Hi Andrew,
Thanks for your response, and I agree with your assessment of undertaking this test without an analyser or oscilloscope (with current leads) – but don’t have.
Couple of things: I replaced the DVM with an analog (coil) ampmeter and the result was much the same, where it could be observed – I don’t doubt there are current spikes in regaining the network etc… but have to accept they are very fast and probably negligible overall.
Not really sure what you mean by “When you have a local current source (ie, the LiPo) in place, any radio transmission current is probably sourced from that, and current from the external power source is averaged out to charge the LiPo. Without the LiPo, the external current will be much more ‘lumpy’.”
If I understand the configuration right , the BQ24195 should not draw from the LiPo by preference over VIN – if that’s what you mean – and the external source should be pretty clean (being a battery). In any case I don’t get how it would be working so hard it draws another 20 odd mA. Might be wrong here and happy to be corrected (maybe one of the Particle Hardware guys might want to jump in).
That said this Particle tutorial and the datasheet suggest Electron in SLEEP_NETWORK_STANDBY should draw under 7 mA – in my test with a LiPo battery attached this is confirmed (I’m drawing around 9mA, but the rest of the circuit in the project draws about 1.3MA).
Regarding the project being at risk from excessive voltage on VIN, good point – but the ratings are pretty solid on the BQ24195, which is actually rated to absolute MAX 22v.
Being a solar configuration on the filtered (by a couple of largish capacitors) LOAD output of the charge controller – and a 15v Zener diode in circuit across VIN in the project – there is not much chance of a transient voltage spike (unlike say, a car battery charged by an alternator) I’ll risk it for a bit more of the testing. I agree it is NOT good practice to exceed recommended op specs with any device – but so far so good. If I can solve this excessive current draw without a LiPo battery, I’ll use a DC/DC converter to drop the supply to 7.5 volts – but it adds another 12 mA to the power draw. I am really trying to minimise the power consumption to reduce costs and size of the solar panel. I’m finding it hard to source a 6 volt solar rig that delivers more than 3 watts – which will be borderline on a device that uses as much power as the Electron.
Last Point – I like the SLEEP_NETWORK_STANDBY mode because of the rapid reconnect to the particle cloud. I’m working on a series of 20 minute sleep cycles, and taking a data sample when they expire (currently at 4 cycles / 80 minutes). If I use the SLEEP_MODE_DEEP option, I’ll reduce sleep power consumption but go through much longer periods of high current drain every time the device wakes up - with cell data signals pretty erratic (due to contention) in Northern Queensland, I could have the device seeking connection for minutes – which could negate much of the low power sleep cycle savings.