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New 5 KVA Lifepo4 lithium voltages


Dname
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Hi all,

So i purchased a new 5kva battery from a local supplier and have a question which I can't seem to find an answer to...

supplier says 54.4v is full charge, however research shows 58-58.4 as full.  Running the latest watchpower software for the Kodak branded axpert shows 54.4 at 72%.

When the inverter bulk charged to 58 inverter showed 100%, then back to 72 for the 54.4. 

I'm getting about 4.5 hours off this battery which seems supremely low. My old bank of 6x12v 105ah battery used to run for considerably longer, this bank cost me half the price of this 24000 new one.

If anyone can assist I would be grateful, currently feels like I've been shafted. 

 

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I assume that you mean 5 kWh (of stored energy, as opposed to 5 kVA of apparent power, which doesn't apply to a DC device like a battery).

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supplier says 54.4v is full charge, however research shows 58-58.4 as full. 

It depends on whether it's a 15S battery or a 16S battery. You didn't say what brand of LFP battery (there are many), but we can guess. 54.4 V is 3.63 VPC average, a very high figure. Usually, it's best not to go over 3.6 VPC ever, and only charge to about 3.50 VPC regularly. 54.4 / 16 = 3.40 VPC; that definitely too low, so it can't be 16S.

58.4 V is a good charge voltage for a lead acid battery. That's a totally different chemistry. 58.4 / 16 = 3.65 VPC, which is absolute max for a 16S battery.

Quote

Running the latest watchpower software for the Kodak branded axpert shows 54.4 at 72%.

Watchpower doesn't know the SOC of a LFP (LiFePO₄) battery unless the inverter is connected to the battery's BMS via a special cable. Without this, it's doing some stupid calculation like (battery voltage - battery cutoff voltage) x 10%. This is a rough guide for lead acid batteries, and totally unusable with LFP batteries.

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When the inverter bulk charged to 58 inverter showed 100%, then back to 72 for the 54.4. 

58 V is dangerously high for your battery. As an example, a Pylontech will disconnect to save itself at 54.0 V.

Quote

I'm getting about 4.5 hours off this battery which seems supremely low.

With 5 kWh = 5000 Wh, using 80% of the nominal capacity leaves 4000 Wh, which is some 4000 / 4.5 = 889 W average (ignoring losses). This seems reasonable to me.

Quote

My old bank of 6x12v 105ah battery used to run for considerably longer, 

That was presumably on a 24 V system. 12 V x 105 Ah = 1260 Wh, times 6 is 7560 Wh, of which you should only have been using 50%, or 3780 Wh. So that's not much less than what you have now. If you abused your old battery and used say 80% of nominal, that would have been about 6 kWh used, or about 50% more than you have usable now.

It's also quite possible that you're not charging your battery fully, despite the scarily high voltage settings you have mentioned. What is your float voltage setting? Do you somehow stop charging when the inverter says it reaches 100% SOC? Can you read the SOC from the battery? At least approximately with a set of 6 or so LEDs?

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1 hour ago, Coulomb said:

I assume that you mean 5 kWh (of stored energy, as opposed to 5 kVA of apparent power, which doesn't apply to a DC device like a battery).

It depends on whether it's a 15S battery or a 16S battery. You didn't say what brand of LFP battery (there are many), but we can guess. 54.4 V is 3.63 VPC average, a very high figure. Usually, it's best not to go over 3.6 VPC ever, and only charge to about 3.50 VPC regularly. 54.4 / 16 = 3.40 VPC; that definitely too low, so it can't be 16S.

58.4 V is a good charge voltage for a lead acid battery. That's a totally different chemistry. 58.4 / 16 = 3.65 VPC, which is absolute max for a 16S battery.

Watchpower doesn't know the SOC of a LFP (LiFePO₄) battery unless the inverter is connected to the battery's BMS via a special cable. Without this, it's doing some stupid calculation like (battery voltage - battery cutoff voltage) x 10%. This is a rough guide for lead acid batteries, and totally unusable with LFP batteries.

58 V is dangerously high for your battery. As an example, a Pylontech will disconnect to save itself at 54.0 V.

With 5 kWh = 5000 Wh, using 80% of the nominal capacity leaves 4000 Wh, which is some 4000 / 4.5 = 889 W average (ignoring losses). This seems reasonable to me.

That was presumably on a 24 V system. 12 V x 105 Ah = 1260 Wh, times 6 is 7560 Wh, of which you should only have been using 50%, or 3780 Wh. So that's not much less than what you have now. If you abused your old battery and used say 80% of nominal, that would have been about 6 kWh used, or about 50% more than you have usable now.

It's also quite possible that you're not charging your battery fully, despite the scarily high voltage settings you have mentioned. What is your float voltage setting? Do you somehow stop charging when the inverter says it reaches 100% SOC? Can you read the SOC from the battery? At least approximately with a set of 6 or so LEDs?

