Adapter specs confusion

[MagicMikeJ]

Hi, I am a newb to the solar panel club, doing my research before diving in. My situation is I'm looking to do some boon docking with our van and I'm obviously looking for some power options.

My main goal is to have a system good enough to power a 12v fan, maybe a few 12v lights and run at least one laptop. The fan would be all night to keep us ventilated, the lights in the evening hours before sleep, and the laptop, not sure..... some hours during the day maybe while the system is being charged, and maybe a couple hours on the battery to watch a movie or something before sleep. 2 laptops would be nice, but I am trying to keep the charging system as inexpensive and small as possible, so I'll be happy with one for now.

What's confusing me is how to figure the power draw of the laptop. I am looking at a 12v adapter for it, and these are the specs:

Max. Power Output: 90W
Voltage Output: 19V
Max. Current: 4.74A
DC Input: DC 10-15v ~ 10A

Do I need to just worry about the 4.74A it's putting out, or 10A that it needs for input?

In looking at the AC adapter for the laptop, it says: Output is 18.5 v/3.5A (65W) and the input is: 100-240v/1.7A.

So I guess I have 2 questions here. Do I need to look at the input amps or the output amps for my calculations?

And the other would be would I be better off running the laptop on my 400W inverter?

It seems that AC always has a lower amp rating, but I'm under the assumption that running 12v stuff would drain the battery less than an inverter with AC stuff. I could be wrong, but I don't think so. Seems that punching that 12vdv up to 110 vac just by itself is going to use a bunch of power.

I'm hoping to get by with one panel, 100 or 150 watt and one battery, but the 90W and 10A has me a bit worried that it won't be enough?

[Mike90250]

Wow.

First, DO NOT plan to run this gear off your vehicle starter battery. You will be sad.

Use the wattage (the highest) as your consumption. You eventually will be working with Watt Hours
so 2 hours with your 90W laptop will = 180wh

Using either a plug-in 12V inverter or a plug-in laptop adapter will result in about the same amount of power consumed, they both transform/convert power and have internal losses.

Your 12V inverter should be a Pure Sine inverter. It will run a fan much better than a cheap square wave inverter will (square waves make motors Buzz and Hum) and motors consume more power on square wave inverters. I like the Morningstar SureSine 300w inverter, it's robust, has 10min 600w surge, and has very efficient power circuitry. There are some other +90% efficient 300-50w inverters and they all cost around $300-$400, quality and efficiency is not cheap.

Sometimes a silent 6 or 8 inch computer cooling fan will be your best bet for low power air movement, or a standard plugin fan from -mart. Just depends on the resources you have.

Lighting, look to RV and boating shops for LED lighting.

Depending on how long you will be parked, you may want to just get a battery isolator and use the vehicle alternator to charge up, or go to several PV panels, or a small 1,000w inverter generator powering a battery charger. These are all choices, with costs and convenience variables.

http://balmar.net/duo-charge.html

[PNjunction]

Mike is on top of it!

If you don't want to just throw money in the air and guess, you need to measure over time.

The fan is easy. Endless Breeze (by Fantastic Vent co) dc rv fan. 1/2/3A switch selectable speeds approximately. How long is all night for you? 4 hours? 12 hours? * fan speed ....

Measure the ACTUAL draw of the laptop under worst case conditions - that is, charging its own li-ion battery pack, running at full cpu power, max brightness etc.

You can do this by purchasing a P3 International Kill-A-Watt meter and looking at the watt draw. From this, we can start making ballpark conclusions based upon your time needs.

That's worst case though. If you pull the laptop's internal battery pack so it doesn't charge, lower your brightness, reduce the cpu speed for non-intensive tasks (it may have a setting to do this for you automatically), then look again at the kill-a-watt to see what your *normal* usage is. Based on that, you may be able to have a smaller system.

In the end, if you don't measure your needs over time, you'll be throwing money away on a system that ends up in the corner of the garage. And as Mike pointed out, going cheap isn't the most cost-effective route when junk craps out prematurely.

[MagicMikeJ]

Thanks for the helpful info. I know better than to run the inverter off the van's starter battery (now) without the van running. A few years back I thought we could watch a movie on the laptop without having to have the van running. 2 hours later, dead battery.

Anyway, I've heard about the Kill a Watt meters, was just hoping I didn't need to get one. Now that I'm looking at them, I see the 4400 model at about $16, and the 4460 which is twice as much, about $31. What's the difference between them?? From reading some reviews on them it looks like the 4460 does some calculations for you to tell how much things will cost to run once you put your cost per kwh into it. I don't need that function at all. Is there anything else I am missing on the differences? I do need to go as inexpensive as possible (on pretty much everything), but don't want to go too cheap and miss functions I need.

[PNjunction]

The original 4400 would do just fine.

Know what you mean about the starter battery. I hope you are thinking along the lines of an auxiliary battery better adept at handling the job, and leaving your starter battery as just that - a starter battery.

[MagicMikeJ]

Yes, I've done enough research to know I need a marine or golf cart batteries, a charger/controller, and a panel or 2.

And I won't be able to plug my laptop with a 12v adapter into the kill a watt, I can only check it running on the ac brick.

[inetdog]

Yes, I've done enough research to know I need a marine or golf cart batteries, a charger/controller, and a panel or 2.

And I won't be able to plug my laptop with a 12v adapter into the kill a watt, I can only check it running on the ac brick.

Assuming that the 12V adapter is reasonably efficient, the AC brick power reading should be good enough for planning.

[Bucho]

Do I need to just worry about the 4.74A it's putting out, or 10A that it needs for input?

It's likely not putting out the max current on the UL listing. Mine certainly uses significantly less. To get a real number you'll likely have to actually measure it.