| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 277.1 | My way you don't gotta buy anything... | LEDS::ZAYAS | | Sun Aug 23 1987 13:56 | 12 |
|
If you are patient...
I just charge the sucker up and place a 20 ohm resistor across
the battery. I then time it and watch the voltage as it discharges
(take a point every 10 minutes). I then sum up the current x times
for these 10 minute intervals and get the capacity. Like and old
physics lab, taking data by hand for about 2 hours and doing the
integral by adding rectangles together...
Like I said, got to be patient. But I only do this at the start
of the season (and after crashes -- grumble, grumble).
|
| 277.2 | YOU NEED TWO !!Y | MAUDIB::CASEYA | THE DESERT RAT RC-AV8R | Tue Aug 25 1987 13:11 | 30 |
| Chris,
You actually need TWO ways to check battery condition if you want
to feel secure regarding the condition of yer' packs: one for use
at the field, and one to "cycle" them in the shop. What Zayas sug-
gests will definitely work (I used to do essentially the same thing
using a glo-plug in place of the resistor) but, if yer' not an elec-
tronics genius (I'm not) and want the ability to conduct dynamic
condition checks on yer' packs, here's what I recommend:
1. For the shop you need an automatic cycler-recharger for use in
periodically checking pack-capacity. I perfer and recommend the
L.R. Taylor unit as it gives you a direct capacity readout in MAH,
no conversion required. If yer' pack is rated at 550 MAH and you
can't get it pumped-up to, say, 500 MAH after repeated cycling,
put the pack in a boat and REPLACE IT !!!
2. For the field you'll want an expanded scale voltmeter (ESV).
This gives you the ability to check the pack-condition "under load,"
an everyday voltmeter (VOM) WILL NOT do! Several of these are on
the market and one's about as good as another. You'll have to put
connectors on the meter leads to match your radios charging jacks
and you're ready to go. This meter allows you to assess remaining
charge "under load" do you can intelligently decide whether you
have enough battery for that "one more flight."
The place to find battery problems/failures is ON THE GROUND and,
frankly, I'd feel absolutely naked flying without these VITAL tools!
Adios, Al
|
| 277.3 | More details... | MJOVAX::BENSON | | Mon Aug 31 1987 10:49 | 8 |
| AL- re ESV's (-.2)
Will a digital voltmeter work (3-1/2 digit autorange)?
What voltages do I look for?
Thanks!
Frank.
|
| 277.4 | VOM, VTVM, DVM WON'T HACK IT !! | GHANI::CASEYA | THE DESERT RAT RC-AV8R | Mon Aug 31 1987 12:08 | 27 |
| Frank,
Sorry, but the answer's no. A digital voltmeter (DVM) is merely
a digital display VOM and neither is capable of checking a pack
dynamically (under load). To my knowledge, only an expanded scale
has this capability, at least for our application.
Why is dynamic checking important? Simply because a battery (any
battery) can show it's rated voltage in a static (no load) condition
but immediately fail when a load is applied (or soon thereafter,
like after you've become airborne...A VERY BAD TIME!) The ONLY
way to have some assurance of dynamic pack condition is to check
it UNDER LOAD. An ESV simulates system load and a pack which main-
tains rated voltage for, say, 10-15 seconds, can safely be assumed
to be healthy and safe to fly. If, on the other hand, the ESV reading
starts off normally (usually 4.8v+ for Rx & 9.6v+ for Tx) then begins
to drop off rapidly, the pack is shot (or needs recharging) and
is NOT safe to fly. Check the suspect pack's behavior after charging/
cycling and you'll KNOW which is the case...no guesswork.
An L.R. Taylor cycler can be had for around $50 if you watch the
Tower Hobbies specials and an ESV goes for around $35 and up. You
only have to spot "ONE" bad pack ON THE GROUND and these devices have
paid fer' themselves. Mine have saved me a fortune (and MANY hours)
in relacement aircraft costs by preventing IN FLIGHT battery failures.
