What voltage to charge min max ?

Hello
Im starting to learn about charging voltages and how to lengthen the life of the battery somim wondering what is the best voltage to charger at, be interested, in what people charge thares at, i know the lower you charge the less capacity you get just wond3ring if there is a sweet spot?
Thank you

The longest is at 3.6-3.6V and not touching it.

Your question is hard to answer and everyone here will give their answer based on things they read.

For instance you never said what type of chemistry you talk about?

Sorry 18650s

18650 is just a size of a cell.

What Chemistry? I guess LiIon but thats not said.. For instance I have LiFe in form factor 18650

Top balanced, 4.05V ~ 3.3V(+/-50mV*) for my powerwall.
I think it's a good balance between capacity and lifespan. Also plenty of safety space if a pack should come out of balance due to faulty cells.

*packs with lower capacity end up at lower voltage

I have top voltage of 4.0 on my LiIon packs. Lower end is 2.8V for protection and normal reconnect is around 3.4V. Its a bit hard to say since its under load and the load differs.

Like Daromer said.
3.4 to 4.0v

Short Version:
I'm running 54.6v (3.90v/cell) float high and 48.5v (3.46v/cell) low.

Long Version of how I got there:
The goal for my system is to
1) Consume (power my house) with 100% of PV array input. Don't want to loose PV power to battery full / float.
2) Extend the battery life as much as possible as long as the grid is available (normal operation). If grid is down (disaster), then battery life is not a top priority.

The battery is 14s260p 18650 Lithium-ion with 780ah@48v - e.g. 40kwh. The PV array is 7kw.

My PV array summer max is 45kwh / day and my average consumption is running 2071kw/hour during inverter on time. My monitoring shows that 30kwh is being consumed 'directly' (during day) and my battery is supplying an average of 15kwh (excess from the day burned off at night). In other words, Inverter on is around 10am and Inverter off is between 1am and 3am.

I started the year with 48v (3.43/cell) inverter off and a 56.4v (4.02v/cell) float but went up to 48.5v (3.46v/cell) inverter off because this is just ahead of the knee of the discharge curve for my battery. I have not yet gotten to 56.4v (4.02v/cell) max - the summer max so far is 54.6 (3.90v/cell). The average for the year is close to 53v (3.80v/cell).

This has resulted in an average of DOD of 34.6% for 178 days so far this year AND the DOD is more at the 3.90v high than 4.0v high - but I allow the system to go up to 4.0v/cell high. I plan to start a thread to document what happens... but I hope that this strategy will lead to my battery running 1000(s) of cycles. I understand the consensus is this hope is not realistic!

Where this has lead me in my thinking....
1) The battery is sized to my overall system so that I have the option to run a low daily DOD. This cost more but will increase the life span... I'm must not sure if extra $ up front will result in less $ down the road - that's partly what this experiment will help me determine.
2) By starting with a lower % battery demand - e.g. 15kwh of 40kwh battery - as the battery degrades I can expand the voltage range and keep delivering 15kwh/day from the battery... even when the battery has degraded to 70% of original capacity.
3) I am adjusting my home consumption options with idea in mind of consuming all the direct PV power (e.g. day time power) that I can. I have increased the options around the house to turn on/off different circuits to adjust the the consumption. I don't want to burn up 45kwh in 4hrs (larger battery strain) but adjust it so that 45kwh is spread thru PV array active (daylight) hours and minimize battery strain and night-time supply. For example, I can flip 2 circuit breakers to enable AC during summer and disable electric water heater to adjust the power consumption - but then reverse that during the winter.

OffGridInTheCity said:

I started the year with 48v (3.43/cell) inverter off and a 56.4v (4.02v/cell) float but went up to 48.5v (3.46v/cell) inverter off because this is just ahead of the knee of the discharge curve for my battery.

Click to expand...

This is how everyone should be determining their low cell voltage - based on observation of the behaviour of their cells in operation. Trying to use the negligible capacity found after the knee curve is tempting fate and not conducive to pack longevity.

Sean said:

OffGridInTheCity said:

I started the year with 48v (3.43/cell) inverter off and a 56.4v (4.02v/cell) float but went up to 48.5v (3.46v/cell) inverter off because this is just ahead of the knee of the discharge curve for my battery.

Click to expand...

This is how everyone should be determining their low cell voltage - based on observation of the behaviour of their cells in operation. Trying to use the negligible capacity found after the knee curve is tempting fate and not conducive to pack longevity.

Click to expand...

To illustrate @Sean's point on my own system (and thanks to Sean for emphasizing the 'knee') here's what my packs looked like when I was going down to 47.5v (3.40v/cell)



This was a 3.31v to 3.44v spread (130mv)

Same batterybut with48.5v (3.45v/cell) bottom



This is a 3.43v to 3.51v spread (80mv)

That's a very good illustration of my point - what are you using to do the /cell charting ?

Interesting.I've set mine to be _just_ below the knee on purpose.Having started with fairly capacity-balancedpacks, it allows me to quickly identify packs that have developedsome sort of issue.


Eg. in this screenshot, 3 packs clearlyneed attention. Had I set the cut off at 3.45V, the differences would not get amplified, andI'd be blissfully unaware of the problem until it became much worse.

Sean said:

That's a very good illustration of my point - what are you using to do the /cell charting ?

Click to expand...

Batrium info savedevery 5 minutes to a database. Then PHP pChart to pull and display in web page.

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ajw22 said:

Interesting.I've set mine to be _just_ below the knee on purpose.Having started with fairly capacity-balancedpacks, it allows me to quickly identify packs that have developedsome sort of issue.


Eg. in this screenshot, 3 packs clearlyneed attention. Had I set the cut off at 3.45V, the differences would not get amplified, andI'd be blissfully unaware of the problem until it became much worse.

Click to expand...

Yes - I understand. In your case it looks like you have a 200mv (or more) difference in the display. In my case it was only 130mv. So in my case - it wasn't enough to be worth it at this point. Later on, hopefully after a few years!!, the battery will degrade and I'll have to expand the voltage range / DOD %. As long as it continues gracefully - e.g. <= 100mv - I'm not going to over-stress about it. However, as the battery ages and I reach 150-200mv range on a pack, then I plan to focus on it.

So I'm opting to take my current yes (e.g.30mv->80mv range with no balancing isperfectly healthy for 42 packs)as a yes and save the extra work for the future.

thanks interesting reading

Might be the wrong place for this, if so Ill move it..
Im about to purchase a Chevy volt gen2 pack..,16s2p 3kw 64v 55ah
The array (already installed) that will connect to charge controller (midnite 150sl) atm is 2s3p 66v 30amps, which I have to rewire to 3s2p 99v 20amps for the cc to have enough voltage to charge the 64v pack properly..
What I need to figure out is how many max amps I should set the cc to charge the pack to not hurt batteries from charging pack to quickly..
Then also need to figure out how many amps I should set my GTIL2 to draw from the pack to not drain the pack to quickly..
Id like for the GTIL2 able to produce 1200w so I was thinking I could set it to draw max of 20amps from the pack.. 1200w wouldnt be needed often in the evenings due to most of our high loads getting done during peak solar output..only time inverter would use 20amps in the evening would be when aircon or heat would come on for 15min at a time..
Eventually I will get another pack and parallel it with the other to be able to use more of the 2000w inverters capacity..
But for now I need help with the amps coming into and out of the pack to not cause harm to it.. very much appreciate any knowledgeable persons time