# Hobby RC car project: Voltage regulator, 8.4v to 6v DC, 5A draw max

#### devilchrist

Joined Apr 17, 2009
2
So I spend $20 bucks on this cheap voltage regulator and it seems to have enough noise to affect the Radio signal quite significantly. to a point with car becomes uncontrollable at +10ft. So I want to make a low noise regulator. Was thinking about running 3 linear regulator's in parallel to handle the load. Here's is what I have to work with. Battery source is two Li-Ion batteries in creating a 8.4v full charge, 7.2v working. Need the voltage dropped to 6v-6.5v with no more than 6.5v at any time. Radio equipment seems to be EXTREMELY suceptable to noise/ripple. Any suggestions would be appreciated, also car mostly aluminum so i can attach regulators to it as a giant heat sink if necessary. Also, I would like to have a LED indicator that lights up when input voltage drops below 6V. it that possible to integrate without too much trouble? #### bertus Joined Apr 5, 2008 19,944 Hello, You could also make a regulator with a power opamp like the LM12C. This can be used like a normal opamp but it has the capability to drive 10 A. See the datasheet that I posted in this thread : http://forum.allaboutcircuits.com/showthread.php?t=22221 Greetings, Bertus #### jpanhalt Joined Jan 18, 2008 7,697 Is this for the radios (i.e., a BEC)? If so, yes you can use a linear regulator, but I would suggest one regulator with a bypass transistor rather than dealing with trying to put three regulators in parallel. If you check the datasheet for the LM317 and most similar regulators, it will show what I am referring too for increasing current handling. In any event, at 5A, you are going to have a fair bit of heat to get rid of. I use Castle Creations' switching regulator with 3S LiPo at 72 MHz and have had no problems. Apparently, some earlier versions of hobby switching regulators did have problems with radio interference. The CC was about$25 last time I checked.

Re: sensitivity to interference. When was the last time you had your transmitter and receiver checked? Crystals drift and after 5 to 7 years, you can be pretty far off frequency. It happened to me, so I get mine retuned and certified about every 2 to 3 years.

John

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#### devilchrist

Joined Apr 17, 2009
2
truck is new.. but possible that it's been sitting in storage for a while i guess.

#### jpanhalt

Joined Jan 18, 2008
7,697
Is the transmitter new too? Is it narrow band (75 MHz in the USA) or the cheaper citizens band at 27 MHz? Are you sure you need 5A?

If it is narrow band and you truly need 5A, my first recommendation would be to get a decent switching supply, as mentioned above. Have you tried moving the regulator away from the receiver?

If you want to use a linear regulator and can't buy one for that level of power, then you need to decide whether you want to use three in parallel or use a pass transistor. The datasheet for the LM317 shows how to do parallel voltage regulators. The small value resistors (0.2 ohm) on the output of each regulator are necessary. Alternatively, you can use a higher power pass transistor. An example is shown also in the LM317 datasheet, but a clearer example is in the datasheet for the MC7806, around p. 21.

Finally, do you have room for a separate, 4 or 5 cell NiMH pack for the electronics?

You can get datasheets at: http://www.alldatasheet.com/view.jsp?Searchword

John