Servo Connector Information
A number of my club members are flying gas or glow powered models. And, more than a few of them have had "I Ain't Got It" crashes over the past year or two.
One of my club members asked me to run a battery analysis on a battery pack that was installed in a model that lost all radio communication.
As received, this battery 1200 Mah Nicad battery pack was tested at 2.5 Amps. The first run showed that the pack had 650 Mah stored in it. After a 12 hour charge at 120 milliamperes, the battery was retested, and showed 1250 Mah.
My Western Mountain CBAII analyzer showed a few blips on the discharge curve, and sure enough, the servo connector was rather warm. Worse, just touching the connector resulted in the CBAII analyzer shutting off due to low voltage.
The battery connector was checked with a digital scale for contact pressure. It only took 1.2 ounces of force to move one of the pins after it was inserted into the connector. I tried several more insertion tests on other servo connectors from the same manufacturer. And got the same results.
A similar test was conducted on a Maxx Products connector, using the same pin for insertion. The force required to move the Maxx products pin was 13 ounces.
Take a look at the two different styles of connectors. Based on this information, I'll NEVER use the "No Name" connectors in any of my models after doing the contact pressure test.
This information will be especially useful for anyone flying big gasser or glow powered models, along with the vibration levels that exist with these power plants.
That is very good information, Denny
Several of the people in my club have had trouble with the no name Deans type T connectors, breaking contact when fully inserted. I believe the true Deans connectors are good, but the copies are not.
I have also a vibration problem inside of one nicad cell. it would deliver power just fine unless it was subjected to any kind of vibration. I now test battery packs by beating them on a table during a discharge cycle.
for what it's worth I have never been able to make an XT 60 connector fail
Thanks - I am always suspicious of a connector that seems loose or wiggly. If plugging it up doesn't take some effort than unplugging by accident can happen. I checked my stuff and am not sure who made what connector-wise but they all seem tight.
Denny, was it you who did the bullet connector thing a while back? That was where a factory installed bullet connector was barely soldered. Scary, caused me to give my factory installs a test yank and the evil eye under a magnifier.
Before retiring, the company I worked for bought some 600 24 volt Nicad Batteries per month for our substation controls. That went on for 30 or 40 years.
Working in the Service department I got to check out countless batteries, analyzing them for cause of failure.
One thing that showed up over and over was poor, or lousy spot welds on the interconnecting straps. We had spot welds that didn't bond the strap to the cell. They'd just lift off. Problem was caused by improper setting of the spot welder used to assemble the packs. Just flex the battery slightly, and you've got an open circuit.
Lately I've been using those A123 cells for backup receiver power in my two giant scale models. Those cells were purchased from www.voltmanbatteries.com at $11.99 each. These cells come with pre-installed tabs that are easy to solder to.
These cells are also available from radicalRC, for $38 per pack, ready to go.
Probably half of my club members have gone to either LiFe or A123 battery packs for their larger models. I personally like the A123's over the LiFe packs simply because the A123's have a metal jacket, versus the plastic baggie for the LiFe packs.
Your model will NEVER have a voltage sagging problem on your 2.4 Ghz receivers while using a two cell A123 pack. Overloading one of those batteries will melt your wires before the battery voltage sags. (Don't ask :censor:)
As for the Deans connectors, I prefer the Anderson Power Pole connectors. The original units, NOT what is commonly available now. I'm running my APP connectors at 75 Amps with zero problems over many many flights.
Anderson Power Poles???
Nice thing about the APP connectors, their wires are crimped, then inserted into the plastic housing. As such, there is no possibility of overheating the plastic shell during the assembly of these APP connectors. The housing has an internal leaf spring that maintains contact pressure.
Last year, one of my club members nearly lost a $$$$$$ kerosene turbine model when a Deans connector lost contact while taxiing out for a take off. The Deans connector was powering the turbine Engine Control Unit. The mfg of the battery pack overheated the Deans connector plastic housing, resulting in deformation of the housing, and zero contact pressure on one of the Deans contacts.
FYI, I just checked some brand new Tower Hobbies TS6 Nano Servos, that use the same connector described above. Using my gram scale, it took only 0.9 Ounces to push one pin into the TS6 servo connector. All three pins on the servo connector measured the same 0.9 ounces.
A check of several brand new Futaba S3102 servos showed a contact pressure of about 4-5 ounces to move the pin into the connector. Even still, that's half of the force required for the MAXX products pins.
FYI, I'm going to replace every one of those type servo connectors with one ounce insertion force before using them on ANY of my models.
Contact Resistance Checks
Just ran a contact resistance check on these two connectors.
As expected, the Maxx products contact resistance was 1/4 that of the "No Name" contact. The Maxx unit measured 1.4 milli-ohms, versus the no-name measuring 5.5 milli-ohms. (The contact resistance was measured by pushing exactly 1.00 Amperes through the connector with an MPJA 3 Amp, 18 Volt variable DC power supply using its current limited function. My Fluke 87V digital meter measures down to 0.01 Millivolts on its high resolution function. the resistance in Milli-ohms is calculated as R=Millivolts/1 Amp)
Both of these values are very low numbers. Briefly pushing 14 Amps through the no-name contact will result in a voltage drop across the contact of 0.077 Volts DC.
That voltage drop is insignificant, compared to the voltage drop across the battery lead itself.
But, again, if that connector only has a few ounces holding it in place, the battery won't do much good if the connector falls out. :eek:
Guess what does save the day is the fact that USUALLY the plastic shell provides the holding force that keeps the connector inserted into its mating connector. You might loose a lot of that plastic holding ability, if you insert a Hitec servo plug into a Futaba servo extension cable. One reason to secure these extension wires, with shrink tubing, duct tape or whatever.
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