quick way of stepping down high DC voltage

Thread Starter

ak52

Joined Oct 15, 2014
197
Hello All,

I have a high DC source , string of PV panels.My open source voltage is aroung 120-125v.When connected to load it drops to around 98-100v.

I was looking for a quick and cheap way to stepdown this voltage to around 15v,to power some circuits.The current consumption would be 800mA to 1 amp.

Here is what i have tried so far.

1.Used a zenner and mosfet based voltage regulator.The mosfet acting as the current buffer.
I am able to run this correctly,but the downside is that the mosfet gets insamely hot after a few minutes.The GP board where i had soldered this was also very hot.If i had left it on for some more time the lead would had started melting. :)
I did a small simulation and the power loss would be around 13watt at 1 amp load.
upload_2017-12-27_14-57-0.png

2.Use a high wattage 15v zenner ,but the maximum i have was a 0.5w zener!

3.Searched for a wide range DCDC regulator.I found a few which are used in railway application.But they are very expensive.

4.Use a switching regulator,but most of them have a upper cuttoff voltage range of around 70v.

5.Using a voltage divider is out of question because the power rating on the resistors eed to be high!

Is there anything else i can try? Please Help
 

Attachments

Last edited:

spinnaker

Joined Oct 29, 2009
7,835
Hello All,

I have a high DC source , string of PV panels.My open source voltage is aroung 120-125v.When connected to load it drops to around 98-100v.

I was looking for a quick and cheap way to stepdown this voltage to around 15v,to power some circuits.The current consumption would be 800mA to 1 amp.

Here is what i have tried so far.

1.Used a zenner and mosfet based voltage regulator.The mosfet acting as the current buffer.
I am able to run this correctly,but the downside is that the mosfet gets insamely hot after a few minutes.The GP board where i had soldered this was also very hot.If i had left it on for some more time the lead would had started melting. :)
I did a small simulation and the power loss would be around 13watt at 1 amp load.
View attachment 142519

2.Use a high wattage 15v zenner ,but the maximum i have was a 0.5w zener!

3.Searched for a wide range DCDC regulator.I found a few which are used in railway application.But they are very expensive.

4.Use a switching regulator,but most of them have a upper cuttoff voltage range of around 70v.

5.Using a voltage divider is out of question because the power rating on the resistors eed to be high!

Is there anything else i can try? Please Help

You are going to have to use a switching regulator as you mentioned. Is there an AC component to the DC? Can you get to it? If so, you can use a step down transformer then just rectify it again or use a wall wart.
 

spinnaker

Joined Oct 29, 2009
7,835

Danko

Joined Nov 22, 2017
1,133
With Solar Power Systems DC mains comes back to houses.
http://chrisgammell.com/can-dc-power-an-entire-home/
Most of modern charge and wall adapters are DC to DC switching converters. They are lightweight (no iron transformer) and have wide range of input voltage, for example 90-240V.
In order to use this converters with AC input voltage, they contain on input diode bridge and ripple smooth capacitor. They work excellent from both AC and DC mains.
 

GopherT

Joined Nov 23, 2012
8,012
See on picture - input : 100-240V 50 / 0 Hz.
0Hz means DC.
And also this switching adapter 15V 1.2 A . It has bridge and capacitor on input and works from AC and DC.
http://www.mini-box.com/18w-15v-1-2A-AC-DC-Power-Adapter?sc=8&category=1364
Why would it work only to 50 Hz? Why not 60? This is the classic issue with knock-off products and the often-cited advice to identify them (look for typos).

If you tell @spinnaker you are right because it is printed on the label, then you are also wrong because it says "AC Adapter" on the label.
 

GopherT

Joined Nov 23, 2012
8,012
And also this switching adapter 15V 1.2 A . It has bridge and capacitor on input and works from AC and DC.
http://www.mini-box.com/18w-15v-1-2A-AC-DC-Power-Adapter?sc=8&category=1364
Please revisit your link above. The title is poorly written, it should say AC-to-DC converter. The specs ONLY list AC as input...

