Mains to 9V DC converter

Thread Starter

garretkelly

Joined Jun 14, 2010
3
I am using an Extech ML720 Multimeter/data logger to measure and log current data from a solar panel. There is no power jack and i have to change and recharge batteries every 3 days.

I am wondering can I connect a DC power supply instead of the battery, or will it damage the meter. The meter uses a 9V DC battery and in the spec it says the power consumption is "2.7mA typical"

I have a "universal AC-DC Adaptor" model "PW00134" but no manufacturers name. I picked it up pretty cheaply a few years ago. It has a switch to change the output to 3V, 4.5V, 6V, 7.5V, 9V or 12V. It also has a power rating of 8.7W and a current rating of "300mA, 3.6V (max)"

If I connect to the mains and check the OC voltage I measure about 12V when set to 9V and measure about 9V when set to 6V.

If I plug into the mutimeter do you think it will blow it? Will it work? What voltage setting do you think I should use (if I should use it at all). mains supply is 230V 50Hz.
 

bertus

Joined Apr 5, 2008
22,266
Hello,

Your powersupply is probably an unregulated one.
You can use a LM317 for the stabalization.
See the datasheet for more info.

Bertus
 

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bertus

Joined Apr 5, 2008
22,266
Hello,

It would work set on the 6 Volts setting (that delivers 9 Volts),
but it is better to have a regulated voltage
as the unregulated might influence the stability of the measurement.

Bertus
 

mcgyvr

Joined Oct 15, 2009
5,394
Try it on 6V but read the voltage again once it is hooked up to see what it is really outputting with the load attached. It might read 9V now but under load it might drop back down closer to the switch setting.
 

retched

Joined Dec 5, 2009
5,208
If you care about the data you are logging, you will want to regulate the power.

Even minor fluctuations can change your ADC rates and accuracy.

You can use the 317 or even get yourself a 7809. That can take your unregulated power and regulate it.

You can even whip up a little 9v battery sized PCB to connect the adapter and the 7809 to. That way it is nice and neat.
 

Audioguru

Joined Dec 20, 2007
11,248
If you care about the data you are logging, you will want to regulate the power.
What are you talking about??
You don't regulate the power. Instead, you regulate the voltage with a voltage regulator IC. You can also limit the current if you want.
 

retched

Joined Dec 5, 2009
5,208
What are you talking about??
You don't regulate the power. Instead, you regulate the voltage with a voltage regulator IC. You can also limit the current if you want.
What a novel idea.

Power Regulation: A device or circuit which maintains a desired
quantity (eg. voltage, current, frequency or mechanical property) at a
predetermined level usually by comparison with a reference source.
I SUPPOSE I could have said regulate the "power supply", but I thought the point was made.
 
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