Omar.M

Wow. See why I love Toronto? If my dollar store was to have any, the 'NiMH' batteries would be alkaline ones with a NiMH wrapper. Ottawa is expensive(er)!

I think I might as well do that. Hopefully I'll find some cheap chargers with batteries around here. I've actually heard that PA has those too, with chargers. If I can find those then I'm in luck eh?

Thanks for your help, will keep you posted.
Omar

blueroomelectronics

Expensive best buy $27
http://www.bestbuy.ca/catalog/prodde...0&catid=22206#

And I think I saw this sort of thing at ToyRUS for about $12 awhile back.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

acrylic

Do not use the diode across the supply pins.

The diode goes from battery +ve to the +ve supply pin of the PIC, pointy end to the PIC. If you inadvertently apply the power supply backwards, no current can flow. The schottky ensures only a small voltage drop from battery to PIC.

bloody-orc

get the diode as close to the battery pack as possible on the PCB. if you connect it only near the PIC then only PIC will survive and all other things will burn connect it near the battery connector but not to the battery pack wires as then they serve no point

__________________
Need Help?
Press F1
If that doesn\'t help you, ask me... I might know better.

Omar.M

That was the most amazing trip I have had to a store-- ever.
Okay, I've been in PA and I thought it was like paradise for me before, PA never seems to surprise me.
So I was looking through the aisles, and soem chargers caught my eye. There was a WHOLE SECTION deticated to this. And they have everything, Energizer Chargers for about 9.99 and even a cheap little NiMH / NiCad charger for 4 DOLLARS!

I picked it up but put it back, I am going to go back once I pick up some NiMH batteries. So my parents wanted to shop, and we stopped at some big store. Behold, there was a wall filled with NiCad batteries. 2 for $1.97. Woah. That was the coolest thing ever.

So, I picked up so much stuff from PA (stuff I didn't even dream of getting today). Aye well, I'll go back there next weekend and buy the charger.
I'm still a little suspicious of the charger. It just looked like a generic charger, black and nothing much written on it. It did have NiCad / NiMH charger (with charging times) written on it. Should I trust this one?

Thanks a lot you guys!
Omar

blueroomelectronics

It's probably fine. PA is pretty neat, bought my digital calipers there.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

bloody-orc

It's probably a "stupid" charger then. you must make sure that the AA batteries you are going to charge are as empty as possible to avoid memory effect (that NiCad batteries have). also you must make/have a timer to make sure you wont overcharge those little bastards (or undercharge).

__________________
Need Help?
Press F1
If that doesn\'t help you, ask me... I might know better.

Omar.M

So every time I want to recharge the batteries, just hook each up to a motor until it is almost drained THEN recharge?

The timer shouldn't be much of a problem, I may need to calculate exact times though.

So other than this memory effect (which should not be a problem if I nearly drain the cells each time and do not under/over charge), is there any other problems with these NiCad batteries?

-Omar

mneary

Modern NiCads shouldn't have a memory effect prominent enough to be worth all that effort.

IMHO, the risk of damaging the battery by reverse charging one cell in a pack is greater.

Omar.M

Oh ok. Thank you VERY much .
I think I will go with the NiCads then.

Bill discussed this, but it seems that there is no LDO voltage regulators at Active Electronics (my only electronics supplier around here).
So for the LM7805 regulator I currently use, I do need an input voltage of above 7.5V.

Bill said he connected the PIC directly to the power supply (with a diode for the ripple regulation). I don't think this will work for me, 6V-- isn't the PIC made for just 5V?

Are there any solutions? I am thinking of giving them a call and seeing if they have any LDO voltage regulators in stock (that are not listed on the website).

Omar

blueroomelectronics

NiCAD & NiMH are 1.25V per cell. 4x1.25=5V

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

Omar.M

AYYEEE! Me being stupid again, I just overlooked that. I thought they were 1.5V like the alkaline rechargeable batteries.
Silly me, thank you sir!

Nigel Goodwin

Their nominal voltage is only 1.2V, so only 4.8V for four in series - as with any battery, voltage will change with degree of charge or discharge, but is nominally:

NiCh/NiMh = 1.2V
Lead Acid = 2V
Normal non-rechargeable = 1.5V

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

bloody-orc

for my experience the recharger batteries have 1.36V in them (NiMH at least). this is on the very edge of the PIC voltage range (5.44V) so a 0.7V drop on a normal 1n4148 diode makes it all good luckily you have some power hoggers on the circuit (motors) so the voltage will drop pretty fast back to the normal 1.2x V and you get your 4.8V per pack again. It would be better to use a PIC that takes anything from 3.3V to 5.5V so the pic will not go bananas when the voltage drops too low. might also invest in a brown out detector (if you don't have one built in the pic); the solution for the bananas problem.

anyway good luck


PS yes the memory problem seems to be a little problem, but better safe than sorry you know especially for those cheap ones. they probably have that memory effect in them... (why else are they so cheap then ). and yes running a small DC motor for some time will do the discharging. you could actualy also make a discharger for faster work, but that's not a must.

__________________
Need Help?
Press F1
If that doesn\'t help you, ask me... I might know better.

mneary

Memory effect takes hundreds of cycles to even become noticeable. If you reverse a cell's polarity even once it is gone!

The cells are probably cheap because they come from a batch that don't meet spec in some way, such as meeting the advertised capacity, integrity of the envelope, etc.