I have run out of ideas, replacing batteries with a wall wart - Page 1
Forum section: electronics / beginners

author: Xplicitt
author_rank: Newbie
timestamp: March 13, 2015, 03:45:17 am
content: Alright. I have a headset, a Turtle Beach X41. 2.4ghz wireless for audio, and is powered by 2 x AAA batteries.This headset was chewing through 4-6 batteries a day, so I decided to power it with a usb wall wart and some lightweight wire.I created a voltage divider, 5v in -> 100 ohm resistor -> 3v -> 150 ohm resistor -> groundworked well, got about 3.16 volts. close enough.now, I was trying to power it from the 5v from a usb cable. plugged it into my laptop, checked it with the meter, 3.16vI used some alligator clips to clamp to the contacts, and..... nothing. I figured that the usb port wasn't providing enough juice.I hooked my contraption into the 5v rail of my 3d printer's power supply. still nothing.just to make sure I wasn't going nuts, I hoked my alligator clips to a battery holder with the 2 x AAA batteries, and it worked fine.I must be missing something here. What am I doing wrong?

author: AG6QR
author_rank: Frequent Contributor
timestamp: March 13, 2015, 04:10:00 am
content: Remember the voltage divider equation? It's derived from Ohm's law, by assuming the current in R1 is equal to the current in R2, so the voltages across the two resistors are proportional to their resistances.The problem is, once you try to draw any current out of the voltage divider, the currents through the resistors are no longer equal, so the voltage divider equation no longer holds. As long as you don't draw any significant current, a meter will show a voltage that's close to what you calculated using the voltage divider equation, but when you try to use it to power something, the voltage will be much less.A voltage divider is nearly useless for powering anything, especially if you want to provide a constant voltage to a varying load.A voltage regulator can be used to do what you want.

author: Xplicitt
author_rank: Newbie
timestamp: March 13, 2015, 04:17:05 am
content: Quote from: AG6QR on March 13, 2015, 04:10:00 amCan you suggest a regulator then? I'm not super electronics literate, I just know enough to scrape by most of the time. More of a mechanical guy.I was looking through LDO regulators on digikey, but I was getting very confused very quickly.I measured the amperage of the headset while on and at full blast, and got about 75ma going through it from the batteries.

author: KM4FER
author_rank: Regular Contributor
timestamp: March 13, 2015, 04:27:25 am
content: Xplicitt,Taking a simplistic (but not totally correct) view shows your problem.Using Ohm's law I = E/R to calculate the current through your 100 ohm resistor:I = ( 5 - 3 ) / 100 = 2/100 = 0.020 A = 20mA.I don't know how much current your headphones require but let's just assume 20mA. Add that to the 20mA already flowing through the 100 ohm resistor and you have 40mA. Plug that back into Ohm's law to calculate the new voltage drop across the resistor:E = IR = 0.040 * 100 = 4V5V input - 4V drop = 1V to the headphones. Not enough.Now you could make the voltage divider stiffer by say reducing the resistance values by a factor of 10 to 10 and 15 ohms but then they will waste a lot of energy, get pretty warm and your wall wart might not be able to provide all the current required.What you probably want to do here is replace the voltage divider with a 3V regulator.earl...

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 13, 2015, 04:27:49 am
content: http://hobbyking.com/hobbyking/store/__48783__A123_3_3V_Lithium_Ion_2500mAh_Single_Cell_Battery.htmlUse these, get a few (make sure they are single cell A123 LiFePo4 ) and get a charger.You only need one battery connected at a time though as they are ~3.3 v. You wouldn't need any sort of regulation just +ve -> +ve and -ve -> -ve.Somehow you will have to make it easy to change, maybe a solder on a white connector and hold it on with a rubber band.Least then you would still be wireless.Apparently LiFePo4 can do a huge amount of recharges.

author: kezat
author_rank: Contributor
timestamp: March 13, 2015, 04:37:24 am
content: You might have better luck with rechargeable battery's and not just because you can recharge them but because rechargeable battery's have deliver higher currents more efficiently then alkaline. Assuming the headset is really drawing that much current.If however your already using rechargeable it could be a cheap type of battery or a bad charger. Also the headset could see the lower voltage of the 1.2v rechargeable battery's causing it to think the battery's are low, if that's the case try Alkaline.

author: Xplicitt
author_rank: Newbie
timestamp: March 13, 2015, 04:43:08 am
content: Quote from: HackedFridgeMagnet on March 13, 2015, 04:27:49 amI don't really care for wireless, which is why I'm going the route I am, a usb connection. I got the headset for free, and it sounds good, so I figured wired power would take away my headache of changing batteries and burning through $5 US of batteries a day.Now, I found a regulator, LD1117V33, which I think would work fine. I assume that I can feed a 3v headset 3.3v with no problem.This is what I need?Edit:Quote from: kezat on March 13, 2015, 04:37:24 amUsing fresh alkaline batteries. I believe the draw, It's a suround headset that communicates with RF. Sounds right to me.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 13, 2015, 05:23:06 am
content: Quote from: Xplicitt on March 13, 2015, 04:43:08 amNot what I said but I take your point.I gave you a good solution for a wireless headset as opposed to a crappy solution that the voltage regulator would give you.But if you don't want wireless, then get a wired headset. So much simpler.

author: Xplicitt
author_rank: Newbie
timestamp: March 13, 2015, 05:36:56 am
content: Quote from: HackedFridgeMagnet on March 13, 2015, 05:23:06 amIt's not as much getting exactly what I want as it's making what I have work for me. I can't afford a to buy a new headset, and this one that I got for free works very well. I just want to make it wired. I'm not sure how the vreg is a crappy solution. Will it make interference? If the headset powers up from a wire when I'm done, I consider that a success. I really just want some help getting to that point.So, again, I assume that the regulator I found would work without making too much heat?

author: Zero999
author_rank: Super Contributor
timestamp: March 13, 2015, 09:05:44 am
content: The easiest and cheapest way to do this is to connect three diodes in series with it. Each diode will drop about 0.6V to 0.8V. Which will give between 3.2V and 2.6V out, depending on the current draw which should be within its operating voltage range.

author: macboy
author_rank: Super Contributor
timestamp: March 13, 2015, 12:46:02 pm
content: Quote from: Xplicitt on March 13, 2015, 04:17:05 amAt 75 mA you should get 10 hours from a good set of NiMh batteries. Some are even 1000 mAh or higher, so you could get 12 hours or more. That should mean one set per day. With 2+ sets and a good conditioning charger (I just got a MH-C9000, love it), you will be all set for years.Or you could use a basic LM317 regulator set to 3 V output. and convert your wireless headset into a wired one. But what's the point of that?

author: Xplicitt
author_rank: Newbie
timestamp: March 13, 2015, 02:01:13 pm
content: Quote from: macboy on March 13, 2015, 12:46:02 pmAlright, lm317 it is. thanks for your help.Still, I'd rather wired than wireless. I just don't feel like faffing around swapping batteries in the middle of a stream or gameplay video, or even worse, in a tournament. I already use mostly wired things anyways, and another wire won't bother me.Again, thanks all for your help.