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Guest

Wed Dec 05, 2018 5:45 pm   



John Doe
Quote:
698839253X6D445TD_at_nospam.org> wrote:
To what voltage level did you charge?

To the level it was before use, the usual level it is charged to, about
4.2 V (no load).


Yes, I use 4.2 V too, use the lab supply with current limit.

Quote:
Why don't we use a simple single pole single throw (SPST) switch instead
of plugging/unplugging the battery? What switch ratings will do for
that?


My drone takes a little over 10 A full throttle at 7.4 V (2 cells).
Switches for that much current are heavy.


Guest

Thu Dec 06, 2018 12:45 am   



On Wed, 05 Dec 2018 16:24:11 GMT, <698839253X6D445TD_at_nospam.org>
wrote:

>Switches for that much current are heavy.

A couple of FETs shouldn't be too heavy. OTOH, good ones (milliohm
RDS(on)), to minimize the heatsink, may be a little heavy on the
pocketbook.

John Doe
Guest

Fri Dec 14, 2018 11:45 pm   



Well this seems interesting...
I bought some lipos, slightly larger than stock. The first flight was
too short, so I applied the drone's voltage level fix so the low-
voltage indicator does not start flashing until it reaches 10 V or
whatever lower realistic voltage. The next flight or two was a good 15
minutes. Then I applied the drone's flip of death fix which makes the
propellers spin up immediately when the drone is armed (ready for
takeoff). Strangely, apparently that fix undoes the low-voltage level
fix. I noticed after a short flight time when the lights started
flashing. So I kept flying until it started losing power, figuring it
would be at least 15 minutes. But it was only about 11 minutes until
it started losing power. So I'm wondering if the low-voltage cut off
does more than just flash lights, but also somehow cripples itself.
Maybe there's some odd electronics scheme going on to do with how it
operates at less than high-voltage. Forcing a landing in order to
protect the batteries from discharging too much?

So I measured the battery voltage after that 11 or 12 minute flight,
at 3.73 V per cell (no load). Seems it should be lower than that.
That's not much less than the lithium ions when the thing could no
longer fly. So I might try plugging the lithium-ion's back in and
using the low-voltage fix. Even if it's double the flight time (12
minutes) that's not enough, but it would suggest the thing is
crippling itself. That would explain, oddly, why there was so much
charge left in the lithium-ions.







I wrote:

Quote:
A measly six minutes in the air.
The batteries were still cool.
With no load they measured 3.86 volts.
I will note the charge.



Guest

Sat Dec 15, 2018 10:45 am   



On a sunny day (Fri, 14 Dec 2018 22:20:06 -0000 (UTC)) it happened John Doe
<always.look_at_message.header> wrote in <pv1aam$8ge$1_at_dont-email.me>:

Quote:
Well this seems interesting...
I bought some lipos, slightly larger than stock. The first flight was
too short, so I applied the drone's voltage level fix so the low-
voltage indicator does not start flashing until it reaches 10 V or
whatever lower realistic voltage. The next flight or two was a good 15
minutes. Then I applied the drone's flip of death fix which makes the
propellers spin up immediately when the drone is armed (ready for
takeoff). Strangely, apparently that fix undoes the low-voltage level
fix. I noticed after a short flight time when the lights started
flashing. So I kept flying until it started losing power, figuring it
would be at least 15 minutes. But it was only about 11 minutes until
it started losing power. So I'm wondering if the low-voltage cut off
does more than just flash lights, but also somehow cripples itself.
Maybe there's some odd electronics scheme going on to do with how it
operates at less than high-voltage. Forcing a landing in order to
protect the batteries from discharging too much?

So I measured the battery voltage after that 11 or 12 minute flight,
at 3.73 V per cell (no load). Seems it should be lower than that.
That's not much less than the lithium ions when the thing could no
longer fly. So I might try plugging the lithium-ion's back in and
using the low-voltage fix. Even if it's double the flight time (12
minutes) that's not enough, but it would suggest the thing is
crippling itself. That would explain, oddly, why there was so much
charge left in the lithium-ions.


