Connector sparking and damage  due to inrush at "mating" time? - Page 1
Forum section: electronics / projects

author: zenerbjt
author_rank: Regular Contributor
timestamp: August 30, 2020, 09:46:55 pm
content: Dear Engineers,We are using the JST connector of Part number = S2B-XH-A. We are using it to connect our 48V battery to our 5Vout DCDC module. (as attached)This comprises an 82uF capacitor at its input. Considering the inrush and sparking at the connector contacts due to the 82uF input capacitor, how long do you think this connector will last?Say, after 10000 connections, what would then be the resistance of this connector?Circuit attached showing where connector is.It will be connected once per day. Every day.S2B-XH-A connectorhttps://docs.rs-online.com/f25e/0900766b81357f2f.pdf

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 30, 2020, 10:00:17 pm
content: Add a small resistor or NTC in series to reduce the inrush. Since your load is small, the additional losses will be minimal.

author: wizard69
author_rank: Super Contributor
timestamp: August 31, 2020, 12:18:51 am
content: Silly question but why are you plugging in while powered up. That seems like asking for trouble on a JST style connector. You might not get a off by one error due to the shroud but those types of connectors tend to get rocked into place. Plus you are exposing whomever is plugging in, to voltages over 24 VDC. That might be a regulatory problem, I just know I've had a enough wire to board connectors, fail to retain the insert contact that I wouldn't like it.Quote from: zenerbjt on August 30, 2020, 09:46:55 pm

author: Psi
author_rank: Super Contributor
timestamp: August 31, 2020, 12:23:38 am
content: yeah, JST really aren't designed for hot plugging power, or hot plugging in general.You could add a mosfet + and RC filter on its gate.Have the mosfet pass through power after a delay from the connector insert. That way the inrush happens once the connector is fully seated not when a tiny area of the conductors first touch.

author: temperance
author_rank: Super Contributor
timestamp: August 31, 2020, 12:30:57 am
content: Just to convince you that a some form of inrush current limiting will be required. The connector is not the only problem.For aluminium electrolytic and film type capacitors: the pin to foil connection will fail.For ceramic capacitors: because of electrostriction they will crack and cause a short and burn out your board before the fuse melts.

author: wraper
author_rank: Unknown
timestamp: August 31, 2020, 12:33:19 am
content: Quote from: zenerbjt on August 30, 2020, 09:46:55 pmGood luck with 10k mating cycles. These connectors are not really designed for large amount of mating cycles. If they survive 500 without significant wear even without any inrush, you will be lucky.

author: oPossum
author_rank: Super Contributor
timestamp: August 31, 2020, 12:43:51 am
content: You could try some 'spark resistant' XT-60 or XT-90 connectors. They have an integrated precharge resistor.Like these:https://lunacycle.com/xt90-spark-resistant-connector-set/

author: temperance
author_rank: Super Contributor
timestamp: August 31, 2020, 12:47:00 am
content: Indeed, most low cost connectors are rated for 20 mating cycles. FCI has some miniature connectors able to survive 1000 cycles...What are you trying to do? Because someone plugging in those low cost connectors seems like a very unusual thing.

author: zenerbjt
author_rank: Regular Contributor
timestamp: August 31, 2020, 09:07:25 am
content: QuoteThanks but sorry i dont understand...we have a 48V battery which we plug into a circuit to power it, this circuit has an 82uF input capacitor, so we get inrush from the battery, through the JST connector.The JST connector has nothing in the datasheet which allows us to absolutely proove that the connector will be damaged by connecting it every day....so we wont get permission to re-do the circuit, as it will mean a PCB re-spin and will cost money.

author: capt bullshot
author_rank: Super Contributor
timestamp: August 31, 2020, 10:45:40 am
content: Quote from: zenerbjt on August 31, 2020, 09:07:25 amNever mind. It'll fail later at higher cost, most probably at someone else's expense / cost center.

