Battery to wall wart conversion help please.  - Page 1
Forum section: electronics / beginners

author: chachdog
author_rank: Newbie
timestamp: May 10, 2016, 01:24:42 pm
content: I am trying to hook up this electric tennis racket link below to a wall plug for an experiment. It takes 2 AA batteries in Series. like --. From what I have read, Series means its 2* 1.5 = 3 volts. How can I figure out the mah? I read going over is okfor mah but am trying to understand how you figure it out.http://www.amazon.com/Executioner-Swat-Mosquito-Swatter-Zapper/dp/B000MU2MJA/ref=pd_sim_86_16?ie=UTF8&dpID=41GMFsNDXaL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=1X8YRW5DF8J6KC15PEYXthanks

author: Signal32
author_rank: Frequent Contributor
timestamp: May 10, 2016, 01:36:30 pm
content: Yes, the voltage would be 2*1.5 = 3V.You can't easily figure out the current without measuring it. But why do you need to? The adapter just has to have enough current to power the device. So a 3V/1A power supply will work. Similarly 3V/2A or 3V/5A will also work. The voltage has to be exact, the adapter current just has to be equal to or grater than the actual current used by the device.And to measure the current used you'll probably need an oscilloscope since the current consumption is likely not constant, it will draw lots of current initially while charging / zapping something then when not doing anything it will draw very little current.

author: chachdog
author_rank: Newbie
timestamp: May 10, 2016, 05:19:26 pm
content: ah good to know. thanks.so any pointers where to get a 3 volt 5 amp wall wart? or just buy any one and cut the end off to get to the cable?

author: Signal32
author_rank: Frequent Contributor
timestamp: May 10, 2016, 06:20:04 pm
content: It doesn't need to be 5A, 1A is more than enough. Yes, get a random one and cut the end off and directly connect the wires.http://www.ebay.com/itm/Universal-US-Plug-DC-3V-1A-Power-Supply-Adaptor-Adapter-100-240-AC-Charger-/281960657454

author: mariush
author_rank: Super Contributor
timestamp: May 10, 2016, 08:33:28 pm
content: Since the device is meant to work with 2 AA batteries, that means it will probably work with a much wider range of voltages.Fresh alkaline batteries (nominal 1.5v) are about 1.65v and they go down to about 1.35v when empty. Rechargeable batteries are about 1.35v when fully charge, about 1.1v when discharged.You can also use a regular 5v adapter (usb phone charger or some basic adapter of any kind with around 5v) and lower the voltage the device actually sees by connecting several diodes in series (you can put those diodes in the battery compartment).For example, a basic1n4001 to 1n4007(click link for datasheet) has a forward voltage as high as 1.1v . See figure 4 in the datasheet, you have 0.8v for a current of 0.2A , and about 0.9v for 1A.So, you could connect 3 of these diodes in series and you'll have a voltage drop of 2.4v, which means that if you use a 5v - 5.5v usb charger/adapter and connect these 3 in series, your device will actually see about 2.5v.. 3vOther common and cheap diodes are1n5817..1n5819(see Figure 2), they have a lower forward voltage of about 0.6v at 0.2A and about 0.8v - 0.9v at 1A. So with 3 of these in series and input of 5v, your device will see about 3.2v at most.dc in + 5v ----------- [===>|] ---- [===>|] ---- [===>|] ------- + (about 3v)dc in - gnd ------------------------------------------------------------ -

author: chachdog
author_rank: Newbie
timestamp: May 21, 2016, 08:36:42 pm
content: I got this working and was wondering what damage if any could be caused to this racket or components if the switch was bypassed and it was just ON when plugged in. It electrifies the racket and makes an electric whine when on. It has a pulse switch but was curious if you left it plugged in for 20 minutes if that would blow it up or start a fire or just break or be fine.

author: uncle_bob
author_rank: Unknown
timestamp: May 22, 2016, 02:54:33 am
content: Quote from: chachdog on May 21, 2016, 08:36:42 pmHiThat gizmo is designed to be turned on for about 2 seconds and then left off for about 60 seconds. If you run it full time, it likely will catch fire.Bob

author: Raj
author_rank: Frequent Contributor
timestamp: May 22, 2016, 02:55:26 pm
content: As noted and quoted by some youtuber, the components inside the racket, specially a transistor gets super hot, its barely strong enough to handle the load

author: Audioguru
author_rank: Super Contributor
timestamp: May 22, 2016, 06:50:40 pm
content: You must havea lotof flies or mosquitos to keep the zapper turned on all the time and use an AC/DC power supply instead of cheap battery cells.Recently I found a zapper that somebody threw away. It had new battery cells in it but of course it did not work. When the battery cover was closed it pushed the battery cells away from the contacts which killed it so I put some foam plastic on top of the cells to keep them from moving and now it zaps perfectly.I use the zapper every few hours to zap a moth in my home. I do not know where the moths are coming from. My city got rid of mosquitos (and bats that ate them) with larvacide in all the ponds and drains. Nothing rots so there are few flies. If I try to zap a bee then they might attack me.

author: chachdog
author_rank: Newbie
timestamp: May 24, 2016, 07:47:05 pm
content: I was going to close it it in an open window, seal around it via cardboard or something, plug it in to turn it on and let the mosquitoes come in the window essentially using me inside as bait. I figured it wasn't designed to run for long periods, I was just curious.i wanted to build an electrified window screen but have no idea where to begin or how to do that. The racket was sort of out of the box doing it.

author: uncle_bob
author_rank: Unknown
timestamp: May 25, 2016, 11:39:22 am
content: Quote from: chachdog on May 24, 2016, 07:47:05 pmHiLike a lot of portable gear, the racket is designed for a *very* low duty cycle. That's what lets them sell it at an attractive price. For a "constant on" gizmo, you need something a bit more industrial strength.Bob