DIY Bus Bars

[Jim Cate]

Originally Posted by coopec43

Why aluminium busbars are gaining ground in low-voltage market

https://www.shapesbyhydro.com/en/mat...oltage-market/

I note that the publishers of this infomercial are, would you believe, purveyors of aluminium. What a surprise that they laud its use in everything, including busbars.

One of the highlights of the article is that the Al stuff dissipates heat so much better than Cu. Seems that if the resistivity wasn't so high there would be much less heat generated and little need to dissipate it.

And the weight issues... dunno 'bout your boat, but the Cu bussbars on our boat don't contribute a measurable fraction of the weight all up. Don't think that this would be an issue, even on a ultra-light cat or mono.

I suspect that low cost is the main driver where Al is used, and those other wonderful features are red herrings.

Jim

[RaymondR]

Aluminium has been used for electrical transmission for many decades now. Many, and probably most, high voltage cross country, power transmission use aluminium electrical conductors wrapped around a steel cable which provides the tensile strength.

There are a couple of reasons we are going to see more aluminium used in electrical power transmission and the two biggest are cost and the extreme practicability of the material. Just as you can with spars you can drop a billet of aluminium into a press with a die and extrude the most complex of section into which you can slide connectors and you can include fins to expand the cooling surface or design the form to maximize structural strength.

The glass stubby appeared to be the ideal solution to drinking beer with ones mates but then came the aluminium can and there's hardly a stubby to be seen these days.

[smac999]

Originally Posted by CassidyNZ

Please help me understand why not.

Whilst I understand the concept of resistance and resistivity, the difference between copper and any other metal is surely important when it’s through a wire (thin and long). But a bus bar is a short, fat block of metal which negates the importance of resistance/resistivity to a large degree.

Just putting an ss washer between a lug and buss or lug and fuse it will get too hot to touch and cause a ~1v drop on high loads like an inverter.

[mlydon]

They used to use aluminium wire in houses, but realized it was a bad idea, because the aluminium expands and contracts much more than copper, the connections would loosen up, potentially causing fires.

I’d splurge on a quality tinned copper bus bar in my many-thousand-dollar boat before I’d try to save a few bucks in this very critical application if I were you.....

Just sayin.....

Matt

[coopec43]

Originally Posted by mlydon

They used to use aluminium wire in houses, but realized it was a bad idea, because the aluminium expands and contracts much more than copper, the connections would loosen up, potentially causing fires.

I’d splurge on a quality tinned copper bus bar in my many-thousand-dollar boat before I’d try to save a few bucks in this very critical application if I were you.....

Just sayin.....

Matt

I'm going to use the multi connection battery terminal





When I was doing a search on eBay had I looked for Terminal block as well as Bus bar I would have got a far bigger selection.

The problem of buying top grade stuff because of the many thousand dollar yacht can get out of hand. But I agree with you as far as vital equipment is concerned (which this is)

My water pump for the galley is Made in China but my bilge pumps are Rule (and very large capacity)

[Wotname]

Originally Posted by CassidyNZ

Please help me understand why not.

Whilst I understand the concept of resistance and resistivity, the difference between copper and any other metal is surely important when it’s through a wire (thin and long). But a bus bar is a short, fat block of metal which negates the importance of resistance/resistivity to a large degree...........

What should I know that I apparently don’t?

Nothing wrong with using SS if you do the numbers and understand the limitations of the material.

Using the link upthread and doing a very rough mental calculation one would need to derate SS bus bar by a factor of about 30.

So for equivalent sizing, a 150 amp copper bar becomes a 5 amp SS bar.

Looking at cross sectional area, a copper bar of say 100 mm2 (20mm x 5mm) needs to be 3,000 mm2 in SS (say 100mm x 30mm) for the same rating. The SS bar now becomes bulky in comparison.

Looking at length with the same cross section, a 300mm copper bar becomes a 10mm bar in SS.

So if one wants to carry significant current loads, SS bar needs to become huge.

But yes, it can be done...

[coopec43]

Wotname

Maybe when they say SS Bus bar they mean SS studs?

If the SS Bus bar is small (short distance) as someone else has pointed out it is not a big deal.

[Wotname]

Originally Posted by coopec43

Wotname

Maybe when they say SS Bus bar they mean SS studs?

If the SS Bus bar is small (short distance) as someone else has pointed out it is not a big deal.

1. I dunno what they mean.
2. You can't dodge physics. When comparing SS bar to copper bar of similar cross section, you either derate the current by a factor of about 30 or you make it 30 times shorter. Making it shorter is not practical in most cases, e.g. a 100 mm copper bar becomes a 3.3mm SS bar.

Derating the current may be suitable in some instances when using the bar only to interconnect low current items.

[coopec43]

Wotname

Earlier today I was thinking the car chassis and motor are used as a negative bus bar. Then I read that when you jump start a car you should put the positive lead onto the positive terminal of the battery and negative lead onto the car chassis.

I've never done that! I have always put the negative lead onto the negative terminal of the battery. I suppose that is wrong because the negative lead from the battery may be poorly earthed to the chassis of the motor car?

[RaymondR]

Originally Posted by smac999

Just putting an ss washer between a lug and buss or lug and fuse it will get too hot to touch and cause a ~1v drop on high loads like an inverter.

Some years ago I replaced both the cranking batteries on my boat and was very disappointed to find the cranking had not improved at all. Pondering on it I realized that both the batteries had come with two washers on each terminal and that I had pit one either side of the terminal. Removed the bottom one so that the terminal bore directly on the lead terminal. Fixed the problem and never had a slow crank.

The resistance through the less than 1 mm or so thickness of the washer at the high ampage required to crank the engine caused a sufficient voltage drop as to prevent the starter motor from developing sufficient power to achieve the crank .

[Wotname]

Originally Posted by coopec43

Wotname

Earlier today I was thinking the car chassis and motor are used as a negative bus bar. Then I read that when you jump start a car you should put the positive lead onto the positive terminal of the battery and negative lead onto the car chassis.

I've never done that! I have always put the negative lead onto the negative terminal of the battery. I suppose that is wrong because the negative lead from the battery may be poorly earthed to the chassis of the motor car?

I've done it both ways - don't reckon it matters much! But yes, any earth lead defect would be exacerbated when connecting to the battery -ve post.

[noelex 77]

I think the advice is mainly to avoid a spark at the battery, potentially causing an explosion.

A connection to the chassis ground keeps the resulting spark away from the battery.

[coopec43]

Originally Posted by noelex 77

I think the advice is mainly to avoid a spark at the battery, potentially causing an explosion.

A connection to the chassis ground keeps the resulting spark away from the battery.

Yep! You are correct.

Of course, it’s technically possible to connect directly to battery negative, and it may even be easier in some cases. So if it’s possible, and it’s essentially the same thing as connecting to some other ground, why go through the trouble? Because you don’t want your battery to explode.

https://www.lifewire.com/dangers-of-...battery-534782

[Wotname]

Gone are the days of bumping the chrome bumpers together

[coopec43]

Originally Posted by Wotname

Gone are the days of bumping the chrome bumpers together

Yes! Dad's FJ Holden (I borrowed) at Birnies Hamburger Bar late one evening.