PPK2 measure low power from peltier module

[larryd]

Hi,

I'm trying to measure and log the low power coming from a peltier module. (TEG seebeck effect).  In Ampere meter mode with LED for load I get nothing.  Replace TEG with button battery (40 mA according to meter) still nothing. yes without PPK2 it works.  I'm using gnd and vin pins in circuit.  PPK2 is powered over one usb cable plugged into data/power usb. Should this be working?  Or is this not how PPK2 functions?  I haven't found anything similar in any videos etc,

thank you,

Larry

[hmolesworth]

Perhaps turn on the slider on the App after setting Ampere Mode - see my notes ppk-2-not-passing-through-external-power-in-amp-mode

[larryd]

The graphs were empty (live enabled) however the dashboard window was showing values for average, max etc.  I restarted the software and it is now working as anticipated.  thank you.

[hmolesworth]

Good news, thanks for update.

Note if the peltier or other voltage generator (piezo, etc) is one of the tiny low-current versions it's possible that the loading of the PPK-II is too much for the module as there are two voltage dividers for voltage measurement to calculate current via (Vout-Vin)/Rc which is (120k + 30k) || (120K + 30k ) = 75k to  Gnd, so at 3 volts that sinks 40uA with nothing connected to Vout. I updated the diagram to show the current sense resistor as well:

// Resistor Rc for current sense is 1k0 in parallel with one or more of 110R, 11R0, 1R0 and 0R051
//
//              <- +ve Supply to DUT From VOUT                               External Battery +ve To VIN
//             +------------------------------+                             +-----------------------+
//             |                              |                             |                       |
//             |              +---------+     |                             |     +---------+       |
//             |              |     GND |     | VOUT                   VIN  |     | GND -ve |       |
//   +=========O=========+    |    +====O=====O=============================O=====O====+    |       | Battery
//   |        Vdd (+)    |    |    |    |     #----+                        |     |    |    |       | + 3 volts
//   |                   |    |    |    |     |    |Rc        AMPERE \      |     |    |    |     +-O-+
//   |                   |    |    |    |     |   +++                 \     |     |    |    |     |   |
//   |                   |    |    |    |     |   | |   +-----------O  O----#     |    |    |     |   |
//   | Device Under Test |    |    |    |     |   | |   |                   |     |    |    |     |   |
//   |       DUT         |    |    |    | 120k|   | |   |                   |120k |    |    |     |   |
//   |                   |    |    |    |    +++  +++   |   \  SOURCE      +++    |    |    |     |   |
//   |                   |    |    |    |    | |   |    |    \             | |    |    |    |     +-O-+
//   |                   |    |    |    |    | |   +----#--O  O-- PPK LDO  | |    |    |    |       | Gnd (-)
//   |                   |    |    |    |    | |                           | |    |    |    +-------+
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     |                             |     |    |
//   |                   |    |    |    |     #-- VDUT                VIN --#     |    |
//   |                   |    |    |    |     |  Sense                Sense |     |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     | 30k                     30k |     |    |
//   |                   |    |    |    +--#--+                             +--#--+    |
//   |                   |    |    |       |                                   |       |
//   |                   |    |    |     =====      <<== Common Gnd ==>>     =====     |
//   |                   |    |    |      ===           (Common -ve)          ===      |
//   |        Gnd (-)    |    |    |       =                                   =       |
//   +=========O=========+    |    +===================================================+
//             |              |     PPK-II
//             +--------------+

[larryd]

ok thanks.  I'm now seeing max 0.18µA for my first tests, enough to keep me moving forward.  thank you for your help.

[Pema]

Hi,

Jumping in on this thread...

So is my understanding correct that when using amp meter mode from a battery, the current measurement will be correct (using the Rc resistance), but another ~40uA will be taken from the battery (outside the current measurement) which goes through the two branches of 120k+30k each?

Regards,

Peter