Calculating power draw for macbook pro laptop

Dilby
Dilby Forum Participant Posts: 20
edited December 2021 in Motorhomes #1

Hi all - I have just got a new laptop (macbook pro) and in the new year plan to do a bit of working from my van. I have a 100ah leisure battery and plan to upgrade my system, but I'm really struggling with the maths on all the electric requirements and was hoping someone could help. 

The charger for the laptop states:

Input 100-240v 2.0A, Output 28v 5A or
20.5 v 5A or 15v 5A or 9v 3A or 5.2v 3A

I hope I'm right in assuming that the most useful unit to end up with are the watt hours, and I know that a 100ah battery will give 1200wh (although it's lead acid do in reality about half).

But I don't know how to work on the real world watt hours for the macbook as it gives so many voltage examples. I'll be on12v so I thought just go with maybe 4A as that's inbetween the 15 & 9A examples, but the watt hour calculation on this really changes; for example, 240v @ 2A is 480 watt hours while 5.2v @ 3A is 27 watt hours.

I hope I haven't confused people more than I am myself, and thanks for any help!

Comments

  • SteveL
    SteveL Club Member Posts: 12,300 ✭✭✭
    5,000 Likes 1000 Comments Name Dropper
    edited December 2021 #2

    If you’ve got USB sockets in your MH, as we have in ours, can’t you just plug directly into one of those, they provide 5 volts. We plug our pads and phones into ours and don’t bother with the supplied 240 volt charger / transformers,  which will of course require an EHU hook up or inverter. If you don’t have any USB sockets on your 12 volt system, you can get adapters that plug into the 12 volt sockets.

  • Unknown
    Unknown Forum Participant
    edited December 2021 #3
    The user and all related content has been Deleted User
  • Dave Nicholson
    Dave Nicholson Forum Participant Posts: 408
    edited December 2021 #4

    As DD states, you will be better using an EHU or a quality, adequately rated Inverter powered from your leisure battery. Forget all of the ‘Output’ figures, they relate to the rating of the laptop charger  The important figures are the 240V 2A input requirements. The 2A relates to the rating of the 240V supply. There will be an inrush or switch-on current that will quickly decay once the charger is running. Hence the need for a 2A supply so  the supply fuse does not rupture on switch-on. The charger will draw nothing like 2 Amps when running.  I think you are worrying too much and trying to read too much into the rating plate on the charger. Relax and have a good Christmas and a happy New Year.

  • cyberyacht
    cyberyacht Forum Participant Posts: 10,218
    1000 Comments
    edited December 2021 #5

    I use a 12V adapter to power my MacBook Pro (2013). It will be a bit kinder to your battery than an inverter. I'd not recommend an inverter with a lead acid battery anyway. Low power inverter requirements are generally better served by a 12V adapter. High power ones  for microwaves etc. really require a decent sized lithium to cope with the demands.

Categories