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Safety Tip - Watch those battery terminals!

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
OK, so it was time to re-install Mikey's battery today, and as I was lying on my stomach (underneath the panel - center-mounted battery) I hooked up the hot meads, then reached forward to attach the ground cables. I noticed a spark as I brought the negative cable into contact, ands thought "ahh - keep-alive loads"...then I smelled something hot, and realized the Carb Heat cable was looking like it wanted to smoke! I quickly grabbed the battery an yanked it away from the ground terminal, then grabbed the carb heat cable - Big Mistake! I now have a "brand" on my thumb of the external braid of the metal carb heat cable!

Bottom line - the carb heat cable was running right next to - OK, in contact with - the positive battery cable. Yup, I should have followed the old rule of hooking up positive last. Once the battery cover is installed, no problem. Hurried, uncomfortable (on my stomach), and tired after a long day.

No damage (except to my thumb) after a thorough checkout of all involved components....but watch that 12 volt DC welding - it can do a number on your body parts!
 
Good tip.

I have a couple of "vent holes" in my firewall where my wrench (working on the positive side) touched.

Lets be carefull out there!
 
Wedding rings.....

.....have brought grief to several of my friends who wouldn't remove them while they were mechanic-ing. One was removing a starter on a car and his wedding band provided the path for current from the wrench to the chassis, glowing red hot before he could yank it away. He barely saved the finger! Remove those rings while wrenching.

Regards,
 
My Finger, too

pierre smith said:
.....have brought grief to several of my friends who wouldn't remove them while they were mechanic-ing. One was removing a starter on a car and his wedding band provided the path for current from the wrench to the chassis, glowing red hot before he could yank it away. He barely saved the finger! Remove those rings while wrenching.

Regards,
Click to expand...

My DAR OK'd the airplane on 8/15/06. On 8/16 I resolved the remaining small issues. I was checking the tightness of the battery, mounted just aft of the oil cooler, aft of the left rear cylinder, using my left hand. The wrench slipped and I contacted the baffles with my wedding ring. Same result; I had a 3rd degree burn all around the finger and some severe damage to a 36 year old ring, too! Both have been repaired, but the finger took a long time and I have a nice scar under the ring. Be careful out there. Oh, btw, I did fly on 8/17 anyhow. A nice touch: flew 17HH on the 17th from runway 7.
 
Learned this many years ago in the Air Force.

Please remove all jewelery while working on airplanes or cars. Not just electrical but mechanical problems can occur as well. I once saw a young Airman lose a finger by getting his wedding ring caught on the top of the ladder coming down out of a C-124 just as he jumped off the bottom rung.
 
Hope you heal quickly, Paul. But the proper way to remove and install battery leads is remove negative first and install negative last. You did it correctly, unfortunately you did have the carb heat cable in contact with the positive terminal.

The reason for handling the leads as I described is to prevent accidental arcing with the wrenches while tightening the terminals. If you do the negative first and strike the wrench to ground, no harm, because that terminal goes to ground. Once the negative is off the battery, and you strike ground removing the positive terminal, no harm because the battery isn't grounded. When installing, putting the positive back first is safe because the battery isn't grounded yet and striking ground, from the postive terminal to the airframe components, won't create a current path. Always a good idea to have an insulated boot over the positive terminal to prevent airframe components coming in contact with it.

Hope this helps,

Roberta
 
And watch those ties, too . . .

I doubt that very many of us wear a necktie when working around our planes, but if you ever do (and I sometimes have one on for flying if I am coming to the airport from work), those can be killers too. I'll never forget the story told by our Machine Design teacher, Prof. Eugene Fisher, back at Santa Clara, who ALWAYS wore bowties. When asked why, he explained that many years earlier, as a cub engineer, he had been wearing a necktie when working with some rotating equipment (a Bridgeport mill, IIRC) and that thing got hold of his tie and brought him very close to major injury (or worse). Not a pretty mental picture.:eek:

My own learning experience came about 20 years ago when checking something on my old 911 while the engine was running, I was leaning into the engine compartment, blipping the throttle, when I happened to glance down and see the cooling fan drawing my necktie up to the edge of the fan shroud, and putting a tiny nip on the end of my tie. That got my attention - never again!
 
Battery terminals

I placed a piece of silver duct tape on the firewall behind the pos terminal. Gives a little insulation and covers the pin hole when you ignore the gnd terminal rule, First off last on.










Bruce RV9A
 
So far, so lucky!

Hi All,

Paul, glad to hear you're not BBQ'ed - or worse!

My dad was working on our boat years ago and had to hook the (large) battery back up when he was done. Tightening up the last nut of the day, the NEG batt lead, he oopsed and let the wrench contact the POS lug. Ka-Bang! Yep, the batt exploded, blew the top right off, covered everything in acid, and knocked him back a few feet. He jumped over the side and was VERY fortunate to not get anything more than humbled and stained shorts:eek:

As luck would have it, that battery was "accessible". Airplane batts aren't always out in the open. Imagine if Paul's batt had decided to grenade? Not a pretty thought - but one you MUST vividly remember whenever you're working with ANY electricity. KEEP IT (YOU) SAFE!

