Stainless Steel bolts vs Brass for power leads?

[Dennisd]

Is there any reason to use brass bolts vs Stainless for the power lugs on the stator? Standard 10' design, 48 volts. I am asking because I have lots of Stainless,but need to special order the brass here (or buy them "each" at a ridiculous price)

[zvizdic]

I used SS bolts and I do not see why not.
Distance is so minimal that higher resistance of SS is minimal.
Bras by the way is corroding (green) so you need to paint spray it or silver plate.

[hayfarmer]

my midnite solar e panel has stainless  bolts  on brass buss bars and required putting anti seize on threads,found this comment on fieldlines and link :

(Your call, go brass, and check tightness at least twice a year, or go stainless, and check it at 3-5 year intervals. )  http://fieldlines.com/board/index.php/topic,142518.0.html

  hayfarmer

[imsmooth]

I went with brass so I could make these fittings for the connections.

http://www.mindchallenger.com/wind/axial9.html

I never had a problem with them, yet.

As far as resistivity goes, there should be no significant difference.

[Flux]

Stainless works ok. The main factor is avoiding rust. As someone said, brass does tend to go green but only on the outside. It stays clean where the connections is made and it matters.

The cost and availability issues are forcing manufacturers to use stainless and it seems ok for many applications where at one time it wouldn't be considered.

Even mild steel will be ok resistance wise but the inevitable rusting makes it a no go area for things exposed to the weather.

Flux

[artv]

Hi Dennisd,...I was planning on soldering a plug-in from an old headlight connection of an old car,they make for a very good weather proof hook up.The only reason it may not work is the size of the wire,I was going to ask this question,would this not work?......thanks artv

[kevbo]

The resistivity of brass is 64 nOhm/m, stainless (the chart I found did not specify alloy) is 720 nOhm/m.  Source: http://physics.info/electric-resistance/

So if the bolt is conducting the current, it matters quite a bit, as brass is almost 10 times better electrical conductor.  If the bolt is just pressing a terminal into a bus bar, then it doesn't matter much.

I have used stainless aircraft cable as low temperature heating wire for motorcycle clothing.  Copper of the required resistance is so small that it breaks too easy.  I also tried to use it for ballast resistance in another application and melted the PVC insulation on 1/4" cable carrying only 15A.  Finally, I had one place where a 1/2" bolt had to be 404 stainless and carry 100A or so.  It was getting too danged warm, so I ended up putting a copper sleeve around it to carry the current.

Additionally, some applications may depend on the fastener to carry heat away from a connection, and stainless is  as poor a thermal conductor as it is electrically. (both related to electron density and mobility)

[ghurd]

The resistivity

Kevbo,
You have a PM from me. 
PM list is in the top left of the page.
At least let me know if you got it.
G-

[RP]

One advantage to brass is ease of soldering your windings to the studs.

[Flux]

The resistivity of brass is 64 nOhm/m, stainless (the chart I found did not specify alloy) is 720 nOhm/m.  Source: http://physics.info/electric-resistance/

So if the bolt is conducting the current, it matters quite a bit, as brass is almost 10 times better electrical conductor.  If the bolt is just pressing a terminal into a bus bar, then it doesn't matter much.

I have used stainless aircraft cable as low temperature heating wire for motorcycle clothing.  Copper of the required resistance is so small that it breaks too easy.  I also tried to use it for ballast resistance in another application and melted the PVC insulation on 1/4" cable carrying only 15A.  Finally, I had one place where a 1/2" bolt had to be 404 stainless and carry 100A or so.  It was getting too danged warm, so I ended up putting a copper sleeve around it to carry the current.

Additionally, some applications may depend on the fastener to carry heat away from a connection, and stainless is  as poor a thermal conductor as it is electrically. (both related to electron density and mobility)

This is perfectly true and stainless is much the same alloy as some of the resistor materials so how you use it does matter.

For a stator then ideally bring the connection out via a copper foil or something and use the stainless to clamp that to the cable lug. In real life as long as you use a decent size bolt it will be ok to carry the current through the 1/4" or so to the outside world and each phase of a stator although carrying the mean dc current it will only be doing so for 2/3 of the time . For a 12v machine  it still could be worth including a copper or brass sleve in the stator moulding.

