Q-104: I’m basically getting started in electric-powered flight and
I’ve noted the use of many different types and styles of electrical connectors.
Is the choice of connector strictly a personal preference or are there some
technical concerns that I should be made aware of?
A-104: There are definitely “technical reasons” involved with the choice of
your electric power connectors. But before I get into that I need to point out
that RC-system connectors, with their traditional three wire contacts, are
completely different from what we use for electric power systems. RC
manufacturers and aftermarket suppliers can provide these three-wire connectors,
which come preassembled and require no soldering.
Now for electric-power-system connectors. The smallest models and usually the
indoor RC variety employ several variations of the JST (white plastic)
microconnectors. These connectors resemble the type used on many cordless-phone
battery packs. They can probably handle as much as approximately 1 amp (1000 mA)
of current.
From a 1- to roughly a 3-amp current level, favorite choice seems to be the JST (red plastic) connector. They are popular with parking lot and backyard flyers. Most battery suppliers will use this popular connector for this current-level application.
The two wires going into this JST connector are preassembled, so when you
purchase a connector it comes with two pigtail lead wires already attached. You
can’t solder the wires to the pins, so installation requires that you splice
into you existing wiring. Any wire splicing must be covered with heat-shrink
tubing to preclude short circuits later.
Some manufacturers and distributors have attempted to extend the use of the RED
JST connector up to approximately 8 amps. This is a no-no! I have subjected the
red JST connectors to 4 amps current and they are getting hot. By 6 or 7 amps
they are beginning to melt.
I questioned one distributor about using this connector for high-current
applications and was told, “We expect that the modeler will not always use full
power and that with normal throttling back the occasional higher current is
acceptable.” I just don’t buy that answer! My limitation for these red JST
connectors is 3 amps maximum, with 2 amps being a better compromise.
The next step up is getting from 2-3 amps up to roughly 7 amps. I’m still not
ready for the Anderson Powerpole (APP)-type connectors, but what is there to use
in between?
I like the Deans four-pin polarized connectors. You can purchase these from
many sources and they can be easily soldered. Because we are using only two
wires and the connector has four pins, the common assembly technique is to
combine two pins into one connection. So you end up with one wire going to two
pins and the other wire going to the other two pins. The photos show this
assembly technique.
Which pins you select for positive and negative battery wires is your choice. My
local club establishes a standard for the Deans pin polarity. That way everyone
using that type connector at our field has the same wiring. If you have to
borrow a battery pack at our our site, you know it will work.
In that same regard we place the hook part of our Velcro tape on the battery
pack and the “fuzzy” part on the inside of our aircraft. This also permits the
easy swapping of battery packs when it becomes necessary.
When soldering wires to the Deans four-pin connectors, use short lengths of
heat-shrink tubing to cover the soldered joints. This acts as a strain relief
and prevents accidental shorts. I usually put a second, larger-diameter
length of heat-shrink tubing over both wires. That makes for easier gripping
when you go to unplug the connector halves. Even though these connectors are
polarized, I place a drop of white correction fluid on the edge marking the
positive pins (red wire usually!).
From about 8 amps on up I always use the popular APP connectors. These same
connectors were also known as Sermos connectors, after the late John Sermos. The
8-amp current level is generally suitable for Speed 400 motor applications. So
it is safe to say use APP connectors for Speed 400 and larger motors, but, yes,
there are other connectors on the market (such as the Deans Ultra and the
AstroFlight Zero Loss).
Wires going to APP connector pins can either be soldered or mechanically crimped
using a special tool. Soldering can be tricky and does require a certain skill
that it is hoped you will acquire with experience. I have owned the expensive
Anderson crimping tool for many years and think it is the only way to go. I can
even install new connectors at the flying field.
Recently West Mountain Radio in Norwalk, Connecticut, came out with its version
of an APP crimping tool that sells for only $49.95. You might want to look into
this special product at
www.westmountainradio.com/PWRcrimp.htm.
The last item to consider is wire gage (or wire diameter). If you select the
right connector for your anticipated current and then use a wire that is too
thin, you can still have a current-carrying problem. The connector pin will
survive, but your wire might melt! Therefore wire gage must be selected based on
your current demands.
Wire is generally referred to by the American Wire Gage (AWG) and a number. For
up to 1 amp current (JST white plastic) for the micro or indoor RC flyer, use a
thin-gage AWG-22 wire. From 1 to 3 amps current and the red JST connector, use
AWG-18. When using Deans four-pin connectors between 3 and 7 amps, use AWG-18.
Using APP connectors in the 8- to 15-amp range, you can employ AWG-16 wire. For 15 and 30 amps, AWG-14 wire is best. For heavy-duty current applications such as 30 to 60 amps, you will need AWG-12 wire. All of this wire is assumed to be the stranded variety, not solid.
My apologies for making this so lengthy, but it is important!