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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Lipo connection spark causing pitting on connectors
03-31-2015 04:08 AM  6 years ago
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emederos

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Miami, Fl Dade

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Lipo connection spark causing pitting on connectors
I need to find a way to reduce or eliminate this nasty pitting and fouling from the spark when connecting my 6s packs. I saw somewhere on the forums before a plug on the positive side that was connected last after the negative was connected to eliminate the spark. I cannot seem to find it anymore. Anyone have any links or suggestions. This is only after 38 flights imagine after 150???? I'll have to remove the connected and install s new one

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03-31-2015 04:35 AM  6 years ago
Heli 770

rrProfessor

USA.

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03-31-2015 06:32 AM  6 years ago
Roamer

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Albuquerque, NM

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What is causing that is inrush current to charge the depleted storage capacitors in the speed control. There is VERY little resistance between the battery and the caps, so it will draw a BIG surge of current from the pack in that first instant, leading to the spark.

The solution is pretty simple. Make a jumper lead with a high power resistor inline to limit the current rush. Use it to connect the battery to the speed controller initially. That will charge the capacitors up to the batteries potential, but it limit the current to a level low enough that it can't melt the contacts on the connector. Then, remove the jumper and connect the battery directly as normally. The caps will hold a charge long enough that the voltage won't drop enough to cause any arcing.

I have no idea exactly how much capacitance your speed controller has, but as an example, let's assume it has four 47uF caps in the input stage.

The time constant for a capacitor is called "tau" and is simply tau=R*C where R is the resistance in Ohms and C is the capacitance in Farads. Let's just guess that a 1k Ohm resistor will work, so that gives us a time constant of tau = 1000 Ohm * 0.000047 Farads = 0.047 seconds.

In generally, you can assume the capacitor is charged after 3 times constants or 3*tau = 3 * 0.047 sec = 0.141 seconds. Pretty much plug it in and then unplug it and things are charged.

But how much current will be flowing when we first plug it in? That is easy as you have a 6S battery or V = 6 * 3.7V = 22.2V (or there about). We know the current limiting resistor is 1000 Ohms, so the current is I = V/R or I = 22.2V / 1000 Ohms, or I = 0.0222A That is low enough that there shouldn't be any damage to the contacts. At least nothing you would be able to see without an microscope.

That resistor is going to dissipate a bit of power, but how much? When you first plug it in the power will be given by P = I^2 * R or P = 0.0222A ^2 * 1000 Ohms or P = 0.49 watts. That will drop as the capacitor is charged and the voltage rises. You could easily get away with a 1/2 watt resistor. But to be save, grab a 1 watt, 1000 ohm resistor and you are on the way.

Even if the capacitors are much larger (say 10 times larger), it just means it will take longer to charge the speed controller. In this case, 1.41 seconds instead of 0.141 seconds. Still not long. And the chance that speed control has more than capacitance than this is slim. But if it does, it just takes a bit longer to charge it.
-RRRoamer
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03-31-2015 02:49 PM  6 years ago
Dr.Ben

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Richmond, VA, USA

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+1

Or go to bullets which take the pitting in the nonessential contact area of the connector.

Deans are the worst about the pitting as you are seeing all too clearly.

Ben Minor
Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA
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03-31-2015 04:03 PM  6 years ago
Ronald Thomas

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Gainesville, Fl, USA

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This is only after 38 flights imagine after 150????
You heli falls out of the sky

That is exactly why I got rid of Deans....EC-5s on larger helis (over a 450)
Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!
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03-31-2015 04:53 PM  6 years ago
Wave

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Illinois

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Most pitting on Deans connectors is at the tip or entry to the plug. The majority of the contact surface maintains its integrity and electrical conductivity.

The pictures above are similar to my 12S deans setup which has no resistor or spark arrestor.

If you are genuinely concerned about it then replace them every season or switch to a different connector.

I have yet to have a failure with a genuine Deans connector. The most likely failure mode is from poor soldering.

2c
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03-31-2015 05:03 PM  6 years ago
GyroFreak

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Sanford Florida ...28N 81W

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Or go to bullets which take the pitting in the nonessential contact area of the connector.
Deans are the worst about the pitting as you are seeing all too clearly
That's what I did. So +1 on that.
The case against politicians simply is that when they legislate for all men, they always omit themselves
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03-31-2015 05:46 PM  6 years ago
Steff Giguere

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St-Eustache, Quebec, Canada

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Or use YGE ESC.Team Synergy, Rail blades, Team Scorpion, V-Team
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04-01-2015 01:55 PM  6 years ago
emederos

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Miami, Fl Dade

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I went with the espirit models 5.5mm bullets with resistor / problem solved
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04-01-2015 02:53 PM  6 years ago
KevinB

rrKey Veteran

Earth

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Or use YGE ESC
Yes, the YGE ESCs have a built in anti-spark circuit.

When I first started on electrics, it was on an Align 450. I started using Deans. However after approx. 100-150 flights, I started to get intermittent battery connections. Switching to EC3 connectors eliminated the problem even without the use of a resistor.

All my electrics now have YGE ESCs and EC3 or EC5 connectors so I no longer see the connector problem.

Glad you got your problem solved.

KevinB
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