Hi,
Maybe I posted about this last year too.
What happened in Feb 2023 was that after a night of heavy frost and
about a week after it was serviced, the battery in my car went dead!
Less than 4V measured on the battery terminals.
Opinion (here or other forums) was that this can happen, and as the
battery was 13 years old, then it was likely time for a new one anyway.
So, I bought one, fitted it, registered it with the onboard computer
stuff (what's that all about?), and it has been totally fine for a year.
The car is seldom used, maybe one two-hundred mile journey every few weeks.
Anyway, no heavy frost, but 2 days after its annual service (last
Friday) the battery is totally flat again. I still had the old battery
which was charged a year ago just to see how broken it was - it seemed
fine. I put this old one into the car today and everything is OK.
The 1 year old battery is now in my garage on charge.

I have a current clamp meter that I stuck on the negative lead to the
battery and measured the current. It idles at about 4-5A, and after half
an hour it is down to about 0.08A (80mA), after various items go into
power down states.
How long would a battery hold a decent charge at a discharge rate of
80mA? Is 80mA reasonable?

But the question is, is it simply a coincidence that after a service the
battery dies, or is there something that the service does that leaves an
item powered up when the car is locked? The headlights are always set to
OFF after a service (not left on AUTO).
Thanks for reading, and sorry for the long post, but hopefully I've
covered all relevant points.

Oh, and I just remembered, there are other wires going to the battery
terminals other than the chunky red and black ones. Maybe there is
something else that takes power that I'm not measuring. I can't get ALL
of the wires into the clamp meter.

Grumps wrote:

> after a night of heavy frost and
> about a week after it was serviced, the battery in my car went dead!
> Less than 4V measured on the battery terminals.
> Opinion (here or other forums) was that this can happen, and as the
> battery was 13 years old, then it was likely time for a new one anyway.
> So, I bought one, fitted it, registered it with the onboard computer
> stuff (what's that all about?)

I think the "coding" is just a hint to the battery module that it should
record the date the battery was changed, and keep track of the ageing.

> and it has been totally fine for a year.
> The car is seldom used, maybe one two-hundred mile journey every few weeks.
> Anyway, no heavy frost, but 2 days after its annual service (last
> Friday) the battery is totally flat again.

The stop/start system on my A5 started "disengaging", VCDS didn't show
an eact reason, consensus on forums was "shagged battery does that",
many suppliers online were out of stock, so ventured to Halfords, their
system took reg plate and decided (wrongly what I needed) took it back
and swapped it for correct physical size.

Swapped battery (jump leads to neighbour's car to prevent any loss of
power/settings) recoded battery with VCDS it was about 2Ah larger
capacity, the computer noticed the change, still showed stop/start
disengaged, decided to let it settle a few days, after some italian
tune-up runs it would sometimes stay engaged, but still isn't entirely
happy ...

Car is perfectly happy to start, run headlights, heated rear screen etc,
so battery itself is happy, just the stop/start.

On Sun, 7 Apr 2024 18:00:38 +0100, Grumps <not@here.com> wrote:

>Hi,
>Maybe I posted about this last year too.
>What happened in Feb 2023 was that after a night of heavy frost and
>about a week after it was serviced, the battery in my car went dead!
>Less than 4V measured on the battery terminals.
>Opinion (here or other forums) was that this can happen, and as the
>battery was 13 years old, then it was likely time for a new one anyway.
>So, I bought one, fitted it, registered it with the onboard computer
>stuff (what's that all about?), and it has been totally fine for a year.
>The car is seldom used, maybe one two-hundred mile journey every few weeks.
>Anyway, no heavy frost, but 2 days after its annual service (last
>Friday) the battery is totally flat again. I still had the old battery
>which was charged a year ago just to see how broken it was - it seemed
>fine. I put this old one into the car today and everything is OK.
>The 1 year old battery is now in my garage on charge.
>
>I have a current clamp meter that I stuck on the negative lead to the
>battery and measured the current. It idles at about 4-5A, and after half
>an hour it is down to about 0.08A (80mA), after various items go into
>power down states.
>How long would a battery hold a decent charge at a discharge rate of
>80mA? Is 80mA reasonable?
>
>But the question is, is it simply a coincidence that after a service the
>battery dies, or is there something that the service does that leaves an
>item powered up when the car is locked? The headlights are always set to
>OFF after a service (not left on AUTO).
>Thanks for reading, and sorry for the long post, but hopefully I've
>covered all relevant points.
>
>Oh, and I just remembered, there are other wires going to the battery
>terminals other than the chunky red and black ones. Maybe there is
>something else that takes power that I'm not measuring. I can't get ALL
>of the wires into the clamp meter.

