Charging a laptop from a bike - Inverter or ???

tommcgee said:

My white MacBook has a 10.8V battery. My 2010 MacBook Pro has an internal battery, but both machines use the same Apple Magsafe Charger. It's a good bet that the MacBook Air also has a 10.8V battery.

There's a small switching power supply inside the Apple power brick, and as I say, it prolly deals fine with inverter input. The big problem with the damn thing is the output cord. The strain relief does not do a proper job. YouTube is loaded with videos about how to fix the cable. Most start with a dremel tool. The thing was not designed to be serviced.

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The voltage required to charge that battery from the DC input on the laptop might be more than twice the battery voltage. Unless you want to remove the battery to charge it, look at the DC OUTPUT of your AC adapter. That will have to match when you charge the laptop.

Or look to see if the input voltage is mentioned on the laptop itself.

-Don-

DonTom said:

The voltage required to charge that battery from the DC input on the laptop might be more than twice the battery voltage. Unless you want to remove the battery to charge it, look at the DC OUTPUT of your AC adapter. That will have to match when you charge the laptop.

Or look to see if the input voltage is mentioned on the laptop itself.

-Don-

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Good point. If we could only get all laptop vendors to mark voltage and current requirements on their products. Chargers usually ARE marked. I don't think I've ever seen a 2X difference in voltage between battery installed in device and charger, 1.5x is more typical. The battery voltage and charger voltage is much closer when charging a standalone battery.

After you have a charger with the right voltage, and you MUST match charger voltage with device voltage, what's equally important is to match charging current because if the charger can't provide enough of that, the battery will not fully charge.

My battery comment was about two different Apple products that use the same input connector. I should have been clearer and more specific. Apple does make three versions of its magsafe charger, a 45 watt, a 60 watt, and an 85 watt. The difference is the current capacity -- all three output the same voltage.

I get bit by this once in awhile because there are at least half a dozen different Apple laptops in the house. They look identical, but if you pick the 45 watt version when you need the 85 watt version, the battery voltage will never make it to 100%.

tommcgee said:

My battery comment was about two different Apple products that use the same input connector. I should have been clearer and more specific. Apple does make three versions of its magsafe charger, a 45 watt, a 60 watt, and an 85 watt. The difference is the current capacity -- all three output the same voltage.

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The labeling on the 45 watt charger for my MacBook Air says 14.5 volts at 3.1 amps. If I ever decide I want to charge the laptop on the bike I'll buy an inverter. In the 20 years I've been carrying a laptop I've not yet needed to charge it on the bike. I think that just means I've not done any long, camping only trips.

tommcgee said:

There's nothing inherently wrong with an inverter, it's just that there's a lot of cheap crap out there. You gotta choose carefully.

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Do I need to lookup the lighter insert style inverter we have from Wally World to make certain it isn't on your "cheap crap" list (and has the curved waves , not square)? FWIW, I didn't choose it and never had the papers either.Thus to avoid frying our laptop?

kantuckid said:

Do I need to lookup the lighter insert style inverter we have from Wally World to make certain it isn't on your "cheap crap" list (and has the curved waves , not square)?

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This is my question as well. I have a 175W inverter.
http://www.radioshack.com/product/index.jsp?productId=3897292&retainProdsInSession=1

It doesn't say sine wave, so I figure it isn't.

I picked up a $10 Phillips surge protector, but reading the fine print, it seems to be more interested in protecting against *surges,* which I suppose to be different from square waves. So, the surge protector may not be helpful.

The inverter has a fuse.

I'd trust the RatShack inverter over the one from WallyWorld. As to square waves, that's how they work. All inverters produce them. The good ones have filtering to take the edge off, so to speak. You can see this stuff on an oscilloscope, but they aren't exactly household items.

I have a Black and Decker 100W inverter. I haven't used it on a lap op but the package says "powers and recharges laptops, electronics and more"

Output wave form: modified sine wave (whatever that means.

Ralph Sims

tommcgee said:

There is one in the Apple Store:

Kensington Inverter

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perfect, thanks tom. h