Electronics > Electronics
3.7 v lipoly powering micro servo? bad idea?
mklrobo:
:) Hello!
(Sorry about the late entry, I had to power off for awhile)
In regards to;
What do you think Mklrobo about this issue of 3.7 v lithium polymer battery to power light usage of a sub micro servo 4.8v?
I would really like to use just a single battery, and preferably not use the heavier NiCd or NiMH battery packs.
In reviewing the latest posts by you and bdeuell, I would make a generalization;
Points have been make concerning voltage dips, brownouts, possible voltage mismatches,
servos that may or may not be used.
To address this, I look back at some power supplies like TVs provide. The circuits (in the old days)
provided all kinds of levels of power supplies; I was not sure why, until now.
In the interests of the aforementioned, and possible future demands, it may be prudent to
have a battery that provides 18 Volts, and can dock into your design. - Why?
Emplace voltage regulators on your design, of any voltage that you need. 5 V, 3.3V, 3.7, 4.8.
The battery that can dock, can easily be replaced, while the other is charging.
The reason for multiple voltages off of a larger voltage, is to keep regulation going to the
sub - power supplies, with no brown outs; and also gives you latitude if you need to replace
a servo with a better one, or need to replace the servo you have, but it has been discontinued.
If you need to add something that you did not expect, you have the flexibility to power that also.
It adds a little more design time, but may save you more in the future. What do you think? :-\
Keep me posted..... :)
mklrobo:
:) hello!
If the direction of the voltage supply is resolved, we can move onto
the actual battery, or other parts of the design.
In the making of the housing of the circuit, battery, and servos, I
could give an idea there. On the website, Instructables, they give
great ideas for do-it-yourself housing construction. Everything from
making a gun case, to repair your car, to special electronic housing; the
latter in this issue. I made my own fiberglass housing for one of my projects,
and worked great. Light as a feather, strong as steel, and pretty as much as your
labor is involved. Resists corrosion, an insulator for temperature as well as electricity,
make a good case for many applications. Keep me posted!..... ;D ;D ;D
mklrobo:
:) Hello!
I reviewed your post on the other thread, but could not review the
item you selected. Will try to access soon..... :)
dmehling:
--- Quote from: bdeuell on February 09, 2015, 08:05:05 PM ---
--- Quote from: dmehling on February 09, 2015, 04:45:57 PM ---Are you sure it would not be possible? ... They suggest that it may not be the ideal, but is workable with light loads.
--- End quote ---
see earlier post:
--- Quote from: bdeuell on February 09, 2015, 03:56:52 PM ---If you want to know for sure buy it and try it out they don't cost too much. ... if you're lucky turns but has very little power
--- End quote ---
if you are engineering a design and want to use something outside if its specified operating parameters you can: A) request additional information about the product, B) conduct your own tests to determine the performance of the product, C) take an educated guess based on previous experience, or D) build it blindly and hope it works (not really engineering or recommended by me). Unfortunately i do not have experience undervolting servos to that degree and cannot offer you direct advice on option C. keep in mind you already have very small servos so your torque is already small without undervolting the servo (not to say it won't work just a caution). Also it doesn't really matter how short of a time you need the torque 1s - 10s the torque you can deliver is the same.
--- Quote from: dmehling on February 09, 2015, 04:45:57 PM ---I would certainly consider using a boost converter as you suggested. If I was doing that, how would I know when the voltage is falling? I intend to put all of the electronics for my project inside of an enclosure, except the servos. Is there some way I could have the voltage voltage be checked internally and then have an LED light up if it goes to low?
--- End quote ---
the battery voltage will continue to decrease as it is used (a datasheet would show this discharge curve). there are many ways to monitor a batteries voltage two common methods are to use an analog input pin on a microcontroller or a comparator circuit that uses a reference voltage to determine when the battery is below a threshold.
--- End quote ---
I'm willing to at least try it since some have apparently managed to do it without any serious issues. The servos I have in mind are quite inexpensive so it would not be that terrible if they malfunctioned.
Having said all that, I would like to know the potential problems. What would be the harm of lower than recommended voltage? Could it damage the battery or the servo? And what is the harm of reduced torque on the servo itself? Could that also be something that could damage the internal components?
With regards to using a voltage booster, the batteries I want to get actually have a voltage of 4.2 v when fully charged, and they go down to 3.7 v when fully depleted. What impact would that have on the ability of the voltage booster to output adequate voltage? Would that make any difference? Does 3.7 v provide enough voltage to be boosted to 4.8 v? And is there a danger of boosting it too high?
I appreciate your patience since many of these concepts are new to me.
mklrobo:
:) Hello!
In regards to your questions;
Having said all that, I would like to know the potential problems. What would be the harm of lower than recommended voltage?
A generic answer to this is an ohms law example; - 50 ohms at 10 volts is .2 amps || 50 ohms at 5 volts is .1 amp.
In that sense, you are loosing amperage( which motors need) and the motor slows down. Like a dimmer switch
on your lights. :) (ohms is the servo load)
Could it damage the battery or the servo? And what is the harm of reduced torque on the servo itself? Could that also be something that could damage the internal components?
Sind you are dealing with small motors, the damage may not show up for awhile, if ever, depending on the
workmanship of the motor. Some motors have saftey feature built in, that prevents most damage.
Bdeuell has posted alot of info on this, on a related thread, dealing with the performance expectations of
a motor. Will have to get back with you about the power booster. ;D ;D
With regards to using a voltage booster, the batteries I want to get actually have a voltage of 4.2 v when fully charged, and they go down to 3.7 v when fully depleted. What impact would that have on the ability of the voltage booster to output adequate voltage? Would that make any difference? Does 3.7 v provide enough voltage to be boosted to 4.8 v? And is there a danger of boosting it too high?
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