Car AC converter or alt portable power (iMac)

Virum

I need a DC->AC power adapter for my car's cigarrette lighter thing that'll be strong enough to power up an intel iMac.

Yes, and iMac. Not an iBook. An iMac. Not a typo.

My friend had one, but the light on it merely blinked when I tried to power up the iMac. The screen of the computer didn't even turn on. I'm guessing it didn't have enough wattage supply/output/something. I'm not an electrician.

So which one do I need to buy?

DrFrylock

Something like this? But of course heed the caveats about the maximum power draw from the cigarette lighter socket. You may need a bigger fuse, or it may not be possible at all...

Virum

That looks pretty close to what I want.

However, I'm open to other suggestions for portable power. Basically, it needs to last a few hours, rechargeable is a must if it's a separate thing.

All that'll be hooked to it is the iMac. (My video camera has to be hooked to an imac to capture HD video).

In fact, what might be best is a separate, preferably small, power source.

vonPoonBurGer

How about a UPS or similar backup power system? They're meant to run computers or appliances anyway, so you know they can handle the draw. My only questions would be how long the battery would last, and can you disable the audible "no main power" alarm so you don't lose your sanity during this project. It would be a fairly expensive solution, though, unless someone had a UPS they could loan you.

Virum

UPS woulnd't work long enough, I looked into that. At least none of the ones I could afford haha.

Maybe this and just have a few car batteries that I could recharge after I'm done?

or maybe this

Or this?

Which do you guys think is best?

vonPoonBurGer

Virum wrote:

or maybe this

That's along the lines of what I was thinking. Essentially, it's a big jeebus battery that provides standard AC/DC outlets. The problem is, I really have no idea how long you could run a computer on this thing, as electrical stuff is not my forte. Surely there's someone in H&A who can answer this question, preferably someone who didn't almost flunk out of electrical shop class in high school like I did...

Ruckus

A 300 Watt Inverter would probably only work for the brand new iMacs, if you have an older one you'll probably need something in the range of 400 to 1000 watts.

More info on your iMac would be useful (if you can check for a silverish plate near the power connector it might tell you the voltage/amperage and possibly the wattage. A model number might be useful too.

Virum

I quickly checked, but I didn't see anything by the power connector.

It's a brand new intel iMac (smaller screen, not the biggest one), I bought it last May if that helps. I'll see if I can find a model number later, but I have to go to school right now.

Virum

vonPoonBurGer wrote:

Virum wrote:

or maybe this

That's along the lines of what I was thinking. Essentially, it's a big jeebus battery that provides standard AC/DC outlets. The problem is, I really have no idea how long you could run a computer on this thing, as electrical stuff is not my forte. Surely there's someone in H&A who can answer this question, preferably someone who didn't almost flunk out of electrical shop class in high school like I did...

I see...

I don't like all the negative reviews, do you know of one that might work better?

Ruckus

Apple.com says all the newest ones use around 180-220 watts, so a 300w inverter should work.

I recommend this inverter from Belkin, it has a 3 year warranty and Belkin's really good for warranty replacing stuff, if it even breaks.

mcdermott

Yeah, if the iMac is only drawing about 200 watts, a 300 watt inverter ought to do the trick. Two things to note, though. One, you likely will not be able to draw 200+ watts through a cigarette lighter socket...they're generally fused to 10A, for a max of 120 watts. You'll need to set up a seperate accessory socket with a larger fuse.

Also, standard 12V car batteries are not going to run this computer for particularly long. You're looking at something on the order of 2-4 hours max*. You'd actually be better off if you can keep the vehicle running (or at least run it off and on).

And yes, you could just buy seperate batteries and hook the inverter straight onto them...in this case you'd actually want to get deep cycle batteries rather than standard car batteries. I think they run about the same, but they're designed to deliver constant low currents rather than larger surges of current (like what is needed to start a car)...also designed to be fully discharged and charged repeatedly.

* - Quick reference for you, so you can do the math when you're looking at these things. Volts*Amps=Watts. So if your computer takes 120V, at 2A, it is drawing 240 Watts. Batteries are generally rated in A*h, which is how many hours it can provide a given level of current. So say a car battery provides 70 A*h...it's at approximately 12V (actually, down to 10 or so by the time it's done), so (12V)*(70Ah)=(840Wh), or 840 watt-hours. This means it can provide 840 watts for one hour, 1 watt for 840 hours, or 210 watts for four hours. Actually less, because again the voltage will drop over time, and your inverter will not be 100% efficient...but good for (very) rough estimates.

