M2 power draw before start

[dess2000]

So now that it’s getting cold again, I’ve decided I should finish my remote start via SMS.

Was doing some testing and wanted to see what would happen when left plugged in all night.

I have it programmed that if I send the M2 a text message requesting a status, it will send back (among other things) the vehicle voltage and output load.

So when I plugged it in and asked for a status, I got 11.35V and 110.00mA draw. 10 hours later, it sent me 11.24V and 109.00mA. This is obviously a problem if I want my truck to start after a few days…

So I started reading about power saving. The one thread I found is a little out of date:

Help wanted - how low can you go?

Let’s see how low we can make the current draw on M2! It sure would be nice to leave M2 plugged into a car and not have to worry about draining the battery. To accomplish this, we’ll need to take advantage of several things, including the “Low Power Control” circuit found on page 4 of the interface board schematic found here. Then, we’ll want to turn off all peripherals, and put the SAM3X into a low power mode. The SAM3X offers several ways of doing this, as shown on this table found on page 2…

But after messing around a bit, I took it to my truck to test some more. This time however, I had the key in with the accessories turned on. When the M2 was able to connect, the draw dropped down to 0.00mA. All night the voltage barely dropped.

I’m clearly happy with this, so I don’t really have any questions on it, but has anyone else noticed this? Is this expected behaviour?

[gpena2087]

Are you saying you implemented the lower power mode and saw that reduction?

[CollinK]

I believe that an M2 will draw around 110ma while running but it will do that while plugged into a USB port. That is, if I measure the power being drawn from the PC it is around 110ma and 5V. So, I would have expected that it would draw less on a 12V input. I don’t remember ever testing on 12V. In theory the M2 should be able to get down to microamps when sleeping. That would show as a very low draw but I would think somewhere around 0.02ma. Chances are it is unable to measure its own draw when you shut it down to a low enough power state. At the low end you are only going to be able to measure the draw with a sensitive external ammeter. And, of course, that will be difficult to do while it is installed in a car. So, testing really would probably need to be done on the bench.