Bullet connectors: yay or nay? - Page 1
Forum section: electronics / projects

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2023, 12:16:24 pm
content: For a project I'm involved in a supplier is supplying modules which come with bullet connectors to carry up to several tens of Amps peak. This is for an outdoor transport application that should work reliably for 10+ years. During testing we already noticed that the bullet connectors let go quite easely. My feeling says that a different connector would be a better option. What is the general consensus about bullet connectors?

author: Messtechniker
author_rank: Frequent Contributor
timestamp: June 12, 2023, 12:26:22 pm
content: Since there are umpteen different types, a pic would help us to decide

author: beanflying
author_rank: Super Contributor
timestamp: June 12, 2023, 12:38:36 pm
content: I have been using 3 and up to 8mm (up to 2-300A peak) Bullets in R/C planes and helis for a few decades and never had one fail electrically so take that as a recommendation electrically.Mechanically never had one fail either but they are not being shaken to death and a lot of the airframes/wiring is really tightly packed so if anything they run a positive push together fit. They are in most cases as easy to slide in or out as any standard lab type of lead into a bit of test gear.However in transport (ground?) I would think you want to look for a locking type of housing to hold the bullets? Grab a packet of 'Amass' (don't buy off brand) XT60 or 90's for a play even without a lock the extra friction from the plastic housings should help.Panel mount XT90'shttps://www.amazon.com.au/dp/B09DBK97VJ/?coliid=IEQVYMS3O4E26&colid=2K1U2SA8AXQGC&psc=1&ref_=list_c_wl_lv_ov_lig_dp_itPanel Mount XT60'shttps://www.amazon.com.au/dp/B09128LHGG?psc=1&ref=ppx_yo2ov_dt_b_product_detailsXT60's MF wired pairshttps://www.amazon.com.au/Amass-Bullet-Connector-Upgrated-Shrink/dp/B074PN6N4K/ref=sr_1_5?keywords=amass&qid=1686573444&sr=8-5Several other options around but these are fairly common worldwide on evilbay/amazon.None of these are a positive lock but also look at Sermos if you want a more positive lock.https://www.andersonpower.com/us/en/resources/SBseriesResourcesPage.html

author: PeteH
author_rank: Unknown
timestamp: June 12, 2023, 02:32:33 pm
content: Can also easily heatshrink (clear) bullet connections, depending on how often these need to be cycled.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 12, 2023, 03:34:30 pm
content: I, too, have used bullet connectors in models and indoors. So-called "charging" connectors (attachment) probably go gy a variety of names. NB: the contacts are not gendered. I have seen them used outdoors, as in APU's for aircraft and golf carts. They probably offer a little protection from the environment. It would seem almost any connector can be tied together so it doesn't come apart easily."Jack knife" connectors are also an option (attachment 2), But may not come in the amperage rating you need. They can be protected in heat shrink.EDIT: Somehow our prehistoric method of adding attachments reversed the order of my two attachments. Sorry.

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2023, 04:08:15 pm
content: Quote from: Messtechniker on June 12, 2023, 12:26:22 pmHmm, I forgot to pay my subscription to Crystal ball Ltd...I mean these kind (not this specific model though):

author: bdunham7
author_rank: Super Contributor
timestamp: June 12, 2023, 04:22:37 pm
content: Quote from: nctnico on June 12, 2023, 12:16:24 pmBritish Leyland used those in products like the MG-B and TR-7. They were terrible. They are still sold today for automotive uses such as trailer hitch wiring, which also have a terrible reputation.

author: Gyro
author_rank: Super Contributor
timestamp: June 12, 2023, 04:45:12 pm
content: Quote from: bdunham7 on June 12, 2023, 04:22:37 pmThey were certainly very bad for moisture and salt exposure in automotive conditions with no attempt at waterproofing, no strain relief and simple tin plated connectors and springs. It wasn't unusual to have the copper wire corrode out of the bullets. They also encouraged solder wicking under the insulation, making them even more fragile.Modern bullets are probably better, but some of these issues may still be relevant.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: June 12, 2023, 04:45:28 pm
content: Quote from: nctnico on June 12, 2023, 04:08:15 pmSeemingly these belong to an el-cheapo range. There are better ones around. Just my opinion.

author: rounin
author_rank: Regular Contributor
timestamp: June 12, 2023, 06:55:34 pm
content: I've had bad luck with bullet connectors and only use them for prototyping when forced to. I usually replace all of the bullets with Anderson power pole 45, high detent force contact variant.I like polarized housings, crimped contacts, and indicating clicks when mated. And a datasheet with specified contact resistance, which few bullet mfgs seem to have. Amass is ok though, as they go.

