DC volts regulator

[morphingstar]

existing circuit has power transformer with split coil and 2 diodes. No capacitors. I want to limit the output to 13 vdc. (The output goes up to 17 vdc, burning 12 volt lights). Total current (load) may be 25 amps.
Note: if input voltage < 13 then output must still deliver, may be 1 volt less than input. Output may not shut off. Distributed output vdc is fused.

Wikipedia shows what I expect might work.
http://en.wikipedia.org/wiki/Voltage_regulator
http://upload.wikimedia.org/wikipedia/commons/e/ef/Voltage_stabiliser_transistor.png

Here is the source principle, it can not be altered
http://en.wikipedia.org/wiki/Center_tap



I need some guidance as to choosing the right power transistor and may be cooling device.

More background
The diodes will be replaced by type NTE ELECTRONICS - NTE5962 - STANDARD DIODE, 25A, 400V
http://canada.newark.com/nte-electr...de-25a-400v/dp/29C4746?Ntt=1n3661#accessories

vdc=volt direct current. split coil = center tap.

thanks

site trouble: page says I am logged in. Preview claims i am not logged in.

 

[(*steve*)]

Is the voltage always high, or does it drop under load? if so, what does it drop to?

It's not DC unless you've got capacitors, it sounds like pulsed DC (essentially rectified AC).

What is the load? just lamps? Any reason it has to be DC?

More information is required before I can give you an answer.

The short answer is that a regulator like the one you suggest is going to be quite an undertaking at these currents. You will need several transistors, and they will require large base currents. The regulation may be poor (unless you go for something more complex). The amount of heat you generate may not be large if the voltage drops under load. The problem then is the voltage drop across the regulator may make your DC voltage sag too low.

 

[duke37]

25 Amps is a lot of current and a lot of heat will be dissipated. Normally, several transitors would be used to lessen the load on each transistor and spread the heat making heat sinking easier.

You could consider replacing the two diodes with thyristors, thus chopping the waveform to give the correct power. This would not generate much heat but would need circuit design.

25A 13V stabilised power supplies are available at a reasonable price, these are used to drive ham radio transmitters. There is the choice of linear stabilisation (heavy) or more modern switch mode design.

 

[morphingstar]

thanks steve and duke 37

<<25A 13V stabilised power supplies are available at a reasonable price>>

sounds interesting, seller? recommended Make ? DC input?

Adding cap^s will drive up the dcv, is not recommended by p/s mfg.
I am fishing for experience with low cost solutions. may be I am lucky.

other helpers
12 volt is dc, who would want the risk of connecting a 12vdc device built for dc to a 12vac outlet.

Yes, the voltage is load dependent, else I would not consider stabilizing it. 16 and more is definitely too much for some stuff, like FL light for 12v, burning out electronic power circuits.

 

[duke37]

I have a Watson supply which is several years old, it uses mains power.

I e-bayed 'power supply ham radio' and got several hits. They are all mains input.
There is a choiice of linear stabilisation (clean but heavy) or switch mode (light but maybe dirty). Newer switch mode supplies can be made clean but you may not mind the amount of interference that a crude switch mode supply can emit.

Looking at your first post again, you say "if input voltage <13" , so is the input mains or battery, AC or DC?
Does the output need to be smoothed or the RMS controlled?

 

[morphingstar]

13 vdc.

to me the logic is clear
voltage lower then 13 ( <13) might be from the rv battery. It depens on the rv's wiring.

Main thing is the dcVolts do not shut off due to low input voltage.
The standard series regulator needs "input dcv > output dcv" to regulate.
Since desired output dcv = 13vdc there is a potential malfunction at a lower input dcv.
The 1st post says the output must not interrupt.

VAC matter only with mains power. It can drop too, e.g. 90 vac instead of 115, but this problem was not included in the question.

Stick with DC.
Rectified DC is always Direct Current, never mind whether it is smooth or inverted sine. It flows in one direction only. The term has been established probably by Edison, I guess he was inexperienced in ONE WAY streets. Else he might have called it One Way current / voltage or Same Direction ... .
Westinghouse built AC generators, alternating current / voltage direction, a sensible terminology.
no more today.

