Author Topic: Back Charging (Read 4395 times)

SteelMyst · « **on:** July 02, 2004, 05:35:30 am »

How much of a risk is it? My current battery pack uses 4 NiMH. If I use a diode will the internal resistance drop the voltage to the point where I need to add more batteries? Also, does anyone know what varience the Zaurus will tolerate on the input voltage?

omega · « **Reply #1 on:** July 02, 2004, 06:26:59 am »

The max input voltage tolerance is quite low as far as peoples experiences goes. I'd suggest that at the very max, 5.5volts should be allowed into the Z. If you put 4 NIMH batteries in series with no diode it should be fine, also i believe that the battery extenders such as the semsons are exactly this... but of course check it out yourself. nimh's are 1.25 x 4 = 5... it may be a little more than that with no load but it shouldn't be too bad.

V-Man · « **Reply #2 on:** July 02, 2004, 12:23:45 pm »

I actually ran the Z with 4 alkaline batteries before I got my NiMh batteries. I would not recommend doing this!!! I just got lucky. With the NiMh batteries, I watch the charging light. When the light goes off (indicating full charge), I disconnect the external battery pack. After a bit (time depends on what I am doing with the Z), I reattach the external battery pack until the charging light goes off. I have found that if you let the external pack and the internal battery go dead, the Z will shutdown very ungracefully and without warning!!

I believe I have a bit of information on the battery packs, voltages, and Z current requirements. Let me know if you want it. I don't have it with me (at work) but can probably still find it all at home.

SteelMyst · « **Reply #3 on:** July 02, 2004, 05:37:38 pm »

Thanks for the info.

Quote

I believe I have a bit of information on the battery packs, voltages, and Z current requirements. Let me know if you want it. I don't have it with me (at work) but can probably still find it all at home.

If its not too much trouble V-Man that would be great.

jamesannan · « **Reply #4 on:** July 19, 2004, 05:56:29 am »

I just made and used a 4xAA battery pack on a long weekend trip - it seemed to work fine. With NiMH batteries I cannot see the voltage being dangerous (potentially, it could be too low at ~4.8V under load). As someone said above, it shuts down fast when the external power fails but does not seem to have come to any harm from it.

I didn't take careful note of how much extra life the AA pack gave me, but it was certainly several hours. At 1550mAh per cell (my set, better are available) it ought to be roughly one full charge worth (of the 1700mAh pack that my 860 uses), probably a bit less in practice.

As it happens, a mains socket was available and the chager would have been lighter..but I didn't know that before I went!

James

Omicron · « **Reply #5 on:** July 19, 2004, 07:27:46 am »

Quote

I just made and used a 4xAA battery pack on a long weekend trip - it seemed to work fine. With NiMH batteries I cannot see the voltage being dangerous (potentially, it could be too low at ~4.8V under load). As someone said above, it shuts down fast when the external power fails but does not seem to have come to any harm from it.

I didn't take careful note of how much extra life the AA pack gave me, but it was certainly several hours. At 1550mAh per cell (my set, better are available) it ought to be roughly one full charge worth (of the 1700mAh pack that my 860 uses), probably a bit less in practice.

As it happens, a mains socket was available and the chager would have been lighter..but I didn't know that before I went!

James

Be careful, alot of people have killed the charging capabilities of their Z (C series) by using too low and/or too high (slightly) chargers....this seems to hapen OVER TIME.

Also, if you write a step by step and PM the URL I will add a HOW TO for everyone to use.

Omicron · « **Reply #6 on:** July 19, 2004, 07:29:14 am »

Quote

I believe I have a bit of information on the battery packs, voltages, and Z current requirements. Let me know if you want it. I don't have it with me (at work) but can probably still find it all at home.

Yes, please post all so I can make a HOW TO (PM me when posted).

omega · « **Reply #7 on:** July 19, 2004, 07:49:42 am »

Too low voltage should not damage the Z. I use the usb-charge cable and occasionally the Z doesn't have enough juice to charge the battery but it will hold it at a certain point (e.g. 70%). I do a bit of work with voltage regulators and stuff, it there's not enough coming it they don't deliver / switch off. no harm there.

Overvoltage though.... a spike longer than 100ms could be all it takes.

Zuber · « **Reply #8 on:** July 19, 2004, 09:28:01 am »

I had a question on this the other day.

Perhaps you guys have a better idea.

With high capacity NiMH batteries fully charged, you get 1.4 volts no load.

So that is 5.6 volts no load with 4 batteries.

I've been using one for ages no problem and likewise with feedback from customers.

But just wondering...

How much of a voltage difference does no load v actual load make in this sort of case ?

By the way, I would not advice anyone to use noramal 1.5 volt AA batteries. We tested the voltage on some battery extenders and got voltages over 7 volts in some cases..

Even ones claiming to have voltage protection managed 6 volts with same cells.

omega · « **Reply #9 on:** July 19, 2004, 09:46:39 am »

Hey Zuber,

Load voltage will drop a bit, because the load on the batteries is quite high (~1A) which is about half the Ah capacity of the battery. So in this case the batteries are being quite heavily drained and should be safe enough.

I suspect that those battery extenders with protective circuitry are nothing more than a diode... A diode can drop "up to" 0.7volts upon full load.... so if measuring with a meter you basically see the full voltage less about 0.2volts...

If you want to use Alkaline batteries I suggest a LM2940 IC... It's a low-dropout 5 volt voltage regulator.... you only need two capacitors with it and it will take care of you.

sittisaks · « **Reply #10 on:** July 19, 2004, 01:53:15 pm »

Most of the charger will charge NiMH with around 1.4 Volt. For the 4 cells of fullly charge will yield around 5.6 V. This kind of device normally we should not go higher than 5.5 V But consider the voltage will drop when on load,so it should be ok. One of the concern is, if on the bad day, some one pick up a bad charger that charge the battry more than 1.4 V. Without any protection circuit at all between batteries and Zaurus, The unit can be harmed.

omega · « **Reply #11 on:** July 20, 2004, 06:48:43 am »

sittisaks, the batteries should not be able to charge further than that... 100% is 100%... if they are overcharged they start to oxidise the electrolyte or otherwise heat up and in any case don't do the batteries any good - but once the batteries are allowed to settle outside of the charger they should drop down to around 1.4volts.

V-man - i haven't had a chance to take measurements myself, and i think it would be really good to have your data.

sittisaks · « **Reply #12 on:** July 20, 2004, 11:05:57 am »

omega, nothing is 100% in electronics world. I am talking about if some one pick a charger that is not very accurate, let say it charge 1.45 V. That 0.05 Volt will not be any different for battery. But when the sum of 4 cells, it will add another 0.2 volt to 5.6 V which will be 5.8 V. That is something. I know that the case is rare. But I try to point out that using 4 AA NiMH alone without any protection circuit or regulator has some risk in it.

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Author Topic: Back Charging (Read 4395 times)