Just wanted to get some tips on proper grounding of an amplifier chassis. It is a four-part chassis. Front plate, rear plate, top, bottom. All pieces are completely anodized aluminum, and thus, there is no significant conduction between each piece as they contact each other.
I definitely want to ground this chassis properly. Does anyone have tips?
Sandpaper at contact points?
I definitely want to ground this chassis properly. Does anyone have tips?
Sandpaper at contact points?
Sand where the connections will be. A small wheel on a Dremel or similar tool will clean it up without too much extra material removed. Use sharp stainless star washers between the ring eye and aluminum as well.
You may need a ground connection to each panel, if the screws joining it all together don't provide a low resistance path.
Each panel could have a welded stud such that interlinking earthing wires are bolted mechanically back to the Protective Earth (PE).
This is especially relevant to panels that are insulated from the Main Chassis.
This is especially relevant to panels that are insulated from the Main Chassis.
A corrosion inhibitor could be used under/over the steel washer.
Very important where different metals are used from the steel washers.
Vaseline (petroleum jelly), or Copaslip (copper loaded grease) are suitable for excluding the air and preventing the corrosion.
A steel washer is a poor choice against aluminum. It will react with aluminum and corrosion will set in quickly regardless of any applied coating. Stainless steel is a much better choice for fasteners and washers. Pentrox can be applied as well.
Stainless steel does corrode !
The difference between stainless steel (ss) corrosion and ordinary steel (fe) corrosion is ss is stable, i.e the corrosion product has the same volume as the parent metal, whereas the fe has a larger volume and is not stable. it leaves gaps during the expanding to let in more air/water. The ss corrosion forms a sealed surface that prevents further air/water getting to the parent metal.
That property of "sealing" is invisible to the naked eye and lures the uninitiated into believing they are looking at the parent metal.
The stainless steel washer must have the corrosion surface broken and the other part similarly have the corrosion surface broken to allow metal to metal contact (i.e. not corrosion product to corrosion product contact). This is where the hard steel serrated washer comes in, it breaks through the corrosion product. Those bared metals then need a film that prevents ingress of air/water to maintain the good metal to metal contact.
Don't use stainless steel washers if you require an electrically conductive joint.
The difference between stainless steel (ss) corrosion and ordinary steel (fe) corrosion is ss is stable, i.e the corrosion product has the same volume as the parent metal, whereas the fe has a larger volume and is not stable. it leaves gaps during the expanding to let in more air/water. The ss corrosion forms a sealed surface that prevents further air/water getting to the parent metal.
That property of "sealing" is invisible to the naked eye and lures the uninitiated into believing they are looking at the parent metal.
The stainless steel washer must have the corrosion surface broken and the other part similarly have the corrosion surface broken to allow metal to metal contact (i.e. not corrosion product to corrosion product contact). This is where the hard steel serrated washer comes in, it breaks through the corrosion product. Those bared metals then need a film that prevents ingress of air/water to maintain the good metal to metal contact.
Don't use stainless steel washers if you require an electrically conductive joint.
Last edited:
The corrosion of the aluminum due to contact with steel is the issue. My experience with this has been marine applications so results may vary. The addition of salt may make a difference. Marine spec is stainless or brass for electrical connections but brass isn't sharp enough to cut the surface.
Yes, but it needs an electrolyte.
Water is the usual.
Keep the water out and the surface is reasonably free from corrosion.
That's where the corrosion inhibitor comes in and hopefully gives a long enough electrical life.
Water is the usual.
Keep the water out and the surface is reasonably free from corrosion.
That's where the corrosion inhibitor comes in and hopefully gives a long enough electrical life.
That's quite possible. Is there any regulations in your part of the world regarding metal type? I'll need to dig into the revised CEC codebook to be sure but as far as I know SS was approved here.
I have had zero difficulties with stainless hardware on aluminum chassis and/or copper to aluminum (capacitors) studs. This for now ~25 years in service.
