Can I charge my laptop battery at 20V and 5A if the specs state 19.5V and 3.33A?

[Silver_Is_Money]

I built a crude prototype of the two resistor voltage divider circuit using 30 KOhm and 5 KOhm resistors.  When fed via my LiFePO4 battery along with my boost converter ramping it up to 19.87V, the divider voltage (voltage between the resistors) to the blue wire (center "Smart" pin) read 2.85V.  Very close to predicted...

The HP Probook440 G3's battery was at 78%, so I shut it down, plugged it into my battery circuit, and then turned the computer back on.  It booted right up and went directly into battery charging mode.  I watch it slowly charge the battery from 78% to 100%, and then the "battery is fully charged" message appeared.  Just as if the computer was on the standard HP 120VAC to 19.5VDC (actually 19.87VDC) power adapter.  When I disconnect the barrel jack a message now pops up and says "battery discharging from 100%", and when I plug it back in this message vanishes. 

BTW, I'm running Linux Mint 21.3.

So far this project seems to be a whopping success!

Edit:  Adding that the tiny LiFePO4 battery (nominally 8Ah, and weighing only 1 Kg.) went from 13.5V (~95% full) to 13.3V (~80% full) during my test run today.  This LiFePO4 battery is at 80% discharged when it hits 12.8V.  70% discharged at 12.9V, and 60% discharged at 13.0V.  I'm going to add an under-voltage protection (battery cut-off) circuit set to 12.9V.

[MrAl]

I built a crude prototype of the two resistor voltage divider circuit using 30 KOhm and 5 KOhm resistors.  When fed via my LiFePO4 battery along with my boost converter ramping it up to 19.87V, the divider voltage (voltage between the resistors) to the blue wire (center "Smart" pin) read 2.85V.  Very close to predicted...

The HP Probook440 G3's battery was at 78%, so I shut it down, plugged it into my battery circuit, and then turned the computer back on.  It booted right up and went directly into battery charging mode.  I watch it slowly charge the battery from 78% to 100%, and then the "battery is fully charged" message appeared.  Just as if the computer was on the standard HP 120VAC to 19.5VDC (actually 19.87VDC) power adapter.  When I disconnect the barrel jack a message now pops up and says "battery discharging from 100%", and when I plug it back in this message vanishes. 

BTW, I'm running Linux Mint 21.3.

So far this project seems to be a whopping success!

Edit:  Adding that the tiny LiFePO4 battery (nominally 8Ah, and weighing only 1 Kg.) went from 13.5V (~95% full) to 13.3V (~80% full) during my test run today.  This LiFePO4 battery is at 80% discharged when it hits 12.8V.  70% discharged at 12.9V, and 60% discharged at 13.0V.  I'm going to add an under-voltage protection (battery cut-off) circuit set to 12.9V.

Sounds good glad you got it working.  I love those LiFePO4 batteries so light weight compared to the lead acid counterparts.

[Solder_Junkie]

An update on my Dell Vostro and 12V to 20V power.

I used an existing laptop car charger that only has 2 wire output. As pushing the plug from the Dell mains charger halfway into the socket on the laptop results in powering, but not charging, the laptop… I tried wiring a suitable 3 wire connector to the 2 wire output of the old adapter.

Unfortunately, while it was possible to power the laptop with the above arrangement, and not needing to charge the battery, subsequently plugging in the mains Dell charger didn’t charge the battery! Panic set in, but I had forgotten that I had adjusted the “MyDell” software to only charge the battery when it had dropped below 50% charged.

So, bottom line is that at least with a Dell Vostro, alternative methods of powering it are a mystery and proceed with caution.

SJ

[nightfire]

Just opened my old and trusty HP Zbook 14 (gen1) and poked around with test leads around the battery connector whilst the system was operating.

Given that I did not got good contact due to the shielded location and not having needle-thin probes, got around 8.8VDC at connector pin 1+2 without charger connected, and around 9.8V with external power supply, when battery was about 90% full.

So no 19V from the PSU are directed directly to the battery.

Battery was a HP 716742-422  rated 11,25V  50Wh. This would point to 3*Lithium cells with 3.7V and some BMS managing the output voltage so that even a nearly discharged Lithium cell with 3V can power the notebook.

[Solder_Junkie]

A friend found info on that mystery IC used in the Dell charger. There is a lot more going on than just a Voltage level:
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Dell uses the ONEWIRE (1-Wire) protocol for communication between notebook and charger, for this reason the Dell charger has a 3-pin EPROM memory with 512 bytes (DS2501 or 9CM543E) that sends a data packet with power specifications, voltage and current through the central pin of the charge connector, and the EC (Super I/O) reads this information.

The data packet can be viewed with the oscilloscope set to 1v/500us. In this PSID data line there is a pullup resistor connected to a voltage of +3.3v.
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I don't know if HP use the same idea.

SJ