author: tggzzz
author_rank: Super Contributor
timestamp: August 31, 2020, 10:55:14 am
content: Quote from: zenerbjt on August 31, 2020, 09:07:25 amAbsence of evidence is not evidence of absence.I'll bet there is nothing in the data sheet that will "enable you to absolutely prove the connector will be damaged by" storage in H2SO4or being hit with a shoe or...

author: zenerbjt
author_rank: Regular Contributor
timestamp: August 31, 2020, 11:43:46 am
content: Thanks but relays have switching operation data (eg "10,000 operations") , so i am surprised that connectors dont have it.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 31, 2020, 12:03:29 pm
content: Did you request the manuals from JST webpage? They are behind a license agreement.http://www.jst-mfg.com/product/detail_e.php?series=277Either way, the point of discussion here is not the electrical life., but mechanical. I don't think they are non rated for live plugging in any case. They are just an easier way to deal with what otherwise would have been solderjoints of screw terminals.I think that before you reach 100 mating cycles you'll have loose wires.

author: ConKbot
author_rank: Super Contributor
timestamp: August 31, 2020, 12:07:05 pm
content: JST connectors like that are for cheap consumer appliances ("white goods") So so they are meant to be plugged in once and left. I wouldn't be surprised if the rated cycle life was 20 cycles. (Edit: Molex picoblade is 30 cycles for comparison to something in a similar market segment)I certainly wouldn't consider them for a 10k cycle application. Even if the contacts were ok, the wires would fatigue and snap off the back of the connector first.Either add a soft start so its not popping every time its plugged in, pick a new connector with a long wipe what will have self cleaning action and some meat on the contacts, or both.

author: langwadt
author_rank: Super Contributor
timestamp: August 31, 2020, 12:09:58 pm
content: Quote from: zenerbjt on August 31, 2020, 11:43:46 amthe connectors that are meant to be plugged and unplugged have it, e.g. standard USB is rated for 1500 cycles and that is with a maximum capacity on 5V of 10uF

author: Nusa
author_rank: Super Contributor
timestamp: August 31, 2020, 01:02:44 pm
content: Any connector rated for 10K or more connections will have it in the datasheet, as well as prominently in their description, since it will be a strong selling point.Ditto if it's designed for hot-plugging. Also a selling point.Datasheets that don't mention it at all are probably rated in the 10s or 100s, depending on the material used for contacts and style of connector. If you are set on XH connectors, contact JST and ask them flat out. Whatever the numbers, special-ordering gold-plated contacts will get you the highest number on the list.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: August 31, 2020, 01:16:21 pm
content: As a comparison look at a mid-range connector from Phoenix:https://www.digikey.com/products/en?keywords=277-16346-NDIt's rated to 25 cycles. Now, that doesn't mean it disintegrates on cycle 26. It means that the datasheet values should be applicable if the connector was used within the ratings of the datasheet. Note that with these connectors the stress is applied to the wire, not the connector housing.As others pointed out various standards may apply. A quick look at 61010 finds some areas of concern. There isn't enough information about the design, product, and application to really dig into it here. Commercial? Industrial? Internal test fixture?Topics to ignore your boss about who is trying to make it faster and cheaper:- Batteries. Lots of safety issues regarding batteries, particularly high-current lithium types.- Environment. 48V lands right in the middle of dry compared to wet location concerns in 61010. Could this be a wet location?- Access. User access to conductive terminals and wires with thin insulation.- Connectors. Terminal spacing, wire size, etc.- Misuse. Foreseeable issues.- Faults. Single and multiple faults. Wire breakage.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 31, 2020, 01:50:04 pm
content: Measure the peak current on connection - likely tens of amps, way over the connector's rating

author: tggzzz
author_rank: Super Contributor
timestamp: August 31, 2020, 02:06:54 pm
content: Quote from: zenerbjt on August 31, 2020, 11:43:46 amSome do. Others don't.In a similar vein, some aircraft specify that spin recovery will take up to X rotations when loaded within the limits. All the aircraft I've piloted do have such a specification, but Boeing 7x7 and Airbus 3xx don't.Now why do you think that might be?

