Voltage reducer for lipo packs?

[atrr]

New to electronics, is there a way to reduce voltage on 3s lipo packs to 7.6volts or equal to 2s lipo packs? :confused:

[AndyOne]

There are a number of devices to do this but which one you choose depends on how much current you need. The more current and the more voltage drop you need, the greater the power dissipation in a linear regulator, switch mode regulators are also available which are more efficient.

Tell us your specification and someone will advise you.

Andy.

[atrr]

I need to reduce voltage but keep current at maximum for my brushless speed control on hummingbird heli. The 3s lipo cause my 10amp cc esc to overheat; it works fine on 2s lipo voltage. Thanks.

John

[stu78]

I need to reduce voltage but keep current at maximum for my brushless speed control on hummingbird heli. The 3s lipo cause my 10amp cc esc to overheat; it works fine on 2s lipo voltage. Thanks.

John

What you want to do is not really practical, I suggest you remove one of the cells and make your 3s into a 2s or simply buy a 2s pack.

by reducing a 3s to 2s voltage levels you are carrying an extra cell, carrying extra electronics and generally making life difficult for yourself.

Anyway, it doesn't sound like this is your problem, the heat is most likely coming from another problem:

1. if you use the same pinion for 2s and 3s, chances are you are running the motor at a lower throttle setting on 3s which is less efficient and causes heat in the ESC and possibly the motor too.

2. your BEC may be causing the heat.

I would first try a smaller pinion and then a separate BEC.

Stuart

[atrr]

Thanks for reply, I have too many 3s lipos and didn't want to purchase more 2s lipos. Will try your suggestion.


John

[ImaBiggles]

Thanks for reply, I have too many 3s lipos and didn't want to purchase more 2s lipos. Will try your suggestion.


John

so split 2 3s packs to make 3 2S packs.

[Norman Adlam]

I need to reduce voltage but keep current at maximum for my brushless speed control on hummingbird heli. The 3s lipo cause my 10amp cc esc to overheat; it works fine on 2s lipo voltage. Thanks.

John

Hi,

You might have to investigate how many servos your BEC is running! Quite often the BEC overheating is the problem, especially if you up the number of Li-Po's.

If that is your problem, then ensuring the linkages are smooth, or getting better quality (lower current) servos may help.

Cheers,

[z-matrix]

hi!
it is possible, and not that hard, but it will be some weight, if you don't mind, you can use a simple buck regulator, there are some ics at www.analog.com for this purpose, if you need many amps, you need an smd mosfet (or more), and a pwm controller ic, like tl494, you must make an undervoltage lockout, to make sure you won't damage your cellls, typical efficiency of 70% is possible with a simple buck regulator design at low voltage, you will have more current at lower voltage, so i whould say, not much point using 3s instead of 2s, but its a bit better, because you will have a stable, regulated output voltage.
More eficiency is possible, with synchronous rectification (mosfet instead of schottky diode), and possibly zvs topology - but this does not help much in low voltage designs, only few %, these are more and more weight, and more cost.

in my opinion it whould be better if the speed controller could work with 3s,
i'm designing right now an esc, i'm planning to make it compatible with 3s and 4s LI-POs - because i see way to do it.

[ImaBiggles]

hi!
it is possible, and not that hard, but it will be some weight, if you don't mind, you can use a simple buck regulator, there are some ics at www.analog.com for this purpose, if you need many amps, you need an smd mosfet (or more), and a pwm controller ic, like tl494, you must make an undervoltage lockout, to make sure you won't damage your cellls, typical efficiency of 70% is possible with a simple buck regulator design at low voltage, you will have more current at lower voltage, so i whould say, not much point using 3s instead of 2s, but its a bit better, because you will have a stable, regulated output voltage.
More eficiency is possible, with synchronous rectification (mosfet instead of schottky diode), and possibly zvs topology - but this does not help much in low voltage designs, only few %, these are more and more weight, and more cost.

in my opinion it whould be better if the speed controller could work with 3s,
i'm designing right now an esc, i'm planning to make it compatible with 3s and 4s LI-POs - because i see way to do it.


It aint easy to do for 10 amps dude.

[atrr]

so split 2 3s packs to make 3 2S packs.

I'm using it on my T-rex heli also which requires 3s.

[ImaBiggles]

what? You asked how to reduce a 3S pack voltage to 2S and then state you heli requires 3S? Im lost.

[GJ KUIPER]

An other way I use to reduce voltage of a 2 pack lipos as use for a 5 volt system is,

Use diodes in series with the output line of the lipo. Each diode will drop 0,7Volts. So you can use as many diodes in series as needed to get the voltage you need.( 2 diodes = 1,4 volt and so on)

The output current is limited to the kind of diodes you use.

G.J

[Nicetie]

Switching regulators are the most efficient way to do this, but 10A is a
lot of current for a single chip. You could use a switching chip with a
power transistor to handle the current. Google switching regulators
and you can find ready made units, but they aren't all that small for
10A. I gave up on this myself since space and weight are limited in
my application.

[Nicetie]

The diode answer is correct, but each one will be dissapating
about 7W at 10A load current. There are rectifiers that can
handle this if they are used with a heat sink. A lot of weight.

[Zlatko]

atrr,

Just thinking out aloud....

Could you put a smaller pinion on your hummingbird motor?
If you can do it, than this would be another way to reduce the current draw.
You would also get realy long flight times ....

Cheers

[JohnMuchow]

You could use standard 6A10 diodes (rated at 6A). They'll have approximately a 0.8V drop across them. Two in parallel will handle the 10A if you have air flow across them. Especially since you're not running at the full 10A all the time. Three in parallel would be a LOT better though if there's no air flow.

They weigh 2.1 grams each but that's with 1" of heavy wire lead coming out each end. Trim those leads down and you can reduce the weight.

There are also 6A05, 6A1, 6A2, 6A4, 6A6, 6A8 diodes with varying voltage ratings (50V lowest). Any of these can be used with your 3S packs so buy the least expensive ones you can find.

[Nicetie]

Might not be that easy to parrallel diodes. The one with the lowest
voltage drop will handle all the current and will dissapate all the power
unless you isolate them with resistors. This isn't a good thing either
since you are looking for high current and the equalizing resistors will drop some
of the voltage and reduce the current. Also the reverse voltage drop
varies with the current and the regulation will be poor. Not always .7V
or .8V. Usually .6v at low current and increasing with current.

[JohnMuchow]

Good points. And I agree, paralleling can be problematic.
But IMHO, three in parallel would easily handle any misbalance between them (no need for resistors and the voltage regulation problems they would bring).

I had checked the datasheet for the diodes I mentioned and though the voltage drop across a diode varies with current, the drop for the 6AXX series is approx 0.8V at 6A and only varies by 50mV down to 3A and up to about 9A. I think this would be tight enough for use here. atrr would have to make sure though.