Will this work?

[Targetlocman]

I know just enough electrical engineering to be dangerous, so I'd love to get comments on a switch design for a hi amperage dc circuit.

I am using a small switch known as a joneswitch in one of my model aircraft. (Find it at vampower.com under accessories.) The model is powered by 37 volts and up to 100 amps dc. The joneswitch cuts all power on and off from the main batteries to the esc, from outside the aircraft. This allows for ultrasafe handling of the model without fear of a stray signal causing your motor to spool up prematurely and you losing a finger or worse.

The problem is due to the high power the switch is arcing and gradually becomes harder and harder to use as the contacts corrode and become irregular. My idea is to add a high ohm resistor (10,000 ohms) in parallel to the switch which would close the circuit prior to the main switch closing and then open just after the switch opens. Simple question, would that stop the arcs from occuring?

[Terry S]

Have you thought of using a capacitor ?

Terry

[coro]

Capacitor across the switch will not help, as it will discharge in short circuit when switching ON and may make arc even worse.
Guys here are using resistor even at gold connectors when connecting battery to ESC.
It works well, however the value of resistance is not high, ordinary value is 10 Ohms or even less.
ESC capacitors must charge fast enough, to avoid troubles. There is the only risk, that ESC caps are charged slowly thru resistor, its mcu starts up and measures voltage somewhere in the midddle, and then ESC low voltage cutoff gets fooled and way too low - if esc cutoff is used, as I do not suppose so..

[Tomapowa]

A 1 ohm, 1/2 watt resistor (in SERIES with either + or - lead) has been proven to work great... just momentarily charge the ESC's caps through the resistor, then bypass the resistor, connecting lead directly to battery... no spark!

Discussed more here:
http://www.rcgroups.com/forums/showthread.php?t=759403

[Targetlocman]

Excellent. I thought a resistor would work, but I didn't know that I could use such a light resistor. Much appreciated guys. Thanks.

[Tomapowa]

Excellent. I thought a resistor would work, but I didn't know that I could use such a light resistor. Much appreciated guys. Thanks.

This concept would be tough to add to that Vampower switch of yours though... (resistor is in series with power, not in parallel with switch as you previously mentioned). You would have to put two of those switches in your model to eliminate the "spark". Switch#1 would be turned on (applies power to ESC through 1 ohm resistor), then you would close Switch#2 (applies power directly to ESC... no resistor in series).

[Acetronics]

HI, Target

Why not simply use one of these controllers that need some stick sequence ( place to brake position to unlock the controller i.e.) to allow the Output stage to be powered ???

Alain

[AndyKunz]

Because that's not safe, Alain. A powered ESC is a dangerous item.

Andy

[Targetlocman]

This concept would be tough to add to that Vampower switch of yours though... (resistor is in series with power, not in parallel with switch as you previously mentioned). You would have to put two of those switches in your model to eliminate the "spark". Switch#1 would be turned on (applies power to ESC through 1 ohm resistor), then you would close Switch#2 (applies power directly to ESC... no resistor in series).

Yes. Actually after a little more thought last night, I am going to add a momentary contact switch that will power the ESC through the resistor on a seperate circuit (it will simply bypass the joneswitch). I will press and hold the momentary switch for a couple of seconds and then close the joneswitch. Of course I would then release the momentary switch and it's off to flying.

I am going to use a 10 watt resistor though. I am not convinced that my 10 cell 5000 mah battery only puts out a 1/2 watt during the cap charge to a 90 amp ESC, especially since I am getting arc welding. Comments on that are welcome.

[AndyKunz]

The ESC ratings and the arc are totally independent of one another. Worst case, for an instant (and a very short one at that), the cap acts like a dead short to the battery, with only a few milliohms of resistance. That's where the arc comes from.

For a worst-case scenario using a 1ohm resistor, the closing of the contacts in the momentary you talked about would be a 42A pulse (4.2V/cell x 10 cells, 1 ohm resistor, Ohms law says amps = volts / resistance). 42A could still give an arc (40A is one of the lower settings on your Lincoln arc welder). For that fraction of a second, there is a 42W blip - but because of the short duration and the thermal mass of just about any resistor, 10watt is mucho overkill. Even a 1/4W resistor will handle this just fine, since the pulse is very short (and probably 1/8W).

