Convert Voltage from 12v to 7v nessessary?

Hello everybody,

I have an Arduino project which measures surface temperatures with an Melexis IR sensor, the air temperature and the humidity. All parameters are measured continuously and the average of an 5min intervall is written down on an micro sd card with a timestamp from an RTC. You can see the setup on the picture. |500x281 The datas will be read out two or three times a week via the USB connection and processing. The arduino itself will be power via the external power input. And here is my question: The power retrieves the power form an Campell Scientific CR1000 logger with an output of 12v. Is it nessessary the downsize the voltage to 7v to prevent overheating? (The Arduino is places in a small waterproof box). If yes, can I simply solder an converter like this one to the cable or should it be on a circuit board?

Thanks a lot banff

If you run the Arduino from a lower voltage its regulator will run cooler. If you use a
DC-DC converter rather than a linear regulator you will reduce the current drawn from
the data-logger too…

The Arduino on-board regulator has to dissipate (Vin-5.0) x I
so reducing Vin from 12 to 7 will reduce dissipation in the regulator by 70%

How much current does your Arduino require?

As MarkT has said, lower volts is lower heat but if you only require minimal current, it may not be enough to worry about.

There are ways to lower the average current and this has been well documented by Nick Gammon

http://gammon.com.au/power

Weedpharma

Thanks for your answers.

weedpharma: How much current does your Arduino require?

If I sum up the declared values from the datasheet of each device the maximum current draw would be round about 300mA. The sd board requires by far the most. When I powered the Arduino with a powerbank with 1A output everything worked fine.

MarkT: If you use a DC-DC converter rather than a linear regulator you will reduce the current drawn from the data-logger too...

I want to use a linear regulator. The current output of the fixed voltage regulator L78S75CV I have is declared with up to to 2A. So if the Logger has an output of 1A, 1A should get into the arduino right?

Thanks you, banff

There are a number of switchmode down-converter/ regulators available, some of which have much the same footprint as the TO-220 regulators.

The reasons not to use the cheapest linear regulator are that because the switchmode regulator is much more efficient (95% instead of 40%), not only do you waste less power from your power supply (which would clearly be quite critical if you were using batteries), but you generate that much less heat within your enclosure - which again would be critical if you were measuring temperature within the enclosure.

Of course if you are using a UNO, you clearly are not operating from batteries.

To power the SDcard you'll need an external 3V3 regulator anyway, the on-board 3V3 regulator isn't normally rated for SDcards which pull a lot of current when written.

If you are doing high precision analog stuff you will need a linear regulator to avoid noise, but DC-DC converters are fine for digital circuitry.

Paul__B: There are a number of switchmode down-converter/ regulators available, some of which have much the same footprint as the TO-220 regulators.

The reasons not to use the cheapest linear regulator are that because the switchmode regulator is much more efficient (95% instead of 40%), not only do you waste less power from your power supply (which would clearly be quite critical if you were using batteries), but you generate that much less heat within your enclosure - which again would be critical if you were measuring temperature within the enclosure.

Of course if you are using a UNO, you clearly are not operating from batteries.

Well, my linear regulator only costs 0,59 cents.. but wasn't the cheapest anyway! The guy at the electronic store recommended it.. For a first test i would try this one, because heat inside the enclosure doesn't matter as long as the arduino, the RTC und the SD breakout board aren't affected. Measurements are taken outside.

Can I solder the cables to the linear regulator as pictured below? Or would it cause problems?

|463x500

MarkT: To power the SDcard you'll need an external 3V3 regulator anyway, the on-board 3V3 regulator isn't normally rated for SDcards which pull a lot of current when written.

If you are doing high precision analog stuff you will need a linear regulator to avoid noise, but DC-DC converters are fine for digital circuitry.

The SD card is powerd with 5V and the sensors and the RTC are connected via I²C and a bidirectional LLC because the IR sensor and the temp/humidity sensor are operating with 3v while the RTC is on 5v.

Thanks for all, banff

Using the linear regulator will just move some of the heat loss from the Arduino to the regulator, it will still consume the same amount of power.

Unless the regulator on the Arduino-board is scorching hot, there is absolutely no problem in powering it with 12V. It looks like you have an 78L05 regulator there - to use it you need to feed it's output voltage to the 5V-pin on the Arduino, and not the DC-jack or Vin-pin, which requires 7 volt or more for the Arduino to function properly. Furthermore it's very important to solder two small capacitors on the regulator - as a rule of thumb 0.1uF works perfectly. Caps on voltage regulator.

// Per.

Zapro: Unless the regulator on the Arduino-board is scorching hot, there is absolutely no problem in powering it with 12V.

If it is not that nessessary I would do it without the regulator. But I want to run the Arduino stable over several month.

Zapro: It looks like you have an 78L05 regulator there - to use it you need to feed it's output voltage to the 5V-pin on the Arduino, and not the DC-jack or Vin-pin, which requires 7 volt or more for the Arduino to function properly. Furthermore it's very important to solder two small capacitors on the regulator - as a rule of thumb 0.1uF works perfectly. Caps on voltage regulator.

// Per.

No, it's not an 78L05, it's an 78S75CV, which regulates down to 7.5 Volts so it is for the DC-jack. Do you mean both capacitors should have 0.1uF? Or the one at Vin side 0.33uF as it's shown in the link you sent?

Thanks, banff

banff: If it is not that nessessary I would do it without the regulator. But I want to run the Arduino stable over several month.

No, it's not an 78L05, it's an 78S75CV, which regulates down to 7.5 Volts so it is for the DC-jack. Do you mean both capacitors should have 0.1uF? Or the one at Vin side 0.33uF as it's shown in the link you sent?

Thanks, banff

Put your finger on the vreg on the Arduino.

Is it hot? : Use the extra vreg.

Is it cold?: Use it as it is.

100nF on each side is plenty, i always use that in my applications and never ever had a problem.

// Per.