0
\$\begingroup\$

I have a sump pump system that includes a 12 volt backup sump pump. It is managed by this Pump Spy system: https://www.amazon.com/PumpSpy-PS2000-Battery-Internet-Monitoring/dp/B07N8FY4L9 I have a 200Ah AGM battery. I'm tired of the AGM batteries losing total capacity so quickly. I'm looking at a 200Ah Lithium Iron Phosphate battery. I understand LiFePO4 needs a different charger that supplies 14+ volts. The Pump Spy brains charges the battery (12 volt) and monitors the health. I'd like to keep the Pump Spy monitoring functions working, but charge the LiFePO4 battery to full capacity. I asked, and there is no supported way to disable the Pump Spy charging function. Is there a good way to connect a proper charger without interfering or conflicting with the built in Pump Spy charger? I'd be fine preventing the PumpSpy charger as long as it is still able to monitor. Thanks.

\$\endgroup\$
1
  • \$\begingroup\$ Unlikely because the Pump Spy because if the Pump Spy is any good, it will know when when the battery isn't properly charging when its trying to charge it and spit an error message. \$\endgroup\$
    – DKNguyen
    Commented May 5, 2021 at 21:33

2 Answers 2

1
\$\begingroup\$

3.4V per cell (13.6V on a 4 cell battery) gets you more than 90% charged

3.65V per cell (14.2V on a 4 cell battery) is also acceptable, but only gets another 10% energy into the battery.

You can probably just connect the LiFePo4 battery in place of the lead acid battery and get acceptable performance. staying below 100% charge will probably result in a longer life for the battery.

\$\endgroup\$
3
  • \$\begingroup\$ Thank you! This is the battery I'm looking at: amazon.com/gp/product/B088RM4W48 The seller answered a similar question with "You can use the lead-aicd battery charger to charge our lithium battery. But we recommend lithium battery charger because on one hand, lead-acid battery charger can only charge our battery to 90% full and might influence our battery performance in long term use. On the other hand, lithium battery charger is designed for our lithium battery and can maximum its performance. And it’s also ok if you use your lead-acid battery charger in a short time." \$\endgroup\$
    – Matthew
    Commented May 6, 2021 at 3:11
  • \$\begingroup\$ If the only real issue is that it charges to 90%, that is fine. \$\endgroup\$
    – Matthew
    Commented May 6, 2021 at 3:11
  • \$\begingroup\$ PumpSpy engineer got back to and said their charger is 13.8V. I think that will be enough for me. It has to be better than the AGM batteries I have where the vendor is overstating their capacity and they lose capacity way to quickly. \$\endgroup\$
    – Matthew
    Commented May 7, 2021 at 16:08
0
\$\begingroup\$

There is no difference between LFP and Lead-Acid battery chargers. Both use the same constant current and constant voltage algorithm. You can buy a drop-in LFP replacement battery for your car. The only difference is the constant voltage setting.

Lead Acid should be fully charged and floated at 13.8 volts to maintain 100% SOC for maximum battery life. Does that voltage sound familiar to you?

LFPs and all lithiums are different animals. LFP can be fully charged (100% SOC) to 3.60 vpc x 4 = 14.4 volts. However, doing so will significantly shorten battery life. EV manufacturers would never allow you to charge their batteries fully; warranty replacements would bankrupt them.

Running the cell voltages at 95% or less SOC will double the battery life. Run at 3.45 vpc, 90% SOC, and triple your battery cycle life. Running LFP at 100% SOC is a foolish leftover from lead-acid batteries. That is why lithium BMS charges to 100% SOC to sell you more replacement batteries.

\$\endgroup\$
4
  • \$\begingroup\$ Thank you. That is interesting. I ended up going down a rabbit hole with someone who seemed pretty knowledgeable. I ended up building a charger. See here for all the details: reddit.com/r/electricians/comments/rk8dtg/… \$\endgroup\$
    – Matthew
    Commented Apr 25 at 0:58
  • \$\begingroup\$ I wouldn't say that. As I said, the charging algorithms are the same. The difference is how you terminate the charge. Consumer-grade LFP batteries often have a BMS integrated into or external to the charger. For example, the car drop-in replacements have a BMS in them. The BMS is made to charge the battery fully to 100% SOC 14.2 volts. If you monitor the vehicle alternator voltage at start-up, you will see 14.2 volts. The VR will hold 14.2 volts until the charge current tapers down to a few amps, indicating full change will reduce the voltage to 13.8 volts and float or hold at 13.8 volt5s \$\endgroup\$
    – Dereck
    Commented Apr 25 at 1:20
  • \$\begingroup\$ I'm not following. What are you referring to with your "I wouldn't say that" statement? Sorry if I am missing something. Thank you again for the information. My current setup is definitely relying on the BMS to take proper care of the battery. \$\endgroup\$
    – Matthew
    Commented Apr 25 at 15:42
  • \$\begingroup\$ I was referring to your comment about going "down the rabbit hole". \$\endgroup\$
    – Dereck
    Commented Apr 25 at 20:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.