I have a Kia Picanto, brand new a year ago. Don't use it a lot. Came
out one morning to find the battery pancake flat. Voltage down to ~5
volts. I didn't know they would ever go that low. Recharged it with my
battery charger OK. I now trickle charge it every Sunday for one hour.
Like you, the current drain by the system when it's parked in the
garage and everything is nominally OFF, is minimal, so I'm still
puzzled as to why it happened, but I'm determined not to let it happen
again.

--
Chris

Chris Hogg <me@privacy.net> wrote:

> I have a Kia Picanto, brand new a year ago. Don't use it a lot. Came
> out one morning to find the battery pancake flat. Voltage down to ~5
> volts. I didn't know they would ever go that low. Recharged it with my
> battery charger OK. I now trickle charge it every Sunday for one hour.
> Like you, the current drain by the system when it's parked in the
> garage and everything is nominally OFF, is minimal, so I'm still
> puzzled as to why it happened, but I'm determined not to let it happen
> again.

I think random software glitches are probably responsible for these events
that seem to hit many modern cars randomly. I’ve had it happen in my Kia
for no good reason and after a recharge all seems fine.

Tim

--
Please don't feed the trolls

There was a mention in the MOT testing manual of a change of proceedure for
testing some models of car. Things were left powered after plugging in to
the OBD socket leading to battery drain.

Grumps <not@here.com> wrote:

> Hi, Maybe I posted about this last year too. What happened in Feb 2023 was
> that after a night of heavy frost and about a week after it was serviced,
> the battery in my car went dead! Less than 4V measured on the battery
> terminals. Opinion (here or other forums) was that this can happen, and as
> the battery was 13 years old, then it was likely time for a new one
> anyway. So, I bought one, fitted it, registered it with the onboard
> computer stuff (what's that all about?), and it has been totally fine for
> a year. The car is seldom used, maybe one two-hundred mile journey every
> few weeks. Anyway, no heavy frost, but 2 days after its annual service
> (last Friday) the battery is totally flat again. I still had the old
> battery which was charged a year ago just to see how broken it was - it
> seemed fine. I put this old one into the car today and everything is OK.
> The 1 year old battery is now in my garage on charge.
>
> I have a current clamp meter that I stuck on the negative lead to the
> battery and measured the current. It idles at about 4-5A, and after half
> an hour it is down to about 0.08A (80mA), after various items go into
> power down states. How long would a battery hold a decent charge at a
> discharge rate of 80mA? Is 80mA reasonable?
>
> But the question is, is it simply a coincidence that after a service the
> battery dies, or is there something that the service does that leaves an
> item powered up when the car is locked? The headlights are always set to
> OFF after a service (not left on AUTO). Thanks for reading, and sorry for
> the long post, but hopefully I've covered all relevant points.
>
> Oh, and I just remembered, there are other wires going to the battery
> terminals other than the chunky red and black ones. Maybe there is
> something else that takes power that I'm not measuring. I can't get ALL of
> the wires into the clamp meter.
>
>
>

--
braind

On 07/04/2024 18:00, Grumps wrote:
> How long would a battery hold a decent charge at a discharge rate of
> 80mA? Is 80mA reasonable?

Appx 1000 hours. which is around 40 days.
80mA is NOT reasonable. should less than 10.

>
> But the question is, is it simply a coincidence that after a service the
> battery dies, or is there something that the service does that leaves an
> item powered up when the car is locked? The headlights are always set to
> OFF after a service (not left on AUTO).

Every time I took my car into a certain garage a strange fault would
appear a few weeks later....

