| Electronics > Projects, Designs, and Technical Stuff |
| 24V UPS using 18650 batteries that charges/discharges using the same bus |
| (1/2) > >> |
| dfindlay:
Hi, I have some equipment that is powered by a 24VDC power supply typically drawing 2-4 amps. The load is directly connected to a power supply and I would like to design a UPS that is in parallel with the power supply/load so that the batteries charge from the power supply and if the power supply is cut, the batteries would start discharging. I would like to use 18650 batteries and my understanding is that I will need a charging circuit and a BMS. My challenge is that any charging circuit I can find uses a separate charging supply than the load the main PS and load are on. Is it possible to do this? If the charging circuit is powered by the same bus, when the UPS kicks in (main PS is lost) the battery would be supplying power, but it would also be trying to charge itself. Has anyone come across this situation before? Thanks in advance for your support! |
| NiHaoMike:
With a 6S pack including a BMS, all you need are two diodes and a resistor. The diodes are used in the usual "diode or" configuration, then a resistor is added from the output back to the battery for charging. The pack would end up at about 4V/cell, which is OK to leave connected indefinitely. If the PSU is OK with backfeed, the diode in series with it is not necessary. If you use a PSU that also allows limiting the output current, you could indeed simplify it to a direct parallel connection as you show. |
| dfindlay:
Hey NiHaoMike, thank you very much for your help here. As I was looking into your solution, I came across a BMS from Amazon that appears to balance charge and discharge on the same wires. I sketched this up based on this part (lh-hp07sa). Do you think this will work, and more importantly work safely? See attached updated sketch. https://www.amazon.ca/dp/B07R58FX1V/ref=cm_sw_em_r_mt_dp_U_.wBpEbJYMSP44 Thanks in advance for your help, I really appreciate it. |
| NiHaoMike:
For that to work, the PSU must tolerate backfeed and limit the output current to within the charge rating of the battery. Otherwise, you'll need the diodes and resistor. That's also a 7S BMS when you want a 6S. |
| dfindlay:
Ok Fantastic. Yes, the power supply can tolerate backfeed, but I might as well add a protection diode(D1). The batteries don't need to charge quickly, in fact, I would prefer them to charge slowly to avoid pulling too much current from the load. Does this diagram make sense? Also, I think that BMS can be used in any configuration from 3S-7S. Correct me if I'm wrong, but to use 6S I would just short out the 7S lead to the 6S right? Thanks!! |
| Navigation |
| Message Index |
| Next page |