Universal car adaptor

I'm in need of charging my Axim while i'm on the go. Living in Canada makes it impossible to find PDA accesories. So i'm resorting to buy an universal adaptor; question is what voltage I should use? The Axim requires 5.4v but I can only choose from 4.5v or 6v.

I checked older post's: someone suggested 6v; but inconclusive.

[JakeRich]

Devices and supplies generally have a 10% tolerance. Theoretically, the Ax should accept gracefully anything between 5.94 and 4.86v. (Plus/Minus .54 from 5.4). The power unit should also be in that 10% range, so the 5 volts could be anywhere from 4.5 to 5.5 and the 6 v anywhere from 5.4 to 6.6.

Ok, so what to do? Well, if you have a multimeter, read the voltage at 6. On my universal it was 5.6, which is in the Axim happy zone. But before you start to use it, now read the 4.5v setting. If it gets up to 4.9, that may be safer. Undervoltage will just mean that the Ax won't charge or use the external power, but overvoltage could lead to smoke, unhappy sounds and generally a toasted Axim.

One more factor: The Ax power supply yields a hefty 2.4 amps, so the Ax may really draw on the universal supply. If it's not well regulated, the 4.5 could start to fluctuate under the load, which is not good for the supply, and stressful to the charging circuits in the Ax.

What some folks have done is to avoid the DC supply problem altogether and gotten the DC/AC converters and plugged the Ax's power supply directly into the 110v outlet. That may be the safest of all because now the pressure is off the Ax completely.

I personally use a 5V supply and the Ax is perfectly happy.

Thanks for the info; time to break out the trusty multimeter.

[maarten]

Originally posted by Optimus@Feb 12 2003, 04:42 AM
Thanks for the info; time to break out the trusty multimeter.

one small point:

Check the adapter under load.

[nath@nbriggs.com]

Hi

I assume you're an internet user since your on the forum, so can I suggest my solution?
I bought a car to USB adaptor from
http://pc-mobile.net
Giving me a 5.5V supply I can then use any USB charger cable for my axim the one I like best is Boxwaves minisync because of its size from
http://www.boxwave.com/products/minisync/
and any good reseller.

The solution is usable for my laptop and other devices which have a USB charge cable!

[JakeRich]

That's a good solution, but remember the Axim power supply is rated for 2.4 amps, which is a LOT of power. Make sure that the USB power converter can handle that kind of load. If it cannot, it may not be able to keep the battery charged. If the Ax doesn't get enough power from the external source, it will tap the battery. If the rate of charge can't keep up with the discharge, the battery will be consumed, albeit more slowly than it would with NO external power. USB is typically only rated at 100-500 mA. The USB charger may only be delivering that kind of flow, which may or may not keep up with the Ax use. It will probably charge the battery ok if the Ax is off, but it may not keep up with it on.

[cavuu]

The Ax battery is 1440 ma.
If we assume that it will run for 6 hours then the power consumption is
1440/6=240 ma.
If we assume that the battery can be charged in 3 hours then 1440/3=480ma.
Total =720 ma (yes, I know there are losses)

If you get an auto adapter rated for 1 amp (1000 ma) you should be safe to both charge and run. I personally would not use a supply that is more than 5.5 volt NO LOAD. The reason is that when you shut the Ax off it still draws power but not much. Also check the polarity of the plug, most can be changed so you have a 50/50 chance of having a neat looking ornament if you are wrong. The Ax may or may not be protected from reverse polarity you don't want to be the guy that tells us. :( Did I say check the polarity!!!! Compare the Ax power supply with your auto one twice!!!

If you are technically inclined you can put 1 or 2 2 amp diodes in series to drop the voltage if necessary.

Tha Ax 2.5 amp power supply is designed to power the Ax, charge it's battery and charge a second battery in the cradle and have a little in reserve so it doesn't toast itself. The battery being charged may also be the 3400 ma version which may draw more current during charge or maybe it just takes longer??

If you want to measure the exact current put an ammeter in series with one of the power leads and measure the current.

[JakeRich]

Good point, cavuu. I hadn't thought about the cradle second battery support. Nice catch!

I come to the message board to be helped on my voltage problem; someone nicely solves the problem and i'm relieved. Next day I check the message board again and someone points out the polarity and load problems I might incur . Being cheap isn't easy these days.

My local auto shop has a AC/DC convertor for $20; peace of mind is worth more than the $15 I would've saved.

[cavuu]

Just to add a little to the paranoia there is a large thread on the sci.geo.satellite NG about the risks of running a laptop with an inverter, a gps running from the car DC supply and having the two connected with a serial cable. Apparently the inverter (may)artificially raises the laptops dc ground above the car/gps ground. The difference in potential may fry the inverter or the laptop. This might also apply with a PDA/gps/serial combination although there was no discussion about it. The suggestion was to put the voltmeter leads across both grounds to check for any stray voltage.
It is an excellent thread with expert posts for anyone thinking of going this route.