--
“Progress is precisely that which rules and regulations did not foresee,”

– Ludwig von Mises

On 07/04/2024 19:40, Chris Hogg wrote:
> On Sun, 7 Apr 2024 18:00:38 +0100, Grumps <not@here.com> wrote:
>
>> Hi,
>> Maybe I posted about this last year too.
>> What happened in Feb 2023 was that after a night of heavy frost and
>> about a week after it was serviced, the battery in my car went dead!
>> Less than 4V measured on the battery terminals.
>> Opinion (here or other forums) was that this can happen, and as the
>> battery was 13 years old, then it was likely time for a new one anyway.
>> So, I bought one, fitted it, registered it with the onboard computer
>> stuff (what's that all about?), and it has been totally fine for a year.
>> The car is seldom used, maybe one two-hundred mile journey every few weeks.
>> Anyway, no heavy frost, but 2 days after its annual service (last
>> Friday) the battery is totally flat again. I still had the old battery
>> which was charged a year ago just to see how broken it was - it seemed
>> fine. I put this old one into the car today and everything is OK.
>> The 1 year old battery is now in my garage on charge.
>>
>> I have a current clamp meter that I stuck on the negative lead to the
>> battery and measured the current. It idles at about 4-5A, and after half
>> an hour it is down to about 0.08A (80mA), after various items go into
>> power down states.
>> How long would a battery hold a decent charge at a discharge rate of
>> 80mA? Is 80mA reasonable?
>>
>> But the question is, is it simply a coincidence that after a service the
>> battery dies, or is there something that the service does that leaves an
>> item powered up when the car is locked? The headlights are always set to
>> OFF after a service (not left on AUTO).
>> Thanks for reading, and sorry for the long post, but hopefully I've
>> covered all relevant points.
>>
>> Oh, and I just remembered, there are other wires going to the battery
>> terminals other than the chunky red and black ones. Maybe there is
>> something else that takes power that I'm not measuring. I can't get ALL
>> of the wires into the clamp meter.
>
> I have a Kia Picanto, brand new a year ago. Don't use it a lot. Came
> out one morning to find the battery pancake flat. Voltage down to ~5
> volts. I didn't know they would ever go that low. Recharged it with my
> battery charger OK. I now trickle charge it every Sunday for one hour.
> Like you, the current drain by the system when it's parked in the
> garage and everything is nominally OFF, is minimal, so I'm still
> puzzled as to why it happened, but I'm determined not to let it happen
> again.

It's just a PITA having to trickle every w/e - just in case it decides
to flatten the battery.
Maybe I can add a solar panel to do the charging.

On 07/04/2024 19:48, Tim+ wrote:
> Chris Hogg <me@privacy.net> wrote:
>
>> I have a Kia Picanto, brand new a year ago. Don't use it a lot. Came
>> out one morning to find the battery pancake flat. Voltage down to ~5
>> volts. I didn't know they would ever go that low. Recharged it with my
>> battery charger OK. I now trickle charge it every Sunday for one hour.
>> Like you, the current drain by the system when it's parked in the
>> garage and everything is nominally OFF, is minimal, so I'm still
>> puzzled as to why it happened, but I'm determined not to let it happen
>> again.
>
> I think random software glitches are probably responsible for these events
> that seem to hit many modern cars randomly. I’ve had it happen in my Kia
> for no good reason and after a recharge all seems fine.

I guess so. Thanks for confirming it's not just me.