Unfortunately I can’t confirm the brand as this is encased In a big white box, warranty void if cover removed. I bought it from the supplier like this. They have said 

“There 16 major cells, the sub cells of that is a few 100, I'm not sure of the number” I will ask them if it’s 16s (sorry, still new to this so will need to find out what that means)

so are you saying the 54.4 float voltage is too low? Should it be a higher value? The 58v is set as a bulk charge value, I’ve noticed it doesn’t stay there for too long. These are the settings the supplier set up on installation. 

my house runs between 300 to 450w during the night. Should I expect more than the 4.5 hours from this? Your rating shows 889 which is quite a bit higher than what I’ve seen(on the inverter)

you are correct the old bank was 24v on an Ellie’s trolley inverter. I monitored the battery levels whilst using it and it never went below 3/4 bars. Assumed this was safe at 75%, and, that that was was correct .
 

so current setting are as per screenshot. 
 

also noticed that battery voltage drops considerably (from 54.4 down to 52.6) over the first few minutes after sunset. It hovers around that voltage for the next while and then falls steadily. 
 

I can’t ready the SOC from the unit, however supplier has told me the Battery management unit is inside.  The charging is controlled by the inverter(only thing I can monitor) 

there’s a 3mb limit on uploads, have many more screenshots I can send highlighting the voltage drop, let me know if you want them. 
 

tried my best to answer your points, so let me know if there’s a missed one.

 

and thanks for the feedback.

713AF318-CDBF-4607-B955-77F19A61A731.png

DA4959E1-6E80-47A2-BAD6-BAA5E42F308F.png

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Just now, Dname said:

Unfortunately I can’t confirm the brand as this is encased In a big white box, warranty void if cover removed. I bought it from the supplier like this. They have said 

“There 16 major cells, the sub cells of that is a few 100, I'm not sure of the number” I will ask them if it’s 16s (sorry, still new to this so will need to find out what that means)

so are you saying the 54.4 float voltage is too low? Should it be a higher value? The 58v is set as a bulk charge value, I’ve noticed it doesn’t stay there for too long. These are the settings the supplier set up on installation. 

my house runs between 300 to 450w during the night. Should I expect more than the 4.5 hours from this? Your rating shows 889 which is quite a bit higher than what I’ve seen(on the inverter)

you are correct the old bank was 24v on an Ellie’s trolley inverter. I monitored the battery levels whilst using it and it never went below 3/4 bars. Assumed this was safe at 75%, and, that that was was correct .
 

so current setting are as per screenshot. 
 

also noticed that battery voltage drops considerably (from 54.4 down to 52.6) over the first few minutes after sunset. It hovers around that voltage for the next while and then falls steadily. 
 

I can’t ready the SOC from the unit, however supplier has told me the Battery management unit is inside.  The charging is controlled by the inverter(only thing I can monitor) 

there’s a 3mb limit on uploads, have many more screenshots I can send highlighting the voltage drop, let me know if you want them. 
 

tried my best to answer your points, so let me know if there’s a missed one.

 

and thanks for the feedback.

713AF318-CDBF-4607-B955-77F19A61A731.png

DA4959E1-6E80-47A2-BAD6-BAA5E42F308F.png

 

53544150-A7EC-49EC-B0D0-CDF5D95A8FA3.jpeg

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23 hours ago, Dname said:

Unfortunately I can’t confirm the brand as this is encased In a big white box, warranty void if cover removed. I bought it from the supplier like this.

Sorry, that sounds so dodgy to me.

Quote

“There 16 major cells, the sub cells of that is a few 100,

That suggests 16S to me (16 cells connected in series). Each with ~100 Ah capacity.

Quote

so are you saying the 54.4 float voltage is too low? Should it be a higher value? The 58v is set as a bulk charge value, I’ve noticed it doesn’t stay there for too long. These are the settings the supplier set up on installation. 

Without knowing what's in there, it's so hard to tell. From the fact that your battery drops to around 52.6 V soon after sunset, I'll now guess that you have a 16S battery. My 16S LFP battery also falls to around 52.6 V soon after sunset. 54.4 is higher than the value I use (53.7 V), but lower than the 16S equivalent of the accepted pylontech voltage (51.8 / 15 * 16 = 55.25 V).

Quote

my house runs between 300 to 450w during the night. Should I expect more than the 4.5 hours from this? Your rating shows 889 which is quite a bit higher than what I’ve seen(on the inverter)

It's really hard to say. There could be intermittent loads that add up a lot.

Quote

you are correct the old bank was 24v on an Ellie’s trolley inverter.

Are those lead acid or LFP?

It looks like your battery doesn't stay very long near the 58 V bulk charging voltage. That's 3.625 VPC average, way too high in my mind, but hopefully the BMS is not disconnecting. Perhaps try setting 27 (bulk/absorb voltage) at 55.2 V (that's the value I use for my 16S LFP battery) and see if it stays there longer. What might be happening is the inverter overshooting the 58.0 V target, and triggering the internal BMS to disconnect from the inverter. That would presumably terminate the bulk charge, though I don't really know.

