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So for an Electric car team I am on, we need isolation between all high voltage and low voltage components. That being said, for the low voltage side, we need to take the battery pack voltage (0V to 300V) and change it into a 0-12V analog signal. Without isolation, this could easily be done with a voltage divider. However, when we have to isolate the two grounds it makes it a lot harder. Any ideas on the best way to accomplish this? Thanks for the help

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    \$\begingroup\$ Depending on the isolation requirement and accuracy requirement, there are numerous optocouplers and transformer-based products designed to transfer analog values across isolation barriers. \$\endgroup\$ – The Photon Apr 5 '16 at 20:43
  • \$\begingroup\$ Please do some research and be more specific (part of the rules), come up with several ways you think this could be done and then ask the question. Also, provide more info about your problem. Keep in mind we arn't going to design anything for you. There are a number of ways to do this, \$\endgroup\$ – Voltage Spike Apr 5 '16 at 21:45
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An easy way to do it would be to PWM encode the HV battery voltage, transmit it across an opto-isolator, low-pass filter it and feed it into an ADC.

enter image description here

  • Use a 300:1 potential divider from your battery and feed the signal into an LTC6992 MOD input.
  • Drive your opto-isolator from the PWM output. You may need a transistor to drive it adequately.
  • Take the opto output, low-pass filter it and feed it into an ADC on your monitor circuit.

Things to watch out for:

  • You'll need a high-speed opto-coupler.
  • You may have to run a calibration on the device. Hook up a pot to the LTC6992 input and vary the voltage from 0 to 1 V while monitoring the signal received on the ADC input. Any offset / scaling can be done in your micro.

Thanks to Andy Aka for introducing me to this chip which pops up in many of his solutions.

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A simple solution would be an isolated DC/DC nonregulated converter; these are off-the-shelf, something like this DC/DC converter would give output proportional to battery 300V, with output attenuation (will need calibration). As a bonus, it can also provide instrument-panel power or backup the existing power supply.

If there are a lot of measurements on the HV side that would be useful, it might be wise to install a computer there (Arduino?) and use Ethernet (the 100baseT specification has hundreds of volts of isolation) to communicate with your console.

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