author: rounin
author_rank: Regular Contributor
timestamp: June 12, 2023, 06:57:40 pm
content: Quote from: jpanhalt on June 12, 2023, 03:34:30 pmThe gray one is Anderson SB50 (or SB120 or SB350). I like these.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 12, 2023, 07:07:32 pm
content: I think the bullet connectors used by modelers like myself are like the two attached images.

author: f4eru
author_rank: Super Contributor
timestamp: June 12, 2023, 07:36:53 pm
content: I use them as crimpable female bananashttps://www.eevblog.com/forum/chat/awesome-cheap-banana-replacementtrick/msg4101874/#msg4101874

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2023, 07:45:25 pm
content: Quote from: jpanhalt on June 12, 2023, 07:07:32 pmThat looks more like a banana connector to me thoughI think I know enough now. I'll push for a multipole (with 5 to 6 contacts in total) connector with crimp contacts. Preferably a sealed one if it fits in the space. Hand soldered connectors is a no-go in production for quality and consistency reasons. I've seen hand soldered connectors go horribly wrong :'(

author: jpanhalt
author_rank: Super Contributor
timestamp: June 12, 2023, 07:53:46 pm
content: Just consider them sabot bullets. I guess there are other ways to describe a cylindrical connector with a rounded end, but not here.

author: Kryptychon
author_rank: Contributor
timestamp: June 12, 2023, 10:09:15 pm
content: Quote from: rounin on June 12, 2023, 06:57:40 pmI'm interested in these connectors as well. It's a nice high current connector but the price for the genuine crimping tool is outrageous.Is there an alternative?

author: james_s
author_rank: Super Contributor
timestamp: June 12, 2023, 10:13:27 pm
content: They work fine provided you crimp them properly and protect them from moisture, but the latter can be easier said than done. I've never had one mechanically let go, more often they stick so firmly that you end up yanking the wire out instead of unplugging it. The gold plated bullet connectors used for electric RC models are much better IMO, they're much more resistant to corrosion and I've had them survive some rather high speed crashes without coming loose. They're a pain to install though.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 12, 2023, 10:23:25 pm
content: Quote from: Kryptychon on June 12, 2023, 10:09:15 pmFor such heavy gauge crimps, I use a hammer crimper for up to 2-0 welding cable (haven't tried heavier). Considerably cheaper than purpose-made hydraulic crimpers. The attachment will give an idea; although, that is not the brand I use.Edit: Ah ha, I found what I actually use at McMaster-Carr. Today, it is about 4x what I paid for mine. New attachment.

author: nctnico
author_rank: Super Contributor
timestamp: June 12, 2023, 10:45:18 pm
content: I'd recommend against using those hammer crimpers. Crimping is a cold flow process which you don't get when hammering a crimp. I've seen those hammered crimps get lose very early on in my career on similarly thick wires (for testing 5V supplies at hundreds of amps).

author: jpanhalt
author_rank: Super Contributor
timestamp: June 12, 2023, 10:47:45 pm
content: I have a small, 10-ton Dako press with pressure gauge. One can use that too. I am not sure a good hammer strike doesn't cause cold flow too -- not multiple taps.

author: beanflying
author_rank: Super Contributor
timestamp: June 13, 2023, 12:43:33 am
content: Quote from: nctnico on June 12, 2023, 04:08:15 pmThe horror of the 1960's and 70's in modern useThey are even worse than decent spade connectors as they trap and hold moisture in and around the joint and no way I would want to push them much over 10A even then.If there is any number of cycles plugging or unplugging them by monkeys then the wires will almost certainly get pulled out or break off for a start. This has been my experience with a couple of Landrovers I owned and one I replaced the loom in to reduce the fire risk from kwality British wiring of the era.

author: wraper
author_rank: Unknown
timestamp: June 13, 2023, 01:17:59 am
content: Quote from: jpanhalt on June 12, 2023, 07:07:32 pmSegway/Ninebot used gold plated connectors similar to these in their electric scooters like ES2 between driver and BLDC motor and they totally suck. Visually they look good and look like they have quite a bit of contact area which should provide low contact resistance. In practice they start overheating and melting wire insulation. Put external battery or use custom firmware for better acceleration and they are guaranteed to fail very soon. I used cheap tin plated 6.3mm fast-on as replacement and the issue has gone, no signs of overheating after prolonged use.

