Zener Diode to Drop 3xQ830 li-Ion Voltage for Tiger Moth - RC Groups
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Feb 24, 2002, 06:57 PM
Registered User

Zener Diode to Drop 3xQ830 li-Ion Voltage for Tiger Moth

Based on comments here it seems the GWS TM is somewhat lethargic with 2 qualcomm 830s. Since 3 cells would put 10.8v through the dxa this would end in disaster (+smoke ). Has anyone thought of adding a simple zener/transistor circuit to the output of a 3 cell pack to clip the voltage to a maximum of say 8.4v? The circuit would be cheap to make, light and since the current is <3A the heat buildup would not be significant. The performance may be a lot closer to a NiMh setup.

Just a thought...

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Feb 24, 2002, 07:35 PM
ClearView Rocks!
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Hi. If you do the math, you might not be too happy with the heat dissipation of the device you are proposing. (About 4.8 watts). Besides, it does waste power that you might otherwise use. An ESC does a great job of translating the battery power to the motor without the attendant losses in a linear circuit. What this means is that if you keep the throttle down, the 3 cell approach will do nicely, except that the stock motor really can't take too much overage for too long. A good idea would be to hook up the 3 cells and put a voltmeter across the motor. Advance the throttle until the voltage reads the maximum that you are willing to subject your motor to. Then note the throttle stick position. Keep you throttle at or below this point in flight and you will be fine. You can probably cheat a little because of reduced load/improved cooling in flight, along with battery voltage sag during discharge.

Feb 24, 2002, 11:04 PM
Registered User
Silicon diodes drop .6V per diode. I've run a rc system off of a 7 cell pack with diodes in line to drop the voltage to the reciever/servos. worked fine. I used 5 A diodes from Radio Shack,

Not having unlimited vertical is part of the TM challenge! If you want something zippy, get a Wattage "Sporty" Flys like you won't believe on a geared 280/300. Not for novices, they are quite fast!