Diodes to reduce voltage Good Idea or Not

[just_lkn]

I've been thinking about using a couple or three 3amp diodes in series to reduce the voltage on some 2 cell lipos to power a receiver and servo's at between 5 and 6 volts..


Your thoughts please.

[Dan Baldwin]

A fully charged 2 cell lipo pack would be about 8.4 volts, and if you put 3 diodes in series, you'll have about 2 volts of drop, giving you about 6.4 volts. On the other end, a fully discharged 2 cell lipo would be about 6 volts, giving you about 4 volts to the receiver/servos.

Why don't you want to use a regular LDO regulator?

Dan

[AndyKunz]

You'd also have a great way to start an oscillator and charge pump.

An LDO (LM2940 or such) is a better way to get 5V.

Andy

[Discharger]

There is a thread on the "other board" re Li-po 2s for on board power and the writer uses the 2s direct without a regulator or voltage dropping diodes and reports that the system works just fine with no problems after many flights and in fact has better servo response with the higher voltage. The Schultze Alpha receivers are rated at 9 volts maximum so I guess that the other brands would be similar, so no problem with 8 + volts here. Most servo specs usually are for 4.8 and 6 volts with no mention of a maximum but i'm tipping that another 1 or 2 volts would be fine. If you are a bit nervous about going direct then one or maybe two diodes in series should also be just fine. As far as setting up an unintentional oscillator (unlikely?) some strategically placed bypassing capacitors should fix that. Please post your results in due course whichever way you go.

[Acetronics]

:rolleyes:
Hi, everybody,

Take care : servo amplifier datasheeets often give 7 volts as an absolute maximum voltage ...
over 7 volts, it's at your own risks ...

Alain

[Romych]

In some receivers, manufacturers uses 6,3 volts capacitors, pay attention! It's may work and may burn... Some other uses 10 volts capasitors on input of LDO regs, I think this receivers will work.

P.S. Diodes not simply drop voltage, this dissipate heat.

FMA Direct start shipping servo DS300, this handle up to 12.6 volts - dream of electroflyers, but weight...

[Texy]

I've been thinking about using a couple or three 3amp diodes in series to reduce the voltage on some 2 cell lipos to power a receiver and servo's at between 5 and 6 volts..


Your thoughts please.

If you really want to keep it that simple, why not use a 5v6 Zener,
rated accordingly, and series resistor to limit current?
A regulator would be the best approach however.

Texy

[Miami Mike]

If you really want to keep it that simple, why not use a 5v6 Zener, rated accordingly, and series resistor to limit current?For a fixed load that might be okay, but it sounds like a really bad idea for powering servos. You'd have to determine the maximum current that the combined servos would draw under extreme conditions, and use a low enough value series resistor to ensure that under those conditions the receiver would still have enough voltage to operate. Then you'd have to use a zener diode capable of dropping the voltage across that resistor to the desired 5.6 volts under a minimum load. It seems to me that such a circuit would waste lots of power and drain the battery quickly.

Like you said, a regulator would be the best approach.