DC AC Inverter - What Wattage Needed for 8200?

Question

Hi, I'm trying to find an adaptor to run my Inspiron 8200 on 12 Volts DC. Dell sells some 12 VDC adaptors that replace the standard AC adaptor for 'selected' Inspiron models but don't mention the 8200 specifically.  Other posts here discuss 70 watt versus 90 watt adaptors - my 'normal' AC adaptor that came with the computer is a P9 series, model PA-1900-05D.  It produces 90 watts; 20 volts @ 4.51 amps. However I can't determine how many watts it draws in order to produce those 90 watts.  I have tried generic car-power inverters rated up to 200 watts continuous / 400 watts peak, and they show an overload when the green 'battery-is-charging' LED blinks on.  (This is with just one battery installed.)  If the computer is turned on AND charging the battery, the inverter is constantly cycling in and out of overload mode.  (And when it is overloaded, it shuts off momentarily, cutting AC power to the adaptor.  Kind of like rapidly plugging in and unplugging it from the wall, which constantly switches the computer between AC and battery.  This can't be doing the adaptor or computer any good.  The inverter also switches to overload with the 8200's batteries removed and the computer on, interrupting the boot-up and leading to more problems.)   Bottom line question, can anybody tell me how many watts the PA-9 AC adaptor draws from the wall outlet when the computer is on and battery is charging - i.e., at maximum load?  Is anybody out there successfully using a PA-1900-05D AC adaptor plugged into a 12 VDC inverter to run an 8200?  If so what's the wattage rating / manufacturer / model etc. of your inverter?     Also as an aside, I've seen lots of posts here referencing the 8200's internal 250+ watt power supply.  How can an AC adaptor that only cranks out 90 watts support this?

HTT Good HT Bad · Answer

your inverter may be able to handle the wattage but can it handle the amperage?

dillopk · Answer

Amperage multiplied by voltage = wattage, so the amperage is already factored in. For example, the output from the AC adaptor is 4.51 amps at 20 volts. Multiply 4.51 * 20 and you get 90.2 watts - hence it's a "90 watt" adaptor.. Likewise the "70 watt" adaptor puts out 3.5 amps at about 20 volts - 3.5 * 20 = 70.

My 90-watt adaptor says it will work with voltages between100 and 240 volts, and draws 1.5 amps. That means the watts it draws are anywhere between 150 (100 V * 1.5 A) and 360 (240 V * 1.5 A). It probably draws less amps at the higher voltage. This does not explain why it's overloading an inverter with a 400 watt peak capacity. I suspect the power requirement spikes briefly whenever the battery charger kicks in and the green "charging" LED on the computer comes on - that's when the inverter overloads. Kind of like the big surge when a motor kicks in. I may already be close to blowing the 20-amp fuse in the car - 20 A * 12 V = 240 watts = the maximum wattage I should be able to get from the cigarette lighter. I'm looking for real-world experience here - somebody who has done this and can share their knowledge.

dillopk · Answer

Well, the last inverter I tried was probably not the highest quality - about $40 from Wal-Mart - but was rated at 200 watts continuous power and 400 watts peak.

HTT Good HT Bad · Answer

you are incoreect with 240 Volts, as the voltage gets higher the amperage lowers so qith 240 it will be drawing about the same power. In my car the power is shared between 2 outlets at 120 Watts a piece, even though your inverter puts out 400 Watts it doesn't mean it draws that.When something draws 4 AMP at 110 it will draw 1-2 AMPs on 230. Also how good is your inverter, is it capable of sustaning 300-400 watts or is that just a peak wattage. I have seen a 850 Watt PSU and it Peaks around at 950 , but it can't keep 950 watts sustained

dillopk · Answer

FYI to those who may find this thread - I finally found a sufficiently powerful inverter, 300 watts with 600 watt peak, at Radio Shack for $99.99, item # 22-146.  It has two outlets, automatic overload and low-battery protection, and comes with a cigarette-lighter plug and also a pair of alligator clips that can be used instead.  More than I had hoped to spend, but it works fine even while using the computer and charging both batteries.

mandy3 · Answer

i have a post in regards to the same question for my xps. i am trying to figure out what inverter to buy to power it in the car to watch dvd's. i was told anything above 150 continous wattage, but i dont know how high to go for the surges. i leave on vacation in 2 days and would liek to figure this out. i plan to hook it up to the battery so i dont have to worry about the cig lighter, but unsure of what inverter to buy. i've seen $100 400watt inverters and $40 ones, what's the diff if they are rated the same? dont mean to high jack the thread, we're just talking the same thing here, just different laptops.

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