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Been looking around the forum a lot to find out the answer to my question. Still not done yet actually. But might as well ask this is the mean time:

I have a driver that can only put out 1Amp at 1.5V (called L293D dual H-Bridge). I have a motor that needs 2.8Amps at 2.1 volts. what happens when I put them together?

Will the driver chip burn out?

How about this combo: driver gives 1 Amp and 4.5V to 36V (called SN754410 quadruple Half H Driver) used with same motor.

I understand that voltage stats are not really important as motors are often run at voltages about thier rated. But rather the current is more important. That's what worries me here. I think know a motor that takes more current than a drive can give will burn out the driver chip.

BTW thanks for all previous help. I just kinda left my previous thread dead as I found more reading material, and will be back to it eventually to beg more help.
« Last Edit: August 05, 2012, 08:54:13 pm by herewego » Logged

Left Coast, CA (USA)
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Been looking around the forum a lot to find out the answer to my question. Still not done yet actually. But might as well ask this is the mean time:

I have a driver that can only put out 1Amp at 1.5V (called L293D dual H-Bridge). I have a motor that needs 2Amps at 2.8 volts. what happens when I put them together?

A motor driver that can only supply 1.5v output, that doesn't sound correct. The problem is of course the current rating well below what the motor can require depending on drive voltage and load on the motor. Some motor drivers have over-current detection and cut-off protection, some I suppose don't and you can risk damage if overdriven.

Will the driver chip burn out?

How about this combo: driver gives 1 Amp and 4.5V to 36V (called SN754410 quadruple Half H Driver) used with same motor.

Still not rated for enough current to support the motor under all conditions. Recall that a driver doesn't 'force' a specific amount of current to it's load, rather the motor tries to draw a specific amount of current given it's resistance, counter EMF, and mechanical load.

I understand that voltage stats are not really important as motors are often run at voltages about thier rated. But rather the current is more important. That's what worries me here. I think know a motor that takes more current than a drive can give will burn out the driver chip.

That is correct, unless the driver has build-in overcurrent protection circuit.

BTW thanks for all previous help. I just kinda left my previous thread dead as I found more reading material, and will be back to it eventually to beg more help.
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New York
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Can I add on some little resistor/transistor type things (not sure what would actually be needed) into the circuit somewhere to supplement some more current to the motor? Kind of like this guy did? :

http://www.azega.com/controlling-a-stepper-motor-with-an-arduino/

Or maybe is it possible the just leave out driver chip and just drive my bipolar stepper with those kind of little black things in the pictures?

Also, a separate question, do you think I would have any trouble using this as a power source here (only need to motor to be moving for 30 seconds or so at a time. kind of in a testing phase here):
Enercell® 6V Zinc Chloride Heavy-Duty Lantern Battery
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I have a driver that can only put out 1Amp at 1.5V (called L293D dual H-Bridge).

Where did you get that info from? An L293D has a voltage range from 4.5V to 36V. Continuous current is 600mA per channel, and peak current is 1.2A per channel.

http://www.ti.com/lit/ds/symlink/l293.pdf
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New York
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Yes you're right, I don't know how I made that mistake. Question stands though: how do I get 2.8 amps to my motor if the driver only gives normally 600 ma? I dont want to order another driver- it'll take time to get here. I was wondering if could use little transitors/resistors form radioshack?
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You can buy a L298 shield from Ebay  http://www.ebay.com/itm/Motor-Controller-Shield-L298N-Drive-2-Motors-for-Arduino-Duemilanove-UNO-Mega-/360473365417?pt=LH_DefaultDomain_0&hash=item53ede30ba9#ht_1593wt_1397 from a US shipper for $8.99 + $1.98 shipping it will work to 46V @ 2A dual motor controller too

Doc
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Thanks. I was hoping i could avoid ordering stuff though. Also I don't think that shield solves the problem of not supplying 2.8 Amps to the motor. So the transistor idea is a no go?
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DESIGN 19
High Current H-Bridge-2
This circuit will deliver up to 3 amps to a 6v motor. Use TIP100 (NPN) and TIP105 (PNP) for 8 amp
H-Bridge.
http://www.talkingelectronics.com/projects/H-Bridge/H-Bridge-1.html
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Design 20 will work as well and it can also be PWM'd... The BC547's are 2N222A's. Actually after having re-read the data sheets on both I'd use the 2N2222A's. One other point re: design 19... 1N4148's are TOTALLY inappropriate as back emf diodes, Use 1N5404 3A 400V PIV diodes...

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the land of sun+snow
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The problem with those sorts of circuits is, they are firecrackers waiting to go
off. If both high and low sides of the bridge get turned on simultaneously for
any reason, you get smoke. Eg, error hooking up. Eg, error when using scope
probe. Eg, one of the other transistors shorts out for some reason, eg,
inductive spike.

I would use a fuse in the battery line.

In my own playing around with h-bridge prototypes, I once literally set a 754410
chip "on fire". I'd seen smoke before, but never actually "fire". LOL. In another
case, the top MOSFET didn't shut off properly, so there was a short through to
the lower MOSFET, and IIRC, they both melted off the pcb, after the smoke.
8 Amp designs are really dealing with quite a bit of current, and low pathway
resistances.

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If both high and low sides of the bridge get turned on simultaneously for any reason, you get smoke.
Design 20 looks more safe on this matter, compare to other options, Two additional low power transistors do great work, to ensure there is no through current. At least at low freq. PWM
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the land of sun+snow
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Design 20 looks more safe on this matter, compare to other options, Two additional low power transistors do great work, to ensure there is no through current. At least at low freq. PWM

Yes, as long as you don't muck up in one of the ways I mentioned. Eg, how many
people have accidentally shorted 2 pins with a scope probe, or dropped a screw
driver on the circuit board. Answer: everyone. The nice thing about integrated
h-bridges is they have a lot of protection built-in. Over-temperature, over-current,
inability to scope internal nodes, etc.

Still, probably best to use a fuse in the power line. Any kind of short will likely
pour in so much current the fuse will pop quickly.
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