Certainly you will run into trouble if you need to use any significant length of stainless to carry current. In that case brass is significantly worse than copper but stainless is no go.

It's interesting to see things used commercially now that years ago were considered totally inappropriate, our earlier equipment was produced on the basis of what was best. Modern stuff gets away with things that would never have been considered but it still does the job, it's largely down to using the cheaper materials in an appropriate way and sometimes doing things a bit differently.

I would infinitely prefer brass but if I had stainless available I wouldn't go out to buy expensive brass for stator connections.

Flux

(Edited: RossW for clarity)

[bob g]

a relatively inexpensive source of brass bolts, at least in the quarter inch size are
brake block bolts that are used to attach brake lining to brake shoes on heavy trucks and trailers.

while most brake blocks/lining is attached with more common rivets bolts are available to do the job as well. they are brass, usually about an inch or better long, fine thread and come with stainless nuts

because of the mass production economies of scale they are about the cheapest source of brass bolts i know of.

they have a flat head with straight slot suitable for a screwdriver, which may or may not be an issue, i have used them in the past by simply laying the copper in the screwdriver slot and soldering it in.

if you check with a brake rebuilder they likely have a few laying about that they would give you if you want to try them  out.

worth a look?

fwiw

bob g

[Kwazai]

I would tend to think that how its put together is a factor, but with the stainless and the brass both it would probably pay to put some zinc (galvanized) in there as the donor for the corrosion (sacrificial zinc?). maybe washers or something..
anyway my .02$
L8r
Mike

[kevbo]

Glen, PM reply sent.

For short lengths, the power loss can be minimal, but the heat may still cause trouble.  For the 1/2" bolt I mentioned previously, it was melting the polyethylene wall it was feeding power through. This caused the connection to become loose, which lead to more heat.  Thermal cycling with mixed materials can also cause threads to loosen over time.

Using large copper terminals tied to heavy gauge copper wire will help. These will pull a lot of heat out of the stainless connector.

Compared to copper ampacity, for brass you need about 4X the cross sectional area, and for Stainless about 40X.

I absolutely agree that you don't have to use the best possible material for a given job.  But it is also helpful to understand the sort of compromises you are making, and the gotchas to be looking out for.

[tanner0441]

Hi

If the terminals on the wire ends are only clamped by the bolt it does not matter what it is made of, as for using a zinc washer. If the zinc washer degrades the clamping pressure will reduce, which can cause problems.

I would think the short length of stainless is not going to be a problem, I have used stainless bolts on battery and starter circuits on quite large marine diesels with no issues at all.

On the other hand I have not read on this site of anyone using brass bolts that have had problems.

Brian.

[hayfarmer]

Greetings, after doing annual check on power plant ,bolt/nut tightness etc.finding several loose set screws on breakers ,fuses ,batteries,combiner box,buss bars ,battery

 monitor, etc. I am pleased to say I am the new owner of 2 amps per hour of lost power due to loose connections. they were on a wide spectrum of connections mostly

 set screw type on buss bar in breaker panel "stainless" but also had brass culprits as well .vast majority of wire is copper thhn  except for the battery cables which are flexable

  Cobra wire , only solid is sense leads to monitors or fans



 (So if the bolt is conducting the current, it matters quite a bit, as brass is almost 10 times better electrical conductor.  If the bolt is just pressing a terminal into a bus bar, then it doesn't matter much.)

  and while  tightening them up watching the MPPT controller increasing in amps, a little here and there totaling 2 amps gained and remote showed running 3 hours with no

  drop in S.O.C. 100% after 530 pm. I was feeling like  a new poppa. proud of my little off spring  


  hayfarmer

[scoraigwind]

I would not dream of having bolt on stator connections on the stator surface.  I always embed the solder joins within the casting, and have tough, flexible insulated wires coming out of there, often leading to a weatherproof box or to reliable copper crimp connections that have no corrosion problems (since there are no dissimilar metals) and could easily be replaced if they did.

[tecker]

The distance is so small the power factors are not affected Stainless is better suited for open frame .