Hope this helps..., adios, Al
|
| 277.5 | Digital meter is O.K. | HPSCAD::WFIELD | | Mon Aug 31 1987 13:09 | 8 |
| Your digital meter will work just fine, if you add a load resistor. An expanded
scale voltmeter simply sets the meter up so that full travel of the meter
needle covers only a very small voltage range. This allows you to detect small
changes in voltage. Your digital meter already has this accuracy, and doesn't
need to be expanded. Simply get a connector for your RX battery pack and add a
resistor in parallel to load down the battery, somewhere around 24 ohms
(assuming that you are using a 500 MAH pack) should be good. A good pack should
maintain somewhere between 4.8 and 5.5 Volts for at least 20 seconds.
|
| 277.6 | | MJOVAX::BENSON | | Thu Sep 03 1987 15:22 | 9 |
| Al-
Thanks for the reply, I was going to ask about adding a load resistor,
but -.5 beat me to it...
Now, what about wattage rating for the load resistor?
Thanks all, in advance!
Frank.
|
| 277.7 | Try this | 39025::GALLANT | | Thu Sep 03 1987 15:31 | 15 |
|
If it were I, I would like to load it as close to possible
to the in flight load, say about 50ma. All you need do is multiply
this by the rated voltage then double it for the sake of longevity
and voyla.
P(ower)=I(load to draw) X V(oltage rating of batt) X 2(for fudge)
Thats what I would do. I guessed at the load but
maybe someone has a better guess at its value.
Mike
|
| 277.8 | I'LL STILL VOTE FOR THE ESV ! | GHANI::CASEYA | THE DESERT RAT RC-AV8R | Thu Sep 03 1987 16:27 | 26 |
| Frank,
You'll do whatever you feel you need to, of course, but I'd still
strongly recommend you use the DVM for continuity/resistance checks
etc. in the shop and purchase an ESV specifically designed for making
capacity checks on the field...they're small, just wrap it in a
sandwich bag and throw in in your tool box where it's "handy" for
making those all-important checks BEFORE that 5th or 6th flight.
Why carry a DVM, loading resistor, conversion table(s), etc. which
might prompt you to side-step the hassle and make that "one-last-
flight" without checking your pack condition?
If you wish, you can also use the ESV for cycling your packs. It
does require that you monitor the discharge cycle and disconnect
the ESV at the minimum per-cell voltage level, then reconnect the
pack to the charger but we did it that way for years before these
fancy automatic cycler/chargers came on the scene.
Again, if it were me, I'd have both the ESV for the field and the
cycler/charger for the shop (which I do and I've never been sorry).
Battery care and maintenance is NOT a very good place to try to
scrimp and save a buck or two. Just one battery-related crash would
MORE than pay for these items, probably two of each. End of ser-
mon.
Adios, Al
|
| 277.9 | Flight Pack Loading and Cycling | LEDS::WATT | | Wed Sep 09 1987 16:16 | 19 |
| From my experience, a four channel flight system draws somewhere
around 250 Ma during flight. This gives about 2 hours on a fully
charged 500 Ma Hr battery if it is healthy. This is the load I
use on my home brew cycler. A 20 ohm resistor will give about the
right load, and it should be 2 watts or larger since the power
dissipation will be 1.25 watts. A simple way to cycle your receiver
pack without any fancy tester is to hook up a 20 ohm load and a
DVM and using a timer, take a reading every 10 minutes. Stop when
the reading gets to 4.4 volts. (1.1 Volts per cell) If you get close
to two hours on a fully charged pack, your battery is functioning
near capacity if it is a 500 mah pack. If you get less time, fully
charge your pack again and try the test over. If you get less than
about 1.5 hours, I would find another use for the batteries and
replace them. By the way, just turning on your flight system does
not impose a normal in flight load on the battery since the servos
are not moving under load. This is why I use a resistor to control
the load at a known level. However, you can turn on the transmitter
and cycle it under its own load since it draws normal current
reguardless of what you are doing with it. (Put the Antenna up!!)
|
| 277.10 | modification to the Tower ESV | GUSHER::RYDER | | Wed Dec 28 1988 07:32 | 117 |
| This note documents a major modification to a Tower Expanded Scale
Voltmeter (ESV).
In the RC hobby an ESV is really two devices combined in the same box:
the obvious device is the voltmeter with the scale expanded in the
region of fully charged RC battery packs and the second device is a
load resistor to simulate somewhat realistic conditions when the
voltage reading is being taken. This combination is convenient under
field conditions and, for users with limited understanding of
electricity, for the workbench. There is a price for this convenience;
the voltmeter cannot be used without this internal load. For example,
the Tower ESV cannot be used to monitor the voltage of a 550 mah
transmitter pack during charging because the ESV draws at least 80 ma
and a C/10 charger puts out only about 55 ma. By itself, the voltmeter
function of the Tower ESV only draws a fraction of what the charger can
supply, namely about 11 ma at 10 volts and about half that from
airborne packs; the rest of the 80 ma is a deliberate load.
