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Default digital ammeter with 'centre zero'.

I'm trying to find a digital voltmeter/ammeter that will read both the
charge and the discharge of a battery. The vast majority of the products
available will only read current 'in one direction'. I need something
that will indicate discharge by showing a minus sign, and will display
the value thereof.

I'm wondering about getting one of these. I've never used anything that
works by the hall effect though. Anyone know (a) if it will do what I
want and (b) what snags I might encounter?

https://www.amazon.co.uk/Battery-Mon...976227978&th=1

The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.


Bill
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Default digital ammeter with 'centre zero'.

On 09/09/2020 15:05, williamwright wrote:

The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.

The only slight snag I have found using a clamp meter with a hall efect
sensor is that they are slightly affected by the position of the wire
inside the loop.

There will also be a constant small drain on the battery to run the
electronics.

As a bonus, the percentage reading is usually wildly inaccurate, so you
need to go by the voltage and accumualted amp hours readings..

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Default digital ammeter with 'centre zero'.

On 09/09/2020 15:05, williamwright wrote:
I'm trying to find a digital voltmeter/ammeter that will read both the
charge and the discharge of a battery. The vast majority of the products
available will only read current 'in one direction'. I need something
that will indicate discharge by showing a minus sign, and will display
the value thereof.

I'm wondering about getting one of these. I've never used anything that
works by the hall effect though. Anyone know (a) if it will do what I
want and (b) what snags I might encounter?

https://www.amazon.co.uk/Battery-Mon...976227978&th=1


The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.


Bill


What about this one which is also cheaper?
https://www.amazon.co.uk/Voltage-Cur.../dp/B015SXP9Y0

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Default digital ammeter with 'centre zero'.

On 09/09/2020 15:25, John Williamson wrote:
On 09/09/2020 15:05, williamwright wrote:

The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.

The only slight snag I have found using a clamp meter with a hall efect
sensor is that they are slightly affected by the position of the wire
inside the loop.

There will also be a constant small drain on the battery to run the
electronics.

As a bonus, the percentage reading is usually wildly inaccurate, so you
need to go by the voltage and accumualted amp hours readings..


Thanks for that. Helpful!

Bill
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On 09/09/2020 15:27, MikeS wrote:

What about this one which is also cheaper?
https://www.amazon.co.uk/Voltage-Cur.../dp/B015SXP9Y0


Ohhh! I think that's a better bet! Thank you!

Bill


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Default digital ammeter with 'centre zero'.

On 09/09/2020 15:45, williamwright wrote:
On 09/09/2020 15:27, MikeS wrote:

What about this one which is also cheaper?
https://www.amazon.co.uk/Voltage-Cur.../dp/B015SXP9Y0


Ohhh! I think that's a better bet! Thank you!


Except you have to cut into your existing wiring and run 4 off 20A+
cables to the meter.


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Default digital ammeter with 'centre zero'.

On 09/09/2020 15:49, alan_m wrote:
On 09/09/2020 15:45, williamwright wrote:
On 09/09/2020 15:27, MikeS wrote:

What about this one which is also cheaper?
https://www.amazon.co.uk/Voltage-Cur.../dp/B015SXP9Y0


Ohhh! I think that's a better bet! Thank you!


Except you have to cut into your existing wiring and run 4 off 20A+
cables to the meter.


and is the +ve -ve indicator just the single LED labelled "charging"?

4 digit display for Volts, and it looks like a 3 digit display for Amps
The headline description says 0 to 30A, the spec says 0 to 9.99A, the
label on the back of the unit says 0 to 20A
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Default digital ammeter with 'centre zero'.

On 09/09/2020 15:49, alan_m wrote:
On 09/09/2020 15:45, williamwright wrote:
On 09/09/2020 15:27, MikeS wrote:

What about this one which is also cheaper?
https://www.amazon.co.uk/Voltage-Cur.../dp/B015SXP9Y0


Ohhh! I think that's a better bet! Thank you!


