Power source for portable monitor.

[GSole1122]

I'm still fairly new to electronics, in the sense of understanding how that work on the lower levels. I turned my laptop monitor into a stand alone monitor and looking for further that into completely portable. So I know I need a battery of some sort, but where I'm stuck is I do not know how to calculate how big of a battery I need, what type, and how to wire it in.

Ideally I would like it to function as a laptop would: Two power sources (battery and wall adapter) and when the wall adapter is plugged in the battery charges and when it's unplugged it runs off the battery. I'd also like to get about 4 hours or more (if possible) on 1 battery pack.
Can anyone help me achieve this goal? How can I measure how much power the monitor requires to use? How do I calculate what size battery I need? Type of battery? and How do I wire it?

 

[dknguyen]

Battery capacity is in Amp-hours or milliamp-hours. So a battery that is 10 amp-hours can theoretically supply 10A for one hour, or 1A for ten hours. In reality, higher currents will drain the battey faster than this and lower currents will drain the battery slower than this due to internal resistance.

Also note that the test used on the battery to get that number matters. The battery rating might be given under a 10 hour test. So any current drains that are higher than the one that allows the battery to last 10 hours, will drain the battery faster than indicated. So if a 10 hour test was used and got a rating of 10 amp-hours, then if your current draw is 1A, then it should last 10 hours. But if it's 10A it will last LESS than 1 hour. If your current is less than 1A, it should last longer.

Wire up a multi-meter as a ammeter and get that number. Google this and make sure you have it right before you power-up or you will blow your meter. It should give you somewhat of an indicative. It just displays a slowly changing number and the monitor could be drawing something that is changing.

 

[GSole1122]

Thank you! Ok, so from what i found, I want to make sure I understand this before doing this, I have to hook everything up and splice my power supply from the wall to the control board of the monitor. Then supply power (from the wall) to my multimeter (set to mA) and then into my control board? If this is correct, I may have to get creative because I only have 1 power supply cord for this board. So I'll have to buy another and splice it, I suppose.

If my explanation above wasn't detailed enough is this clearer of what I am thinking?
Take power cable, cut wire, take positive feed and attach positive terminal of multimeter to 1 part and the negative to the other part of the positive lead. Set multimeter to mA. Plug in and measure?


*Thought* Since it is a barrel connector, instead of cutting the wire, would I be able to (in theory) just make 2 leads, one coming from the ground of the male end (the outside) to the pressure tab (ground) of the female barrel connector on the board and another lead from the inside of the male barrel connector to the probe of the female end on the board? Or is that just too dangerous?


Is there anything that I'm incorrect on?

 

[dknguyen]

That looks right. It's fine because the wall wart is isolated, current limited and low voltage output. But it's finicky. Much easier to use something like

https://www.adafruit.com/product/368

https://www.adafruit.com/product/1328

 

[GSole1122]

So on that, cuz I will definitely go that route. Do they make those in 2.35mm? Cuz that's what my connectors are. Or do they only come in 2.1mm and if so, what alternative can I go with?

 

[dknguyen]

I'm not sure. I've never needed anything other than 2.1mm.

 

[GSole1122]

Alright, I'll figure something out. So after I figure out that information and get my battery, what do I have to do to wiring it in so that when it's plugged in to the wall the battery will charge and when i unplug it it'll run off the battery?