author: bdunham7
author_rank: Super Contributor
timestamp: August 31, 2020, 02:16:19 pm
content: Treez, is that you?JST connector and 10K mating cycles? The same JST connectors that I carefully pry out with two plastic picks when I have to repair something and hope I don't hurt them? Yes, they are commonly used for battery packs and the like, but the housings just aren't going to hold up to your long-term expectations.The amount ofenergythat it takes to charge up an 82uF cap is pretty small, even at 48VDC. I doubt your JST life is going to be determined by how long it takes to arc the contacts down to a nub. Just make sure that either the connector is accessible and repairable or that your product is disposable. Or, you can just blame the inevitable problems on user abuse.

author: Gyro
author_rank: Super Contributor
timestamp: August 31, 2020, 05:36:04 pm
content: Of course it's treez, who else thanks every post regardless.Also:https://www.eevblog.com/forum/renewable-energy/contactor-sparking-with-multi-kw-equipment-is-just-normal-accepted-practice/

author: tggzzz
author_rank: Super Contributor
timestamp: August 31, 2020, 05:43:24 pm
content: Quote from: Gyro on August 31, 2020, 05:36:04 pmShush! He could easily change that characteristic tell-tale, thus making identification a little less trivial and obvious.The evidence is that he can't change his posting style and content, though.

author: silverback
author_rank: Contributor
timestamp: August 31, 2020, 05:56:26 pm
content: what about the poor old capacitor surge current

author: jbb
author_rank: Super Contributor
timestamp: August 31, 2020, 06:43:06 pm
content: Sounds like your management subscribes to a time honoured management tradition: “We don’t have time to do it right but we do have time to do it twice.”I suspect you won’t get near the lifetime you want, so I suggest you actually test it. Get yourself a fully charged battery and a board and cycle that sucker. Plug it in, unplug it, wait for 82uF cap to discharge, repeat (add a fair load to 5V output to discharge cap).I suggest a pair of safety glasses in case it fails with sparks and some fine gloves so you don’t wear the skin off your fingertips.

author: bson
author_rank: Unknown
timestamp: August 31, 2020, 07:51:53 pm
content: Quote from: NiHaoMike on August 30, 2020, 10:00:17 pmIn particular, put the NTC on the supply side of the connector to keep the voltage down and hence minimize arcing.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: September 01, 2020, 04:56:37 am
content: Quote from: bdunham7 on August 31, 2020, 02:16:19 pmI would say probably 50% of JST connectors one encounters in random pieces of equipment are Chinese-made clones, that are markedly different in quality compared to the genuine thing.In particular I find the plastics are softer and less rigid, which for friction-retention connectors like XH or PH series means they get pretty loose after only a few mating cycles. Also, for some reason the clones have terrible attachment between header pins and the plastic. Half the time when you go to unplug, the receptacle comes with it.So yeah, sometimes you have to treat them delicately simply because they're cheap, crappy clone parts, but the genuine thing are a bit more robust.

author: wizard69
author_rank: Super Contributor
timestamp: September 02, 2020, 11:56:30 am
content: Quote from: zenerbjt on August 31, 2020, 09:07:25 amThat is all well and good but you didn't answer the question, why are you hot plugging, especially a connector not designed for it. 48 VDC is high enough voltage to present a safety risk to anybody handling such a connector.QuoteI can't possibly imagine any success in a court of law with an attitude like that. If you want to plug something like this daily you need to have a connector that can survive such usage and can also be handled safely by whomever is plugging in daily. As for the JST data sheet there should be some sort of cycle parameter that would specify the number of insertion cycles the connector can handle. JST make a range of connectors so I have no idea what the cycle limit would be on the connector you have but many of these connectors start to have issues after 10-50 cycles.