Solar Powered MobilePro 900

Before the site crash a few months ago, I started a thread about using a solar charger to power a MobilePro 900 and wanted to report back on the results.

The one I got from Amazon recharges a battery pack of 10 1.2v AA batteries. The vendor claims that the unit will recharge the batteries in a day of being exposed to direct sunlight. I replaced the stock batteries with duracells rated at 2650mAh, which in series are comparable with the original battery for the MP900 (2300mAh). After recharging the batteries over several sunny days, I tried plugging in the MP900 through the unit's cigarette lighter connection to the MP900 through an auto adapter.

Although the cigarette adapter led light illuminates, the AC power light on the MP900 does not seem to come on. I was hoping to recharge the MP900 battery in this manner for the odd hiking trips away from power...

hi voneschenbach

brief form

1) make sure your NEC gets power using a multimeter to check voltage value
2)check for right polarity that is, the male connector going to NEC must have + on tip and - on external contact.
3)Check also voltage when connector is plugged in, I mean under load (I.E. charging battery and/or powering computer)

voltage should not drop below 10.9V otherwise charging circuit gets overloaded and to protect itself stop working.


long form

I made some test on my palm T3, hp 720 and nec900 to solar power them. I did succeded and I can say it is possibile to

stay away from grid power for long but also found it's really important to supply right voltage to power connector.
Should be clear that original battery and computer have to be considered togheter, that is, charging circuit wich is

inside computer is made to work with its battery and related charger, this is even more true with Li-ion batteries.

Having said that, it is safer to use original battery and have it recharged supplying power to computer connector giving

the voltage supplied form original power supply. NEC900 power supply gives open circuit (IE not plugged into computer)

11,72V (here in 230V Ac land) while under load (Ie plugged into NEC turned on and charging battery standard 2200mAh)

gives 11,53V and 770mAh, while charging only the current lowers to 530mAh. Doing more testing I've discovered that if

supplied voltage drops to 10,8v charging current drops to zero showing clearly that charging circuit is not happy of that

and shuts down to prevent overcurrent damage

So if you want to charge original battery pack 2200mAh you should supply a steady 11,5V and 550mah capable FV panel. A

simple math shows that you need 11,5v X 0,550mAh= 6,32w (full sunshine) of power to charge your device as if it is

conected to grid power wich charges 2200 mAh battery in 3-4 hours. If you accept longer charging periods say 8 hours, you

can run a 3W FV panel (again full sunshine) and still be happy to run solar. If you can count on 4-5 hours of bright

sunshine all wil be ok, your battery will may not be totally charged but at least will last days of work. If it is cloudy

hope your FV panel is able to supply at least 10,9V othervise no charge will ever happen due to charging circuit

"feature".
Note that inserting the multimeter to measure charging current showed clearly that the LED wich should lit to orange

didn't lit but battery was charging despite led saying no, since it was drawing 530mAh...so don't trust that led too

much, use a multimeter set to amps measuring instead to make sure your device is being charged or not and how much.
Last but not least there is a higher capacity battery for nec rated 4400mAh. When I bought my NEC from E-bay I got one

standard battery 2200mAh and two "extended capacity battery". Let's say normal battery don't last long, I've reached 90

min of continuos work before shutdown; maybe the battery is old but don't think will ever last longer than two hours even

a new one. The bigger battery (a brand new one) ensure almost five hours of continuos work.

Bye

For grins, I hooked up a power lead to a fully charged small motorcycle size wet cell battery. I hooked up my 900 to it and after 5 days of constant use it was still running. Less fragile than solar cells and maybe more efficient for long term use. I figure with intermitted normal use it would last a couple of weeks.

Rich

Thanks killproc! I appreciate the long description, being at the 1001 Electronics Kit stage of hardware hacking My panel is probably much too small, so I'll have to get a bigger one. The 6 watt panels are about 15"x15". I'll get a multimeter and try checking the voltage as you suggested.

Rich: I am assuming that the motorcycle battery was 12v? If that worked, it might make sense to recharge the motorcycle battery from the panel and then use an inverter.

Yeah, it was 12V and I hooked it up directly to the terminal. Luckily, as is with most current solid state devices, they only draw the current they need so having a higher rated power source doesn't fry them. Using an inverter would be a substantial current draw and unnecesary as you would be converting DC to AC and then using the standard transformer/adapter to convert it back to DC again.

But using a solar cell system to trickle charge a battery, now that would provide unlimited power. Actually there are already many marine solar cell rechargers out there you could use if you didn't want to fabricate your own circuitry.

Edited by Rich Hawley 2007-05-04 11:23 AM

two small comments


1. mAh = mA

2. the standard battery if in good condition lasts 3-7 hours, normal usage would be 4 for me.

Did I misunderstand? I thought mAh referred to milliamp hours, or the total charge of a battery over it's normal usage period? Is that different from MilliAmps?

mAh in the above post for example "while under load (Ie plugged into NEC turned on and charging battery standard 2200mAh) gives 11,53V and 770mAh, while charging only the current lowers to 530mAh" is mA except for the 2200 mAh, which is indeed mAh.
current = x mA
charge stored = x mAh

Edited by cmonex 2007-05-05 5:19 PM

You say patato...I say potato...as the old song goes. I think you are both in agreement.

But to clarify for the novices out there...a battery rated at 1000 mAh simply means that it will supply a current of 1 milliamp for 1000 hours. Or it will supply 100 millamps for 10 hours before it runs down.

You will notice that your a/c adapters are rated in mA, not mAh because they run indefinitely and do not hold a stored charge. So in that case, the rating shows you the amount of current the adapter can provide. And as Cmonex mentions, that amount of current delivered varies on the amount drawn. Turned off, the unit as a whole draws less since since the unit is dormant. Turned on with the screen running and such, then it draws more.

The lesson here: When using an aftermarket a/c adapter make sure it is rated high enough, that is it provides enough current to simultaneously both charge and run your device, otherwise you may not be able to charge your battery properly, and this can eventually lead to failure of your cell to charge at all.

Rich

ooops I made a mistake...shame on me while I was writing I had a bad toothache and that unpleasant situation led me to write lies . I wrote mAh when I meant mA about power supply while talking about battery capacity it was right to write mAh since it means the capacity of a battery to sustain a current of X for a certain amount of time

sorry again

it is no problem! btw did you manage to fix the 900c rom??

Thanks Rich - that is very helpful for those of us who enjoy the gadget but are clueless about the electronics inside