A reluctant LiFePo4 convert...

[TimC]

I put off a battery replacement purchase while making double, triple, fourple sure my AGMs were dead. For my last camping trip with my brother I stole the battery out of my mower to make the trip comfortable with exhaust fans and some lights.

Thankfully Lauren was persistent at encouraging me to convert. So thank you Lauren. I received my 100 aHr kit today and so far I'm very happy with the service, price and quick delivery (6 days - the lead time for Ali-battery-baba was just to much of a deterrent.

I'm sure I'll have a few questions along the way. Lauren has already made me comfortable about the tasks before me. A bench power supply will be here in a few days. I chose to go ahead with that as my brother and son will likely replace their AGMs and when they do I can help them or borrow the PS for their use.

I'll document the build and install but it won't be for a week or two. I'll do it like Lauren did his LiFePo4 "recipe" he recently posted. I am as green as they come in the this battery building world so don't expect much technical blabber.

I am not endorsing this supplier but the question will inevitably come up. This is a 100 aHr kit with BMS and low temp protection. It is from batteryhookup.com. So far I've only asked one question via email and in less than 24 hours I knew the batteries are not top balanced. Their web site points you to Fakebook for tech advice. I'm not on there and I prefer tnttt. But I'm glad they were OK with email.

[Capebuild]

Good luck with your new lot in life (coming over to the Lithium Dark Side).... and good luck with building your battery. Sounds like an great adventure.
I find building a teardrop challenging enough at this point.... but if I had a trailer already built, I think it would be interesting researching and building a battery.

John

[TimC]

Received the bench power supply two days ago and watched a couple YouTube how to videos on using the power supply. I was surprised to see Will P's video titled "How to top balance... quickly" because he had the same bench power supply I bought. I'm sure he uses something a little more hi-tech in normal everyday charging. I like how he teaches with equipment that a beginner would be using. Anyway he suggested wiring up the new bank 4S and putting a 12v charger on it to bring it up to full charge before balancing.

I wired the kit up as 4S and hooked up my Noco 7.2a charger. It immediately selected Lithium and read 13.25v so that was encouraging. I left it charge for five hours and when the charging voltage showed 13.44 I got nervous and disconnected it and rewired the pack in parallel to continue top balancing. I was advised to be patient. Power supply is a 30v, 10a basic model. I am using 12awg wires with ring terminals on each end instead of the banana plug and alligator clip wires of unknown gauge that came with the power supply.

I set the power supply voltage at constant voltage of 3.5v and cranked the amps all the way up (10a). When I turned it on the readout reflected what the bank voltage is, not what you set it for. That was confusing until I remembered the videos said that this is normal. I tried to be patient as Lauren suggested this could take many days and new cells could have a 30% charge or an 80% charge so I was prepared for the long haul. I was pleased late this afternoon, after less than 48 hours, that the amperage of the power supply began to drop. It's now been around 55 hours and the amperage is at 1.75a. I think I will turn off the charging for the night and see what voltage the pack settles at in the morning. Then I'll crank it up to 3.65v and keep an eye on it. I hope that will not take more than a couple more hours. I'll then let it rest for a couple more hours and charge again if it drops below 3.5v.

Doing a capacity test after all this top balancing might be another long process. I don't have an inverter so drawing power out of the bank could take a while running fans and lights and maybe a fridge. I don't have a spare ammeter and shunt laying around so I might just install the bank in the camper and turn a bunch of stuff on and use those ammeters values. I don't know if running the fridge would help because it has a low voltage shut off and will probably shut down long before the battery is exhausted.

Update: At 10:30p top balancing is at 3.51v and is down to 1.0a charging. Probably under 60 hours top balancing so far. I unplugged and will let it rest overnight.
Update: At 9am after an overnight rest period the cells have settled to 3.4v. I turned the power supply back on and it quickly topped off at 3.5v in about a half hour. Then I reset the power supply to charge up to 3.6 and cranked the amps. It quickly started to drop amperage and in about two minutes was down to about 6a and still falling. I'll watch it for a while to see how that is going and then give it another rest. Probably an hour and then measure "resting" voltage.

[TimC]

So confused...