Important is the voltage under load where the system cuts off.
This is very different from the no load voltage you measure after flight.
In my case with the H501S I can read battery voltage from the remote,
it is displayed there, else you need ground testing with a voltmeter:
http://panteltje.com/pub/hubsan_h501s_current_test_full_throttle_IMG_6290.JPG
that is with amp meter, but adding - or only using a voltmeter should be easy.
Did you try flying with 2 lipos in parallel?
Oh, and do not connect a full and an empty lipo together in parallel,
things may go up in flames as a huge current can flow, charge both to full first.

I have never done any mods to the battery sensors, not even sure such a mod exists for the Hubsan.

John Doe
Guest

Sat Dec 15, 2018 3:45 pm   



<698839253X6D445TD_at_nospam.org> wrote:

Quote:
John Doe <always.look_at_message.header> wrote in
pv1aam$8ge$1_at_dont-email.me>:

Well this seems interesting... I bought some lipos, slightly
larger than stock. The first flight was too short, so I applied
the drone's voltage level fix so the low- voltage indicator does
not start flashing until it reaches 10 V or whatever lower
realistic voltage. The next flight or two was a good 15 minutes.
Then I applied the drone's flip of death fix which makes the
propellers spin up immediately when the drone is armed (ready for
takeoff). Strangely, apparently that fix undoes the low-voltage
level fix. I noticed after a short flight time when the lights
started flashing. So I kept flying until it started losing power,
figuring it would be at least 15 minutes. But it was only about 11
minutes until it started losing power. So I'm wondering if the
low-voltage cut off does more than just flash lights, but also
somehow cripples itself. Maybe there's some odd electronics scheme
going on to do with how it operates at less than high-voltage.
Forcing a landing in order to protect the batteries from
discharging too much?

So I measured the battery voltage after that 11 or 12 minute
flight, at 3.73 V per cell (no load). Seems it should be lower
than that. That's not much less than the lithium ions when the
thing could no longer fly. So I might try plugging the
lithium-ion's back in and using the low-voltage fix. Even if it's
double the flight time (12 minutes) that's not enough, but it
would suggest the thing is crippling itself. That would explain,
oddly, why there was so much charge left in the lithium-ions.

Important is the voltage under load where the system cuts off.
This is very different from the no load voltage you measure after
flight.


As written, it just happened with the lithium polymer battery, as
well.

I'm sticking the lithium-ion 3x battery holder back onto the thing.
Then I will flash it for the low battery indicator fix. Then I will
run outside and do a flight and see what happens.

I should have done the low battery fix before removing the
lithium-ion holder the first time, but oh well.




Quote:
In my case with the H501S I can read battery voltage from the
remote, it is displayed there


I will be observing battery voltage when FPV is working. Both new
cameras I ordered have on-screen display of battery voltage, instead
of using my crap flight controller.

Quote:
else you need ground testing with a voltmeter:
http://panteltje.com/pub/hubsan_h501s_current_test_full_throttle_I
MG_6290.JPG


Yes, a current meter would be cool. My old Digi-Key B&K Precision
multimeter goes up to 10 A.

Seems like maybe a clamp-on amp meter would be good.

Quote:
that is with amp meter, but adding - or only using a voltmeter
should be easy.
Did you try flying with 2 lipos in parallel?


You mean ions. No. I'm not that bullheaded.

Quote:
Oh, and do not connect a full and an empty lipo together in
parallel, things may go up in flames as a huge current can flow,
charge both to full first.


That's one concern about adding a capacitor to a lithium-ion
battery. Even if a sufficient capacitor were light and compact
enough, I guess there would be potentially damaging current every
time the battery is connected.


Guest

Sat Dec 15, 2018 4:45 pm   



John Doe wrote
Quote:
698839253X6D445TD_at_nospam.org> wrote:
Did you try flying with 2 lipos in parallel?

You mean ions. No. I'm not that bullheaded.


No I meant lipos, could give you 25 minutes flying time.

About metering:
BTW I use a MASTECH MS2108 Digital True RMS Clamp Multimeter AC DC Voltage Frequency Tester
was about 31 $ IIRC ebay auction, now these cost 65 $ it seems.
So far it works OK.
Not all clamp on meters are DC capable, the AC ones are just transformers,
so beware.
But a normal 10 A meter should perhaps work too, you will lose some voltage,

John Doe
Guest

Sat Dec 15, 2018 6:45 pm   



<698839253X6D445TD_at_nospam.org> wrote:

> [double the lipos] could give you 25 minutes flying time.

