Thermal Energy Harvesting power supply w/ LTC3108 and supercapacitor storage

Based on LTC3108 with 1F and 0,1F storage caps and selectable output voltages
DC/DC converter ideal for harvesting and managing surplus energy from extremely low input voltage sources such as TEGs (thermoelectric generators) and thermopiles. The step-up topology operates from input voltages as low as 20mV. It is a power source for wireless sensor applications where a Peltier element can be used on the input side.

Operation
The DC/DC converter uses a small transformer to create an ultra low input voltage step-up. It is ideally suited for low power wireless sensors and other applications in which surplus energy harvesting is used to generate system power because traditional battery power is inconvenient or impractical. The LTC3108 manages the charging and regulation of multiple outputs in a system in which the average power draw is very low, but there may be periodic pulses of higher load current required. This is typical of wireless sensor applications, where the quiescent power draw is extremely low most of the time, except for transmit bursts when circuitry is powered up to make measurements and transmit data. The converter can also be used to trickle charge a standard capacitor, super capacitor or rechargeable battery, using energy harvested from a Peltier element. A storage capacitor provides power when the input voltage source is unavailable.
This converter has three power outputs:
1. A LDO voltage regulator with fixed 2.2V output
2. Vout with selectable voltage and
3. Vout2 which follows Vout in terms of voltage level

Output voltage level is selected on the two solder jumpers, where the following combination is used:
1+3 Vout = 5V
1+4 Vout = 4.1V
2+3 Vout = 3.3V
2+4 Vout = 2.35V

In the above example, images, the selected Vout is 4.1 volts.

There are also two control signals:

1. PGood indicator signals the host micro-controller that the main output voltage is within regulation.

2. Vout2_en is an input to the converter which is used to turn on the Vout2 output.

Question From Ebay Customer:

Hello, I tried the circuit again today, with an experienced technician. Upon soldering jumpers 1 and 3 (for 5 volts) and connecting the thermoelectric module and heating it up, the output voltage is very minimal, on the order of about 0.2 or 0.3 volts. However, measuring the voltage drop across jumper 1 and ground, and jumper 3 and ground, I get 2.5 volts each for a total of 5 volts. But somehow, this voltage is not reaching the output pins. Can you please help or offer some operating procedures?
I would really appreciate your prompt reply as this is an urgent matter. Thank you for your help.

Answer:
The mentioned 2.5V is the ICs internal power rail. It powers the main ICs internal
circuitry. This voltage will not be available on the output.
If you are already observing and measuring voltages then focus on the Vout pin's voltage.
You should be able to see a slight raise of this voltage over time. It can take a while
for this voltage to reach regulation. Super capacitors are fairly large and need time to charge.

Comment From Ebay Customer.

Thank you so much for your help, my friend. I really appreciate your response. I tried this and you are correct! When the thermoelectric module provides a voltage of about 0.3V or higher, 5V is instantly available from the LTC3108.

Q
Hi, will the LTC3108 provide 5V at the Vout terminals from an input of ~200mV to Vin from a peltier tile to light an LED? Is there any other soldering required besides the 2 jumpers?

A
Yes, the board will provide 5V from 200mV input. It might take a while
for the output to reach regulated voltage, since capacitors are fairly large.

q
I asked the piece to zoom from 20 mV to 1 mV and when I connected the numbers 1 + 3 and connected the input source I was surprised that the output was 1.3 mV !!!

A
It takes time to charge the output capacitors. An hour or more.
They can observe the output voltage with DVM. It will slowly rise

q
Hi
but if the flow changes voltage plus with minus ???
Thanks ..
and what is maximum input voltage ?

A
The first question probably refers to input reverse polarity. The board can tolerate -300mV on the input, but it is not meant to be used this way. And it will not operate.
Input voltage should be kept under 500mV.

Question

Dear Electonic Nuts:

I purchased this attached board from amazon. I have trouble understanding where to connect the LED 3.0V bulb.

I’m using Peltier tiles as I pout voltage source. I believe my issue is where to connect the bulb to get 3V on the board. Please see pictures attached.

Please feel free to call me at ### or email me. I’m trying to help my daughter on her science project due tomorrow. Thanks in advance for your immediate attention to the matter.

Answer from engineer:

Please see one of the image on this page: the one with Diod.

And tell him to wait for the capacitors to charge.

Or remove the bottom two capacitors for instant LED light up.

Question:

Do you have min and max specs for Thermal Energy Harvesting power supply w/ LTC3108 and supercapacitor storage. I am trying to figure out what the maximum supported input voltage is. I am curious whether I could use a combination of thermal and solar input power.

Answer :

The maximum input voltage is 500mV. The -300mV refers to the IC itself. It should not be applied to the input. Minimum input voltage should be above 20mV.

Question:

which resister and which diod is that in the one of the image

Answer:

As far as LED goes, low forward-currend LED should be used, here are some examples:

https://www.newark.com/w/c/optoelectronics-displays/led-products/standard-single-color-leds-under-75ma?forward-current-if=2ma

Resistor, 1k4 - 1k8.

Question: 

i tried all , i charged the capacitor to its full .

but though it took days, 

After that when I connected led it discharged quickly even I connected peltier tile and created temp difference , the voltage is continusely decreasing..

Answer:

It seems too weak power source.

Add more temperature difference for higher current.

Capacitors should be charged in about an hour with high current input.

Question:

I purchased your thermal energy harvester with LTC3108 on amazon.com.  I am having a problem powering up a small 40mmx40mm 5V .18A brushless motor fan.  Here is what I have done so far.  Please let me know if I missed something.

1) solder 1+3 Vout to get 5V.
2) bridged Vout2_EN pins.
3) connect Vout2 to my motor.
4) connect Vin to my pelter module.

Note: Tested pelter module output on multimeter showing ~300mV.  Tested Vout2 on multimeter showing 25mV.

Doing this as a science project to demonstrate capability.  Can I remove capacitors to get this to work without waiting for charge?  If so, which ones? 

Answer

He is going to need the super capacitors. They shouldn't be removed.

Let me explain:

The power required to run the motor is 5V x 180mA = 0.9W

Power available from input is 300mV x 200mA (a high estimate) = 0.06W

He is trying to use 15x more power, than what is available.

In order to run the motor for a short period of time, super capacitors have to hold the accumulated energy.

They are reservoirs for the power needed to operate the motor.

One other thing - super capacitors are connected to Vout1, rather than Vout2.