Electrical Safety Check

[Timothy McGowen]

Thought I would pass on a safety issue. While at the rally this past weekend I started having some odd electrical problems. I noticed intermittent low voltages that would increase after cycling the power.

Upon returning home I went to check the electrical system. Upon reaching into the compartment containing the dual battery system I immediately noticed arcing. I then noticed the negative battery post cover was melted. The nut holding the negative wires was spinning free on the battery post.

My guess is that the nut was loose from previous trips and completely loosened during the off road tour we went on. It would serve you well to check your battery connections. I'm glad I avoided a fire.

Stay safe and Happy Trails.

 

[SeatoSea]

Good tip thanks, hope things are ok.

 

[Wandering Sagebrush]

Timothy, i agree great trip. If there isn’t a lock washer, you might want to add one.

 

[ntsqd]

Vehemently opposed to lock washers myself. I throw away all of them supplied with whatever. Never had a properly torqued nut come loose, and by that I don't mean to imply that I carry a torque wrench around all of the time. Where "Mission Critical" I use a nylock, a prevailing torque lock-nut, safety wire, or some form of Lock-tite. In applications similar to the "Jesus Nut" on a helicopter I use two or more of these methods on the same fastener.

Highly recommend reading "Engineer to Win" by Carroll Smith. He covers a lot of this sort of thing along with a lot of other topics pertinent to race cars but that also have applications in this niche.

 

[Wandering Sagebrush]

Having seen a H46 crash and kill the crew (MCAS Kaneohe Bay) because the Jesus nut wasn’t even installed, I tend to like belt and suspender solutions. Proper torque (I often carry a torque wrench for lug nuts) is absolutely important, but it won’t always mitigate vibration.

 

[ntsqd]

Neither will a so-called lock washer. They aren't used on aircraft or pro built race cars. If there is a vibe concern some other means is used to stop the fastener from working loose.

 

[ckent323]

Aircraft and spacecraft most often use Belleville washers or epoxy staking or wire nuts.

Belleville washers are "wavy" washers and are similar to a lock washer.

I have also seen nylock nuts used but they can only be tightened once.

That written I have never had a problem with a lock washer on any of the dozen or so vehicles that I have owned over the past 40 years. Several of them I used off road. ;-)

Regards,
Craig

 

[CougarCouple]

Thanks Tim
Glad it worked out and that's all it was. Will do a quick check on ours.
Russ

 

[ntsqd]

Belleville washers are not wavy, they are conic as they are used as short-stroke, high rate springs. By alternating them or nest-stacking them you can 'build' a spring with a rate and stroke to suit the need. BT, DT in several designs.

The basic premise of a lock-washer is that it's spring loading keeps the fastener assembled in the joint. It will not keep the joint tight. The problem is that very few joints are viable with a loose fastener. So a failed joint is one with a loose fastener, something that the lock-washer can not and did not prevent. Couple that with the frequent experience with split type lock washers having broken in half, creating that loose joint in the process, and I see no need to use them for anything other than ballast to keep my trash cans from floating away. YMMV

 

[Squatch]

Being a boater I always use big wingnuts on my battery terminals. This allows me to easily check them often. When in doubt a little blue Loc-Tite goes a long way.

Glad you found this before it caused a real problem.

Is your battery strapped down? Main cause of cables getting loose in my experience is a battery shifting around slightly.

 

[ckent323]

"Belleville washers are not wavy, they are conic"

Yup, my mistake. We did not use them very often on our Spaceborne instruments.

We most often use appropriately torqued fasteners with 2216 epoxy staking.

Proper torque is important.

 

[Timothy McGowen]

While I generally agree with torque and wire lock solutions, not in this application. Torque runs too high a risk of internally damaging the battery and lock wires are just that, bare wires.

The battery is securely strapped. I like the wing nut idea. Partially because I am one. Lock washers are an interesting thought. I'll have to give that some thought.

Thanks for the replies. Stay safe my friends.

 

[ntsqd]

A trick that I've seen work effectively some times and not others (depends on how sharp the threads are) is to thread a piece of dental floss or thin nylon string thru the nut before threading it on. Creates some degree of locking function in the absence of lock-tite or similar.

 

[Bill D]

Is your battery strapped down? Main cause of cables getting loose in my experience is a battery shifting around slightly.

Thank you Squatch. I don't think "rocket science" is needed here.
Just a quick reminder to check that your battery is secure along with the terminal connections.