Moreover, this deliberate load is not heavy enough to be realistic. My
receiver draws about 400 to 600 ma *PER ACTIVE SERVO*; the low voltage
side of my ESV draws less than half that. My Futaba transmitter draws
about 200 ma, far over the 80 ma load of that side of the ESV. An
external (to the ESV) resistor must be used to apply an operational
load; the internal load isn't realistic. I do not have sufficient RC
experience to judge if a light load is enough to always do the job of
identifying a questionable pack.
I decided to delete the as-manufactured internal load of the ESV and to
add a heavier load controlled by a switch. At the same time I added my
version of a standard battery connector for bench use; these phono
jacks were added in parallel to the original binding post (banana plug)
connectors. So the external appearance has a few changes at the top
front of the meter --- a jack in each corner and a tiny toggle switch
handle in the center with two LED's next to it to indicate the use of a
load. The rest of this note documents the electrical modifications.
The basic circuit of the Tower ESV is:
input ----+----- zener diode ----+----- trim resistor ----+
| | |
| | |
load bias meter
resistor resistor |
| | |
| | |
ground ---+----------------------+------------------------+
The zener diode "expands" the scale by subtracting off the low limit.
The bias resistor draws enough current to keep the zener working
correctly. The variable trim resistor is used by the factory to
calibrate the upper limit of the ESV. Because the ESV has two inputs
for the two popular RC voltages, this basic circuit is duplicated
except for the meter itself where the two circuits are joined together.
low high
input --+-- zener --+-- trim --+-- trim --+-- zener --+-- input
| | | | |
load bias meter bias load
| | | | |
+-----------+------- ground ------+-----------+
Isolation is provided not by the diodes but by the relative values
of the various resistors.
4.8 v --+-- 4. v --+-- .8 k --+-- .8 k --+-- 8.8 v --+-- 9.6 v
| | | | |
.027 k .1 k ??? .1 k .18 k
| | | | |
+-----------+------- ground ------+-----------+
The circuit changes are shown in the following diagram. The SPDT
switch selects which side to ground; to apply a deliberate load the
toggle switch handle is pushed to the side being used. For the minimum
load condition for either side, the switch is pushed away. The
resulting deliberate loads are about 220 ma and 440 ma for the
transmitter and receiver respectively, and the minimum loads remain at
about 5 ma and 11 ma. (Details below.)
low high
input -+---- zener --+-- trim --+-- trim --+-- zener -----+- input
| | | | |
| bias meter bias |
| | | | |
| +------- ground ------+ |
existing | | |
........ | | |
new stuff | | |
+-- 10 Ohms, 3 w --+-- switch --+-- 50 Ohms, 3 w --+
| | | |
+-- .15 k -- LED --+ +-- .39 k -- LED --+
There is a beneficial side effect in this circuit. With the stock
ESV you cannot distinguish between a poor test connection and a
weak battery; the meter reading can be the same for both. With
this modification a briefly applied load will light an LED if the
connections are OK and the battery has at least a drop of juice.
This modification was checked out on some battery packs including a
three cell flashlight assembly and a pack from a well used Makita
drill. (I guess I should be thankful that I don't have a barely
bad pack to try out. Eric H., where are you with your collection?)
pack open meter only with new load
---- ---- --------------- ----------------
airborne 5.2 v 4.3 ma @ 5.2 v 440. ma @ 4.5 v
transmitter 10.3 v 11.7 ma @ 10.2 v 220. ma @ 9.8 v
Makita drill 10.0 v 10.9 ma @ 10.0 v 220. ma @ 9.6 v
flashlight 4.1 v 0.4 ma @ 4.1 v 315. ma @ 3.6 v
The non-linear current draw at sub-standard voltages is probably
a consequence of the zener diode.
|
| 277.13 | experience needed re testing packs | GUSHER::RYDER | | Wed Dec 28 1988 18:04 | 41 |
| Eric, I typed some answers to questions in 277.11, but then my clumsy
fingers deleted the entire effort. Grrr. Will re-type later.
