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Small charging circuit
#1
I'm building a 4s25p battery out off recycled cells which will fit in a 19" rack enclosure for my work. I have some spare room so I'd love to build the charging system into the box too however I can't seem to find any suitable chargers...

I've considered fitting something like the isdt q6 or similar however these chargers all require external input to begin charging and I'd like something that is plug and play.

Can anyone recommend a solution? Could I just do a constant current / constant voltage charge method (using a standard power supply set at 16.8v)?

Thanks.
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#2
https://www.aliexpress.com/item/32872607...4c4dY3QW9w

I would use this one, you can set any voltige you like.
I thought a normal power supply will deliver voltige to the max current it can give, up to the point when your cells are full, your cells won't like this.
A buck converter you can set on the voltige you want and the highest A.
If the buck almost charges to the full state of the li ion cells the current will drop.

Best
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#3
I originally bought a compact RC charger for a 4s10p 26650 build. It works great. The problem is that it won't start charging until I push the button. So I just bought a victron DC-DC converter to replace the RC charger. I don't have much room to work so I need to redesign the interior portions to fit the different shaped charger, but it will work.
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#4
I have done it in the past, but it’s absolutely not as convenient.

That’s the only downside to trying to use an RC charger for these types of applications as they require user input to start

If they had an auto-start option, it would just about be perfect for DC-DC charging because its balance aware.
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#5
(11-20-2019, 05:30 PM)100kwh-hunter Wrote: https://www.aliexpress.com/item/32872607...4c4dY3QW9w

I would use this one, you can set any voltige you like.
I thought a normal power supply will deliver voltige to the max current it can give, up to the point when your cells are full, your cells won't like this.
A buck converter you can set on the voltige you want and the highest A.
If the buck almost charges to the full state of the li ion cells the current will drop.

Best

So you're saying it'll do a stage two saturation charge such as in this article? https://batteryuniversity.com/learn/arti..._batteries
I would've thought it'd just keep trying to pump electrons while connected?

(11-20-2019, 07:50 PM)gpn Wrote: I originally bought a compact RC charger for a 4s10p 26650 build. It works great. The problem is that it won't start charging until I push the button. So I just bought a victron DC-DC converter to replace the RC charger. I don't have much room to work so I need to redesign the interior portions to fit the different shaped charger, but it will work.

Again, will this do a proper saturation charge? Like described in this article? https://batteryuniversity.com/learn/arti..._batteries

It seems if I only do cc cv then my battery will only reach 85%SOC...?
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#6
(11-30-2019, 07:05 AM)twobitburrito Wrote: will this do a proper saturation charge? Like described in this article? https://batteryuniversity.com/learn/arti..._batteries

It seems if I only do cc cv then my battery will only reach 85%SOC...?


I think you're misunderstanding something.  It may not the fastest method, but CC+CV will safely charge lithium cells to 100%SoC.

Going by the graph on your link:
The CC phase (aka Bulk Charging; 0 ~ 0.7h on the graph) gets the cell to about 60%SoC quickly.
Followed by the CV phase (aka Saturation Charge; 0.7 ~ 3.0h on the graph), which gets the cell to 100%SoC, albeit at an ever slowing rate.  Many chargers will lie and display "full" when current flow has reduced to a sufficiently low rate (perhaps at around 1.5h / 95%).

The graphed CC/CV is quite aggressive, particularly when using recycled cells from mixed sources.  You'll probably want to use a lower CC rate and lower CV level.  And definitely use a BMS that can stop the charging+discharging when things start to look wrong.  Otherwise you risk starting a fire.
I don't think a standard power supply (aka power brick) will do, as you don't know how accurate or reliable the current limiting feature is, and you don't want it running at 100% either.  An adjustable lab power supply would be perfectly fine.

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#7
Ah I see. Thanks for the clarification!

So just let me ensure that I understand correctly...As I need to reduce the size factor and ensure this can fit in my specified enclosure a lab bench psu isn't really an option however I could use a high quality military grade psu such as this: https://www.powerbox.com.au/ac-dc-power-...ox-dba1200
Using the 15v PSU set to 16.5v it looks like I could set it to do around 50Amps. How does that sound as a charging setup for my 4s25p portable battery system?
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#8
50A in a 25p setup is "most likely" way to high to charge at, unless they are high drain cells; ie, powertool cells.

You "can" charge at 2A/cell "if" these are 2000mAh cells and they are rated at 1C charge rate. Otherwise, it's best to charge no more 500mA per cell to get a longer life out of them. So that would be closer 12A charge rate on 25p.

Since you don't tell us what type of cells you are using, it's kinda hard to say which charge current limit would be best. "From recycled cells" doesn't give a lot of information, except that they may be random cells from various manufacturers at different states of life cycle and varying degrees of degradation.
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#9
The "POWERBOX DEFENSE LINE DBA1200 Series" does not seem to have a configurable, current limiter on the output side. Just a safety feature that shuts off(?) output when max current is reached.
Lithium batteries will merrily suck in unsafe level of current, leading to overheating and other more serious and permanent issues. So attaching the DBA1200 straight to the cells will probably not be safe.

You could use something like this:
http://s.click.aliexpress.com/e/lkAJIGVS
These metal can chargers are basically lab power supplies, with the 2 potentiometers for CC/CV settings hidden inside. The fans often suck though.

Are you hoping to charge the battery from a DC or AC source? And what voltage?
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#10
I been using these buck converters 8 dollars with a laptop power supply to charge my 3s16p. It would work on your situation with the larger power supply you plan on getting. For higher amp output you need a fan blowing on the buck converter. The buck converter is small it won't take up much space.

Once you adjust the voltage/amps on the buck converter to the max you want outputted its pratically plug and play. They are very reliable and since you adjust the voltage with a multimeter, the output voltage is accurate. The closer you get to the max voltage the amps drop considerally, it will take hours to get a full charge, but it will get you to at least 90 percent quickly. I use to use my ISDT balance charger to charge all my small lithiums but now prefer to use the buck converters.

I also highly recommend you get a tenergy lipo checker (11 dollars) so you can keep an eye on the balancing. I recommend this one because it has very loud alarm if the cell voltage goes above 4.22 volts, its also lcd so it uses insignificant power.


buck converter 300 watts


tenergy lipo checker with low/high alarms
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