Axpert battery recomended charge voltage

[Colin]

What would the recommended bulk and float voltage be on these vision batteries?

Am I correct in saying 57.6V - 58.8V bulk and 54.4V - 55.2V float, these seem a bit high especially the bulk charge

Axpert 5kVa 4KW inverter

Vision 6FM100P-X.pdf

[___]

1 hour ago, Colin said:

Am I correct in saying 57.6V - 58.8V bulk and 54.4V - 55.2V float, these seem a bit high especially the bulk charge

Bulk? You mean Absorption I'm sure, by definition bulk is the constant current phase when you're still dragging the voltage up :-)

14.8V is pretty typical for flooded lead acids, which these aren't, so even the 14.7V seems a tad high. 14.5V again is pretty typical for AGM, so that seems good to me. So 58V should be good. And then I'd go with 13.8V for float, because contrary what many people think, the batteries aren't completely full when chargers go to float, so holding to the higher end can only help a cyclically used battery.

So 55.2V float, and 58V Absorb is what I'd use.

[Colin]

Thanks @plonkster, attached from Axpert manual, they do call it "bulk", I assume we talking of the same setting?

 

[___]

11 minutes ago, Colin said:

I assume we talking of the same setting?

Yes, I'm sure it is the same thing. I've been trained lately to not interchange the two, I do it too... and then I confuse people. So I'm particularly aware of it.

[Coulomb]

15 hours ago, Colin said:

from Axpert manual, they do call it "bulk", I assume we talking of the same setting?

Also agreed. Axpert manuals aren't the best examples of clear, scientific English writing. After all, the manuals are from the same people that gave us "Updata sucess!" (SIC). Fortunately, we can largely work around these limitations.

[Guest]

6 hours ago, Coulomb said:

... manuals aren't the best examples of clear, scientific English writing.

On a whole new note. Why is that? I have had my fun at Chinese translations but why is it so?

I mean, Chinese people are bloody good at what they do, not?

So I am thinking, seeing as their language (with regional variations to boot) makes it interesting to translate back to basic Ingelish?

For surely they have people whom can translate Chinese dialects to proper English?

[Coulomb]

1 hour ago, The Terrible Triplett said:

For surely they have people whom can translate Chinese dialects to proper English?

I get the feeling that there are hierarchies of expertise. I suspect that the guy who wrote the code for the inverter interrupt routine isn't the same guy who messed up the charge algorithm. For whatever reason, I suspect that manual writing is delegated to the lower levels of that expertise hierarchy.

Perhaps it has something to do with western arrogance, too. As far as I know, all C compilers take code written purely in English (comments are almost exclusively in Chinese, from other projects); a while loop always starts with the English word "while". Their variable names are all in English too. How hard would it be to write a C compiler, or fork GCC, to take Chinese text? Though in this case, they'd have to duplicate a DSP compiler, which would not be trivial. I don't see Texas Instruments supporting a Chinese version. Maybe this western bias is a source of irritation to them, and they unconsciously or otherwise make the documentation bad as a sort of revenge for that.

International scientific conferences are all in English too; convenient for us, but there are way more of them now and Chinese nationals are writing a larger and larger proportion of papers these days. With their very large numbers of top quality universities, perhaps that's changing for many intra-national scientific papers, which may gradually become the majority, as they see less and less need to share their technology with the rest of the world. It will be interesting to see how the next few decades goes.

[Guest]

1 hour ago, Coulomb said:

It will be interesting to see how the next few decades goes.

Imagine the western world must translate all they produce, and not vice versa ... that would be very interesting.

The "hierarchies of expertise" makes sense.

[___]

10 hours ago, The Terrible Triplett said:

For surely they have people whom can translate Chinese dialects to proper English?

A lot of people who do speak or understand English are unaware how badly it's influenced by their local context. I proof read and change a lot of stuff for the company I work for. One thing I do a lot is swap the word order around and remove commas to fix the flow. I also fix sentences that start with "Also, ...". :-)

It's a bit of a running joke really... using the Saffer to proof read the English :-) I mean, we have our own mannerisms!

[Gabriël]

about 40 years ago my old lady tried to get her sons to learn mandarin... she said the chinese are going to take over and you'd better be able to communicate with them... wise old lady!

we did not

[Colin]

I have noticed that the Axpert will only go to 57.8V bulk charge if the available charge is at least 50Amps, as current drops, so does the voltage.