Meanwhile, Eric and Rat, can you shed some experienced light on
the question implicit in 277.10,
"[Is] a light load is enough to always do the job of
identifying a questionable pack."
Have you ever had a pack that tested good but wouldn't hack it when
you put a heavy load on it? e.g. Maybe failed during high speed,
multi-servo-at-once maneuvers.
The airborne load data in 277.10 came from this test:
Instrumented receiver to measure voltage and current during
operation at the workbench. (no, not in the air!)
Observed idle current value (and have now forgotten it)
Operated elevator and observed current
Arrested the elevator motionless in my hand. Repeated
the R/C command to move the elevator.
Arrested or not, it seemed that as long as the servo
wanted to move it was drawing about 400 ma; arresting it
just gave me more time to read the instrumentation (and
stress the system). The value, 400 ma, was a quick
reading; I was uncomfortable about abusing the system.
Arrested both elevator and rudder and issued R/C commands.
Noticed that the load currents seemed to simply add
up to nearly an entire amp of current! And through
those wimpy, wispy wires. Worried about frying the
system!
Concluded that the ESV load was not realistic.
But that doesn't say that it is inadequate for the task.
|
| 277.14 | inevitably inaccurate instruments | GUSHER::RYDER | | Thu Dec 29 1988 07:51 | 73 |
| re Note 277.11 The [JR] display says 10.4v and my ESV says 11.6v
I can think of several reasons why the two might differ. In my
personally estimated decreasing order of likelihood:
1. The loads may differ (as you guessed).
The voltage at the battery terminals depends very much upon the
current being drawn --- mostly because of internal resistance.
2. The object of the measurements may have changed.
This cannot be overlooked. Unless the two measurements were taken
concurrently with both meters connected and nothing changed during
the readings (not even to touch the power switch), at least slight
differences are inevitable, and large differences are possible.
The condition of a battery is dependent upon temperature and the
state of charge, both of which are going to change at least a bit
when you make a measurement and may have changed a whole lot.
However, I wouldn't expect the difference you observed if the ESV
reading was taken after the transmitter reading.
3. The ESV may be incorrect. These are not precision instruments.
The offset may be incorrect. The lower limit of the ESV scale is
determined by the internal zener diode. That is subject to
manufacturing variations and probably to temperature changes.
The scale calibration might also be incorrect, but I would
not expect the ESV to be off by almost a volt for either reason.
I agree with your guess that the differences in the readings are
apt to reflect differences in the applied load.
re Note 277.11 the PCM set must have a load
I doubt if it has a dummy load. More likely, the entire load is
the natural, operational load of the transmitter circuitry.
re Note 277.11 capacity of .. pack is 430mah ... should be 500mah.
Again, this can have several explanations.
1. The capacity might actually be 430 mah.
Unlike the battery voltage which is tied to chemistry and has certain
natural values, the capacity depends upon design and manufacturing
and very much upon temperature. And, of course, upon battery history.
2. The cycler reading is almost certainly incorrect.
Accurate measurements of battery capacity with inexpensive instruments
(read "inexpensive" to mean "non-computing or non-calculating") is not
trivial, is probably not really needed, and is probably not being done
by your cycler. My Taylor doesn't even try to be accurate. The Taylor
drives an ordinary electric clock off the AC line frequency and stops
the clock when the battery voltage drops to a given value; that
approach presumes that both the cut-off voltage and the current drain
are constant and predictable, but neither is either, especially the
current. A DC motor driven by this current would be potentially more
accurate but probably more expensive to manufacture, calibrate, and
maintain.
However, I don't have the experience to judge how inaccurate these
inexpensive cyclers might be. Or how much accuracy we need.
re Note 277.11 tell me what resistors etc to use.
I'll put this into a separate reply. What brand ESV do you have?
|
| 277.15 | PROBABLY NOT MUCH HELP...... | PNO::CASEYA | THE DESERT RAT (I-RC-AV8) | Thu Dec 29 1988 09:42 | 15 |
| Re: .13, Al,
Sorry but I'm not gonna' be of much assistance regarding yer' question
as I've never gone to the extremes you cite in checking my batteries.
