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Old Jun 15, 2006, 12:13 PM
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Kings Park, New York
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Resistor in line with battery to power up ESC?

Sorry for the barrage of questions! This is another about setting up an R50 Titan with the A50 motor and CC85 ESC for TP 10s2p 4200.

This will be my largest heli to date, and I've read that when using Lipo's with more than 3-cells, it's a good idea to first connect with a resistor in line, than to complete the connection bypassing the resistor. Since I use Dean's connectors, this will require two sets of connectors wired in parallel, with the first set connected having the resistor in the red wire, and the second set straight through. This is not a great explanation; I hope it makes sense.

Does anyone do this? Do you know what size resistor is needed to provide adequate ESC protection, that will allow the ESC to arm, and that won't blow from the current while the ESC caps are charging. I've read that a 100 ohm/1W resistor will work, but I imagine that the size would vary depending on the ESC that you use??
Thanks!
Ken
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Old Jun 15, 2006, 12:47 PM
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Motions's Avatar
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And what is the purpose of this exactly? If you put a resistor in series on a Deans connector your not even using, how does this do anything? It sounds like you trying to put it inline with the battery trying to cause a voltage drop across the resistor. Why do you need this? Sounds like shade tree electronics to me.
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Old Jun 15, 2006, 12:47 PM
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United States, CA, Bear Valley Springs
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What resistor?
I've never used one nor felt that one was needed. Most ESC manufacturers apparently feel the same unless you may be talking about a Schottkey diode.

mw
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Old Jun 15, 2006, 01:04 PM
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San Carlos, California, United States
Joined May 2002
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Quote:
Originally Posted by kenmalecki
Sorry for the barrage of questions! This is another about setting up an R50 Titan with the A50 motor and CC85 ESC for TP 10s2p 4200.

This will be my largest heli to date, and I've read that when using Lipo's with more than 3-cells, it's a good idea to first connect with a resistor in line, than to complete the connection bypassing the resistor. Since I use Dean's connectors, this will require two sets of connectors wired in parallel, with the first set connected having the resistor in the red wire, and the second set straight through. This is not a great explanation; I hope it makes sense.

Does anyone do this? Do you know what size resistor is needed to provide adequate ESC protection, that will allow the ESC to arm, and that won't blow from the current while the ESC caps are charging. I've read that a 100 ohm/1W resistor will work, but I imagine that the size would vary depending on the ESC that you use??
Thanks!
Ken
Yah. There was a thread here earlier about using a secondary connector with a series resistor to eliminate the spark when plugging in the battery plug. If you look around, you should be able to find it.

Toshi
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Old Jun 15, 2006, 01:18 PM
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glloq2's Avatar
Corsica
Joined Apr 2006
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Kenmaleki,

Your description is perfectly right.

The purpose of this 100 ohms 1 watt resistor is to avoid the spark created at the connector just when you first connect.

This spark is caused by the surge of voltage and current at the very begining of the capacitors charge.
This happens mostly with voltages of 6S and above, no problems from 2S to say 6S.

This initial spark very often damages the gold plating or even the copper of the connectors. However, the spark does not damage the power side of the controller because they are designed for that.

Those sparks were really a problem on my Jazz controler at 10S on my 3DMP, I had to change the 4 mm2 gold plated positive connector every 5 or 6 flights because it was burnt by the sparks.......
On top of that, the spark makes quite a noise and it is really a bit frightening.....

After using a resistor on an auxiliary connector just like you describe, no more sparks and no more burnt or damaged connectors.


