How does a charger discharge ?

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discharged
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How does a charger discharge ?

Tried to search but not having much luck, can anyone point me to links?

XXX-Man
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Don’t have any links, but (unless it’s constant current discharge) it discharges by connecting battery to resistor and that way turning battery power to heat.

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flydiver
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Most use a resistor. That’s why they get warm/hot and are limited in the discharge amps. This is one area where a cooling fan is useful, as much as some people seem to dislike them.

Lexel
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flydiver wrote:
Most use a resistor. That’s why they get warm/hot and are limited in the discharge amps. This is one area where a cooling fan is useful, as much as some people seem to dislike them.

You are wrong all those analyzing chargers use a MOSFET and a current sense shunt to regulate a constant current during the discharge,
the voltage drop on the shunt is kept constant while on the MOSFET the gate voltage is regulated to pass the needed amount of current between source and drain

A simple resistor would not result in a constant current and not working with different chemistry or battery type

flydiver
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Mmmm, so I checked MOSFET in Wikipedia. That is WAY beyond my understanding.

But they still DO get hot, right? And the heat does limit their discharge capacity? Whatever does the ‘work’ heat seems to be the problem.

I have a number of analyzing chargers. For general battery testing they are OK and reasonably consistent with one another….generally. Occasionally they do seem to get a bit wild.

So I got one of these: https://syonyk.blogspot.com/2016/01/zb206-battery-tester.html
This unit is far more flexible for discharge, and seems far more accurate with repeatable tests. It’s way better for that than any analyzing charger I’m familiar with, including a couple hobby chargers.

[Instead of using a fixed ohm load, this type of tester uses a semiconductor to drain the battery. The fine grained control means that if you specify a 1A draw, it draws 1A, regardless of the state of battery charge. The heat is dissipated in the semiconductor, which has a large heatsink attached to it.]

The “fixed ohm load” refereed to is a resistor?
The semiconductor referred to is a MSOFET

HKJ
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Lexel wrote:

You are wrong all those analyzing chargers use a MOSFET and a current sense shunt to regulate a constant current during the discharge,
the voltage drop on the shunt is kept constant while on the MOSFET the gate voltage is regulated to pass the needed amount of current between source and drain

A simple resistor would not result in a constant current and not working with different chemistry or battery type

Some chargers uses a MOSFET transistor and regulates it to constant current, other uses a resistor and a MOSFET in PWM mode.

The discharged power will always be converted to heat, this means a fan is required for higher discharge power.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

discharged
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Thank you all for the info. Presumably those chargers which can discharge regulate the level ? and can any suggestions be made as to which units should be considered/avoided-price is secondary to quality and performance.

My need is both for charging and being able to store 18650’s properly.

wle
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i would guess usually it is a resistor as the load, plus a mosfet and current sense, to control the current

wle

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discharged wrote:
and can any suggestions be made as to which units should be considered/avoided-price is secondary to quality and performance.

If price is of no concern, SkyRC MC3000 offers the most features, but it is more complex. You can specify things like minimum discharge voltage, for example, if you’re interested in discharging a cell to a specific level.

Cheaper/less advanced popular chargers with discharge capabilities include Opus C3100 and Lii-500.

Look here for a list of chargers that HKJ tested. If it says “Analyzer” in the “Extra” column, it means it can discharge cells.

Link

Enderman
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It’s basically a smart variable resistor that changes its resistance to keep the current flow constant. (to avoid overheating or explosions)
Then the energy just gets converted to heat.

flydiver
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So…..depending on WHAT is doing the work of discharge, is the current kept constant as the voltage drops?
I think in my analyzing chargers (Opus, Lii-500, Zanflare C4) they all seem to decrease the current with voltage drop. I have no good way to measure that. That’s why I got a dedicated discharger + it does accurate, or at least repeatable, IR.