Except you have to cut into your existing wiring and run 4 off 20A+
cables to the meter.


That's not a problem.

Bill
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Default digital ammeter with 'centre zero'.

On 09/09/2020 16:03, alan_m wrote:
On 09/09/2020 15:49, alan_m wrote:
On 09/09/2020 15:45, williamwright wrote:
On 09/09/2020 15:27, MikeS wrote:

What about this one which is also cheaper?
https://www.amazon.co.uk/Voltage-Cur.../dp/B015SXP9Y0


Ohhh! I think that's a better bet! Thank you!


Except you have to cut into your existing wiring and run 4 off 20A+
cables to the meter.


and is the +ve -ve indicator just the single LED labelled "charging"?

4 digit display for Volts, and it looks like a 3 digit display for Amps
The headline description says 0 to 30A, the spec says 0 to 9.99A, the
label on the back of the unit says 0 to 20A


Ha! I'll report back when it arrives.

Bill
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Default digital ammeter with 'centre zero'.

Two meters with blocking diodes?
Brian

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Note this Signature is meaningless.!
"williamwright" wrote in message
...
I'm trying to find a digital voltmeter/ammeter that will read both the
charge and the discharge of a battery. The vast majority of the products
available will only read current 'in one direction'. I need something that
will indicate discharge by showing a minus sign, and will display the
value thereof.

I'm wondering about getting one of these. I've never used anything that
works by the hall effect though. Anyone know (a) if it will do what I want
and (b) what snags I might encounter?

https://www.amazon.co.uk/Battery-Mon...976227978&th=1

The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.


Bill





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On 09/09/2020 21:36, Brian Gaff (Sofa) wrote:
Two meters with blocking diodes?
Brian

I wondered about two LEDs!

Bill
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Default digital ammeter with 'centre zero'.

Well you used to be able to get dual colour leds that were wired back to
back to show the direction of current flow.
Brian

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On 09/09/2020 21:36, Brian Gaff (Sofa) wrote:
Two meters with blocking diodes?
Brian

I wondered about two LEDs!

Bill



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Default digital ammeter with 'centre zero'.

williamwright wrote:
On 09/09/2020 15:25, John Williamson wrote:
On 09/09/2020 15:05, williamwright wrote:

The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.

The only slight snag I have found using a clamp meter with a hall
efect sensor is that they are slightly affected by the position of the
wire inside the loop.

There will also be a constant small drain on the battery to run the
electronics.

As a bonus, the percentage reading is usually wildly inaccurate, so
you need to go by the voltage and accumualted amp hours readings..


Thanks for that. Helpful!

Bill


This article goes over some methods for estimating
SOC (State of Charge) in a battery. Once it drifts into
Kalman filters and Fuzzy logic, you know something is wrong :-)
Finding such references tells you it's a hard problem to solve.

https://www.hindawi.com/journals/isrn/2013/953792/

Your laptop has a "fuel gauge", and the chip tracks
how many times the pack has been charged. As the pack
goes through charge cycles, its amp-hour capacity changes.
Fuel gauge chips attempt to track this for you. Occasional
"calibration cycles" help the unit in your laptop pack,
from drifting too far off using its estimation methods.
The "wide range discharge cycle" of Li packs, helps this
process too.

This is an example of a fuel gauge chip. It uses the
impedance sensing method, where the "stiffness" of the
battery output is a measure of the state of charge.
This device claims up to 1% accuracy, but that's not going
to happen without a manufacturer of energy storage solutions,
programming the device. It's not magical. It's not
consumer ready. Battery gauges are meant to stay with
the pack, and that's why this one has Flash Memory inside
the chip, and it is good for 20,000 write cycles.
Perhaps it would have some parameters written after
each charge cycle. If the charge process was discontinuous
("cloudy periods" day), this thing might pooch on you after
a while, because this one is meant more for laptop cycling
(fast charge for two hours, use for N hours, repeat tomorrow).

https://www.ti.com/lit/ds/symlink/bq34z100-g1.pdf

That fuel gauge chip has up to 16 LEDs for a readout
and uses a shift register to drive more LEDs than there
are legs on the chip for drive. Display driving then, is
augmented externally. You might have noticed on some old
battery packs for laptops, they have four LEDs, and if
all four light, it's 100% full, three light, it's 75%
full. And there used to be a button, to cause the LED
display to light up (as you want the fuel gauge sleeping
when not in usage, and using microamps of current).