It seems that the 4 mm2 connectors we use in Europe are more prone to damage than the Deans connectors you guys generally use in the US, but even the Dean connectors can be damaged pretty fast by the sparks


Many people use those auxiliary resistors, specially for 10S or above, and I would really recomend that you do it for your raptor if you do not want to change your connectors very often

Cheers
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Old Jun 15, 2006, 02:18 PM
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Got it. Here it is for those interested:
Fat spark thread

mw
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Old Jun 15, 2006, 02:54 PM
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Kings Park, New York
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Thanks guys! Sounds like a 100 Ohm / 1 Watt resistor is the best size. Actually, someone told me that (4) 100 Ohm / .25 Watt resistors in parallel are an equivalent and LIGHTER solution.
Ken
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Old Jun 15, 2006, 03:02 PM
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Fort Worth, TX
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Actually you would have to use four 400 ohm .25 watt resistors in parallel or you could use the four 100 ohm resistors in series/parallel.

Uncle Bud
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Old Jun 15, 2006, 03:58 PM
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Creteil, France
Joined Nov 2003
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That's totally correct.
Actually when you power up the ESC, during the first miliseconds (or microseconds) the discharged capacitor behaves allmost like a short circuit. This is the reason why you get a spark and this is not so good for life of the capacitor.
If you plug with a resistor in line first (for instance 100 Ohm 1W which is equivalent to 4 400 Ohms 0.25W in parallel) the resistor limits the current which is better for life of capacitor (and possibly battery)
The point is then to remove the resistor and plug the ESC back quickly enough so that the capacitor does not have time to discharge too much. If you want to know what "quickly enough" is, just connect a voltmeter on the ESC and look for how long it takes for the voltage to drop to say 1/2 of the battery voltage after you disconnect the battery.

Vincent
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Old Jun 16, 2006, 06:44 PM
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Does anyone have a photo of their spark arrestor? I am thinking I need one after looking at the contacts on my Dean's. They are pitted. But I am not sure of the most efficient approach for wiring the resistor and shunt.
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Old Jun 17, 2006, 01:56 PM
Good engineer, BAD pilot
glloq2's Avatar
Corsica
Joined Apr 2006
30 Posts
Quote:
Originally Posted by vpersiani
That's totally correct.
Actually when you power up the ESC, during the first miliseconds (or microseconds) the discharged capacitor behaves allmost like a short circuit. This is the reason why you get a spark and this is not so good for life of the capacitor.
If you plug with a resistor in line first (for instance 100 Ohm 1W which is equivalent to 4 400 Ohms 0.25W in parallel) the resistor limits the current which is better for life of capacitor (and possibly battery)
The point is then to remove the resistor and plug the ESC back quickly enough so that the capacitor does not have time to discharge too much. If you want to know what "quickly enough" is, just connect a voltmeter on the ESC and look for how long it takes for the voltage to drop to say 1/2 of the battery voltage after you disconnect the battery.

Vincent
Salut Vincent,

You do not have to disconnect anything, you just put one small auxiliary connector with a small wire and the resistor in parallele with your main positive connector.
You first connect your main negative connector, then the small positve one with the resistor and about 1 second later, the main positive one and you leave all the 3 connectors on.
This completely solves the spark problems, no more damage on the connectors or to the controller.
This is no problem to have the 3 connectors on at the same time because you can leave the resistor in parallele with the main connector and it makes no difference at all , you can just fly like this.
To disconnect, you can disconnect any of the 3 connectors in any order, no problem because there is no sparking when you disconnect, only when you connect.

This is exactly what we do for the big controllers (Convertisseurs de frequence up to 25 megawhatts and up to 36 kilovolts) that we use in marine propulsion for the propeller motors of the big ships to avoid destructive sparking at the contacts of the main circuit breaker during the time the huge capacitors in the controller charge when we power up the controller.

Some guy in the thread above mentionned that the controller measures the battery voltage at start up and that the resistor might prevent the controller to get the right voltage. This is probably true with the cheaply designed controllers but the good (and expensive ) ones have a delay of 3 to 5 seconds before checking the voltage so if you connect your main positve connector quickly after the small resistor one, no problems.

You also mention rightly that the current surge might damage the capacitors, the controller or even the battery.
I did check this with the Germans (Kontronik and Shultze) and they said that their controllers are protected against any damage at start up and that there is no problems.
I dont know about the other American or Asiatic brands of controllers because I only buy European anyway .....

