Global 5120 - Theory of Operation

GlobalPowerTechnologies  1-5
5120
Rated Power: Theamountofpoweragen-
eratorcanbeoperatedatwhentheambient
temperatureofthesiteisexpectedtopeakat
65ºC.Astheambienttemperatureincreases
therated-powerdecreases.
Rated V
set
: TheamountofV
set
a generator
can be operated at when the ambient tem-
perature of the site is expected to peak at
65ºC.Astheambienttemperatureincreases
theratedV
set
decreases.
Open Circuit Voltage, V
OC
:  The voltage
attheterminals ofapower sourcewhenno
appreciablecurrentisowing.
1.4 Theory of Operation
A thermoelectric generator (TEG) produces
electricalpowerthroughthedirectconversion
ofheatenergyintoelectricalenergy.
This is done by joining two dissimilar, thermoelectric materials at one end and then heating
thejunctionendtoahighertemperaturethantheotherend.Thiscreatesavoltageacrossthe
coolerend.Sincethisvoltageisrelativelysmall,thejunctionsarejoinedinseriestoachieve
ausefulelectricaloutput.Ifthetemperaturedi󰀨erenceismaintained,electricalpowercanbe
deliveredtoaloadplacedinthiscircuit.
Figure 1 illustrates how this is done in the model 5120 TEG.  A thermocouple is formed by
P type and N type thermoelectric elements joined together at one end by a hot electrode.
Adjacentthermocouplesarejoinedattheotherendbycoldelectrodes.Eightythermocouples,
eachproducing84mVareconnectedinseriessothattheTEGproduces120Vat6.7Vand
18Amps.
TheTEGvoltagevariesaccordingtothetemperaturedi󰀨erenceatthethermocouplejunction.
Thehotsideofthethermocouplesismaintainedatatemperaturearound538ºC(1000ºF)by
aburnerwhich operatesonpropane, ornaturalgas. Thecold sideofthe thermocouplesis
maintainedatalowertemperature,around163ºC(325ºF),bythecoolingnswhichtransferthe
heattothesurroundingair.Thistemperaturedi󰀨erenceiscontrolledbyadjustingtheamount
offuelsuppliedtotheburner.
The TEG is supplied with a precision load resistorthatprovidestheoptimumloadcondition.
ThisresistorisusedbothinadjustingtheTEGforproperoperationandinevaluatingitsper-
formance.Thefuelowtotheburnerisadjustedsothatthepropervoltageexistsacrossthis
precisionresistor.AtthisconditiontheTEGisoperatingattheintendedjunctiontemperature
andisdeliveringmaximumpower.
Figure 1TEGDesign