DIY Binding posts - Page 1
Forum section: electronics / beginners

author: Stuartambient
author_rank: Regular Contributor
timestamp: July 29, 2016, 01:55:20 pm
content: Are brass bolts are viable option for binding posts. I don't care about the banana 4mm bullet connection. Alligator clips for this particular usage would be fine. I'd say the ability to pass 10 to 20A would be nice. I'm just looking to avoid the price for this particular application of high priced connectors like the Pomona.

author: whalphen
author_rank: Regular Contributor
timestamp: July 29, 2016, 03:08:42 pm
content: Certainly, you can use brass bolts as binding posts. If you use a bit of flux, you can easily solder them, as well. Just be aware that they have more resistance than copper wire and in high current applications they could cause a small voltage drop and some heating.I've used them in antenna construction, soldering them to copper pipe hangar strips which serve as connectors to the feedline. The bolts are then used to bear the weight of the long antenna wires. That's a low current application, though.

author: Stuartambient
author_rank: Regular Contributor
timestamp: July 29, 2016, 05:10:42 pm
content: Okay, I looked at a metals chart and see it is about 4x the resistance of copper. I'd prefer to minimize voltage drop and resistance. Seems most of the decent commercial posts are brass (or tin) but gold plated which makes sense. Guess I'll take the commercial route. I wonder though about the ones that do not have a current rating.

author: Gyro
author_rank: Super Contributor
timestamp: July 29, 2016, 05:37:36 pm
content: A bit of gold plating isn't going to make any difference to the bulk resistance of the terminal. Yes most terminals are made of brass anyway. You can't use copper unless to alloy it with something else, and that's only for low thermal EMF use. Brass nuts and bolts are a time-honoured method of making terminals. As long as the cross section area of the bolt is at least 4 times that of the wire you're connecting then you don't have a problem.

author: mtdoc
author_rank: Super Contributor
timestamp: July 29, 2016, 05:42:29 pm
content: I think acopper split boltwould make a nice DIY binding post. They come in multiple sizes from small to very large.

author: Stuartambient
author_rank: Regular Contributor
timestamp: July 29, 2016, 07:23:04 pm
content: Quote from: Gyro on July 29, 2016, 05:37:36 pm4 x the wire is good to know, thanks! They are cheap enough so I can do some testing.

author: Stuartambient
author_rank: Regular Contributor
timestamp: July 29, 2016, 07:27:19 pm
content: Quote from: mtdoc on July 29, 2016, 05:42:29 pmI looked at those but on the HomeDepot site was put off by the price though the sizes were a bit larger. They were going for around $4 piece but yeah they would also be worth a try. I'll have to check the local hardware store.

author: Back2Volts
author_rank: Unknown
timestamp: July 30, 2016, 05:15:06 am
content: If you want to hand tight, you can explore using knurled nuts.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: July 31, 2016, 01:26:35 am
content: If it is just for alligator clips then perhaps a little half loop of 10 gauge solid copper wire would suffice. It would get chewed up, but would be cheap and easy to replace.I like banana jacks, as they are pretty standard, and lots of things connect to them in lots of ways.

author: Back2Volts
author_rank: Unknown
timestamp: July 31, 2016, 02:17:21 am
content: Quote from: Stuartambient on July 29, 2016, 01:55:20 pmPomona dual binding post 30A at low voltage, $2.69http://www.mouser.com/ProductDetail/Pomona-Electronics/6883/?qs=sGAEpiMZZMv8kklI404QlS1lY6X45RXS

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 31, 2016, 03:30:36 am
content: Terminal blocks (solder lugs on the back, screws to hold lugs on the front) are available, though not usually from global distributors (IIRC, Digikey's catalog is pretty thin in the >50A range); you'll have to do the old fashioned call-a-sales-guy routine with a local electrical distributor to see if you can get some samples for a modest price.Brass bolts are okay, and yes, as mentioned, they do need to be large to manage the resistance and heat (and, by the way, don't discount contact resistance -- it's probably a bigger deal than bulk material resistance, unless the bolt needs to be quite long).If you insist on designing the connection yourself, the best method is to avoid current in the bolt at all -- connect the high-current terminals to a heavy copper block, and bring that out to the front. Then put a bolt through that, to clamp on whatever lugs are needed. That way, the bolts don't need to be special at all; they can be mild steel, for all you care!Tim

author: Stuartambient
author_rank: Regular Contributor
timestamp: July 31, 2016, 11:30:42 am
content: Quote from: T3sl4co1l on July 31, 2016, 03:30:36 amSounds like you are talking about a kind of busbar which I did think about but would be overkill for this application. Plus copper blocks alone are going to cost me more then high quality posts. I do have some terminal blocks so I might try those. I don't think they were rated for amperage but have had 10-15A going through without any issues.I should say what I'm doing here. I bought two current sense resistors T0-220 style. The application notes for the resistors suggest various types of heat sinks and listed an aluminum enclosure (7"x5"x2"x.04") as 2 degree C/W. This was the option I went with and will mount them inside the case with a 1 degree C/W thermal tape interface. Probably a bit of overkill in all but 2 C/W heatsinks were 2 to 3x the price of the enclosure.I did some calculation just on wire and with less then a foot of 14awg or 12awg of wire off the leads there was no resistance. I imagine adding a post, either diy or commercial ones will add some resistance which is what I want to test. I was kind of inspired by the attached picture. This person used 4 or 5 power resistors in parallel, mounted to the heatsink and then the banana jacks in the front.I found some knurled screws,http://www.homedepot.com/p/Crown-Bolt-8-32-x-3-4-in-Knurled-Screw-in-Brass-3-Pack-99178/203537752. I'd test them before installing but also need to insulate them if i install into the aluminum case. I also have some 3.5mm bullets that can pass 15A so that is something I'm going to test as well.Thanks all for the suggestions and info!

author: David Hess
author_rank: Super Contributor
timestamp: July 31, 2016, 07:35:14 pm
content: Quote from: FlyingHacker on July 31, 2016, 01:26:35 amA loop of plated copper bus bar wire is what I use for test points when alligator clips or something smaller can be used to grab on.Brass works fine for binding posts and better than most of the alternatives except for being slightly difficult to solder but mechanical cleaning and the right flux helps a lot.Do not rely on low temperature solder for a reliable mechanical connection!Bolt the brass binding post into place.