ABCs of con­nec­tors


Model Airplane News - - MODEL ENGINE MAESTRO -

Mod­ern con­nec­tors come in two ba­sic types: those with flat blade-style con­tacts and those with round pin-and-socket con­tacts, known as bul­let con­nec­tors. Both styles have ad­van­tages and dis­ad­van­tages, and mak­ing a choice can be dif­fi­cult.


There are quite a few types of bul­let con­nec­tors avail­able to­day. In their sim­plest form, they’re used plain and al­most bare, with the pin, or male, part of the hous­ing com­pletely un­cov­ered so that it can plug into the socket, or fe­male part. The socket and the base of the pin should be cov­ered by heat-shrink tub­ing so that the con­nected pair is fully in­su­lated. With care they can be used safely, but there is no standard ori­en­ta­tion for them, and that can lead to prob­lems. I have shorted plain bul­let con­nec­tors be­fore and seen oth­ers do it, and it’s no fun.

A so­lu­tion for some of the short­com­ings of the plain bul­let con­nec­tor is to de­velop a hous­ing that pro­tects the con­nec­tors from com­ing into un­wanted con­tact, in­su­lates them both in use and stor­age, po­lar­izes them so that it’s not pos­si­ble to plug them to­gether in the wrong ori­en­ta­tion, and helps the user grip them for con­nect­ing and dis­con­nect­ing. Not sur­pris­ingly, there have been sev­eral dif­fer­ent de­signs brought to mar­ket, so the elec­tric-power flier has a wide range of choices.


Hori­zon Hobby uses blue EC3 and EC5 con­nec­tors, which are bul­let con­nec­tors snapped into a po­lar­ized hous­ing. The EC3 uses a 3.5mm con­nec­tor and is rated at 60 amps. The EC5 has 5mm bul­let con­nec­tors and is rated at 120A. Both con­nec­tors share the same ba­sic shape and are as­sem­bled sim­i­larly. The wires and con­nec­tors are sol­dered

to­gether and then the con­nec­tors snap se­curely into the hous­ings. They’re im­pos­si­ble to con­nect in­cor­rectly, are easy to grip and use, and pro­vide good pro­tec­tion from elec­tri­cal shorts.


XT con­nec­tors are bul­let con­nec­tors that are molded into a uniquely shaped yel­low ny­lon hous­ing. XT60s have 3.5mm bul­let con­nec­tors with a rat­ing of 60A, while XT90s have a 5mm bul­let and 90A rat­ing. Since the con­nec­tors are molded into the hous­ing when man­u­fac­tured, wire is sol­dered to them in place and cov­ered with heat-shrink tub­ing to in­su­late the bases of the con­nec­tors. Some XT con­nec­tors have a molded cover that snaps to the base of the plug and pro­vides in­su­la­tion for the wires. They’re easy to as­sem­ble, are well po­lar­ized to pre­vent con­nec­tion mis­takes, and have good grip­ping sur­faces.


Cas­tle Creations has a green plas­tic con­nec­tor hous­ing of­fered in a cou­ple of sizes. The smaller one uses 4mm bul­let con­nec­tors and is rated at 75A. The large size car­ries 6.5mm bullets and has a 200A rat­ing. Both sizes are po­lar­ized, are easy to grip, of­fer great pro­tec­tion, and use Cas­tle’s solid pin con­tact de­sign in­stead of a spring de­sign. To as­sem­ble them, the wires are passed through the hous­ing and sol­dered into the cups on the base of the con­nec­tors. Then the con­nec­tors snap se­curely into the hous­ings. Cas­tle also sells bare bul­let con­nec­tors in 4mm, 5.5mm, 6.5mm, and 8mm sizes, which are well suited for con­nec­tions be­tween the speed con­trol and mo­tor.


A sec­ond type of con­tact uti­lizes flat con­nec­tors. Elec­tri­cal con­nec­tion is made by two blades of con­duc­tive metal slid­ing to­gether that are held in tight con­tact by a spring in the hous­ing. Like bul­let con­nec­tors, these con­nec­tors have good con­nec­tion prop­er­ties when prop­erly as­sem­bled.


These con­nec­tors get their name be­cause the ori­en­ta­tion of the blades in the molded body re­sem­bles the let­ter “T.” The Deans Ul­tra plug was the first of this style and has been in wide use in elec­tric-power equip­ment since the late 1990s. The com­pany doesn’t pub­lish a cur­rent rat­ing, but many peo­ple who use them con­sider 50 or 60 amps to be a good limit. To as­sem­ble a T-plug, the wires are laid on the flat blade and sol­dered to it, then cov­ered with heat-shrink tub­ing for in­su­la­tion. Some peo­ple who use them have trou­ble dis­con­nect­ing them, and they can be fid­dly to solder prop­erly. They are po­lar­ized, so plug­ging them to­gether in­cor­rectly is very hard to do.

