Are stainless busbars such an awful thing?

[GHA]

Bit of a rewire going on, so why not oversized stainless busbars? Looking at the data, seems copper is something like 44 times more conductive than 316. And found stashed away a bluesea tin plates copper busbar @ 19mm x 3mm rated at 150A continuous DC. Looking at probably 100A for the windlass, and 40 x 12 flat bar with 10mm studding welded for the busbar - fag packet brings that to be 480mm^2 / 57mm^2 ~= 8.4 more sectional area, ~=5.5 more resistance. Could double up the flat bar which would take it to more like 2.75 X more resistance plus studs will be a little closer so less still.
Or as there are only a couple of high current paths needed maybe double up those on a single stud?

Would be nice to fab something made for the job in hefty stainless rather than over priced chandlery bits but would a few uOhms more resistance be a big deal?

Thoughts welcome

 

[rogerthebodger]

I use aluminium bus bars for the main supply to my bow thruster/winslass from my batteries via a main fuse and switch.

I then covered then with red (positive) and blue (negative) duck tape.

Any also all connections to the bus bars were by drilling and tapping M8 with 50 sq mm welding cable and ring crimps.

If I wish to add any more connections it easy to drill/tap and bolt a crimped connector to the bus bars.

 

[GHA]

I use aluminium bus bars for the main supply to my bow thruster/winslass from my batteries via a main fuse and switch.

I then covered then with red (positive) and blue (negative) duck tape.

Any also all connections to the bus bars were by drilling and tapping M8 with 50 sq mm welding cable and ring crimps.

If I wish to add any more connections it easy to drill/tap and bolt a crimped connector to the bus bars.

Ta. Did you use stainless studs into the Ali?

Looking at the resistivity figures, doubled 40 x 12 wouldn't be much more than the battery monitor shunt.

 

[RichardS]

Aluminium seems a good option but, in the real world over such short lengths, I cannot imagine you will notice any difference between copper and stainless steel. I use stainless steel connectors on all my cables and battery connections on the boat and, although I've read online that this is not recommended, I've never had any problems.

Richard

 

[lw395]

Stainless isn't favoured for serious electrical work due to its oxides.
I think you can get some interesting crevice corrosion effects too.

I think copper is likely to be more cost effective than SS.
Ali is worth a look.

A bit of copper rated at 150A continuous will be designed bearing in mind temperature rise due to resistive heating as well as loss of system performance due to voltage drop.
I can tell you I've put a whole lot more than 150A through 1/8 by 3/4 copper.
If you have more ohms in your stainless, it will get hotter. When it gets hotter, I think its resistance will increase much faster than copper.
For a windlass, you may not need 'continous' of course.
Copper is also not very stiff, so doesn't generate such big thermal stresses if you heat it.

 

[rogerthebodger]

Ta. Did you use stainless studs into the Ali?

Looking at the resistivity figures, doubled 40 x 12 wouldn't be much more than the battery monitor shunt.

I used M8 brass hex head setscrews with brass washers between the screw head and the connector.

 

[pvb]

Would be nice to fab something made for the job in hefty stainless rather than over priced chandlery bits but would a few uOhms more resistance be a big deal?

No big deal. The distance involved is very short, so the resistance will be minimal. Rather than compare with the resistance of copper, work out the actual resistance between 2 studs on your stainless bar, and see for yourself how little it is. Then work out how many milliwatts of heat will be produced, and you'll find that lw395's dire warning of it getting hot is rather an exaggeration.

 

[lw395]

In stainless, 1 sqmm is about an ohm per metre
So 480 sqmm is about 1/480 of an ohm, at 100A that would be 0.21V, or 21Watts per metre.

That's assuming you don't get any localised issues from the poor surface characteristics of SS as a conductor.
The copper will be about ten quid a metre? So why not do it properly?

 

[pvb]

In stainless, 1 sqmm is about an ohm per metre
So 480 sqmm is about 1/480 of an ohm, at 100A that would be 0.21V, or 21Watts per metre.

That's assuming you don't get any localised issues from the poor surface characteristics of SS as a conductor.
The copper will be about ten quid a metre? So why not do it properly?

So with a centimetre or so between studs, the heating effect would be about 0.2W. That's not going to start a fire...

Don't think surface effects are likely to be relevant.

 

[rogerthebodger]

In stainless, 1 sqmm is about an ohm per metre
So 480 sqmm is about 1/480 of an ohm, at 100A that would be 0.21V, or 21Watts per metre.

That's assuming you don't get any localised issues from the poor surface characteristics of SS as a conductor.
The copper will be about ten quid a metre? So why not do it properly?

On my boat there are only 3 items that draw a significant current, there are the engine starter motor, the windlass, the bow thruster (600Amp). Non of these would operate for any significant length of time, so any cable heating would be only for a short time and then the cable would cool so heating would not be any significant effect.

 

[lw395]

I suspected we were talking about something a bit longer.
Obviously pvb knows better than the electrical industry....

 

[pvb]

I suspected we were talking about something a bit longer.
Obviously pvb knows better than the electrical industry....

Not at all, but in reality the OP's plan isn't going to cause any problems. It sounds like he's got the bits and can do the job himself.