Logged in as morphingstar
You are not logged in or you do not have permission to access this page.
All on the same page.

stupid time waster

 

[(*steve*)]

Logged in as morphingstar
You are not logged in or you do not have permission to access this page.
All on the same page.

stupid time waster

OK, you've complained about that twice now.

I'll take a look.

 

[davenn]

13 vdc.

to me the logic is clear
voltage lower then 13 ( <13) might be from the rv battery. It depens on the rv's wiring.

Main thing is the dcVolts do not shut off due to low input voltage.
The standard series regulator needs "input dcv > output dcv" to regulate.
Since desired output dcv = 13vdc there is a potential malfunction at a lower input dcv.
The 1st post says the output must not interrupt.

VAC matter only with mains power. It can drop too, e.g. 90 vac instead of 115, but this problem was not included in the question.

Stick with DC.
Rectified DC is always Direct Current, never mind whether it is smooth or inverted sine. It flows in one direction only. The term has been established probably by Edison, I guess he was inexperienced in ONE WAY streets. Else he might have called it One Way current / voltage or Same Direction ... .
Westinghouse built AC generators, alternating current / voltage direction, a sensible terminology.
no more today.

OK what is NOT clear to all of us is what you are really trying to do

In your first post you are talking about centre tapped transformers and rectifiers etc
now in this post you are talking about 12V battery from an RV vehicle

Soooooo .... do you really want a AC to DC supply or a DC to DC supply ?
give us all a choice of one or the other in this thread and we aill do what we can to stear you down the right path

Dave

 

[morphingstar]

Power supply, battery and the lot

I agree things on my thread looked almost a confused than they looked in my motor home. I am now able to add some information which might untangle things a little.

I measured the 12 vdc values at an internal indesc. light (bulb), unless context specified battery. That is where the voltage jumped about 10 - 16 vdc.
Here is what I never found out until recently:

When I connected a digital display panel (for a camera) to the bulb and switches it on the voltage shown at the bulb using digital meter increased 3 volts, e.g. 13 to 16. The >=15 watt bulb became brighter.

There is a little "power" box in the feed line of the panel. I opened it. No circuit diagram, but definitely a transformer and a (storage) capacitor may be 1x1/2 inch.
The consumption of the panel is about 200 mA, or less.

The bulb circuitry is not fed from the 12 vdc battery when 115 vac is present.
A relay switches the distribution circuit to the battery (and back) when 115 vac are off (on).

Therefore the increasing voltage (16 vdc) is not related to the battery (13 vdc) condition. I was always wondering where these 3 volts were hiding. Now this matter is cleared. The pulsating dc increases.

I have yet to find a way to avoid a few bulbs getting 16 vdc, lasting less hours. Easiest is turn on more bulbs in other parts of the MH, somewhat inconvenient during the night when the camera circuitry should operate and the panel be on. At this time other matters are more important, the voltage increasing video panel is not in operation.

Just to be complete: The mentioned voltage 10 vdc was a result of an undiscovered intermittent overload on the same wire. Corrected.

I do not plan the replace the 2 power diodes. The source of the nasty over-voltage effect seems clear and not related to diode age.

This concludes the matter for me: The cause has been found and the results returned to this forum. I prefer not to add capacitors the the centered transformer 2-diode output, as this might kill the diodes upon maximum load (30 amps).
Thanks everybody.

 

[weird_dave]

Your DC voltage is an average of 12v, it peaks at around 16/17v. When you add the display, the internal capacitor is smoothing out your DC, making it 17v.

There are 2 simple solutions to this:
(1) add a diode to the input of your display panel, this will stop the internal capacitance affecting your lighting, but the panel must be capable of running from 17v (or keep adding diodes until you're down to 12v)

(2) use a transformer with a lower output voltage and add capacitors to the output to give you a nice smooth 12v DC


Edit: Typo's!

 

[morphingstar]

weird_dave
thanks for the series diode tip, this might work.
What surprised me is the very sall capacitor can keep up the "peak" voltage while so many incandescent light loads on ON, pulling on the voltage.