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Need some help with ROF voltage drop in RS

rof rs afterburner 2 stage

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#1 Deathless

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Posted 11 June 2016 - 12:36 PM

I'm working on a 2 stage RS (2190's + 2850's) on 3s, with a 2850(honey badger) as the pusher. I will be using a rocker switch to switch between full rof (14dps), and dropped rof (8-9dps). By my calculations, I need to to drop the voltage by 2-2.5v. The only info I could find was to use 1N5400 3A diodes that drop the voltage 0.7V each (so that I would need to use 3 in series).

Now my question is; are 3A diodes going to be safe to use with my particular setup? (I estimate my motors at full stall to be in the neighborhood of 75A). If not, what would be a better diode to serve my application? Perhaps there is something else I should be using.

Any help, suggestions or clarification would be much appreciated as my knowledge of circuitry is quite basic.


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#2 DjOnslaught

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Posted 11 June 2016 - 08:38 PM

I'm working on a 2 stage RS (2190's + 2850's) on 3s, with a 2850(honey badger) as the pusher. I will be using a rocker switch to switch between full rof (14dps), and dropped rof (8-9dps). By my calculations, I need to to drop the voltage by 2-2.5v. The only info I could find was to use 1N5400 3A diodes that drop the voltage 0.7V each (so that I would need to use 3 in series).
Now my question is; are 3A diodes going to be safe to use with my particular setup? (I estimate my motors at full stall to be in the neighborhood of 75A). If not, what would be a better diode to serve my application? Perhaps there is something else I should be using.
Any help, suggestions or clarification would be much appreciated as my knowledge of circuitry is quite basic.


Are you using anything like a arduino or something to control it? If so there is a great mod in the forum to look at.
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#3 Zack the Mack

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Posted 11 June 2016 - 11:06 PM

It seems crude to use diodes to drop voltage. Generally, you should use PWM to control motors.

 

You can use an N-channel MOSFET or an NPN transistor on the low side, connected to a PWM pin on an Arduino or other microcontroller, to vary the power more efficiently.

 

Those are all Google-able, if your circuits knowledge is a bit rusty.

 

EDIT: The problem with dropping voltage with diodes is heat. The extra voltage is dissipated as heat, and the more current the motors draw, the more heat is wasted. Laziness and ignorance are not viable reasons to waste 30% of your battery power.


Edited by Zack the Mack, 11 June 2016 - 11:09 PM.

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#4 Deathless

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Posted 12 June 2016 - 12:59 AM

It seems crude to use diodes to drop voltage. Generally, you should use PWM to control motors.

 

You can use an N-channel MOSFET or an NPN transistor on the low side, connected to a PWM pin on an Arduino or other microcontroller, to vary the power more efficiently.

 

Those are all Google-able, if your circuits knowledge is a bit rusty.

 

EDIT: The problem with dropping voltage with diodes is heat. The extra voltage is dissipated as heat, and the more current the motors draw, the more heat is wasted. Laziness and ignorance are not viable reasons to waste 30% of your battery power.

 

I​ was intending to drop the voltage of the pusher motor only, and preferably in the simplest way. I'll look into other options, I was just under the assumption that diodes was common practice in a nerf  rate of fire application.


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#5 DjOnslaught

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Posted 12 June 2016 - 08:48 AM

 
I​ was intending to drop the voltage of the pusher motor only, and preferably in the simplest way. I'll look into other options, I was just under the assumption that diodes was common practice in a nerf  rate of fire application.


In no write ups have I seen just diodes utilized in that method. Zack is completely correct about the waste of battery power and heat issue. If you want to use anything like that you'd want a resistor but again you would run into a heat issue (and resistors don't like overheating)

You can always step down your voltage (aka a smaller battery pack)
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