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Need help running hobby motor

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redmonkey

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Hello there,

I'm new this stuff and don't know much.

I have a question here. I have a Twin Motor Gear Box (Twin Motor Gearbox) that uses two FA-130 motors (
Mabuchi FA-130 Motor) and 2 D Cell Batteries (D Cell Batteries I use are about 1.5V-8000mAh). I need to run the motors as fast and as strong as possible with the 2 D Cell batteries, it doesn't matter that the batteries last 10 minutes. I was thinking of connecting the batteries in series which will give me 3V-8000mAh. Then have a circuit that will change 3V-8000mAh into about 6V-2500mAh. I need help finding the circuitry that will do that. I know the circuit won't have 100% efficiency, I'm only looking for about 50-70% efficiency. Battery run time does not matter, I only need about 10 minutes of run time. Currently the batteries will run the motors for 1 day, batteries in series, motors in parallel.

I don't really know what to search on google, so any help is appreciated.
If anything I said up there is wrong, please correct me.

If any of this doesn't make sense, please ask. I really need help.
All help appreciated.
Thanks in advance.

Thanks.
 
Have you tried hooking the motors to 4 D-cells in series to see if the 1.5v-3v motor will last 10 minutes at 6v?

Ken
 
Yeah...:)...but, better than spending the time and money building a DC-DC inverter...only to come out with the same result. :(

Ken
 
I would definitely try that first =) If you stall those motors at twice the voltage the coils will probably melt into little puddles =\ Instead of 2 D's How about using 3 C cells?
 
The motors can run at 6V from 4 D Cells easily. They don't burn out and run perfectly fine for much more then 10 minutes. Is there a way to get the same speed and power from only 2 D Cells, less run time does not really matter, I only need about 10 minutes, before I change the batteries.

The person who asked about 3 C Cells instead of 2 D Cells, I can only use D Cell Batteries.
 
Is this for a competition or school project...thus the limitation?

Ken
 
Well you'd need an oscillator circuit powering a transistor to pulse a step up transformer the re-rectify it to power the motor, problem is the voltage is so low you'd be lucky to get 25% efficiency out of it, the other 75% would be wasted as heat. You really need to add more cells in series to get a higher voltage with any degree of usability. The batteries simple can't provide enough current after conversion losses.
 
@KMoffett: This is for a robotics race, that's why there's these restrictions.

@Sceadwian: I didn't get what you said in the first part, haha, if you say efficiency if about 25%, then 3V-8000mAh would equal to about 6V-1000mAh. And what I'm getting that your saying is, I won't be able to run the motor any better then if I connected them to the motor directly. Right? So it's not possible?
 
Impossible? Not really, but not exactly practical (with limited knowledge). You're looking for a 2A boost converter that accepts an input of 2.4 volts.

One thing that might help is an external low current source of 6-12V to bootstrap it. If you don't already have 6V, then you could build a LM2698 circuit with about 9 components for up to $6. This won't be beefy enough to drive the motor.

Then you could use a fairly common boost controller to drive the gate of a couple of MOSFETs. I say a couple, because you'll need multiple switches to keep the ripple in the battery down.
 
mneary, think about the efficiency for a few minutes, then get come back to this post =) We're not talking advanced semi conductor electronics and a high degree of circuit prep. The OP has much simpler goals.
 
Last edited:
The OP has much simpler goals.
Considering his starting point, true. If he can't handle the LM2698 for starters, his project is dead. Kind of an entrance exam. :eek:

Maybe I'll try to build one and see where the problems lie.
 
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