Laptop Power

[Aidan]

Hey all,

As my AP setup starts to take shape, I'm now looking at how best to power everything.  I'll be getting a power tank sorted for all the 12v stuff and along with the Celestron LiFe I use on my LS8, I don't see any problems.

the thing I have not yet sorted is Laptop power.  I have got a 300w invertor which will work.   Imaging sessions will be at max 3 hours.  I have to travel, so time is limited.

Will a halfords 12v 17aH  with the invertor be enough to power the laptop for around 2-3 hours?   I want to keep things as easy to carry as possible even if it's just from the house to the car and car to site... Both only 50yds or so!

cherrs

Aidi

 

[RayD]

What Voltage/wattage is your current laptop power supply (should be noted as the output figure on the back of the brick supply)?

[Aidan]

Guess i should have posted that!    Its a 2010 Macbook Pro that i plan on using.  PSU states:   Output is 16.5v 3.65A   its the 60watt version.

[RayD]

Ok no problem.  With them you are resigned to using an invertor. I just got one of those little micro PC's (Intel i5, 8gb RAM and 256GB SSD) as they run on 12v and are fanless, so pretty energy efficient.  

17AH should give you 3 hours no problem.  The capacity will drop as it's running through an invertor, but for that length of time not enough to be of concern.  It's probably not going to give you a full charge from empty on your Mac, particularly whilst using it, but for what you want it's fine.

I would start with a full battery on your Mac, but don't plug the invertor in until you're down to about 20%.  Also keep your screen brightness down, and Wifi/bluetooth off unless you need them.  This way you're not going to keep pushing the battery down to it's discharge limits.

Finally I would just do a check first before committing to the battery that the Mac is happy with the invertor.  Most of the smaller 300W and similar ones are modified sine wave, and not true sine wave, which can cause issues with overheating and noise in some power supplies.  Should be ok as Apple's power supplies are pretty good, but just worth a check, otherwise you're saddled with more cost for a true sine wave invertor.

 

[Aidan]

Thanks very much.  I can do a test.. I have an old power station somewhere to see if it will work.  

Yep, charge at home, use then plug into invertor.  Like that approach.   

My main concern was plugging in the invertor, starting it charging only for it to drain too quickly.  The 17ah power tank was the smallest I was lik,I got at.  I'll go for the slightly higher capacity if I can stretch that far... Can only improve the situation!

 

Many thanks!

[Jokehoba]

I think Maplin do DC/DC PSU's. Not sure whether they have a suitable one to power your laptop. It's just that by using an inverter and your 60W PSU, you are converting DC to AC and back to DC again, which is inefficient and wastes power (and you probably want as much as that as possible!). Just a thought.

[silios]

Inverters are notoriously bad at efficiency as stated above, + potentially hazardous in a dew rich environment (i got zapped once with mine..)
You could go full 12v with a charger like this ( http://www.ebay.com/itm/Magsafe1-Car-DC-charger-for-apple-45w-60w-85w-MacBook-Pro-MacBook-laptop-/251898456484?var=&hash=item3aa65169a4)
I have been using one for 2 years with a car battery and it works fine.

With the halfords suggested battery the above charger would last you for almost 10 hours straight if you remove the battery from the mac, or 5 hours with the battery constantly charging.

some numbers for clarity :

Halfords battery = 12v x 17Ah = 204watthours
Mac charger with inverter = 16.5v x 3.65A 60watthours (not exactly though since the inverter is not running at 100% efficiency)
The following numbers are from bench testing mine,with the suggestions as above (no wifi, minimum screen brightness etc)
Mac charger 12V w/o battery at all  =    12v x 1.5A  =  18watthours
MAc charger 12V w battery  =   12v  x 3A = 36watthours

 

 

 

[RayD]

33 minutes ago, silios said:

 

Inverters are notoriously bad at efficiency as stated above, + potentially hazardous in a dew rich environment (i got zapped once with mine..)
You could go full 12v with a charger like this ( http://www.ebay.com/itm/Magsafe1-Car-DC-charger-for-apple-45w-60w-85w-MacBook-Pro-MacBook-laptop-/251898456484?var=&hash=item3aa65169a4)
I have been using one for 2 years with a car battery and it works fine.

 

Great idea, I didn't know they did these types of DC-DC convertors.  

With Mac's on batteries the issue has always been a combination of voltage and the plug, which is Mac specific.  This would do the job nicely and be more efficient than an invertor for sure.