charging with car's AC - how many devices can be charged

Started Jan 31, 2014 | Discussions
veeco5150 Contributing Member • Posts: 502
charging with car's AC - how many devices can be charged

Hello,

I am going on a road trip through NZ and I will be driving a lot and be out in the wild for extended periods of time doing photography work. I have a number of devices that need to be recharged by USB and it looks like my car's cigarette lighter may be the only option at times.

I have an inverter that changes the lighter into a 3 pronged standard plug and I also have a power strip. How many devices can I plug into this power strip to be charged by the car's AC port? Is there any danger there? Obviously I need to be cautious when the car is not running and not kill battery, but while driving; would I risk damage to devices or would it just not charge at all or charge very very slowly?

With the engine off would the power drain from car battery be the same regardless of the amount of items that I am charging?

Sadly these days, we are so dependent on rechargeable batteries. I will need to charge and power these items:

Necessary:

Batteries for Canon DSLR's

AA battery chargers for flash

macbook pro battery (4 yrs old so very little battery life as is...mostly just to keep running while downloading mem cards and backing up on external HD's)

Not completely necessary:

Ipod

Iphone

backup iphone battery

Ideally, at the same time while driving; I'd like to charge an iPod, charge DSLR camera batteries, and power a laptop while backing up onto an ext. HD.

thanks so much for the help and advice!

Cheers,

Micah

GodSpeaks
GodSpeaks Forum Pro • Posts: 12,750
Re: charging with car's AC - how many devices can be charged

Your invertor will have a power rating, either in watts or possibly amps.

Each charger will also have a power rating, usually in amps or milliamps.

Just do not exceed the power rating of the invertor.  In fact, it would probably be a good idea to limit yourself and stay under 75 or 80% of the invertor rating.

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OP veeco5150 Contributing Member • Posts: 502
Re: charging with car's AC - how many devices can be charged

thank you so much for the advice! If if it should happen that the inverter goes above that amount, would it blow the fuse normally before damaging the gear? Of course I know there is no guarantee, but is that how it is supposed to function.

Since my laptop is the most valuable, I figure I will only have that plugged in by itself; but the other somewhat less valuable items, I might try to plug 2 in at a time....A macbook pro should be able to be fine plugged into an AC by itself right?

Lee Jay Forum Pro • Posts: 52,344
Re: charging with car's AC - how many devices can be charged

GodSpeaks wrote:

Your invertor will have a power rating, either in watts or possibly amps.

But the limit may well be the fuse running the 12V socket in the car, not the inverter.  If it has a 10A fuse, for example, it's not going to run a 300W inverter.

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Doss Senior Member • Posts: 2,080
Re: charging with car's AC - how many devices can be charged

veeco5150 wrote:

thank you so much for the advice! If if it should happen that the inverter goes above that amount, would it blow the fuse normally before damaging the gear? Of course I know there is no guarantee, but is that how it is supposed to function.

Since my laptop is the most valuable, I figure I will only have that plugged in by itself; but the other somewhat less valuable items, I might try to plug 2 in at a time....A macbook pro should be able to be fine plugged into an AC by itself right?

Hmmmm....This is a question I've dealt with and looked into lots. I've concluded - there is no straight answer!

USB type devices/standard camera battery chargers/mobile phones/ipod. etc all draw a very small charge. Your main concern is running your laptop. However, all the devices you list WHILST DRIVING will be charging just fine. I've regularly charged a laptop, x3 mobile phones, a camera battery charger, a satnav and an ipod either using one cigar lighter (with splitters) and/or an invertor. Though all together the charge may be slower than you're used to from your home mains socket.

But as previous reply has said - check your invertor rating fulfills total ampage. Also note: Invertors are actual not lossless - ie they will drain battery power themselves (c.10%). There are also different types of invertor - If memory serves you want a cyclical invertor. You could google the different types and makes - but, believe me - There's a mindfield of (contradicting) info' out there.