Battery cells are top balanced at 3.65v. Rewired to 4S configuration for 12v nominal. Battery voltage is now at 14.27v after resting for a couple hours. Wired into the teardrop and...nothing. Tested the battery at + and - posts and it is still at 14.27v. Testing the battery at the C- post of the BMS and + post of battery and I get 2.4v. Retraced all BMS leads and they are all correct. Unplugged the BMS wire bundle and plugged back in and it still shows only 2.4v. Oh boy, mother told me there's be days like these!

I'll sleep on it and call the supplier in the morning.

[flboy]

I am not sure what type of BMS you have, but some need to be activated by putting the charger on the batteries and turning it on. Charger needs to put out 14.6V or be higher voltage than resting voltage of your bank to activate. I struggled with that on my first battery build before I figured it out. Not sure if that is unique to my BMS or something others needs as well.

If you do call, ask how to activate the BMS.

Sent from my SM-N970U using Tapatalk

[TimC]

...some need to be activated by putting the charger on the batteries and turning it on. Charger needs to put out 14.6V or be higher voltage than resting voltage of your bank to activate. I struggled with that on my first battery build before I figured it out. Not sure if that is unique to my BMS or something others needs as well.

If you do call, ask how to activate the BMS.

Sent from my SM-N970U using Tapatalk

I'll give that a go flboy. Thanks... sounds simple enough. Will update if it works!

[saltydawg]

Yes most bms do need the activation, its also how you wake it up if it ever shuts down from low voltage.

[TimC]

Yay! You guys beat the folks over at diysolar forum with the correct answer. Winner, winner, chicken dinner!

I hooked up my Noco 7.2a but it refused to go into any function other than power supply, 5a. I hope I didn't fry it! I'll hook that up to another battery tomorrow and check it.

Then I thought, I have a bench power supply! I cranked that up to max amps and 14.3v constant. Battery was reading 14.25v. Connected the power supply to the battery downstream of the BMS, turned it on and after about a minute I shut off the power supply and everything still was humming. I'm happy.

Starting my capacity test. This could take a while. I have almost everything turned on and I'm burning 4.5a.

[flboy]

Glad that's all you needed and you are up and running! Congratulations on your battery build!!

[TimC]

Capacity testing is still in process. I'm only burning about 5 amps when the fridge is running which is infrequent overnight. It should run more today with highs expected near 90. I'm OK with the slow burn as maybe that real world rate will result in more accurate data. It's been close to 12 hours since I started the capacity test. Used 447 wh and battery is at 13.12v. At 12v that is 37.5aHr. So I am hopefully around 37% of the time I will need to finish the test (if the bank tests out at ~100aHr.

I can't remember if the bayite ammeters will hold data when the voltage drops and they stop recording. Top meter is load. Someday I have to label these!

[saltydawg]

If you want to speed the test up crack open the freezer door, or heck just open it all the way.

[TimC]

If you want to speed the test up crack open the freezer door, or heck just open it all the way.

Yup, that helped. So I am close to 24 hours for this capacity test. Here's the latest ammeter reading. If my calculations are correct I am over 120 aHr on this 100 aHr rated battery.




Everything is still running. Fridge is set at low cut off voltage and is still operating. Should I end this test or is the standard practice to run until the BMS stops providing current?

Am I in any danger of damaging appliances or the battery? I don't know when the BMS is rated to shut down.

Thanks, Tim

[flboy]

Tim, your appliances should have a low voltage shut down and the BMS is designed to protect your batteries; however, if the purpose of your test was to make sure you got 100aH and got what you paid for, then it was a successful test. Your call.

I shut mine down after I verified capacity. No point to go further.

Sent from my SM-N970U using Tapatalk

[John61CT]

Be aware that there is no "accuracy" with capacity tests, only precision in the sense of standardisation of the relevant variables yielding **repeatable** results.

The current C-rate dictates a very widely varying end result of Ah capacity, see Peukert's law.

So if the maker is honest, but used a 20-hour CC discharge rate, you won't get anywhere near that Ah number using a 5-hour rate

and you will get much higher Ah capacity if your CC load goes out longer than 20 hours.

Best practice is to keep the time factor constant, and keep repeating the tests until you hit the C-rate that depletes the cell in that time-frame.

So when benchmarking over time, it's always an X-hour test, but the CC current used declines to match the reduced capacity of the cell.

[TimC]

Thanks. Just after I posted that the BMS (I'm assuming) shut off current. I'm now starting to charge the bank and the end result of my test shows this...



I'm happy if 1483 ah is 123.5 aHr