In your lead acid application, you'd probably need all 16 LEDs
and you would be walking the region from, say, 11 LEDs on
to 16 LEDs on. Taking the automotive battery below 11 LEDs
on state, would endanger the capacity measured as a couple
hundred charge cycles. A deep discharge lead acid, could
use more of the "range of LEDs on", but with some impact
on battery life. When the above fuel gauge is used for
LiLon, practically all the LEDs could be used. You'd
have almost the whole display range at your disposal.

*******

Now, counting LEDs seems pretty hammy, as an interface. But,
these devices either integrate coulombs, or use other methods
to keep track of charge.

Reading the open cell voltage of the battery (neither charging
nor loading), the first article says the battery has to settle
for two hours, before a valid reading can be taken. And some
battery chemistries have a rather non-linear relationship between
voltage and SOC.

In the case of lead acid, it probably is a bit more predictable,
but you need the application to be resting once a day, if you,
say, expected to "validate" your SOC once a day. It would be
pretty hard to rest the battery and make multiple determinations
using that method all during the day.

*******

It's possible to know *precisely*, what state the battery is in.
Using an electrolyte density meter (hydrometer), and temperature
correcting the measured density, tells you the state of charge.
The battery cannot be stratified, for this to work. Some batteries,
the acid "settles out", and there is a layer of acid, with a layer
of "distilled water" on top, in a sense. At an automotive shop,
they sometimes "boil" a battery with their charger, in an attempt
to reduce the stratification in the battery. (The gases released
should be vented to open air - don't keep a maintenance-type
battery in a shed, fill the shed with hydrogen, and then be
surprised at the results.)

So we could measure density, assuming the battery is reasonably
healthy. The local conditions in the cell, would be just as
dynamic as the "SOC by open circuit voltage method", in the sense
that if you were pumping 20 amps into the battery with your solar
cells, the gas bubbles rising off the plates, screw up the
density reading. You might consider then, that the battery
still has to "settle for two hours to take a reading".

And I'm not aware of anyone making a continuous density
readout as an electromechanical device of some sort.
12M H2SO4 is a pretty intense environment for a sensor
to work in.

*******

OK, so you've intuitively settled on your own coulombometric
method. Looking at the amps, counting them, working out
how many hours it will take to fill. In terms of fuel, the
battery gives back energy at a variable rate. When using
a heavy discharge, the capacity of the battery is reduced.
If running a 50mA LED off the 12V battery, well, it probably
runs for days on end, and you also "milk the max amp-hours"
from the thing that way. Maybe you get half the amp hours,
by running a 20A motor load instead. Think of it as "efficiency",
where the battery gets a bit warm and wastes some of the
energy as heat, when the motor load runs.

So if you take readings in that sense, you need to take the
readings with sufficient frequency (for integration purposes).
And you need to store the results somewhere while working this
out. Some of the Amazon products with an "amp-hour" readout,
are doing this sort of simple-minded, bipolar "amps-in" versus
"amps-out". And this is a hopeless method, because when a
motor loads the battery, the "amps-out" are a penalty on the
process. Whereas proper fuel gauge chips, they take more
specifics of the battery chemistry into account (the
academic paper up top, had some quadratic function to
estimate the relationship). But they also require someone
qualified in this sort of mumbo-jumbo, to set the parameters
for the battery type. The "bank balance method" used by the
Amazon hall probe meter, doesn't take the battery efficiency
into account when doing coulombimetry.

