Using DVR backup battery to USB charger.   - Page 1
Forum section: electronics / projects

author: Rodville
author_rank: Contributor
timestamp: July 16, 2014, 08:27:46 pm
content: I have this Belkin battery backup that was given to me by my cable provider to insure I don't miss (or lose) TV shows when the power goes out. The cool part is they never want the backups back and have given me a new one every time the DVR has issues and is replaced. So I have taken to re-purposing them to other uses. I have one one my internet modem and my wireless router. In them I have had internet for almost 9 hours when some idiot doing the construction on the freeway near me knocked down the power pole to my area with a crane. I am thankful I had had my phone on the charger so it lasted the whole time and didn't need to be charged until the internet batteries died. So I have one more battery backup that I think would be awesome to use as a backup to the USB charger for my wife's and my phones. I want to basically make a device with one preferably two USB outlets that I can plug into the backup battery and use to charge. The backup battery has an output voltage of 12V at 3A so I am not sure if it will charge the iPad (if someone that knows could tell me) but it should be fine to charge an iPhone and a Galaxy Mega. I thought of just using a car charger but the ones I have tried barely charge one phone (takes 4+ hours) when plugged in it takes less than two. Not really an issue at night as they will just be plugged in and left but I don't know how it will charge two at once. I want one that won't have an issue charging charging both devices at the same time and doing so at least close to the same time it takes plugged in to a household outlet. There is an Instructible that shows someone building one out of a Ryobi battery at 18V I was thinking about using that as a guide but I know some components would have to be changed to use 12V instead of 18V. I will provide pics of my backup battery and the link to the Instructible showing the Ryobi battery build.Basically what I would like is for someone that knows easily what components would need to be changed or if there is a pre-made device that will work for what I want to do. Thank you for your time.My backup battery.And the Instructible that cage me the ideal to begin with.http://www.instructables.com/id/Cordless-tool-battery-to-USB-charger/

author: Rodville
author_rank: Contributor
timestamp: July 16, 2014, 10:38:42 pm
content: I just found this Instructible that makes a battery powered charger using a 9V battery. This one makes mention of Apple needing a 2V current on the data pins to charge correctly. And would this design work with the 12V coming from my backup battery? It seems like a better design that the first one.http://www.instructables.com/id/Make-a-USB-iPhone-iPod-Charger-On-The-Cheep/?ALLSTEPS

author: suicidaleggroll
author_rank: Super Contributor
timestamp: July 16, 2014, 10:48:14 pm
content: Quote from: Rodville on July 16, 2014, 10:38:42 pmThat uses a linear reg. With a 12v input and 5v output you're going to have an efficiency of about 40%, which means for every 1 Wh that goes into your phone, you'd be pulling 2.4 Wh out of the battery. Not great for a battery powered application (and his original design using a 9v isn't much better). The first link you posted is MUCH better in this regard.If you want that battery to last reasonably long, you should use a switching regulator that has optimal efficiency at your desired load, such as the switching regulator used in that first link. What's your load? Depends on what you're charging. For Apple devices:~1A if you run D- at 2.75v, D+ at 2v~2A if you run D- at 2v, D+ at 2.75vhttp://www.voltaicsystems.com/blog/choosing-usb-pin-voltages-for-iphones-and-ipads/

author: kingofkya
author_rank: Regular Contributor
timestamp: July 16, 2014, 11:13:15 pm
content: IF you search ebay for dc to dc converters you can find some 0-30v 1-2amp units pretty easily. Assuming you want to tap into the dc of the batteries.I keep quite a few of theses around very handy.http://www.ebay.com/itm/LM2596-DC-DC-3-2-40V-to-1-5-35V-Step-Down-Adjustable-Converter-Power-Module-/290967166103?pt=LH_DefaultDomain_0&hash=item43befe9c97http://www.ebay.com/itm/DC-DC-Boost-Buck-Converter-Step-Up-Step-Down-Supply-Module-3-35V-to-2-2-30V-EK-/181307186702?pt=Home_Automation_Modules&hash=item2a36c01e0eAlso you could always go dismantle some car cell charges you can find at almost any store:) Or ask around and get some for free when the wire breaks.

author: Kevman
author_rank: Regular Contributor
timestamp: July 17, 2014, 06:08:54 pm
content: You can get cheap buck converters on Amazon.http://www.amazon.com/KEEDOX%C2%AE-Converter-Power-Supply-Module/dp/B00A71CMDU/ref=pd_sim_e_3?ie=UTF8&refRID=0JZ07RGGKPEFS9CX60RZWill probably work for 1 tablet OR maybe 2 phones at once...Or you could gethttp://www.amazon.com/DROK-Voltage-Converter-Regulator-Waterproof/dp/B00CEP3A0Q/ref=pd_sim_e_15?ie=UTF8&refRID=1J3NPAED1EFBQ3F8ES71That one would be enough to charge probably 5 phones at once.From there, you'd just need to wire up your D+ and D- resistor dividers to your USB ports.Or you could just wire up a car lighter port to your battery and use car chargers.