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Fasttrack
07-28-2012, 01:35 PM
Well, I don't even know enough terminology to do a Google search.

Suppose I've got a 28 volt signal capable of sourcing 100 mA. I've also got a battery at 12.7 volts and 40+ amps.

What I want is to have a power supply of 28 volts capable of sourcing ~ 10 amps. Is this possible using simple (e.g. cheap) components?

Right now, I'm taking the 12.7 volt signal and chopping it up and feeding it to a flyback transformer to get my 28 volts, but the components used for this can't handle large currents. (Actually, I'm using TI's "Simple Switcher", the LM2576-adj http://www.ti.com/product/lm2576)

Stuart Br
07-28-2012, 02:06 PM
What you should be searching for is DC to DC boost converter. or DC to DC step-up. Lots of web links out there.

Fasttrack
07-28-2012, 02:14 PM
What you should be searching for is DC to DC boost converter. or DC to DC step-up. Lots of web links out there.

I have a DC-DC boost converter, but it can't handle the current. That's how I'm getting the 28 volts. I guess what I was hoping to find was some sort of arrangement of power transistors that would allow me to increase the current available at 28 volts.

Stuart Br
07-28-2012, 03:36 PM
Well I suppose the crude answer is that you need a bigger converter.. The main issue is going to handling input current needed, which will be in excess of 23A to get your 280watts output. Most commercial products seem to go to 24V input at these power levels, it's lot easier to handle higher voltages than currents.

Fasttrack
07-28-2012, 04:00 PM
Nuts. That's what I suspected. Thanks!

rdfeil
07-28-2012, 04:49 PM
Tom,

The short answer to your question is NO. To do the boost conversion you will need hefty transistors / FETs and a transformer to get to the required voltage and current then more stuff to get filtered DC....

Now for a simpler (but not necessarily cheap) solution....

I will go on the assumption that this needs to be battery powered.
You could simply series some batteries to get the required voltage and current. If 24 volts would work you simply connect 2, 12 volt auto batteries in series. If you NEED 28 volts then use 1, 12 volt battery and 2, 8 volt cart batteries in series. To get 10 amps the batteries don't need to be very large. This is simple but it will require battery chargers and depending on how long the batteries need to supply this power things may get larger and more expensive.

The next option is as said above, get a DC to DC converter with high enough ratings (28 volt at 10 amp+). There are several companies that make such an animal, ICT (check model ICT1224-15A) and others. The converters are not the cheapest piece of equipment (the one above is $225.00 +-) but they are simple and do work well.

MrSleepy
07-28-2012, 04:56 PM
There are lots of DC/DC boost converters on ebay for the car audio fraternity..

eg 24Vdc output...http://www.ebay.co.uk/itm/NEW-High-Quality-DC-DC-Step-up-Converter-500W-Watt-Input-12V-Output-24V-20A-Amp-/221067452782

They seem to have outputs ranging from 24 - 35Vdc in the 100-500W range

Rob

flylo
07-28-2012, 05:17 PM
Just what you need! All the 28V you'll ever want!
Here's the C/L ad if still up, http://southbend.craigslist.org/tls/3166129936.html if not I can post pics. It's military, looks new as it still has plastic on the panel. I assume it's some kind of welding power supply. It weighs about 500#, has 2/0 welding cable on one side, 8/4 on the other about 50' of each,3 phase I assume. 4 60amp breakers all connected, 28VDC, model jla 5592, p/n jla 05-1111, made by Spectro Sort,DC amp gaude goes to 60 amps.

Fasttrack
07-28-2012, 08:39 PM
Thanks Robin!

Actually, it doesn't have to be 28 volts on the spot. I just had a small booster already built for exciting some transducers, but thought I might be able to repurpose it. I also had a very large 1000 cca car battery here.

Looks like the easiest thing, though, is to pick up a pair of 12 volt ATV or lawnmower batteries... or maybe some sealed batteries from a UPS.

