Author Topic: need programmable resistor  (Read 895 times)

0 Members and 1 Guest are viewing this topic.

Offline AdminTopic starter

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
need programmable resistor
« on: June 27, 2011, 09:49:17 AM »
I was tasked with putting together 24 potentiostats (programmable resistors) to control voltages across 24 'magic batteries'. This is one single system - not independent systems.

These 'magic batteries' (I can't talk about them) have an optimal voltage, yet the voltage changes given environmental influences, so they must be shorted with a resistor to keep the voltage constant.

The typical resistance required is under 100 ohms.

I have a list of ideas on how to do this, but they are all over-complex and not very scalable . . . so I'm looking for other ideas from anyone familiar with potentiostats.


edit: a scientist on my team decided < 100 ohms is better
« Last Edit: June 27, 2011, 12:29:58 PM by Admin »

Offline waltr

  • Supreme Robot
  • *****
  • Posts: 1,939
  • Helpful? 98
Re: need programmable resistor
« Reply #1 on: June 27, 2011, 01:19:29 PM »
I'm thinking of a MOSFET, variable resistance, controlled with a feed-back circuit.
How much current does the "<100 Ohm resistor" need to pass?

Offline AdminTopic starter

  • Administrator
  • Supreme Robot
  • *****
  • Posts: 11,658
  • Helpful? 169
    • Society of Robots
Re: need programmable resistor
« Reply #2 on: June 27, 2011, 01:48:20 PM »
The MOSFET + resistor idea was the first thing I thought of, but having 24 of them doing this at the same time makes it challenging. More importantly, it really complicates current measurement when it's an on/off PWM (I forgot to mention that current must also be measured). The scientists on the project don't [yet] know what a PWM'd short, or capacitors, would do to the batteries.

How much current does the "<100 Ohm resistor" need to pass?
Current varies, but it'll be under 100mA.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: need programmable resistor
« Reply #3 on: June 27, 2011, 03:12:58 PM »
Hi,

These 'magic batteries' (I can't talk about them) have an optimal voltage, yet the voltage changes given environmental influences, so they must be shorted with a resistor to keep the voltage constant.

The typical resistance required is under 100 ohms.
A MOSFET controlled by a high gain rail-rail op-amp, where the the battery voltage is compared to a reference voltage would be able to keep the voltage pretty constant.
If a power op-amp is used, the MOSFET isn't needed.
This will be linear (i.e. not on/off or PWM but a linear).

What voltage is available to run the circuit?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


Get Your Ad Here

data_list