On cloudy day with only 1KW available from solar (10A into battery), battery voltage will only be about 52V

 -When I run geny, battery voltage climbs with current, 30Amps into batteries - voltage at 54V, 40Amps -55.5V, then only gets to the 57.8 at 50Amps.

Then again as batteries nearing full, current trailing down, voltage drops along with the current. Should this voltage not stay constant at 57.8V till current drops enough?

Running 73.00b with setting 32 - bulk charging time set to aut

Edit: The above was when batteries needing charge.

Once nearing full however, the voltage does stay at 57.8V, possibly due to lower resistance?

However it then does not appear to drop to float voltage, charge current now falls to 5Amps on Axpert (BMV702 reads 7A), but voltage now stays at 57.8V

 

 

[Coulomb]

13 hours ago, Colin said:

I have noticed that the Axpert will only go to 57.8V bulk charge if the available charge is at least 50Amps, as current drops, so does the voltage.

That's how batteries are. You can't get them to full voltage without a lot of current, when they need charge. They need that extra charge to make their internal ideal-battery voltage higher. It's nothing to do with Axperts; all chargers will be this way.

That's the bulk charging stage; where current is limited by the available charge power, and voltage will slowly rise from a little above resting voltage to the absorb voltage. The bulk stage is also called the CC stage - Constant Current.

For lead acid batteries, and to a lesser extent for other chemistries, there is an absorb stage where the battery voltage is kept relatively constant. This absorb state is also called the CV stage - Constant Voltage.

Once the battery is deemed to be full, absorb stage is terminated, and float stage is started. This is another constant voltage phase, but the voltage is lower, so that lead acid batteries don't bubble off hydrogen, and lithium batteries don't do bad reactions that reduce life. In this phase, there is very little charging; it's mostly there to replace charge lost by loads.

As for when to go to float, since you have setting 32 set to Aut, float should be reached when the battery charge current falls below (total charge current for all paralleled machines) divided by 5. If that figure is less than 5 A per paralleled machine, the threshold becomes 5 A per machine, i.e. 5 A per machine minimum. If you have a single machine and its maximum charge current setting is (5+1) * 5 = 30 A or more, then this should be low enough to trigger the float stage. Otherwise, your current has to fall to 4 A before it will go to float.

The current has to be less than this threshold for 30 seconds (some 1,500 measurements) without exception. So if you have fleeting shade, that could ruin that set of measurements, and it has to start again. So it may take several minutes before it manages 30 seconds without one measurement of 6 A or more. Perhaps try AC charging once it's down to 5 A of PV charging (turn off your panels for this test). AC charging doesn't have intermittent shading to cloud the issue, so to speak.

[Colin]

5 hours ago, Coulomb said:

If you have a single machine and its maximum charge current setting is (5+1) * 5 = 30 A or more, then this should be low enough to trigger the float stage. Otherwise, your current has to fall to 4 A before it will go to float. 

Thanks for above @Coulomb, I understand you explanation, only issue is I have charge set to 50Amps, thus should float not start at 9Amps?

[Coulomb]

18 hours ago, Colin said:

I have charge set to 50Amps, thus should float not start at 9Amps?

Yes, unless you are running the lithium ferrite version of the patched firmware by mistake. Your main firmware version page on the LC Display should say LC1 73 00b, not LF1 73 00b. If the latter, then the threshold would be 4 amps or less.

 

[Colin]

5 hours ago, Coulomb said:

unless you are running the lithium ferrite version of the patched firmware by mistake. Your main firmware version page on the LC Display should say LC1 73 00b, not LF1 73 00b. If the latter, then the threshold would be 4 amps or less.

I think you correct, will double check, I may have downloaded wrong firmware

[Colin]

Bingo, many thanks @Coulomb

I did have the LC1, upgraded to BC1 73 00c and now goes down to the set 56V at 9Amps charge

Simple fix, but totally ove1looked without your help

[Coulomb]

15 hours ago, Colin said:

I did have the LC1, upgraded to BC1 73 00c and now goes down to the set 56V at 9Amps charge

Well, I'm at a loss as to why that fixed the problem. But glad to see that it's all good now.

[Kilowatt Power]

On 2018/05/21 at 3:13 AM, Coulomb said:

As for when to go to float, since you have setting 32 set to Aut, float should be reached when the battery charge current falls below (total charge current for all paralleled machines) divided by 5.

