Monitor the battery power

[Thang Nguyen]

Hi,

I am working on a project in which the power consumption is the critical issue. I want to use LabVIEW to measure the power consumption of the battery. I already have the Compact Fieldpoint. So what I think is I need an instrument to convert the current to the input of the FP (ADC). Could anyone tell me which device I should use to do this?

I highly appreciate your time for reading and answering this question.

Thang Nguyen.

[Chris Davis]

The AI-110 is a good module for high resolution, slow speed (1 per second at best) analog input measurements. Its manual has instructions on how to set it up to read typical industrial contol currents. I don't think that is what you want here though. If you want to measure high currents, which my be present in your battery system, you'll have to convert your current to voltage using a known value of resistor (I think). I can't tell you what resistor, it will depend on the maximum amount of current you expect to measure...

[Thang Nguyen]

Hi Chrisdavis,

I forgot about the AI-110 :headbang: . The current for the system is really small about 100mA. In this case, if I have the battery connect to the system, how should I connect to the AI-110 as a current source to measure the current?

I also need a voltage converter from 12V - 5V. Because this is a low power system, I want to look for a good converter. Could you recommend me any product?

Thank you so much,

Thang Nguyen.

QUOTE(chrisdavis @ Mar 19 2007, 09:59 PM)

The http://sine.ni.com/nips/cds/view/p/lang/en/nid/11581' target="_blank">AI-110 is a good module for high resolution, slow speed (1 per second at best) analog input measurements. Its manual has instructions on how to set it up to read typical industrial contol currents. I don't think that is what you want here though. If you want to measure high currents, which my be present in your battery system, you'll have to convert your current to voltage using a known value of resistor (I think). I can't tell you what resistor, it will depend on the maximum amount of current you expect to measure...

[Chris Davis]

QUOTE(Thang Nguyen @ Mar 20 2007, 09:20 AM)

Hi Chrisdavis,

I forgot about the AI-110 :headbang: . The current for the system is really small about 100mA. In this case, if I have the battery connect to the system, how should I connect to the AI-110 as a current source to measure the current?

I also need a voltage converter from 12V - 5V. Because this is a low power system, I want to look for a good converter. Could you recommend me any product?

Thank you so much,

Thang Nguyen.

Sorry I can't help you much more, we've stepped outside my area of expertise. You should be able to ask an electrical engineer, who would be able to help you out with the circuit design and connections needed to turn current into voltage. As for DC to DC converters, look at http://www.digikey.com' target="_blank">DigiKey, they have a ton of them, and can help you pick one out to fit your exact needs.

Sorry I can't be of more help.

Chris

[AnalogKid2DigitalMan]

QUOTE(Thang Nguyen @ Mar 20 2007, 08:20 AM)

I also need a voltage converter from 12V - 5V. Because this is a low power system, I want to look for a good converter. Could you recommend me any product?

Thang:

The good ol 7805 is a robust 5V regulator. Heres a link for a sample circuit.

http://www.eidusa.com/Electronics_Voltage_Regulator.htm''>http://www.eidusa.com/Electronics_Voltage_Regulator.htm' target="_blank">http://www.eidusa.com/Electronics_Voltage_Regulator.htm

[dthomson]

>The good ol 7805 is a robust 5V regulator. Heres a link for a sample circuit.

The 7805 is simple to use and a great solution for many situations. Keep in mind the efficiency, though. Running a 7805 off 12 volts means you'll get less than 40% efficiency, so for each Watt of 5V power you use, you'll be putting 1.5 Watts of heat into your system. A DC-DC converter, on the other hand, can be found with at least 80% efficiency, so the same 1 Watt of 5V power would only dump 250mW of waste heat. Since you mentioned that it is a low power system and you were concerned about efficiency, I thought it might be worth pointing out.

Dave T

[AnalogKid2DigitalMan]

QUOTE(dthomson @ Mar 22 2007, 12:42 PM)

>The good ol 7805 is a robust 5V regulator. Heres a link for a sample circuit.

The 7805 is simple to use and a great solution for many situations. Keep in mind the efficiency, though. Running a 7805 off 12 volts means you'll get less than 40% efficiency, so for each Watt of 5V power you use, you'll be putting 1.5 Watts of heat into your system. A DC-DC converter, on the other hand, can be found with at least 80% efficiency, so the same 1 Watt of 5V power would only dump 250mW of waste heat. Since you mentioned that it is a low power system and you were concerned about efficiency, I thought it might be worth pointing out.

Dave T

Good point Dave. I took low power to mean low current requirements on the load, not that it was power limited. Power consumption is the crirtcal issue- taken from a battery, I figured his system had other power sources to power it. Not too many details to go on.

[Thang Nguyen]

@ AnalogKid2DigitalMan

Thank you for your answer. I know about the 7805, but I usually use it to regular the power source as well as convert from 9V to 5V. My system is used in transportation with a independent battery for a long time, so I want to limit the power consumption as much as possible.

Thanks again.