author: bill_c
author_rank: Regular Contributor
timestamp: June 13, 2023, 03:49:12 am
content: Quote from: jpanhalt on June 12, 2023, 03:34:30 pmI have tried to find the name of these for a year. Thanks!

author: Siwastaja
author_rank: Super Contributor
timestamp: June 13, 2023, 07:33:35 am
content: That particular type automotive bullet connector is total shit, maybe a good brand when inserted only once could work out by luck.Those machined (turned) brass things with two slots cut perpendicular to each other, with very snug fit into the respective female (e.g., as used in XT60 connectors), can be pretty good but as wraper showed even those can fail, manufacturing tolerances are critical.

author: uer166
author_rank: Super Contributor
timestamp: June 14, 2023, 04:43:06 am
content: Quote from: wraper on June 13, 2023, 01:17:59 amWeird, I've been using XT90 connectors with very similar construction and it seems ok. I wonder what went wrong with the Ninebot ones. It'll be 4 point-contacts regardless of tolerance, so not sure what the failure mechanism is specifically.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 14, 2023, 05:50:53 am
content: Quote from: uer166 on June 14, 2023, 04:43:06 amMost likely manufacturing tolerances, male part being 0.000000001 picometers too small for a snug fit. I have seen this when mixing counterfeit XT90 connectors from different manufacturers, some combinations are loose.

author: beanflying
author_rank: Super Contributor
timestamp: June 14, 2023, 07:22:20 am
content: It was way worse with the Fake Deans connectors than the faked Amass ones. I didn't offer Deans as an alternate here mainly as availability is more hit or miss worldwide and more garbage than 'real' ones.For the really high power gear we are actually running Gold Plated bullets without housings partly for space reasons in F5B or D airframes. These are another step up from the XT ones.

author: wraper
author_rank: Unknown
timestamp: June 14, 2023, 09:31:25 am
content: Quote from: Siwastaja on June 14, 2023, 05:50:53 amThey fit snugly, not loose. They may be fine in scooter variants which are limited to 20 km/h and lower power in firmware. But if you say have ES4 (ES2 with external battery), have larger weight than average Asian and ride in sport mode, they are guaranteed to fail epically.

author: rounin
author_rank: Regular Contributor
timestamp: June 14, 2023, 09:53:28 pm
content: Quote from: Kryptychon on June 12, 2023, 10:09:15 pmThese guys sell an ok aftermarket crimper:SB series:https://powerwerx.com/hex-crimping-tool-sb-series-powerpolePP series:https://powerwerx.com/tricrimp-powerpole-connector-crimping-toolI have both and use them for prototyping / lab use. YMMV for "production".

author: thm_w
author_rank: Super Contributor
timestamp: June 14, 2023, 10:44:53 pm
content: Quote from: wraper on June 14, 2023, 09:31:25 amThere are many scooters with far higher power motors using the same connectors. ES4 is 800W peak, some of these devices are 2000W+ peak power.So its not a matter of the connector design itself not being capable of handling the current. Either manufacturing tolerance as Siwastaja says, or they had poor crimping, plating, whatever.This guy is saying its cable issue, not sure I'm convinced as your photo looks more like the heat was from the connector, but, the cable does seem quite stiff if its something thats constantly bouncing around.

author: wraper
author_rank: Unknown
timestamp: June 15, 2023, 12:14:49 am
content: Quote from: thm_w on June 14, 2023, 10:44:53 pmConnector overheats and melts its own insulation and as heat travels over copper wire its insulation in close proximity of connector melts too but to lesser extentQuoteHigher power scooters do not use these connectors, the may be similar looking bur not these. KickScooter MAX has the same connectors, nothing bounces there but they have the same melting issue.

author: thm_w
author_rank: Super Contributor
timestamp: June 15, 2023, 12:24:14 am
content: Quote from: wraper on June 15, 2023, 12:14:49 amSeems likelyQuoteYeah thats the problem, how do you know what is exactly that connector, who knows. They are unbranded usually. Or are you saying something specific about those connectors that can be identified?Here is the inmotion V12 motor:https://www.aliexpress.us/item/1005004016683553.htmlCapable of 2500W (claimed 5kW peak).

author: beanflying
author_rank: Super Contributor
timestamp: June 15, 2023, 12:52:10 am
content: Railing about one use case with connectors with unknown origin is OT and frankly as pointless as me adding photos of my Land Rover Loom using the same 'style' of connectors the OP showed in use. It was in this case for what it is worth undersized cable getting hot and melting the insulation combined with running 'factory' 30A fuses.The bottom line is if you use trash unknown connectors or marginal cable or even garbage heat shrink then why would you be surprised when you are pushing high currents