A last thought... 'lectrical guys please clarify.... you should hook up the NEG side last - prevents more serious sparking and batt energy "surge"? AND a technique I've always used - never just "put" the last lead on the batt - gently/momentarily touch the lead to the terminal and watch for a spark. Big spark=big problem:rolleyes:

PS - FLIPPED THE CANOE! YAHOO!!
 
robertahegy said:
Hope you heal quickly, Paul. But the proper way to remove and install battery leads is remove negative first and install negative last. You did it correctly, unfortunately you did have the carb heat cable in contact with the positive terminal.
Click to expand...

Roberta's right....and it's what I would have written if I hadn't had tried to post after two glasses of anasthetic/wine for the pain in my thumb...;)

(The stupid thing of course is that I've been disconnecting batteries under emergency situations for 25 years as a firefighter....you'd think I could do it without screwing up! And yes, I've also seen them explode, and having that happen in the confined space under the panel would be horrible...)

Paul
 
direction of flow

deleted......

sayed the wrong way. Will change

(current needed to be charges-- sorta)
 
Last edited:
Confusing as ever...

L.Adamson said:
deleted......

sayed the wrong way. Will change

(current needed to be charges-- sorta)
Click to expand...

We all (at least most) know that when we design D/C circuits for our airplanes, that power comes from the positive terminal, does it's work, then returns to the common ground (negative terminal) of the battery.

Yet, as a kid, I was told that current actually flows from the negative terminal to positive, yet circuits are designed as flowing from positive to negative.

However, a google search will farther confuse the issue. Some say that current does indeed flow from negative to positive, while others define current as moving from positive to negative, while the charges (electrons) are actually moving from negative to positive.

Confussed????

It gets worse. Others define moving electrons as the "current", while the above paragraph seperates charges and current as two individual items.

Well...................I'm confused! :D

But regardless, I've been working with electricity for a good 30+ years, and design low voltage DC circuits with postive to negative, while supplying ample wire size & breaker/fuse circuits for the application. I do disconnect the negative terminals while working on equipment, and shield the positive leads from nearby metal structures.

I guess that's what matters! :)

L.Adamson
 
electrons

electrons are what move, they are negatively charged. electron theory supports the negative to positive..conventional theory is from positive to negative.....either works just dont mix and match theorys. theory is supposed to be a concept based on fact, so one isnt a theory one is a hypothesis..i'll let you decide.:rolleyes:
 
Yes, the electrical theory is confusing, but since we use the negative side of a battery for our ground and the positive side to our devices, it is safest to remove the ground first and install it last.

Roberta
 
robertahegy said:
Yes, the electrical theory is confusing
Click to expand...

After spending SO much time, reading "electrical theory" this morning....

I have concluded that it fit's right in with the age old question of "what causes lift" :D

You think you're reading "fact", only to come upon numerous views and explanations which contradict one another!

L.Adamson :confused:
 
There's nothing that scares me more than to be quietly working on an airplane and suddenly sparks are flying due to some tool grounding a hot lead....it's probably the best cardiac check one can endure, I always figure I'm good for a couple more years after the smoke clears.

Sorry to hear you cooked a finger. That isn't fun. :(
 
Shocking

My building partner is mad as **** at me for touching the allen wrench to the firewall and positive battery post which created a small vent hole. Not only did I get shocked, but he was yelling less than nice words, nouns and adjectives, which hurt my (fragile) feelings.
He spent 20 minutes preparing this pinhole to place a rivet in, calling me names the whole time.
I almost would have preferred to have burned my thumb!
Just one of those days. I had to remind him that this happened on MY plane...not his.
He still yells at me over this minor imperfection to the firewall. Claims we will never get an award now.

Pat Garboden ("charged individual")
Ozark, MO
RV-9A 942PT (reserved) tip up w/O-320 in wiring stage with firewall pinhole

Todd Wiechman (yell master)
Wichita, KS
RV-7

RV-9A 942WG (For Sale) slider w/O-235 flying
 
That baloney about the air going faster over the top of the wing, creating lift, is a bunch of HOOEY!!!! We all know that the reason planes get off the ground is that stack of hundred dollar bills beneath the wings.:D

Roberta
 
There are different ways of looking at electricity that work for practical purposes. The direction of electron flow doesn't really matter for us, what matters is that the airframe is at one potential and the positive battery terminal is at another. We don't want those two to meet in an uncontrolled way because they are going to want to get together in a warm hurry.

The practical aspects of electricity were worked out before the sub-atomic physics was really understood. That has caused a lot of confusion over the years.
 
It's good practice to check the resistance (ohms) between the positive and negative battery cables (NOT THE BATTERY ITSELF!!) BEFORE you connect the cables to the battery, especially on a new installation, or one that has been worked on. A low reading should be cause to investigate.

BTW, as others said, it is best practice to hook up the "hot" side of the battery cable first, then the ground, and remove the ground first if DISconnecting. If you happen to accidentally contact the airframe while the wrench is on the "hot" terminal of the battery, then not having the ground terminal connected prevents those "vent holes".
 
The old theory that they taught us about lift in flight school is all wrong. It has nothing to do with the high and low pressures of air moving over the wing. The only thing that causes an airplane to fly is money. No money no lift. Try it someday and you will then be a new believer in the real theory of flight.

L.Adamson said:
After spending SO much time, reading "electrical theory" this morning....

I have concluded that it fit's right in with the age old question of "what causes lift" :D

You think you're reading "fact", only to come upon numerous views and explanations which contradict one another!

L.Adamson :confused:
Click to expand...
 
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