Recent content by j_t_l

One other use: Some chargers try to be "smart" and won't output any current unless it sees a voltage on the line first. But if a BMS turns off the output FETs (say to protect the pack from low voltage), then the "smart" charger won't charge it -- and the BMS won't go back to normal operation...

It's really too bad the Renogy doesn't have more configuration options. That's disappointing. For their "Lithium" profile: 14.4v is probably too high for charging a 4s pack. You could try to top balance your cells (again...) to see if the 14.4v will work, but it doesn't leave much room for any...

As Zorlig said, you are the bms :) It should be fine as long as you make sure: Each cell stays within the proper voltage range Conservatively 3.0v-3.4v per cell Don't charge/discharge outside of temperature limits You mentioned cold weather -- especially don't charge if the batteries are...

I'd go with "no, not safe". It depends on what you mean by safe... Everything will be fine as long as no cell goes over the voltage limit. Cells get damaged over 4.2v, and degrade a lot faster over about 3.6v. Over about 3.5v the voltage spikes up VERY quickly even with only 8 amps of charging...

To add two things: 1) If there is a difference in the resistance of the batteries (which could be due to anything -- internal resistance, wiring, different connectors, etc), that will also cause imbalances. When the load (or charge) is removed, you can see the low-resistance battery will start...

Unfortunately, voltage curves for lifepo4 batteries are either really complicated or only semi-useful. I think the quick answer is "don't do it" -- but no one likes that answer :). Depending on the use case: do you really care exactly what the SOC is? If you just want a rough hand-wavy guide...

There's a difference between "charge voltage" and "float voltage". The charging spec for lifepo4 batteries is "charge to 3.65v and then stop charging". It is not "charge to 3.65v and hold at 3.65v". I haven't seen a manufacturer recommended float voltage. You can search the internet and read a...

You can run about 1200 watts of equipment off of the battery and stay within the 120a limit. Do you have more than 1200 watts of equipment you plan on plugging in? If you do, the BMS will shut down when it detects the overcurrent condition. Note that there's a timeline for overcurrent. The BMS...

Yes, that could be an issue. You'll have to make sure the batteries are nearly the same voltage before reconnecting both of them. If the voltage is different enough, it'll cause the over-current or short-circuit protection to trip. If they're close enough (less than 0.1v), a few 10s of amps...

I'm thinking of wiring that resistor across the BMS with a normally open push-button switch. So the turn-on procedure will look something like this: Hold down precharge push-button for 10ish seconds Turn on BMS output switch Release precharge button I'm only slightly worried about running...

One of the BMS options is "LoadDetect" -- which (in the sparse documentation I could find) tries to see if there's still a short-circuit before turning the BMS back on again: Load detect: after short protect, if BMS detect the load, then do not release, only the load removed then release protect...