How do fast chargers work?

I've got a lithium-ion battery that can do 1C. It's rated with 50Ah capacity so in theory it can handle 50amp changing. When I hook it up to a charger, or a lab power supply and feed it with 4.2v it only draws about 3amps (being at 3.6V at that moment).

I don't quite understand how fast chargers work, you can't push 50amps by force, right? I assume they bump up the voltage and max out the amp?For this battery, I could pump the voltage up to charge it quicker as long as it does not pass 4.2volts internally?

4.1V would be better for longevity

But yes the greater the charger's output voltage is compared to the battery the higher the amps pulled by the battery

There must be something wrong with your battery or your power supply is limiting, or your cables or the contact is bad.

If I load my cells with 1C my cells rise only 0.1V.

The voltage at the cell should not get over 4.2V

If the cells are depleted, say below 3.8V

and the charge source **capable of** 1C is set to 4.1V

then you should see a 1C rate at first

that rate will decline as SoC / resistance rises and the battery voltage approaches the charge source output voltage.

None of this has much to do with how the source works

just a function of the battery chemistry interacting with volts and amps.

The only regulation going on by the source's circuits is

1. limiting the current drawn

2. keeping the voltage capped once the CV setpoint is reached

Above is true for even the dumbest PSU or DCDC converter.

With a charger, add the intelligence to estimate the battery reaching Full, so the charge process can be auto terminated.

But for Lithium, and normal usage cycling, nothing fancier than an HVC is required.

The "fast" charger simply is capable of delivering a higher current - what is "fast" for a 3Ah cell is very different for a 300Ah cell.

With something wrong I mean the resistance of the cell or the cable can be to high to get more amps.

What you see, is the term, " compliance voltage of a circuit."

I can hit any cell with a CC power up to (infinite? ) amps if the source can pull it.. but.. if the cell reaches the (chargers CV phase) 4.2v.. the top voltage, current transmission will drop... as long as the circuitis not providing a constant voltage higher than 4.2v.

Chargers handle this many, many ways. They do get very complicated in the power delivery patterns. The temperature curves and whatnot.

I mean.. I can hit a 400mA cell with 40A...(100C) but the time it gets to the CV phase, the current will drop cause charger is designed not to go over 4.2v. It will reach CV very fast for it is a tiny cell.. But yes it will take that 40A if I try until it reached the compliance voltage of the design.

Compliance voltage is the range of output voltage of a constant current power supply, over which the load regulation is within certain limits. It represents the maximum voltage a current source will reach as it attempts to produce the desired current.

Click to expand...

IF you set the charger output to 5v ( anywhere over 4.2v, where the cell resistance climbs and stops storing energy, (like all batteries, regardless of chemistry or charger do a t top and bottom of cycle)) and continue to hit the cell.. Yes it will not comply at 4.2.. but keep going. Sand given the circuit resistance, the pwoer will flow.. ( probally burn a house down.. ) ..

I can set my charger to MAX 4.5v/cell. .. I canterminate ( reach CV phase, begin taper) from 2.36v through 4.5v / cell. for I have a high end charger.

Further reading: https://en.wikipedia.org/wiki/Current_source ( SEE ALSO too.. )

Problem with LI specifically, contrast with lead batts, is they will draw **far** higher C-rate charging than what is healthy for longevity

or even safety, especially when well worn approaching EoL.

That's why whether a charger or a dumb PSU/DC converter, **current limiting** is critical.

1C may not sound like much to some people, but that is over double what is good for longevity.

But offering 40A to a 3Ah cell is a recipe for disaster.

john61ct said:

But offering 40A to a 3Ah cell is a recipe for disaster.

Click to expand...

yup. cetrainly.

So here's the scenario.

I have 5 50Ah cells in parallel. They can do 1C of charging which means they can pull 50amps.

Currently they are at 3.69v



When I set the PSU to 4.2V CV and hook it up, they draw only 2.5AMP.



If I momentarily bump the voltage higher they draw more amps.

This PSU can only do 30V/10A max.

The question is, can I set the PSU to say 20V and charge faster provided that the cell internal voltage does not exceed 4.2V? I know it means I need to keep sampling the cell to make sure they don't go over, probably to reduce the voltage to 4.2 when they get close.

