Power consumption question

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Tõnis · #1 Post by **Tõnis** » Thu Sep 17, 2009 11:00 am

I use my ThinkPad in my van a lot and keep the 90 watt travel adapter plugged in to the cigarette lighter. I noticed (in power manager) that it says the current being drawn is around 2 amps when the battery is charging. Then, when it reaches 100%, the current is zero and Power Manager says "no activity. Of course, when the battery stops charging, the battery meter stays at 100% if I leave it plugged in. Thus, it must be drawing something when still plugged in. Is it trickle charging? Is it two amps, less, or more? I realize car batteries are made for short bursts of cold cranking amps and not for long, slow, draws, but I'm wondering how long I can leave the unit plugged in with the van off (at 100%, "no activity," per power manager) before my van battery gets so low that the van won't start. I mean, how much is it all drawing, ThinkPad in use (i.e. on and not in sleep mode), battery (trickle) charging, charger transformer connected. TIA for your thoughts.

dr_st · #2 Post by **dr_st** » Thu Sep 17, 2009 11:12 am

The power manager measures the current that goes only through the battery. Whatever your PC is drawing directly, bypassing the battery is not monitored.

Tõnis · #3 Post by **Tõnis** » Thu Sep 17, 2009 11:40 am

Thank you. Any idea what the notebook itself draws, just sitting there with the monitor on with some medium brightness? Is it 2 amps, more, or, less? The reason I ask is that even with the notebook on and battery charging, the van still starts after like an hour. The two amps for charging seems to be nothing, but I have no idea what the PC draws. I don't have a meter for measuring DC amperage (only the clamp type for measuring AC).

dr_st · #4 Post by **dr_st** » Thu Sep 17, 2009 1:47 pm

Tõnis wrote:Thank you. Any idea what the notebook itself draws, just sitting there with the monitor on with some medium brightness? Is it 2 amps, more, or, less?

Idling at medium brightness should draw less than 2 amps. You can easily find out by disconnecting it from the power and seeing how much is drawn from the battery.

Tõnis · #5 Post by **Tõnis** » Thu Sep 17, 2009 2:25 pm

Great idea! Thanks! I can't believe I didn't think of that ...

yak · #6 Post by **yak** » Thu Sep 17, 2009 4:14 pm

dr_st wrote:You can easily find out by disconnecting it from the power and seeing how much is drawn from the battery.

Just make sure the laptop won't change the power settings. The Power Manager schemes have different settings for "AC" and battery.

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