TGP-751 datasheet(27/35 Pages) ETC2

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Micropelt - preliminary - Datasheet TE-CORE /RF v1.4 | Page 27

Thermoharvesting Wireless Sensor System

Micropelt TE-CORE /RF

5.6 Energy Storage Simulation

The “Capacity” of the rechargeable (battery or capaci-

tor) must be entered in mAh as indicated by the re-

spective field caption. A capacitor’s energy content

needs to be converted using the formula:

Some useful unit conversions:

CB[mAh] = (U[V] * CC[F]) / 3.6 with

U: Voltage of the considered storage unit at full

charge,

CC : Capacity of a capacitor in Farad

CB: Capacity of the same capacitor in mAh

Note: This formula does not reflect that a capacitor’s

energy can be used only between its maximum charge

level and the minimum operating voltage of the pow-

ered system. The mAh capacity given on rechargeables

usually include this restriction.

“Energy Storage” Simulation

Ensure the “Voltage” field is set to the voltage of the

considered storage unit at full charge.

The “Efficiency” field indicates the remaining percent-

age of energy from the TGP after subtracting all as-

sumed or known losses of the Energy Harvesting mod-

ule or other used power conditioning The default value

of 70% is at the lower end of the performance. If the

attached energy storage features significant charging

losses it is recommendable to include these losses by

reducing the “Efficiency” value accordingly.

Whatever “Efficiency” has been set by the user, it will

be multiplied with the gross harvesting power shown

in the TE-Power SCOPE main window. The result is

shown as “Generated TGP Power”, again assuming

that the attached load resistance is matched to that of

the power conditioning circuit. For the Energy Harvest-

ing module, load matching occurs between 7 and 10

kOhms.

The charge level of the energy storage is visual-

ized dynamically by the “Stored Energy” battery

symbol. The smaller the “Capacity” the faster the

indicated charge progress at any given harvesting in-

put.

The length of the colored bar indicates the percentage

of charge based on the set capacity. The absolute val-

ue of energy stored is displayed to the left of the bat-

tery symbol. Once the stored ener-

gy reaches the value set under

“Capacity”, e.g. 0.001 mAh, the indicator bar will hit the

top end of the scale. Doubling the “Capacity” value will

bring it back to 50% in the middle.

A green bar indicates charging in progress, red

means discharging - due to a negative “Power

balance” which occurs whenever the virtuall at-

tached load draws more energy than is currently up-

plied by the generator.

Note: Entering realistic “Capacity”

values, e.g. for a thin film battery, will cause the battery

charge indication to slow or virtually stop as it always

scales to the set “Capacity”.

“Harvesting Time” indicates the accumulated active

time of the TE-CORE /RF. If it does not transmit it does

not charge either.

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