Is there a cheap way to convert 12vdc to 36vdc with 30amp input current?

Thread Starter

LEDIY

Joined Dec 2, 2016
26
Boost converters are cheap but only up to 10amps input. The rated power is always 10 x input voltage.

I have found a supply of cheap high power 12v psu's capable of up to 60 amp output but have read that I cannot connect boost converters in parallel from the supply, something to do with the return voltage being different? Is this true?

Is there a more efficient way to do this? I don't need a variable output voltage or current just 36v at 10 amps.
 

tcmtech

Joined Nov 4, 2013
2,868
I've paralleled converters for higher power applications many times without problems.

If they are all identical units the unit to unit output voltage variances between them are so tiny its inconsequential and they will run parallel just fine.
 

Thread Starter

LEDIY

Joined Dec 2, 2016
26
Really!? Even with the chea
I've paralleled converters for higher power applications many times without problems.

If they are all identical units the unit to unit output voltage variances between them are so tiny its inconsequential and they will run parallel just fine.
Really!? Even the cheap ebay boost converters or are more expensive ones from electronic stores?

If this is possible it would solve all my power issues!

Is there any issue with safety? Is there anything I could do to regulate the output voltage from the converters or is this not necessary?
 

Thread Starter

LEDIY

Joined Dec 2, 2016
26
The end result of this will be to drive high power cob LEDs. I was planning on using step up converters to step up the voltage and then use an LM350 to regulate the final current to the LEDs as they are going to need 0.8 to 1.2amps with a Vf of 34v.

I have seen XL6007 DC-DC Step-up boost Converter which could step up to 36v with a max current capacity of 4amps.

It has a pot but only for Voltage so is the current just going to be directly proportionate. i.e for 36v @ 1amp would be 12v @ 3amp on the input.

These are really cheap so could I do, for example 8 XL6007's in parallel with the 12v PSU, then wire my LM350 circuit in series with each one drawing 1amp @ 34v with each LED in series with the LM350.
 

Papabravo

Joined Feb 24, 2006
12,983
Unless you can find one that exists, there is no cheap way I know of to do what you need. The engineering alone for such a device will cost you about as much as a new Lincoln.
 

Thread Starter

LEDIY

Joined Dec 2, 2016
26
Unless you can find one that exists, there is no cheap way I know of to do what you need. The engineering alone for such a device will cost you about as much as a new Lincoln.
Hi Papa Bravo,

All of the heavy lifting would be done by the 12 volt PSU though. The ones that I have found are salvaged from very high power machines its just converting that into the voltage I need.

Would step up converters in parallel not work? I respect what you're saying but why?
 

tcmtech

Joined Nov 4, 2013
2,868
Really!? Even with the chea


Really!? Even the cheap ebay boost converters or are more expensive ones from electronic stores?

If this is possible it would solve all my power issues!

Is there any issue with safety? Is there anything I could do to regulate the output voltage from the converters or is this not necessary?
Yes. Cheap eBay ones are the only ones I will buy.

Safety is relevant to the user. If you find 12 - 36 volts DC at a few tens of amps to be dangerous you might as will give up living now.

Theoretically ideal and what works well in reality are not the same. Reality wins every time.
 

Thread Starter

LEDIY

Joined Dec 2, 2016
26
Yes. Cheap eBay ones are the only ones I will buy.

Safety is relevant to the user. If you find 12 - 36 volts DC at a few tens of amps to be dangerous you might as will give up living now.

Theoretically ideal and what works well in reality are not the same. Reality wins every time.
Thanks for the advice I think I am going to just take buy the stuff and test it. I just didnt want the PSU to blow up and burn my house down!

The step up converters are these:

Screenshot_20161210-191448.png

There is no current control. Which is why I want to then connect the output to an LM350 and a resistor to set the current to drive the LED. Is there any issue with this?
 

