Watch those amps champs!

[mbianka]

Well after five years with electric propulsion I guess it was bound to happen. I was installing some new terminal connections for my helm mounted battery instrumentation project when a interconnect cable touched the terminal of the next battery. It was less than a second of contact but, lit up the space like a flashbulb. No major damage done except to the heavy duty cable lug which you can see here:
THE BIANKA LOG BLOG: MISTAKES OF AN ELECTRIC SAILOR
Got to respect what 200 DC amps can do!

[Tellie]

Don't feel bad. Anyone that works on their electrical systems and says this hasn't happened to them are the same ones that tell you they've never run aground.

[Snore]

Nice!! I still have a 30 year old ground connection from a meter can just to remind me of my mistake.

When I was much younger and working for an electric utility I was trained to physically isolate connections on different phases of a meter pan or bottom feed cabinet using rubber sheeting... By the book they wanted a physical barrier to prevent guys from what happened to you. A slip of the hand flash.

In reality, in the field, "some guys" were known to us a piece of cardboard to stop a slip of the hand cross-phase connection. Being an electric sailer, the rubberized mats fabric or a cardboard collection may be useful addition to your tool kit.

Bill

[mbianka]

Originally Posted by Snore

Nice!! I still have a 30 year old ground connection from a meter can just to remind me of my mistake.

When I was much younger and working for an electric utility I was trained to physically isolate connections on different phases of a meter pan or bottom feed cabinet using rubber sheeting... By the book they wanted a physical barrier to prevent guys from what happened to you. A slip of the hand flash.

In reality, in the field, "some guys" were known to us a piece of cardboard to stop a slip of the hand cross-phase connection. Being an electric sailer, the rubberized mats fabric or a cardboard collection may be useful addition to your tool kit.

Bill

Bill:

Yeah, I do have rubber mats I put over the terminals when working from inside the cabin. I this case I had just gotten a little lazy as it was just a quick disconnect to put the additional terminal connector on and reconnect. That and the fact this battery interconnect cable was a little longer than it needed to be when I installed the electric propulsion system five years ago. It was on my list of things to change at some point. So this incident got me to get that done. I like the cardboard idea too or some type of insulating board in between the batteries when working around the lugs. I think I'll incorporate that in the future.

[David M]

Don't feel bad, it has happened to everyone who has spent enough time doing electrical work.

[mbianka]

Originally Posted by David M

Don't feel bad, it has happened to everyone who has spent enough time doing electrical work.

Dave:

Well, I don't feel bad because at least nothing blew up or caught fire. Just wanted to share what could happen when a wire goes someplace it should not. I've since replaced the lug and am now on a fall cruise.

[GordMay]

Greetings and welcome aboard the CF, Richieg1g.

[Maine Sail]

Originally Posted by mbianka

Dave:

Well, I don't feel bad because at least nothing blew up or caught fire. Just wanted to share what could happen when a wire goes someplace it should not. I've since replaced the lug and am now on a fall cruise.

No over-current protection in that circuit? You might consider some fusing...

Keep in mind that the short circuit current available from even a group 27 deep cycle battery can exceed 1500A at 70F.. So a 200Ah bank or a battery with a CCA of 700 at 0F will pump a LOT more than 700A into a dead short at normal boating temps. Add a few batteries in parallel and the short circuit capability is then multiplied. It is not unusual to exceed 5000A of short circuit capability in a battery bank.

Some batteries throw a lot more than others into a short. For example the Odyssey TPPL AGM in group 31 size can supply 5000A of short circuit current per battery. A bank of four would be 20,000A of current into a dead short.... Ouch!!!!

[mbianka]

Originally Posted by Maine Sail

No over-current protection in that circuit? You might consider some fusing...

Keep in mind that the short circuit current available from even a group 27 deep cycle battery can exceed 1500A at 70F.. So a 200Ah bank or a battery with a CCA of 700 at 0F will pump a LOT more than 700A into a dead short at normal boating temps. Add a few batteries in parallel and the short circuit capability is then multiplied. It is not unusual to exceed 5000A of short circuit capability in a battery bank.

Some batteries throw a lot more than others into a short. For example the Odyssey TPPL AGM in group 31 size can supply 5000A of short circuit current per battery. A bank of four would be 20,000A of current into a dead short.... Ouch!!!!

Well the lug did act as a fuse in this case. The bank is fused on the output which was disconnected at the time. Putting fuses in the battery interconnects would still require 100 amp fuses and add more connections and possible failure points into the circuitry. I do have the new helm battery monitor wiring fused at the battery connection ends though. I will certainly be more cautious should I have to do something with these connections in the future.

[rebel heart]

I just barely crossed a 1 gauge past a negative terminal one time, the spark was quite impressive, as was the heat that generated in the wire in a split second. I have the battery banks fused, and I think the house is fused to 100amp but since it was thermal it didn't trip. Kind of neat in a dangerous sort of way to learn all that.

[GordMay]

I like to slide a short (±4") piece of clear hose over the positive cable lug(s); so that it normally sits over the cable insulation, but can be pulled down to protect the lug, when removed from the terminal post. This helps prevent a “loose” cable from shorting out on a negative post, or ground.

[CarlF]

I have a couple of old beach towels that I throw over everything and then peel just enough back to get at the spots I need. The towel also makes a good non-conductive place to rest tools.

Carl

[FlyingCloud1937]

Originally Posted by CarlF

I have a couple of old beach towels that I throw over everything and then peel just enough back to get at the spots I need. The towel also makes a good non-conductive place to rest tools.

Carl

That may work for 12 volt single bats, but it is still a huge risk. First a beach towel made of cotton or some other fabric, isn't really an insulator.

Any moisture at all will conduct enough to cause a spark at the very least...now if the bats are at or recently were at gassing stage, then the spark causes an explosion, and the towel adds fuel to the fire. It may even be that the towel creates the environment for the explosion by containing the hydrogen gas cloud in a density that can explode. Now if we are talking 24,32,36, or 48 volt systems then a towel is of no value.

Boiling battery acid, is explosive at 4% by volume in open air. Battery acid starts boiling 12.3 volts at a 12 volt nominal, or 2.1 volts times the number of cells in the bat.

Before working on a live bank, make sure there has been no charge\discharge source to the bats for at least 2 hrs and the area is well ventilated for at least 2 hrs after charge\discharge.

Always disconnect the the ships neg to battery first, then disconnect each neg in the string, secure the cables from arc with a short piece of rubber hose, then secure each neg bat post, with a cap.

Now you can follow the same routine with the pos. cables/posts.

one marine average 12 volt battery has a potential of 1.3kw arc.


Lloyd

[mbianka]

Originally Posted by GordMay

I like to slide a short (±4") piece of clear hose over the positive cable lug(s); so that it normally sits over the cable insulation, but can be pulled down to protect the lug, when removed from the terminal post. This helps prevent a “loose” cable from shorting out on a negative post, or ground.

Good idea. I do have some Blue Sea battery covers over the battery terminals normally but, this could be additional protection when working on the interconnects.

[Jim Cate]

And w hile on this subject, it's a good idea to not wear rings or metal watchbands whilst working around the electrics. Knew a chap who lost a finger when his gold wedding ring got shorted across a car battery. Pretty ugly...

Cheers,

Jim