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Energy Harvesting

Monitoring MFC output

Using the MFC for Energy Harvesting Applications

Moderator: TPD

Monitoring MFC output

Postby drsiana » Thu Jan 18, 2018 7:13 am

I have purchased a couple of MFC modules, an EH300 and CL50, but not the Smart Charge module.
I wish to be able to see a measure of the accumulated charge in the capacitors on the EH300 or CL50 (i.e. before there is sufficient to switch the outputs for use of external load.
Can I do this with what I have ordered (by probing with high impedance oscillator probe?), or is this only possible with the smart charge? (the datasheets do not have much information on the schematics of the modules which makes it difficult to determine this).

What is my best set-up to achieve this?

Thanks.
drsiana
 
Posts: 3
Joined: Thu Jan 18, 2018 7:07 am

Re: Monitoring MFC output

Postby TPD » Thu Jan 18, 2018 12:50 pm

The two conditioners EH300 and CL-50 will not allow you to read out the onboard storage devices.
Since you want to measure the accumulated charge, the SmartCharge won't help either.

Best approach is to use a diode bridge rectifier, using low reverse current diodes, connect a 22µF low leakage capacitor to the DC output of the bridge and measure the voltage over time. The generated energy will be
E=1/2 C*U^2 the accumulated charge Q=C*U
TPD
Smart Material Support Team
---------------------------
"That's not right, it's not even wrong."
Wolfgang Pauli, 1945 Nobel Laureate - Physics.
TPD
 
Posts: 98
Joined: Tue Aug 11, 2015 12:46 pm
Location: Florida, USA

Re: Monitoring MFC output

Postby drsiana » Fri Jan 19, 2018 11:46 am

Ah! Thanks. I think I got confused because I watched a couple of your videos on youtube and the SmartCharge looks very similar (with the DIP switches) to the "energy measurement circuitry" described as one of the modules in the Energy Harvesting tutorial 1.3 which sounded like what I wanted to do.

Okay, I can build a bridge rectifier. Would the US1A-E3 diode (http://docs-europe.electrocomponents.co ... a93565.pdf) do the trick? I happen to have bought these already for another project.

One more query - can you clarify what the ENABLE pin does on the CL50? As I understand it, when HIGH, energy is stored until there is sufficient to deliver 3.3V to the output. The Youtube video says that when it reaches a certain level stored, 3.3V is supplied. Does this happen whilst ENABLE is still high?
What happens when it is LOW? As described, it says that all the energy is transferred to the output when EN is low - does this mean regardless of how much energy is available? Or that you have to switch it LOW to get the 3.3V out? (which seems to contradict the statement that 3.3V is supplied when a certain level is reached.
Or, is the ENABLE pin both an input and an output - so it is sent low by the circuitry when sufficient energy is stored.
Sorry, but it is not clear.

Thanks for your help.
drsiana
 
Posts: 3
Joined: Thu Jan 18, 2018 7:07 am

Re: Monitoring MFC output

Postby TPD » Sat Jan 20, 2018 9:53 am

Yes, this Rectifier board is part of the Energy Harvesting Evaluation Kit. We are currently not selling it as a single board but are looking into the possibility.

The DC-Reverse current of the diode you listed is waaay to high with 10µA. You need to get something below 0.1µA. Just Google it there are several types out there.

Yes, unfortunately the Enable pin on the CL-50 is often misinterpreted. The name Enable is in principle wrong it should be Discharge. This forum has many question concerning it. It is basically a leftover for testing the time between a completely empty onboard storage until the stabilized voltage is available in a specific EH configuration. The Enable just discharges all leftover energy on the board, so in a full EH application one can time when the electronics will see the driving voltage after the harvester has been dormant.
I would just leave the Pin alone (High) for what you are doing.
TPD
Smart Material Support Team
---------------------------
"That's not right, it's not even wrong."
Wolfgang Pauli, 1945 Nobel Laureate - Physics.
TPD
 
Posts: 98
Joined: Tue Aug 11, 2015 12:46 pm
Location: Florida, USA


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