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I am building a DYI solar power plant with custom built wi-fi connected power meter with two 20 A, ACS712 current sensors.

I put everything in a plastic box with banana connectors, on picture here:

Metering box

I thought these banana plugs are going to be enough because they look like a big piece of metal, but after over a month of smooth operation, during very sunny day one of connectors melted:

Melted

Current that was going through was about 15 A at the time, it seems that while banana plug is quite big, its metal plates have very small points where they touch the opposing connector and as such they get hot very easily with higher currents. I noticed all eight connectors were eventually getting warm.

What type of connector is best suited for this kind of application, so that it is reasonably cheap, common, doesn't exceed 60°C when under 20 A and of similar size? (Not too bulky like MC4, ideally possible to screw to plastic box like this.)

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    \$\begingroup\$ Any connector will always generate heat when carrying current. How much heat is tolerable? \$\endgroup\$
    – Hearth
    Commented Oct 5, 2022 at 19:36
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    \$\begingroup\$ And how much is that? That's also a difficult question because it's not heat that does either of those things, it's temperature. And temperature is very complicated to calculate. I would suggest just looking for connectors that are rated for 15 A; that's a pretty large amount of current, but not large enough that it's hard to find suitable connectors. I've even seen banana plugs rated for it (actually rated for quite a lot more, and quite expensive; not what you want here), though they're quite different from your normal banana plugs. \$\endgroup\$
    – Hearth
    Commented Oct 5, 2022 at 19:40
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    \$\begingroup\$ Personally, I would probably use Anderson powerpole connectors here, but I don't know your use case and what other requirements you might have. Shop around. Good distributors like Mouser or Digikey have parametric search, so you can search by rated current. \$\endgroup\$
    – Hearth
    Commented Oct 5, 2022 at 19:41
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    \$\begingroup\$ If you're looking for something cheap and easy to find, consider using connectors designed for car batteries and similar. \$\endgroup\$
    – jonathanjo
    Commented Oct 5, 2022 at 19:42
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    \$\begingroup\$ Look for '4mm gold bullet' connectors, which are commonly used for electric RC racing cars eg. amainhobbies.com/… \$\endgroup\$ Commented Oct 6, 2022 at 20:07

3 Answers 3

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There are high current 4mm banana plugs, and lightweight, cheap, ones.

Unfortunately, you get what you pay for, and the better ones will cost more. They will probably only be obtainable from reputable electronic suppliers, not the auction-type sites. You should look for a 'bunched pin' type, which has multiple spring rods. Types with a single spring rod, or a loose spring cage, are not going to give you a much higher contact resistance.

A good solid turned socket will also help dissipate heat better than one formed from thin stock.

That only gets you to the better end of a banana plug connection. It would be better to use connectors rated for the current.

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  • \$\begingroup\$ I have banana plugs at my workplace that are rated for 500 A (pulsed only); they're on (relatively) enormous 6-gauge wire and have an unusual construction--by screwing down a collar on them, the banana plug itself expands outward, pressing tightly into the sides of the jack. I have no idea where you would buy them; they came with an extraordinarily expensive piece of test equipment. \$\endgroup\$
    – Hearth
    Commented Oct 5, 2022 at 20:03
  • \$\begingroup\$ I worked in the stock room at General Radio, briefly in my college years. They made their own banana plugs, and other sundry connectors where they made a difference to precision measurements. \$\endgroup\$
    – TimWescott
    Commented Oct 6, 2022 at 19:45
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"What type of connector" may be the wrong question. The broad category of connectors you're looking for is connectors designed to carry current or handle power.

The only reliable way to buy a connector and be reasonably certain that it'll stand a given current is to find one from a reputable source (i.e. not an auction site, or a hobby site, or a company that specializes in selling floor-sweepings from countries known for low quality products). Then read the datasheet. You want to find that your connector is specified for your current or more, at your operating temperature. If the data sheet doesn't specify a current and an operating temperature, then that's a strong indication that whoever is selling it to you didn't pay attention to making it work under those circumstances.

This is one of those areas where attempting to save money by buying stuff off of the hobby or auction market will leave you endlessly messing around with marginal stuff. If you already know what you're doing there's some surplus vendors that have decent stuff -- but that's a huge roll of the dice, and again, you need to know exactly what you want and who you're dealing with. Assuming that you live in a country with a robust electronics industry, just find a reliable distributor* that'll sell stuff in quantity 1, and accept that the price will be higher than flea-market prices.

* I.e., DigiKey, Mouser or Newark in the USA, Farnell in the UK. Unfortunately my knowledge of who sells what doesn't go beyond that.

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    \$\begingroup\$ RS Components is also a big one in the UK, and Arrow in the US (might be worldwide?). Mouser operates worldwide as well, though they're based in the US. \$\endgroup\$
    – Hearth
    Commented Oct 5, 2022 at 20:30
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For your application, I recommend plastic power circular connectors (my site), a broad class of relatively inexpensive connectors for exterior use (accessible to the end user) and high current. For example, the Weipu SP or SY series which are readily available from eBay and Amazon.

enter image description here

{Courtesy Weipu}

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  • \$\begingroup\$ I was actually considering those, but I am not sure how could I mount them to that plastic box, they look more like connectors for connecting two wires together. The box is indoors so it doesn't need to have IP rating. \$\endgroup\$
    – Petr
    Commented Oct 6, 2022 at 17:56

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