Nessus

So I searched and searched on here and read just about all the battery extender threads there are. I thought I had a pretty good handle of what I needed to do and what to expect. I thought I did everything right:

I bought this battery extender by Gomadic which includes the appropriate tip.

I bought 4 AA NIMH which are 1.2v, 2100mah.

Thing is, I don't get the screen flicker problem because it just plain doesn't recognize it as external power. Plugging in the extender (with the Dell battery at 100%), nothing happens. No orange power light, no change in battery status screen. Charge goes down just as normal.

With the Axim powered off, I do get the orange power light and it seems that the battery does charge, though fairly slowly. But that's not very useful, now is it?

Any ideas?

Graham2456

That just doesn't make sense. If you have a multimeter I would check each rechargeable to make sure it is OK. Also (and I don't mean to be insulting) check the way you have inserted the batteries. If all is OK I would be guessing you have a dud unit.

Nessus

Thanks for the reply. Yeah, it really doesn't make any sense. I suppose that based on the fact that (when active) the Axim doesn't recognize any change in power source, the only logical conclusion is that it isn't getting enough voltage to "trigger" that switch.

These are brand new NiMH rechargeables, is it possible that they need to be cycled a couple times first? I know that fresh batteries usually need a couple cycles to realize their full capacity, but the output voltage shouldn't be effected.

Man, I really hope this isn't a dud unit. I'm doing a couple cross country flights next week.

Any other ideas/suggestions?

w3iner

You need like 5.4v at 2450 mah if I am not mistaken. I don't think 4 1.2v double A's is enough to charge and run at the same time.

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twmiller

Originally Posted by w3iner

You need like 5.4v at 2450 mah if I am not mistaken. I don't think 4 1.2v double A's is enough to charge and run at the same time.

Yep - I think your right.

Maximum Dude

Originally Posted by Nessus

These are brand new NiMH rechargeables, is it possible that they need to be cycled a couple times first? I know that fresh batteries usually need a couple cycles to realize their full capacity, but the output voltage shouldn't be effected. Any other ideas/suggestions?

Dude, try some fresh alkaline batteries to see if it is a battery issue. I don't recommend using the alkaline batteries to power the unit, just to test it.

PocketBrain

Second the alkalines test. And, w3iner, wtf means "5.4V at 2450mAH?" Non-engineers, please refrain.
In my experiments, I find you can charge an X5x() series with anything from 4.9V to 5.4V. Many 2nd-party chargers use USB power to charge your Ax, or just a 5.0V regulator if they don't rely on USB. My home-made external battery uses a +5.0V regulator to deliver the power. It's my standard, at-work charger, plugged in every day.
Others have tested and shown that you can recharge Axim on, no WiFi, with a flat standard (1100) mAH battery with about 850 mA or less. Good to have the full 2 Amps capacity in your charger, however. NiMH batteries have low internal resistance, so they tend to dip less than alkalines in voltage when you load them, and their cell voltage is about 1.4V apiece unloaded, fully charged. Drops to 1.3 or so and down from there while discharging.

If you're getting no lights whatsoever and all the batteries are connected, everything is plugged in properly, you have a dud unit.


.

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w3iner

Originally Posted by PocketBrain

Second the alkalines test. And, w3iner, wtf means "5.4V at 2450mAH?" Non-engineers, please refrain. In my experiments, I find you can charge an X5x() series with anything from 4.9V to 5.4V. Many 2nd-party chargers use USB power to charge your Ax, or just a 5.0V regulator if they don't rely on USB. My home-made external battery uses a +5.0V regulator to deliver the power. It's my standard, at-work charger, plugged in every day. Others have tested and shown that you can recharge Axim on, no WiFi, with a flat standard (1100) mAH battery with about 850 mA or less. Good to have the full 2 Amps capacity in your charger, however. NiMH batteries have low internal resistance, so they tend to dip less than alkalines in voltage when you load them, and their cell voltage is about 1.4V apiece unloaded, fully charged. Drops to 1.3 or so and down from there while discharging. If you're getting no lights whatsoever and all the batteries are connected, everything is plugged in properly, you have a dud unit. .

