Electronics > Power/Renewable Energy/EV's

Lesser nerd requires LiFePO advice

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IRIdiot:
Evenin'

I require the advice of far greater nerds than I. The query is regarding undervoltage of LiFePO cells.

My wife and I recently had solar and battery storage installed. We went for Givenergy batteries which use LiFePO tech. The batteries were installed yesterday and what should have been a two hour commissioning job took eight hours. Whilst I'd have loved to watch and ask questions galore, I know there's nothing worse than the homeowner looking over your shoulder whilst you're trying to work a problem. So I left them to it. They were exceptionally honest with me about the issues. The batteries have a usable capacity of 5.2kW each and we have two. They appear to be connected in series to the inverter.

The batteries should have arrived ready to go with some charge in them. They arrived with no firmware installed and, on installing the firmware, the BMS immediately alarmed saying the battery was under voltage. This alarm can trigger on a per-cell basis but appears to have been on an overall battery voltage basis. The voltage at the start of them force charging the battery was 24-30V (large variation) and the undervolt alarm triggers at 45V. A decent working voltage for this pack seems to be around 55-60V. It took several hours to come up to 45V.

They set the batteries to charge whereby they sucked in circa 6kWh and shut down one after the other. The breaker hasn't tripped but the batteries have totally shut down (even inactive they should register as present and have lights on). They should probably have taken close to 12kWh if they were under capacity. I suspect the BMS has detected cells outside safety limits and shut the batteries down entirely. An engineer is coming Monday. Replacement is on the table. On examining the data that I have access to, there are other very weird things happening, like the battery voltage dropping to single digits and the temperature readout going from a healthy 30C to -20C. The garage was about 14C-20C.

My question, after all that prattling, is how much I should push for the batteries replacing assuming that the bugs are worked out and it's just they were at very low voltage? I know that with Li-ion cells, the under voltage could be a serious issue but I have no experience using LiFePO. Are there any specific tests I can ask to be done to look for permanent damage (like cell impedance or other indicators of lithium plating)? I'm reliant on them because I simply don't have access to per-cell data, just fairly high level stuff but, with some prep, I can at least demand some kind of proof that it's functioning entirely within spec and hasn't suffered damage if they do manage to revive the system.

Any advice would be appreciated.

thm_w:
The ones I see here list 58.5V as charge voltage: https://www.givenergy.co.uk/pdf/Version%202.0/Giv-Bat%202.6.pdf

So that would mean 16S, 16 series cells. The fully discharged voltage would be 40V (manual says operating only goes down to 43V). 24V at 16S could mean 1.5V on some cells, which is very low, and can result in lost capacity, or if lucky no loss at all (anecdotes here).
Its odd that they would self discharge that much, unless they have been sitting around for long time, or the BMS has some flaw.

Surely their app has a way to determine capacity or draw? Do a full discharge and see how long it lasts. Let us know what kWh you get.

Temperature readout showing -20C may be concerning if it stops you from charging the pack when it displays that.

Siwastaja:
What does "force charging" mean? Bypassing the internal contactor/power switch and accessing the unprotected battery terminals?

If yes, then this seems one of the simplest cases:

The batteries were DOA, and should have been returned for refund or shipment of new batteries instead of trying to fix something that cannot be safely fixed.

OTOH, faulty temperature reading suggests some problem with the measurement system (say, ADC).

But this is something only the manufacturer can work out.

If the total pack voltage was merely 24V, that means some of the cells are likely dead, and the thing is dangerous to use. Obviously, the BMS is preventing you to use it. It was broken to begin with and should not have been messed with.

Faringdon:
I used to work for a major Battery/Inverter/Charger company.
I am surprised by what you say. Before we installed any system, we had the entire system set up in our premises. We would then conduct five consecutive full charge/discharge tests. We would note the voltage of every single cell throughout this (it was shown on a graphing software program). Ie, we would check for any cell imbalance throughout that. Any imbalanced cell was removed and replaced. We would also note the capacity of the battery was OK. We woudl also check all the efficiencies of charger and inverter, and that temperature readings were correct etc etc........ Then we would ship that exact  system to customer. So the installer just had to rig up and connect the internet to it. The internet was used to continuously collect electrical data from the customer throughout the product life. The customer had their own software App which they used to get limited data, eg state of charge graphs etc. If a customer’s cell went rogue at some point , we could see this at head office, and despatch a new battery. So I would think those tests need doing for you. So presumably after install, your system will go into test mode for some time?.....and your system is connected to the internet, and the data will go back to their head office?......i think it needs to.