Papabravo

Joined Feb 24, 2006
12,983
You ask why such a converter might be unavailable or difficult to construct. Here is the problem:
  1. Your output requirement is 36VDC @ 10 Amperes, that is 360 Watts of output power.
  2. Assuming a converter that was 80% efficient, it will require 360 / 0.8 = 450 Watts
  3. For the 12VDC supply to deliver this power it would have to be capable of supplying 37.5 Amperes.
Assuming you could find a suitable 12VDC supply you would have to pick an inductor that could handle twice the input current or 75 amperes. I don't know if you have ever tried to design such an inductor, but I'm here to tell you that it won't be easy. Next you have to find ultra low ESR capacitors. Then you have to pick a switch with an ultra low rDS(on). Then you have to do a careful PCB layout with particular attention to the thickness and width of your PCB tracks. If you are not yet suffering from technological whiplash -- go ahead and try to design such an animal. As for paralleling converters I don't recommend it, but hey this is your problem, go ahead and try anything to get you where you want to go.
 

Thread Starter

LEDIY

Joined Dec 2, 2016
26
To get an LED driver that matches my requirements would be about £250. Car batterys would be too big for my requirements.

The 12v PSU is cheap, high quality and capable of almost 600w output.

I have ordered the boost converters and will try to use them to individually power 1 LED per converter. The LEDs only actually need 1 amp each, the converters are rated for up to 4 amps input.

I will then wite the boost converters to an LM350 and resistor like:

Screenshot_20161211-134611.jpg

But will use a 1.25ohm resistor to get a constant current of 1amp from the converter.

If, in reality, the boost converters dont have an issue working in parallel I can't see why this wont work.
 

ronv

Joined Nov 12, 2008
3,770
To get an LED driver that matches my requirements would be about £250. Car batterys would be too big for my requirements.

The 12v PSU is cheap, high quality and capable of almost 600w output.

I have ordered the boost converters and will try to use them to individually power 1 LED per converter. The LEDs only actually need 1 amp each, the converters are rated for up to 4 amps input.

I will then wite the boost converters to an LM350 and resistor like:

View attachment 116679

But will use a 1.25ohm resistor to get a constant current of 1amp from the converter.

If, in reality, the boost converters dont have an issue working in parallel I can't see why this wont work.
You can also put three of your 12 volt supplies in series. You just need to make sure you isolate AC and DC grounds.
I see heart ache in your future trying to parallel boost regulators that are not designed for it.
http://www.linear.com/solutions/5464
 

Papabravo

Joined Feb 24, 2006
12,983
I just spent a whole 3 minutes and found this one
http://www.powerstream.com/dc36.htm
7.5 amps at 36 volt (275 W)

Are you sure you have devoted sufficient time and effort to your search?
I don't see where it meets the stated requirements. It is 85% efficient, which is a little better than the 80% rule of thumb figure I used for my estimate. Lastly, $159.00 is hardly in the category of cheap. I think it fails on two out of three requirements. There may or may not be something better out there. When you find it be sure and let us know.
 

Thread Starter

LEDIY

Joined Dec 2, 2016
26
I purchased one of these things originally for £40. It came with a coil rattling around the case. And was packaged with polystyrene and bubble wrap. It led me to believe it was too good to be true.

You can also put three of your 12 volt supplies in series. You just need to make sure you isolate AC and DC grounds.
I see heart ache in your future trying to parallel boost regulators that are not designed for it.
http://www.linear.com/solutions/5464
Heart ache as in disappointment or losing my house to an electrical induced inferno? I have read the article. The LT3790 looks perfect for my requirements. I will be sure to investigate how simple it would be to make my own boost converter with it.

As I understand it differences in output voltage cause a current inrush to the converters which in turn causes the components to fail on boost converters that arent designed for it. Obviously with the load having a constant current regulator this shouldnt be an issue for the LEDs themselves at the end so its more about protecting the converter's components. Im looking into current limiting in series before the booster to solve this problem. Maybe with a PPCT resettable
 
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