In fact I found that the only problem created by the spark was the big damage caused to the connectors themselves.

I dont know about possible damage to the battery itself but the current surge is so short that it probably do not damage even the more sensitive of the LIPO batteries, the initial surge is so fast that it is very difficult to see it even on a very fast oscilloscope (400 Mhz)

For the Kontronics Jazz controller I have on my 3DMP with a 10S LIPO battery, the small resistor in parallel works very well and I do not change any connectors any more since I use it.
Without the resistor, I had sometimes to change the positive 4 mm gold plated connector after only 4 or 5 flights because it was all burned out and melted by the sparks.
I would strongly recomend to use the resistor on any high voltage systems of more that 6S, it is very easy to make and cost only a few Euros.

The Germans must be right because I never had any damage on the controller, capacitors or battery even when I was not using the resistor and having big and noisy sparks.


Amities de Serge alias glloq
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Old Jun 17, 2006, 03:15 PM
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Creteil, France
Joined Nov 2003
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Bonjour Serge,

Thanks for the long and detailed feedback.
I agree with the auxilary connector: that's probably the easiest and smartest way to do it.

However I would not fully trust the comments from "the Germans (Kontronik and Shultze)": as far as I can see, the capacitors are pretty standard capacitors and are connected directly on the battery side. As an automotive electronics engineer, we did this same design on one product quite some years ago and ran into some trouble (in the automotive, problems start a few ppm ie a few parts per million). The current surge through the capacitor slowly damages the chemical product between the two electrodes and after a few hundreds / thousands connections, a few parts over a million will fail.
Considering the numbers, the probability of having a failure for one of us here in RCG is quite remote, but in principle Shulte and Kontronik ESCs, as long as they have their capacitors directly on the battery input are subject to failure one day if not protected by a resistor.

For the batteries, I also do believe that the current surge is too short to really have an impact.

PS: It's a nice heli that you have. The only one in Corsica and on of the very few in France?
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Old Jun 18, 2006, 01:45 PM
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glloq2's Avatar
Corsica
Joined Apr 2006
30 Posts
Salut Vincent,

Thanks for the feed back on the possible capacitor failure, it is true that they are connected direct across the terminals without any resistor, I looked....
So it seems that Kontronik or Shultze are less concerned about the one failure in a million than Renault or PSA....Considering their small production numbers compared to yours, I am not surprised .

Good to know that our small resistor trick also makes our capacitors live longer, I did not think about that because I always assume wrongly that a capacitor is a static component that cannot fail......I was originally just concerned by the erosion of the contacts by the spark and I dont like sparks anyway, a good electrical installation should not make any sparks as long as it is not the ignition of an engine.....

This possible capacitor failure is another very valid reason to use the resistor on our high voltage (???) DC systems

Yes, the 3DMP is a very good helico, probably one of the best in the market, very well designed and fabricated and very light but still tough. It also flys very very well.
I also like the philosophy of its engineer / designer / programer / machinist / accountant / clerk, Herr Jan Henseleit.
Unfortunately, the helico is much much better than what I need because I am not a very good pilot.....
Anyway, it is very interesting to try to control a machine like this, even if it cost quite a lot in spare parts

I dont know how many 3DMP there is in France but I really think that more people should buy them because when you compare the price with the price of say a good Raptor of the same size plus all the parts to make it really work, plus all the parts to convert it to electric, ect ect... it costs you almost the same price at the end of the day and you still end up with a machine designed and made by accountants and Chineese subcontractors rather than by a proper engineer......

I am indeed from Corsica but I unfortunately do not go there very often, most of the time I work in Baku, Azerbaijan and I have my helico there where I fly with guys which mostly have old methanol Raptors or Hirobos.

If you want, send me a PM or a mail (In French of course), my emails are: scamplan@mcdermott.com (Work) or yc6wdb@noos.fr (Home).

Amities,

Serge dit glloq
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