The charge discharge test needs doing at full power, as otherwise the inverter and charger are not at their most efficient....and we need to check that efficiency.

There was never any need for an installer to do analytics......they just connected unit to internet, and then we at head office coudl see everything about their system from there. We could then take charge of the system and  get eg the 2 batteries to charge to the same voltage prior to connecting them etc etc.

Sometimes a customer would phone up and say the system wasnt giving them the full battery capacity......so we would download their data to head office and look at it....sometimes they would have a tiny load in the house for ages......and of course, the inverter is much more  inefficient at light loads, so we could see this and tell them this. Some customers would say the unit was causing spikes on their supply....then we looked from head office and we could see that they just had some malfunctioning load somewhere in there house, nothing to do with our system.

There are some things about the system that customers often queried......eg, the loading needed to be at least 400W before the inverter would kick in...even then, the inverter always took at least 4 mins to come on....this was some regulatory thing that applies to all  grid tied inverters.

We actually had some software system which used to manage their useage.......it did it so that  the battery energy was not shipped out to the grid (since customers dont get payed much for export)....have you got that software in yours?...i think its needed, otherwise your solar will be getting  exported to grid and you dont get payed muich for that....so the system needs current measurement devices on the battery and on the electricity coming into the house....and these are wired up to the software in the system. There has to be software which ensures that your inverter doesnt ever  take energy from your batteries and ship it out to the grid. The accuracy of these current  reading devices was checked at our premises when we did all the pre-install checks.

There was also a calibration thing that we could do for customers, so as to maximise the accuracy of their electric current readings.......we coudl do that from head office.....we just did a forced charge or discharge and noted the current, then we'd calibrate for them...but not everyone wanted to bother with  this.

Also, any unbalanced cell woudl trigger a software alarm, so we could immediately( from head office)  see which customers cells had gone unbalanced..........this is needed...as otherwise, how does the company know that the batteries that are being supplied are good ones. (we had a 10 yr warrantee on batts)

Some customers woudl  phone up and say there energy bills werent going down as much as expected...then we would download their electrical data graphs...and we'd see that there batteries were hardly being discharged at all each day,  and they were importing energy instead from the grid, so we'd help them to get their batteries to do a full charge and discharge into their load every day, then they woudl get their moneys worth....we could see this from the electrical data and give the advice over the  phone....we could even set their system to our recomended settings, which maximised their payback.

For some customers we could make it shutdown in the small hours, so the fans didnt make their noise in the night


Here is some quotes on battery/inverter/charger systems
https://www.greenmatch.co.uk/blog/2018/07/solar-battery-storage-system-cost

....but one company does it much much cheaper if you allow the power company to sometimes take control of your system in order to do grid balancing....AYK it obviosuly needs an internet connection for that, which they provide.
it woudl be interesting to hear the cost difference with your own system, but please dont divulge if you are uncomfortable

Dave Jones, owner of this site, may have a battery/inverter/charger video telling just what you want to know.

It wouldnt surprise me if you were to tell that you actually tried to purchase a system from the co that i worked for....but you were unable to get one, due to the massive demand that we were experiencing at the time.....i  was always taking phone calls from people screaming at me about nobody having contacted them about their wish to buy our system....the demand was phenominal, and must be even more now with electricity costs.......i wonder if some  undesirable competitiors have slipped in their now, in order to tap into the enormous demand levels for this kit  now.

woodchips:
You are in the UK, the goods have to be of mechantable quality, they obviously aren't, so get your money back.

Seem to me to be rejects from another sale, and you are expected to accept them with open arms.

You need a battery tester that will give you how many Ah charge are stored, and it needs to be more than 100% of the rated number since they are, supposed to be, new.

You have now paid for many kW electricity to charge them, and you want that money reimbursed.

Being picky? No, bought a battery for an original Mac laptop, and it was obviously well secondhand, but they refused to swap so ended up with a not very cheap battery with less then half the life it should have.

Why have lithium batteries in any case? Use lead acid batteries, much cheaper, much more robust, worth money when you need to change. The only benefit lithium gives is lighter weight, not much use in a static application.

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