Hi! first of all I'd like to say hello cause I'm new here
What I'm trying to do is to meassure the voltage of a 36 V battery with Arduino, and of course, power the Arduino with the same battery.
I've made a Voltage divider with 1K and 390 Ohm resistors (ceramic resistors) in order to obtain 12 V to power Arduino, whitch I've meassured with a polymeter.
When I connect the Arduino I find that there is not current enought to make it work properly. LED's just blink quickly. Anyone can help me? Thanks
You're drawing too much current. Use an external 5v regulator (a simple 7805 would do) to power the arduino (and 36V is too high for the Uno's regulator input), and use a voltage divider for the ADC input only (which has high impedance and will draw very little current).
If you need more current than a 7805 can handle (i.e. driving external components), I'd suggest a buck regulator: http://www.fasttech.com/products/0/10002934/1219200-dc-dc-3-40v-to-1-5-35v-3a-buck-converter-stepdown
markrock90:
I've made a Voltage divider with 1K and 390 Ohm resistors (ceramic resistors) in order to obtain 12 V to power Arduino, whitch I've meassured with a polymeter.
Three problems:
a) When you add the Arduino you're changing the resistance of the "390 Ohm" resistor by adding something else in parallel
b) 12V isn't the ideal voltage for Arduinos, not a good place to aim for
c) A 1K resistor will only let 0.024 Amps through it at 24V - nowhere near enough.
Bottom line: Voltage dividers do not make power supplies You may have 12V at the resistor junction but power supplies need amps as well as volts..
The way I read the datasheet it's safe to use 40V in with 5V out, but you have to derate the power output, since power dissipation is based on Vin - Vout.
The way I read the datasheet it's safe to use 40V in with 5V out, but you have to derate the power output, since power dissipation is based on Vin - Vout.
If you are stepping down that far in voltage, I would highly recommend using a buck converter. You will be disappating vastly more power as heat from a linear regulator than you would consume using the arduino. I would recommend something like stepping down to 9V using a buck converter, then using the onboard regulator to step it down the rest of the way for simplicity's sake. Its not ideal, but it will probably be better.
If the 36V battery is lead-acid, be aware that when freshly charged it could be
as high as 42V, so I'd make sure whatever regulator you do use is rated at 42V
or more to prevent expensive failure.
For other battery chemistries do a little research on highest voltages after charging
If the battery is powering big motors, up that to 50V to allow for voltage spike
and other nasties.
You can use a lm317 to reduce a relatively high voltage by some amount (the standard lm317 circuit doesn't connect directly to gnd), and you can set up a string of such circuits to distribute the power dissipation across as many devices as needed (ending with the 5V regulator that's on the Arduino itself.)
If you look at the Operating Conditions and Characteristics starting on page 4
you will see that the parts have recommended upper limits for incoming voltage at a specified output current. The note in the excerpt even says operation above the recommended voltage is not guaranteed.
If you want to input that high a voltage, I'd recommend a DC-DC Switching Regulator, some examples:
I've finally solved it.
I've done a tension divider with 2 390k ceramic resistor (18 V). Arduino works, but, I know that volatge is too high so I will use a 9V regulator because we all know that Arduino has its own voltage regulator and the voltage recomended is between 7-12V.
markrock90:
I've finally solved it.
I've done a tension divider with 2 390k ceramic resistor (18 V). Arduino works, but, I know that volatge is too high so I will use a 9V regulator because we all know that Arduino has its own voltage regulator and the voltage recomended is between 7-12V.
The buck converter is also an excellent option.
Thank you for all your answers
"I've done a tension divider with 2 390k ceramic resistor (18 V)"
and that actually powers the Arduino? I don't see how there's enough current flowing and putting it through a voltage regulator will probably lead you back to square one, you'd be just as well off using just 1 resistor to accomplish the same thing.
