Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. Today I discuss why it’s important for DIYers to take a picture before they start a repair project, and why working with 12-volt batteries can be dangerous.
Dear Mike,
Looks like I really goofed up and installed my battery terminals backwards. My converter made a pop and let out a puff of smoke. I only had the wires on it for a second, so I’m surprised this happened so quickly. My neighbor says he can replace the fuses in the converter for me, but what do I need to do next time to avoid making this same mistake again? —Dizzy in Duluth
Dear Dizzy,
I’m going to cover two important ideas in this JAM session. First of all, working with 12-volt batteries is very dangerous. Do not assume for a second that because it’s only 12 volts it must be safe. While you are safe from electrocution at such low DC voltages, any 12-volt RV or vehicle battery is capable of creating hundreds of amperes of fault current. And that’s enough to quickly heat up any metal jewelry you’re wearing, as well as melting down wiring in seconds. And yes, you can also make a battery explode if connected incorrectly. I’ve actually seen this happen in the wild, and it wasn’t pretty. (No, I didn’t do it.)
Don’t wear metal jewelry around batteries
That’s why you should never wear anything metal while working on a battery. (Yes, take off your metal bracelet or wedding ring or put on Nitrile gloves if your ring won’t come off.)
I know this picture is hard to look at, but it was sent to me by a reader who asked that I use it to make a point about battery safety. He got his thin metal bracelet made from a bicycle spoke tangled up in the alternator wiring behind the dashboard of his truck. And that was enough to turn that piece of metal red hot in seconds, which welded it into the wiring until he could pull free. Read my full article on battery safety HERE. But be warned, it has some pretty gruesome pictures.
Take a picture – it will last longer…
But the main point of this JAM session is that you should NEVER attempt to commit any wiring connections to memory. In your pocket you probably have one of the greatest inventions of all times for DIY fixers, a cell phone with a camera.
So, before you take anything apart, take plenty of pictures of it from every angle possible. And if all the wires are the same color, get a roll of yellow or white electrical tape and a Sharpie marker. Then mark each pair of connections as 1, 2, 3 … or A, B, C …. Plus, again, take plenty of pictures! No matter how many times I do something, I still try to take pictures to help me reassemble whatever it is.
It works for brake shoes, too…
A few months back I needed to help my son change the rear brake shoes on his Honda. It’s a good thing I took plenty of pictures before I removed the old shoes. (Yes, that’s one of the actual pictures I took for this brake job.)
While I used to do multiple brake jobs every day when I worked for a gas station back in the ’70s, it’s been a while since I took apart all the emergency brake levers and auto-adjusting mechanism. So, by referring to my pictures of the assembly before taking it apart, I was able to sort out how the new parts went back together. If I can’t trust my own memory, you shouldn’t trust yours either.
No, this will not make you an expert!
I’m not implying that if you take pictures before disassembly that you will become an expert who can fix anything. But it certainly helps avoid the pain of things like reconnecting house batteries up backwards and doing hundreds of dollars (or more) in damage.
And be aware that if you’re really unlucky you can blow the top off of your battery and get a face full of sulfuric acid. So, yes, eye protection is needed for any electrical jobs.
Warp speed, Mr. Sulu…
Remember, electrons travel at the speed of light, which is around 186,000 miles per second (I think that’s Warp 1 IIRC).
There is no way that you’re faster than the speed of light and able to disconnect something electronic before it’s damaged from reversed polarity. So always double- and triple-check your photographic notes BEFORE reassembly and lighting the fires. Don’t let out the magic smoke, as we like to joke.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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Since working around or near high wattage HF/VHF transmitters, starting in 1965, I have never worn anything metal in my hands or around my neck.
Had a fellow tech who had a finger perfectly removed, by shorting across an active HF system.
I exited the vehicle and swung the door closed. I worked for the highway department as an inspector. I was in and out of my car very frequently. It was my practice to grab the door with my left hand and swing the door closed as I exited. One time my wedding ring got stuck on the edge of the door and the momentum of the door was sufficient to strip the skin off the back of my finger. I stopped wearing my wedding ring when working outside. This was even more important when working around heavy machinery, like gravel crushers and hot plants. Jewelry is for dress up occasions, and office work, but NOT for wear around electricity or machinery.
When I was maybe 10 years old I watched my dad try to use jumper cables to get his car started, and he hooked them up backwards. The sulfuric acid boiled up out of the dead battery and squirted out the vent hole, hitting him in the eye. Luckily he reacted fast enough and blinked, and we were in the carport near the kitchen, so I walked him to the sink and we quickly flushed it out with water. But he could have easily been blinded in that eye had I not been there to help him. I’ve had a lot of respect for car batteries ever since…
A number of my pro-sound colleagues still work on stage flying speakers and hooking up power. Some of them have switched to wearing silicone wedding rings while on a gig.
Another thing I used to worry about when I was designing and building packaging machines in the 70’s was getting my necktie caught in a lathe or packaging machine. The dress code of the day was a white short sleeved shirt with a necktie and a pocket protector (of course). But I soon switched to clip-on ties instead of a necktie tied around my neck when I saw all the moving machinery I had to get close to.
Mike I will never understand why 12 volt wiring in RVs uses house code rather than automotive code. One of the first things I do with any new RV to me is I put red and black heat shrink around the wiring ends so I know which is positive and which is negative.
Great idea! Every visual clue helps.
I do that and go one step farther. I put red electrical tape on the battery near the + terminal and black tape near the – terminal (if the battery isn’t black).
The molded + and – on lead acid batteries can be hard to see.
I painted a red ring around the positive terminal. Previously I had never connected the battery backward, but I did catch myself once when i was in a hurry. Now it’s obvious.
I always remove the battery when the trailer is in storage so reconnecting is more often than normal. Too many batteries are stolen in storage lots.
Thanks Mike!. Another word of advice you may want to include in future articles, is which battery terminal to hook up first and last, both connecting, then removing. I’ve seen this problem numerous times, including those trying to JUMP another battery! Repetitive words pay off!
I always remove all jewelry when working on anything that moves, has electricity, or can get caught on something. A case in point about 45 years ago working as an industrial mechanic a fellow worker had recently gotten married, I cautioned him many times to remove his wedding ring at work not only to protect his ring from all the nasty things we got on our hands but for safety. “I’ll never take this ring off” was always his answer, one day while climbing down the ladder off a hydraulic press his foot slipped, there was “traction “buttons” built into the ladder rungs to help keep your shoe from slipping off” his foot slipped probably due to smooth soles and his ring caught on one of those “buttons” and he hung by his ring finger. Luckily I was able to get him down but a trip to the ER, his ring had to be cut off, and his finger reconnected to the knuckle. After returning to work in several weeks and a new ring he always removed his jewelry at work.
The “Reverse Battery Protection” fuses will blow in milliseconds. That’s way faster than the time it takes to realize you’ve connected your wires backwards. They save you from having a new converter.
But sometimes those fuses are really hard to change.
Same thing goes for plumbing and heating. Professional Plumber.
One graphic example of the dangers of low-voltage, high-current circuits was shown to me during Air Force electronics technical school. One of the instructors hooked a small metal ring (almost finger-sized) to a 5-volt power supply and placed it around a hotdog. When he threw the switch and shorted the circuit, the ring had burnt nearly through the hotdog by the time the fuse blew.
This was re-emphasized to me when I was wiring a CB radio slide-bracket (1980’s tech) in a friend’s car. I managed to short my wristwatch links across the slide contacts and fused several of them together. OUCH! I’ve removed all metal when working on electronics since.