Electronics > Projects, Designs, and Technical Stuff
Electrical contacting on aluminium busbar
damien22:
Hi There,
Posting here after Months of unsuccessful research and I hope there gonna be some smart guys with good idea.
In a equipment I'm building, I need to carry large current to many PCBs. To do so, I've planned to use busbar. Those busbar have a length of 1.3 meter and are 7x8mm to which the PCB are screwed with M4 screws and the current goes trough it.
Now there are two issues, one is the electrical contact, because of the oxidation of the material which is an issue for the electrical contact and another is the strength of the material to avoid the bar to be bend during manufacturing.
We are trying to use Aluminium for this, but raw aluminium cannot be directly connected due to the oxide layer.
We have looked a lot to do surface treatment such as plating or coating but it seems impossible to find anybody that can do that on bars that are 1.3 meter long and I cannot split them unfortunately.
The solution we are looking at currently is to use inserts. As the insert a pressed fit or screwed on the aluminium, it breaks the oxide layer and then stay in place. We know of some companies doing so using ARCAP inserts.
However, one of the issue, is that there isn't much space to allow much bigger hole size (M4 on 7mm wide bars), as the insert would need to be at least 2mm thick on M4 would mean a hole ~6mm, leaving only 0.5mm of material.
Then I found Helicoil inserts which have the advantage of not needing a much larger hole size and that would mechanically fit.
https://blog.baysupply.com/common-uses-for-helical-inserts-and-why-you-need-them
However, there are very little information about using this for contacting on aluminium as an insert. The best information I found is "This makes tangless inserts particularly vital to automotive and electrical applications".
Question being, is there anyone having experience with that, perhaps have recommendation or other ideas to contact those busbars, help would be very much appreciated.
[EDIT]
The equipment is for indoor and lab.
Thanks
beanflying:
Ok I will bite.
First question is what Current? and also what Voltage (AC or DC) and are you running one or two bars for a Ground/Neutral?
What are your reasons for not using a Copper Alloy (Brass) of some sort and what are the reasons for your tight dimensional constraints?
Also will you be supporting the busbar along the length or have you or does it need to be self supporting which from your description seems your choice?
What weight does it need to support?
Reason for the questions is we are not clairvoyants ;)
coromonadalix:
In my shop we discarded / ditched the aluminum bars and gone to copper ones ..... master electricians at our shop recommended this over aluminum ??
They said aluminum strech and expand over time, problematics for contacts / wiring / screwing .... at they require checking time to time for eveything connected to them, but they did not talk about oxidation ??
We replaced bars in our pcb oven, and pick and place machines power distribution circuits , (they are not American made) we have around 6 kw 347vac of power passing thru them ... not as long as your 1.3 meter, but thicker (around 3/4 inch, maybe 1 inch thick) but we dont have any pcb's connected directly on them, all wiring.
You surely have some master electrician(s) in your country who could give you more insights ?? Do's and Dont ???
damien22:
Hi Beanflying.
We tried brass, the problem is that the manufacturer (we tried 2) are not able to process the bar without bending it, by handling I suppose.
Also there are questions, as brass also oxidize, what would be the long term impact. I had somehow divergent input about this and also couldn't find much solid information about that. Brass also have about half conductivity of aluminium.
The bars, once installed are supported and there is not much mechanical stress, so there is no issues on that side.
There are several voltages rails, ranging from 15V to 90V DC. The current is up to 120A at the extremity of the GND busbar but this is a pulsed current of about 500ms every 15 seconds, not continuous.
For the size constrain, the width of the bars are constrained by the PCB design and space available, for the length is due to the system design. No chance to change those unfortunately.
damien22:
Hi coromonadalix,
We also thought of copper but as being very soft material, the bending issue we already have with brass would only be worse. Copper also oxidize and usually those are treated when used on electrical installation.
On electrical installation, and EV for example, more and more copper (or other material) plated aluminium busbar are being used as it's cheaper and lighter. We cannot do so because ours are too long.
Unfortunately electricians weren't of help as usually in electrical installation you use either copper or copper plated aluminium busbar which you can have stock.
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