I am looking for some ideas for a project I need to put together.
I have a device that uses 56v batteries and I need the ability to automaically "swap" the batteries during the discharge and charge cycles.
The batteries have a charger so I don't want to replace that or have to deal with any of the issues with battery management.
The scenario I am thinking of is
Discharge Scenario
- Arduino monitors the charge level of all batteries
- The device runs from a single battery at a time
- When a battery gets to 10-20% it will swap to the next battery in the line
Charge scenario
- The existing battery charger is connected
- The system will connect one battery at a time direct to the existing charger. This allows the battery charger to do its thing.
If the system messes up and leaves a battery connected it won't matter because the battery charger handles this state. - Once the charge of the battery is full, it will switch to the next line in the battery, going through each until it is fully charged.
- I am able to get the battery charging % from the charging unit itself to the Arduino.
The reason for "swapping" instead of wiring them together is due to battery management of the charging side.
I was looking at using a simple voltage divider to measure the voltage of each battery to determine the discharge.
But I understand Lithium batteries don't have a voltage curve to determine an accurate percent. But since I really only need to know full or almost empty, do people think this would work in this scenario?
Or is there a better solution? I did look into Coulomb Counters but I can't find anything that would work within the 56v range.
Just been reading up on the ACS712 Hall effect current sensor. Im thinking this maybe an alternative but I have never used one of these.
I have already had a bit of a play around with a voltage divider that will allow me to turn on and off the battery measurement and im getting voltage readings into an Arduino.
For the switching side, when charging im looking at an Arduino switch a transistor which will in turn switch a mosfet for the positive side of the battery and two SSRs for the battery data lines. This would be for the charge side.
For the load side, the Arduino would switch a single mosfet to connect the positive to the load.
All the negative sides would be tied together and to the Arduino ground.
Im keen for any thoughts, anything I have missed out. Let me know if I have also mised out any important detail that will help with feedback.
Thanks.
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