*******

As John Williamson points out,

"the percentage reading is usually wildly inaccurate"

he is bang on, and I hope that doing a few Googles, you'll
find other papers on these black arts. You can pretend
to build a fuel gauge, and some chemistries make this
easier than others. Perhaps even a purchased "energy bank"
would come with a fuel gauge fitted to the unit.

But if you expect to bodge this with your favorite Amazon
panel meter, it's a solar charger (all over the place on a
minute by minute basis), you would be hard pressed to
reach any precise conclusions. And the open circuit voltage
can't be used to sense SOC, because the battery might only
be sleeping at night. And you'd only get the one SOC calc
per day that way. At 3PM, you might not have a clue
precisely how much fuel is left. If the motor (pump)
runs all night, on a cyclic basis, now the open cell voltage
is modified in the negative direction. I tried this on my
car battery, and got all sorts of inappropriate info by
doing that (I would have concluded the battery had expended
the 25% energy it was safe to extract because it was
reading 11 volts or so).

As a consequence of all these observations (this isn't the
first time I've lightly researched this), my conclusion would be:

1) You're getting a plus/minus amps meter here. Time to celebrate!
This is the absolute minimum equipment for a solar charger dude.

https://www.amazon.co.uk/Battery-Mon.../dp/B07D31K454

2) Don't bother staring at the SOC display at the top. Rubbish.

3) If the current measures zero for 2 hours, measure the OC voltage
on the right, measure the air temperature around the setup,
consult temperature correction tables or use the equation,
compute the normalized to 25C OC voltage value, and determine
from that, how much fuel is left. Maybe don't run the battery
below 11V or so. The nominal might be 12.6 or so. Right after
charging, it could be 13.8V for a while, but then we allow
hours and hours to pass for the battery to settle properly,
to discover it is 12.6 at 25C and it's um, "full".

4) With Lead Acid systems and these sorts of half-assed
estimation methods, you could be off by as much as 50%.
That's my result from working with automotive batteries
casually. Temperature compensation is important. Settling
time at zero load is important (if using open circuit SOC
estimation methods).

Purchasing the above product only gives you an approximate handle
on what is going on. It's better than nothing, but it's much
worse than a properly engineered fuel gauge for the particular
battery you're using. That amazon product has the little battery
symbol in the upper left corner, but it's not subject to the
careful maths that the ti.com device is doing. And that TI device
is impedance based (or so they claim), while other ones are
colombimetric but with corrections based on the chemistry.
The corrections are different for Li than for Pb.

*******

Take a look around too, for more recommendations on end-voltage.

https://forum.allaboutcircuits.com/t...apacity.14221/

Actually, 12.7v is considered fully charged,
and 11.4v is considered fully discharged, for lead-acid batteries.

[At 25C. Don't forget temperature compensation...]

And the 11.4v value, would be measured when the battery has
rested for two hours. Makes it kinda hard, while the motor
is running, to figure out what voltage value to use to
open the relay. Maybe if the battery was still stiff at
that point, it might be reading 11.0V while running the motor,
then if stopped for two hours to rest, it might rise to 11.4V.

This site has good articles. And it has yet different
values for percentage charge.

https://batteryuniversity.com/learn/...d_acid_battery

100% 12.65 \
75% 12.45 \
50% 12.24 \___ Notice we need a 3 1/2 digit DMM for voltage.
25% 12.06 / The Amazon meter does not have 3 1/2 digits for voltage.
0% 11.89 / The current measurement requirements are different

https://batteryuniversity.com/index....tate_of_charge

Battery roulette is loads of fun. Right ?

Paul
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On 09/09/2020 21:52, Brian Gaff (Sofa) wrote:
Well you used to be able to get dual colour leds that were wired back to
back to show the direction of current flow.
Brian


But they would need approx 2V to 3V across them to work. So if you are
considering just wiring them in parallel with the shunt the shunt would
have to drop 2V across it when the equipment takes 2A. When the
equipment takes 20A the volts drop across the same shunt would be 20V,
but long after the equipment stopped working due to a lack of a power
supply from the 12V battery

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Default digital ammeter with 'centre zero'.

