Meanie said:
I'm searching for a second power source for my HP laptop but trying to
avoid the high OEM cost. Therefore, I've been searching for aftermarket
adapters which don't quite match-up to the exact specs of the OEM.
The OEM specs are as followed:
input: 100-240v~50-60Hz 2.0A
output: 19.5v--6.15A
I have found aftermarkets with specs of 100-240v~50-60Hz (input) and
18.5v--6.5A (output).
That minor 1v less and .35A more of a difference in output is what makes
me apprehensive. Am I being overcautious or is it a legit concern?
Thank you
But you can find a power source with those specs. It's just a matter
of chopping off the connector, and fitting the connector that works
with your laptop, if necessary. I can find instances of adapters
with that exact voltage and current.
http://www.amazon.com/6-15A-19-5V-adapter-Sony-laptops/dp/B003Q3B8BI
*******
All I can tell you, is the experience of one poster. He used an adapter
with a voltage which was 1 volt more than the nominal amount. And the
laptop stopped working roughly one month after starting to use the
new adapter.
The rest of the laptop, is designed on the assumption that voltage
is tightly controlled (i.e. regulated).
Here are some possibilities:
1) Voltage too high - something overheats in charge controller or
regulator inside laptop. The laptop can charge the battery, when
the laptop fan is not running, so the charge controller has no
"good cooling" going on in some situations.
2) Voltage too low - battery does not charge completely, laptop runtime
compromised. Perhaps even, charge termination doesn't work properly.
3) Another possibility, is the laptop actually has a voltage check, and
won't run with an incorrect adapter (unlikely, but you never know).
The specs are somewhere around +/- 0.5V on voltage. Something like that.
As far as the laptop circuit designer is concerned, the incoming voltage
varies from 19V to 20V in your case.
But I can't be sure about all of this, because I don't have a pile
of reference schematics to go through, to see what the consequences
would be either way (voltage too high, voltage too low). With the
voltage too low, at least the overheat option is a little less likely.
(The heat generated, is delta_V * I.)
At least one laptop, it seemed to be capable of operating with
a sub-standard adapter. You could take a 19.5V 6A adapter
and replace it with a 19.5V 3A adapter. It just would not
survive (would shut off), if you did something like play a
3D game or run a demanding application like the Prime95 torture test.
So my understanding is, if the max current capability is on the low side,
it doesn't immediately shut down. It may only shut down, if you
ramp up the CPU loading. They may not actually charge the
battery in such a way, as to draw full power. It could be,
that the extra power on one of those "double the juice" adapters,
helps with the graphics module or quad core CPU, and isn't
necessarily there to blast the battery full in one hour.
When Li-ion charges, the first charging phase is constant current.
This implies, that the laptop designer can take the incoming
current flow limits (say, the 6 amps), and give a percentage for
battery charging (say, 3 amps). Then, a 3A adapter can charge
the battery, if the CPU isn't doing anything demanding (laptop is
sleeping or is in shutdown state). If, on the other hand, the
constant current phase of charging used 4A, then a 3A charger
could (eventually) shutdown on overheat or shutdown immediately
on overcurrent. But if the CPU/GPU start drawing current (taking
the current draw up to the expected adapter limits), then that's
likely to be too much for a 19.5V 3A adapter.
http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
If the voltage was only 18.5V, it might depend on how much differential
there is between the "full battery voltage" of the battery pack, and
the reduced operating voltage. Circuits sometimes need a minimum
differential, to work properly. For example, when I use an LM317
as a constant current source, for home projects, that regulator
needs a 3V differential between input and output to work properly.
If I was charging a battery with my LM317, and the battery was say
16.5V when full, then I would need a 19.5V source to feed my circuit.
If the input to the regulator was 18.5V and the output reached a
level of 16.5V, the regulator may no longer perform as expected.
(The current flow level might be a lot less than expected - and
cause whatever I was doing, to take a lot longer than expected.)
*******
If there is any possibility at all, of damaging the laptop, I
wouldn't save a few bucks on the adapter. A laptop using 19.5V 6A,
is a high end laptop, meaning you paid a high price for it, And
it would cost a fortune for any trip to the repair shop (because
they'll always be telling you "we need to replace the motherboard").
Repair people don't know how to repair those things, without
just doing a board swap. They may not even have the documentation
needed, to repair the thing the "old fashioned way, with a soldering
iron".
Paul
