DC-DC circuit

LarryR

I'm building a custom platform using Parallax motors and controllers, and need to find a DC-DC converter circuit, or module (?).

The power supply (NiMH battery pack @ 4200mAH) is 12V.· The motors (2) are 7.2V, and draw .27A current each under no load,·4.8A each at stall.
Might anyone have a DC-DC converter circuit diagram which would be applicable for my use?

If a single DC-DC converter circuit is used for the motors would it have to handle up to ~10A, in case both motors are stalled, or maybe even during start-up?· Might it be better to have separate DC-DC circuits for each motor?

Thanks much!
·

Mike Green

That's a difficult problem. You'd need a switching converter that can handle the maximum stall current. You would be much better off to use a 7.2V power supply to begin with.

LarryR

Thank you Mike.· If I use a 7.2V battery pack, would·the voltage not almost immediately drop below 7.2V during use?· My thinking was to·use a 12V battery pack, step down the voltage to 7.2V, then would have more-stable voltage over·time.· Also, could step down to other voltages for other devices, like for an audio amp.· Thanks again.· -Larry

Peter KG6LSE

Now this is "Just Me"

But If I made this device and absolutely needed to make sure the motors never saw over there rated voltage I would run the full 12V to the motors FETS and Use the same PWM system to control the motors "on" "off" and "throttle" to also actively read the batt and adjust the PWM offset to the motors power ..

EG lest just say you are using a 10 V Batt and you want a 100% power Signal to go to the Drive motors .
This would equal 72% PWM

Let a math function scale that to all was = 7.2 V

But if the batt dropped to lets say 9 V the PWM amount that equaled " FULL ON" would go up to compensate...

Its Just some ADC inputs and some math ..

Or evan with out a batt sense you could still scale the PWM drive to never excced the 7.2V margin....

Mind you I run my roomba's 14.4V motors on 36V all the time with no heat issues ..

IMHO running 12 flat in to a 7.2 motor is not going to kill it as long as it can't over speed and tear up the armature .


I would put a Reg on the logic side to prevent brown outs tho ..


Peter KG6LSE.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"Carpe Ducktum" "seize the tape!!"
peterthethinker.com/tesla/Venom/Venom.html
Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway. —Tanenbaum, Andrew S.
LOL