Sorry for a dumb question but I have two relatively identical 4 cell 280 ah LiFePo4 batteries each with its own BMS. I want to run them in series for a 24 volt system. How do I connect the two batteries together with separate BMSes. Do I connect both primary leads on the first BMS to battery terminals? If the correct answer is get an 8s BMS I am OK with that but would like to run them together in the interim. The BMSes are undersized anyway so I think I will have to replace them regardless. But I am hoping there is a simple solution so I can gradually build up my battery solution as my overall system grows.
How to connect 2 4s batteries together
- Thread starter willc99
- Start date
The real concern is if a BMS shuts down and is not rated to stop 24 volts. Choose the operating range conservatively.
Otherwise you just need a jumper from the negative of the first battery to the positive of the second battery. Nothing else connects to this jumper or the terminals. This leaves the positive of the first battery and the negative of the second battery to supply 24v.
https://www.usbattery.com/info-center/configuration/configuration-1/
Otherwise you just need a jumper from the negative of the first battery to the positive of the second battery. Nothing else connects to this jumper or the terminals. This leaves the positive of the first battery and the negative of the second battery to supply 24v.
https://www.usbattery.com/info-center/configuration/configuration-1/
So where does the B wire go for the first BMS? Does it go unconnected, or is it connected to the positive terminal of the first set of batteries? Right now I left it disconnected as I am only charging the batteries, there is no load on the batteries.
Usually the BMS controls the negative side of the battery. B+ would be the positive battery terminal. The B+ terminal (see right battery pictured above) would connect to the BMS C- terminal of the other battery (shown on the left).
This leaves the B+ on the left battery open to connect to the 24v load (+). The right battery BMS C- terminal would be open to connect the 24v load (-).
This leaves the B+ on the left battery open to connect to the 24v load (+). The right battery BMS C- terminal would be open to connect the 24v load (-).
So, I would assume that the same configuration would apply when connecting two 8S batteries with two BMS's together? And what do you mean, "Choose the operating range conservatively?" ThanksThe real concern is if a BMS shuts down and is not rated to stop 24 volts. Choose the operating range conservatively.
Otherwise you just need a jumper from the negative of the first battery to the positive of the second battery. Nothing else connects to this jumper or the terminals. This leaves the positive of the first battery and the negative of the second battery to supply 24v.
https://www.usbattery.com/info-center/configuration/configuration-1/
Attachments
Make sure the separate BMS is rated capable of stopping the full battery voltage. Otherwise if what you have must be used it is best for the BMS not to trip off for any voltage or other faults and hence "choose the operating range conservatively". Series balance can also cause issue with having the BMS shut down.
Similar threads