On 07/04/2024 21:30, me9 wrote:
> There was a mention in the MOT testing manual of a change of proceedure for
> testing some models of car. Things were left powered after plugging in to
> the OBD socket leading to battery drain.
>
>
> Grumps <not@here.com> wrote:
>
>> Hi, Maybe I posted about this last year too. What happened in Feb 2023 was
>> that after a night of heavy frost and about a week after it was serviced,
>> the battery in my car went dead! Less than 4V measured on the battery
>> terminals. Opinion (here or other forums) was that this can happen, and as
>> the battery was 13 years old, then it was likely time for a new one
>> anyway. So, I bought one, fitted it, registered it with the onboard
>> computer stuff (what's that all about?), and it has been totally fine for
>> a year. The car is seldom used, maybe one two-hundred mile journey every
>> few weeks. Anyway, no heavy frost, but 2 days after its annual service
>> (last Friday) the battery is totally flat again. I still had the old
>> battery which was charged a year ago just to see how broken it was - it
>> seemed fine. I put this old one into the car today and everything is OK.
>> The 1 year old battery is now in my garage on charge.
>>
>> I have a current clamp meter that I stuck on the negative lead to the
>> battery and measured the current. It idles at about 4-5A, and after half
>> an hour it is down to about 0.08A (80mA), after various items go into
>> power down states. How long would a battery hold a decent charge at a
>> discharge rate of 80mA? Is 80mA reasonable?
>>
>> But the question is, is it simply a coincidence that after a service the
>> battery dies, or is there something that the service does that leaves an
>> item powered up when the car is locked? The headlights are always set to
>> OFF after a service (not left on AUTO). Thanks for reading, and sorry for
>> the long post, but hopefully I've covered all relevant points.
>>
>> Oh, and I just remembered, there are other wires going to the battery
>> terminals other than the chunky red and black ones. Maybe there is
>> something else that takes power that I'm not measuring. I can't get ALL of
>> the wires into the clamp meter.

Have you got any further info on that? Seems like it could lead to the
cause.

On 08/04/2024 08:58, The Natural Philosopher wrote:
> On 07/04/2024 18:00, Grumps wrote:
>> How long would a battery hold a decent charge at a discharge rate of
>> 80mA? Is 80mA reasonable?
>
> Appx 1000 hours. which is around 40 days.
> 80mA is NOT reasonable. should less than 10.

So there must be something draining far more than 80mA as the battery
went flat in less than two days.

>
>>
>> But the question is, is it simply a coincidence that after a service
>> the battery dies, or is there something that the service does that
>> leaves an item powered up when the car is locked? The headlights are
>> always set to OFF after a service (not left on AUTO).
>
> Every time I took my car into a certain garage a strange fault would
> appear a few weeks later....

Care to elaborate, or was it the start of some humour?

On 4/8/2024 11:28 AM, Grumps wrote:
> On 08/04/2024 08:58, The Natural Philosopher wrote:
>> On 07/04/2024 18:00, Grumps wrote:
>>> How long would a battery hold a decent charge at a discharge rate of 80mA? Is 80mA reasonable?
>>
>> Appx 1000 hours. which is around 40 days.
>> 80mA is NOT reasonable. should less than 10.
>
> So there must be something draining far more than 80mA as the battery went flat in less than two days.
>
>>
>>>
>>> But the question is, is it simply a coincidence that after a service the battery dies, or is there something that the service does that leaves an item powered up when the car is locked? The headlights are always set to OFF after a service (not left on AUTO).
>>
>> Every time I took my car into a certain garage a strange fault would appear a few weeks later....
>
> Care to elaborate, or was it the start of some humour?
>

It could be factual, if a service visit requires connection
of the vehicle, to their bus tester that connects to the
comms bus. If it leaves any of the car computers in a
high power state, that might be sufficient to drain the battery.

I could find a report today, where the entertainment system
was drawing 6 amps from the battery after the car was off.
And after things where shut down in a particular order,
the current drain dropped to 0.140 amps. Which is still not
spectacularly good, and should be fixed. But at least that
won't flatten the battery by the next morning. Just leave
the battery "half-there".

Using a clamp-on ammeter, my car was somewhere around 20mA,
but the ammeter did not have a sensitive enough range for the
determination. Hall probe sensors can be made more sensitive
than that, because I made some circuit boards for that
in one of my jobs.

The reason you use a clamp on meter, is if you slide the battery
cable off the terminal and insert a regular multimeter on amps
into the circuit, the act of adding the meter to the circuit,
causes all the computers to reset and "removes the flaky scenario".
This is why you try not to disturb the "car full of computers",
and measure it in a non-disturbing way. In this way, you can be
an "impartial observer", and watch some computer go from
full-power to snooze to sleep to "Off" (which likely is not off).

Nothing is as "Off" as an older car was. The current on those
only needed to be enough to run the car clock, which is 10uA
(with the display dark).

Paul

On 09/04/2024 07:54, Paul wrote:
> On 4/8/2024 11:28 AM, Grumps wrote:
>> On 08/04/2024 08:58, The Natural Philosopher wrote:
>>> On 07/04/2024 18:00, Grumps wrote:
>>>> How long would a battery hold a decent charge at a discharge rate of 80mA? Is 80mA reasonable?
>>>
>>> Appx 1000 hours. which is around 40 days.
>>> 80mA is NOT reasonable. should less than 10.
>>
>> So there must be something draining far more than 80mA as the battery went flat in less than two days.
>>
>>>
>>>>
>>>> But the question is, is it simply a coincidence that after a service the battery dies, or is there something that the service does that leaves an item powered up when the car is locked? The headlights are always set to OFF after a service (not left on AUTO).
>>>
>>> Every time I took my car into a certain garage a strange fault would appear a few weeks later....
>>
>> Care to elaborate, or was it the start of some humour?
>>
>
> It could be factual, if a service visit requires connection
> of the vehicle, to their bus tester that connects to the
> comms bus. If it leaves any of the car computers in a
> high power state, that might be sufficient to drain the battery.
>
> I could find a report today, where the entertainment system
> was drawing 6 amps from the battery after the car was off.
> And after things where shut down in a particular order,
> the current drain dropped to 0.140 amps. Which is still not
> spectacularly good, and should be fixed. But at least that
> won't flatten the battery by the next morning. Just leave
> the battery "half-there".
>
> Using a clamp-on ammeter, my car was somewhere around 20mA,
> but the ammeter did not have a sensitive enough range for the
> determination. Hall probe sensors can be made more sensitive
> than that, because I made some circuit boards for that
> in one of my jobs.
>
> The reason you use a clamp on meter, is if you slide the battery
> cable off the terminal and insert a regular multimeter on amps
> into the circuit, the act of adding the meter to the circuit,
> causes all the computers to reset and "removes the flaky scenario".
> This is why you try not to disturb the "car full of computers",
> and measure it in a non-disturbing way. In this way, you can be
> an "impartial observer", and watch some computer go from
> full-power to snooze to sleep to "Off" (which likely is not off).
>
> Nothing is as "Off" as an older car was. The current on those
> only needed to be enough to run the car clock, which is 10uA
> (with the display dark).
>
> Paul

I'll probably have to wait until next year when it has its service. Then
I can measure the battery current with my clamp. See if it holds at a
high reading when it's supposed to be asleep.

Grumps <not@here.com> wrote:
> >
> > Nothing is as "Off" as an older car was. The current on those
> > only needed to be enough to run the car clock, which is 10uA
> > (with the display dark).
> >
>
> I'll probably have to wait until next year when it has its service. Then
> I can measure the battery current with my clamp. See if it holds at a
> high reading when it's supposed to be asleep.
>
I wouldn't have thought a clamp meter is going to tell you much down
at the amp or so that you're concerned about.

--
Chris Green
·

On 09/04/2024 17:07, Chris Green wrote:
> Grumps <not@here.com> wrote:
>>>
>>> Nothing is as "Off" as an older car was. The current on those
>>> only needed to be enough to run the car clock, which is 10uA
>>> (with the display dark).
>>>
>>
>> I'll probably have to wait until next year when it has its service. Then
>> I can measure the battery current with my clamp. See if it holds at a
>> high reading when it's supposed to be asleep.
>>
> I wouldn't have thought a clamp meter is going to tell you much down
> at the amp or so that you're concerned about.

I would say 10s mA would be the threshold for a clamp meter.

