Battery powering PC and charging - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: October 10, 2024, 02:26:53 am
content: Hi,So I have a 24V 25Ah LiFePO4 battery and charger, I want to use this to power a computer overnight, the computer has a 19v 65w brick PSU and can apparently run on 12-19v, the computer uses an average of 30w of power measured at the wall.What is the cleanest off-the-shelf way to get the 19V?I'll put the charger on my automation to come on when the sun is up.I'll grab a shunt that I can network to get the charge state into my automation, any one used anything cheaper than the Victron smartshunts?Thanks!

author: Rick Law
author_rank: Super Contributor
timestamp: October 10, 2024, 03:21:58 am
content: Do a search for DC to DC buck converter, you will find a lot of choices.As you stated, the original PSU is 19v 65w brick, so that is 3.4A @ 19V.- To have some leeway, hunt for one with 5A output. A lot of buck converters has max at 3A, but that is below your requirement.- Input voltage generally is a range for buck converters, you should find plenty with input up to 30+ V. You should use DMM to make sure what your battery voltage is -- because a 24V battery may be well above 24V when fully charge. You must of course hunt for one that can take input above your battery's fully charge voltage.- Most buck will have adjustable output voltage. Range must of course cover 12V to 19V as that would be your requirement.- While current limit is not needed, having it would be preferable. Set it to 4A or something like that, you will have some head room while you know your buck is running within specs of below the 5A max.Now all you need is to find the plugs and wire to connect the buck converter to your computers as "replacement" PSU. You will need to figure out how you want to handle charging your 24volt pack. To switch between your battery+buck to/from original PSU would need a power down of your computer.You could use a pair of diodes as power-selector. That is, connect the PSU via diode to computer and your battery+buck via a diode to computer -- and set your buck's output a bit below the PSU. Say your buck is at 18V (and your PSU is 19V), it will draw power from your PSU when PSU is on, but draw from the battery+buck when PSU presents no power.

author: rthorntn
author_rank: Frequent Contributor
timestamp: October 10, 2024, 03:33:44 am
content: Thanks, I was sort of thinking that I could have the charger and computer (via the buck) permanently connected to the battery and switch the charger off overnight (with a zigbee smart socket), in effect when the charger (10A) is charging it's powering the buck and therefore the PC?So as long as the buck has an input voltage range that covers the charger and the battery I would be alright, or it doesn't work like that, or do I have to add some smarts to do this?

author: Rick Law
author_rank: Super Contributor
timestamp: October 10, 2024, 03:56:08 am
content: Quote from: rthorntn on October 10, 2024, 03:33:44 amThat would depend on the design of your battery pack and charger. Some are designed to be able to charge while in use and some are not...If your battery is connected to some load while charging, the current drawn will make your charger think the battery is not full and thus keep charging -- that would mean keeping your battery at a higher voltage so as to put charge into it. That is not healthy to your battery when kept at charge voltage continuously. In fact, I killed a Li-Ion phone battery (swell up to 2x it thickness) when I kept it on the charger for a month while running a data-collection app on the phone in that duration.You must add some kind of disconnection (between charger and battery) strategy in your design or your battery will die rather quick...