Jump to content
Electronics-Lab.com Community

BENCH POWER SUPPLY


Um...Me123
 Share

Recommended Posts

Hey guys got a couple things for the supply(and general use) from radio shack the other day and the online parts should be here any time now.
I have a quick question about something not related to power supply but I didn't want to create a whole new thread.
I had a RC car from my child hood years (which in my case isn't very long ago) that I took appart.  The remote used 2 forward backward switches for each real wheel.  (the kind where you push one forward and one back and it gives you 360 spin)  It had 1 motor for each tire and just reversed the polarity to go backwards.  Looking at the remote the buttons for each tire are essentially a SPDT (its a thin strip of metal in a "N" shape where the center is neg and the two outsides are bent down to make a connection).
Because the output to these motors is a decent sized voltage/amperage I was thing of making some type of wireless switches out of it.  I want to be able to control 4 relays individually with 4 SPSTs instead of the 2 SPDTs that reversed the polarity.  How do I turn the reversing polarity into 2 seperate circuits.
Sorry if I did a bad job explaining it.

Link to comment
Share on other sites

[glow=blue,1,900]I think we should just re-name this Um...Me123's questions thread ::)

Ok I have dilema.

My circuit consists of:
2AA supply (3V)
two 3.2+V 30mA white LEDs--wired in parallel
two 1.7V 20mA red LEDs---wired in series

With being wired the way they are there is no need for a resistor right?
My problem: If I touch the wires for the whites they work fine.

Link to comment
Share on other sites

Hi Um...Me,
Measure the output voltage of the 3V wall adapter. It is rated to give an output of 3.0V only when it has a load of 300mA.
But its output voltage isn't regulated and your load draws much less than 300mA, so its output voltage is high enough to light 3.2V white LEDs but not high enough to light two 1.7V red LEDs in series (3.4V).

There are only 2 conditions where LEDs don't need a current limiting resistor:
1) You are using tiny button cell bateries where the current limiting is provided by the internal resistance of the battery cells.
2) You are using a wall adapter with a low current rating. The high resistance of the windings limits the current.

If you use brand new batteries or replace the wall adapter then the LEDs could smoke and burn-out without current limiting resistors. 

Link to comment
Share on other sites

Hi again

I'm a little confused by this...do you mean I can't have 120V going to 2 outlets and to the transformer of the supply on one side and the 9V from the battery going to LEDs and LCD??

Hey boy, how do you think the lamp in the switch is powered?
The lamp is powered from the switch:s both secondary terminals! Connected across them! I send up a little picture of whats right and wrong later

The (DPST) switch is rated for 120V (up to 250VAC I think) (it's lighted with a 120V neon)

The switch is rated for 250 V AC and the lamp is 220V AC!
Never ever connect anything belonging to the secondary side on a mains switch, it's not safe!

//Staigen
Link to comment
Share on other sites

OK!  I'll take your word for it even though I'm still not sure what you mean by mains and secondary.  It said the neon works fine with 120V by the way.

Looking back at the schematic is it ok if I run the other DC things off the approx. 24VDC the transformer and bridge put out?  What I mean is, can I run seperate wires comming off this circut between the 2200u cap and the 100n cap?  I thought I read somewhere that the 2200u was called a smothing cap in this case so I would think to put the wires after (to the right of) that.  Is that right or just branch off right after the bridge?

PLEASE CHECK OUT MY RELAY QUESTION ABOVE.

Link to comment
Share on other sites

Hi again Um...Me123

Looking back at the schematic is it ok if I run the other DC things off the approx. 24VDC the transformer and bridge put out?

Of course you can, but it is not 24 Volts there, its moore, like Audioguru said :)

PLEASE CHECK OUT MY RELAY QUESTION ABOVE.

I belive i can help you, but then you have to make two schematics, one of the transmitter and one of the receiver!

I promised you a pic of whats wrong and right about mains switches earlier, and here it is, i made it in ExpressSCH. The two pics on the left is wrong and the two to the right is the right way to do it, the one at upper left can be used, but it's not right, it have only one of the live wires switched. Here in Sweden that is almost forbidden!

Oops! A little aditional information. The left bottom pic is what you was trying to do. The lamp is connected internally between the ouput terminals of the switch, and connect the LCD voltmeter to the mains! Dangerous!

//Staigen

post-282-14279142409906_thumb.gif

Link to comment
Share on other sites

OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO :o ;D
I get it now.  The DPST (or at least the type I was talking about) is designed for turning mains (thats what you call the 120V AC from the wall?) on and off and thats why that neon is bridged between!

Ok so about those relays...you say to put a R-B diode accross the coil so you mean between the two terminals for the lower voltage input (I know...very poor terminalogy but I'm learning to explain better).  So if I want the electricity to only go one direction I need a diode right (like those 4 things in the bridge rec. right?)  What kind is this because there are all sorts of different kinds.  Can someone tell me how to put a picture in?  What do you put in the "img" tag?  The file name?  This way I can show you what my idea is that I think will work.

Link to comment
Share on other sites

Hi

The DPST (or at least the type I was talking about) is designed for turning mains (thats what you call the 120V AC from the wall?) on and off and thats why that neon is bridged between!

Yes, the 120 V AC from the wall is called the main voltage, not only by me, everybody call it that in circuits and schematics. Even if you have a DPST switch without a lamp it is not safe to have one of the switches to operate something that you can come in contact with. The insulation inside the switch is not good enough, even if there is a plastic wall on the outside, so it look safe enough!

Ok so about those relays...you say to put a R-B diode accross the coil so you mean between the two terminals for the lower voltage input (I know...very poor terminalogy but I'm learning to explain better).

No, it was Audioguru who said that. But, yes, if you want the current to go only in one direction, you put a diode there!

Can someone tell me how to put a picture in?

Shure, if you look to the left, just under the window you type in, there is a text, saying "Additional Options...", just klick on that one, and woops, you have some moore options, amongst others theres "Attach:", klick on the button to the right of the first window there, for the first file, and on the lower for the second file, if you need to send up moore than one file. Also look at the text under those two windows, there you can see which type of files that are allowed and the maximum size!

//Staigen
Link to comment
Share on other sites

The LED's wires are completely separate from the switch. Why not leave it that way?
Use the switch contacts to switch both wires of the mains to the transformer, and connect the LED through a suitable current-limiting resistor to the DC in the circuit.
Then when you turn-on the switch, the circuit is powered and also the LED. ::)

Link to comment
Share on other sites

Hi Um...Me123

I wouldn't have done it this way, i would have connected the leds via a cap and a resistor in series and a diode connected backwards over the led and the whole thing connected directly to the mains outputs! A picture should have explained things, but i have difficulties making one at the moment, it take long time for me just now. Maybee later, if you can wait a few days.

//Staigen

Link to comment
Share on other sites

  • 3 weeks later...

Hmmm well it's not done.  Have been really busy with school and I'm just taking a break from the project.  At first I was thinking "where did all my messages go?"  I continued with this project in the board meant for the LM317 supply and I can't remember if you had made any replies in there or not but if you go look you will learn that I hooked up the LM317 backwards and fried it and the pot.  I then re-wired it the write way and thats when I figured out the LM317 was bad so now I have de-solder it all again and guy new stuff and it's just a big mess.  So I took a little break until next time we happen to go by radioshack.b

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
  • Create New...