Greetings all,
I'm very new to Open Energy Monitor, and don't own one yet but I do have an OpenEVSE and a broken TED5000 with six(3 pairs for US 240VAC split phase) 0-3V split core voltage type 200A CTs.
I read this article on choosing CTs and burden resistors:
https://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface
I know my CTs are 0-3V but do not know what the burden resistor or turn ratio is. I'm going to try and open up a CT and see what is in it. Can I get an accurate measure of the burden resistor by just measuring resistance out of circuit at the CT leads since the burden resistor is parallel? I'm fairly certain I will have to change the burden resistors
What will the reference voltage be in the EmonPi? I'll be buying the assembled kit and couldn't figure out if the shield is based on EmonTXv3 or v2, or something special. Also I couldn't find what the built in burden resistor values are or if they can be changed, since I don't know what EmonPi's shield is like.
https://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface
These CTs seem to be very accurate as TED5000 was very sensitive to low loads, so I would really like to use them to minimize the spend on CTs for US configurations. In 'Magnelab money' these CTs are worth $240-300.
Many many thanks for your advice in advance. I'll just be starting with the EmonPi and two CTs to measure my 200A service.
Benjamin
Re: TED is DEAD: 0-3V 200A split core CTs from TED5000 on OpenEMON
I've asked the TED forum (which is mostly dead also) and TED support what the burden resistor is.
Re: TED is DEAD: 0-3V 200A split core CTs from TED5000 on OpenEMON
If it is at all difficult to get inside your CT to check the burden resistor value, don't bother. It is probably safer (against risk of damage) and easier to add an external burden resistor in parallel with the existing and measure the resulting voltage - but you do need to be able to measure (or at least set to a constant value) the primary current and measure the output voltage simultaneously. Measuring the parallel combination of internal burden resistor and secondary winding won't help you.
Set up your CT with a steady primary current. Measure the output voltage. Now add another burden resistor external to the CT. Choose the value (or use a rheostat) so that the voltage is exactly halved. The value of the internal burden resistor is exactly the same as the value of the external one. (Note: it is always safe to short-circuit a CT.)
Full details of the emonPi are in Resources, in the Wiki. Like the emonTx, it has an internal burden resistor of 120 Ω, and you should be aiming for 1.1 V rms at the input. If the combined resistance or your internal burden and the emonPi's in parallel give you more than 1.1 V at maximum current, you can add another parallel resistor (either in the plug or on the emonPi pcb - there are holes for a wire-ended resistor) and if not, you can unsolder the internal burden and add the correct value instead.