volts???

Kidd · 2004-10-19 18:58

i just started learning about the basic stamp...i·have my basic stamp on·the breadboard with a L293D H-Bridge...but the 9 volt battery im using wont run my motor, by the time it goes through the L293D its only outputting 7.5 v. I have a battery from an old electric screwdriver that says its 3.6v and when i hook that up to the motor it moves really good. Why is the 3.6v battery more powerful than the 9v? Is it safe to hook·the 3.6v·battery up to the breadboard?·and how many volts can the L293D handle and for how long? thanks for the help.

Don · 2004-10-19 20:26

Volts are only part of the story.· You also need to know amps - both the ability of your power source (battery, in this case) to supply·them and the amps demanded·by the load (in this case, mainly the motor).· My guess is that the motor requires too high a current for the puny 9V battery to supply.· The cordless driver battery has the ability to supply higher current, apparently more in line with what the motor draws.

The first step is to get electrical data on your motor.· Sometimes, the voltage and amperage are specified on the motor's nameplate.· If not, you'll have to do some research.· If that doesn't prove useful, you can get some empirical data by measuring the current drawn by the motor in both no-load and maximum load situation.

A run-of-the-mill alkaline 9V battery can provide perhaps 50 milliamps of current.· The capacity of these batteries is only about 500mAh meaning that at a 50mA draw, they will only last around 10 hours.· Also, the voltage drops as the battery's charge dwindles.· Likewise, its ability to provide current to a load drops as well.

It is highly likely that you are going to need a separate supply for the motor.· What size you need depends on what you find out about your motor.

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Don Kinzer

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Kidd · 2004-10-20 16:56

I know that the motor is handling the power from the 3.6v battery fine, what I need to know is will the basic stamp or the H bridge be damaged by using this battery?

cyberbiota · 2004-10-20 17:32

Kidd-

You need to know how much amperage the motors are drawing, and whether the H bridge is capable of sourcing that much current.· Check the spec sheet for the H bridge, and find out how much current the motors are drawing.· The Stamp is on the low side of the bridge, so it should be fine.

peter

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Dr. Peter C. Charles

Director, Research and Technology
CyberBiota, Incorporated
Peter.charles@cyberbiota.com
http://www.cyberbiota.com

Kidd · 2004-10-20 19:41

How can I test how much amps the motor is drawing with a multi-tester?

Thanks

KenM · 2004-10-20 20:07

If your handheld multi-tester has an AMP scale, you can read the current that way. Every DVOM I have seen that will measure current uses the same port for the minus lead, and a seperate port for the plus amperage lead.

Generally, you would want to start out on the highest scale the meter has.....typically 10A.

The meter goes in series with either the positive or negative supply lead. Don't worry about polarity, if wrong, the meter will display minus amps, just omit the minus sign.

If your meter does not have an amp scale, you can install a small value resistor in series with the positive or negative lead, then measure voltage across the resistor. The amperage = voltage measured divided by the resistance.
Using this method, to minimize the impact on the actual circuit, the resistance value should be as small as possible.....0.01 ohms, but if the current is really small, you wont get much voltage across the resistor.

In short, an amp meter is better, but a resistor (for a short quick measurement) will get you close.

Kidd · 2004-10-21 03:05

I've done some testing and when a battery is hooked to the motor it draws 2.0 amps but when i hook it up to the basic stamp and the h bridge and do the same testing the motor can only draw 1.2 amps and doesnt run, Do I need a new motor or a new H bridge? also my h bridge says it can handle 600 Ma can someone help me out.

Thanks

Kidd · 2004-10-21 03:06

the H bridge can handle 600 mA sorry

cyberbiota · 2004-10-21 03:44

Kidd-

Your motors are drawing more amps than the H bridge can deliver.· It is likely overheating and shutting down.· You need a more robust H bridge, or motors that draw less than the 600 mA that the H bridge can deliver.

peter

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Dr. Peter C. Charles

Director, Research and Technology
CyberBiota, Incorporated
Peter.charles@cyberbiota.com
http://www.cyberbiota.com

Kidd · 2004-10-21 04:25

Well the funny think is that the H bridge doesnt feel like it is overheating also what does 600 mA convert to in Amps?

cyberbiota · 2004-10-21 04:37

Kidd-

The internal circuitry of the L293D may overheat before you can feel the epoxy case getting hot.· 600 mA is equal to 0.600 Amps, or less than a third of the current that your motors need.

peter

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Dr. Peter C. Charles

Director, Research and Technology
CyberBiota, Incorporated
Peter.charles@cyberbiota.com
http://www.cyberbiota.com

Kidd · 2004-10-21 04:47

Thanks for all the help could you maybe suggest an H bridge that can handle that amperage?

cyberbiota · 2004-10-21 05:14

Kidd-

Try these...

http://www.allegromicro.com/ic/bridge.asp

peter

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Dr. Peter C. Charles

Director, Research and Technology
CyberBiota, Incorporated
Peter.charles@cyberbiota.com
http://www.cyberbiota.com

volts???

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