Author Topic: Dumb question on power supply  (Read 861 times)

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Offline J4e8a16nTopic starter

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    • Jean Pierre Daviau
Dumb question on power supply
« on: February 20, 2018, 12:43:41 pm »
Hi,


If I put a 1 ohm  motor  across the voltage wire of a regulated power supply

1-  If I set the voltage to 3 volts and the amps at 4 amps  the motor will overcome one or the other

2-  If I put the amps at 3 amps and the voltage at 4:  the motor will overcome one or the other


What is the use of a preset amperage?

I can control the voltage  OR the amperage, not both.

Dumb guy
Equipment Fluke, PSup..5-30V 3.4A, Owon SDS7102, Victor SGenerator,
Isn't this suppose to be a technical and exact science?
 

Offline Nerull

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Re: Dumb question on power supply
« Reply #1 on: February 20, 2018, 12:47:53 pm »
What happens when you spend a few hours breadboarding a new circuit and you accidentally miswire something, creating a short, and then you connect this circuit to a unregulated supply with no current limit?

What happens when you want to charge a lithium ion battery, which needs an inital charge at some given constant current and then needs a final slow charge at a given constant voltage?

And of course you can't control voltage and amperage at the same time. That's physics. Think ohms law - for a given resistance and voltage, current is fixed. There's no way you can force a circuit to pass more or less current than ohms law allows, and the same with voltage at a given current.
« Last Edit: February 20, 2018, 12:51:53 pm by Nerull »
 
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Offline andtfoot

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Re: Dumb question on power supply
« Reply #2 on: February 20, 2018, 12:53:20 pm »
In terms of a lab power supply when setting the voltage and current:
- The supply will keep a constant voltage as long as the current is below the setting
- When the current hits the set limit, the supply will keep that current constant. It will do this by dropping the voltage to suit.

So for your examples (assuming a purely resistive load):
1 - voltage will be kept at 3V, current then is 3A (below the limit, so supply is in constant voltage mode)
2 - voltage will be dropped down to 3V, to keep the current at 3A (supply is in constant current mode)

Just think Ohm's law and it might make more sense.
 
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