Fredxx <fredxx@spam.invalid> wrote:
> On 09/04/2024 17:07, Chris Green wrote:
> > Grumps <not@here.com> wrote:
> >>>
> >>> Nothing is as "Off" as an older car was. The current on those
> >>> only needed to be enough to run the car clock, which is 10uA
> >>> (with the display dark).
> >>>
> >>
> >> I'll probably have to wait until next year when it has its service. Then
> >> I can measure the battery current with my clamp. See if it holds at a
> >> high reading when it's supposed to be asleep.
> >>
> > I wouldn't have thought a clamp meter is going to tell you much down
> > at the amp or so that you're concerned about.
>
> I would say 10s mA would be the threshold for a clamp meter.
>
Is that just a typo "10s mA"? If you mean 10mA then I think it's
pushing beyond the limit.

A typical DC clamp meter will have a smallest full scale range of 40
amps. Looking at one from CPC it's 40amps at ±(2.5 % + 5 digits).
2.5% of 40 amps is 1 amp. Very often it's down near zero current that
one finds it's almost impossible to decide which way the current is
going even!

--
Chris Green
·

On 07/04/2024 18:00, Grumps wrote:
> I have a current clamp meter that I stuck on the negative lead to the
> battery and measured the current. It idles at about 4-5A, and after half
> an hour it is down to about 0.08A (80mA), after various items go into
> power down states.
> How long would a battery hold a decent charge at a discharge rate of
> 80mA? Is 80mA reasonable?

80mA means the battery should be discharged to around half it's
capacity, after around 300 hours, if not run to recharge, or four weeks.
Short runs, after cranking over, do not really help - how frequently
does it do the 200mile run?

The garages, might have had it sat a while, with thing left on,
flattening the battery even more.

I had a discharge of around that level, eventually traced to my voltage
sensing relay, clicking on and off, which would flatten my battery if
parked for an extended period. After resolving it, parked up, it drops
to 18mA.

On 07/04/2024 19:40, Chris Hogg wrote:
> I have a Kia Picanto, brand new a year ago. Don't use it a lot. Came
> out one morning to find the battery pancake flat. Voltage down to ~5
> volts. I didn't know they would ever go that low. Recharged it with my
> battery charger OK. I now trickle charge it every Sunday for one hour.
> Like you, the current drain by the system when it's parked in the
> garage and everything is nominally OFF, is minimal, so I'm still
> puzzled as to why it happened, but I'm determined not to let it happen
> again.

Always when parked in my garage, I plug the car into a charger. The
charger is switched on each day, by Alexa, for 20 minutes.

The charge cable hangs from the garage roof, with a ciggy plug, by the
drivers door. To ensure it makes a good connection, I use a 555 time IC,
which flashes an LED, when the lead 'sees' 12v. Basically - plug in, and
check the LED is flashing and forget it.

On 07/04/2024 18:00, Grumps wrote:
> Oh, and I just remembered, there are other wires going to the battery
> terminals other than the chunky red and black ones. Maybe there is
> something else that takes power that I'm not measuring. I can't get ALL
> of the wires into the clamp meter.

You can measure them individually, and add the amounts together.

On 09/04/2024 07:54, Paul wrote:
> The reason you use a clamp on meter, is if you slide the battery
> cable off the terminal and insert a regular multimeter on amps
> into the circuit, the act of adding the meter to the circuit,
> causes all the computers to reset and "removes the flaky scenario".
> This is why you try not to disturb the "car full of computers",
> and measure it in a non-disturbing way. In this way, you can be
> an "impartial observer", and watch some computer go from
> full-power to snooze to sleep to "Off" (which likely is not off).

Handily, my car has a removable link in the main power cable, for all
but the starter. Connect an ammeter in series with the link, disconnect
the link, and you can precisely measure down to 1mA.

On 09/04/2024 20:09, Chris Green wrote:
> Fredxx <fredxx@spam.invalid> wrote:
>> On 09/04/2024 17:07, Chris Green wrote:
>>> Grumps <not@here.com> wrote:
>>>>>
>>>>> Nothing is as "Off" as an older car was. The current on those
>>>>> only needed to be enough to run the car clock, which is 10uA
>>>>> (with the display dark).
>>>>>
>>>>
>>>> I'll probably have to wait until next year when it has its service. Then
>>>> I can measure the battery current with my clamp. See if it holds at a
>>>> high reading when it's supposed to be asleep.
>>>>
>>> I wouldn't have thought a clamp meter is going to tell you much down
>>> at the amp or so that you're concerned about.
>>
>> I would say 10s mA would be the threshold for a clamp meter.
>>
> Is that just a typo "10s mA"? If you mean 10mA then I think it's
> pushing beyond the limit.

