Getting more current, sacraficing voltage
Getting more current, sacraficing voltage
(OP)
I have a system that runs on 28V and can provide 1A. I would like to run a motor using this power. However, the motor runs on 5V and between 3 and 4 A to get the torque that I need. It seems like I should be able to sacrafice some voltage and increase my available current, but I don't have any experience designing a circuit for this. What do you guys think would be the best way to go about it?





RE: Getting more current, sacraficing voltage
This must be a DC supply or is it AC? Just going by the wattage, it looks like your supply can source this power. I would see what the supply is capable of sourcing (transformer size, regulator size, or whatever the source originates from). You should also consider the conductor size (I dont believe this will be an issue but would definately check size). Also the overcurrent protection should be reviewed.
If its AC, you could use a transformer (might be hard to find one with 28V pri and 5V sec) or build a switching supply.
If its DC, you could use a regulator but it would probably be best to build a switching supply to reduce heating.
RE: Getting more current, sacraficing voltage
RE: Getting more current, sacraficing voltage
A bare 5V regulator will not increase the current as you asked.
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
RE: Getting more current, sacraficing voltage
For circuits, check www.National.com, www.micrel.com, www.ti.com. Ther are other companies as well. You might just check the TI site first as they acquired a company several years ago (Power Trends) which made modules that might meet this input/output requirement.
RE: Getting more current, sacraficing voltage
ht
It sounds to me like the supply is from a 3 pin regulator and if this is the case, you better test well. Might be better to find a 28V motor. Also, depending on the switcher, some will not start when they have a nonlinear load connected to it. I am not well versed with DC motors but I believe they are nonlinear loads just as an AC motor is (might be wrong on this, sure someone will correct me though).
Since it only has to run once and for only 2-3 seconds, this will probably mean your fine with a switcher provided you dont take out the supply you have in the meantime. I just wanted you to be aware of the fine line you may be walking with the supply they have given you.
RE: Getting more current, sacraficing voltage
Use the 28v at 1A max to slowly charge a supercap (perhaps 10 or 20F) to 5 volts. The supercap can easily supply 4A for several seconds. This assumes that you have time (30-60 seconds) to charge the supercap.
"...and only once."
Or use a separate battery.
RE: Getting more current, sacraficing voltage
RE: Getting more current, sacraficing voltage
RE: Getting more current, sacraficing voltage
RE: Getting more current, sacraficing voltage
The tricky bit will be the 5 volts versus the common 2.3 volt rating of many supercaps. Even two in series is only 4.6v, so you'll need three in series and that means you have to buy at least 36F at 2.3v to reach 12F at 6.9v. It would be very much worth searching for one with a 5v rating.
RE: Getting more current, sacraficing voltage
As Comcokid says, have a look at the TI modules the former Power Trends ones. They're using TI's buck converters, of course, only leaving the input and output caps to add, and maybe some ferrites or chokes for the noise.
RE: Getting more current, sacraficing voltage
http://www.maxim-ic.com/PowerSupplies.cfm
And supercaps can discharge at incredibly high currents. They really are super.....
A
RE: Getting more current, sacraficing voltage
Yes - they're good for high currents.