wle
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flydiver wrote:
So…..depending on WHAT is doing the work of discharge, is the current kept constant as the voltage drops? I think in my analyzing chargers (Opus, Lii-500, Zanflare C4) they all seem to decrease the current with voltage drop. I have no good way to measure that. That’s why I got a dedicated discharger + it does accurate, or at least repeatable, IR.

they might be doing that as the cell gets toward the end of its capacity, so it doesn;t get below a min voltage

they should be indicating real discharge current [not just what you set it for] on the display

you could rig up something with alligator clips and wires and a DVM to verify it, if it matters

also the manual may explain what it is doing better.

wle

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Pete7874
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wle wrote:
flydiver wrote:
So…..depending on WHAT is doing the work of discharge, is the current kept constant as the voltage drops? I think in my analyzing chargers (Opus, Lii-500, Zanflare C4) they all seem to decrease the current with voltage drop. I have no good way to measure that. That’s why I got a dedicated discharger + it does accurate, or at least repeatable, IR.

they might be doing that as the cell gets toward the end of its capacity, so it doesn;t get below a min voltage

they should be indicating real discharge current [not just what you set it for] on the display


The two chargers he mentioned (Lii-500, C4) only indicate the preset current rate, not actual. Not sure about the Opus one.
flydiver
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Same with the Opus, just the preset rate. One of the main advantages of the Opus is the higher current discharge, but even that is too low for many real world applications, and to do more than a low grade drain test on a battery.

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Wouldn’t mind spending the cash on a dedicated hobby discharger, they start around $100 usd but that is without a holder of any kind, seems that this equipment is pretty much intended for battery packs. I have seen diy holders but to me, not an electronics person, total voltage would be measured not individual-does this really work well for maintaining multiple 18650’s ?

BurningPlayd0h
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You don’t need to discharge cells to nominal voltage to store them unless you’ll be cycling lots of them in and out of storage repeatedly, in which case you might start to see performance reduced, but still over a long period of time.

discharged
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I did purchase 16 Fenix ARB-18 3500 a few months back (great deal from Fenix Lighting) and would like them to last as long as possible, a few hours at an upper mid range output does get the potential down to 3.4/3.7 or so (the chargers are also Fenix and the voltage displayed is consistent with the very high end mm’s that I have -two are true rms, the rest are ‘vintage’ Fluke digital dmm models so old that they were made in the US.
Severely ar/oc….

flydiver
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I have 4x hobby chargers. Great for RC packs. Pain to use with can cells. I almost never use them anymore since I haven’t done RC for a good while.

The Opus BT C3100 has a hidden switch on the underside that can be accessed by cutting a small hole in the shell. Then you can set it to CHARGE to storage level. You cannot discharge to storage level automatically.
Or get a small charger that does LiFe cells and charge it from below storage voltage using that algorithm. It’ll terminate around storage level for Li-on.
50% storage is not that critical. Anything from 40-60% for long term is fine. Just keeping them below 80% makes a big difference.

You can also just use a decent analyzing charger like the Lii-500, charge at a low rate and monitor the voltage. Pull it when it’s close enough.

discharged
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thank you, is my concern regarding the quality of the discharge, or recharge for that matter, when one cobs together a holder-valid ?

flydiver
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If you went DIY multi-cell holder and a hobby charger I’d do it in parallel. Then all the cells would balance and read out would be consistent across the group.
You could cobble together a holder that would have balance taps; more accurate at the individual cell level, more control, and more complicated and fussy.

Be aware, if you discharge a large number of cells in parallel, it acts as one big cell, so large capacity. Unless you went really high end hobby charger they are also discharge limited because of heat so it would take a good while.

Frankly it’s simply easier to use them, and then charge them up to ~ storage level. Pinpoint accuracy not really required.

discharged
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Sounds like good advice, thank you and all again.

jimmyharisson
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I can recommend linking to Wikipedia. There you can find enough information that you can learn to find answers for your questions about battery charging.

Hire the grademiners.com services and you will get what you need. Do not lose such a great opportunity.