Fuse?
salik
Posts: 9
Just as a safety precation should I put a fuse inbetween the battery and the stamp controller ? I don't want to fry the board in anyway. And if so what fuse should I use... its a Basic Stamp 1
Comments
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Chris Savage
Parallax Tech Support
csavage@parallax.com
There are no stupid questions, but some answers can be doubtful.· Chris often doesn't have much time to explain as he is an employee.· Consider the following:
If you try to buy a less than a 100ma fuse, you will find two things.
1. Nearly impossible to locate any fuse in that small size [noparse][[/noparse]so someone is amused].
2. Such small fuses cause a big voltage drop due to internal resistance, so you need a higher voltage supply.
Generally fuses are to protect people from shock and fire. Overload is usual when too much is put on a small wire. But, the BasicStamp is really way below that as the wire diameter [noparse][[/noparse]at 20 gauge] is comparatively huge.
In some cases,·fuse can provide immediate shut down when a motor is jammed.
An excellent alternative is a 'current limiting' device; usually a transistor or a voltage regulator that has been especially configured. These can handle small loads, but they do waste a lot of battery life.
Your concerns for protection should be looking at the I/O pins. Some people prefer to use 220 ohm resistors to prevent damage to the BasicStamp.
As you start plugging things into the BasicStamp, it will draw more power and BS2 uses much less than the BS2SX.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 3/16/2006 8:31:51 AM GMT
Your intentions are indeed honorable, but there is some practicality missing. There are a number of areas, so let me try to point them out to you, for your consideration.
First, your thinking about a battery or any other power source needs to be expanded a bit. When used in or on a computer or computer-like system (microcontrollers included), think of them more like the electrical utility company, rather than something you drop into a flashlight. What is most true about this concept is that the electic utility can provide many different forms of electricity, based on their cutomers needs. So too a power supply may provide (say) 12 VDC @ 2A, which is used as a power source for driving small DC motors, 5 VDC @ 500 mA which is used for some of the older style chips, and 3.3 VDC @ 200 mA for supplying voltage and currrent to some of the newer style chips. One fuse can not and will not protect all of this, and one size fuse would be inappropriate as well. Any fuse placed at or near the power source(s) can only be intended to protect the power source itself from a dead short, nothing more. If one has done their homework, in providing appropriate down-stream overcurrent protection, this will usually be unnecessary. More on this below.
Second, think of any electrical or electronics circuitry as a network, or series of pathways (conductors), with intersections and cross-overs (tie points), bridges (jumpers) and final terminations (end of circuit), with electrical or electronics devices interspersed within.
Third, all of the elements within an electrical or electronics circuit deserve over-current protection. This can occur in a number of ways. Briefly, these elements or components may be self-limiting as to current consumption and provide their own current regulation, current limited by an over-current protection device (fuse, circuit breaker, etc), or current tolerant and designed to fail apppropriately. An appropriately sized fuse which blows has provided the protection intended, but it self-destructs (usually nicely) in the process. A diode can also be used sometimes as a self-destrucing, overcurrent protection device.
Fourth, the farther down-stream overcurrent protection is afforded, the greater the total system protection will be. In other words, one places a fuse inline with a motor, and one with every motor, to protect the rest of the 12 VDC (in our system) upstream of the motors. The fuse may blow on any one motor, but the rest of the 12 VDC system remains intact.
Fifth, protecting the "wires" or current conductors is what over-current protection is mostly about. It may not seem that way in the case above, but what you are really protecting is the tiny wires inside the motors. If the fuse is appropriately sized, the fuse will blow before the tiny wires have a chance to heat up and melt. As in the case of this motor, many wires you can not even see. There are (often tiny) wires inside of integrated circuits, transistors, potentiometers, etc. and most electronics components.
The best protections you can afford a microcontroller are two-fold. One is at the regulator which supplies the power to it (usually self-regulating), and second at the pin ports where external devices are connected.
Now, here is the rub about protecting pin ports. They only provide very small amounts of current, usually less than 50 mA. Standard fuses just don't come in values that small. So, what's to be done to protect them? We can either use a device which will limit the current output (an appropriate resistor) or, if available, use some reasonably inexpensive device which will self-destruct if an overcurrent condition exists. Usually an appropriately sized resistor is used to protect microcontroller pin ports.
As you somewhat pointed out, one must be careful when soldering, since solder bridges can end up creating unexpected current paths! Sadly, there is not a lot one can do, other than checking the circuits carefully BEFORE applying power, to prevent damage caused by soldering deficiencies.
I hope you find that basic information helpful.
Regards,
Bruce Bates
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In general, people don't worry about fusing at these low voltages and low currents. Fusing is usually used with 120 VAC, to prevent fires and electrocution. Fusing is to protect people, mostly.
Note that the linear regulator on the BOE board does its own over-current protection.
·· First of all I would like to thank you!· Parallax is always looking for feedback on ways we can improve ourselves and I feel that perhaps you have made me more aware of something I wasn't.· Recently our customer base is growing very rapidly.· With the changes like the SX Line coming to Parallax directly and with the Propeller and other new products things have been a bit stretched out here.· But that is no reason to let our support standards falter.· Some of my more recent explanations have probably been too general and in the future I will make every effort to answer posts as I used to a year ago.· I appreciate you helping me realize this.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
But I have learned to look at my circuits and double check the power and ground lines before I plug in my BasicStamp. Your knowledge will do far more to protect both you and the BasicStamp than relying on a fuse.
Chris,
I am happy to hear you are growing. We all are.
Seems work is always demanding, chaotic, and tiring. [noparse][[/noparse]What else is new!]
FYI,
I know you have to read and consider everything --- I don't.
I can pick and choose who I answer. Or I can take a week off.
You have to respond in a more responsible manner for the sake of protecting the user and your enterprise --- Sometimes a short response makes things much clearer as a starting point.
{Even when the user really wants a long dialogue or to parry pro and con.}
And I know that the Propeller is demanding everyone work harder lately. {But I am really looking forward to seeing something so new and different.}
The neatest thing about Parallax is that we do get contrasts and sometimes a learner needs a different presentation than the one you or I try.
I certainly flub my share and quietly go away. No one 'bats 1000' and I am learning through writing. It forces me to look critically at what I know.
Of course, Jon Williams is our resident 'past-master' of the BasicStamp and seems to often manage to do far more with less words. [noparse][[/noparse]I suppose that is why he is such a popular writer too].
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan