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Old 09-23-2010, 01:09 AM
bassplayer142 bassplayer142 is offline
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Default Time Delay Fuse for DC Motor

Does anyone have any information about time delay fuses in series with a DC motor for protection against over current. If a DC motor is rated at 32 Amp stall current, what value of a fuse should I have? 30 Amps? An H-bridge I'm looking into is rated at 20Amps continuous with 30Amp peak.

Any help is greatly appreciated. Thanks in advance!
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Old 09-23-2010, 01:21 AM
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You may want to look at a bridge that will handle more current, or use individual mosfets and use a h-bridge driver ic. Another thing you may want to look into is using current sensing and the associated control methods instead of time delay fuses. What are the motor specifications and what type of control do you need (what will the motor be used for)?
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Old 09-23-2010, 01:40 AM
Jaguarjoe Jaguarjoe is offline
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This might work for overload protection:

http://www.sensata.com/klixon/motor-protector-6ap.htm

They will give you free samples, so if you only need one, you'll be all set.

sgardner025 is right- you need a heftier bridge if you want trouble free operation.
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Old 09-23-2010, 01:46 AM
t_n_k t_n_k is offline
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Quote:
Originally Posted by bassplayer142 View Post
Does anyone have any information about time delay fuses in series with a DC motor for protection against over current. If a DC motor is rated at 32 Amp stall current, what value of a fuse should I have? 30 Amps? An H-bridge I'm looking into is rated at 20Amps continuous with 30Amp peak.

Any help is greatly appreciated. Thanks in advance!
You would probably better focus attention on protecting the power semiconductors rather than the DC motor - which in terms of over-current is a fairly robust device in comparison to a semiconductor switch.

Normal practice is to use fast acting fuses for semiconductor protection so using time delay fuses may not be desirable. Perhaps a combination of the two types is required. Alternatively, graded motor protection might be accomplished with an adjustable thermal overload relay of some sort. Depends on your budget and the degree of 'sophistication' required.
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Old 09-23-2010, 02:46 AM
bassplayer142 bassplayer142 is offline
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Thanks for the prompt and helpful replies! I will need to power two motors to drive a tank style robot up a stairs at a 32deg angle. The robot will probably be 20+ lbs.

The type of motors I am looking at are below with a large gear ratio for higher torque. The H-bridge I am looking into is also shown below. The protection circuitry is just extra stuff to make sure I don't burn anything from mistakes. I haven't decided on a power supply yet so just neglect that for now.

http://www.robotmarketplace.com/products/0-HG312.html
http://www.robotshop.ca/cytron-10-30...ontroller.html
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Old 09-23-2010, 03:09 AM
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A lot of the power window circuits on automobiles utilize a very fast overcurrent switch on the driving motor.

Then there are Polyfuses, they work pretty well too.
http://www.littelfuse.com/data/en/Pr...lyfuse_PTC.pdf

Most standard motor protectors for AC are built into the motor starters themselves and operate both via a magnetic overcurrent and a thermal heating strip. The heating strips are interchangeable to match the motors.
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Old 09-23-2010, 03:44 AM
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Code calls for a 150% FLA rating, be it time delay, non time delay, or circuit breaker.
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Old 09-23-2010, 11:21 AM
Jaguarjoe Jaguarjoe is offline
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There's code for toy robot motors?
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Old 09-23-2010, 11:50 AM
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Sorry, missed the hobby robot thing.
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Old 09-23-2010, 12:17 PM
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The driver unit you're considering most likely contains a VNH2SP30-E IC, which is a fully integrated H-bridge motor driver with PWM.
Datasheet: http://www.st.com/stonline/books/pdf/docs/10832.pdf

It will likely be one of the most compact and low weight solutions that you'll find; both pretty important considerations for a robot - not to mention the relative simplicity of integration.

Marshallf3's Polyfuse suggestion is a very good one. Compact, inexpensive, and automatically resets. You could also use an automotive-type circuit breaker, but it would be larger, heavier, and likely more expensive.
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