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Laptop pwr supply

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cdnmatt:
The Low Down

I have a Dell laptop charger/power supply that I am not using for its intended purpose, but using it to charge my own custom battery pack for an e-bike.
Charger output is 19.50V(dc) and rated for 6.70A
Charger input is 115V(ac) and rated for 2.50A

Plug charger output to battery, charger reads battery voltage. Unplug charger goes to zero, battery is fine.
Replug in the charger, even quickly, the charger will read normal voltage.
Yes I have the correct wiring for charging, as I have one working, others are not working.


The Question

Is it the inrush current from the ac input side of the charger, disabling/turning off the chargers output?


More details below


What I have

I am using it to charge up a 5S10P Li-Ion battery (LiMn) that at its max is 21.00V
Batteries are Sony Konion 18650-V from a bunch of tool packs for drills and what have you.
I do not mind the 19.50V final charge voltage, ideally I like a 20.00V/20.25/20.50V final charge voltage for some headroom. That modification will come later to increase the final voltage without using external buck converter.

I bought 4 of the exact same units.
One is working but gets a bit hot, easy fix with alum fins from ebay.

Normally when I plug in the good charger, the charger itself will go to 17.50V from a 15.00V battery and start pumping juice in.
I have not measured the current into the battery, nor the input. I just read the voltage, and it does the normal cc/cv charge rate where V slowly increases 0.01V at a time.

The Problem

The others will not output voltage when I plug it into the battery and I just measure the battery voltage.
I unplug the output cable and the charger starts dropping to zero.

Once I plug in the battery to the charger, the charger must be asking for too much input current causing inrush fault condition.
I have googled lots and using a Thermistor NTC on both AC input lines should suffice.

With the battery disconnected from charger, and charger falling to zero or at zero, I unplug charger, quickly plug it back it again and its reading 19.50V.

HOW DO I CALCULATE WHICH NTC TO USE?
Do I just go 115V / 2.5A = 46-ohms
25 and 33 ohms on mouser
local store has 100, 120, 22 ohms

----------

I opened one up to take a look inside, as I like to do that. At first I was confused with the OneWire Protocol, went on a day long hunt searching.
I do not see any disc like thermistors on the ac input side, so what I think is happening is the laptop itself controls what the charger is seeing and compensates, probably following some predetermined charging rate where the laptop doesnt ask too much of the charger.

spec:
Hi cdnmatt

Firstly, it would be advisable to stop charging the batteries as you describe. :palm:

Instead get one of the low-cost  battery controller boards from ebay etc and connect the controller board to the batteries. Then power the controller board with the laptop PSU. It is probably a good idea to put a 1mF (1000uF), or larger, capacitor across the output of the laptop PSU. The voltage rating of the capacitor should be 35V or higher.

That should solve your problem and also give the batteries an easier life :)

cdnmatt:
Thanks for the reply, I really appreciate it.

I've been playing around a bit tonight and searching for a solution.

I tried installing an old hot plate, one coil of 40ohm on the hot wire of ac, it fluctuated the output.
Cancelled that experiment.

I then plugged one charger in, took it out quickly and plugged in a second charger.
After a few attempts I got the "good" charger going again. Temp of case is at a steady 40C and slowly increasing normally.

The usual fault condition of the charger occurred when I measured the voltage of the unplugged charger.
Meaning it slowly decreased to zero, in a total span of under a minute.

I noticed too that when I plugged in a charger, it would increase the battery voltage by 0.10V, but would never chooch no juice. Unplug the charger, charger goes to 0V.

Thank you spec for your input, as I said I really appreciate it. This is the first time I have heard/read about the low cost battery control boards, I will have a quick look at them right now. I thought perhaps you mean a BMS (Battery Management System) but I have not been using them as these cells stay stable as long as I do not abuse them, they are always well within balance spec. When I do need to balance, I have a wimpy and slow 50W RC charger that can do 6S but only 1P at a time. So you can imagine how slow a process it can be. I bulk charge them to 4.10V then apply balance charge, but usually I manually get the ones way out of line exactly, but this method happens infrequently. I open them up every few months, they are stable. I just dont drain them too much to get out of wack.

I typed in "battery controller boards" into ebay search.
Titles such as "XY-L10A Lithium Battery Charge Controller Protection Board 6-60V LCD Display" come up
Reading the description, I do not have a problem with the end voltage, 21.00V is my max, chargers only go to 19.50-19.75V.
I built my pack to achieve the correct C-rate for charging. 5S10P put in series with another 5S10P = 10S10P giving my 21V 30Ah x2 in series = 42V 30Ah (new)
These chargers are 6.7A on 21V 30Ah. Its equal to a ~14A charge on a 42V 30Ah.
My old Mean Well's were pumping out 15A on 10S10P, but were much larger and heavier.
I know now I am rambling, it just baffles me is all. Learning all this new jargon, but yet its fascinating how all the lego pieces work to do what it does.

I will buy a few caps tomorrow, plus a range of NTC's
I assume this cap just slows the current down, by storing the charge up so the charger has time to compensate.
I was also thinking of using a diode/one way valve so the current from the battery doesnt trip up the charger when I plug it in.
Thanks again. I will report back tomorrow as its late night here now.

--- Quote ---1mF (1000uF), or larger, capacitor across the output of the laptop PSU. The voltage rating of the capacitor should be 35V or higher.
--- End quote ---


cdnmatt:
One last bit of info to add.

I did cut off the Ferrite Bead / Choke from the end of the DC side charge cable.
I thought it was just to keep the EMF from the laptop away / off the power grid.
These chargers come with a 3rd wire on the output, OneWire Protocol that talks back and forth from the laptop to the charger. My best guess is the chargers are "dumb" and its the laptop thats the "brains" also more then likely its a propriety head lock keeping the laptop owner chained up. All club soda man, no boozie booze for a long long time on my end. Full moon ya know. Fun aside.

I've been thinking that perhaps it does more then that EMF protection. Luckily I kept one, the other I cut up trying to figure out what it was.  :-[
Luckily I have one un touched charger, and another charger I opened up to look at the components inside.

mvs:

--- Quote from: cdnmatt on November 23, 2018, 01:57:15 am ---The Low Down
I have a Dell laptop charger/power supply that I am not using for its intended purpose, but using it to charge my own custom battery pack for an e-bike.

--- End quote ---
What you call a charger is actually just a power supply, constant voltage power source. Charging circuit (step down converter with constant current-constant voltage control) is in laptop.
Usually switched mode power supplies do have over-current protection to prevent transformer saturation, typically implemented as current limiting and therefore one can misuse them as chargers. But in this case the over-current protection seems to have latched operation. If it trips, then you need unplug input from mains to reset it.


--- Quote ---These chargers come with a 3rd wire on the output, OneWire Protocol that talks back and forth from the laptop to the charger. My best guess is the chargers are "dumb" and its the laptop thats the "brains" also more then likely its a propriety head lock keeping the laptop owner chained up.
--- End quote ---
Its common this days to have some 1-wire ID/EEPROM chip in laptop PSU. Its used for identification only and has no effect on operation of PSU.

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