I need a voltage follower with >= 1Amp output for experiments

[Gazza_AU]

Simplicity:
1) Use an array of ULN2003 switches with a current limiting resistor to deliver the charge from a capacitor (supercap?) across each cell individually. Have the super cap charged to the peak desired cell voltage before applying to each battery.
2) Cycle this continually, the cells with lower charge will receive extra charge, and you will approach cell balance after sufficient iterations.

2 ULN2003 switches per cell, one needs to source the other sink?
What is the difference in circuit for each using ULN2003 Darlingtons?

I like the idea, not sure if the current would be sufficient or not.
Paralleling ULN2003 Darlingtons for 1A, might make an alternative more attractive.
Would I need to compensate for any voltage drop across Darlingtons??

 

[Gazza_AU]

Divider Charger Logic using real components:

Capacitor - Maxwell Technologies BCAP0350 $16.07 AUD
https://www.mouser.com/ds/2/257/Maxwell_BCSeries_DS_1017105-4-341252.pdf
350 F
ESR 3.2 mΩ
2.85 V
Leakage Current 0.30 mA
Thermal Characteristics - Maximum Continuous Current 21A RMS @15C.
-
2x Maxwell BCAP0350 Capacitor in Series.
175 F
ESR 6.4 mΩ
5.7v
10.5A RMS
------------------------------------------

Darlington - TIP100 60v
https://www.onsemi.com/pub/Collateral/TIP100-D.PDF
Collector Current
Continuous 8A
Peak 15A

Design for 4v 10A Max.
10Amps / 4V = 0.4 ohm resistor.

Common Anode Dual Rectifier - MUR1620CTRG (Not sure if I need diodes or not???)
https://www.mouser.com/ds/2/308/MUR1620CTR-D-79742.pdf
Average Rectified Forward Current 8A
Peak Repetitive Surge Current 16A

Operational Amplifier (JFET-input) - TL082
Mouser Part No: 595-TL082IPE4 (not sure if this is the right version?)
https://au.mouser.com/ProductDetail/Texas-Instruments/TL082IPE4/?qs=odmYgEirbwxFprZo7erKcw==
Datasheet: https://www.ti.com/lit/ds/symlink/tl082.pdf

I cannot workout what information to use and how to work out the maximum resistance for TL082 inputs?
Can you give me an example of resistor values for my circuit schematic?

Thanks,
Gary

 

[Mosaic]

If you're going discrete for more power I suggest NFETs with high pulse current capability such as IRFP3206 units. You can drive them with pnp bipolar transistors or NPN emitter followers and I'd use a 28 pin PIC micro to sequence the whole thing cleanly with dead time to prevent possible shoot thru. You should check the ESR of the batteries with an ESR meter so you know the size of the current pulse.

BISS type bipolars are optimum as Switching bipolars go.

One day I'm going to have to do this for Forklift 2V Lead Acid cells and that's how I"d do it as the PIC can also allow voltage sampling to actually optimise which cells get the charge balancing.

This can be a guide:
https://www.linear.com/product/LTC3305

This is more info on Li Ion balancing
https://www.linear.com/solutions/5673

Buck converter balancing: **broken link removed**

 

[Gazza_AU]

If you're going discrete for more power I suggest NFETs with high pulse current capability such as IRFP3206 units. You can drive them with pnp bipolar transistors or NPN emitter followers and I'd use a 28 pin PIC micro to sequence the whole thing cleanly with dead time to prevent possible shoot thru. You should check the ESR of the batteries with an ESR meter so you know the size of the current pulse.

BISS type bipolars are optimum as Switching bipolars go.

One day I'm going to have to do this for Forklift 2V Lead Acid cells and that's how I"d do it as the PIC can also allow voltage sampling to actually optimise which cells get the charge balancing.

Thanks for links to charging information, but I have covered existing products and understand the charging properties very well.
This is about making a particular piece of test equipment.
I am not really up for a cell charging discussion, perhaps when the equipment design is further progressed!

I am using Picaxe 28x2 for the experimental stages.
Coded Several Types of Sequence to cover tests.

In regards to higher current replacement for relay.
Every second person suggests I use MOSFET, but no one has been able to demonstrate how it would be done with real components for this task!
Not suggesting it is the case with everybody, but many people suggest MOSFET because they know it has been done.
With no idea how to do it.

I thought it might be done with Bi-Directional P-Channel MOSFET/Power Switch per Cell.
https://www.mouser.com/ds/2/427/70785-241024.pdf
Using the Switches only for flow from Cap to Cell, but having the benefit of sourcing or sinking in one package?
Designing it correctly for the job is the problem!

Any voltage drop would need to be compensated, the we would need a source and sink version for each cell.
As with my previous questions?

Are you up for giving me an example?

 

[Mosaic]

Did u look at the LTC3305 sample circuit?

 

[Gazza_AU]

LTC3305

Sorry mate, missed the 5 on the end. Thought you were linking the Lifepo4 FlyBack version.

I will need to save the image and zoom to see.
What do you make of it while I take a look?

Forgot to add: You would not think the current transfer from Capacitor to cell would be high?
The voltage difference between cap and cell would be the determinate!
Because the design started with relays, I have treated the maximum current as equivalent to a fully charged cell discharging to a fully discharged Capacitor.

But this whole basis could be different if the switching behavior is different.
Mainly if the switch allows reverse flow, or only acts in one direction?

 

[Mosaic]

MOSFET allow current in either direction.
So you can potentially not have to charge the super cap, it will take charge from the higher voltage batts and send charge into the lower voltage batts thereby charge balancing fairly efficiently.

Charge Q= I x T,
I think a 1F super cap should be sufficient for the job as the process is limited by the battery chemistry and cannot take place faster than the charge acceptance that the chemistry allows. That said you'd probably be able to do it with more economical MOSFETs or even Dual Mosfets which would make for better sync in switching. No ballast resistors are required.

 

[Gazza_AU]

MOSFET allow current in either direction.
So you can potentially not have to charge the super cap, it will take charge from the higher voltage batts and send charge into the lower voltage batts thereby charge balancing fairly efficiently.

This is obvious, but please do not introduce this logic into the design process.
I understand information is free, and people only offer advice if they wish.
Because everybody has their own ideas, often very good ideas, but it has made this project really hard in some cases.

I will give you my information on passive design separate, so I can stay on track with this project.

Hope you understand.

Thanks,
Gary

 

[Gazza_AU]

Quote: "Mainly if the switch allows reverse flow, or only acts in one direction?"

A system that only switches towards the Cell,
Current from Cell cannot charge Capacitor, switch current is "Cap voltage above cell voltage".
The Lifepo4 Prismatic are 2.5v LVD.
Maximum Charge Voltage 3.65v

So for this particular design the switching method, the existence or absence of reverse current makes a lot of difference.

Suggesting switching is fine, but if you hijack the thread to peruse your idea I would be pissed.
A lot of people have done it, some are likely the same people with different identities across sites.

 

[Mosaic]

Here is the theory of operation
https://www.google.com/url?sa=t&rct...uDgXqEpJg&sig2=lIiPANRHTYPzPCg8WKVe3w&cad=rja

If you don't know how to make MOSFETs do the switching you need to understand how they work first.

What is your level of MOSFET experience?

Is this a school project?

 

[Gazza_AU]

I have your document and quite a few more.

This thread has run its race, good luck with your charger.