Hob­bico’s Star Plug is an im­proved vari­ant of the T-plug, with a nicely shaped hous­ing that has grips molded in. There’s a rear cap with a cen­ter iso­la­tor that snaps se­curely onto the hous­ing to sep­a­rate and in­su­late the wires, and it pro­vides ad­di­tional grip­ping area for eas­ier dis­con­nec­tion.


An­der­son Pow­er­pole con­nec­tors are flat­bladed pin con­nec­tors that have cups formed into the rear for wire in­ser­tion. They can be sol­dered or crimped, and the pin snaps into a plas­tic hous­ing that can key into other hous­ings to make po­lar­ized plugs in sev­eral vari­a­tions. Powerpoles come in 15-, 30-, and 45-amp pins that all fit into the same hous­ing. Used singly they’re not po­lar­ized at all, and are easy to con­nect im­prop­erly, caus­ing dan­ger­ous shorts. I know; I’ve done it my­self sev­eral times.

That said, I’ve used Powerpoles for go­ing on 30 years. I bought a crimper from West Moun­tain Ra­dio that makes them fast and easy to as­sem­ble, with a bet­ter con­nec­tion than sol­der­ing. Since I’ve started al­ways key­ing the in­di­vid­ual hous­ings to­gether to make po­lar­ized plugs, they’re per­fectly safe, even for me. I’ve found them to be con­ser­va­tively rated by An­der­son, and I use the 45-amp con­nec­tor reg­u­larly in power sys­tems that ex­ceed 75 amps with no heat buildup or other prob­lems.


“Hey, I left my charger at home. Can I use yours?” “Do you have a 3-cell bat­tery I can use for a flight?” I can’t tell you how many times I’ve been asked these ques­tions, and with all the dif­fer­ent types of plugs used by dif­fer­ent ven­dors, it’s of­ten hard to say “yes” be­cause my con­nec­tors aren’t com­pat­i­ble with theirs. Adapters are the so­lu­tion.

Adapters are sim­ply one type of con­nec­tor (the one that you use the most) con­nected to an­other type. They can be at ei­ther end of lengths of wire, or sol­dered di­rectly to­gether if pos­si­ble. After a while, a mod­eler can end up with quite the col­lec­tion of adapters.


One of the nice things about be­ing an elec­tricpower flier to­day is the wide va­ri­ety of choices we have in con­nec­tors as well as in other gear. That wasn’t the case when I was start­ing out.

I’ve stan­dard­ized on An­der­son Powerpoles for bat­tery and charger con­nec­tions, and plain bullets for speed-con­trol-to-mo­tor con­nec­tions since they don’t get dis­con­nected of­ten. If I were just get­ting into elec­tric power to­day, I’d use one of the bul­let con­nec­tor hous­ings as they’re all good choices. All the types dis­cussed here have good con­tact re­sis­tance for rea­son­ably low losses if used within their rat­ings. Re­gard­less of which con­nec­tor you choose, it’s im­por­tant to learn how to as­sem­ble them well, with good sol­der­ing for low-re­sis­tance con­nec­tions.

The orig­i­nal red Deans Ul­tra con­nec­tor and an im­proved ver­sion of the Star Plug. The Star Plug has grips molded into the plas­tic and a seg­mented cover for the solder con­nec­tions that helps pre­vent wire con­tact.

The XT60 plug is fast be­com­ing the standard for mul­ti­ro­tors and rac­ing quads. Some charger man­u­fac­tur­ers are us­ing them in place of the com­monly used ba­nana jacks and plugs.

The EC5 con­nec­tor is a po­lar­ized hous­ing for 5mm bul­let con­nec­tors used by Hori­zon and E-flite, among oth­ers.

Jim Ryan’s Grum­man F4F-3 Wild­cat flies a sor­tie over Michi­gan. Weigh­ing 18 ounces and pow­ered by a Mega 16/15/6 on a 2S LiPo, it’s a great-look­ing model. Jim de­signed it in 2004 and first flew it with a Speed 400 brushed mo­tor.

The 4mm bul­let con­nec­tor on the left has a spring-type con­tact, while the Cas­tle Creations 6.5mm bul­let con­nec­tor is a solid de­sign. The larger, more mas­sive con­nec­tor has lower con­tact re­sis­tance and car­ries more cur­rent.

This mon­strous “oc­to­pus” charge adapter has just about ev­ery plug known to man on it. While it seems a lit­tle ridicu­lous, it has come in handy a cou­ple of times at the field. Some of the au­thor’s home­made adapter col­lec­tion. Some are for charger...

These bat­tery adapters con­vert from XT60 to T-plugs, EC3s, and An­der­son Powerpoles. The red and blue adapters are from Venom Power.

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