In uk.d-i-y williamwright wrote:
I'm trying to find a digital voltmeter/ammeter that will read both the
charge and the discharge of a battery. The vast majority of the products
available will only read current 'in one direction'. I need something
that will indicate discharge by showing a minus sign, and will display
the value thereof.

Huh!? Just about every digital meter I have ever come across works
'both ways', you just get a number (for +ve) or a number with a - sign
in front (for -ve).

My little 4 digit displays that I use with my BeagleBone black are (if
I remember right) 100mV full scale, but that means +- 100mV and they
have a - sign.

--
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In article ,
John Williamson wrote:
On 09/09/2020 15:05, williamwright wrote:


The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.

The only slight snag I have found using a clamp meter with a hall efect
sensor is that they are slightly affected by the position of the wire
inside the loop.


There will also be a constant small drain on the battery to run the
electronics.


As a bonus, the percentage reading is usually wildly inaccurate, so you
need to go by the voltage and accumualted amp hours readings..


What I've found too. Although don't have a brand new DC clamp meter.
They're fine for large currents, but near useless for measuring small
(less than say 10A) accurately. Which is mostly what I need.

--
*Why do we say something is out of whack? What is a whack? *

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To e-mail, change noise into sound.
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On 10/09/2020 10:46, Chris Green wrote:
In uk.d-i-y williamwright wrote:
I'm trying to find a digital voltmeter/ammeter that will read both the
charge and the discharge of a battery. The vast majority of the products
available will only read current 'in one direction'. I need something
that will indicate discharge by showing a minus sign, and will display
the value thereof.

Huh!? Just about every digital meter I have ever come across works
'both ways', you just get a number (for +ve) or a number with a - sign
in front (for -ve).


That's what I thought. (I've never actually tried it out for current
with my little Sinometer from Maplin though.)

--
Max Demian
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On Thu, 10 Sep 2020 11:38:54 +0100, Max Demian
wrote:

On 10/09/2020 10:46, Chris Green wrote:
In uk.d-i-y williamwright wrote:
I'm trying to find a digital voltmeter/ammeter that will read both the
charge and the discharge of a battery. The vast majority of the products
available will only read current 'in one direction'. I need something
that will indicate discharge by showing a minus sign, and will display
the value thereof.

Huh!? Just about every digital meter I have ever come across works
'both ways', you just get a number (for +ve) or a number with a - sign
in front (for -ve).


That's what I thought. (I've never actually tried it out for current
with my little Sinometer from Maplin though.)


I think Bill is conflating battery current charge / discharge with
capacity (or has two different projects).

I have a similar issue in that I have an 'in-line' power meter that
logs watts and monitors volts and amps that I want to use on a
mobility scooter but it seems to be unidirectional, in that it has a
'Source' and 'Load'.

So, whilst it will log the power drawn from the battery, I think it's
a cumulative thing till reset and wouldn't monitor any power being put
back into the battery.

I have (somewhere) something I bought a while ago that is in two
parts, with the base part being a shunt and a remote (wired or
wireless) that shows all the data. I think they were designed to be
used on the likes of narrow boats with solar panels so you could both
monitor / log the energy in / out the battery and do so remotely.

I believe that also 'learns' the battery capacity (an issue I believe
I've been seeing when charging the scooter batteries (two scooters) on
the bench rather than though the scooters themselves.

Cheers, T i m


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On Thu, 10 Sep 2020 at 04:41:09, Paul wrote:
[huge snip]
this isn't the
first time I've lightly researched this

[]
Paul


I think those of us who'd got that far through your treatise had guessed
that by then (-:

(Excellent work, by the way.)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

.... basically it's another language and unless you've studied it, it's
difficult to grasp. I know people get outraged at me saying it, but it's only
my opinion. I'm not telling people who adore Shakespeare to stop adoring it
this minute. - Jane Horrocks, in Radio Times 30 July - 5 August 2011
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In article ,
Max Demian wrote:
On 10/09/2020 10:46, Chris Green wrote:
In uk.d-i-y williamwright wrote:
I'm trying to find a digital voltmeter/ammeter that will read both the
charge and the discharge of a battery. The vast majority of the products
available will only read current 'in one direction'. I need something
that will indicate discharge by showing a minus sign, and will display
the value thereof.

