Newbie question, Current limiting.

[Desp]

Unfortunately I know very little about electronics (wish I knew more) but I'm trying to limit amperage on a power supply while keeping voltage constant. I'm working with 12v and 100+ amps. I'm basically going to be shorting it out so I need a way to control the amount so I don't burn up my power supply. Cheap suggestions?

 

[Nigel Goodwin]

You can't really limit current without having some effect on the voltage.

But you really need to give more details of what you're trying to do.

Basically though you're probably looking at a very low resistance, very high wattage, resistor.

 

[Desp]

Well I wanted to use it for anodizing and or welding, both which can have the effect of an open circuit with very little to no resistance. With using the welding idea I'd need some way to limit the current and vary it on the fly. So by putting low resistant high wattage resistors in line it'd only change the voltage by a small amount, but control the current?

 

[Nigel Goodwin]

Well I wanted to use it for anodizing and or welding, both which can have the effect of an open circuit with very little to no resistance. With using the welding idea I'd need some way to limit the current and vary it on the fly. So by putting low resistant high wattage resistors in line it'd only change the voltage by a small amount, but control the current?

It'll drop more and more voltage as the current increases, but the voltage probably doesn't matter, it's the current that does.

 

[CheapSlider]

Back to my favourite - light bulbs.

A light bulb makes a good current limiter. Its filament has a very low resistance when cold which increases as it gets warmer (IE the current increases).

An advantage of using bulbs is that you can see how much the current is being limited by the brightness of the bulbs.


At 12 Volts at 100 watt headlight bulb will take a max of just over 8 Amps (100/12= 8.333)
A 55 watt bulb 4.6 Amps. (55/12=4.583).

The bulb(s) are connected in series with the load and switched in or out - the more bulbs switched in the more current.

 

[Desp]

Back to my favourite - light bulbs.

A light bulb makes a good current limiter. Its filament has a very low resistance when cold which increases as it gets warmer (IE the current increases).

An advantage of using bulbs is that you can see how much the current is being limited by the brightness of the bulbs.


At 12 Volts at 100 watt headlight bulb will take a max of just over 8 Amps (100/12= 8.333)
A 55 watt bulb 4.6 Amps. (55/12=4.583).

The bulb(s) are connected in series with the load and switched in or out - the more bulbs switched in the more current.

So with say 20, 55w 12v light bulbs in series that would have a total draw of 92A, and I could take it down in 4.6A increments by switching one bulb out of the series at a time. If that is correct then I understand what you're saying. It's beautifully simple but is there a more practical way of doing it?

 

[Nigel Goodwin]

I think he means in parallel, not series - essentially the bulbs are used as resistors.