Ripple Current ?

[starfury1]

Re: Ripple Current ?

Hi Joe

Its not rocket science mate...sure you can get very technical
but its just mostly understanding Ohms Law
what Voltage is, what Current and what Resistance is
some understanding on what DC is AC and frequency and a some magnetics
Then a little understanding on some components and you have pretty much got the basics..well enough to do what you want to do.

look of the links posted thought out this thread and you will find other stuff too.

just remember 3 things about voltage and current resistance
voltage exist across (or between 2 points)
current flows through (from one point to the other)
resistance is opposition to current flow
but it has an inverse property of allowing flow of current too (conductance)
(so you have to takes with it, how well it blocks or how well it allows current to flow.... depends on which side of the fence you want to look at it from )

I know the above seems way way simple
but if you can grasp it and apply it to what you read on the net it will dawn on you whats happening.

you got any questions post away

just remember with electrolytic caps, don't ever exceed the voltage marked on them (or stickem in back to front)

Thats quite a clever use for the cap thought, using it as a spare short term supply when a contact goes open circuit...makes perfect sense of your term flywheel too

Hope it helps

Cheers Joe

[Joe Rampolla]

Re: Ripple Current ?

Hi StarFury1,

Again, thanks to you and everyone here for all the kind help!

I didn't coin the term "electronic flywheel" and I didn't invent the idea. Some clever people before me did that. Some used a small resistor to slow the discharge of the cap, others used computer grade super caps, recently. The best thing is the bipolar cap, but they, last time I checked, only go up to 16 volts for 3300 MFD. (When I use the bipolar 16 volt cap, I only give the track a fixed 7 VDC from a wall transformer that has some sort of filtering.) Again, size limitations are the problem. However if there is room in other pieces of rollingstock, caps can be placed in other cars on the trains. Also longer locomotives with many wheels often don't need flywheel circuit. Some locomotives have actual brass flywheels.

I admire all of you with your knowledge and hard work studying and applying your skills and talent! Check out the model train stuff in person at a hobby shop if you can. The inexpensive stuff can benefit from the simple electronic techniques.

Take care, Joe

[starfury1]

Re: Ripple Current ?

I realize that re flywheel that you didn't
just that it made more sense when you explained lack of voltage (on track) as the real reason its there...think bonez picked up on that I was more thinking varying DC due to your question on ripple.

well if it works ok on 7V DC but you just want it a little better filtered a cap is the answer (with in reason)
The only limitation is the Transformer is it able to supple enough juice for your circuit regardless of filtering
(wall warts arn't what I call a power house of energy and I some what take the max with a dose of salt)

just remember that there are trade offs with everything you do
to much capacitance for example can lead to huge peak currents through Diodes etc

Changing things will have an effect. the idea is to know what the effect is and if it will be ok

have a look for Linear PSU design links and sites

Cheers Joe
and yeah you got me thinking on trains.

[Joe Rampolla]

Re: Ripple Current ?

Hi StarFury1,

Thanks for the info!

I don't need a lot of power for most of these little projects when I use the "wall warts." Most of them have some sort of filtering, and a fuse which affords some protection. I usually use another fuse or little circuit breaker on the line, and another little diode just to help me remember the positive wire. (I like to use regular little diodes to give me some voltage reduction. My favorite low tech way to get a few volts reduction is just to use a string of diodes and allow for their extra heat.) I like to find the wall warts that can be opened up so you can replace the fuse inside. Many of my projects are just about 9 VDC at less than .5 amp. Most of my projects don't require voltage regulation, but it would help.

One standard use of caps for model train people is to filter DC from a rectifier used on AC supplies. They also use a "capacitor discharge circuit" to power the solenoids in some turnouts. Very simple circuits that a beginner can understand. The other stuff can get very complicated. These techniques are decades old.

I will be looking into building regulated power supplies, which is a readily available circuit for model train hobbyists. If I run into problems, I'll be asking questions again!

Thanks!

Take care, Joe.

[starfury1]

Re: Ripple Current ?

No worries Joe
we are a friendly bunch here

Take care, Cheers

[PCBONEZ]

Re: Ripple Current ?

I haven't had my coffee yet so pardon if I read something wrong and wander off the path.

capacitor basically *open circuit

The cap is never actually open circuit because the motor's winding is in parallel with it.
-
If circuit condition exists (via a switch or other change) where the motor is disconnected from the cap *while it is charged* then you should use a load resistor. This is a high resistance resistor in parallel with the cap to assume the role of load if the motor is disconnected. It is a high enough resistance to be nearly irrelevant when the motor is connected and powered but if the motor is disconnected it prevents an open circuit situation and also provides a discharge path to drain the cap. The resistance is high to minimize current going through it (the resistor) when the motor is operating. (And thereby reduce power lost by sending current through the resistor that would otherwise go through the motor.)
-
If the cap is never disconnected from the motor I don't think you'll need a separate load resistor for this. You will never have open circuit and with input power removed the cap will act like a battery to the motor until it is drained and so won't be sitting there charged up.


Joe
You are doing fine.
For FYI Davimax is the authority on this stuff.
He's actually used this stuff professionally his whole life I think.
I had a year+ of intensive (60+ hrs/week) training in electronics as part of my 'basic training' for working in NUC power plants but that was in the early 80's and in my job didn't call on me to actually use that training often. Also in that field creativity isn't an option,, and so I'm a bit rusty on creative circuitry.
Starfury has an unusual writing style but don't let that fool you. He knows what he's doing too.
In fact there are a LOT of smart people here at Badcaps.net.

Anyway. That's why I keep asking other's to review my suggestions.
Been a long time for in this particular area and I'm re-learning as I go.

.

[Joe Rampolla]

Re: Ripple Current ?

Hi Folks,

Again, thanks, everyone, for the help!

Take care, Joe.

[starfury1]

Re: Ripple Current ?

EDIT: you cause me to pick up a right royal STUFF UP in my thinking PC Bonze, Thanks

The cap is never actually open circuit because the motor's winding is in parallel with it.

Id have to go re read were I put that PCbonze but you are quite correct.
dont think you needed the coffee for that one mate.

if you got a coil in parallel

Ok found it, and thinking further on my further thinking...I think I "stuffed up" cause
if you control the speed by varying the DC voltage (and this is the bit I am really unsure of, I am thinking its zero to whatever DC voltage)

For it to be in stopped mode the voltage has to be low or none.

So there goes that theory...... (somewhat see further down)

Anyway just to clear up why the cap is open circuit....(in my statement)

If you put an uncharged cap across a DC voltage
it will initially appear like a short circuit, large inrush current till it charges up then appears more or less as an open circuit to DC rails
(voltage across it will be whatever the DC rails are)
(there is of course a Time Constant(TC not owner of forum) with the actual resistance of the wire etc but can somewhat be neglected but it does exist and then there is the actual leakage of the cap)

so really thats for a cap only and more at an ideal sense "not the true reality of things"

the below quote is from the original post of mine and is "flawed logic" in regards to the motor state VS applied DC voltage from rails
(also as bonze has pointed out you DO have the motor in parallel with the cap, which I was really "neglecting".. ergo the statement" "basically" open circuit" )

but thinking it though further ...
if the train is in stopped mode, motor doesn't pull current therefore No Vdrop across resistor, capacitor basically *open circuit so therefore Voltage across capacitor becomes the track Voltage DC.
(*except for leakage current)
If that is higher then 16V.... bye bye cap (I think)

This is really a side point (and provided my Thinking is clear?)

I think if you are "@ voltage" it would still hold water but it then becomes more complex as you would have to take into consideration the motor coil and current drawn (@ whatever DC voltage point)

Now for something I can't answer
Is the current more liable to be drawn from the cap or via the dropping resistor ?
I am thinking possibly a bit of both (depending) and if so how much from each ?

I suppose this would come back to source impedances and Kirchoff's voltage and current laws (and the specifications of components used plus the DC voltage point)

Oh my head hurts already
What do you guys think ?...am I on the right track or did I just derail myself again (all pun intended )



I think this gets really tricky cause even thought we are talking DC its actually quite a dynamic circuit.

I got too caught up in looking at the trees and forgot the Forrest I was in I guess.

Thanks Bonze
I actually lie a lot (well bent the truth somewhat)
to try and convey a concept or idea,
so its never really the truth of the matter in a hard core sense
(or even full disclosure...I'll post links if I can find them for that)
(i'll re read your post on the other stuff but think we are basically on the same page with it)

Davmax and you speak the language of Maths much much better then I
and that is the "correct accurate method" to "convey concepts and ideas" in the Electronics world so I tend to leave the finer points to you guys

so corrections thoughts etc please post guys. if I've stuffed it again let me know.

No worries Joe good luck with it any quires please post

you have actually given us a can of worms to play with so I guess it will get tossed around for a while.

Cheers

[starfury1]

Re: Ripple Current ?

old hands would know this one
but what I am was talking about above follows this type of thing Resistor cube

For those budding electronics enthusiasts this will help you think about things
Hopefully not scare you off.

Also above I think a more correct term might be Node analysis

A little lesson on it HERE

Start adding some dynamic aspects to this (different points in time)

now you know why my brain hurts....

Not going to try and solve this
but thought id post it for a bit of completion to what I was waffling about...

Cheers

[Joe Rampolla]

Re: Ripple Current ?

Hi Folks,

Although this is not about ripple current, I figured that you guys know my shortcomings and have helped me here before.

I want to build this simple circuit.





This is from the site: http://www.electronics-project-desig...mingLight.html

"This analog timing light project uses RC circuit as a delay OFF timer to control the duration an incandescent light turns ON. When the accuracy of a timer is not critical, the use of RC circuit is a good choice as it is more cost effective and simple. Once the normally open switch SW is pressed, the light will turn ON for a duration of 10 - 20 seconds before it turns OFF. The duration of the turn ON time can be varied by varying the values of R1, R2 and E1."

"When SW is pressed, the base of the transistor Q1 is forward bias and it turns ON. This turns ON the 12V relay that is connected to the transistor. The contact of the relay RLY must be able to withstand the current of the load. At the same time, the electrolytic capacitor E1 is being charged to a voltage of approximately 0.7V.
Once SW is released, E1 will discharged through resistor R2 and the base of the transistor. After some time, When the voltage across E1 drops to approximately 0.5V, the transistor will turn OFF. This in turn will cause the relay to turn OFF and the incandescent light will turn OFF. The timing of the turn OFF can be changed by changing the values of E1, R1 and R2."


I figure that if I increased the value of capacitor E1 to about 470uF, then I would get about 30-40 seconds of relay activation. I am willing to play around with the values of the cap and resistors. I am not certain of what R1 does in this circuit. What is the purpose of R1 and C1 in this circuit? The rest I think I understand.

Any ideas about the circuit will be appreciated. I don't want it for a light bulb, but rather to turn on and off animation.

Thanks!!!!

Take care, Joe.

[Joe Rampolla]

Re: Ripple Current ?

Hi again Folks,

To simplify my question, would this work just as well?


Thanks!

Take care, Joe.

[PCBONEZ]

Re: Ripple Current ?

D1 is there to as a path to burn off the inductive kick when the field in the relay's coil collapses.
C1 dampens the voltage spike.
C1 will also dump EMI out of the DC.
It's a good idea to have it but it would probably work without.

Contrary to the description: R1 is the discharge path for E1.
R1 is in parallel with [R2 + Q1] but during the time E1 is discharging Q1 is passing current in the OTHER (not E1 discharge) direction for the transistor to still be ON.
If the transistor is not ON -> the light is already out.
When the transistor is OFF Q1 is still not a discharge path for E1.
In a NPN the Base->Emitter is a high resistance in that direction and considered open circuit. The only current (if any) will be a small leakage current.
- Summary: Without R1 it could take several minutes to several hours for the light to go out. Depending on the value of E1 and how much it charges up possibly even days.

Here is a little calculation related info:
- R1/E1 Voltage drop rate will be a logarithmic curve, fast change at first, slow change near the end.
- For most standard transistors when base-emitter voltage is 0.7v (0.6v-0.8v) or more the transistor will be on. When it goes below that it will turn off.
- The starting voltage on the top of E1 will be 12v when discharge starts.

You should be able to 'ball-park' calculate the delay time by the values of uF and R1 alone.
- Ignore R2 and Q1.
(Because the current change through Q1 base-emitter and hence through R2 is a logarithmic function during E1 discharge and that makes the voltage drop across R2 also a logarithmic function with time,, as current through Q1 goes down the emitter-base resistance goes up,, so,, you would be calculating numerous variables that are all changing logarithmically at different rates at the same time,, and,, you don't feel like calculus today anyway,, do ya?)

- The transistor should be off just before the voltage on E1 drops to 0.7v.
Just before Q1 turns off the emitter-base resistance will be high and so current through Q1 and R2 low. Current is low so the voltage dropped across R2 will be negligible and Vbase (Vb) is essentially the same voltage as on the top of E1.

~~~
At least that's how I see it.
I could be all wet.

.

[Joe Rampolla]

Re: Ripple Current ?

Hi PCBONEZ,

Many thanks for your help and great explanation!!!!!!!!!

So I going to order some resistors and caps in values I don't already have, and give it a try. I can't find the transistor 2SC2002, but I am going to substitute a TIP31C.

Take care, Joe.

[Gianni]

Re: Ripple Current ?

You must use a good power switch otherwise its contacts can melt after few operation. E1 sink high current to charge itself.

Gianni

[Joe Rampolla]

Re: Ripple Current ?

Hi Gianni,

Thanks for the warning! I intend to use a switch rated 5 Amps @ 125VAC. I assume that will be heavy enough for a 12 VDC, 500 ma power supply, and an electrolytic cap 470 uF, 35V or as high as 1000 uF, 35 V.

Take care, Joe.

[Joe Rampolla]

Re: Ripple Current ?

Hi PCBONEZ, Gianni, and Folks,

I learned the hard way about the importance of snubber diodes when I had a reed switch's contacts burn out prematurely. Would a little capacitor across the reed switch also help protect the reed's contacts? I use this circuit quite a lot, but without any cap across the reed. Am I correct in using a cap this way? Thanks!



Take care, Joe.

[Gianni]

Re: Ripple Current ?

Hi Joe

I'm not expert with relay but as I suppose the cap across the contact discharge an high current when the contact close since it gets shorted.

I have found this document and you can see that a resistor is needed to limit the peak current during cap discharge.
In your case the cap is very small so probably the current is not so dangerous.

But as I said I'm not an expert on relay but I have never used cap across contact in all the circuit I have worked with.

Wait to see what other members suggest you.

Ciao
Gianni

[PCBONEZ]

Re: Ripple Current ?

Go from left side of reed switch to ground instead of to +12v.

.

[Joe Rampolla]

Re: Ripple Current ?

Hi Gianni,
Thanks for the information about the relay contacts! I am learning something new all the time!

Take care, Joe.

[Joe Rampolla]

Re: Ripple Current ?

Hi PCBONEZ,

Thanks for the correction! Once I redrew it according to your directions, it now makes sense to me.




Take care, Joe.