I'd recommend getting some better leads for that power supply. If the power supply is putting out 4.2V and 2.5A, yet the voltage at the cells is still 3.69V, that voltage difference is being wasted in the wires. With better wires you'd be able to put out higher current with the same 4.2V setting.

Addy said:

I'd recommend getting some better leads for that power supply. If the power supply is putting out 4.2V and 2.5A, yet the voltage at the cells is still 3.69V, that voltage difference is being wasted in the wires. With better wires you'd be able to put out higher current with the same 4.2V setting.

Click to expand...

OMG that made a massive difference! Now it's pulling 10 amps! Thanks.

bymannan said:

Addy said:

I'd recommend getting some better leads for that power supply. If the power supply is putting out 4.2V and 2.5A, yet the voltage at the cells is still 3.69V, that voltage difference is being wasted in the wires. With better wires you'd be able to put out higher current with the same 4.2V setting.

Click to expand...

OMG that made a massive difference! Now it's pulling 10 amps! Thanks.

Click to expand...

HEY ARE YOU SURE THEY ARE LITHIUM ION< NOT LiFePo4? !!!!!!! STOP CHARGING RIGHT NOW IF THEY ARE LIFEPO! 3.65v IS ABSOLUTE MAX FOR LIFEPO!

DANGER RANGER! DANGER DANGER!

Please show us the listing where you bought themm.. I have seen this before, some thinking the LiFePo4 is supplosed to charge like Lithium Ion... But.. !!! NOOOOOOOOOOOOO! 3.65v MAXIMUM!!! EMERGENCY!!! ( if they are lifepo.. ) ( they look like a lIfepo4... that is typically 1C.. 3C peak, prismatic, 3.65v max per))

..(if they are lithium ion.. then yea 4.2v/cell and if thenignore this)

Addy said:

I'd recommend getting some better leads for that power supply. If the power supply is putting out 4.2V and 2.5A, yet the voltage at the cells is still 3.69V, that voltage difference is being wasted in the wires. With better wires you'd be able to put out higher current with the same 4.2V setting.

Click to expand...

This is not true. This is false.

bymannan said:

The question is, can I set the PSU to say 20V and charge faster provided that the cell internal voltage does not exceed 4.2V? I know it means I need to keep sampling the cell to make sure they don't go over, probably to reduce the voltage to 4.2 when they get close.

Click to expand...

DO NOT DO THIS. THIS NEGATES THE CONSTANT VOLTAGE PHASE OF LITHIUM CHARGING. Creates an extreme hazard to the point of the maximum power of teh power supply, or the potential energy in the cell(s).


Watch this for god damn sake. Or buy a real charger before you burn something. Please. My friend. Watch both of them. Right now if you must charge right now. Please.

https://www.youtube.com/watch?v=AQK7RyecVW0

https://www.youtube.com/watch?v=A6mKd5_-abk&t=637s

bymannan said:

So here's the scenario.

I have 5 50Ah cells in parallel. They can do 1C of charging which means they can pull 50amps.

Click to expand...

THis one statement shows your misunderstanding. My friend. Whn you place cells in parallel.

5x ( 1c, 50Ah cells in parallel... ) = 250A. Two-Hundred and Fifty amps. Is a "1C" "pull" ( discharge, charge, whatever. )


Thy can "pull" ( whatever this means) 250A.. and that is a 1C "pull" ( charge or discharge)... For that 250Ah, 1C, 250A battery.

YOu can charge that 1s5p stack at 250 amps. NOT 50 amps. This shows a limited understanding of battery cell hierarchy and electrochemisty...

There is math for this. ..

...........


......per datasheet.. but... always a but.... trust me they can be FED ( charged) at 2C.. 200c.. 20000C.. they will just burn in a matter of time. Higher rate, above catastrophic levels the cell cannot sustain, the faster the burn... the faster the puff.... the faster the offgassing... ( explode much?)

DogDipstick said:

bymannan said:

So here's the scenario.

I have 5 50Ah cells in parallel. They can do 1C of charging which means they can pull 50amps.

Click to expand...

