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  • March 28, 2024, 02:11:49 PM

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Author Topic: Arming plug - again  (Read 1283 times)

Offline Matt Piatkowski

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Arming plug - again
« on: February 26, 2021, 07:43:19 AM »
Hello,
Please see the attached and advise.

Does this connection really need a resistor? A battery is 4-6S.
If yes:  where do I solder the resistor?
What is the resistance value of this resistor?

Thank you,
M

Offline Igor Burger

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Re: Arming plug - again
« Reply #1 on: February 26, 2021, 09:51:40 AM »
Matt, I answered in mail, but I can again:

Does this connection really need a resistor? A battery is 4-6S.

Depends how often you want replace connectors. Especially with 6s battery.

where do I solder the resistor?

You need another plug with resistor. It will charge capacitors, then you can replace normal flight plug without resistor.

What is the resistance value of this resistor?

I use 10 ohms.


For others: this will work well with Jeti Spins, another ESC with smaller capacitor or higher idle current can discharge capacitor quickly.

Offline Matt Piatkowski

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Re: Arming plug - again
« Reply #2 on: February 28, 2021, 10:11:14 AM »
Igor,
Can "10 Ohms" be treated as the standard resistor for the stunt / F2B ECSs?
Stunt / F2B fliers use mostly Spin66, Spin44, Castle Creation 50 / 60 Amps for the full-size models (1500 - 1550mm. span and 1800-1900 grams RTF. weight).

Sometimes, somebody uses another ESC but it is also in the 40-70 Amps range and it has similar capacitors.

Can you explain, please, what the resistor does in the circuit with ESC?

It prevents sparking but how?

When the battery is connected but the circuit is not closed yet (the arming device plug is not inserted), there is no current flowing.
When the 10 Ohms resistor in series is closing the circuit, the current starts flowing from the battery through this resistor and is charging the ESC capacitors.

Is this what some call a trickle charge? The current is very small: for 6S it will be 25V / 10 Ohms = 2.5 Amps.
Did I calculate this correctly?

Why there is no spark on the resistor when this resistor is exposed to the current?

When the resistor is closing the circuit (your second plug), there is always a moment in which you are closing the air gaps.

I believe it would be advantageous for everybody flying electric stunt / F2B to fully understand all these details.
Thank you,
M



 

Offline Matt Piatkowski

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Re: Arming plug - again
« Reply #3 on: February 28, 2021, 12:24:12 PM »
I have found a very simple and well-written explanation of the phenomenon on https://courses.lumenlearning.com/physics/chapter/21-6-dc-circuits-containing-resistors-and-capacitors/.
Unfortunately, this explanation does not explain why there is no spark "on resistor" when the plug with this resistor is being connected.

Perhaps the current that "wants" or "is allowed" to flow through the resistor is too small to create sparks?

If yes, this may mean that the resistor "controls" the current that wants to flow through it.

If there is no resistor, the current that "wants" to flow through the connection about to be created is not controlled, reaches a higher value and the sparks appear.

M


Offline Igor Burger

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Re: Arming plug - again
« Reply #4 on: March 01, 2021, 02:53:16 AM »
Spark is initiated by voltage. That defines how "long" the spark is going to be. The current starts in ionized air BEFORE real metal connection. In out voltages it is practically 0 but still enough "over" zero to make a spark.

Spark is not our problem, our problem is erosion. Erosion depends on current. That is what can melt metal, and transfer particles. That will damage connector if you do not prevent it. So the question if to use it or not is more question how often you want replace connectors.

So that means - if you have battery with more cells (like 6) and with thick wires able to give enough current, and you are going to connect it to capacitor which is specially designed to accept high current with low serial resistance (that is why there is that low ESR capacitor), you are connecting 26V to charge that capacitor from 0V. It will make spark transferring some certain electric charge to capacitor in very short time and it will melt metal on the spot where spark started.

If you put resistor in series and you do the same, spark will appear, but the same charge will be transferred in longer time by small and safe current which will not damage connector, because heat transfer will be able to stop heating on low and safe temperature. I did not read your link, but I saw there is explained that time depending on capacity and resistance.

So the point of resistor is to charge capacitor slowly (low current will not transfer particles) and only then to make flight connection with low resistance. You will connect it when voltage of capacitor is the same or similar to battery voltage, so it will not make that spark.

