Hi guys,

I've got a power supply with UPS functionality (using a standard PB 12v Battery) which is supposed to give away 12v DC, but instead is giving 12,90v. This voltage is higher than the -/+ 5% recommended by most manufacturers.
Behind this PowerSupply there is an expensive device (DVR) which needs 12vDC and 1-5A-2A. Powering up this device at 12,90 might damage/degrade its components over time.

I need to reduce that voltage a little bit between 12v to 12,60v. Any ideas?

-I've tried with a resistor; It successfully reduced the voltage to 12,40v but was drawing too much current and the device did not power up.
-If I use a diode, it will introduce voltage fluctuations :-(
-Use an LM317/LM350 ? never used them. This will also consume current and may not let the device power up? shall I combine with it some resistors, regulators or capacitors?
-Other ideas?

Thanks

 

The diode should have worked pretty well.

What kind of voltage fluctuations did you see, and how tight do you need to hold the voltage?
What kind of diode did you try?

Reexamine your assumptions as to why dropping that 300 mv is important. It probably isn't.

If the diode really is unsuitable, One way to go would be to get a 10 volt low dropout regulator and adjust the output to 11.4 volts -You might not be able to get it to work all the way up to 12.0 volts.

Another approach is to use a buck orbuck-boos switching converter to drop the voltage.

 

I've still not used any diode. I just know that diodes have a forward voltage that can cause damage to sensitive PCB's/equipment.
I've read that Schottky diodes have a very low forward voltage, but not sure which model fits my needs and whether I will be able to find it in my local store. Which diode shall I use? a resistor and a capacitator shall also be used? if yes, how?

The recommended is to reduce it 900mv, but my assumption is that such devices can tolerate at maximum 1,60v (- 300mv from our actual measurements).

In regards to the 10v dropout regulator, won't work with less than 12v. As I said before that board/device is pain in the ass.

I am investigating that "buck orbuck-boost converter", but it seems that it reverses the polarity. Not sure how to handle it.

Thanks,

 

I highly doubt 0.9V difference will degrade components overtime, since the DVR will have voltage regulators powering the various stages of the unit.
Did you care to look at the DVR input regulators ?

If you are still concerned then I suggest look for 10Amp Schottky diodes.
Further more look at the diode specs about the Vf vs If.

by the way, A Schottky will solve your problem.

 

I just know that diodes have a forward voltage that can cause damage to sensitive PCB's/equipment.

Where did you learn that ??
How could an equipment be damaged if the Input requirements are met ?

I am investigating that "buck orbuck-boost converter", but it seems that it reverses the polarity. Not sure how to handle it.

Why would a buck or boost reverses the voltage ??
It would if you made it that way.

 

Did you care to look at the DVR input regulators ?

Nope, I will do when I get home, but are in micro SMD and I do not have a good magnifier.

Where did you learn that ??
How could an equipment be damaged if the Input requirements are met ?

I believe that because behind that Schottky diode, there is a big PowerSupply board with complex circuitry.

Why would a buck or boost reverses the voltage ??
It would if you made it that way.

Never mind .

If you are still concerned then I suggest look for 10Amp Schottky diodes.
Further more look at the diode specs about the Vf vs If.

Then i will stick with your proposal. The power supply is rated for 20A, but has 18 separated outputs at 1100mA each. To wire the DVR will be wiring in parallel two outputs, and stick in the positive line the Schottky diode.
Will this or this other diode work?
Shall I put a 1k resistor (or something else) behind the diode?

Lots of thanks

 

If your power output is 20 separate outputs, you can put a 1 ohm, two watt resistor on each to "buffer" the output in case ant are at different voltages from each other. Or, use a diode (2amp) and a 0.22 ohm resistor (0.5 watt) in series at each output. Then connect the output of each resistor together. That should give you the desired 0.9 v drop and insure the load is not carried by the output that has a slightly higher output voltage (the all never match exactly).

 

I believe to recall all outputs were at the same voltage. I will double check thanks.
Last questions, I promise

Will this or this other Schottky diodes work?
I've read that this other diode might work. Any (dis)advantage on using this one?

Shall I put a 1k resistor (or something else) behind the diode?

 

A little concerned about your power source. You said it's a PB 12 V battery. Lead acid batteries when fully charged should be at 12.6 volts optimally. When being charged they should be run up to 14.4 volts (or thereabouts, depending on how depleted they have been) and then should sink back down to 13.6 volts (float voltage).

Are you saying you're using one of those battery boosters meant to be charged and then kept in your trunk until you have a dead car battery? If so, I'd suspect those aren't going to do well as a "Power Supply". What I'd do (or advise) is go to an Xfinity store and ask if they have any 12 volt power plugs designed to power their satellite DVR receivers. All you have to do is plug it in. I have a couple I got from them FOR FREE!

Now, in case you're wanting to use this outdoors (camping), a fully charged car battery should not be more than 12.6 volts. Directly wiring that to your DVR - well, I don't want to say this and become responsible for you damaging your equipment, but I don't honestly believe a car battery is going to harm your DVR. At least not OVER voltage. But running it off the car battery while still in the car and engine running - yes, you'll see much higher voltages than desired. In THAT case I'd opt for an inverter to convert the unstable 12 volts to 120 volts and then power the DVR from a power supply that is meant to be plugged in.

As for what others are saying about dropping 900 mV, yeah, a simple 10 amp diode should do the trick. Can't see why you'd get any fluctuation out of that. But you know better than we do what it is you're trying to accomplish.

Well, that's all this peanut has to offer for now.

 

VS-95SQ015 9A (Vf:0,25V)
SB560 5A (Vf: Vf: 0,70V)
1N5822 3A (Vf: 0,52V)
6A05 6A (Vf: 1,1v) NO!
TO220AC 16A (Vf: 0,57V)

I am answering myself. The first one is the ideal. What I do not know if I still need a resistor before or after the diode.

Thanks,

 

Hello,

At the 6A05 you say NO.
The 1.1 Volts is given at 6 Amperes.
The voltage at 1 to 2 Volts are about 0.8 Volts:



Bertus