Those converters on ebay are interesting, though. Thanks MrSleepy!

Flylo - that may be a little too much weight! I want this thing to be portable ;)

J Tiers
07-29-2012, 12:36 AM
A DC-DC boost converter can be made with a small sized (but high current) mosfet..... you want mosfets for their low conduction losses, you don't have much voltage to work with.

other than that. you need only an inductor capable of the required current (whatever that is... evidently about 10A, so your inductor might need to handle 25A or so without problems. (peak current might be higher or lower, depending on inductor value and switch frequency) And a diode ditto.

This, with some control circuitry, will get you a non-isolated 28V from 12V. If you need isolation, you will have to have a transformer, along with more complicated circuitry, and that design is more complicated than a straight boost with an inductor.

A potentially useful mosfet is http://www.digikey.com/product-detail/en/IPP50N10S3L-16/IPP50N10S3L-16-ND/2081179 , although I might go with a lower on-resistance if possible. You can parallel them for lower effective on-resistance.

macona
07-29-2012, 12:36 AM
You might be able to put a couple of these in parallel:

http://www.ebay.com/itm/DC-DC-Converter-10-32V-12-35V-150W-Boost-Power-Supply-Module-Notebook-/150829920844?_trksid=p4340.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%2 6asc%3D39%26meid%3D940360587558376687%26pid%3D1000 11%26prg%3D1027%26rk%3D3%26#ht_5432wt_1361

Thats might. Some switchers do not like paralleling. Isolated each other with diodes so they dont see each other.

You either have something aircraft or military?

-Jerry

flylo
07-29-2012, 02:37 AM
I'm telling you it's portable 5-700#s worth. It's got long cords. I think i could have gotten it free. They were moving to CA, it was the last thing in the storage locker & when they saw my crane they were the happiest people I saw all day,

J Tiers
07-29-2012, 10:34 AM
You might be able to put a couple of these in parallel:

http://www.ebay.com/itm/DC-DC-Converter-10-32V-12-35V-150W-Boost-Power-Supply-Module-Notebook-/150829920844?_trksid=p4340.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%2 6asc%3D39%26meid%3D940360587558376687%26pid%3D1000 11%26prg%3D1027%26rk%3D3%26#ht_5432wt_1361

Thats might. Some switchers do not like paralleling. Isolated each other with diodes so they dont see each other.

-Jerry

Boosts are easier to parallel than anything else, since they act as current sources.

Those gizmos there are essentially exactly what I described..... probably would parallel OK, set for very slightly different voltages. The one with the slightly higher output voltage would be the only one "on" at low current, and when the output sags a little under load the other would come on.

Fasttrack
07-29-2012, 10:56 PM
Thanks guys. Never thought about putting a bunch of boost circuits in parallel.

In this case, I think a second battery is easier. I'm building a new, digital/computer controlled firing system for pyrotechnics. I currently have a 12 volt battery that I had been using and I just wondered if I could easily bump this up to 24 volts.

J Tiers
07-30-2012, 01:30 AM
Thanks guys. Never thought about putting a bunch of boost circuits in parallel.

In this case, I think a second battery is easier. I'm building a new, digital/computer controlled firing system for pyrotechnics. I currently have a 12 volt battery that I had been using and I just wondered if I could easily bump this up to 24 volts.

"bumping to 24V" is easier than 28V....

But of course two batteries can be charged in parallel and used in series, which is the simplest of all.

darryl
07-30-2012, 02:05 AM
Just had a look at that regulator chip. It has the built-in pass transistor, which is what is limiting the current output. You could continue to use the chip, but add an external transistor to boost the current capacity of the circuit. The diode would be changed to a higher current device, and the inductor would need to be made physically larger with thicker wire to handle the current. Not sure what should be done with the capacitor- JT would have the right answer for this output network.

If 24 volts or thereabouts is fine for your application, then as JT suggested the simplest way to do it is with a pair of 12v batteries. Charge in parallel and use in series- no electronics required. Often times, simplest is best.