But, as I'm sure you know... Doubling the battery weight reduces flight
time, how much depends on the drone.

Quote:
BTW I use a MASTECH MS2108 Digital True RMS Clamp Multimeter AC DC
Voltage Frequency Tester


How useful is it for this hobby? Given the voltage reading on your FPV.

I just bought a heat gun, my first. Should've bought one decades ago.
Probably useful for shaping hot melt glue, in addition to heat shrink
tubing.

After testing again...

The 3000 mA hour 20700x3 homemade battery pack weighs 225 g.
It flew for 9 minutes before the alarm, then stopped flying at 11
minutes.

The 2800 mA hour lithium polymer battery pack weighs 209 g.
It flew for 15 minutes before the alarm, then stopped flying 25 seconds
later.

Lithium ions go out with a sputter.


Guest

Sat Dec 15, 2018 8:45 pm   



John Doe wrote
Quote:
698839253X6D445TD_at_nospam.org> wrote:

[double the lipos] could give you 25 minutes flying time.

But, as I'm sure you know... Doubling the battery weight reduces flight
time, how much depends on the drone.


Yes, but it does not double the total weight (drone + batteries).
so there always is some gain,. provided you get lift-off.


Quote:
BTW I use a MASTECH MS2108 Digital True RMS Clamp Multimeter AC DC
Voltage Frequency Tester

How useful is it for this hobby? Given the voltage reading on your FPV.


I wanted to know how much current the Hubsan draws at full throttle,
so what [ebay] converter to buy to convert 3 liion to 7.2 V.
And because I have been testing some batteries with these resistors:
http://panteltje.com/pub/power_resistors_IMG_6291.JPG
And also for the indefinite flight time project:
http://panteltje.com/pub/h501s_drone_remote_power_test_ground_control_1_IMG_6276.JPG
http://panteltje.com/pub/h501s_drone_remote_power_flight_test_1_IMG_6274.JPG
drone powered via thin coax, will stay in the air forever.
The idea being to use it to put an antenna very high up there...

The DC capable clamp-on meters are great,
measuring current while charging batteries, in your car, in your boat,
any place were you need to measure high DC current and do not want -
or cannot cut the cables to put an amp meter in series.
Thing works from 50 to 100 mA upwards
I also have a cheap AC only one, never use that,



Quote:
I just bought a heat gun, my first. Should've bought one decades ago.
Probably useful for shaping hot melt glue, in addition to heat shrink
tubing.


I use a lighter for heat shrink tubing....
Or the soldering iron (clean afterwards).


Quote:
After testing again...

The 3000 mA hour 20700x3 homemade battery pack weighs 225 g.
It flew for 9 minutes before the alarm, then stopped flying at 11
minutes.

The 2800 mA hour lithium polymer battery pack weighs 209 g.
It flew for 15 minutes before the alarm, then stopped flying 25 seconds
later.

Lithium ions go out with a sputter.


Yes I am sure they are good for many things, but not so much for drones.

Jeff Liebermann
Guest

Sun Dec 16, 2018 12:45 am   



On Sat, 15 Dec 2018 15:04:25 GMT, <698839253X6D445TD_at_nospam.org>
wrote:

Quote:
About metering:
BTW I use a MASTECH MS2108 Digital True RMS Clamp Multimeter AC DC Voltage Frequency Tester
was about 31 $ IIRC ebay auction, now these cost 65 $ it seems.
So far it works OK.


I've been shopping for a clamp type DC ammeter to replace various
lesser quality devices which I use for measuring DC stick arc welder
current, spot welder DC peak current, automobile charging current, DC
starter current, LED flashlight current, radio transmitter DC current,
solar panel short circuit current, etc. I didn't know that the
MS2018a would measure DC current through the clamp. Looks like it
should work. However, I'm tempted to buy a Mastech MS2109a, which is
similar but has a better front panel layout and adds a thermocouple
thermometer and NCV (Non-Contact Voltage) AC tester for approximately
the same price.
<https://www.ebay.com/sch/i.html?_nkw=MASTECH+MS2109a>

Quote:
Not all clamp on meters are DC capable, the AC ones are just transformers,
so beware.