Having adapters plugged straight into a cigar lighter are kinder on your battery, but not your devices. Surges can result and blow your gear (though the exception rather than the norm). Whereas an invertor (if fused correctly) will prevent this. If you go for the cigar lighter route I recommend you unplug devices when starting up the engine (again - a variable, depending on how the vehicle is wired).

There is another variable - Your alternator. In some vehicles idling the engine will keep the battery topped and charge/power your gear. In others it will still drain the starter battery.

One important thing is to make sure your vehicle battery is in good condition, and avoid draining it low - besides the impending doom of a flat in the middle of nowhere, it will also quickly render your battery useless.

The best, but perhaps least practical, option is to go for a dual battery set up with your 2nd battery being a leisure type.

Good luck!

Doss Senior Member • Posts: 2,080
Re: charging with car's AC - how many devices can be charged

Lee Jay wrote:

GodSpeaks wrote:

Your invertor will have a power rating, either in watts or possibly amps.

But the limit may well be the fuse running the 12V socket in the car, not the inverter. If it has a 10A fuse, for example, it's not going to run a 300W inverter.

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Lee Jay

At first I thought that was irrelevant from Lee Jay then I re-read the OP - "I have an inverter that changes the lighter into a 3 pronged standard plug"

Yeah - sorry. My advice is based on an inverter wired directly to the starter battery (for which you place the correct fuse on the wiring yourself). I wouldn't use the types that plug into the cigar lighter themselves - They are not usually that good. Better to get yourself purpose made cigar lighter adapters for your devices.

PenPix Senior Member • Posts: 3,261
Re: charging with car's AC - how many devices can be charged

As above, +1… It is possible to blow up your GPS if you plug in with power on! 

I've charged fully my phone, camera battery (I've bought a 3rd party accessory charger for my camera battery), and 4xAA using an inverter on the car battery alone… not at the same time as the need never arose.  This posed no problem as the car battery has more than enough capacity to charge these small items, and I have a mid-sized import so the battery is not large.

With the car running, laptop and 2 of the above charging is also no problem.

Running a laptop on the car battery for 2 hours has not caused any problems for me.  In an RV with dual batteries, I've run a cabin light and laptop for 4 hours.  In both cases, I could have run it longer but I've never pushed those times further.   I check the voltmeter periodically to make sure I'm not getting to low.

OP veeco5150 Contributing Member • Posts: 502
Re: charging with car's AC - how many devices can be charged

thanks for all the info...especially real life experience with actually using a number of devices charging through one cigarette lighter. that's a lot of devices on one AC outlet.

I looked at my Power inverter and it says 150W input 12V output AC110V...not sure if this helps out at all.

Seems like I will stick with charging only my laptop when needed, and then trying a different number of other battery charging devices together when needed...but keeping the laptop solo as it is the most important.

I'm guessing the AC fuse in the car is the standard fuse for a cigarette lighter...the fuse mentioned previously is prob the one.

AnthonyL Senior Member • Posts: 2,581
Re: charging with car's AC - how many devices can be charged

veeco5150 wrote:

I'm guessing the AC fuse in the car is the standard fuse for a cigarette lighter...the fuse mentioned previously is prob the one.

It might be a good precaution to know the rating of that fuse, where it is, how to change it and take a couple of spares just in case you do overload.

Invertors lose power, so that's an additional loss on top of transformer losses.  So use USB adapters where you can.  Why not get yourself some extra leeway and buy a new battery for your laptop?

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PenPix Senior Member • Posts: 3,261
Re: charging with car's AC - how many devices can be charged

Is the inverter rating an output of 150 watts and 110 volts, (not input of 150 watts)? You can correct me if this is not what it shows

A quick Google search shows a 5 year old mcBook pro consumes a maximum of 85 watts. If you inverter is rated with an output of 150 watts, you have a safe overhead for using the devices together.

Have fun on your road trip!

John1940
John1940 Senior Member • Posts: 2,726
Re: charging with car's AC - how many devices can be charged

PenPix wrote:

Is the inverter rating an output of 150 watts and 110 volts, (not input of 150 watts)? You can correct me if this is not what it shows

A quick Google search shows a 5 year old mcBook pro consumes a maximum of 85 watts. If you inverter is rated with an output of 150 watts, you have a safe overhead for using the devices together.