I meant plural of 10

> A typical DC clamp meter will have a smallest full scale range of 40
> amps. Looking at one from CPC it's 40amps at ±(2.5 % + 5 digits).
> 2.5% of 40 amps is 1 amp. Very often it's down near zero current that
> one finds it's almost impossible to decide which way the current is
> going even!

It can normally be nulled, to a few 10s of mA. Or at least I can with a
couple of meters I have.

On 09/04/2024 20:09, Chris Green wrote:
> Fredxx <fredxx@spam.invalid> wrote:
>> On 09/04/2024 17:07, Chris Green wrote:
>>> Grumps <not@here.com> wrote:
>>>>>
>>>>> Nothing is as "Off" as an older car was. The current on those
>>>>> only needed to be enough to run the car clock, which is 10uA
>>>>> (with the display dark).
>>>>>
>>>>
>>>> I'll probably have to wait until next year when it has its service. Then
>>>> I can measure the battery current with my clamp. See if it holds at a
>>>> high reading when it's supposed to be asleep.
>>>>
>>> I wouldn't have thought a clamp meter is going to tell you much down
>>> at the amp or so that you're concerned about.
>>
>> I would say 10s mA would be the threshold for a clamp meter.
>>
> Is that just a typo "10s mA"? If you mean 10mA then I think it's
> pushing beyond the limit.
>
> A typical DC clamp meter will have a smallest full scale range of 40
> amps. Looking at one from CPC it's 40amps at ±(2.5 % + 5 digits).
> 2.5% of 40 amps is 1 amp. Very often it's down near zero current that
> one finds it's almost impossible to decide which way the current is
> going even!
>

That's not how a typical specification reads

It's 2.5% of the amperage being measured (what's being displayed). So if
you are measuring 100mA that part of the error would be +/-2.5mA

But what kills the accuracy at low currents is the +/- 5 digits.

If the lowest range was 40A full scale and the meter had a resolution of
2 decimal places then this error would be +/-50mA and if the meter only
had a resolution to 1 decimal place this error would be 500mA.

As you indicate, other factors may play some part in the measurement
with a clamp meter and attempting to measure 10mA on a meter with a
lowest full scale range of 40A is probably an exercise in futility.

The positioning of the wire(s) within the clamp opening can also
increase the inaccuracy of the reading especially if the wires are much
smaller than the opening.

The cheap clamp meters read AC current and not DC as would be seen from
the steady state drain current from a battery.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

alan_m <junk@admac.myzen.co.uk> wrote:
> On 09/04/2024 20:09, Chris Green wrote:
> > Fredxx <fredxx@spam.invalid> wrote:
> >> On 09/04/2024 17:07, Chris Green wrote:
> >>> Grumps <not@here.com> wrote:
> >>>>>
> >>>>> Nothing is as "Off" as an older car was. The current on those
> >>>>> only needed to be enough to run the car clock, which is 10uA
> >>>>> (with the display dark).
> >>>>>
> >>>>
> >>>> I'll probably have to wait until next year when it has its service. Then
> >>>> I can measure the battery current with my clamp. See if it holds at a
> >>>> high reading when it's supposed to be asleep.
> >>>>
> >>> I wouldn't have thought a clamp meter is going to tell you much down
> >>> at the amp or so that you're concerned about.
> >>
> >> I would say 10s mA would be the threshold for a clamp meter.
> >>
> > Is that just a typo "10s mA"? If you mean 10mA then I think it's
> > pushing beyond the limit.
> >
> > A typical DC clamp meter will have a smallest full scale range of 40
> > amps. Looking at one from CPC it's 40amps at ±(2.5 % + 5 digits).
> > 2.5% of 40 amps is 1 amp. Very often it's down near zero current that
> > one finds it's almost impossible to decide which way the current is
> > going even!
> >
>
>
> That's not how a typical specification reads
>
> It's 2.5% of the amperage being measured (what's being displayed). So if
> you are measuring 100mA that part of the error would be +/-2.5mA
>
Surely it means 2.5% of full scale, that's the normal meaning isn't it?

