| Author |
Message |
    
Dirk Hazeleger
Registered
Username: Dirk
Post Number: 13
Registered: 12-2005
| | Posted on Saturday, June 10, 2006 - 12:28 am: | 
|
I've got a quick question as to sizing fuses. Should they be fused acording to amps drawn on stepper, or did I read you should just use a 5 amp. I was planning on quick blows sized to amp of motor. Any input?
Dirk |
Gerald_D
Registered
Username: Gerald_d
Post Number: 120
Registered: 11-2005
| | Posted on Saturday, June 10, 2006 - 06:14 am: |
|
The GeckoDrive recommendation is: "It is good practice to use a fuse (5 Amp, fast blow) for each drive. This way if a fault develops such as a short to ground, windings shorted, etc. the fuse will blow and protect the drive and power supply. It is cheap insurance."
Note that the fuse is not there to protect the motor. Even if the current limit of the motor is 1 Amp, the Gecko remains a 5 Amp device and a 5 Amp fuse will protect it, but the motor could toast without the fuse blowing.
I somehow don't think that automotive style fuses qualify as fast blow? But, the modern automotive electronic components probably require as fast a blow as any other device, maybe they do qualify as fast blow? Come to think of it, is anyone really that concerned about the speed of blow when they buy or make a fuse? |
Dirk Hazeleger
Registered
Username: Dirk
Post Number: 14
Registered: 12-2005
| | Posted on Saturday, June 10, 2006 - 06:53 am: |
|
Thanks Gerald.
So if you need to use a fuse no more than 5 amps, what happens when youre driving a big motor and have the current set at a full 7? Is it one of those cases that there's really not 7 amps going through the fuse, or are you going to start blowing fuses?
Dirk |
Gerald_D
Registered
Username: Gerald_d
Post Number: 121
Registered: 11-2005
| | Posted on Saturday, June 10, 2006 - 08:15 am: |
|
Dirk, I was wondering that myself, and that's why I wandered into the issue of speed of blowing...
Maybe the 7 Amp draws are so few and far between that they don't blow the fuse? Maybe the 7amp is an "AC" peak current of the steps on the output, and the DC input is a smoothed lower value? Maybe there is a misprint in the Gecko instruction from long ago?
I have asked the following on the Gecko forum:
"The G200's can drive 7 amp, the recommended fuse is 5 amp. Is this because the output 7 amp is the "peak" value while the smoothed input is a lower value?
If the G200 is current limited to say 1 amp, is there any merit in a lower value fuse?"
|
Mike Richards
Registered
Username: Richards
Post Number: 14
Registered: 05-2006
| | Posted on Saturday, June 10, 2006 - 05:08 pm: |
|
The general rule of thumb for fast-blow fuses and circuit breakers is that the fuse is guaranteed to blow at the rated current. Most fuses will also blow at some point between 0.75% and full current if that current is contineous. Of course, you should check the spec. sheet for the fuse that you intend to use.
When I fuse something, my greatest concern is to first protect the main wiring so that I don't cause a fire by overheating the wiring. (15amp breaker with 14 guage wire, etc.) Next I select a fuse to protect the weakest part in the circuit. In the case of stepper motors, if the motor were rated at 3amps and the driver were rated at 7amps, I would use a 3amp fuse (ideal world conditions where the fuse held until 3amps passed).
If it was certain that the weakest link could handle short bursts of higher current, I might use a slow-blow fuse instead of a fast-blow fuse.
In my opinion, Mariss lists 5amp to keep us from blowing up his drives. None of the motors that I've ever tested are rated anywhere near 5amps, so a 5amp fuse wouldn't help there. In theory, the current setting resistor would limit the amount of current available to the motor, but using a fuse would be my preference. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 126
Registered: 11-2005
| | Posted on Tuesday, June 13, 2006 - 07:01 pm: |
|
Steve Stallings (of PMDX) replied at the Gecko forum:
".......The chopping action of the motor driver acts to "transform" the higher voltage, moderate current power input into the higher, regulated current at lower voltage that actually drives the motor coils. As a result the fuse does not need to be rated at the motor current. The fuse will not be fast enough to protect the MOSFETs on the driver anyway. It primarily serves to limit damage to the etched circuit board and wiring so that repairs may be possible, and to prevent more severe consequences like fire." |
vadeem
Registered
Username: Vid1900
Post Number: 33
Registered: 10-2006
| | Posted on Tuesday, February 13, 2007 - 09:15 pm: |
|
Gerald,
I see that you are using auto blade fuses. The auto blade fuses I can find are all rated at 12v, not 120v (or even 80v).
Are yours rated at 12v ? |
Gerald_D
Registered
Username: Gerald_d
Post Number: 881
Registered: 11-2005
| | Posted on Tuesday, February 13, 2007 - 09:54 pm: |
|
80V Auto fuses
Fuseholder example |
Power Supplies