Current control circuit power supply

Thread Starter

potatofarmer

Joined Jan 7, 2022
10
I have a 5 VDC 60 amp power supply. I cannot control amps, is there a circuit I can make to go from zero amps up to about 20 amps. I have built a couple of circuits to no avail, can anyone help me or offer suggestions, I would certainly appreciate any help, Thank you
 

dendad

Joined Feb 20, 2016
4,110
Do you want a current limit facility, or be able to drive a set current into your load?
As it is, the amps will be a function of the load resistance.
A power supply can control the voltage (fixed voltage) OR the current (constant current) over variable load, but not both at the same time.
So, what are you actually trying to do?
What is the load?
 

Thread Starter

potatofarmer

Joined Jan 7, 2022
10
Do you want a current limit facility, or be able to drive a set current into your load?
As it is, the amps will be a function of the load resistance.
A power supply can control the voltage (fixed voltage) OR the current (constant current) over variable load, but not both at the same time.
So, what are you actually trying to do?
What is the load?
Drive a set current into load, maintain constant current
 

MrChips

Joined Oct 2, 2009
25,919
It may be difficult to do that with a 5V supply.
Ohm's law applies. What is the resistance of your load?

20A @ 5V requires R = V / I = 5V / 20A = 0.25Ω

To have 0-20A from a 5V supply requires a load that is 0.25Ω max, i.e. it has to be almost a dead short.
 

MrChips

Joined Oct 2, 2009
25,919
LoeQCab this is exactly what I was looking for, I already got my 5 volts this looks like adjustable amps, I forgot to mention this is for a electrolysis solution will it still work, Thank you
You are very unlikely to get below 1Ω in electrolysis solution.
 

Thread Starter

potatofarmer

Joined Jan 7, 2022
10
It may be difficult to do that with a 5V supply.
Ohm's law applies. What is the resistance of your load?

20A @ 5V requires R = V / I = 5V / 20A = 0.25Ω

To have 0-20A from a 5V supply requires a load that is 0.25Ω max, i.e. it has to be almost a dead short.
I have another supply now that does that 5 VDC & 70 amps both constant and adjustable, but this other supply is 5 VDC out constant amps run wild
 

MrChips

Joined Oct 2, 2009
25,919
Think Ohm's Law.

Just for example, suppose the resistance is 1Ω.
In order to supply 20A you would need a 20V supply.

If the resistancs is 10Ω, you would need a 200V supply in order to deliver 20A.

5V does not cut it.
 

Thread Starter

potatofarmer

Joined Jan 7, 2022
10
Think Ohm's Law.

Just for example, suppose the resistance is 1Ω.
In order to supply 20A you would need a 20V supply.

If the resistancs is 10Ω, you would need a 200V supply in order to deliver 20A.

5V does not cut it.
On my one supply I have been running 5 VDC. 20 amps both constant, for 1 week tomorrow morning
 

LowQCab

Joined Nov 6, 2012
1,914
LoeQCab this is exactly what I was looking for, I already got my 5 volts this looks like adjustable amps, I forgot to mention this is for a electrolysis solution will it still work, Thank you
It will give complete control if your Load can actually pull more than ~10-Amps at 5-Volts.
Make the Current-Sense-Resistor 0.1-Ohms to try to get
the maximum Current possible with this type of Circuit.
If ~15 or so Amps is not enough, a Hall-Sensor-type Current-Sensor will be required,
but its not difficult to make that change.
.
.
.
 

Thread Starter

potatofarmer

Joined Jan 7, 2022
10
Perhaps you are using a special electrolyte and size of tank that gives a very low resistance.
@L NaCL or KCL it does'nt matter both work well, I just wanted to put a control on this other supply, I did not realize it was that big of a problem, but live and learn
 

MrChips

Joined Oct 2, 2009
25,919
Resistance is given as

R = ρ x d / A

where R is resistance in ohms
ρ = resistivity in ohm-m
d = plate separation
A = plate area

The resistivity of saturated NaCl at 25°C is about 5 ohm-cm.
 
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