I haven't found a way to filter Google or eBay searches for clamp
meters that will work with DC through the clamp. Most meters will do
both AC and DC current through the test leads, some will do AC through
the clamp, but very few will do AC and DC through the clamp. One
trick I've found is to look at the silk screening on the ammeter
ranges. If it shows a stylized sine wave over a solid line, it should
work with both AC and DC. The clamp also has + and - markings.

>But a normal 10 A meter should perhaps work too, you will lose some voltage,

Very little voltage drop. A 10A 100mv shunt has a resistance of 0.01
ohms and will drop, umm... 100mv at 10amps:
<https://www.murata-ps.com/data/meters/dpm_shunts.pdf>

I have some opinions on what's wrong with the quadcopter. However,
I'll wait until I see some voltage and current measurements and graphs
performed in a test stand (like your chair test). My guess(tm) is
that this sounds like a high resistance connection between the battery
and the ESC (electronic speed control). Something seems to be
prematurely announcing that the battery is depleted. An unwanted
voltage drop in the wiring would do that.

--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Carl
Guest

Sun Dec 16, 2018 3:45 am   



"Jeff Liebermann" wrote in message
news:uu0b1ela5h7jte6hctg1hlkejkai5e9ob7_at_4ax.com...
Quote:

On Sat, 15 Dec 2018 15:04:25 GMT, <698839253X6D445TD_at_nospam.org
wrote:

About metering:
BTW I use a MASTECH MS2108 Digital True RMS Clamp Multimeter AC DC Voltage
Frequency Tester
was about 31 $ IIRC ebay auction, now these cost 65 $ it seems.
So far it works OK.

I've been shopping for a clamp type DC ammeter to replace various
lesser quality devices which I use for measuring DC stick arc welder
current, spot welder DC peak current, automobile charging current, DC
starter current, LED flashlight current, radio transmitter DC current,
solar panel short circuit current, etc. I didn't know that the
MS2018a would measure DC current through the clamp. Looks like it
should work. However, I'm tempted to buy a Mastech MS2109a, which is
similar but has a better front panel layout and adds a thermocouple
thermometer and NCV (Non-Contact Voltage) AC tester for approximately
the same price.
https://www.ebay.com/sch/i.html?_nkw=MASTECH+MS2109a

Not all clamp on meters are DC capable, the AC ones are just transformers,
so beware.

I haven't found a way to filter Google or eBay searches for clamp
meters that will work with DC through the clamp. Most meters will do
both AC and DC current through the test leads, some will do AC through
the clamp, but very few will do AC and DC through the clamp. One
trick I've found is to look at the silk screening on the ammeter
ranges. If it shows a stylized sine wave over a solid line, it should
work with both AC and DC. The clamp also has + and - markings.

But a normal 10 A meter should perhaps work too, you will lose some
voltage,

Very little voltage drop. A 10A 100mv shunt has a resistance of 0.01
ohms and will drop, umm... 100mv at 10amps:
https://www.murata-ps.com/data/meters/dpm_shunts.pdf

I have some opinions on what's wrong with the quadcopter. However,
I'll wait until I see some voltage and current measurements and graphs
performed in a test stand (like your chair test). My guess(tm) is
that this sounds like a high resistance connection between the battery
and the ESC (electronic speed control). Something seems to be
prematurely announcing that the battery is depleted. An unwanted
voltage drop in the wiring would do that.


I've got two Uni-T meters (http://www.uni-trend.com/), both 4000 count
models, one a true RMS autoranging DVM and the other a clamp ammeter DVM,
model UT204 which does AC and DC and autoranges between 40A and 400A scales.
I've used it to check starter draw on a car and the output of a 10W solar
panel (0.22 A that day) and I'm happy with it. They have lots of models
with different features, and lots of sellers on amazon and ebay. The Uni-T
meters seems to have good accuracy and useful features, but get their low
cost from slow settling times. Over a second per screen update and often
three updates to get a stable reading so 3-5 seconds total. For my needs
that works.

If you don't use a clamp-on meter be sure to check the manual for your
meter. Lots of the cheaper meters with a 10A scale bury a truly wimpy duty
cycle in the fine print. I've seen 15 seconds of 10A measurement followed
by ten-plus minutes of required cooldown in at least one of the Uni-T meters
and some other brand I can't remember right now.

