# Using battery to power projector - exceeding battery's max power?

Discussion in 'Power Electronics' started by halplz, Feb 2, 2017.

1. ### halplz

1
0
Feb 2, 2017
Hello all, I can't believe I can't find the answer to this question.

I want to run a 260 watt projector on a battery. I found some "ac power banks" on amazon for around \$50-\$150, but they have a 'max power' of 100w, or 'rated power' of 100 watts. I can't find anything above that.

What does this mean, and more importantly, will the projector work?

Items in question:

https://www.amazon.com/ViewSonic-PJ...refinements=p_n_feature_browse-bin:2358236011

2. ### Harald KappModeratorModerator

12,455
2,985
Nov 17, 2011
It means the power bank is designed to supply at max. 85 W to an AC load. If it is well dseigned, it will shit down if you try to get more than 85 W power from it. If it is not well designed, it runs a chance of being destroyed and in the course of it may even burst into fire, You don't know.
In both cases the projector will not work.

What you can do is use a suitably rated inverter which produces 110 V AC from 12 V Dc (a typical application for use in cars, mobile homes etc.) plus a beefy battery.
Assuming the inverter has 80 % effciency (I couldn't find the exact value on the website), the required output power of 260 W translates to 260 W/0.8 = 325 W at the input.
325 W from a 12 V car battery translates into 325W/12V = 27 A.
27 A means you need AWG12 wire or thicker to minimize losses on the cable from the battery to the inverter.
27 A also means that for every 27 Ah of battery capacity you get approx. 1 hour of operating the beamer under these conditions (less when the battery ages), 2 hours with a typical 54 Ah battery.