General Question on spark suppressor on 12 S motor setup ( 600 size)

[helicc16]

A while back, Westy posted a thread showing how to building a spark suppressor for big helis by shunting the main battery connection with a 10 Ohm 10 Watt power resistor. Following these instructions, I installed spark suppressors on all of my big birds. And it has been working like a charm.

Yesterday, I popped the said resistor on a Trex 700 by a silly mistake. Instead of waiting for days to receive a replacement resistor in the mail, I went to Radioshack and got 50 Ohm 10 Watt wirewound power resistor. Have not installed it on the heli yet because I have the following questions:

1) Why 10 Ohm 10 Watt? Can the replacement resistor I bought from Radioshack be safely used?

2) Is it necessary disconnect the spark suppressor once the main battery connection has been made?

Please advise.

 

[pvolcko]

50 ohm 10 watt should be fine. The higher resistance will reduce the current flow through it more than the 10ohm so the 10W rating will be plenty.

As for disconnecting it. Not necessary, I believe.

The higher the resistance, the less power that will flow through it in flight. If 30A is being drawn from the battery, then the main connector and the resistor will share the current load proportionally. Since the main connector is presumably very near to no resistance, it will take the vast majority of the power handling. Worst case, high smack flight pulling 100A nearly continuous and a crazy high resistance of the main connector of .1ohm. That's a total parallel resistance of .099ohms and about a 10V drop across the main connection/50ohm resistance parallel portion of the circuit at 100A. The 50ohm resistor will see .2A of it, which is 2W, well within rating of the resistor and at .2A is a basically negligible loss given we're talking about a 100A draw. And that's assuming the main connector resistance of .1Ohm. It is almost certainly far less than that, which means it will take that much more of the current load and the voltage drop across it will be less, meaning that much less current and power flowing through that 50ohm resistor.

The danger is that in leaving it connected you will at some point forget to plug the main connector and will attempt to fly with just the spark arresting resistor connection. This would not go well. The resistor would very quickly pop and perhaps do damage to the ESC in the process due to both the relatively highly resistive source and then the sudden loss of power under load. I'm not sure it would do anything to the ESC, but I wouldn't want to try it.

- - - Updated - - -

AS always with my answers to electrical questions, take with a large grain of your favored skeptical spice. I very often get them wrong in the first go, or two... or three.

 

[Tony]

Yes it will work, and yes you cna leave it plugged in. Electricity will ALWAYS follow the path with the least resistance.

 

[Island Breeze]

50 ohm 10 watt should be fine. The higher resistance will reduce the current flow through it more than the 10ohm so the 10W rating will be plenty.

As for disconnecting it. Not necessary, I believe.

The higher the resistance, the less power that will flow through it in flight. If 30A is being drawn from the battery, then the main connector and the resistor will share the current load proportionally. Since the main connector is presumably very near to no resistance, it will take the vast majority of the power handling. Worst case, high smack flight pulling 100A nearly continuous and a crazy high resistance of the main connector of .1ohm. That's a total parallel resistance of .099ohms and about a 10V drop across the main connection/50ohm resistance parallel portion of the circuit at 100A. The 50ohm resistor will see .2A of it, which is 2W, well within rating of the resistor and at .2A is a basically negligible loss given we're talking about a 100A draw. And that's assuming the main connector resistance of .1Ohm. It is almost certainly far less than that, which means it will take that much more of the current load and the voltage drop across it will be less, meaning that much less current and power flowing through that 50ohm resistor.

The danger is that in leaving it connected you will at some point forget to plug the main connector and will attempt to fly with just the spark arresting resistor connection. This would not go well. The resistor would very quickly pop and perhaps do damage to the ESC in the process due to both the relatively highly resistive source and then the sudden loss of power under load. I'm not sure it would do anything to the ESC, but I wouldn't want to try it.

- - - Updated - - -

AS always with my answers to electrical questions, take with a large grain of your favored skeptical spice. I very often get them wrong in the first go, or two... or three.

Lol..that was a lot to absorb there partner. Hell! I like to play it safe with them big dangerous birds up there.

 

[helicc16]

The danger is that in leaving it connected you will at some point forget to plug the main connector and will attempt to fly with just the spark arresting resistor connection. This would not go well. The resistor would very quickly pop and perhaps do damage to the ESC in the process due to both the relatively highly resistive source and then the sudden loss of power under load. I'm not sure it would do anything to the ESC, but I wouldn't want to try it.

- - - Updated - - -

AS always with my answers to electrical questions, take with a large grain of your favored skeptical spice. I very often get them wrong in the first go, or two... or three.

Pvolcko, that exactly how I popped the poor the little resistor. Luckily the heli flew well without any problem after that.

Thanks for taking time out to provide such a thorough explanation. I didn't have to reread the answer to understand it.

I've installed the new resistor and tested the connection. Have not smelled anything burn yet ( knock on wood)

- - - Updated - - -

Yes it will work, and yes you cna leave it plugged in. Electricity will ALWAYS follow the path with the least resistance.

Agree. Basic electrical principle.

Thanks for taking time out, despite being in such a bad shape and situation, to answer my questions, including the silly question about "spotter" in hardcore 3D videos.

If I had won the Powerball this past week, I wouldn't have hooked you up with nice loan that would make all problems disappear.

Hang on tight, Bro.