CC / CV using Rigol DP832?

[AJhowl]

Hello!
Can the Rigol DP832 be programmed to perform CC and switch over to CV ?
CC = constant current
CV = constant voltage
(the above definitions for othet n00bs like me!)

And, can the unit stop charging when it reaches the set voltage?

Say I'm charging a single 18650 battery cell.
Can the DP832 do CC while it ramps up to 4.2v, then switch over to CV until it's supplying 300-400 mA?
Thank you!

[Siwastaja]

Yes, of course. That is the very basic functionality of any half-decent lab power supply.

And yes, you can use CC-CV lab supply to charge a lithium ion cell. You are responsible for taking the few missing steps a dedicated charger would do, though:
1) Starting voltage qualification: measure cell voltage before trying to charge. If <2V or so, consider the cell dead and understand the risk involved
2) Temperature qualification: do not charge below approx. 0 degC
3) Stopping: disconnect the cell when in CV and charging current drops below termination current (usually C/20)

Note that not stopping is not disastrous. You can float charge a lithium ion cell despite not being recommended by some. Float voltage of 4.20V will result in a very slightly overcharged (like 102% or so) cell, though, so you might want to set CV voltage to 4.15V or so.

Automating the charging (including stopping) is possible by writing some simple control script on a PC and connecting to the PSU through USB/LAN/RS232 ports available but I don't know if it's worth it for occasional charging.

[AJhowl]

Thank you Siwastaja!

I do have individual chargers... yet I have two issues:
#1 I really want to buy the Rigol DP832 even though I don't need it.
I believe there is a support group for this malise in these forums?

#2 say I have two banks of 18650 cells.
One bank is at 3.18 and the other is at 3.80
I'd like to be able to charge up the bank up to 3.80 before hooking them up.

What do you think?
Thanks!

[rstofer]

I prefer the term "current limit" rather than "constant current".  You would set the DP832 to output a constant end voltage and then set the current limit to whatever charge rate you wanted.  The output would be at some lower voltage (limited by current) until the current dropped under the current limit and then charge at constant voltage as long as the current is below the limit.

The DP832 has two current limits (and voltage limits).  The first is the operating limit and the second (higher) is the shutdown limit.  This shutdown limit can protect the supply from a shorted battery or, perhaps, reverse polarity.

It's difficult to call a lab supply "constant current" when you want 1A delivered into a 1 MOhm resistor.  Consider what happens when the supply is set for 5V and the circuit is being limited to 1A and then you pull the leads.  The current does not try to maintain 1A (constant), it simply drops to 0A, 5V.  A true constant current PS would generate a bazillion volts in an attempt to maintain the current.

It might be possible to use the voltage shutdown limit in conjunction with the current limit to get where you want.  I haven't tried it, chargers are too cheap to tie up a high dollar PS.

[Siwastaja]

I prefer the term "current limit" rather than "constant current".

You can prefer what you want, but the problem with term "current limit" is that there area many different ways to implement it: constant current behavior, or latching "overcurrent fault" mode, for example.

Constant current describes the behavior where current is actively regulated to be exactly at the setpoint. "Current limitation" often implies something more crude, like protection: inaccurate, time-limited CC, foldback limiting, hickup mode, latching fault mode until reset, and so on.

Your logic that constant current operation cannot be achieved with 1M ohm resistor is broken, because by the very same logic you could not talk about constant voltage supplies either because they would fail to deliver constant voltage into 1µ ohm resistor. Yet we all talk about constant voltage supplies all the time.

Hence, ignoring products that just blow up, realistic power supplies are one of the three classes:

Constant voltage with current limit - behavior of current limit can be anything, including shut-down. Typical example: wall-wart or PC PSU
Constant current with voltage limit - behavior of voltage limit can be anything, including shut-down. Typical example: LED PSU
CC-CV supply: behavior is well defined, at any point in time either CC or CV applies, whichever is the limiting factor. Of course you can't call it just CC supply, because it has CV, too. It has to be CC-CV; if not, it's one of the previous two types. Typical example: lab PSU.

Calling a lab supply "constant voltage + current limit" will only cause endless confusion. "Voltage limit + current limit" is a tad better because no one says that and it forces the listener to check up what the heck you are talking about.

[BrokenYugo]

It's very simple, you dial in the highest voltage you want to see, and you dial in the highest current you want to see. The supply will then try it's hardest to not exceed either. The CV/CC behavior is automatic, if the current setting is exceeded by the load, the supply will lower the voltage until the current setpoint can be maintained, if you short the output it will go to near 0 volts. If the load reduces itself (e.g. a battery taking charge) the voltage will climb to maintain the set current, until voltage hits the set point, then voltage holds and current falls off. It becomes intuitive fast if you sit down and play with one.

A CV/CC bench supply is one of those tools where you don't know how you did anything without it, tons of applications.

That said, a bench supply is not really suited to charging batteries. For performance reasons there is typically little protection on the outputs, they are not designed to have a power source connected to them and will be damaged if caution and/or external protection circuitry is not used. If you have a suitable charger that will do the job, use it.

[Siwastaja]

That said, a bench supply is not really suited to charging batteries. For performance reasons there is typically little protection on the outputs, they are not designed to have a power source connected to them and will be damaged if caution and/or external protection circuitry is not used. If you have a suitable charger that will do the job, use it.

Proper lab supply won't be damaged by external voltage source connected to its output, as long as the voltage is within the normal rated limits of the supply.

This is because such supplies are very regularly used to power devices under test with very large input capacitance - tens of thousand uF - and power loss during work is normal. If they'd blow up, you would see a lot of dead power supplies.

Also battery charging / testing is a normal use case.

I'm 99.999999% sure the Rigol will be just fine. I have seen worst-offender super cheap Chinese no-name lab supplies - those with relays clicking different ranges on the transformer, unable to limit current below Vout<1.2V or at all, and other design faults - blow up with external voltage connected to their output.