Omar.M

Hello!
Okay, I lied. There is no crisis =P, but I just was hoping to get some ideas for which power source to use.
My robot is quite light, and I am using a twin Tamiya Gearbox so weight is not really an issue. But the price on the other hand, is.

I am in need of two power supplies, one for the PIC and circuitry, and the other for the motors. The motors are relatively small, requiring about .6 A per motor.
The motor driver I'm using (suggested by Mr. Hank Fletcher) is the SN754410 H-Bridge and using PWM from a 555 timer, the output is about 2.5V.

The circuitry needs 5V regulated, and the motors need nothing more than 5V themselves. I've been looking at many batteries-- it's down to NiMH, NiCad and Alkaline (rechargeable). But the first two cost so much. Just for four AA batteries (plus charger), we're looking at 30 dollars CAD. The Alkaline are the cheapest, but I'm not sure if they are any good.

Is there a way to get some other batteries and build your own charger? Or is that not worth it?
Any help would be appreciated, thank you very much!

-Omar

bloody-orc

get yourself GP rechargeables. NiMH. they are good and last you almost forever.
look for a bundle 4 NiMH+charger in one package.
take 4AA's for motors + 1 9V krona for electronics. or if your circuit can run on 3.3 use a button cell.

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Omar.M

Well thank you.
A pack of four AA (NiMH) is $16.99.
Rechargeable 9V battery is $9.99.
The charger is ~$25.
That'll set be back so much. I am just a student, parents are my only source for money :P.

-Omar

bloody-orc

so am I so ask for an early Christmas present or birthday's present
It does seem a lot of money, but it will be a LOT cheaper than buying Alkalines all the time...

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Jirka46

[QUOTEThat'll set be back so much. I am just a student, parents are my only source for money :P.

-Omar[/quote]
Check out Princess Auto there is a store somewhere in Ottawa. They usually have some surplus batteries in stock. Once I bought 12V 2.4Ah gel-cell batteries ther for $1.99 each. They also have other surplus like motors and gears which you might find usefull.
Jirka

blueroomelectronics

I'm running the Mongoose directly off the 4x NiMH batteries. I have a 1N5819 diode to avoid reverse polarity for the PIC. Works fine. No Need for 9V.
The only 9V rechargeables I could find were NiCAD @ 250mah.

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Hank Fletcher

The PA surplus section, and every surplus and dollar store in the Ottawa area are your new hang-outs. Welcome to the world of discount robotics.

Omar.M

Those ideas are great, except I don't celebrate Christmas and I've sort of maxed out on the "early birthday present" stuff. My parents are awesome that way though.

Bill, that seems like a really good idea then, just running them off the one battery supply (it would save my so much money!) The diode is across the PIC VSS and VDD lines, correct?

To the rest of you:
Heh, don't you worry, I've got about 12 PA flyers in my house, ones I keep collecting for just the batteries. I'm hoping to pop by tomorrow and will see what I can get (I've heard about their surplus batteries before, never thought of it as an option until now).

I think it would be cheapest, but I do not know how I would recharge any of those batteries that I may pick up at PA. Any clues?

Thank you very much, all of you. It is all very much appreciated!
-Omar

blueroomelectronics

It's not regulated but if your PIC has a settable brownout it'll reset when the voltage is too low for normal operation.
As for batteries & chargers you should be able to find something cheap.
http://factorydirect.ca/catalog/cate...t.php?cat=2320

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Omar.M

Thank you very much Bill.
I wasn't aware that I could power both things from the same source (when I tried multiple times the robot went crazy). But now that I know, I can regulate on one side and connect directly on the other (even using 7.5V packs).

I have heard that PA has lots of batteries, which is good, but most of their batteries are in those packs (like cordless phone batteries). So charging that might be an issue, I think.
Would you know anything about that?

Sceadwian

Cordless phone batteries can be removed from their packaging if necasary, and you can make new packs out of htem if you can find a decent source of them. Problem is you shouldn't mix newer and older cells from different packs in the same pack as the voltages don't ballance.

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blueroomelectronics

7.5V you'll need a low dropout regulator like the LM2940

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Oznog

Alkalines are also not as capable of producing high current outputs as NiMH, especially at states of partial discharge.

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I thought what I'd do was I'd pretend I was one of those deaf-mutes.

Omar.M

Okay, so far: go to PA and buy surplus batteries or NiMH batteries-- none else.
The Schottkey diode across PIC terminals will be good.

I was hoping for there to be an easy solutions with the batteries from the surplus store (such as the ones in a battery pack). I really don't want to fiddle with them; taking them out of the packaging and into different chargers. Is it possible to connect a wall wart to the battery and let it charge for an hour or so? Or is that too dangerous?

The batteries from PA might be cheap, but if you can't do anything with them... what's the point you know?

blueroomelectronics

Don't charge em in circuit as the charge voltage may get higher than you expect. Also if a battery comes loose while charging the PIC will get the full brunt of the wall wart.

Seriously skip lunch and buy a AA NiMH charger with batteries, you should be able to find them for $20 or so, even in Ottawa.

My local $1 store has NiCAD AA for $1 for 2 (800mah)

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