Have fun on your road trip!

In my experience with small inverters the 150 watts is the input so the maximum output power is lower. However, your conclusion is right anyway. The 85-watt rating for the MacBook is the maximum draw if the battery is almost discharged and the computer is running a very processing-intensive program with lots of graphics.

The maximum car alternator output power to charge its battery is over 700 watts even for a small car. The fuse for the cigarette lighter is usually either 10 or 15 amps. If it's 10 amps (120 watt draw) the fuse will protect the inverter and its load. (Good reason to have a spare fuse.) If it's 15 amps (180 watts) then something else (such as the inverter's fuse, if any) will blow or the inverter will shut off if it has that capability (perhaps thermal protector).

If I were the OP, I'd get a second battery for the laptop. It can provide USB power for other devices such as a USB disk drive. I'd also do a complete dry run at home with a small car and a largely discharged laptop battery plus all other devices being charged.

And, I'd buy a digital volt meter with auto-ranging (a feature that makes it easier to use). I would also only charge up the laptop when the car is running. If the car battery voltage drops below 12 volts then, depending on temperature and engine size, it's time to start it and get the alternator running. Most car batteries stabilize at 12.3+ volts when topped up. (That's why a good digital voltmeter is useful.)

(One more thing: the MacBook has a good capability to show its battery charge status.)

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hotdog321
hotdog321 Forum Pro • Posts: 18,262
No problem.
1

I've used inverters after Hurricane Ike, field assignments and to charge during trips. I also spoke to Houston Chronicle photographers who covered New Orleans after Katrina and they used car inverters to keep all their gear charged. I've never heard of anyone having a problem.

Those little laptop, cellphone and camera batteries draw very little current while charging. I even powered an electric drill with an inverter after Ike to remove protective plywood from my house and had no problem at all.

Most decent inverters have built-in protective circuit breakers or fuses--ditto your car cigarette lighter. The worst that might happen is you might pop the circuit breaker or fuse. But I'm pretty sure you are good to go--try plugging in everything at once before your trip to verify.

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(unknown member) Contributing Member • Posts: 947
Re: charging with car's AC - how many devices can be charged

I used to have an inverter in my van to charge my camera batteries and laptop. In my case 12v to 240v. Be aware an inverter takes a lot of amps to convert 12v to 110 / 240, depending on what you use.

You wouldn't get more than a couple of amps from an inverter before you blow the cigarette lighter fuse and make sure you run the engine while using the inverter.

My mk2 solution involves 2 12v batteries in series at 24v running a 24v inverter which halves the amp load from the vehicle. The batteries are trickle charged by a 12v-24v trickle charger.

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scorrpio
scorrpio Veteran Member • Posts: 3,595
Re: charging with car's AC - how many devices can be charged
1

A typical car alternator puts out 50-65 amps at 14V, or about 700-900W.    Bigger car (i.e. a truck) might have a 100 amp alternator.  An RV will have even more.   Every connected electrical device is rated for a certain power draw, protected by a fuse.    A 10 amp fuse on a 12V accessory socket will blow if you pull more than 120W.   If you want more power, you need direct wiring.   I.e. when I installed a 250W RMS sub amp in my car, I ran a 6AWG wire straight to the battery with an inline 30A fuse.    In retrospect, 6AWG was an overkill.

The fuse is there mainly to protect the wiring.    If you overdraw a wire can overheat and catch fire.    You want that happening inside the fuse, not in a wire harness next to the fuel line.

Anyways, a 150W inverter can be safely plugged into the typical 'lighter' outlet without much capacity loss.   A 400W inverter needs to be wired directly if you want all its power.

Then again, how much you need?    A typical laptop power brick is about 75W.    A tablet charger usually wants about 15W, and most  phones charge fine on 10W or less.    A DSLR battery charger might take 15-20.    In other words, I think you can plug a laptop, a phone, a tablet and a DSLR charger into a single 150W inverter plugged into a lighter socket and still have some leftover headroom.

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