You would do much better to put a 10ohm resistor in there (giving you a 4.2A pulse but for a much longer duration).

Remember, resistors are rated according to their continuous dissipation capability. The fraction of a second that it takes to charge the cap to a reasonable level (ie, one that doesn't spark any more) is not going to heat up the resistor at all.

Andy

[Targetlocman]

Thanks Andy.

But since I already had the 10 watt resistor and the model is pretty large, the overkill is not an issue.

I completed the installation tonight using a momentary pushbutton switch which bypasses the joneswitch. I used a 10 ohm 10 watt resistor and it works flawlessly. I simply hold the momentary switch button down, listen for the ESC to respond (less than a second) and then pull closed the joneswitch and then release the momentary. It's convenient as well, since pushing the momentary switch and pulling the joneswitch are equal and opposite forces and the plane stays put (I placed them side by side). Before, when pulling on the joneswitch, I would have to hold the plane still while I did it, or it would stress the rudder servo (tail wheel would drag and try to turn the rudder).

No more arc welding now! and the joneswitch is operating smoothly as the contacts wear in. Thanks to all for your input.

[coro]

....
For a worst-case scenario using a 1ohm resistor, the closing of the contacts in the momentary you talked about would be a 42A pulse (4.2V/cell x 10 cells, 1 ohm resistor, Ohms law says amps = volts / resistance). 42A could still give an arc (40A is one of the lower settings on your Lincoln arc welder). For that fraction of a second, there is a 42W blip ....
All is true except watts.
At 42Volts across 1 Ohm, current is really 42A, but it gives Power=volts * amps
here P = 42V*42A = 1764Watts. Crazy number, isn't it?
However, it is just a theory, resistor mostly has some inductance and the moment of connecting the switch closing lasts long enough in manner of microseconds we are talking about. Spike is much lower and lasts really so small fraction of a time that 1/8W resistor survives without any harm.

[Vamooska]

We are reviewing posts to try and better our products for you. Thanks everyone!
Vammy

[Kito]

I know just enough electrical engineering to be dangerous, so I'd love to get comments on a switch design for a hi amperage dc circuit.

I am using a small switch known as a joneswitch in one of my model aircraft. (Find it at vampower.com under accessories.) The model is powered by 37 volts and up to 100 amps dc. The joneswitch cuts all power on and off from the main batteries to the esc, from outside the aircraft. This allows for ultrasafe handling of the model without fear of a stray signal causing your motor to spool up prematurely and you losing a finger or worse.

The problem is due to the high power the switch is arcing and gradually becomes harder and harder to use as the contacts corrode and become irregular. My idea is to add a high ohm resistor (10,000 ohms) in parallel to the switch which would close the circuit prior to the main switch closing and then open just after the switch opens. Simple question, would that stop the arcs from occuring?

Usually we use a Double Break contact.

thats how a standard Motor Contactor breaks a circuit.

look and see if you can get a single phase breaker of some sort.

if this unit doesnt have weight constraints look on Ebay, of if you ive in MN i got a Siemens three phase contactor here, might have to toss 15-20 dollars at it but its in great shape and would handle high amperage.

Also if your amperage only Peaks at 100 but runs at 40
you can get a 40 amp breaker, usually Overloads are designed to handle 250% inrush, but can handle more if its momentary

[Flash1940]

You may consider using a 4-pole double throw relay....tie the poles all in parallel for the BIG current demand. The only bad thing about this idea is the weight and physical size of the relay....good thing....switch current would be quite reasonable...

Flash

[Tomapowa]

You may consider using a 4-pole double throw relay....tie the poles all in parallel for the BIG current demand. The only bad thing about this idea is the weight and physical size of the relay....good thing....switch current would be quite reasonable...

Flash

Relay?... No thanks! If you said a 4-pole mechanical switch... that is an option. A relay is just another thing that could fail (i.e. arc'd contacts, open actuator coil, etc...). The less stuff inline (in series) with my power, the better! A simple mechanical switch is my recommendation. Anderson Power Poles are great... silver contacts, positive contact during insertion and they make them to handle up to 150 amps if that is what you require.

Here's an option I fumbled with... (handles very high surge current)
Couple this with the momentary pushbutton idea (via 1-10ohm resistor) and your all set!
http://www.harborfreight.com/cpi/photos/92600-92699/92688.gif
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92688