What are the implications of changing setting 32 - Bulk charging time from AUt to say 600 minutes with a maximum utility charging current of 20A?

I'm asking because I have a set of 1 year old 4 x 200Ah Gaston GT12-200AG polygel (AGM+GEL) batteries that discharge pretty fast (< 3 hours) from >48V to 42V low DC cut-off voltage at an average load of 600W and suspect they are not getting sufficient absorb time.

[Coulomb]

9 hours ago, Kilowatt Power said:

the implications of changing setting 32 - Bulk charging time from AUt to say 600 minutes

If that's not a typo, it would charge all day aiming for the bulk/absorb voltage. You could achieve the same effect by changing the float voltage to be the same as the absorb voltage.

It means it would leave the battery near the gassing voltage for a long time. As long as it didn't actually gas (assuming sealed battery modules), that would be safe, and might bring them back towards nominal capacity. If they're sulphated, then charging them longer won't help much if at all.

Also watch for them getting warm or even hot. If so, terminate the charge (go back to AUt) until they cool down. A little warmth is OK and inevitable.

[Kilowatt Power]

Thanks Coulomb. The batteries are VRLA Polygel  (a mix of AGM+GEL chemistry) with the following characteristics:

• Standby use - 13.5V - 13.8V, initial current - no limit
• Cyclic use - 14.4V - 15.0V, initial current - 50A max.

I couldn't possibly sit and wait 10 hours (600 mins) watching them charge so I'll try 4 hours bulk charging time at 50A, 13.8V per block as per the attached charge characteristic graph. 

I'll therefore change settings 02 -> 50A, 11 -> 50A, 26 -> 55.2V (i.e. 4*13.8V - below gassing voltage ), 27 -> 54.0V (i.e. 4*13.5V) and 32 -> 240 minutes then see if performance improves.

P.S: I tested individual batteries using a 100A load tester and voltage dropped from an average 13.6 to 11.9V within 5 seconds. A second test using a conductance battery analyser did not reveal any internal resistance > 3 milliohms. 

[Blowdart18]

Just picking some brains here, the Narada 12NDF120 says it has a maximum charge current of 50A.

 

4 of them wired to create a 48V system will also only only accept a maximum of 50A

 

However . . . and I might be wrong, the google search has not been strong with me this morning.

When wiring 48V banks in parallel does that not split the charging current?

So I set 50A in Axpert, and I have x2 48v Narada, will the charging current theoretically be 25A for each bank. 

[Coulomb]

On 2020/04/20 at 3:06 AM, Kilowatt Power said:

What are the implications of changing setting 32 - Bulk charging time from AUt to say 600 minutes with a maximum utility charging current of 20A?

I really don't know lead acid that well. My understanding is that as long as the charge voltage is under the gassing voltage (about 14.4V per module at 25°C), it should not harm the battery or overcharge it. It may heat the battery though, so that can lead to runaway and boiling the cells. So you need to watch for signs of gassing or heating. 

[Coulomb]

19 minutes ago, Blowdart18 said:

When wiring 48V banks in parallel does that not split the charging current?

Yes. So if you have 8 modules, you need twice the 50A (i.e. 100A) to charge all the modules at 50A.

[Blowdart18]

57 minutes ago, Coulomb said:

Yes. So if you have 8 modules, you need twice the 50A (i.e. 100A) to charge all the modules at 50A.

So technically once again, if you have 12 modules, you will need tree times the current to charge all modules at 50A. i.e 150A

 

However theoretically once again, you would want to find a balance between this considering the following:

 

1) cable size

2) fuse size between battery and axpert

[Coulomb]

2 hours ago, Blowdart18 said:

So technically once again, if you have 12 modules, you will need tree times the current to charge all modules at 50A. i.e 150A

Yes.

2 hours ago, Blowdart18 said:

However theoretically once again, you would want to find a balance between this considering the following:

1) cable size

2) fuse size between battery and axpert

Well yes, but also one inverter likely can't produce 150 A, and even models that can produce 140 A can only do that with 80 A of PV charging and 60 A of utility charging working together.

It's isn't necessary to charge at the maximum possible rate, though it's usually a good idea to tell the Axpert about that maximum if possible, since it uses that setting (setting 02, maximum charge current) to figure out when to switch from absorb to float stages.

As an aside, you may find it challenging to balance these and protect them against excessive discharge. Some of these 12 V lithium modules aren't even allowed to be connected in series (doing so voids the warranty).