How long does it take to charge 48v, 280ah bank?

TLJester

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Hi
New to this, searched and could find an answer.
Trying to get a ballpark (sanity reassurance) on how long it takes to charge my 48v battery bank.
its been sitting around 53-54v for a couple of days now. Starts off at 53v in the morning, and ends at 54v in the evening

Bank is made of 16x280ah EVE cells with a DALY BMS (48v 250a, non-smart)
Solar is via 6x350w (2 banks fo 3 panels, one bank for each MPPT), 40voc, 9amp, panels in series which daily im getting an average of low of 300w peak of 700w as the day progresses
have 2x MPP PIP LV 3048 charger/inverters, MPPT 144voc, 80a
each unit is outputting about roughly 400w, 90v, 9amps for 6 hours of the day
Battery settings are:
Bulk, 58v
Float, 54.4v
Low, 48v

Given all this, what is the realistic time it should take to charge this sized bank, are we talking hours/days/weeks ?
not really sure what to expect so really just checking my sanity and what i should realistically expect.

Feel like i got to from 52v (about 3.3v per cell) to 53.5v (about 3.35v per cell) pretty quickly. but since then its dragging.
Thanks for any insight you can give me
 

Ampster

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I find it simpler to track the Watthours that go into and out of the battery. Consumption and production vary by hour and therefore time is not a good metric. The good thing about Lithium versus Pb is that you do not have to fully charge Lithium every day. It sounds like your batteries are at a healthy voltage.
 

TLJester

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I have no usage/draw on the system. Setup on my work bench for testing prior to full install.
so im really just wanting to fully charge the batteries and get a sense of how long that will take :)
 

Ampster

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3.35 volts per cell is about the resting voltage of a fully charged cell. Your batteries may be fully charged. If you have no usage it won't take long. If you have a lot of usage it will take a long time. Time is a relative measure that depends on Watts in and Watts out. Does your equipment give you any data? You have stated some assumptions but actual data does vary by the hour. I can't give a more definitive answer without actual data.
 
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upnorthandpersonal

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Let's do a quick calculation based on some hypothetical numbers.

Suppose the battery is 50% full
Suppose you have 400W from your panels coming, for 6 hours a day

50% of the 280Ah/51.2V nominal battery represents 7kWh

400W for 6 hours represents 2.4kWh

So based on those numbers, it would take you three days to charge from 50% to 100%.
 

TLJester

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Let's do a quick calculation based on some hypothetical numbers.

Suppose the battery is 50% full
Suppose you have 400W from your panels coming, for 6 hours a day

50% of the 280Ah/51.2V nominal battery represents 7kWh

400W for 6 hours represents 2.4kWh

So based on those numbers, it would take you three days to charge from 50% to 100%.
Thanks, thats what i was looking for. A sanity check on how long (roughly) it will take :)
 

TLJester

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Here are actual data points:

Shunt readings:
54.6 V
13.01 A
740 W
11.17 kWh
207AH
04.0 Ohms (External Resistance)
99 mOhms (internal Resistance)

Unit #1:
Screen Shot 2021-10-11 at 1.25.00 PM.png

Unit #2:
Screen Shot 2021-10-11 at 1.25.09 PM.png


Battery settings:
Screen Shot 2021-10-11 at 1.21.36 PM.png
 

Ampster

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Assuming 740 Watts an hour it would take 15 hours to put 11.17 kWhs into the battery. There are not 15 hours of solar per day so it would take longer.
 

TLJester

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I've been running/charging for 3 days... hence my concern.
Each day has been clear blue skies.
Today ironically is slight overcast 🙃

.. but what i am hearing is it doesn't sound too far off, and that i just need to be patient ? ;)
Is that as the charge/discharge curve for LifePo4 cells are so flat between 3.3v and 3.5v per cell ?
 