People get carried away with theory - Nigel Calder once made an utter fool of himself in one of the magazines by suggesting that we shouldn't use stainless washers in bolted high current connections, because they could overheat and cause a fire! Complete bollocks, obviously, but things like that get passed into boaty folklore.

 

[rogerthebodger]

Not at all, but in reality the OP's plan isn't going to cause any problems. It sounds like he's got the bits and can do the job himself.

People get carried away with theory - Nigel Calder once made an utter fool of himself in one of the magazines by suggesting that we shouldn't use stainless washers in bolted high current connections, because they could overheat and cause a fire! Complete bollocks, obviously, but things like that get passed into boaty folklore.

A little knowledge can be a danger thing !!!

This is why I like to know ALL the facts so a proper considered analysis can be formulated.

 

[GHA]

On my boat there are only 3 items that draw a significant current, there are the engine starter motor, the windlass, the bow thruster (600Amp). Non of these would operate for any significant length of time, so any cable heating would be only for a short time and then the cable would cool so heating would not be any significant effect.

Similar but less, just starter motor & windlass. Windlass will trip a 100A breaker if you really annoy it. Starter motor maybe similar, poss touch higher. I did a quick look at power loss through such a small resistance and yes, next to nothing. So seems not great chaos awaits and since there's some flat bar sitting outside earmarked for something else which changed ight as well go for it.
So did you get your right first time?
Just started drawing up , prob a Tee with the 3 high current cables on 10mm studs and a few 6mm studs for the other bits a pieces which seem to appear over time. Inside an enclosure.
Anything you'd do different if making yours again?

Then more contentious....
Fuse the positive at the battery?.....

Tempted as it would be easy but a bit wary, if it blew I'd loose all power for a few minutes.... maybe ultra careful with cable runs instead. Been fine for many years so far..Hmmm.

And *really* contentious would be the untidy sketched schematic, 2 x 12Both switches!!!

 

[greeny]

Similar but less, just starter motor & windlass. Windlass will trip a 100A breaker if you really annoy it. Starter motor maybe similar, poss touch higher. I did a quick look at power loss through such a small resistance and yes, next to nothing. So seems not great chaos awaits and since there's some flat bar sitting outside earmarked for something else which changed ight as well go for it.
So did you get your right first time?
Just started drawing up , prob a Tee with the 3 high current cables on 10mm studs and a few 6mm studs for the other bits a pieces which seem to appear over time. Inside an enclosure.
Anything you'd do different if making yours again?

Then more contentious....
Fuse the positive at the battery?.....

Tempted as it would be easy but a bit wary, if it blew I'd loose all power for a few minutes.... maybe ultra careful with cable runs instead. Been fine for many years so far..Hmmm.

And *really* contentious would be the untidy sketched schematic, 2 x 12Both switches!!!

Fuse at the battery. If it blows it means something has probably shorted. If something shorted and you didn't fit a fuse at the battery you'll wish you had. My thoughts for what they're worth.
I once accidentally shorted out live to neg at the battery switches. Big flash but I was so glad i had fuses on the battery terminal.

 

[thinwater]

I've seen aluminum and stainless used as bus bars on boats and in testing. Either immediately or overtime, both were glaring failures.

Tin plated copper is the gold standard for a whole lot of good reasons, corrosion resistance and conductivity being unbeatable. It does NOT need to come from a marine source, since it is common in industry too, just not the local hardware. Stainless is really dumb (sorry if that is rude) and aluminum is far too great a corrosion risk in a marine environment.

 

[GHA]

I've seen aluminum and stainless used as bus bars on boats and in testing. Either immediately or overtime, both were glaring failures.

Tin plated copper is the gold standard for a whole lot of good reasons, corrosion resistance and conductivity being unbeatable. It does NOT need to come from a marine source, since it is common in industry too, just not the local hardware. Stainless is really dumb (sorry if that is rude) and aluminum is far too great a corrosion risk in a marine environment.

Not very helpful without going into why the stainless failed....
Hard to see how resistivity could be a factor with the few mOhms, not much different to the battery monitor shunt. Far too small to measure on the fluke multi meter.

So where would you get some copper flat bar on the high street anyone? Some very skinny din rail stuff in the local b&q type place buy not seen anything else.

 

[rogerthebodger]

Corrosion on aluminium bus bars inside would be less of an issue. This is also why I used brass screws and not stainless as we know stainless in aluminium does corrode and cause a high resistance joint.

I did also use aluminium for my negative low current bus with M4 brass screws tapped in to the bar.

I fitted 600 Amp fuses as close to the batteries as possible. I also replaced the main shunts with hall effect shunts.

 

[pvb]

Fuse at the battery. If it blows it means something has probably shorted. If something shorted and you didn't fit a fuse at the battery you'll wish you had. My thoughts for what they're worth.
I once accidentally shorted out live to neg at the battery switches. Big flash but I was so glad i had fuses on the battery terminal.

Yes, agree. Something like a MegaFuse right next to the battery can help to prevent a fire in extreme cases. I managed to wire a replacement alternator wrongly on my old boat, turned the main switch on and there was a soft pffft noise as the MegaFuse I'd installed blew.

 

[PaulRainbow]

With proper busbars costing less than £10 i have to wonder why anyone would want to make them.