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car charger for laptop (slightly) underpowered


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#1
digikiwi

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I bought a universal car charger/adaptor to power my HP nc8430 laptop when the battery runs out as I often use the laptop in the back of my van between appointments.

Now the mains adapter for the laptop runs at 19.5 V with an output of 4.74 A. That means it would rate at 92.43 W (W=AV).

The universal car adaptor has different Voltage settings and I have locked mine in at 19V. It is rated for 90W and the guy at the shop says that this is just fine. However when I plugged it in for the first (and only time) yesterday a message came up on the laptop screen saying that the adapter was not delivering enough power.

Shop guy says don't worry about it, it might just take a little longer to charge the battery, but it's no problem and won't hurt the computer. I asked him if he'd put that in writing and he got a little shirty with me, saying if I don't want it I can bring it back.

My question is: Is he right - that 2.43 W won't make a difference? Or is running at a slightly lower voltage and Watt rating risking damaging the laptop?

Thanks in advance for your educated answers

Digikiwi
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#2
Major Payne

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It's not so much the wattage, but the initial charging current requirements at the rated battery voltage you need to look at. Also, is that charger well enough filtered from all external engine noises, spikes, etc.? More than likely the battery charge current has caused a further voltage drop which has caused a change in the charging current again. This may have generated the message.

The battery MUST be charged at its rated voltage to be able to charge to its full current capacity. Might check to make sure battery is not overheating during the initial charge as this could ruin the battery. Have you checked HP for a proper car charger unit?

Edited by Major Payne, 26 March 2009 - 09:13 AM.

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#3
digikiwi

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The Major to the rescue, nice to see you're still on this forum a good few years later :).

Essentially I'm not really interested in charging the battery, and if the battery was overheating or otherwise stressed I could just as soon remove the battery. What I'm really after is power to run the laptop.

I think I understand what you mean by spikes, noise and voltage drops but have no idea how to test for these.

the initial charging current requirements at the rated battery voltage

Where do I find these requirements?

Cheers

Digikiwi
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#4
Major Payne

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Battery: 8-cell (69Whr) high capacity Lithium-Ion type.

Looks like what you have may be ok as this unit is advertised for your model:

HP Compaq 52Whr Secondary Travel Battery

This ac adapter is specified for your laptop: HP 90W Smart AC Adapter

The HP 90W Smart Auto Adapter enables you to power your HP Business Notebook in your car, and charge the internal battery simultaneously.


Not sure why you got the message now, but it may be that you could go in and reset the power options for monitoring.
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