LIFePo4 UPS and BMS

[curto]

Guys,

I have read through all the threads on here and can not find a definitive answer before i proceed.

I have a number of APC UPS that support extended Runtime modules - they are 48v internal and 48v external.

I am sick and tired of replacing SLAs every couple of years so thought that Lithium would be a better bet.

I have read through here in relation to changing the relevant voltage levels to better match the profile of the Lithium batteries.

My plan was to run a 200a Seplos BMS through to the 16s 50ah battery pack - using the Seplos to control the correct charging and balancing of the pack - essentially using the UPS battery cable as a DC source to the Seplos.

I see two issues with this and want to confirm others thoughts

1) Once the batteries are topped off - i assume the Seplos will disconnect them - how quickly will it reconnect if power fails and the batteries have to step up and start supplying power ?

2) If i want to cycle the batteries each day i could put a mains disconnect switch (Sonoff PowR3 for instance) on the input to the UPS, have it turn off the mains to the UPS for a couple of hours (say during peak time to get some extra benefit) and then back on again - thus forcing the UPS to go into charging mode and exercising the batteries.

Does this sounds like it would work ?

My biggest concern is 1) above - will the BMS kick in quickly enough on a call for power ?

Craig

 

[wholybee]

Guys,

I have read through all the threads on here and can not find a definitive answer before i proceed.

I have a number of APC UPS that support extended Runtime modules - they are 48v internal and 48v external.

I am sick and tired of replacing SLAs every couple of years so thought that Lithium would be a better bet.

I have read through here in relation to changing the relevant voltage levels to better match the profile of the Lithium batteries.

My plan was to run a 200a Seplos BMS through to the 16s 50ah battery pack - using the Seplos to control the correct charging and balancing of the pack - essentially using the UPS battery cable as a DC source to the Seplos.

I see two issues with this and want to confirm others thoughts

1) Once the batteries are topped off - i assume the Seplos will disconnect them - how quickly will it reconnect if power fails and the batteries have to step up and start supplying power ?

The BMS will disconnect charging, without disconnecting discharge. So power will always be available.

2) If i want to cycle the batteries each day i could put a mains disconnect switch (Sonoff PowR3 for instance) on the input to the UPS, have it turn off the mains to the UPS for a couple of hours (say during peak time to get some extra benefit) and then back on again - thus forcing the UPS to go into charging mode and exercising the batteries.

I expect that could work.

Does this sounds like it would work ?

My biggest concern is 1) above - will the BMS kick in quickly enough on a call for power ?

Craig

An interesting project, but probably more complicated than you expect. The APC (at least the ones I have been responsible for) monitors the battery voltage to determine condition and SOC. The voltages on LFP are different, and so unless you are able to modify the code in the APC, it will act funny. I don't know to what extent, but I expect the APC will see the battery as fully charged when it is quite low. A fully charged SLA will be about 50.8V, and LFP 54.4. Also, if the BMS disconnects charging, what will the APC do? It will probably notice the sudden lack of charge current, and set an alarm condition, and might not switch to battery power. It might be worth some experimentation to see how the APC really reacts to it, I just don't expect it will be a simple swap.
Also, LFP are not ideal for standby batteries. They might last as long or a bit longer then SLA, but you won't get the rated number of cycles if they are held at full charge waiting for the power to go out.

 

[curto]

Thanks for the informed answers.

1) My plan to make sure the batteries are not held at full charge is to essentially cycle them each day - i could for instance turn off mains to the UPS each day at say 5am (knowing what the normal static draw was) and leave it to run on battery for 3 hours - lets say that ran down to 30% SOC on the battery pack

2) I could then re-enable the mains and the UPS would start to slowly charge the pack throughout the day from mains power (which is provided by my solar panels most days) - this slow charge would bring the unit back up to full power for any outages over night and i could then rinse and repeat the next day

3) There is a thread on here that details how to get into the programming of the UPS to set the various voltages - i would do that to better match the Lithium profiles.

Interesting problem you note with the UPS possibly going into alarm mode if the battery charging is disconnected.

Will report back if i get this project off the ground

Craig

 

[perpetual]

This thread has some good info
https://diysolarforum.com/threads/upgrading-apc-ups-battery.1503/post-13602

 

[curto]

Just as an update on this one guys. I purchased 16 x LIFePO4 batteries and a Seplos BMS.

Hooked them up to a 2200va APC Smart-UPS and all works as expected.

I can not go any larger than 2200va though as they then move from 48v battery packs to 72v and above.

My plan now that i have seen this all work is to actually move to an AC coupled Inverter - here in Australia we have the GoodWe SBP 5000 which can be treated as a true online UPS by hooking up a load to the Backup port.

My plan is to replace the Current APC UPS with this unit - i already have 3 of these units so have a reasonable amount of experience with them - so this one will slot in nicely and costs me less than $1500 AUD

With the current 100AH batteries and my combined computer loads in the house of about 1KW - we should get a good runtime

I will implement the peak shaving code to enable daily cycling of the batteries.

Will report back once this is all up and running

Craig

 

[Mithril]

Just as an update on this one guys. I purchased 16 x LIFePO4 batteries and a Seplos BMS.

Hooked them up to a 2200va APC Smart-UPS and all works as expected.

I can not go any larger than 2200va though as they then move from 48v battery packs to 72v and above.

My plan now that i have seen this all work is to actually move to an AC coupled Inverter - here in Australia we have the GoodWe SBP 5000 which can be treated as a true online UPS by hooking up a load to the Backup port.

My plan is to replace the Current APC UPS with this unit - i already have 3 of these units so have a reasonable amount of experience with them - so this one will slot in nicely and costs me less than $1500 AUD

With the current 100AH batteries and my combined computer loads in the house of about 1KW - we should get a good runtime

I will implement the peak shaving code to enable daily cycling of the batteries.

Will report back once this is all up and running

Craig

Any updates? Fairly similar to what I'm looking to do.