Control Amperage

Hiyas, I was wondering if you could point me in the right direction. I was wanting to build or buy something I could control Amp input. The system would be 12 -14 v dc and I want to be able to limit the input to say... 25 - 30 amps. So if a system would naturally draw more amps I want to be able to control the system be limiting the amp input...if that is making any sense. Got any thoughts ??? tks Huchleberry

sort by: active | newest | oldest
Huchleberry....I have a controller that you are looking for. But I need to know what voltage you are using and what the min & max amperage you want. The unit is controlled by a cable/pot box...manually....send me a direct email if you want more info
twl48_1957 @yahoo.com
shane129 years ago
I have been looking for a variable amperage regulator for few days. Cant find one...last night, i put 2 inline fuse holders and plan to test output amperage tonight when i get home...dont know if a fuse regulates amperage, but will know tonight...
gmoon9 years ago
Just my own two cents...

Current limiting (as V-Man737 suggests) certainly is a form of current control, but it's not active control. I.E., the current is constant only if the source voltage and the load remain constant.

Think of it as a manual water value; it cannot sense the amount of water passing through, or the pressure of that water, and react accordingly....

For devices like electric motors, where the electrical load changes with the mechanical load and speed, current-limiting resistance would not function as constant-current source...

Depends on your use. If the supply voltage and the load are constant, then it's fine.
huchleberry (author)  gmoon9 years ago
he is using a gas engine so the amperage and the voltage would not be constant. Could I use a capacitor to limit the amount of amperage in?
Most voltage regulators can be converted to current regulators, also (check their datasheets.) This page has an LM317 based high-current regulator. Scroll down to the High Current Regulated Supply section.

It's capable of supply 15 amps, so looks like you'll have to add more power transistors in parallel (or use higher current transistors.) But that's a hefty amount of current to regulate, and a bit out of my knowledge base....

The text describes how to alter the output voltage by changing the resistor values in the voltage divider (that's a pretty massive capacitor, good luck with that...) There's a separate voltage reference for the LM317, higher than the output (marked +10, with a separate transformer coil), but that's explained, too.

One point--if you're varying the load, but holding a constant current, the output voltage has to change. It's the only way to satisfy Ohm's Law....

(There is such a beast as a current-limiting transformer, too...but I don't have any experience with 'em. And any 30 amp transformer will be expensive, by it's very nature... )
V-Man7379 years ago
Remember, V = IR
So if you are using 12-14 volts and want to modulate the amperage (I), you'll need control over the resistance (R). Controlling resistance calls for a potentiometer, and in your specific case you'll want one that provides between 1.786 to 2.5 ohms. Hmm... That doesn't seem very common...
I've heard that using a large length of wire can give you a tiny bit of resistance (the resistance you need), and sliding the place where the circuit connects with it varies the resistance. I've never tried it, though...
huchleberry (author)  V-Man7379 years ago
so If I go looking fo a potentiometer with an ohm resistance that you stated and 12 v dc . I should work for me?? sorry I'm dense sometimes .... tks huckleberry
Yes. Oops, looks like I inverted my fractions... With 12 volts steady, you'd need a 0.4 - 0.48 ohm resistor, which sounds really difficult to do. I spent about a half hour searching the 'net for a variable resistor (potentiometer) that can do that, but it seems like most of them are higher-end resistors, like between 500 and 500k ohms. Good luck finding it, and let me know if you do! And if you don't (very likely), try experimenting with the variable length of wire. Cable. 30 amps is a lot to push through something. Be careful.
huchleberry (author)  V-Man7379 years ago
I have some experience ....is there a site or book you suggest that would help me " eyes on" explain how to go about doing such a thing? A tech manual ? I have 4 yrs elect. experience on aircraft. So I not completely inapt :) tks again ,sorry for being a pain and tks ALOT for taking the time with me .
No need to double post a forum topic. Make sense, not sure how you do it, hopefully one of the electronics gurus can help, can you delete the other topic, it's pointless and wasting space...