KEEPING UP THE POWER SUPPLY FOR THE TELEMETRY STATIONS AND SAMPLERS

KEEPING UP THE POWER SUPPLY FOR THE TELEMETRY STATIONS AND SAMPLERS

It is a priority to maintain power supply for the telemetry stations and the samplers in our sites. So, here are some of the calculations, observations I have made, pending tasks and suggestions. I will write here about the telemetry stations in Kirton.

TELEMETRY STATIONS IN KIRTON. POWER CONSIDERATIONS

A9, B9 and C9 have the following hardware components

Raven modem, CR10, AM416, Rain gauge and 2 depth sensors.

I calculated the power consumed by these components, taking the information provided in each manual.

PLEASE note that all of these calculations, considerations and suggestions are subject to review and might contain errors so I kindly recommend careful study of all the content of this document. I followed the method of power calculation used by Campbell in the CR10 manual.

AM416 Power consumption according to manual	Our requirements	Total average power draw
17 mA current draw when active	Our scan rate is 5 sec for table 1 which checks pump cycles and 15 min for table 2 which checks battery voltages	17 mA/5 + 17mA/900 = 3.42 mA

CR10 Power consumption according to manual	Our requirements	Total average power draw
0.5 mA quiescent 13 mA processing 35 mA analog measurements	Table 1 (every 5 sec) 19 processing instructions and 17 measurement instructions. Time for processing instructions= 1.3 ms16+0.1ms+0.1ms+1.2ms = 22.2 ms Time for measurement instructions= 10.2 ms17 = 173.4 ms	Average draw = [22.2 ms13mA + 173ms35mA +4.80.5mA]/5 s = 1.752mA*
	Table 2 (every 900 s) Time for processing instructions= 0.1ms+0.1ms16+0.1ms+4.4ms+53.6ms = 59.8ms Time for measurement instructions= 1.9ms+5.4ms16+5.4ms+9.6ms= 103.3ms	Average draw= [59.8ms13mA+103.3ms35mA]/900=4uA
		Total draw = 1.752mA + 4uA = 1.756mA

Sensors Power according to manual	Our requirements	Total average power draw
50 mA max	NA	It was not measured in the field and the manual only refers to the MAX power consumption.

Raven Modem Power according to manual	Our requirements	Total average power draw
50 mA when Receiving (12V) 280mA when transmiting (12V)	Data is transmitted every 900 sec. Assume maximum one minute of connection time (is actually much more less than that). Note: the Raven is in constant communication with the CDPD network. Due to the difficulty of knowing how long these CDPD level connections last, they are not considered here. Instead we assume a very long connection time of one minute when transmitting actual data to PC208 in the office.	[280mA30sec + 50mA30sec]/900 = 11mA

The total power consumption of each telemetry station would be the sum of each component power draw. which is:

[ 3.42mA + 1.756mA + 11 mA ] * 12V = 194mW (? so little????)

The stations are powered by a 12 V power supply (~45Amp/h). If the current draw was around 17mA, the battery would last theoretically for more than three months.

The battery is being charged with a 4.5W solar panel connected to the in built regulator from a control unit. My observations of this configuration are:

The battery in the telemetry stations is holding only for one month, showing that the solar panel/charger system is not putting enough power to keep the battery fully charged and that more then 194mW are definitely consumed by the system.
The 4.5W solar panel delivers to the current load (Control Unit regulator, battery) maximum 3W with full sun light, that is ~18V, ~160mA. But this is only in full sun light. During cloudy days, this power can go down to 1W or much less if it is really overcast. A rough calculation I do is:

If we suppose 1W/8 hours: ~300mW during the whole day delivered by solar panel(???): In a 12V system, 25 mA current would be delivered by regulator. The power supply is lasting one month, so the draw from the power supply is being 45Amphour/720hour = 62mA.

The balance in the battery looks like this: -62mA = Input I from charger - Output I from system

That is: -62mA = 25mA - Ioutput, so the system is consuming ~87mA!!!!, not 17mA!!!???

I do not think that power is being delivered back into the regulator. A small current goes into the regulator output resistors, but that is only 1 mA (12V/11kohm), so my thought is that the CR10/mux etc hardware consumes more of what my calculations say. Also, consider errors in the battery Amphour numbers...

In conclusion, our solar panels have to be updated. New 20W solar panels were acquired and have to be installed in the field. I recommend using the regulators (orange ones) and not the control unit regulator.

Labelle, January 17/ 2003