--
Chris Green
·

Chris Green <cl@isbd.net> wrote:
> alan_m <junk@admac.myzen.co.uk> wrote:
> > On 09/04/2024 20:09, Chris Green wrote:
> > > Fredxx <fredxx@spam.invalid> wrote:
> > >> On 09/04/2024 17:07, Chris Green wrote:
> > >>> Grumps <not@here.com> wrote:
> > >>>>>
> > >>>>> Nothing is as "Off" as an older car was. The current on those
> > >>>>> only needed to be enough to run the car clock, which is 10uA
> > >>>>> (with the display dark).
> > >>>>>
> > >>>>
> > >>>> I'll probably have to wait until next year when it has its service. Then
> > >>>> I can measure the battery current with my clamp. See if it holds at a
> > >>>> high reading when it's supposed to be asleep.
> > >>>>
> > >>> I wouldn't have thought a clamp meter is going to tell you much down
> > >>> at the amp or so that you're concerned about.
> > >>
> > >> I would say 10s mA would be the threshold for a clamp meter.
> > >>
> > > Is that just a typo "10s mA"? If you mean 10mA then I think it's
> > > pushing beyond the limit.
> > >
> > > A typical DC clamp meter will have a smallest full scale range of 40
> > > amps. Looking at one from CPC it's 40amps at ±(2.5 % + 5 digits).
> > > 2.5% of 40 amps is 1 amp. Very often it's down near zero current that
> > > one finds it's almost impossible to decide which way the current is
> > > going even!
> > >
> >
> >
> > That's not how a typical specification reads
> >
> > It's 2.5% of the amperage being measured (what's being displayed). So if
> > you are measuring 100mA that part of the error would be +/-2.5mA
> >
> Surely it means 2.5% of full scale, that's the normal meaning isn't it?
>
No, sorry, I'm talking rubbish! I obviously had my analogue hat on.

However I've never found my (several) clamp meters very useful at
anything below an amp or so. They are always heavily influanced by
the placement of the meter jaws around the wire and by the proximity
(or otherwise) of other wires in the vicinity. In addition for DC you
have to clear any initial offset, presumably due to local magnetic
fields.

--
Chris Green
·

Chris Green <cl@isbd.net> writes:

> A typical DC clamp meter will have a smallest full scale range of 40
> amps. Looking at one from CPC it's 40amps at ±(2.5 % + 5 digits).
> 2.5% of 40 amps is 1 amp. Very often it's down near zero current that
> one finds it's almost impossible to decide which way the current is
> going even!

My UNI-T UT210E has a 2A range, resolution 1mA. Look at the manual,
rather than the Specifications page which is general for several models.

https://meters.uni-trend.com/product/ut210-series/#Docs

As seen on Big Clive's Youtube channel, about £40 on eBay.

With a split open USB cable plugged into a fully charged powerbank,
it shows 4mA to run the display and backlight, dropping back to 0
when unplugged.

--
Alan J. Wylie https://www.wylie.me.uk/

Dance like no-one's watching. / Encrypt like everyone is.
Security is inversely proportional to convenience

On 09/04/2024 17:07, Chris Green wrote:
> Grumps <not@here.com> wrote:
>>>
>>> Nothing is as "Off" as an older car was. The current on those
>>> only needed to be enough to run the car clock, which is 10uA
>>> (with the display dark).
>>>
>>
>> I'll probably have to wait until next year when it has its service. Then
>> I can measure the battery current with my clamp. See if it holds at a
>> high reading when it's supposed to be asleep.
>>
> I wouldn't have thought a clamp meter is going to tell you much down
> at the amp or so that you're concerned about.
>

The clamp meter has a resolution of 10mA in the 60A range setting.
Testing the accuracy with my current-limiting bench PSU and a normal DMM
seems reasonably promising.
With the PSU set to 100mA, the DMM reads 100mA and the clamp (mostly)
says 0.11A.
(mostly = the reading is not stable, so I took the most common reading)