THis one statement shows your misunderstanding. My friend. Whn you place cells in parallel.

5x ( 1c, 50Ah cells in parallel... ) = 250A. Two-Hundred and Fifty amps. Is a "1C" "pull" ( discharge, charge, whatever. )


Thy can "pull" ( whatever this means) 250A.. and that is a 1C "pull" ( charge or discharge)... For that 250Ah, 1C, 250A battery.

YOu can charge that 1s5p stack at 250 amps. NOT 50 amps. This shows a limited understanding of battery cell hierarchy and electrochemisty...

There is math for this. ..

...........


......per datasheet.. but... always a but.... trust me they can be FED ( charged) at 2C.. 200c.. 20000C.. they will just burn in a matter of time. Higher rate, above catastrophic levels the cell cannot sustain, the faster the burn... the faster the puff.... the faster the offgassing... ( explode much?)

Click to expand...

I meant for each cell, not for all of them. In any case, I do not have anything the can remotely provide 50A

DogDipstick said:

bymannan said:

Addy said:

I'd recommend getting some better leads for that power supply. If the power supply is putting out 4.2V and 2.5A, yet the voltage at the cells is still 3.69V, that voltage difference is being wasted in the wires. With better wires you'd be able to put out higher current with the same 4.2V setting.

Click to expand...

OMG that made a massive difference! Now it's pulling 10 amps! Thanks.

Click to expand...

HEY ARE YOU SURE THEY ARE LITHIUM ION< NOT LiFePo4? !!!!!!! STOP CHARGING RIGHT NOW IF THEY ARE LIFEPO! 3.65v IS ABSOLUTE MAX FOR LIFEPO!

DANGER RANGER! DANGER DANGER!

Please show us the listing where you bought themm.. I have seen this before, some thinking the LiFePo4 is supplosed to charge like Lithium Ion... But.. !!! NOOOOOOOOOOOOO! 3.65v MAXIMUM!!! EMERGENCY!!! ( if they are lifepo.. ) ( they look like a lIfepo4... that is typically 1C.. 3C peak, prismatic, 3.65v max per))

..(if they are lithium ion.. then yea 4.2v/cell and if thenignore this)

Click to expand...

They are Lithium Ion .

I meant for each cell, not for all of them. In any case, I do not have anything the can remotely provide 50A
[/quote]

Understood.

In parallel it IS one big cell.

Please tell me they are Lithium -Ion, NOT LIfePo4, like I am assuming, and the inherent 4.2v charge voltage vs the 3.65v charge voltage of the two different chemistries. Please eas my mind. I may be wrong.. but..

I have installed over a hundred LiFePo cells. IN solar installations.. . and they looked.. almost identical to your cells. ... Like that.. and charged to 3.68v max.

I may be wrong.. but please tell me they are 100% Lion, not Lifepo.

Gotcha. Thankyou for the reassurance. Thankyou thankyou/.

DogDipstick said:

I meant for each cell, not for all of them. In any case, I do not have anything the can remotely provide 50A

Click to expand...

Understood.

In parallel it IS one big cell.

Please tell me they are Lithium -Ion, NOT LIfePo4, like I am assuming, and the inherent 4.2v charge voltage vs the 3.65v charge voltage of the two different chemistries. Please eas my mind. I may be wrong.. but..

I have installed over a hundred LiFePo cells. IN solar installations.. . and they looked.. almost identical to your cells. ... Like that.. and charged to 3.68v max.

I may be wrong.. but please tell me they are 100% Lion, not Lifepo.

Gotcha. Thankyou for the reassurance. Thankyou thankyou/.
[/quote]


Does this help my friend?

Looks very close to a ( slightly puffed, b/c of the valve pressure or a vacume.. because of the valve pressure. is optical illusion) lifepo cell. Lemme guess the positive is black and the negative is tan? Maybe?

Yeah 3.62v185wH say right there. I do hope thats nominal, lol. Ty. I guess its lithium ion. 3.62v nominal, right?

YOU could tell by a controlled discharge and see where the voltage droops off.... 3.2-3.4v, Lithium..Dead... 2.5v... LIfepo dead.

