Laptop pwr supply - Page 1
Forum section: electronics / beginners

author: cdnmatt
author_rank: Newbie
timestamp: November 23, 2018, 01:57:15 am
content: The Low DownI 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 6.70ACharger input is 115V(ac) and rated for 2.50APlug 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 QuestionIs it the inrush current from the ac input side of the charger, disabling/turning off the chargers output?More details belowWhat I haveI am using it to charge up a 5S10P Li-Ion battery (LiMn) that at its max is 21.00VBatteries 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 ProblemThe 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-ohms25 and 33 ohms on mouserlocal 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.

author: spec
author_rank: Frequent Contributor
timestamp: November 23, 2018, 07:58:51 am
content: Hi cdnmattFirstly, it would be advisable to stop charging the batteries as you describe.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

author: cdnmatt
author_rank: Newbie
timestamp: November 23, 2018, 09:19:53 am
content: 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 upReading 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'sI 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

author: cdnmatt
author_rank: Newbie
timestamp: November 23, 2018, 09:28:56 am
content: 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.

author: mvs
author_rank: Frequent Contributor
timestamp: November 23, 2018, 11:00:28 am
content: Quote from: cdnmatt on November 23, 2018, 01:57:15 amWhat 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.QuoteIts 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.

author: cdnmatt
author_rank: Newbie
timestamp: November 23, 2018, 07:30:26 pm
content: Thank you mvsIf I may dumb it down for myself.The laptop unit "charger" is really a Power Supply Unit (PSU) that is Constant Voltage (CV), and that the Constant Current (CC) comes from inside of the laptop, starting at the input of the charger cable inside the laptop. Then the laptop does its magic to control the flow of energy, then charges the laptop battery.Reworded...The CV part of these 19.50V 7A Dell laptop chargers give that pumping action of the electrons trying to reach equilibrium in trying to get the batteries to 19.50V in whatever way the charger can. These Dell chargers have no CC. The laptop charger is pumping out too much juice and is tripping an internal charger safety mechanism and disconnecting the chargers input.Has nothing to do with inrush from the input AC side of the charger.Has to do with outrush from the output DC side of the charger trying to reach that equillibrium/equalization of 19.50V.That makes sense to me now.It explains a few things to me, why these units are so small, compared to my Mean Well HRP's (24V 15A) that have been doing the charging for me the last few years and have been robustly solid. Side note: Others use LED driver psu's (HLG 's) that have cc/cv, "RSP" 's, modifying model "S" 's.Solution...Then it would be wise for me to buy or build a DC-DC boost converter with CC/CV able to handle 7A and have a boost of 1.00V from 19.50V + 1.00V. This is probably the most economical way to achieve my goals. Its just the wait time for delivery for the price isn't ideal. That is why it'd be cool to find a circuit online, buy the parts, and get soldering.Some have put these laptop psu's in series with a Mean Well that have that cc/cv characteristics. This is where that cc/cv control come from that controlls the laptop psu. Then buying a Mean Well with that control (cc/cv) such as a led unit, hrp, rsp would suffice. The lowest I've seen are 3.30V with adj down to 2.90V or more depending on luck, or some sort of modification to the potentiometer. I just might do this as I do need a solution to get riding again, as this is my only means of transportation.It is all strange to me because I can get one working and it acts like my Mean Well HRP's I've been using. But as mentioned, its pumping out an uncontrolled amount of juice and the safety mechanism is not kicking in. Makes sense. I really do need to buy some fuses and get my dmm's able to measure current. I need to see how much current.I have a few goals to achieve then.Quote from: mvs on November 23, 2018, 11:00:28 am

author: cdnmatt
author_rank: Newbie
timestamp: November 25, 2018, 06:44:08 pm
content: What is the white powdery substance on the inside of the heating element that surrounds the small coiled up wire?Coiled up wire, white powdery substance, then a metal outter casing.https://en.wikipedia.org/wiki/Heating_elementQuoteQuoteI hope its not unhealthy, as it falls out trying to get the small coiled up wire.I got the laptop power supply aka charger to work and I did some measurements.What I did was to place inline on the + side of the charger a cut heating element of 10 ohms.Do I need a power resistor or can a NTC Thermistor handle it?7A is the current rated on the Dell "charger" and the power rating of the thermistors is 500mW.I bought some 100W - 2/1/0.5ohm power resistors, should take a month to come from China.In the meantime I have a bunch of small heating elements cut from a grill cheese maker.I measured current and voltage.The characteristics of the charge was that the current would hover around 5 to 7A and the voltage would slowly increase 0.01V until 19.50V at which point the current would be 200mA. I never left it on to see if it would shut down or not. That will be my next observation.The charger would always be at 25-40C at the spot where the tapped transformer coil is, with the plastic housing on of course.The heating element would get to about 30C in the beginning, but would cool off and I could take it off later, and it would still work.I have a DC-DC booster that is rated for 10A so I will try that out today, go from 19.50V to 20.25-20.50V.There is just one potentiometer for voltage. I did see some on ebay that had current and voltage potentiometers.I however made a mistake and bought 2 units with just voltage.Other then that I blew a handful of fuses, but scored a good deal on $10 Crappy Tire DMM's with wire strippers and pliers!