Amps, lamps and milliamps

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Post by Resistance is Futile on Tue Dec 18, 2012 8:14 pm


Try a variable power supply starting at 6 volts and slowly go up till you see how bright or Dim you want them. A 10% lower voltage will make a big difference in longevity. if you don't have a variable supply. Try a variac plugged into the wall then with a step down transformer. Slowly raise the voltage till you have the brightness you want as long as you stay less than 12 volts on the secondary.
Measure the voltage and the current and the calculate the resistance from your figures. if you don't have a variable voltage supply Either use a rheostat or a potentiometer of no less than 2 watts for 1 bulb. Have fun.

Another way is to stack power diodes in series with the bulb as each diode has a .6 volt drop. So 4 would drop the voltage through the bulb by 2.4 volts so you bulb voltage would be 2.4 - 12 = 9.6v use more or less to achieve what you want. Most diodes will handle the current in the 1N4000 series. and those are very common at radio shack.
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Post by terrydec on Wed Dec 19, 2012 12:30 am

I have both a Variac, (actually a really nice EICO 1078 with both volt and amp meters), and a variable DC power supply. The diodes I have are 1N4004. So I have everything to do the experiments.

After weeks of nothing I suddenly have a bunch of neat bench projects waiting, including this one, working on an RC helicopter, replacing some dial lamps in a Marantz and fixing a DUAL 1009 turntable.
Cool! cyclops
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Post by Resistance is Futile on Wed Dec 19, 2012 1:15 pm

Wow!, let me know about the Marantz.
I have to replace several bulbs too. I have thought about using LED's but am leary. The Lights are called festoons. Shaped like a fuse. I saw one suggestion of LED's for 8 volts and AC usable. Mine are white. Marantz model 2000. Found no reference to that model.
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Post by simplex1040 on Wed Dec 19, 2012 1:28 pm

I replaced a few indicator lamps in receivers using warm white LEDs with dropping resistors. ( to replace the fuse looking lamps) worked really well and customer was happy to have lights again.

Got my LED from a cheap LED Christmas light string I bough after Christmas
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Post by Resistance is Futile on Wed Dec 19, 2012 4:10 pm

I have wondered about the AC operated LEDs vs just using a dropping resistor. I have heard and read there may be problems running an LED without a rectifier in series. My thinking is Hey the LED is a diode so whats that problem? The bulbs in the Marantz 2000 receiver use 8 volts AC. I see no problem with LEDs as less current draw and longer life. santa


by simplex1040 Today at 9:28 am
"I replaced a few indicator lamps in receivers using warm white LEDs with dropping resistors. ( to replace the fuse looking lamps) worked really well and customer was happy to have lights again.
Got my LED from a cheap LED Christmas light string I bough after Christmas"


Excellent Idea.
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Post by terrydec on Fri Dec 21, 2012 4:57 pm

I’ve got all of the parts and the VU meters are next to the bench but there’s been a set back. When your dog jerks on his leash and you trip on a crack in the asphalt, DON’T use a rib to cushion your fall. It hurts, and instead of licking your face and staying next to you, he’ll take advantage of the situation to go rummage through the neighbor’s trash.
And don’t go to an emergency room unless your rib is floating around puncturing lungs and stuff. After waiting five hours they take a cute picture of your insides, (sorry, no 8x10’s), decide that they’ve milked you insurance as much as they can and advise you to “Go home and rest. And here, take some of these white pills, we can charge for them too”.

So I’m propped up on the couch trying not to breathe. Hopefully I’ll be back in business soon. Until then-
Ouch, Rocky just jumped up in my lap.
Perfect.
Neutral
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Post by N7ZAL on Fri Dec 21, 2012 5:22 pm

As I mentioned in another thread, blame it on the Mayans. Laughing
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Post by Resistance is Futile on Fri Dec 21, 2012 6:03 pm

LOL, sorry! ouch! LOL

On HeeHaw, The boys used to sing Gloom, despair, and agony on me.
Click Here for Gloom Dispare and Misery

Gloom, despair, and agony on me
Deep, dark depression, excessive misery
If it weren't for bad luck, I'd have no luck at all
Gloom, despair, and agony on me

-----------------------
I have asthma and cough so bad that 2 years ago I fractured my ribs, and it hurt so bad I screamed all the way to the hospital in an ambulance every time we Hit potholes and boulders in the road.

Now when I cough I still have back and side pain from cold weather effecting my ribs.
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Post by terrydec on Fri Dec 21, 2012 8:51 pm

I'm glad youse guys got my back, and keep me on track.

Seriously though- the only downside to moving into this house is that I've lost my support structure. At my old apartment I could run downstairs and have somebody check me out; or if I did have to go to the hospital there were people around to feed the animals and walk Rocky. I've lost that. I have my nephew and my old landlord to keep an eye on me, but they have lives too.

