What did I miss?

[jhead67]

I tried putting together the top-off system in a past issue. I connected everything up as shown, so I think anyway. What DC voltage should I be getting after the 2k resistor? I still have over 110 volts DC. I'm figuring I should be getting less than 32 VDC to make the relay work.

Where am I going wrong?

I used a meter to measure the voltage at the wall 123.5 VAC. I wired the bridge rectifier to the AC current and got 111 VDC output.(which I expected) Then I put the 2.2K ohms resistor inline and got 110.5 VDC on the other side of that. This is not what I expected. I double checked the resistor and it measures 2.15K ohms. I was orignally going to step down the 120VAC to 12VAC then run it to the bridge rectifier. And before that I was going to use transformers instead of recitifers. But after looking at this and beerguys setup I figured any idiot could do this without transformers and save money and space. I was only half right, this idiot can't figure it out.

Any ideas what's up? I have to be missing something here. I'm no electrical genius but I can do math. What formula can I use to get the expected voltage drop? If I can just get this down to 12-32 VDC I can make this work like I want it to I think.

Thanks for your help.

 

[Snailman]

If you are measuring the voltage on the resister without it connected to anything then there is no current flowing through the resister so there will be no voltage drop across it. If you hook a 4.7K ohm resister between the 2.1K ohm resister and ground you will complete the circuit and will be able to see the voltage drop. HTH

 

[jhead67]

I hooked up the 47k and measured 35VDC across the 2.2 and 75VDC across the 47K.

I have a radio shack 4pdt 12V relay that I'm try to get it hook up to, I have a 12V voltage regulator that I running it through to get the 35VDC to 12VDC. I measured resistance on the relay coil it was 160 ohms, no where near the 47K resistor. The relay engaged when I hooked it up but the resistor smoked, kind of expected that but for 10 cents it was worth a try. I know it shouldn't be it this hard but it's simply not working for me. I've wired ballast's and computer junk for years and never had a problem like this. But then again this is my first experience with bridge rectifiers.

Anyway, Iââ"šÂ¬Ã¢"žÂ¢m going to do the ohm's law 101 thing here in a few minutes and see if i can figure out what resistance I need to get the drop the relay requires. I haven't put the float switch on it yet. I'm just wiring it as a closed circuit until it figure it out.

I hate being this close to something and not getting it to work.


BTW, I loved your new tank. The small one on the bottom was a very cool idea. Don't remember what post I saw it on it stuck in my mind.