Lithium charging ?

[Bossrox]

I just got my 1st set of lith's & the top off is myffin' me. I have a weak charger to do the initial top off but here's what's perplexing me. With lead/acid you can see the voltage gradually rise & the amps decrease as it charges. I haven't got my 1st lith topped off yet & what I'm seeing so far is no voltage rise, it stays at 3.4v.
So what I'm wondering is, should I see a gradual volt rise like with lead/acid, or does it stay pretty flat until it reaches nearly charged then start to rise rapidly? Charging @ 3.65v & once a 3.2v lith is fully charged & disconnected from the charger, what volt reading should I expect & what is a normal resting voltage well after fully charged.

 

[DJSmiley]

LFP has a flat curve.

How many amps can you charge and what are the batteries?

Assuming 10A charger, 280Ah cells arriving at 40% SOC, requires 170Ah to charge -> approx 17 hours
You won't see much increase in voltage till 16 hours or so (once you're entering the last few %)

4 cells in parallel: approx 68 hours when charging at only 10 amps.

 

[Bvillebob]

When you get it operating you'll see that's a great feature of lithium cells. With my FLA bank they get to 90 percent charge and then go into absorption phase and it seems to take forever to top them up full. With the lead acid they get to 90 percent and just keep taking the full 90 amps until all of a sudden they get full and it drops to near zero. The time to recharge from 90 percent to 100 percent is far less with lithium than with lead. When you have patchy sun like we do here in Oregon in the winter it makes a big difference in how full they stay.

 

[JoeHam]

Charge curve looks like this:

https://www.powerstream.com/z/charge.jpg

Be VERY careful when you get into the knees (the sharp parts of the curve).

Perhaps someone smarter than me can get that jpg to show, instead of the link or the truncated pic below.

 

[Bud Martin]

Are you using 10AWG wires and ring terminals for connections between the power supply and the cell?
What is the Ah of the battery?

 

[Bossrox]

LFP has a flat curve.

How many amps can you charge and what are the batteries?

Assuming 10A charger, 280Ah cells arriving at 40% SOC, requires 170Ah to charge -> approx 17 hours
You won't see much increase in voltage till 16 hours or so (once you're entering the last few %)

4 cells in parallel: approx 68 hours when charging at only 10 amps.

Yes, they are 280's & the charger I got is variable so I can charge @ 3.65 but the charger will only push out 5 amps @ that voltage. Can I jump up the volts to speed it up & just watch it carefully for a drop in amp draw indicating it's near charged?

 

[740GLE]

Just don’t

If you want to speed it up create a 12/24v battery with a BMS then crank the watts to the unit, let the BMS shut off on high cell voltage, then disable and finish top up individual cells.

 

[Bud Martin]

Yes, they are 280's & the charger I got is variable so I can charge @ 3.65 but the charger will only push out 5 amps @ that voltage. Can I jump up the volts to speed it up & just watch it carefully for a drop in amp draw indicating it's near charged?

Can you show us the pictures of your setup?

 

[DJSmiley]

If your charger is only 5A it wont push more at a higher voltage.

If it can output more but you’re not reaching it, your wires are crap. (Eg the included leads which come with some)

Voltage increase above 3.65v: dont do it.
Never recommended, unless you really know what your doing and exactly know the curves. Still not suggested, since you will increase the chances to fail with 99%

With the basic questions you’re asking: just be patient. In the meantime, do some research so you know what you’re actually doing.
A good research to start is the overkill solar bms document. Also handles topbalancing

 

[Bossrox]

If your charger is only 5A it wont push more at a higher voltage.

If it can output more but you’re not reaching it, your wires are crap. (Eg the included leads which come with some)

Voltage increase above 3.65v: dont do it.
Never recommended, unless you really know what your doing and exactly know the curves. Still not suggested, since you will increase the chances to fail with 99%

With the basic questions you’re asking: just be patient. In the meantime, do some research so you know what you’re actually doing.
A good research to start is the overkill solar bms document. Also handles topbalancing

Yeah, if I crank it up to 4.2v it'll put out 10 amps so that's what I'm doing & keeping a close eye on it with a 2nd a meter on it & watching it closely for it to reach 3.65 & then cut it back to 3.65 til it show 0 amps charging. I think that'll be my fastest way to get them charged.

 

[DJSmiley]

Thats a huge risk you're taking

Do you use proper wires? You should charge with 10A without any problems. This clearly indicates crappy wires.

Charging with 4.2V.. Unless you're CONTINOUSLY are monitoring the cells for the next 16 hours... and are NOT leaving for more than 1min... fine. But that's impossible.

Charge at 3.65V max, period.

You won't be the first to accidentally forget for 10min and find the cells overcharged at 4.2V....

 

[Bossrox]

Thats a huge risk you're taking

Do you use proper wires? You should charge with 10A without any problems. This clearly indicates crappy wires.

Charging with 4.2V.. Unless you're CONTINOUSLY are monitoring the cells for the next 16 hours... and are NOT leaving for more than 1min... fine. But that's impossible.

Charge at 3.65V max, period.

You won't be the first to accidentally forget for 10min and find the cells overcharged at 4.2V....

I'm watching them like a hawk & thx for the warning. Sounds like they're unforgiving if you screw up.

 

[Bossrox]

I'm watching them like a hawk & thx for the warning. Sounds like they're unforgiving if you screw up.

BTW, my 1st lith is now @ 3.55v, any idea how long away it's from reaching 3.65 @ 10 amps?