You can do it either:

1/  you can connect resistor (button, another small connector etc.) in series with battery and then to short it by flight connector

2/ you can connect battery temporarily with resistor in series (specially designed connectors connecting first resistor and then flight connection, or simply external resistor in series etc.), that will charge capacitor and then immediately disconnect it and connect flight connector without resistor ... capacitor will not discharge during that short time - and that is your case, make another plug having resistor instead that blue wire - then put it in, let capacitor to charge (you not need to insert it fully, enough to touch) and then quickly replace with normal flight plug

However this can fail on some ESCs. For example if ESC immediately "beeps" with motor, it can load resistor so much that it can for example burn, or ESC can try to measure connected battery and loaded resistor will show wrong battery parameters etc. That is reason why some makers did not recommend antispark resistors in past. I think actually it should be solved since 10 cell batteries are common in R/C and there is antispark absolutely necessary, some ESCs have them even integrated. But ESCs with switch do not make those problems like larger Jeti Spins etc.

Offline Matt Piatkowski

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Re: Arming plug - again
« Reply #5 on: March 01, 2021, 08:36:23 AM »
The issue has been solved. Thanks Igor.
The solution will be published on this forum.
This solution satisfies the AMA Stunt and F2B FAI requirements and it is easy to use in any electrically powered stunt/F2B model.
Happy Spring Flying,
M

Offline Brent Williams

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Re: Arming plug - again
« Reply #6 on: March 01, 2021, 10:35:41 AM »
Here's a link to a previous thread on this topic with some pictures of Igor's parallel connector/resistor implementation.
https://stunthanger.com/smf/gettin-all-amp'ed-up!/arc-spark-when-attaching-battery/


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Offline Matt Piatkowski

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Re: Arming plug - again
« Reply #7 on: March 01, 2021, 10:59:05 AM »
Hi Brent,
I saw these photos.
What I still do not understand is how a 10 Ohms resistor, having most likely a very typical power rating of 1/4 Watts, survives a 6S generated current during the 2 seconds needed to charge the ESC capacitors.
Perhaps the time is so short that this resistor does not heat up?
If it heats up, everything will burn to a cinder.
Regards,
M

Offline Wolfgang Nieuwkamp

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Re: Arming plug - again
« Reply #8 on: March 01, 2021, 11:32:34 AM »
Matt,
the resistor is only in function during less than 1/10 second, because it will be short-circuited during the insertion of the connector.
No problem-
Regards,
Wolfgang

Online John Rist

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Re: Arming plug - again
« Reply #9 on: March 01, 2021, 11:37:05 AM »


A video on how a capacitor works.  Of interest look at the current charge and discharge curves.  If you notice the current jumps to a very high level when the connection is first made.  However it falls off very quickly.  So the power dissipated in the resistor starts at a very high level but drops off almost instantly.  A resister has a thermal reaction time that tends to average out the heat generated by the current.  I suspect that the time it takes for the current to stop flowing is less than a second.  Definitely the high current is less than a second.  My point is that a 1/4 W resistor has no problem handling the heat generated from charging a capacitor one time and one time only.  The other point that can be made from all this is that a capacitor, at the start of the charging process, looks like a dead short.  All of our heavy wiring looks like a dead short.  Our LiPo batteries can deliver unlimited current in to a dead short.  So the 10 ohm resistor limits the current to a safe level while the capacitor charges up to battery voltage level.  As a sport flyer I only uses 3 to 4 cell batteries and I really don't fly that much.  I have not seen the need to full with any of this.  To date I haven't  seen any significate damage to my battery connectors.
John Rist
AMA 56277

Offline Igor Burger

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Re: Arming plug - again
« Reply #10 on: March 01, 2021, 11:39:47 AM »
Hi Brent,
I saw these photos.
What I still do not understand is how a 10 Ohms resistor, having most likely a very typical power rating of 1/4 Watts, survives a 6S generated current during the 2 seconds needed to charge the ESC capacitors.
Perhaps the time is so short that this resistor does not heat up?
If it heats up, everything will burn to a cinder.
Regards,
M
Does not matter how long you connect resistor and does not matter what is the resistance. There is finite energy of capacitor charged to battery voltage, so whatever combination of parameters you use, resistor will heat exactly to temperature equivalent to that energy.

The point is to heat relatively large resistor instead of microvolume of metal where spark appears.

Offline Igor Burger

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Re: Arming plug - again
« Reply #11 on: March 01, 2021, 11:49:45 AM »
Here's a link to a previous thread on this topic with some pictures of Igor's parallel connector/resistor implementation.
https://stunthanger.com/smf/gettin-all-amp'ed-up!/arc-spark-when-attaching-battery/

Thanks Brent, yes that i my bullet proof solution which we all use here. But he is asking how to combine it with arming plug on fuselage side. Here I see simple solution with 10 ohm jumper and then iserting the plug, I do not know what we are trying to solve here, for me absoltely clear and simple  8)

Offline Matt Piatkowski

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Re: Arming plug - again
« Reply #12 on: March 01, 2021, 01:53:39 PM »
Hi John,
Hi Wolfgang,
Thank you. Sometimes it takes a while to receive the most important details.
Now I know exactly how it works - the rest is just simple soldering.

Best Regards, Stay Safe and Fly Safely,
M


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