I'd not use vaseline or any similar petroleum product as they are insulators. I understand the desire to keep moisture out. I'd use one of the conductive products, like the ones spec'd for aluminum/copper electrical connections, if I was going to use something.
Ymmv.
For the chassis, IF the threads were anodized, then a tap needs to be run through those threads. Where the head of the screw sits the anodize layer also need to be removed. You'd not want to use "sandpaper", you must use AlO, aluminum oxide paper, if you use an abrasive paper at all.
Depending on the type of screw, a tool to machine the surface is the best way. If the hole is countersinked, then a counter sink, if it is a flat surface then a shoulder cutter is the optimal way to do that.
How careful you want to be depends on how much the aesthetics of the spot being cleaned off is. For things like flat pieces that are butt against another panel, it may be sufficient to clear the area around screws on both pieces to make a back side flat connection, but how well this works depends somewhat on the flatness of the pieces and the assumption that they will make contact.
So, to some extent the idea of affixing lockwasher style solder lugs to each panel and connecting them that way has some merit as it simplifies the process.
I'd not use vaseline or any similar petroleum product as they are insulators. I understand the desire to keep moisture out. I'd use one of the conductive products, like the ones spec'd for aluminum/copper electrical connections, if I was going to use something.
Ymmv.
For the chassis, IF the threads were anodized, then a tap needs to be run through those threads. Where the head of the screw sits the anodize layer also need to be removed. You'd not want to use "sandpaper", you must use AlO, aluminum oxide paper, if you use an abrasive paper at all.
Depending on the type of screw, a tool to machine the surface is the best way. If the hole is countersinked, then a counter sink, if it is a flat surface then a shoulder cutter is the optimal way to do that.
How careful you want to be depends on how much the aesthetics of the spot being cleaned off is. For things like flat pieces that are butt against another panel, it may be sufficient to clear the area around screws on both pieces to make a back side flat connection, but how well this works depends somewhat on the flatness of the pieces and the assumption that they will make contact.
So, to some extent the idea of affixing lockwasher style solder lugs to each panel and connecting them that way has some merit as it simplifies the process.
Last edited:
What you do depends on how much you need to get perfect shielding or not. Ideally, after you sand or grind a spot to bare metal you would use a screw (or a machine screw with nut) into the metal with a solder tab under it that has teeth to it so that they will pierce the oxide that forms immediately. Then run wires from piece to piece to bond them all together and to your AC input ground.
Gust grinding/sanding mating edges will not do much as aluminum forms a clear insulating oxide very quickly. There has to be some sort of tooth to punch through the oxide.
One reason where I work we use mainly plated cold rolled steel for panels so we can make a good faraday cage in order to pass FCC and CE.
Gust grinding/sanding mating edges will not do much as aluminum forms a clear insulating oxide very quickly. There has to be some sort of tooth to punch through the oxide.
One reason where I work we use mainly plated cold rolled steel for panels so we can make a good faraday cage in order to pass FCC and CE.
Is CRS alone good enough for a Faraday cage or do you need to line it with Mu Metal film?
A conductive material is all that is needed.
It can be continuous sheets/panels or can be perforated sheets, or can be chicken wire mesh.
All will work.
The interference gets through the gaps. A long skinny gap (50mm long by 0.1mm wide) lets through just about as much as the 50mm holes in chicken wire mesh.
Two adjacent panels secured at 175mm centres with tight metal to metal bolts is effectively a "gap" that is 173mm long, equals useless for a Faraday cage.
It can be continuous sheets/panels or can be perforated sheets, or can be chicken wire mesh.
All will work.
The interference gets through the gaps. A long skinny gap (50mm long by 0.1mm wide) lets through just about as much as the 50mm holes in chicken wire mesh.
Two adjacent panels secured at 175mm centres with tight metal to metal bolts is effectively a "gap" that is 173mm long, equals useless for a Faraday cage.
- Status
- Not open for further replies.