I cannot get my phone to scan. Are all the QR codes that blurry? Do ya got a clearer one? Were they all rubbed off? I have seen that before too. IDKY they do it.

DogDipstick said:

Looks very close to a ( slightly puffed, b/c of the valve pressure) lifepo cell. Lemme guess the positive is black and the negative is tan? Maybe?

Yeah 3.62v185wH say right there. I do hope thats nominal, lol. Ty. I guess its lithium ion. 3.62v nominal, right?

Click to expand...

I'm betting my house it's nominal lol

bymannan said:

I'm betting my house it's nominal lol

Click to expand...

Yeah. Its a shame they quite often destroy the QR codes. The solar forums are literally RIDDLED with questions about the QR code deciphering and destruction.

DogDipstick said:

Addy said:

I'd recommend getting some better leads for that power supply. If the power supply is putting out 4.2V and 2.5A, yet the voltage at the cells is still 3.69V, that voltage difference is being wasted in the wires. With better wires you'd be able to put out higher current with the same 4.2V setting.

Click to expand...

This is not true. This is false.

Click to expand...

It's not false, it's basic electronics. How about you provide some kind of reasoning or proof before you go around mistakenly telling people that they are wrong?

It's not false, it's basic electronics. How about you provide some kind of reasoning or proof before you go around mistakenly telling people that they are wrong?
[/quote]

You are not dropping half a volt on 20 gauge wire with 2.5A through it at 3.6 volts. .. That is the first clue. . This is the basis for why , what you say , is incorrect. Look at it.

V=IR if you would like the math.

V-Ir.

20 gage wire is 10.15 Ohms / 1000 feet.

1 foot is 0.0105 Ohms.

Do the math.

1 foot, 20 gage wire, 0.0105 Ohm..


V=Ir.

You do not drop halgf a volt (0,5v) through a resistance of ten miliiohms. The dissipate power is.. (VrDrop)


In a closed short circuit... The equivalent resistance of your circuit is 0.01 Ω.
The current through the circuit is 370 A.
The power dissipated by Resistor 1 is 1400 watts.
The total power dissipated is 1400 watts.

Do the math.

V=Ir.


P=V^2/R



The voltage drop V in volts (V) is equal to the wire current I in amps (A) times twice
the wire length L in meters (m) times the wire resistance per 1000 meters R in ohms
(Ω / km) divided by 1000:
Vdrop (V) = Iwire (A) × Rwire (Ω)
= Iwire (A) × (2 × L (m) × Rwire (Ω / km) / 1000 (m / km))


... So that ( 20 gage ) wire is .. ghoing to have to be.. 200 Milliohm to drop (half a volt) 0.5v @ 2.5A and 3.7v.

That wire is not 200 milliohm.. ( 0.2 OHM), We already established that a length of 20 gage wire, a foot of it... Is much much lower...In the magnitudes of tens ( 10^2)... being that.. that wire.. is not .. 200mOh.. but.. tht wire .. is 10 millioohms.. (0.010OHM)

It is not dropping the half a volt. Wire sixe should make no difference. It isnt even heating up 2.5 or 5A.. 20 gage can take that amperage without heating up at all in a foot, let alone.. dropping a votl.

So its something else. Its the compliance voltage of the circuit. Watch the vid Linked earlier on basis of DC theory.

You could have done the math and seen. I am not mistaken. Multimeter leads are even thicker than 20g.. and would be dropping less.. and... can take 20A easy usually. I got about 200 Pomonas here right now on my switchboard. The standard gage of a test lead is 18g.

4.2v does not drop to 3.6v when run at 2.5A through a foot of 18g multi meter line. Nosiree. I could tell you what it would drop, using V=IR. ......Or I could measure it with a Wheatstone....empirically to find the actual

V is known. I is known. R is known.. in this eq.

Dont be mistaken/.

bymannan said:

They can do 1C of charging which means they can pull 50amps.

Click to expand...

To clarify, they CAN pull lots more, but it is important to keep the current limited. 0.4C or lower, best fot longevity.

> When I set the PSU to 4.2V CV and hook it up, they draw only 2.5AMP.

Def something wrong there.

Link to your purchase source / datasheet for both the cells and the PSU.