How to tell the resistance of a coil on a PV

[Zanderist]

I'm currently stuck at trying to figure out how to read the resistance of coil, is there a schematic or method on how to do it?

[CraigHB]

There's two methods, measure voltage and current then divide, or use a voltage divider in a fashion to create an ohmmeter.  The voltage over current method is good because it can be done on the fly while the atomizer is under power.  However, you have to measure current.  The ohmmeter method is good because it's pretty simple and requires less parts, the down side being you have to power down the atomizer to take a measurement.

Either of these methods require an MCU (microcontroller chip), though I've seen one module on Fasttech that provides voltage, current, and resistance data.  It's posted in a recent thread here, but I don't think I can find it.   Maybe someone can link it for you.

[Zanderist]

There's two methods, measure voltage and current then divide, or use a voltage divider in a fashion to create an ohmmeter.  The voltage over current method is good because it can be done on the fly while the atomizer is under power.  However, you have to measure current.  The ohmmeter method is good because it's pretty simple and requires less parts, the down side being you have to power down the atomizer to take a measurement.

Either of these methods require an MCU (microcontroller chip), though I've seen one module on Fasttech that provides voltage, current, and resistance data.  It's posted in a recent thread here, but I don't think I can find it.   Maybe someone can link it for you.

What I had thought originally that, as an example, the MVP 2.0 was reading the coil in real time.

To accomplish this I thought it used a voltage reference and multiplexing to keep the output uninterrupted.

I'll have to post what I have in mind, which basically is a voltage divider that gets formed between a mosfet and coil then gets sent to a preamp to then be used in a micro controller.

[CraigHB]

Sounds reasonable, both methods are viable.  I prefer the volts over amps method because it's dynamic and it's always good for the circuit to be aware of the current demand.

[Zanderist]

The issue I have is a sensor that I could put in a series with the load that has a high amp draw.

Best I've seen is 6 amps. I'm looking for more of a 30 amp type sensor.

[CraigHB]

Don't really understand why you're having an issue with current demand using a divider.  If you switch in a 10 Ohm resistor in series with the atomizer you won't get really big currents.  There isn't any need to go with a large high power resistor either.  It shouldn't take more than a few hundred micro-seconds to take reading so there should be little issue with heating.  Most ADCs can take a sample in only a few micro-seconds.  Even the slowest ones don't take more than a hundred micro-seconds.  That being the case, a 1/4 watt resistor won't even heat up in the slightest with higher wattages when on for that short of a time.

Otherwise if you are talking about measuring current, you can use a single chip solution that utilizes a hall effect sensor.  There's only one maker I know of and they offer sensors that can handle those current levels. 

http://www.allegromicro.com/en/Products/Current-Sensor-ICs.aspx

The most common solution for current sensing is a current sense resistor and op-amp.  Some MCUs have milli-Volt ADCs which eliminates the need for an op-amp.  If you go with a low enough value current sense resistor, like 1 mOhm, you can go up to 50A without using a large footprint resistor.  Ones in a 6.4x3.2mm SMD package can handle up to 3W which would get you upwards of 50A.  There is some issue with noise sensitivity when using a sense resistor of that low value, I haven't gone that low myself, but it should be possible with some heavy filtering.