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Jasen Betts wrote:
Impossible for power out to be greater than power in.
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On 2015-10-09, Robert Baer wrote:
Jasen Betts wrote:
Impossible for power out to be greater than power in.


I said it's a good deal if you don't look too closely.


Possibly it's measuring average current and voltage, and not RMS.
Or it mught just be reading innacurately. It was like $7 and
change for the pair.

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Jasen Betts wrote:
On 2015-10-09, Robert wrote:
Jasen Betts wrote:
Impossible for power out to be greater than power in.


I said it's a good deal if you don't look too closely.


Possibly it's measuring average current and voltage, and not RMS.
Or it mught just be reading innacurately. It was like $7 and
change for the pair.

....remember, if you DO see a power gain, that you cannot patent it, as
the USPTO rejects such patent claims.

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On 10/9/2015 5:38 AM, Jasen Betts wrote:
On 2015-10-09, Robert Baer wrote:
Jasen Betts wrote:
Impossible for power out to be greater than power in.


I said it's a good deal if you don't look too closely.


Possibly it's measuring average current and voltage, and not RMS.
Or it mught just be reading innacurately. It was like $7 and
change for the pair.


Or the in and out labels are in the wrong places and you have
an 87% efficient boost DC-DC converter. :-)

For what they are, it's really not too bad. 4 meters - $1.50 per
meter - with maybe +/- 3.3% error each. At that low cost, they
undoubtedly were not "factory calibrated". So if you wanted to take
the time and effort, you might be able to spin a pot and file
(or add solder to) a shunt to get better accuracy. But really,
these meters should be used just to give one a rough idea of
voltage & current.

Ed


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On 2015-10-10, ehsjr wrote:
On 10/9/2015 5:38 AM, Jasen Betts wrote:
On 2015-10-09, Robert Baer wrote:
Jasen Betts wrote:
Impossible for power out to be greater than power in.


I said it's a good deal if you don't look too closely.


Possibly it's measuring average current and voltage, and not RMS.
Or it mught just be reading innacurately. It was like $7 and
change for the pair.


Or the in and out labels are in the wrong places and you have
an 87% efficient boost DC-DC converter. :-)

For what they are, it's really not too bad. 4 meters - $1.50 per
meter - with maybe +/- 3.3% error each. At that low cost, they
undoubtedly were not "factory calibrated". So if you wanted to take
the time and effort, you might be able to spin a pot and file
(or add solder to) a shunt to get better accuracy. But really,
these meters should be used just to give one a rough idea of
voltage & current.


I'll swap them on monday and see if the error moves, and also do
some comparisons against some slightly more expensive meters.


--
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On 2015-10-10, Jasen Betts wrote:
On 2015-10-10, ehsjr wrote:
On 10/9/2015 5:38 AM, Jasen Betts wrote:
On 2015-10-09, Robert Baer wrote:
Jasen Betts wrote:
Impossible for power out to be greater than power in.

I said it's a good deal if you don't look too closely.


Possibly it's measuring average current and voltage, and not RMS.
Or it mught just be reading innacurately. It was like $7 and
change for the pair.


Or the in and out labels are in the wrong places and you have
an 87% efficient boost DC-DC converter. :-)

For what they are, it's really not too bad. 4 meters - $1.50 per
meter - with maybe +/- 3.3% error each. At that low cost, they
undoubtedly were not "factory calibrated". So if you wanted to take
the time and effort, you might be able to spin a pot and file
(or add solder to) a shunt to get better accuracy. But really,
these meters should be used just to give one a rough idea of
voltage & current.


I'll swap them on monday and see if the error moves, and also do
some comparisons against some slightly more expensive meters.


Monday update as promised.

It turns out that I was shorting out the return path with my scope's earth
clip resulting in the supply current being under-reported by about 250mA.


+10V -------+----[BUCK]---+-----.
| | | |
| | | [load]
| | | |
0V ---+----[M1]----+-----[M2]---'
| v
--- |
- | ground clip

additional isolated powersupply for meter 2 not shown.
meter 1 is powered from the +10



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On 2015-10-10, ehsjr wrote:

For what they are, it's really not too bad. 4 meters - $1.50 per
meter - with maybe +/- 3.3% error each. At that low cost, they
undoubtedly were not "factory calibrated". So if you wanted to take
the time and effort, you might be able to spin a pot and file
(or add solder to) a shunt to get better accuracy.


Thanks for suggesting that. Close inspection of the rear of he meters
revealed tiny open-frame preset pots for both voltage and current trim.
The meters now agree with my cheap multimeters, and with each other.

The pots seem fairly crummy though, I'm not sure that they will stay
set.

--
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