DC step up 24v to 48v at 15amps


Thread Starter


I'm trying to convert 24v to 48v at 10amps. My source is two car batteries.
<P>I don't quite understand what it is you are asking. However, in order to get 48v you'll need 4 car batteries connected in series, plus to minus.</P>

+ 48v -

| |
| |
+----------------+ +---------------+
| |
| |
+--+ +------+ +-----+ +-----+ +--+
| | | | | | | |
+^---^+ +^---^+ +^---^+ +^---^+
| + - | | + - | | + - | | + - |
| 12v | | 12v | | 12v | | 12v |
+-----+ +-----+ -----+ +-----+

<P>[email protected]</P>


You can do just what the othe guy said of conecting 4 batteries in series, if you can only use 2 batteries 12 that form a 24 volt one, then the only way is to use a transformer with a turn ratio 2:1, make sure tha transformer is at
least 48V*10Amp=480 watts, and also, your batteries must have a current capacity of at least 20 amps
Your question does'nt quite explain what you want.

There is nothing known as dc to dc voltage conversion to get a higher voltage directly.

You can either used a down convertor, which takes in a higher voltage and gives out a lower voltage.
You can use a voltage doubler, or tripler, which can provide you a higher voltage by using capacitors and diodes. But the source must be AC,
and it has a limitation of the amount of current you can draw.
you can use voltage doubler IC's which provide you double the voltage supplied,...but something like 10-15 amps of current..i dont know of
an ic with that kind of current carrying capacity available in the market.
as shown by Terrance, you can add up any # of bateries in series, and have as much voltage and current required. Many telephone exchanges
have this arrangement as a worst case backup plan.

...so whats the application btw?

Michael R. Batchelor

10 amps (or is it 15 like the subject says?) is a lot of current to be plowing through a DC-DC converter. Since you're using two car batteries I would suspect your doing this on the cheap. Probably the cheapest way you're going to find is to get two more car batteries and use 4 batteries instead.

Michael R. Batchelor - Industrial Informatics & Instrumentation, Inc.
Linux is like a wigwam...
No windows, no gates.
Apache inside.

Curt Wuollet

Quite a few of the switching power supply manufacturers also make DC-DC converters. 48V is common for telecomm equipment. You shouldn't
have a lot of trouble finding one for this. What you probably really want is a 48V supply with a 9-30 VDC input. Hit google with 750W DC-DC converter and see what pops up. I did, and got pages of hits.



Michael R. Batchelor

> if you cand only use 2 batteries 12 that form a 24 volt one, then
> the only way is to use a transformer with a turn ratio 2:1, make sure tha
> transformer is at least 48V*10Amp=480 watts, and also, your batteries must
> have a current capacity of at leat 20 amps

I'd like to buy the patent on those transformers to convert DC to DC.

Michael R. Batchelor - Industrial Informatics & Instrumentation, Inc.
Linux is like a wigwam...
No windows, no gates.
Apache inside.

Peter Whalley


DO NOT connect a transformer across your batteries. This creates a race condition where the transformer races the batteries to see which one will explode first! Exploding transformers are very smelly. Exploding batteries spray acid everywhere.

Transformers are designed for operation on AC supplies. Batteries are DC. They are not compatible.

If you are stuck with only 2 x 12 volt batteries then you would need a DC to DC converter and a big one. Try a Google search.


Peter Whalley
This is on the on the lighter side:
Caution and Hint:
Run away as soon as you connect the transformer to the batteries. Also if you have miniature remote control to switch the connection, Eureka!
Boom! you have invented a remote controlled explosive device.
Hi List,

DC transformers really do exist. I know it's still not something you can buy at Radio Shack, but here are some links on how it works:


Vladimir Zyubin probably knows the guy who wrote this one (Adobe Acrobat file):

Have fun!

Willy Smith
Numatics, Inc.
Costa Rica
Hi Willy

I stand corrected and somewhat chagrined. I suspect these may be beyond the capabilities of the requester however. The switching converter route seems considerably more practical than most suggested.


I have wound wire around a tube, created a spring like object, then, taken one end of the wire and connected it to the postive and one to the negative portion of 4 C batteries and it was capable of projecting a metal object through it at a notable velocity. This is the process of creating EMF (Electro Motive Force) which is the basis of electric generators/motors, transformers, inductors, and anything that holds a magnetic charge based on EMF.

All of this brings me to the question of why thermal runaway would happen when / if a transformer became the only load across 2 batteries in parallel? Especially if the requestor took care to include a small high watt capable resistor to take load in the series connection of the transformer.

I may not know vector matrice physics in creating DC-DC Transformation (using EMF!) with superconductive thin materials....but I do have an outstanding basic knowlege of AC/DC Theory, EMF, Generators and Motors.

Connecting a 2:1 transformer not only seems logical, but is it that it creates a STG by having no load? The same would happen with AC. Or is the alternating collapsing lines of flux that create the EMF needed on the opposite windings for the secondary tap of the transformer to produce the current needed. And if that is the case, why wouldn't a different angled winding yield the same results with DC. As we well know, current will be generated in a single wire when the wire is placed at a 90 degree angle cutting the lines of flux of a magnetic field.

Please let me know.

Dustin Juliano
dustinjuliano @yahoo.com

Steven Eyberg

Why shouldn't you connect a transformer across a DC source? well, take a look at exactly what a transformer is... basically just a long conductor wound into loops, so that its electric field lines cut those of another isolated coil (secondary coil), and also its own coils. so, connecting this conductor across a DC source capable of supplying a very large current for a couple of seconds (your car/truck/whatever battery), will result in a huge amount of power being dissipated, causing your thermal runaway. a standard car battery is capable of supplying upwards of 600 amps for about 30 seconds (CCA). Power given as P = VIt, thats 12 x 600 x 30 = 216 000W of power! Besides the fact that you'll be dissipating enough power to heat my tiny flat for a year, if you know your theory for transformers, you'll know that they need a changing electromagnetic field to function. alternating current is the only way to provide this changing field. Go try it out with a penlight battery and a transformer. you'll get a short pulse across the secondary coil of the transformer, and then the voltage will fall to 0V. the only reason you still have hands left after your small experiment with the coil shooting projectiles is that the battery you're using is only capable of supplying small currents.
I stand corrected. :p I was confused on how mutual inductance worked and your right a changing magnet field OR a moving conductor through that magnetic field must take place.

I recently made an inverter using a 555 timer and a small isolation transformer. My new battle is to tweak its freq and current by removing or adding resistance, and finding a good boost transformer to do the trick.

If you can buy a 2000w continous supply inverter for your car, my only question is what is the difference between a 150w inverter for a car and a 2000w inverter for the car.. is it the transformer, added capacators, inductors? All three?

Dustin Juliano
A different angled winding wouldn't help because:
As you mentioned yourself, it must be cutting the lines of flux. IE, in motion.
It is the change in flux that produces the EMF, which, by the way, is Voltage not mechanical motion. When you connect a transformer to DC you will get a voltage for a short period of time. The current rises exponentially and when it
approaches the value limited by the resistance in the circuit, the voltage has gone away. To use a transformer with DC, we switch the DC at a frequency higher than the time for the voltage to decay. For efficiency, this is often done with
a center tapped circuit or an H bridge to reverse the voltage. This square wave is then rectified and filtered and you have a rudimentary DC-DC converter.
As an aside, since after the short interval, the current is only limited by the resistance in the circuit, 120 VDC would fry a 120 VAC winding. For AC the current is limited primarily by the inductive reactance, which is quite high in
practical transformers. This is greatly simplified, real world magnetics are complex networks of ideal and parasitic quantities.