--
Regards,
Carl Ijames

John Doe
Guest

Sun Dec 16, 2018 3:45 am   



Jeff Liebermann <jeffl_at_cruzio.com> wrote:

Quote:
I have some opinions on what's wrong with the quadcopter. However,
I'll wait until I see some voltage and current measurements and graphs
performed in a test stand (like your chair test). My guess(tm) is
that this sounds like a high resistance connection between the battery
and the ESC (electronic speed control). Something seems to be
prematurely announcing that the battery is depleted. An unwanted
voltage drop in the wiring would do that.


I suspect there's something weird going on in this particular drone, but
the low-voltage warning can be set low enough to get full use out of
lithium polymer batteries.

I might try lithium ions for some other drone, but that's it for this
one. The lithium-ion pack I made for the controller is working superbly.

Jeff Liebermann
Guest

Sun Dec 16, 2018 7:45 am   



On Sat, 15 Dec 2018 21:14:59 -0500, "Carl"
<carl.ijamesXYZ_at_ZYXverizon.net> wrote:

>><https://www.ebay.com/sch/i.html?_nkw=MASTECH+MS2109a>

MS2109a data sheet:
<http://www.mastech-group.com/products.php?cate=95&PNo=209>

More Mastech clamp meters:
<http://www.mastech-group.com/products.php?cate=95>
<http://www.mastech-group.com/products.php?cate=95&page=2>

Quote:
I've got two Uni-T meters (http://www.uni-trend.com/), both 4000 count
models, one a true RMS autoranging DVM and the other a clamp ammeter DVM,
model UT204 which does AC and DC and autoranges between 40A and 400A scales.


True RMS would be nice to have, but is not necessary for what I expect
to be mostly DC current measurements.

Sigh. I went to the Uni-T web pile and tried to look for meters.
Every link link I click returns a "404" (nobody home). Despite my
having an uncontrollable urge to buy something immediately, I'll wait
a day or two for someone to fix the Uni-T web pile or server.

Quote:
I've used it to check starter draw on a car and the output of a 10W solar
panel (0.22 A that day) and I'm happy with it. They have lots of models
with different features, and lots of sellers on amazon and ebay. The Uni-T
meters seems to have good accuracy and useful features,


Thanks. I'll do some reading and see what they have to offer.

Quote:
but get their low
cost from slow settling times. Over a second per screen update and often
three updates to get a stable reading so 3-5 seconds total. For my needs
that works.

If you don't use a clamp-on meter be sure to check the manual for your
meter. Lots of the cheaper meters with a 10A scale bury a truly wimpy duty
cycle in the fine print. I've seen 15 seconds of 10A measurement followed
by ten-plus minutes of required cooldown in at least one of the Uni-T meters
and some other brand I can't remember right now.


Argh. I didn't realize that this was a problem with DC clamp meters.
I just skimmed the Mastech MS2109a manual
<https://panda-bg.com/datasheet/2145-340549-MS2109A-clamp-meter-mastech.pdf>
but didn't find any mention of a cool down period.
For sampling rate, it claims:
"Sampling rate: about 3 times/s, simulation bar 30 times/s."
Incidentally, the highest count is 5999 which is needed for the 600A
scale.


--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann
Guest

Sun Dec 16, 2018 8:45 am   



On Sun, 16 Dec 2018 02:14:18 -0000 (UTC), John Doe
<always.look_at_message.header> wrote:

Quote:
Jeff Liebermann <jeffl_at_cruzio.com> wrote:

I have some opinions on what's wrong with the quadcopter. However,
I'll wait until I see some voltage and current measurements and graphs
performed in a test stand (like your chair test). My guess(tm) is
that this sounds like a high resistance connection between the battery
and the ESC (electronic speed control). Something seems to be
prematurely announcing that the battery is depleted. An unwanted
voltage drop in the wiring would do that.

I suspect there's something weird going on in this particular drone, but
the low-voltage warning can be set low enough to get full use out of
lithium polymer batteries.


I can see that I'm not getting through to you. Please excuse my
abrasive, rude, undiplomatic, and short tempered manners.

