Motor Shield Power Supply issue

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daftyi
 
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Motor Shield Power Supply issue

Post by daftyi »

Ive recently bought the MotorShield with the possiblilty to connect the 4 motors. Added the shield to my Mega 2560 main board.
Programmed it, all fine. Put the external 30volt supply (Motors im using require 30volts) to the shield. Mega board powered from
the USB (Motor shield 5volt Jumper taken out) Program seems to be ok for a moment and then Capacitor C8 blows completely.

On reading the web page - www.ladyada.net/make/msheild it states that these shields can operate between 4v to 36volts.
So question is, why did it blow a capacitor? Not sure what else has damaged it. (30volt supply is correct in polority, and is a 0.83amp)

Anyone know the problem??

Steve

adafruit
 
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Re: Motor Shield Power Supply issue

Post by adafruit »

We ship 25V capacitors with the shield, we've updated the documentation to reflect this. if you need new capacitors, email [email protected] and use 25V (which should be fine for a 30V motor). Alternately you can purchase 47uF 50V capacitors at an electronics shop

daftyi
 
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Re: Motor Shield Power Supply issue

Post by daftyi »

Many thanks in replying.

I thought this might be the case. The capacitor is to small. Ill replace this cap with a larger voltage.
Next query - On the current board that the caps blown, would you think its damaged any other companents.
Or just the cap itself?

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adafruit_support_bill
 
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Re: Motor Shield Power Supply issue

Post by adafruit_support_bill »

Likely just the caps. The L293D's can handle that voltage no problem.

daftyi
 
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Re: Motor Shield Power Supply issue

Post by daftyi »

Ive changed the Cap to 100uf 50volt. So thats handling it ok.
Next hurdle is the L293D chip starts to heat up.
Read the www.ladyada.net website and mentions trying a SN754410 Chip.
Same again. Heats up. Is Piggy backing the L293D chip advisable?

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adafruit_support_bill
 
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Re: Motor Shield Power Supply issue

Post by adafruit_support_bill »

They do get warm in normal operation. The question is whether they will get hot enough to trip the thermal protection shutdown - or cause permanent damage.

What are the specs on your motor? The L293D's will safely handle up to 600mA.

daftyi
 
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Re: Motor Shield Power Supply issue

Post by daftyi »

Seems power is an issue.

The thermal shutdown did occur. The Motor is a 30volt Pittman motor
with a Gearbox attached. It is a heavy motor as its come from a moving light.
So im guessing current could be an issue. Ive attached a 12volt supply, seems happy
But when i connect a 30v DC supply, the LED on the motor shield flashes. Motor struggles
to turn and the chip gets hot. Theres not much info regarding this motor as its old,
But the Power supply is 30volt 0.83amps.

http://www.clickautomation.com/products ... 97&cid=236

Above is a link of something simialr to it.

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adafruit_support_bill
 
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Re: Motor Shield Power Supply issue

Post by adafruit_support_bill »

Piggybacking is an option. 2x L293D's will get you a little further than an SN754410. 2x SN754410's will get you close to 2A.
Any heat-sinking you can add will help.
You can also run at a lower voltage. Using the lowest voltage that gives you the torque you need will put less stress on the bridge chips.

daftyi
 
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Re: Motor Shield Power Supply issue

Post by daftyi »

Hi there.

Almost there. Piggy backed another L293D ontop of the L293D . Switched on. And away it went.
Motor was running fine for a few moments. Then it went back stop and start. Stop and start
with the on board LED flicker. So, question. Can i piggy back another chip ontop or is this taking it to far?

But like you say, lower the voltage is the option if the above dosent work.

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adafruit_support_bill
 
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Re: Motor Shield Power Supply issue

Post by adafruit_support_bill »

You can add more, but there are diminishing returns. The main issue is heat dissipation from the stacked chips.

daftyi
 
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Re: Motor Shield Power Supply issue

Post by daftyi »

Hi again.

Just for info really. Ive not added the next chip. Kept it to a two chip array. As for some reason, i switched of the
power, put it back on again and seems to be running fine. Had it running for a good 15mins this morning.
And now ive put it back on again this afternoon. And seems to be very happy.

So far, so good. Seems to be working well. So many thanks for the help. Looks
like i can move on with my project.

daftyi
 
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Re: Motor Shield Power Supply issue

Post by daftyi »

Ps.

There is some heat coming from the chips. But not as much as before.

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Re: Motor Shield Power Supply issue

Post by adafruit_support_bill »

Good you got it running. :D

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