helps!

More project stories coming up! Wait till you see the picture of my Aceca backing off the side of the loading ramp (I was not driving) on the delivery truck. Yup. Got stuck on its side for 4 hours. Details to follow.




Cheers,


Glenn
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