Current limiting as a Variable Resistor

[anon86]

Hi guys,

Im currently trying to design a power supply which is capable of simulating a solar cell. This basically means simulating the voltage-current characteristic (which looks like a constant current over an initial range of voltages to a threshold where the current drops down quickly to zero).

I have done some research as well as receiving plenty of advice and have decided to connect a variable voltage source (to give the ability to simulate several types of cells theoretically) with a current limiting circuit.

The current limiting circuit needs to be able to be adjusted via a microcontroller to give a range of voltages (thus simulating a variable resistor). I have been struggling with simulations and was wondering if there was any easy solution for the current limiting that anyone knew?

I have a very limited understanding of this type of circuit so any help would be greatly appreciated. Cheers.

 

[on7nh]

i am searshing for a similar item
han you found someting?

Carl

 

[dknguyen]

THe LM317 voltage regulator can also be wired up as a current source...see it's datasheet to find out how.

But current limiting tends to be done by measuring the voltage drop across a current sense resistor using a comparator or ADC along with microcontroller code (seems a bit extravagant for what you need, especially since it's so low power).

 

[on7nh]

Lm317 is possible,
my problem is, that i need a Current-limiter in with a maximum curent of 160 Amps.....

i was thinking to make this using switching technology....

 

[blueroomelectronics]

At a 160Amps you'd probably be better off just to buy a commercial regulator for your very expensive solar array.

 

[on7nh]

it is not for a solar array, but for connecting the neutral on a power transformer to earth....

 

[Hero999]

Please expand more.

The electrical codes state that the neutral can only be connected to eath at one place: the supply.

To answer your other question: it's probably far cheaper to integrate the current source into the power supply.

If you want an off the shelf solution, you can buy laboratory power supplies which can be controlled from a PC. The output voltage and current limit can both be computer controlled, all you need to do is get one with an open protocol and right the software.

 

[on7nh]

in the area where i live, there are a lot of power transformers station where the neutral is not grounded, (transformers 3*230volt sec without neutral)

the power company like to generate a neutral en ground it...
this is easy to do with e Y transformer.
th idea is to build smal Y transformers, max 25 ams/phase and ground them

but if there is a failure , we like to limit the Ground Current for safety
(pls do not view this local... it is for use over a larger area)

 

[blueroomelectronics]

I would contact a local electrician about the code requirements for such things.

 

[on7nh]

Bill...
plz read my answer again, after this, read it again...
I Am dealing with the power compagny....They are searching for this.....

A local oulet-electricial d'ont untherstand the aerting tachnology of power stations (dealing with 20,15 or 10KV)
thanks

 

[Hero999]

The neutral is normally taken to earth on low voltage supplies (LV is defined as <1kV AC or 1.5kVDC) because it prevents the supply from floating at a high voltage.

Extra low voltage (ELV is defined as <50VAC or 120VDC) supplies are often left floating (not bonded to earth) because it reduces the risk of electric shock.

You can use an isolation transformer and connect the neutral to ground if you like but normally the whole point of an isolation transformer is not to have the neutral bonded for safety reasons.

Use a circuit breaker or fuse to limit the current by disconnecting the supply if there is an overload.