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Ampster

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I've been running/charging for 3 days... hence my concern.
Each day has been clear blue skies.
Today ironically is slight overcast 🙃

.. but what i am hearing is it doesn't sound too far off, and that i just need to be patient ? ;)
I understand that your equipment has been hooked up for three days. Is the 11.17 kWh the amount of energy that your system has been putting into the batteries during those three days? If so, it may be safe to assume that your batteries were approximately 80% discharged. I can't tell if they ever reached the 58 volt bulk setting but if they did the current voltage of 53 or 54 volts is close to the voltage that fully charge cells settle at. The data is not consistant. For example, one screen says 10 Amps which would be 540 Watts but another data point says 740 Watts. That would make time estimates different.
I am not sure what your concern is about? Your battery does not seem to be overcharged if the resting voltage is 54 volts.
 

upnorthandpersonal

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.. but what i am hearing is it doesn't sound too far off, and that i just need to be patient ? ;)
Is that as the charge/discharge curve for LifePo4 cells are so flat between 3.3v and 3.5v per cell ?

Yes, and yes.

Also, keep in mind that the voltage the battery gets to depends also on the current you're pumping in. Higher currents lead to higher voltage faster:

qidwvcdb3z4i.jpg
 

TLJester

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Should i configure my solar panels to have higher watts or amps then to charge the batteries faster ?
(Serial or parallel) ?
right now they are in series + to - etc
Could swap to parallel + to + etc
 

chrisski

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Won’t make much difference in ideal conditions charging between series and parallel unless;

1) Min or max voltage requirements not maintained. Min the system won’t turn on. Max the MPPT could smoke and die.

2). If your array has shading, even a single panel, output can plummet. Then parallel is better, but then there’s voltage loss because of lower voltage, distance and higher amps. If you have a tree, a smokestack, or an antenna, may need to go parallel/

My RV I put panels in series to avoid voltage loss, but saw some shading really killed the output, so I have three arrays: 3S2P; 2P; and 4P.
 

upnorthandpersonal

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Should i configure my solar panels to have higher watts or amps then to charge the batteries faster ?

Power is power - you can't generate 'more amps' with the same amount of panels. Your charge controller takes the power it gets and turns it into the power your battery needs (Watts in == Watts out). Unless you put more power in, you can't get more power (aka 'amps') out.
 

MrM1

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I'm in a similar boat as the OP. Just upgraded to a LFP 460Ah bank, and the array is barely keeping up. Want to increase this to a 690Ah bank. So need to make some changes

I have a 2565w array of 9 x 285 panels in a 3s3p arrangement. Right now I am capable of at most 10kwh per day in NE Fl. This is about (10000w / 4.5 sun hours = ) 2222w of usable power per hour. So I plan to over panel, but not sure what is the best plan.

I want to go either 12 x 285 = 3420 ... OR ... 15 x 285 = 4275w array. I have a MidNite Solar Classic 150. It is cable of charging at 96 amps.

I did check with MidNite, they said with the Classic 150 CC I can over panel all I like, and it will just clip once it hits 96 amps charging. So in full sun any extra is wasted. For a 24v system with a charging voltage of an average of 27.2v that puts me somewhere around a max 2600 watts of input (which is not the same as the array size). That would equal 96 amps of battery charging.

Right now I have a 3s3p. I could go out to a 4s3p, but that puts my volts at about 145v. Not out of spec for the Classic at 150v input, AND the classic also has Hyper VOC which is 150 + battery voltage. So if it were to go over on cold mornings it would simply go to sleep until the voltage got under 150. But then it's asleep some times. Could also stretch it out to 4s4p

OR, just go 3s4p or 3s5p and keep my input voltage as under 105v input. (I checked and this is on almost any day I could check records).

Question is, would i get better overall charging results say on average and in cloudy days and early morning / late afternoons with ...

3s voltage of 105v input and either ...
1. 3s4p = 3420w array​
2. or go big with a 3s5p = 4275w array​

Or a 4s voltage of 140v input (which would put the CC to sleep after 150v input) and either ...
1. 4s3p = 3420w array​
2 or go bigger with a 4s4p = 4560w array​

Looking for what arrangement would give me the most bang for buck WITHOUT over spending on overpaneling.

Might be better to stick with the smaller array versions since at peak times anything above would go to waste. But in any case above, does higher voltage get better amp output in lower light, or does higher panel wattage preform better.

I hope this makes since. (It's hard for me to wrap my head around it)
 
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