Right or wrong, I rely solely upon my L.R. Talyor cycler: if it
indicates good I fly; if it indicates marginal or low capacity,
I replace the pack...a go/no-go situation. I've _NEVER_ had an
in-flight battery failure since starting to use cyclers 15+ years
ago so I've considered this level of checking more than adequate.
|
| | 00 Adios, Al
|_|_| ( >o
| Z__(O_\_ (The Desert Rat)
|
| 277.16 | Comments on ESV Load test | LEDS::WATT | | Thu Dec 29 1988 10:10 | 17 |
| re .10 ect
The load that the esv puts on the pack should be about 250 ma.
The higher currents are only present during heavy servo loads.
A typical 4 channel setup averages about 250 ma during flight if
all controls are free to move. The biggest problem I have seen
is stalled throttle servos due to improper setup in the full throttle
position. This can double the current draw from the battery. If
things are right, you can get two hours on a 4 channel setup with
a good 500 mah pack. I don't recommend testing with a greater load
than this. A cycler should be used to determine capacity and the
ESV is really only a way of checking for cell failure or a rough
estimate of state of charge. By the way, the voltage reading is
fairly sensitive to temperature.
Charlie
|
| 277.17 | Taylor may have had the answer about loads | GUSHER::RYDER | | Fri Dec 30 1988 00:02 | 14 |
| re Note 277.15 Al Casey: "I rely solely upon my L.R. Talyor cycler"
Indirectly, that is an answer. You had said it before long ago,
but I had lost memory of it.
For both receiver and transmitter packs, during the discharge cycle the
Taylor drains about 500 ma. (Through three 10 ohm, 5 watt resistors,
Eric H.) That takes about an hour, not much when you consider the 15
hour charge time that must follow, so Taylor could have used a lighter
load without much impact on the user. He could have saved an iota of
manufacturing cost (I think) by using 15 ohm, 2 watt resistors,
extending the discharge time thereby to one tenth the charge time.
I think I'd like to ask Taylor about the rational of these heavier loads.
|
| 277.18 | shopping for resistors | GUSHER::RYDER | | Fri Dec 30 1988 01:41 | 74 |
| re Note 277.11 "what resistors etc to use ... [to match ESV to TX]"
What follows isn't elegant, but it should be easy. I started to give
instructions on diddling the internals of an unknown ESV. What follows
instead is a way to accomplish the same electrical and procedural
result with out opening or permanently modifying the ESV. Once the
correct resistors have been identified, they will be connected
semi-permanently to the external connection mechanisms of the ESV
(binding posts on my Tower unit). Easy, if not esthetic.
At your local Radio Shack buy some of the following resistors:
271-120 8 ohm, 20 watts, 1.39 ea.
271-132 10 ohm, 10 watts, two/pk .99/2
271-133 50 ohm, 10 watts, two/pk .99/2
271-010 68 ohm, 1/2 watts, two/pk .19/2
You are going to add and remove these from the ESV until you get
the drain where you want it --- presumably matched to the pack's
typical load. When you get the right sets (different for transmitter
and receiver), the sets will be taped or heat-shrinked or whatever
to the ESV case and forgotten. The arrangement during trial will
look sort of like this:
+---------------------+
| |
| _______ |
| / ^ \ |
| | |
| |
| ESV |
| |
| 4.8v GND 9.6v |
| |
| X X X |
| |
+---------------------+
^ ^ ^
| | |
| | |
|+----+|+----+|
++ R1 +++ T1 ++
|+----+|+----+|
| | |
|+----+|+----+|
++ R2 +++ T2 ++
|+----+|+----+
| |
|+----+|
++ R3 ++
+----+
On the receiver side, each 10 ohm resistor added will draw another 500
ma, each 50 ohm another 100 ma, and each 68 ohm another 70 ma. These
currents are in addition to whatever current is already being drawn. So
if R1 is 50 ohms, and R2 and R3 are both 68 ohms, the drain will
be about 240 ma more than it had been before, and only trial will
tell how much lower the voltage reading will now be.
On the transmitter side, don't use the 68 ohm resistors; they don't
have the necessary wattage. The 8 ohm resistor will draw 1200 ma,
probably too much --- as is the 1000 ma draw of the 10 ohm resistors.
The 50 ohm resistors will draw about 200 ma. One 50 ohm is probably
all you need here. If you want to fine tune it, connect two 68
ohm resistors in series; the result will draw 70 ma from the 9.6
volt source and handle the resulting wattage. And you can connect
several of these paired 68 ohm resistors for multiples of 70 ma.
Does this sound reasonable?
|