I'm trying to build a wireless/mobile monitor. The monitor will be included in a wheeled cart, so I have some limited storage available in the cavity behind the monitor, but not much. The cart itself will not have access to power most of the time. The monitor will be showing the screen of a computer located at a fixed point in the room. I'm looking for something that can run off of a small battery for about 6-8 hours during the day. The cart can be plugged in to recharge overnight.

I've started with this item as the display:


And one of these for the wireless signaling:


And this setup already works well when I can plug them into a wall outlet. Now I just need the power packs. I was hoping to use these:


Based on the draws from the display and receiver, that should provide enough power to go about 10.5 hours, so it will meet my 8 hour goal even after it's had some wear.

Unfortunately, I can't get it to work. The power pack will charge a phone, but it won't stay active when the display and receiver are connected; it just shuts off after a few seconds, before the devices can even turn on. I feel like the power pack is expecting a special charging signal from them that these devices are not providing, because they have no batteries of their own, but I don't really know what's going on.

So that's my question: what is going on here? I also hope to learn what I need to know to find a battery pack (or hack the one I have, if possible, and this can include soldering the battery to a different board) that will work for this concept.

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    Note that I'm not looking for a specific product recommendation. I'm looking for a broader understanding of how these battery packs function, so that I can (hopefully) learn enough to find a product or fix on my own. – Joel Coehoorn Sep 30 '14 at 15:42
  • perhaps the display and receiver draw too much power and its shutting down for safety? – Keltari Sep 30 '14 at 15:47
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    IMO, this seems like a question better suited to the Electronics Engineering SE rather than SU. – Ƭᴇcʜιᴇ007 Sep 30 '14 at 15:49
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    Joel, your edit bumped this old question to the main page. The link to the display is now dead, so critical information needed to answer is unavailable. It also looks like the previous answers didn't solve the problem. Has the problem been overtaken by events or did you solve it? If so, consider updating the status, maybe posting an answer. If an answer would still be useful, can you link to an equivalent monitor? I suspect the issue relates to the nature of the power required, but the question isn't answerable as-is, and not really of much use to others in the thread's current state. – fixer1234 Dec 3 '17 at 21:16

From my experience using unexpected (aka no-name) batteries with some "smart" chargers will result in no charging.

From my understanding the failure to charge is because the charger is not getting expected capacity information from the battery, and so doesn't know it's current charge, or maximum charge, and so it decides it's safer to just not charge it vs. possibly overcharging and starting a fire (or something else equally unwanted).

I'm thinking you're running into the same thing here -- Since your monitor and WiFi devices aren't batteries (or devices with rechargeable batteries) they won't report their current charge or capacity, and so the charger/battery pack just won't power them.


Most of the time the external battery will wait for a current draw from the devices being charged/powered for a fixed time and then shut down to limit discharge and to provide a fail-safe in case the protection circuitry on the device side fails and to prevent shocks and short circuits. The USB power specification doesn't require any "communication" to occur between devices (USB charging chips don't actually connect to the digital data pins of the USB connector.)

My guess is that your devices aren't initiating a draw quickly enough and the battery pack is shutting down. Try pushing the activation button on the batter pack and the devices in quick succession.

Also, the battery pack could just be defective and is definitely not suited to the application you are describing.

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