# DIY Arduino BMS - Help



## majorpayne (Mar 27, 2011)

Alright, my motorcycle conversion has already got an RFID keyless ignition i designed and coded that closes the contactor using a MOSFET. And i was thinkin, if i've already got an arduino on there, why not exploit it to its full potential?

So basically what i want this arduino BMS to do is (all displayed on a 16x2 LCD):
1) After the RFID card has been swiped, Begin pre-charing.

2) While pre-charging, a status bar graph appears on the LCD and once it is 
full(after a designated amount of time, about 3 seconds) close the contactor

3) Measure voltage in real time, voltage divider? what value resistors? (or maybe average over every 10 reads or so) 

4) Measure current in real time (which is more important to measure, the current from the motor wires or the battery wires?)

5) Read speed. I know the math behind this, but how should i pull it off? use a hall effect near the wheel and it gets driven by a magnet attached to the spoke? then get the Arduino to do the calculations of wheel diameter, distance moved per revolution and so on. OR should i do a similar setup except on the motor shaft? I'm running a Mars ME0708.


I am pretty good at coding for the Arduino, but I might need some help with some parts. I'm only 16 so I don't have a total understanding behind when to use a FET or a relay and such. So i mainly need help with what parts to use and how to wire them up.

Thanks!
Tyler


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## Salty9 (Jul 13, 2009)

Google "Lee Hart BMS". My Internet is running slow so I can't pull up a precise URL.


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## majorpayne (Mar 27, 2011)

Thanks, I forgot to mention that I want it to balance the batteries when charging. And this seems alot more simple than getting the Arduino to do it.

But I'm still confused by how this works. I understand what a zener diode is, but how to wire it and in this application i'm still confused. The site that apparently had a good explanation of it was unfortunately on Yahoo Geocitites and so is dead now. Could you help explain it to me?


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## rwaudio (May 22, 2008)

majorpayne said:


> Alright, my motorcycle conversion has already got an RFID keyless ignition i designed and coded that closes the contactor using a MOSFET. And i was thinkin, if i've already got an arduino on there, why not exploit it to its full potential?
> 
> So basically what i want this arduino BMS to do is (all displayed on a 16x2 LCD):
> 1) After the RFID card has been swiped, Begin pre-charing.
> ...


Hey Tyler,

I'm also doing an arduino setup, however hardware is my specialty and software is where my skills are lacking.

Do you want to monitor total pack voltage or each cell voltage?
Current is pretty easy, personally I would track battery current then you can use the arduino to give you a SOC as well.

Good luck with your setup!


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## majorpayne (Mar 27, 2011)

I'd rather monitor total pack voltage. I'm not too worried about range since the district i live in is rather small. So monitoring each cell voltage and charge balancing is of the least priority.

I want to use a voltage divider because of its simplicity, or will it waste too much voltage? Also for measuring current should i use the shunt i have or would it be worth it to get a hall effect sensor for isolation reasons?


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