Power Consumption

The wireless devices from Digi look really good, and I’m looking in to them as a possible solution for something I’m working on. However I’m somewhat concerned over the 400mA quoted max power consumption.

Given that its a wireless device, needless to say its battery powered! If we take the worst case situation, 400mA running off the standard 2.5Ah battery would be dead in 6 hours - no good for a device that must keep running for at least 14 hours - and thats not counting the fact it uses 80mA (at the moment) for the other stuff in it.

What I need to know is, what can I realistically expect the power usage to be? There will be two modes, active and standby. In standby it needs to receive only and it could conceivably only need to power up for a second or so once every 5-10 seconds if that makes a big difference. In active mode it’ll probably send a small data packet (from 10 to 100 bytes) typically once every 5 seconds or so and receive an ACK back.

The actual device is powered from a 9.6v NiMH battery and the main circuit currently operates at 5v using a 7805. I’m looking at bringing the logic level components down to 3.3v (some run off the 9.6v directly). I’m aware that moving to switch mode power supply solutions increases power convesion efficiency, however I also understand that they aren’t good for radio devices (along with LDO devices)… can anyone advise on this at all? What are people using to generate the 3.3v in battery powered applications?

I’d love to use this device as it’ll cut dev time right down and hopefully bring security and reliability to the device I’m trying to make. However if the power consumption is too high then it makes it inpractical.

Any suggestions happily received!

Thank you.



Not much about the wi-me, but the solution for the power should quite much depend on how you want to do it.

Depending on power usage, i would use a low-drop regulator or use switching power supply. Pros and cons in both. I don’t think that switching power supply will be bad for wireless, as they are used in almost every device nowadays, even in the wireless ones. 400mA is still so much current, that you propably want to use switching PSU.

If i had to maximize battery life, I would of course minimize powerlosses in PSU and try to figure out some powersaving modes for the device. Can the radio be turned off / on by software in Wi-Me? And are there any specs about the power usage in these situations (yes, I was lazy, didn’t look through the datasheets as I suppose it wasn’t told there because of this thread :slight_smile:

Just my 2cents, after hard day at work…