With the inverter-charger not charging the battery properly, that's likely the cause of your short run time. You need to see the battery voltage over about 55 V for 1-2 hours to charge it properly.

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41 minutes ago, Coulomb said:

Sorry, that sounds so dodgy to me.

That suggests 16S to me (16 cells connected in series). Each with ~100 Ah capacity.

Without knowing what's in there, it's so hard to tell. From the fact that your battery drops to around 52.6 V soon after sunset, I'll now guess that you have a 16S battery. My 16S LFP battery also falls to around 52.6 V soon after sunset. 54.4 is higher than the value I use (53.7 V), but lower than the 16S equivalent of the accepted pylontech voltage (51.8 / 15 * 16 = 55.25 V).

It's really hard to say. There could be intermittent loads that add up a lot.

Are those lead acid or LFP?

It looks like your battery doesn't stay very long near the 58 V bulk charging voltage. That's 3.625 VPC average, way too high in my mind, but hopefully the BMS is not disconnecting. Perhaps try setting 27 (bulk/absorb voltage) at 55.2 V (that's the value I use for my 16S LFP battery) and see if it stays there longer. What might be happening is the inverter overshooting the 58.0 V target, and triggering the internal BMS to disconnect from the inverter. That would presumably terminate the bulk charge, though I don't really know.

With the inverter-charger not charging the battery properly, that's likely the cause of your short run time. You need to see the battery voltage over about 55 V for 1-2 hours to charge it properly.

Dodgy, agreed. Since I’ve been querying this battery with them, support has become non existent, even dodgier.

the old bank are calcium lead acids.

thanks for the input, it’s appreciated. Will see what the guys say, if they haven’t cut support totally.

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49 minutes ago, Dname said:

So I’ve received the battery specifications , see attached. Does this help?

Alas, they sent you the specifications for the cells used, not the whole battery.

There is a clue though: the cells are 6 Ah. So it's likely to contain 16S16P for 256 x 3.2 x 6 = 4 915 Wh, which they'd market as 5000 Wh.

If it was 15S, it would have to be 17P, for a total of 4 896 Wh. Not impossible, but it seems less likely.

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41 minutes ago, Coulomb said:

Alas, they sent you the specifications for the cells used, not the whole battery.

There is a clue though: the cells are 6 Ah. So it's likely to contain 16S16P for 256 x 3.2 x 6 = 4 915 Wh, which they'd market as 5000 Wh.

If it was 15S, it would have to be 17P, for a total of 4 896 Wh. Not impossible, but it seems less likely.

Correct, that’s exactly what they said. 
They also refused to disclose the manufacturer. Dodgy.

so they’ve also said they float to 3.4v per cell, which seems low as per your previous input?  Or is this fine for these cells? I’m curious about the bulk as well. If the 58 bulk and float are correct then I can then assume the settings on the inverter are correct ?

as they won’t tell me who made these cells I’m thinking they just cheap CE, which would mean I’ve been ripped yet again by these people on battery too.

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16 hours ago, Dname said:

so they’ve also said they float to 3.4v per cell, which seems low as per your previous input?

Well, that confirms that it's 16S: 54.4 / 3.40 = 16.

I use 53.7 V myself, which is 3.356 VPC average. Lower float voltages lead to longer cell life.

But yes, it's low compared to what the Pylontech manufacturer recommends, and even slightly lower than what the forum has settled on for Pylontechs (51.8 / 15 = 3.454 VPC).

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On 2020/10/08 at 5:18 AM, Dname said:

what values would you set for back to grid and back to discharge?

I use 51 and 53 most of the time (note for others: I have a 16S LFP battery).

[ Edit: PFP → LFP ]

Edited by Coulomb
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1 hour ago, Coulomb said:

I use 51 and 53 most of the time (note for others: I have a 16S PFP battery).

Hmm, I wonder why mine are set to 52-54. 
 

sorry for spamming you, but how would I calculate what my battery percentage is on these cells? 
 

i.e 10% - 49v, 20% - 50 etc. I’ve googled and pulled down tables that are quite conflicting.

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6 minutes ago, Dname said:

Hmm, I wonder why mine are set to 52-54. 
 

sorry for spamming you, but how would I calculate what my battery percentage is on these cells? 
 

i.e 10% - 49v, 20% - 50 etc. I’ve googled and pulled down tables that are quite conflicting.

Eg...

2DE9615F-A3C1-444B-95BC-7ECD36733F81.png

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23 hours ago, Dname said:

sorry for spamming you, but how would I calculate what my battery percentage is on these cells? 

Except at very low and very high states of charge, this is not possible (it is for lead acid batteries, and most other lithium chemistries). That's why the inverter's guesstimate of state of charge (based solely on battery voltage) is almost completely useless for LFP batteries.

You have to use coulomb counting, either direct from the BMS itself, or from something like a Victron BMV.

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