Author Topic: parallel Dc motor conexion problem  (Read 718 times)

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Offline oscyesTopic starter

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parallel Dc motor conexion problem
« on: March 13, 2013, 08:31:07 PM »
hello everybody thank you so much for reading this post,

i am making a robot which has 12 micromotors, and i need to controll them for moving my robot, i am conecting all my motors in a parallel conexion.

i am going to tell you what happens: when i connect my first micromotor it consumes 1 ampere (this at 6V and with no rpm i mean stopped doing full torque), with 1 ampere my micromotor has enough torque for what i need to do.

when i connect my second micromotor to the same power supply, the power supply shows me a total consumption of 1.5 amperes. It isnt supposed to consume 2 amperes with my two micromotors? the thing is that with these 1.5 amperes my motors dont have enough torque for moving, i need each of my 12 micromotors to consume 1 ampere  using the same power supply (is it possible?)

the same happens whe i connect 5 of my motors, the total consumption is like 3 amperes and i need like 5 ampere, 1 ampere for each motor how could i do it?


thank you so much for your help =)


Offline mstacho

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Re: parallel Dc motor conexion problem
« Reply #1 on: March 14, 2013, 06:53:26 AM »
Sounds like you need better batteries or a better power supply :-D  Think of it like this: if I took a AAA size battery and hooked it up to a 0.1 Ohm resistor, then it's supposed to give me 15A, right?  Well...the battery isn't really capable of providing that much current (I think AAAs, in my example, can't really give much beyond 1 or 2 A).

Assuming all the motor resistances are the exact same, then with the correct power supply it should just double the current when they are placed in parrallel and all stalled.

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline oscyesTopic starter

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Re: parallel Dc motor conexion problem
« Reply #2 on: March 14, 2013, 07:54:18 AM »
thank you so much, i am using a 250 w and it has a 3A fuse so it is supposed to give 3 A.

but even when my power suply is capable to suply 3A when i connect my 2 motors they just consume 1.5 A and if i connect one motor alone it consumes 1A. If my power supply is capable with 3A why doesnt it supply 2 A with my two motors?

should i use a capacitor or something or it is my power supply.

Also i have a 1500ma/h battery with 20C but it seems not to work either. thank you so much for your help

Offline mstacho

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Re: parallel Dc motor conexion problem
« Reply #3 on: March 14, 2013, 08:09:53 AM »
Try to see what the voltage is across the motors.  Test the voltage across one motor while stalled, then add the other motor, stall them both, and test the voltage across them.  Your power supply might be able to supply 250W at some voltage, but with a 3A fuse and 6V output that would mean you'll burn the fuse with 18W, not 250.

I suspect that the power supply is not able to supply 3A at 6V.  And remember, if your fuse is a 3A fuse, you'd want to be sure you aren't anywhere NEAR 3A, because you run the risk of blowing up your fuse anyway :-P

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline oscyesTopic starter

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Re: parallel Dc motor conexion problem
« Reply #4 on: March 14, 2013, 09:21:42 AM »
thank you so much for your help, i just did what you told me and i am using my power supply set to 5V and i have 5 micromotors connected but the voltage across each micromotor is just 1.34 V thats why my micromotors are not consuming the current i need.

It is like there was a loss of voltage every time i connect one micromotor to the circuit in parallel so if i connect one micromotor, the volktage across it is 5V, When i connect 2 micromotors the voltage across each one is 2V and the same successively.

what could i do for getting 5V across each micromotor in order to get the expected current? thank you so much for your help again =)

Offline mstacho

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Re: parallel Dc motor conexion problem
« Reply #5 on: March 14, 2013, 10:48:39 AM »
It sounds like your power supply is just not able to supply the current *at that voltage*.  You'll need a better supply, unless anyone else around here knows a better way?

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline jwatte

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Re: parallel Dc motor conexion problem
« Reply #6 on: March 14, 2013, 10:52:41 AM »
I would think you need a much beefier power supply. The power supply you have may say it's 250W, but from what you're telling us, that seems to be a lie.
Here are some example power supplies of various quality levels that would probably work in your situation (assuming 5V is your target):
http://www.digikey.com/product-detail/en/LS100-5/285-1810-ND/1918821
http://www.digikey.com/product-detail/en/SWS755/285-1638-ND/1631805
http://www.digikey.com/product-detail/en/VMS-100-5/102-2511-ND/2803515

An alternative would be to get a high-capacity Lithium Ion battery (7.4V, 2000 mAh or more, and at least 20C current capable) which could also supply the necessary current, but only for some amount of time before needing to be re-charged. You'd also have to take care not to over-discharge the battery, because that could kill it (and maybe even make it explode.)

Offline waltr

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Re: parallel Dc motor conexion problem
« Reply #7 on: March 14, 2013, 09:17:22 PM »
There could be a issue with under sized wires instead of the PS.
In addition of measuring the Voltage at the motors, measure the Voltage at the PS terminals or just after the Fuze when the motors are running and stalled.
If the PS output stay constant or nearly constant and the Voltage at the motors drop as per previous post then the Voltage drop is in the wires.

Another way is to connect the Voltmeter to each end of a wire that carries current to the motors.  If the the Voltage measured is more than a few 10's of mV when the motors are on then the wires are too thin.


Offline oscyesTopic starter

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Re: parallel Dc motor conexion problem
« Reply #8 on: March 15, 2013, 09:21:46 AM »
Hi everybody,
I've fixed the problem by changing wire's size, I was not taking account on this.

Thank you so much waltr.

Offline waltr

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Re: parallel Dc motor conexion problem
« Reply #9 on: March 15, 2013, 06:22:15 PM »
Ok. Great that it now works.

 


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