|
Originally Posted by bill_n_opus
|
PocketBrain, the regulated powerpack looks like a great idea!
Can you tell me why it's much better than a regular 4xAA battery extender? (of which I have).
I'm guessing that:
- the regulated 5v DC helps the Ax behave much better. In that the NiMh cells will push out 5v DC straight without fluctuation? I've no idea on what i'm talking about. I'm not an EE. :) The 4xAA pack is sensitive to load current: voltage dips when the load is high. If the pack's voltage drops below ~4.8V (rated cell voltage is 1.2v, X4 = 4.8V; 100% charged cell is ~1.4V, X4 = 5.6V), then the PPC will switch to the internal battery.
- You can use more than the usual 4xAA NiMh of which I noticed you used 6. So, wired in parallel (or it series?) you'll get 2500mAh at a voltage of ~ 7.2V but regulated to 5V. As the mAh rating drops so does the V i'm guessing but it will be still useable for a longer period of time compared to an unregulated battery extender? Wired in series, for ~7.2V. Regulated to 5V, so the extra 2.2V is "lost." The battery pack voltage will have to drop below about 6.6V, however, before the regulator starts to dip, and it will discharge down to about 6.4V (<1.1V per cell) before the regulator's output drops below 4.8V. This way, much more of the battery capacity is used.
I've noticed that using my 4xAA battery extender (bought from pc-mobile.com) really needs quality NiMh cells.
When i've used lower quality NiMh cells i've noticed that the extender will power and charge the Axim x51v as long as you have at least 75% left ... maybe as low as 60% if i'm using freshly charged NiMh quality cells (I need to do more testing). As the cells discharge, of course, voltage drops, so they don't need to drop in % charge very much before they aren't doing anything. The cheaper cells have higher internal resistance, therefore are more sensitive to load current.
I've also noticed the strange phenomenon in that my cells were low and it ended doing some strange reverse charging thing with my Ax. When I checked the Axim later on I found the battery almost totally dead which alarmed me. I'm still not sure of the EE background of this situation. All I know is that if I want to charge my Ax I better have fresh charged cells ready to go.
|
answers in bold.
Note that the regulator has an overhead of approximately 1.6V, meaning that it has to have an input of 6.6V or so to output 5.0V.
A "buck" switching regulator will boost the efficiency considerably, and the loss of energy as heat will be cut. If I use a "boost" regulator on it, as well, then the batteries can discharge almost completely before becoming useless. The regulator itself can also reduce the "back-charging" effect, wherein the battery pack is a load to your internal battery. Also note that a more-deeply discharged pack will show more sensitivity to load current, so the practical range of voltage per cell will likely be lower.