Using a 9V battery on a 1.5 to 3V motor? - Page 1
Forum section: electronics / beginners

author: jproject
author_rank: Contributor
timestamp: June 15, 2011, 04:18:59 am
content: Hello everyone,I recently got a tank kit for my robot and it uses this motor:http://www.earthshineelectronics.com/46-101-large/3v-dc-motor.jpgand I was wondering if it's alright to use a 9V battery instead of 3V.I need a little bit more juice (well in this case, I guess it's a lot)!Thank you.

author: sacherjj
author_rank: Frequent Contributor
timestamp: June 15, 2011, 04:24:57 am
content: In short, NO.There are two problems with that. First is the winding will have a certain resistance. Tripling the voltage will triple the current. The windings may or may not be able to handle that. If they can't, they will fuse. And you will have no more motor.If it can handle the current, the motor may spin too fast and tear itself apart.You will not hit full current until the motor comes under load. So you may not kill the motor, until it tries to do something that requires more torque.

author: jproject
author_rank: Contributor
timestamp: June 15, 2011, 04:27:37 am
content: how about 4.5V or 6V instead of 3? This tank is running slow............................ my transistors' voltages are messing with ma tank batteries!EDIT: i forgot to mention, there are 4 transistors between my batteries but only 2 are activated at a time (one pnp and one npn darlington transistors).EDIT2: Screw it, I've ran for 2 minutes using the 9V battery and nothing is over heating and my microcontroller is still rolling

author: Simon
author_rank: Unknown
timestamp: June 15, 2011, 06:01:39 am
content: you will burn it out eventually if you give the motor 9V but it sounds like your driving transistors may not be saturated, this means that they are already making more heat than need be and will make even more on 9V so you risk burning them out too. i suggest you look at the motor drive control and see what the problem is there. If you have no choice but use a higher voltage you can use PWM to drive the motor.

author: pklawit
author_rank: Contributor
timestamp: June 15, 2011, 07:04:25 am
content: One remark about the 9V battery - if you mean the small rectangular 6F22, its capacity (mAh)is much much lower comparing to standard 1.5 AA cells.This 9V battery is build of 6 tiny 1.5 cells and they are not intended to drive hard loads like motors, etc.It will be dead very quickly.P.

author: Lawsen
author_rank: Frequent Contributor
timestamp: June 15, 2011, 07:07:14 am
content: I vaguely remembered doing this when I was younger. I have a fascination electric motors. I built a few motors myself with coil copper wires and studied them. It is more than 9V DC that I worried about, but the current. The current helps the motor to spin harder, but there is heat. The coils get hot, when the motor is run for sustained motion for over ten minutes. I would not recommend 9V unless the motor coils are specially made for it. That is why Bosch electric tools will not allow a 12 V DC battery pack to fit a 9.6 V DC powered tool or 14.4 V DC to fit a 12 V DC powered tool. The battery packs appear the same, but a plastic molded stop block is on the top to prevent wrong current and voltage interchanging.Lawsen

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 15, 2011, 07:07:43 am
content: Quote from: jproject on June 15, 2011, 04:18:59 amthat smelly and smoky juice!. you need more juice? you buy more powerfull amperage motor.

author: Psi
author_rank: Super Contributor
timestamp: June 15, 2011, 08:05:46 am
content: Quote from: sacherjj on June 15, 2011, 04:24:57 amyes, but more importantly,If you triple the voltage and that causes triple the current to flow then you get9x the power!.Feeding 9x the rated power into any device is going to end badlyQuote from: jproject on June 15, 2011, 04:27:37 amWhat voltage is across the motor when its running? i suspect it's not 9V, the 9V battery probably can't handle the current and its voltage is dropping to something like 5V. If this is the case you might run into problems later if you connect a 9v power supply that can deliver more current.The only other thing i can think of is that it may not be 3V motors, it might actually be rated for 3-6V or something like that.I'm pretty sure i've seen motors that look the same as your one which are rated for 4.5V

author: tecman
author_rank: Frequent Contributor
timestamp: June 15, 2011, 01:41:17 pm
content: You can use a small buck converter. The other option is a simple PWM driver + freewheel diode to drive the motor. You can use a fixed 30% PWM signal, or make it variable for speed control. A 555 and small power transistor is all that is needed.paul

author: sacherjj
author_rank: Frequent Contributor
timestamp: June 15, 2011, 03:42:14 pm
content: Quote from: tecman on June 15, 2011, 01:41:17 pmThat is an elegant solution for making the motor run in spec using a higher voltage. I think the OP is trying to get more power out of it. The bottom line is you can't get something for nothing. It would be like someone posting in a Auto forum asking how they can get 300 HP out of their little economy 4 banger engine. If could be done, but not in a way that lets the engine run for long.He needs a more powerful motor, if he wants more power. Or gear it down and deal with the slower speed to get the torque required to do the job.

author: Zero999
author_rank: Super Contributor
timestamp: June 15, 2011, 04:29:27 pm
content: Quote from: Psi on June 15, 2011, 08:05:46 amNot necessarily. That's only true if the load is Ohmic and motor is not Ohmic.QuoteYes, the solution is to use a couple of AAs for the motor and a boost converter if the logic requires a higher voltage.

author: Lawsen
author_rank: Frequent Contributor
timestamp: June 15, 2011, 04:52:13 pm
content: It is that O3(g), ozone smell that I remembered, when I was younger. The ozone smells were sweet smells. I usually smells ozone from toy and model DC motors and my parent's coffee bean bar grinder.O2(g) + O-2 electric arcs from the motor's commutator brushes ---->O3(g) ozone gasIf it works without over heating, then the coil and coil wires are able to handle it.Lawsen