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Current control.

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Doctore

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Hi, I have to build circuit that will control current(current limiting) with display that show adjusted amperage via potentiometer and display with actual current.
Parameters:
-Voltage <30VDC
-Amperage, hmm, I want about 80Amps but if this circuit will be big, ameprage can be smaller to optimize sizes/costs.
Any suggestions?
 
80a is a lot of current, what do you intend on controlling.
PWM might be the way to go as disspation will be much much less, with a linera setup the heatsink might well swamp the rest of the project.
Also with linear techniques noise can be an issue.
 
OK, maybe a switching controller chip is the way to go, such as a tl494, and some seperate mosfets and drivers with a current limit circuit using the '494's op amps, there are several examples of various smps chips used for constant current led drivers, maybe you could upscale something
 
Upscale means increase the scale, raise to higher level, in context, take a design and make it better to achieve what you want it to do
 
What do you want to happen when it reaches the current limit?
In other words, you could drop the voltage to maintain the current or maybe you want to shut it off?
 
Wilksey got it in one.

Take a design rated for say 2 amps and increase it to what you want.
80 amps however may involve some special techniques, such as mosfet drivers and maybe a current transformer (instead of a sense resistor).
 
Meybe I tell what I want to do with PSU and this circuit.
I want to build 30V/80A bench PS using these two 15V/90A PSU in series.
I know how to adjust output voltage in these PSU's, but I have to make circuit that control output current.
So if I set eg. 50Amps and receiving device wan't to get eg. 300A, I want to still have 50V on output, no more.
And I hope this will don't make too much heat, actually I have to use two huge 15W fans for only these PSU's :D
 
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So if I set eg. 50Amps and receiving device wan't to get eg. 300A, I want to still have 50V on output, no more.
And I hope this will don't make too much heat, actually I have to use two huge 15W fans for only these PSU's :D
Do you mean you want the output limited to 50A (not 50V)? If you limit the amps then the voltage has to drop.

A linear current limit can generate a great deal of heat, equal to the voltage drop across the limiter times the current limit value.
 
A linear current limit can generate a great deal of heat, equal to the voltage drop across the limiter times the current limit value.
I would like to avoid this...
There are no other methods?

What about this what said pepper?
OK, maybe a switching controller chip is the way to go, such as a tl494, and some seperate mosfets and drivers with a current limit circuit using the '494's op amps





Take a design rated for say 2 amps and increase it to what you want.
I think that most of these low-power in internet are not efficent, so increasing this I get big amount of heat...

Do you mean you want the output limited to 50A
I want adjust/set amperage what I want and maximum is 80A

EG.:
I set output to 20A max. connecting device to PS>device want to get 15A, so flowwing current is 15A, but I connect other device what want to get eg. 22A so MY circuit limiting this to 20A I set previously.
 
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What Pepper talks about is how your big supply works. The problem is that it is trying to maintain constant voltage, not limit current. Do you have a schematic of your big supplies. They might be able to be modified, but it would not be easy. The only other way I can think of is a linear current limiter and that would create a lot of heat. Water cooled again, I think.
 
A linear current limit can generate a great deal of heat, equal to the voltage drop across the limiter times the current limit value.
I would like to avoid this...
There are no other methods?
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To minimize power you could go to a hiccup (switching) current limiter. That cuts off the power for a second or two and then reapplies the power. If the current is still too high, it again rapidly cuts off the power. It keeps repeating this cycle as long as the current is higher than the limit setting.
 
Your supplies probably already have current limiting built in set to the max rated current for the supply itself. This will protect the supplies against short circuits.

Adjustable current is a hole other thing and may not be that easy to do.
I most cases its just as easy to make a hole new supply as it is to add it to an existing supply.
Thats why you can not find any good info on the World wide web about doing this, its just not worth it.
Do you really want to go through all the time and money to do it?

Really need to try and modify your existing supply if its posible.
Do you have the schematics? or model number?
 
Current limit isnt much more difficult with switchers than regulating voltage, and a large supply like that 90% efficiency or about that is doable, however dealing with such high currents requires a level of expertise.

Modding the original supplies to have adjustable current limit is probably a good place to start.
 
Yes, Yes, Yes, these serwer PSU have build-in current limiting for redundant systems, if we want to use two of these in parallel we have to connect in both, "Current Share" pin that showing voltage depend on load, eg. 0A/300mV-CS, 10A/1v etc...
Moding this PSU for current limiting is the best choice, I aggre this what you tell guys, BUT WHEN I START TOPIC ABOUT MODING THIS PSU ANYONE HELP ME!
But this can be hard to do, I dont have any schematics and second PCB in this PSU, that is controlling PSU(V,A,W/P,OVP,OLP etc.), named sometimes "Daughterboard" is made from 3-4 layer PCB!
I can make only simplified schematics of some parts of PCB, excluding daughterboard(1-2 layers invisible).
This PSU is "086GNR" or "ATSN MODEL 7000245" PSU used in 6650 Dell Servers.
Photo of main PCB I take:
6504521100_1388602109.jpg


Image don't showing: daughetrboard, two fans, 220v filtering PCB with inductors/caps, case and two diodes showing existing 220V
Under biggest black heatsing are soldered on bottom, schottky rectifiers, and output caps/inductors on PCB.
If this is need I can give transformer names, there are three, small for 3V3 line and two bigger connected in parallel for 12V line.
 
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The daughter board probably has the controller chip on it, can you see what it is?
There is a chance that the whole thing could be controlled using discrete circuitry, in which case things are difficult.
 
3xLM393, 358, 358A, 5x339, 2xLM324AD, 2xUC3525ADW, ATMEL252 24C02N and in transistor package 3xZVN4206
Quality of this photo is low, I will try to rent nikon 3200...
daughterboard.jpg
 
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