For Terry

[jon_d]

A good example of why wiring has to be neat and protected from heat.

There are a lot of wires and sheaths near by which could have been close to melting and catching on fire.

[T1 Terry]

Having another look at that pic I would be saying "fuse?? what fuse??'

An inverter pulling say 2,000w @ 10v would be around 200 amps. If the battery was fully charged there would be close to 14v available allowing for a max of a 4v drop across that joint before the voltage at he inverter dropped below 10v and it dropped out. That works out to around a max of 800w available for heating .....I wonder how many watts it would take to get that nut glowing red?

[jon_d]

I pondered the same thought.....

Remember, it's 800watts @ 1cm2 That's quite an intense heat source. Different to 800watts in a heating element.

[T1 Terry]

Good point, plus it is the nut glowing, is there enough heat transfer in the other materials to dissipate some of the heat but the lack of good contact doesn't allow the nut to transfer its heat other than to the surrounding air? That would explain why only the nut is glowing yet the surrounding area only shows the signs of serious heating. That then leads to the suggestion the problem is the nut is not applying sufficient clamping force causing the poor electrical contact?

[supersparky]

Do you think that maybe it was a little loose to start with , or do you think that maybe it is a dissimilar metal to the bolt it is attached to, thereby causing it to expand and contract at a different rate and with every heating/cooling cycle it just becomes looser and looser?
I still have problems with blokes at work who put stainless nuts on mild steel bolts or vice versa and wonder why things get loose and make a poor contact, draw heaps of amps and then nuke the termination.

[jon_d]

I reckon the nut has wound up the thread a whisker.

and the lug is welded to the nut and lifting away from the bus bar.

and the eye lug/connector is making some contact with the nut and none with the bus bar.

You really need a voltmeter meter to probe the;

1. bolt to nut voltage
2. bolt to eye lug voltage
3. eye lug to bus-bar voltage
4. eye lug to nut voltage.

to work out where the drop is occurring.


Dave, you're right. I recall a good set up should be using (strangely) aluminium nuts and bolts in a bus bar. I don't know the full reasons but I think it has to do with corrosion and expansion. (Have anyone noticed that good batteries come with ally bolts/nuts?)

[T1 Terry]

Hmm.... Stainless nuts on stainless bolts will often end up with thread seizure resulting in the nut having to be cut off the bolt and then the bolt/stud having to be replaced. Stainless bolts and steel nuts don't seem to suffer that problem, but stainless bolts as weaker than high tensile bolts. 316 stainless is probably the weakest, the more expensive and the least likely to tread bind.
As far as the loosening, common with lithium installations where high current is involved and often cause by conductor that is being clamped by the nut expanding and contracting eventually wearing the contact face away a bit so the tension is lost. then vibration undoes the nut.
This conductor movement is the reason we use multiple thin layers of copper with hump in the middle for the inter cell connections, so the movement happens there rather than under the bolt. This doesn't mean the battery pack doesn't need a spanner run over it every so often just to check the bolts are tight and that goes for all the connections. Basic electrical maintenance really, a run over every joint with a thermal laser gun is another good maintenance tool, easier to find bad connection like the one Wayne has show before it gets to that point.

T1 Terry

[supersparky]

Stainless on stainless rarely galls if you apply a little dab of Never Seize or something like that. It is the universal standard on all water and sewer connections world wide.
What I was trying to say in my earlier post is that if you fasten any electrical connection with a stainless bolt and nut and it draws a reasonable current, then it will come loose as it will expand at a different rate to the connectors. Whatever happened to brass bolts?

[T1 Terry]

We only use stainless bolts, nuts and washers, but we still get about a 10% galling problem. Never seize aka galactic grease does help, but we fit a lot of bolts and nuts over a 12mth period and I reckon it would have migrated to your place after 18mths or so Just about every industrial site I worked at had banned the stuff because of the migration problem. It took 3 days at the Berrima cement work to make it from the job to the managers desk, a 24hr shift from the job to the shower room and half a shift from the job to the lunch room
Alminox is bad enough, not gunna tempt fate with galactic grease

[bagmaker]

whoa! SS fasteners on electrical?? Surely not!! I thought only brass or aluminium is recommended due to the pathetic ability of stainless to transfer electrons (heat).
I have failed here in the past, a stainless bolt and nut earthing a hell cable. Got super hot. Changed to brass, not a problem.
( Cleaned the actual contact points -even less of a problem.)