high-amp battery-power DC-DC voltage conversion

Hi!
I have a number of LiIon battery-powered applications with the following voltage/load power:
24V, 250W
36V, 250W
36V, 350W
48V, 350W
48V, 450W

(a.) A 12V/1.2A output is needed in each instance to run some auxiliary loads. Already experimented with putting together a voltage regulator using LM317. But this IC gives off a lot of heat even at just 180mA, considerably warming up the batt compartment, which is already near the maximum design temp. limit for the batt when the main load is running at full power; in a hot summer day I’m afraid it may melt the wire wrapping or plastic insulations. Any advice for other better alternatives which are reasonably cost-efficient?

(b.) I want to have the option of swapping around the batteries at will to run the different main loads, e.g., using a 24V battery to power a 36V load, or using a 36V battery to power a 24V load, or using a 24V battery to power a 48V load, or using a 36V battery to power a 24V load, etc. I’m thinking of building a voltage regulator, ideally, only one regulator design is built to handle all different input voltages to power the different loads. Any suggestions on ICs/schematics for a regulator design that has minimum circuit complexity and minimum heat dissipation?


Many thanks!

LM3I7 is an adjustable voltage regulator which can load max of 1.5A, the problem with these adjustable one's is that the output voltage fluctuates a lot due to changes in values of adjusting resistor and various other factors also dissipates a lot of heat. using a number of power transistor like 2N3055 in conjunction with LM317 or similar will help to load that much current without creating much heat.

Batteries you are mentioning normally comes with lots of amperes like 50, 100, 150A etc so its not at all safe to experiment unless you have a trusted circuit with carefully designed PCB with large gauge wires (very very thick which require massive soldering etc) which will be able to handle that much current, manually switching over the best option to consider in these kind of situations as a tiny short circuit can bring about a catastrophic explosion.

prince213 said:

LM3I7 is an adjustable voltage regulator which can load max of 1.5A, the problem with these adjustable one's is that the output voltage fluctuates a lot due to changes in values of adjusting resistor and various other factors also dissipates a lot of heat. using a number of power transistor like 2N3055 in conjunction with LM317 or similar will help to load that much current without creating much heat.

Click to expand...

That is a bit incorrect, having done it myself. The same amount of heat is generated, BUT spread over more devices capable of dissipating that heat. Makes sense when you think about it. When your supplying 1A@12V from an input of 24V, you must dissipate a power of 12WATTS. This dissipation is the same whether it is by one device or total of many devices.

The OP should be seeking a switch mode power supply, then the same rule does not apply.

xaccto said:

That is a bit incorrect, having done it myself. The same amount of heat is generated, BUT spread over more devices capable of dissipating that heat. Makes sense when you think about it. When your supplying 1A@12V from an input of 24V, you must dissipate a power of 12WATTS. This dissipation is the same whether it is by one device or total of many devices.

The OP should be seeking a switch mode power supply, then the same rule does not apply.

Click to expand...

I mean when power transistors are used, heat across LM317 will be lesser so this will prolong its life, also increases the stability.

The uncluttered “Typical Application” schematics shown in the datasheets for LM2672EP, LM2675EP, LM2592HV, LM2593HV look quite appealing for newbie like myself. The same datasheets also mentioned “wide input voltage range” from 8V to 40V or 60V, does that implies that when such an IC is used in a step-down regulator, that as long as the input voltage is above the output voltage, the output voltage will remain constant? Or do I have to worry about the varying battery voltage when setting the output voltage, e.g., setting the output at 13.5V to power a 12V load?
Thx

Usually adjustable voltage regulator IC's will not provide accurate results, using fixed one's is far better, but it usually comes in standard voltage ranges like 5V, 12V etc. If 12V nearly accurate regulated supply irrespective of input supply fluctuations is needed then choosing fixed one's is far better than adjustable one's.

Input unregulated input voltage need at least 2V above required voltage, i.e, for 12V DC output input = 12V+2V = ~ 14V DC or above.