Adding Battery Pack to RC Car
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Adding Battery Pack to RC Car

by JRMN on Mon Dec 03, 2012 11:28 am

I recently bought an old 1991 Tyco RC Fast Traxx car from eBay. I got a really good deal on the car because didn’t come with a battery pack and charger. I know it original came with a NiCd 9.6V 700mAh battery, going to replace it with 9.6V 1600mAh or 2000mAh Ni-MH battery pack.

I also have a Spy Gear TRAKR that takes six AA batteries. I would like to wire up the TRAKR to use the same battery pack that I am going to get for my Tyco Fast Traxx. I’m not too worried about opening the TRAKR because it’s well documented and I know Radio Shack sells the connector I need.

Is there anything that I sure be worried about and would using the 9.6V battery pack fry my TRAKR? Thanks
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Re: Adding Battery Pack to RC Car

by adafruit_support_bill on Mon Dec 03, 2012 12:02 pm

6x alkaline AAs will give you close to 9.6v when fresh. But a freshly charged 9.6v NiMH pack will be more like 11.2v. I don't know how tolerant the trakr is of overvoltage. But to be safe, you could always put a diode in line to drop the voltage a little.
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Re: Adding Battery Pack to RC Car

by JRMN on Mon Dec 03, 2012 12:43 pm

That's what I was afraid of. What about a 3 Amp UBEC (I still need to read up on it)? I just read that's what most RC people use. Is there any way I can find out if the TRAKR has a voltage regulator built-in and how many amps the TRAKR draws?
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Re: Adding Battery Pack to RC Car

by adafruit_support_bill on Mon Dec 03, 2012 12:58 pm

A UBEC should work. I'd expect 3A is enough. Unless it is published somewhere, the best way to find out the actual current draw is to measure it. http://learn.adafruit.com/multimeters/current
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Re: Adding Battery Pack to RC Car

by JRMN on Mon Dec 03, 2012 3:21 pm

Thanks for the link, I will read up on it tonight. This is what I do know, the H-bridge driver circuit is made up of B772 (lower row) and D882 (upper row) transistors with a 7805 voltage regulator (5V fixed) on one end.
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Re: Adding Battery Pack to RC Car

by adafruit_support_bill on Mon Dec 03, 2012 3:53 pm

7805's are good for up to 1A, but I suspect that is just for powering the logic. B772s and D882s are rated for up to 3A.
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