The other rating you'll see often on deep-cycle batteries is "Reserve Capacity." Wikipedia tells me this is the duration for which the battery can provide 25A of current which, conveniently, is approximately what your iMac will draw. All the batteries I'm seeing online run from $100 to $200 for anywhere from 90 minutes to 3+ hours of reserve capacity.

So basically you need to look at how long you need to run this rig without recharging, and whether leaving a vehicle running is doable (if noise is an issue, you could run an extension cord from the vehicle to the site). I do not recomment running an inverter off of your car battery without the vehicle running...it's the kind of thing you can do for short bursts in a pinch, but car batteries (unlike deep cycle batteries) are not designed for repeated full discharges.

Lastly I'd recommend a small UPS...not for running the computer for long stints, but for keeping it running during battery swaps or if your inverter output drops below what's needed to run it. Though I don't know what a UPS will draw from the inverter wattage wise, so perhaps that wouldn't work....hopefully somebody more knowledgable that myself can help out on that one.

Virum

Great info mcdermott. Do you have any specific products to recommend with that advice? Regardless it'll help my search a lot.

Now deep cycle batteries take a long time to charge right? Just making sure, because if I go that route (as opposed to hooking up to a running car which would work most of the time but could cause problems later on) I'll probably want about three of them.

CailYoung

Virum wrote:

All that'll be hooked to it is the iMac. (My video camera has to be hooked to an imac to capture HD video).

I'm more interested in this bit of information. What camera is it, and what are you shooting?

Virum

3rd party modded DVX100b. http://www.reel-stream.com/andromeda.php

Shooting lots of stuff. Shorts mainly but I was working on a feature that got delayed.

CailYoung

Ah, so not HD, but 4:4:4 from a prosumer MiniDV camera - cool!

Have you looked into using a FireStore or similar? Might be more reliable in the long run.

Virum

It is HD too:

"Allows for output up to 1540x990"

And no, the video is captured using Sculptor HD - It needs a mac of some sort on the other end of the USB cord.

CailYoung

Yeah, but that's including the pixel-shift, which is cheating. (Look at the mid-range areas of the bedroom test shot; the vast amount of colour noise in there is a direct result of the pixel-shift sampling)

Does it have to run off a car? A small generator may work for you.

Virum

I disagree. If pixel shift is cheating then the majority of prosumer HD cameras aren't HD. The only exception I can think of is the JDC HD100 which is only 720p... I can't remember if the Canon was native, but it's faux 24p so. The HVX200 utilizes pixelshift. Any prosumer camera will, and I obviously don't have the funds to afford a "real" HD camera. The only difference is these prosumer HD cameras and this is that the pixelshift is hardware, not software, so it can't really be improved upon whereas the andromeda system can and has been.

Come on, you can't get this kind of imagery out of an SD camera:

http://www.reel-stream.com/magik_test.php/rs_1115cc.tif?type(jpg)
http://www.reel-stream.com/magik_test.php/0719_OOmicro35-dvxHD.jpg?type(png)

You have to agree, this isn't SD, so if it's not HD what is it? It's not fullsensored HD but pixel shifting is an okay thing, many cameras do it. Obviously it's not as good as the real thing, but then you have to pay more for that because to pack in more pixels in a sensor, you need bigger sensor or you start getting more noise. I think it's an okay balance.

---

The generator is a great idea, I hadn't considered that. Of course, I'd like to work inside a car as well so I'll probably go for a battery pack for now but a gas generator for exteriors might be a good idea.

CailYoung

Virum wrote:

You have to agree, this isn't SD, so if it's not HD what is it? It's not fullsensored HD but pixel shifting is an okay thing, many cameras do it. Obviously it's not as good as the real thing, but then you have to pay more for that because to pack in more pixels in a sensor, you need bigger sensor or you start getting more noise. I think it's an okay balance.

Oh, it's definitely an okay balance, and it's the absolute best you're going to get out of the DVX camera, which I'm all for. I'm coming at the 'HD' name from the high end though (I'm buying a Red camera next year) so I like my pixels to be real, but I definitely understand the need to get quality on a bootlace, if not a shoestring.

Virum

Ah yes.

I'm hoping I'll have enough for a red camera by then, but that's still a lot of money to swing, and then you have to get a quality lens and storage system. And I should probably use the money to pay for college.

Adromeda will do for now. If I actually start making copious amounts of cash with the stuff I make, then I think I'll be able to justify upgrading.