Hi everyone, Im currently building a golf cart computer for my dad (my first arduino project) and i want to add a battery meter to it. After doing some research on how to do it i ran across a blog explaining a voltage divider. I think i am correct on bulding the circuit but i am a little apprehensive to hook it up without a second opinion. I wanted to make a divider for a max voltage of 55v stepped down to 5v. Attached is a really bad diagram of my circuit any help, thoughts, or opinions would be greatly appreciated.
That's about right, although I would use 10K and 1K (or even 100K and 10K) rather than 1K and 100 ohms - there no point in drawing so much current from the 48V battery. The 12V regulator will probably have a common ground terminal for input and output.
Thanks.
I did not know that the higher the resistor the less current it would pull. thank you for that. I have about 2 days worth of electronics experience
I am looking at the resistors i have in my starter pack. I have 10k and 100k resistors, do you suggest i pick up even higher or will the current draw be low enough with those? I dont want to drain the battery with this thing.
If you go above 10K/100K then you need to take additional precautions to ensure an accurate reading (e.g. connect a capacitor in parallel with the lower resistor in the divider). 10K/100K will give a current draw of about 0.5mA, which I think is probably insignificant in the context of a golf cart battery.
Make sure you put the resistors the right way around.
Your arrangement will give the arduino analog input, 1/11 of the battery voltage.
Which would be 5v if the battery is 55v.
You would want to be very carefull that the battery voltage cannot exceed this. Be aware
that a 12V battery can have a terminal reading almost up to 14V when charging. I guess
multiply that by 4 for 4 batteries.
You want to make sure you don't have more than 5v on the analog input.
If it was me, I'd choose resistors so that only 1/15 th or 1/20 th of the battery voltage
was being applied to the arduino. It doesn't need to be 5V.
You can't use an off-the-shelf linear regulator from 48V, please note, they usually have a max input around 25 to 35V.
A DC-DC converter would be much more efficient anyway, find one that will handle 48V input and has enough
output power for the Arduino and any displays etc.
Your initial values of 100 and 1k would melt/catch fire if you used standard 1/2W resistors as the 1k would dissipate
2W. Definitely use 10k and 100k, perfectly good enough. Adding a 100nF cap across the smaller resistor would
filter out noise from the motor controller and give more consistent ADC readings.
BTW with a 100k in the high side you will be able to cope with battery voltage a lot higher than 55V as the 100k
limits the current through the Arduino protection diode adequately for even 100V input.
Be careful to route the incoming 48V wire well away from anything but the DC-DC converter and one end of the
100k resistor - accidental shorting would instantly destroy everything, so insulate it (tape, glue gun, etc).
Add a ~200mA fuse in the 48V incoming line at the battery end - fusing is essential for anything connected to
a lead acid battery pack or other supply capable of large currents (it protects against the wiring burning up
and starting fires).
Thank you for all the help. I ended up going with a ratio of 1/12 giving me 60v after checking the battery bank with a multimeter while it was charging, the highest it got to was 57. . I'm also using 10k and 100k resistors MarkT i checked my amazon order i did use a voltage converter . It is specifically made for 48v carts to have 12v for lights. I also mounted the voltage divider about 2 feet away from the arduino with only one small wiring carrying the 5v signal to the board. The glue gun has also been my best friend this project. Thanks for the tip for the fuse i totally forgot about that and will be picking one up in the morning.
One last question when you say " Adding a 100nF cap across the smaller resistor would
filter out noise from the motor controller and give more consistent ADC readings."
