2 9Vs to 3V & 12V - Page 1
Forum section: electronics / beginners

author: maxkarlmiller
author_rank: Newbie
timestamp: April 04, 2015, 10:56:03 am
content: Alright, this is my first post on this forum. I have this crappy camera I've made into a night vision camerahttp://www.instructables.com/id/Night-Vision-Camera-1/, but the battery is terrible (for the camera) (2 AAA batteries, so I think 3V, although my volt meter says ~3.5V) and the IR LEDs require 12V. is it possible to get 2 9V batteries to have a 3/3.5V output and a 12V output? If it is, how?

author: Psi
author_rank: Super Contributor
timestamp: April 04, 2015, 11:21:01 am
content: Using 9 volt batteries are usually a bad idea, they are less energy dense and only designed for low current.If you're currently using 2x AAA then 4x AA's are a much better option for more power/capacityHave 2x 2cell in parallel, so the voltage is still ~3VYou could reconfigure the IR led array to run on a lower voltage by having more parallel strings of less leds in series.

author: Ian.M
author_rank: Super Contributor
timestamp: April 04, 2015, 12:36:22 pm
content: The LED light design used in the instructable you referenced isn't very good.TheLEDs usedare 1.28V Vf @100mA and the instructable wires them in parallel in three groups each group with a 220R series resistor. If built as illustrated that gives a mere 4.4mA per LED and probably significant current hogging in a few of them.Redesigning the light to use series strings of 4 individual LEDs each string with its own current limit resistor off two LiPO cells should be a high priority then the camera could be run off a switching 3.3V regulator module from the same battery.Before connecting to the camera, the output voltage should be checked and the regulator may need to be either adjusted if the feedback divider is accessible on its board or one or two Schottky diodes added in series to the output to drop a little voltage and get closer to 3.0VUse a small 2 cell RC LiPO pack and an appropriate balance charger for it.

author: maxkarlmiller
author_rank: Newbie
timestamp: April 04, 2015, 01:36:28 pm
content: I didn't use the LEDs used in the instuctable, I used this:http://www.amazon.com/gp/product/B00FZMQ8EA/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

author: Ian.M
author_rank: Super Contributor
timestamp: April 04, 2015, 03:35:45 pm
content: Start with a battery pack to suite the light and drop it to 3 volts for the camera with a LM2596 adjustable regulator module which are cheap and plentiful on EBAY.If you want maximum rechargable battery life in minimum volume and all with off the shelf modules, you may be better off with a 14.8V 4 cell LiPO pack and balance charger and another LM2596 module to power the light at 12V.Otherwise if you are determined to use primary cells (disposables), 8 x alkaline AA cells could run the light directly for a few bucks from the pound/dollar store or go up to D cells if weigt/size isn't an issue but battery life is.

author: maxkarlmiller
author_rank: Newbie
timestamp: April 04, 2015, 08:59:18 pm
content: Quote from: Ian.M on April 04, 2015, 03:35:45 pmIs this correct? If it is I'll get 2http://www.amazon.com/Converter-Module-LM2596-Supply-1-23V-30V/dp/B00VC2FQR2. could you also link me to a place where I find out how to use it? I think I'll get a 14.8V LiPo battery pack and use the two voltage regulators to output 3V and 11.8V (I want to have one rechargeable battery for the whole thing.) Is this a good general balance chargerhttp://www.amazon.com/Battery-Balance-Charger-Li-ion-Batteries/dp/B005EF15Q4? Also is this a good batteryhttp://www.amazon.com/Turnigy-5000mAh-4S1P-14-8v-hardcase/dp/B00FXL7XJC? And thanks for all the help

author: JesusCB
author_rank: Contributor
timestamp: April 04, 2015, 11:03:19 pm
content: Max, I have been reading a lot about step down converters, I bought one cheap made in china (It will arrive in a month), but the circuit is really easy, and I will make my own regulator with a LM2575 (similar to the LM2596).To adjust the output voltage you turn the little screw in the potentiometer (trimpot). There are other modules with 3 trimpots, with those you can regulate the current and voltage.

author: Ian.M
author_rank: Super Contributor
timestamp: April 05, 2015, 02:12:32 am
content: The reason I suggested pre-built DC-DC converter modules is that some of the chips on the market for these applications can be *EXTREMELY* fussy about layout and choice of inductor, to the point that small changes from the manufacturer's evaluation board layout or substituting an inductor of the same value but different construction can result in greatly reduced output current , or worse, instability. Back in the 90's I scratch-built a switching regulator module to replace a linear regulator that was overheating and it was such a P.I.T.A to get working properly that I vowed never to do that again without a properly designed double sided PCB.It certainly wouldn't have been novice friendly - which I wasn't as my first hacked together switching regulator was back in days when Bob Widlar's µA723 was still in common use.