I am making new friends here, but I'm not at that point with any of them yet.

Oh well, stuff happens, what is is, and life goes on.
Tonight "Avatar"- (courtesy of Netflix), and tomorrow "Back to the Bench!! (I hope)
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Post by N7ZAL on Fri Dec 21, 2012 9:19 pm

Seriously though- the only downside to moving into this house is that I've lost my support structure.

Well Terry, you have friends on the forum you can lean on...but I understand the best thing is for those physical friends. Once you settle in I'm sure things will settle down. But, remember your not 25 anymore. I say that because I try to do things beyond what I should. Shocked
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Post by terrydec on Sat Dec 22, 2012 12:16 am

I know that I have forum friends. Really good ones who have demonstrated that friendship not only in the virtual world but the real one. And I feel more comfortable here than on any other forum, (YEA Bill).
And I'm a tough old bird. In fact I've noticed that I'm not having nearly as many physical and emotional problems as I did in my old place.
Stress makes a mess!
Quiet and relaxed-not so much!
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Post by terrydec on Mon Dec 24, 2012 1:04 pm

I'm going with the diode in series with the 'hot', (not really hot, just red of red and black wires coming from the transformer),lead. I've cleaned up the leads using a terminal strip. I've also put heat shrink tubing on the lamp leads at the meters to stabilize them. It's gonna make it a hassle if I have to replace them.
I might be able to post photos.
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Post by terrydec on Tue Dec 25, 2012 3:29 pm

Well, I've put the diode in series with the lamps and they came on. That's a good thing, a very good thing. They are a little dim but bright enough because the studio isn't very bright either. I'm hoping of course that the slight drop in current will keep them from burning out. Only time will tell.
Thanks y'all.
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Post by terrydec on Tue Dec 25, 2012 3:57 pm

Too much voltage drop. I guess I wanted it to work but the diode makes the lamps too dim. Time to back up and try something else.
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Post by N7ZAL on Tue Dec 25, 2012 4:34 pm

You could put a potentiometer in series with the bulb, adjust for brightness, then read the resistance with an ohm meter. That will give you the value of a fixed resistor(s) you can put in.
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Post by terrydec on Tue Dec 25, 2012 6:21 pm

That's a good idea. The problem is that all I have are a bunch of 10K and an 8 ohm L Pad, nothing in between.

I could use my variable power supply, find a useful voltage between say, 6 and 9 volts that looks bright enough, and use The Law to find the resistance.

For instance 9 volts @.025A= 360 ohm
6 volts @ .025A=240.

I am doing this right, right?
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Post by terrydec on Wed Dec 26, 2012 12:42 am

Wrong-
4 lamps that use 25ma in parallel will be drawing 100ma, or .10 A.

That really makes it simple-
9 volts=90 0hms @1/10th watt, (actually .09).
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Post by terrydec on Wed Dec 26, 2012 2:37 pm

Experiment complete. It takes 12 volts. No real surprise there. Last question, (I promise)- Is there a capacitor that I can put across or inline to limit the turn on surge? That might help.
I have the darned thing in pieces so I anxiously await a reply.
A free virtual Tee Shirt, (whatever that means), to the corect answer.
Thanks.
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Post by Bill Cahill on Wed Dec 26, 2012 4:07 pm

None that I'm aware of...........
Bill Cahill

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Post by terrydec on Wed Dec 26, 2012 5:55 pm

Darn! Oh well, back to square one. I guess I'll just keep some extras around.

(Interesting thread though)
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Post by Resistance is Futile on Thu Dec 27, 2012 6:55 pm

Using A.C. do some math and try using different capacitor values in series. It involves reactance. You also might use a Zener in parallel to take initial voltage surge.
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Post by terrydec on Thu Dec 27, 2012 7:26 pm

Thanks- these are excellent suggestions but way beyond my experience or knowledge. I'd have no idea where to start.

P.S. I failed math in high school AND college. It kept me off the dean's list.
I was REALLY good with writing classes though. Wink
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Post by terrydec on Thu Dec 27, 2012 7:35 pm

What's an MOV? I notice it being mentioned in several articles online about preventing or suppressing turn on current surge.
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Post by Resistance is Futile on Thu Dec 27, 2012 8:12 pm

Metal Oxide Varistor.
from wikipedia


The most common type of varistor is the metal-oxide varistor (MOV). This contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction, which allows current to flow in only one direction. The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs.[1] When a small or moderate voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, and a large current flows. The result of this behavior is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages.
A varistor remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its "clamping voltage", so varistors are typically used to suppress line voltage surges.
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Post by terrydec on Thu Dec 27, 2012 11:21 pm

Wow! So, will it work?
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