AC-DC 15V, 1.2A/ 18W Switching Power Adapter (110/220V)

- Model No. AH1815-B
- High Efficiency AC adapter
- AC INPUT: 100 -240 VAC. <<<< HERE
- DC OUTPUT: 15V, 1.2A, high power (18watt)
- 5.5mm/2.1mm barrel power jack - Cable: 22AWG. 6FT- Works with Alix2 and Alix3 boards
- RoHS compliant
- LPS/CE/FCC/UL

PS, your link to the DC powered house doesn't address the issue very well...
Converting devices
  • Conversions would be required from DC->DC instead of AC->DC. A possible solution would be to set up the wall sockets to have selectable DC output (perhaps the home runs on 100V DC and each socket can convert this down to 24V, 12V, 5V, 3V).
 

Dodgydave

Joined Jun 22, 2012
10,050
Only two options ideally,

1) use a laptop psu open it up and put your HV DC across the input capacitor.

2) use a buck down converter chip.
 

spinnaker

Joined Oct 29, 2009
7,835
With Solar Power Systems DC mains comes back to houses.
http://chrisgammell.com/can-dc-power-an-entire-home/
Most of modern charge and wall adapters are DC to DC switching converters. They are lightweight (no iron transformer) and have wide range of input voltage, for example 90-240V.
In order to use this converters with AC input voltage, they contain on input diode bridge and ripple smooth capacitor. They work excellent from both AC and DC mains.

How many people in the world have their home wired for DC to accommodate solar? About .00001% ? Mains are not DC they are dc.
 

GopherT

Joined Nov 23, 2012
8,012
Hello All,

I have a high DC source , string of PV panels.My open source voltage is aroung 120-125v.When connected to load it drops to around 98-100v.

I was looking for a quick and cheap way to stepdown this voltage to around 15v,to power some circuits.The current consumption would be 800mA to 1 amp.

Here is what i have tried so far.

1.Used a zenner and mosfet based voltage regulator.The mosfet acting as the current buffer.
I am able to run this correctly,but the downside is that the mosfet gets insamely hot after a few minutes.The GP board where i had soldered this was also very hot.If i had left it on for some more time the lead would had started melting. :)
I did a small simulation and the power loss would be around 13watt at 1 amp load.
View attachment 142519

2.Use a high wattage 15v zenner ,but the maximum i have was a 0.5w zener!

3.Searched for a wide range DCDC regulator.I found a few which are used in railway application.But they are very expensive.

4.Use a switching regulator,but most of them have a upper cuttoff voltage range of around 70v.

5.Using a voltage divider is out of question because the power rating on the resistors eed to be high!

Is there anything else i can try? Please Help

The best solution would be to buy a 90V DC to AC inverter. An INVERTER converts DC to AC. You'll have to look for a 90v device but they are available. Once you have the DC inverted to 120V or 240v AC, you can plug a standard AC-to-DC adapter into the unit.
 

Alec_t

Joined Sep 17, 2013
12,199
1) use a laptop psu open it up and put your HV DC across the input capacitor.
Would that really be necessary? If the input feeds straight into a bridge rectifier (as most, or all, seem to) then an AC input would use all 4 diodes of the bridge whereas a DC input would use only 2. For a given adapter power rating, those 2 would be dissipating more power than they would for an AC input, but (1) provided the diodes are generously rated that should be ok, or (2) an adapter with twice the power rating should do the business.
 

Dodgydave

Joined Jun 22, 2012
10,050
Would that really be necessary? If the input feeds straight into a bridge rectifier (as most, or all, seem to) then an AC input would use all 4 diodes of the bridge whereas a DC input would use only 2. For a given adapter power rating, those 2 would be dissipating more power than they would for an AC input, but (1) provided the diodes are generously rated that should be ok, or (2) an adapter with twice the power rating should do the business.
I said put the DC straight across the DC smoothing capacitor, this would bypass the bridge....

As most laptop bricks run from 95 to 230V Ac
 

Danko

Joined Nov 22, 2017
1,133
We have only two ways for converter choice.
1. See on label and think nothing.
2. Turn ON brain and look at diagram.
Laptop.png
 

shortbus

Joined Sep 30, 2009
8,803
@GopherT , @spinnaker , I think maybe you're wrong about the power supply. As Alec said, in post #14, if it is a switching supply the first stop into it is conversion to DC.

A VFD will also work on DC giving out 3 phase AC because of the same reason.

Danko types faster than me, and gave a picture. :)
 

bertus

Joined Apr 5, 2008
21,532
Hello,

When using the adapter on DC, you must take the AC to DC conversion factor in account.
100 Volts AC will be about 140 Volts DC, so the adapter might have troubles with 100 Volts DC.

Bertus
 
Top