I am no engineer either, but the Dell Wall Plug puts out 5.4v at 2450 mah, while there are 4 1.2v(which i guess adds up to 4.8 v or volts, not the 4.9 to 5.4 you stated.) at 2100 miliampheres(which is 8400 mah which seems enough). I am no expert but It seems to me that you have enough amps but not enough volts? Try following Pocket Brains idea of using Nickel based batteries and that might give you enough volts.

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40th Floor

Originally Posted by w3iner

...while there are 4 1.2v(which i guess adds up to 4.8 v or volts, not the 4.9 to 5.4 you stated.) at 2100 miliampheres(which is 8400 mah which seems enough). I am no expert but...

Batteries in series (+ to -) then you add voltage (current remains constant). If in parallel (all + tied together, all - together), voltage remains constant, and current adds together. Four 1.5V, 2000mAH batteries in series gets you 6V @ 2AH. The same batteries in parallel gets you 1.5V @ 8 AH. You can also get 3V @ 4 AH (two each in series, and that pair in parallel).

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w3iner

Originally Posted by 40th Floor

Batteries in series (+ to -) then you add voltage (current remains constant). If in parallel (all + tied together, all - together), voltage remains constant, and current adds together. Four 1.5V, 2000mAH batteries in series gets you 6V @ 2AH. The same batteries in parallel gets you 1.5V @ 8 AH. You can also get 3V @ 4 AH (two each in series, and that pair in parallel).

Thank you floor. I guess he will need his battires is series.

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Graham2456

Originally Posted by w3iner

I am no engineer either, but the Dell Wall Plug puts out 5.4v at 2450 mah, while there are 4 1.2v(which i guess adds up to 4.8 v or volts, not the 4.9 to 5.4 you stated.) at 2100 miliampheres(which is 8400 mah which seems enough). I am no expert but It seems to me that you have enough amps but not enough volts? Try following Pocket Brains idea of using Nickel based batteries and that might give you enough volts.

I think everyone is getting too caught up with voltage. Voltage is not important, it is current that charges the battery. Voltage is only necessary to get the current flowing.
The Axim battery is rated at 3.7 volts, therefore any voltage source above this level will cause current to flow into the battery (and thus charge it).
The big variable is the amount of current flowing in which affects how fast the battery charges. The current flowing in is a function of the voltage driving it and the ability of the source to supply it. This is why USB chargers are not very satisfactory. Their voltage level is OK but their ability to supply current is very limited.
Referring back to Ohm's Law, a higher voltage will cause more current to flow but unless the source is capable of supplying it the source voltage will drop (and the current along with it). The ideal would be a "constant current" source in a storage device (battery) but unfortunately they are not available. The nearest we can get is the NiMH so stick with them.
I lived on a yacht for 6 years so if I got my charging wrong I sat in the dark.

Bern

G'day,
The tech stuff is over my mathematically-challenged head. However I did get a battery extender for my Ipaq which worked fine in providing power when Ipaq was on. When I looked at a similar extender from the same seller for the Axim the seller specifically stated in their ad that with the X51v you could only charge whilst unit off (and if I recall correctly not a completely drained battery) given the higher power draw (in very layman speak) of the x51V.
Cheers
Bern

protochu

How to build an extended battery
Axim Power Pins

If you put 6 2500mah NiMH batteries in series, you get 7.2 volts with 2500mah current. Slap a +5VDC voltage regulator on there, and you get a steady 5 Volts, 2500mah (roughly 625mA, correct?). This provides more current than needed to charge the battery and use the axim at the same time (I am totally assuming that), since the axim likes around 500mA when charging.

Somebody either tell me I'm correct, or tell me how it really is

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