Huh!? Just about every digital meter I have ever come across works
'both ways', you just get a number (for +ve) or a number with a - sign
in front (for -ve).


That's what I thought. (I've never actually tried it out for current
with my little Sinometer from Maplin though.)


Just checked with mine - and you do get a minus sign when you reverse the
leads. Not something I was sure about, as apart from with a charging
system like on a car, not usually important.

--
*HOW DO THEY GET DEER TO CROSS THE ROAD ONLY AT THOSE YELLOW ROAD SIGNS?

Dave Plowman London SW
To e-mail, change noise into sound.


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On Thu, 10 Sep 2020 14:04:40 +0100, "Dave Plowman (News)"
wrote:

snip

Huh!? Just about every digital meter I have ever come across works
'both ways', you just get a number (for +ve) or a number with a - sign
in front (for -ve).


That's what I thought. (I've never actually tried it out for current
with my little Sinometer from Maplin though.)


Just checked with mine - and you do get a minus sign when you reverse the
leads. Not something I was sure about, as apart from with a charging
system like on a car, not usually important.


I rely on it often when checking (specifically) for polarity on stuff
and make use of it when I cba to put the red lead on the +ve. ;-)

I would mentally 'note' that a battery was displaying -13.6(V) when
I'm only interested in the numbers.

It's not often you would regular read both +ve and -ve in a domestic
situation (other than when it's going at 50Hz g), unless you were
say testing a PC PSU (volts) or the current in and out a solar charged
battery.

I have a very nice multi chemistry, multi cell charger that I've got
doing some cycling of a 7.2V NiMh stick packs (RC Car type). It only
displays the current but prepends that with C or D, depending on what
part of the cycle it's on (not +/- etc).

3300mA packs, 1A charge (Delta peak), 10 min wait, 1A discharge (down
to 1V / cell), 10 min wait, charge etc. Currently on '2 Cycles'.

Cheers, T i m
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Default digital ammeter with 'centre zero'.

Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
On 09/09/2020 15:05, williamwright wrote:


The problem with using an analogue meter is that if it's scaled for 25A
(which I need) small currents such as 2A hardly move the needle.

The only slight snag I have found using a clamp meter with a hall efect
sensor is that they are slightly affected by the position of the wire
inside the loop.


There will also be a constant small drain on the battery to run the
electronics.


As a bonus, the percentage reading is usually wildly inaccurate, so you
need to go by the voltage and accumualted amp hours readings..


What I've found too. Although don't have a brand new DC clamp meter.
They're fine for large currents, but near useless for measuring small
(less than say 10A) accurately. Which is mostly what I need.


I found one that's pretty weird. It almost looks like it's autoranging,
so you can get an extra digit after the decimal point. The pictures don't
tell you here, what's in the box.

https://imall.com/product/DC-Battery.../144-170622/en

The Amazon version shows a box which might be a "transmitter".
The second box with display is the "receiver". Range
suggests it might be Bluetooth (lowest class). It uses
a Hall Probe. It has a sign bit, that shows in some
pictures and not others in the imall picture set.

https://www.amazon.com/DYKB-Wireless.../dp/B07GD3BS4B

It's quite a tease, and you might end up buying it from Aliexpress.

Like most of these products, totally untraceable, can't get a manual.
And based on other product purchases of this type, the documentation
in the box is the "single sheet, good luck" kind.

I've been trying to find someone to vend just the Hall Probe part,
in the hope of finding a lower-amps one. These things *do* work
at lower currents, because the first one I ever worked on, at
work, was at lower currents. That was a long time ago for that
project. Even back then, you could see the stuff drift a bit
with time. I was making a PCB for student lab usage (a lab
about Hall Probes).

Paul
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