High Current Controller

Thread Starter

DC_Kid

Joined Feb 25, 2008
794
looking for a crude way to do current control from about 10-40A of low vDC (12-24v marine battery) or 120/240vAC(60Hz).
i need to lab up a test using some #14 NM-B wire, basically measuring wire temp vs amps.

basically looking to short a piece of #14 to the power supply, but control the amps, etc.

ideas?
 
Last edited:

mcgyvr

Joined Oct 15, 2009
5,394
#1- why? wire gauges are already defined and standards exist for proper sizing based on current through the wire.

#2- Just build/rent/buy a load bank using resistors/lightbulbs/heating elements or whatever

and 14 AWG is NOT suitable for 40 Amps.. 20A max
See NEC table 310.16 (or 310.17 for free air applications)
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
794
ah, my lab testing does have to do with NEC ampacity #'s (which are partially derived from Neher–McGrath). its too complicated to explain here in detail.

this post is a Q around a current controller, variable would be nice, fixed also works as long as i can swap a component to get different currents, etc.

so make a load bank using a bunch 500w halogen sticks? that would work as i could use incrementals to get the between currents. i can then use my amp clamp to get accurate amps reading. sounds simple and crude.

was also wondering about something crude using triac, etc.
 

#12

Joined Nov 30, 2010
18,162
Work with the obvious. I think I saw 65 watt headlights. That's about 5 amps per bulb on a 12 volt source.
Not cheap? Try a junque yard.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
794
i can use the T3 halogen sticks, 240vAC 1kW each. i can just stack them, etc. this can get be the load i need for testing. $32 for ten of them.
 

mcgyvr

Joined Oct 15, 2009
5,394
ah, my lab testing does have to do with NEC ampacity #'s (which are partially derived from Neher–McGrath). its too complicated to explain here in detail.
I'd love to know just a bit of detail.. curiosity
NM-B wire wouldn't be used inside someones product and no building code inspector (AHJ) is going to disregard standards based on your lab testing so I can't possibly imagine why you would need to test it for anything..
 

ronv

Joined Nov 12, 2008
3,770
looking for a crude way to do current control from about 10-40A of low vDC (12-24v marine battery) or 120/240vAC(60Hz).
i need to lab up a test using some #14 NM-B wire, basically measuring wire temp vs amps.

basically looking to short a piece of #14 to the power supply, but control the amps, etc.

ideas?
When you say short. How short?
Important only because what isn't dissipated in the wire is dissipated in the device.
 

AnalogKid

Joined Aug 1, 2013
8,157
Light bulbs work well if you don't need better than 5% or 10% accuracy. For better than that you need a true control loop.

If you search for current regulator circuit you will find many schematics that cook down to 2 or 3 basic approaches. All of them rely on a current sense shunt resistor. A bank of transistors to handle 40 A is relatively easy, as is a large heatsink with a fan (you don't say how long each test runs). The expensive part is a 40 A shunt that is accurate over temperature; its error usually swamps all other error sources in the circuit.

Another approach is to use a closed loop Hall effect sensor.

ak
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
794
well, i switched the setup over to a 120vac 20A variac feeding a large microwave xfrmer (mot) where secondary has been removed and wound with a few turns of large wire.
 
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