Here's what you should be doing:

1. Setup your drone in a manner similar to Jan Panteltje's test
chair:
<http://panteltje.com/pub/hubsan_h501s_current_test_full_throttle_IMG_6290.JPG>

2. Take DVM and place it across the battery terminals as close to the
actual battery as possible. You want to measure the actual battery
voltage.

3. Take a 2nd DVM and place it as close to the place where the ESC
distributes the power to the various motors. That would be the DC
input to the ESC. If the low voltage measurement device is located
elsewhere, use that connection.

4. If you have an adapter for your XT60 battery connector for current
measurement, attach it and also record the current draw ever 30
seconds.

5. Run the drone in the chair at something resembling normal flight
RPM (not full power). With a paper pad and pen, record the voltages
every 30 seconds. When the low voltage alarm is triggered, record the
time. Let it run until the controller or ESC declares the battery to
be discharged. Draw a graph. If my guess is correct, the graph will
look very strange and that there will be a substantial voltage
difference between the battery terminal voltage and the ESC voltage.

Quote:
I might try lithium ions for some other drone, but that's it for this
one. The lithium-ion pack I made for the controller is working superbly.


Really. Have you calculated what your runtime should be based on the
average current drain and battery ma-hr rating? Be sure to check the
data sheet for the LiIon cells for the ma-hr capacity at whatever
current your motors are drawing. How close is your flight time to the
theoretical runtime?

--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


Guest

Sun Dec 16, 2018 10:45 am   



Jeff Liebermann wrote
Quote:
On Sat, 15 Dec 2018 15:04:25 GMT, <698839253X6D445TD_at_nospam.org
wrote:

About metering:
BTW I use a MASTECH MS2108 Digital True RMS Clamp Multimeter AC DC Voltage Frequency Tester
was about 31 $ IIRC ebay auction, now these cost 65 $ it seems.
So far it works OK.

I've been shopping for a clamp type DC ammeter to replace various
lesser quality devices which I use for measuring DC stick arc welder
current, spot welder DC peak current, automobile charging current, DC
starter current, LED flashlight current, radio transmitter DC current,
solar panel short circuit current, etc. I didn't know that the
MS2018a would measure DC current through the clamp. Looks like it
should work. However, I'm tempted to buy a Mastech MS2109a, which is
similar but has a better front panel layout and adds a thermocouple
thermometer and NCV (Non-Contact Voltage) AC tester for approximately
the same price.
https://www.ebay.com/sch/i.html?_nkw=MASTECH+MS2109a


Yes, those things are getting better all the time,
I notice that if I google
'MS2109a user manual'
then I get all the info on that thing as pdf.



Quote:
But a normal 10 A meter should perhaps work too, you will lose some voltage,

Very little voltage drop. A 10A 100mv shunt has a resistance of 0.01
ohms and will drop, umm... 100mv at 10amps:
https://www.murata-ps.com/data/meters/dpm_shunts.pdf


Indeed, external shunt,
but if he uses a multimeter meter those test leads are very thin and crap,
for current, you will need short thick test leads to the meter,


Quote:
I have some opinions on what's wrong with the quadcopter. However,
I'll wait until I see some voltage and current measurements and graphs
performed in a test stand (like your chair test). My guess(tm) is
that this sounds like a high resistance connection between the battery
and the ESC (electronic speed control). Something seems to be
prematurely announcing that the battery is depleted. An unwanted
voltage drop in the wiring would do that.


For the original lipos the wiring is very short, big connectors,
don't know his setup.


Guest

Sun Dec 16, 2018 11:45 am   



Jeff Liebermann wrote

Quote:
I just skimmed the Mastech MS2109a manual
https://panda-bg.com/datasheet/2145-340549-MS2109A-clamp-meter-mastech.pdf
but didn't find any mention of a cool down period.
For sampling rate, it claims:
"Sampling rate: about 3 times/s, simulation bar 30 times/s."


I can confirm that for the Mastech MS2108,
I can set the current limit for my battery charger with it and it reacts as fast as I can turn that 10 turns trimpot.

Do not know about a cool down period, never measure high DC currents for a very long time.
Before measuring I press the zero button once.
And I did put 3 eneloop 1.5 V AAA batteries in it so it is always ready.

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