> Easy build setup with SFH485P, Anyone can build this ! (for 5v Usb serial build see Page 2)
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nadrealista |
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benmeijer @ 19/02/2010 - 00h01 a dit: ...If you're setup has 18 ohm resistors and you will use 3 v, the current is 90 mA and < 100mA (max.)...
Sorry to interfere but rechargeables are 1.2V not 1.5V 
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zoog |
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nadrealista @ 19/02/2010 - 10h45 a dit: benmeijer @ 19/02/2010 - 00h01 a dit: ...If you're setup has 18 ohm resistors and you will use 3 v, the current is 90 mA and < 100mA (max.)...
Sorry to interfere but rechargeables are 1.2V not 1.5V
But the answer is correct though, I asked what would happen if I use normal batteries instead of rechargeables, so 3V
Edited by zoog on 19/02/2010 at 11h32. |
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nadrealista |
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Sorry, omitted that part |
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allabakash |
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its very informative
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boys room décor
extra virgin olive oil |
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allabakash |
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Locheed |
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Hey all,
I just registered here and was looking forward to create my own USB based Freetrack clip. I have already found almost all components, only need to find a suitable PTC fuse.
I have looked many component dealers websites but can't find a component with an 200ma (ihold) and max 300ma (itrip). Many shops don't even tell these values in their website. Place where I buy all other components has only 4 PTC's listed there with a values:
Epcos C860
Tref=120°C
15ohm 265V
1500/140mA(Is/Ir)
Epcos C883
Tref=120°C
120ohm 265V
400/35mA (Is/Ir)
Epcos C886
Tref=120°C
1,5kohm 550V
100/12mA(Is/Ir)
Epcos C960
Tref=120°C
5,6ohm 80V
500/25mA(Is/Ir)
I asked about suitable PTC from them directly, but only got answer for IR-leds.
Edit: btw. How it is calculated what PTC is suitable for it?
- Mika
Edited by Locheed on 26/02/2010 at 12h49. |
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benmeijer |
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see this topic: http://forum.free-track.net/index.php?showtopic=2296
You should find a PTC that will hold, while the current is below aprox. 200 mA, but block when the request for current is high (short-circuiting).
If the power request is above 200 mA the PTC warms up and the resistor value increases. If the request is > 300 or 400 mA it should block totally, and so protecting your usb-port on motherboard. When you release power the PTC fuse resets.
A PTC with a value of 250 mA means ..... below it let the current through, above that it should increase resistance and heatens up and cut off the power.
The values in my serial build are values I think it should be, but you're free to choose your own values, they don't have to be the exact values.
Maybe it's save to use 150 mA (hold) and 250 (trip).
found on wikipedia:
Holding current: Safe current through the device.
Trip current: Where the device interrupts the current. |
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Locheed |
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I checked local part shops and couldn't find suitable PTC fuse. There is not even a values displayed like PTC with a value 250mA.
Neares is a 250mA (hold) and 500mA (trip).
Farnell has a much better components, but price of a delivery is too high.
- Mika
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benmeijer |
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You don't need a PTC for the build to work, if you are sure you don't short-circuiting your build.
The PTC is there for protection of your USB ports on your motherboard in case there's a problem
In my own build I don't use a PTC because I use external power.
5v USB power adaptor.
or use
5V stabilized power
Price ? 7.50 - 10 euro's |
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Milla |
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Are these the correct resistors for the rechargeable battery version?
http://uk.farnell.com/multicomp/mcf-0-25w-18r/resistor-0-25w-5-18r/dp/9339221
http://uk.farnell.com/multicomp/mf25-18r/resistor-0-25w-1-18r/dp/9341463
I'm guessing the metal film version is better since it has 1% tolerance instead of 5% for the carbon film (plus the metal film is more expensive - 2p instead of 1p!)? |
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nadrealista |
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I use metal film ones. You can use carbon ones also (47-52mA variance in your case).
Minimal order is 50pcs. And you will get them for only 1.1GBP.  |
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benmeijer |
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Here are 2 links to sites with good info about resistors:
http://www.doctronics.co.uk/resistor.htm
http://www.electronics-tutorials.ws/resistor/res_1.html
if you read this: "Metal Film Resistors have much better temperature stability than their carbon equivalents" and the tolerance is 1% I think the better choise is metal-film.
I heard that if you blow up your resistor the metal-film cuts the power R --> infinite, while the carbon value of R --> 0. Who can confirm this? |
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nadrealista |
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I heard that if you blow up your resistor the metal-film cuts the power R --> infinite, while the carbon value of R --> 0. Who can confirm this?
Its not true. Both will make circuit break.
You can see how they're made (same) here
http://www.ami.ac.uk/courses/ami4817_dti/u02/index.asp#1.2
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benmeijer |
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Wikipedia: http://en.wikipedia.org/wiki/Resistor
read the Failure-mode section: http://en.wikipedia.org/wiki/Resistor#Failure_modes
"Carbon composition resistors and metal film resistors typically fail as open circuits. Carbon-film resistors may decrease or increase in resistance. Carbon film and composition resistors can open if running close to their maximum dissipation"
is it the same as ?
"All resistors can be destroyed, usually by going open-circuit" |
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nadrealista |
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Well, I've just tried to check up that (16) citation but it is dead link 
Possible explanation could mean that carbon film resistor can increase its resistivity and because of that start to dissipate too much heat and failure itself or in case of decreasing resistivity produce failure on other components.
I don't know what they meant without seeing that document first...
EDIT: I found it.
http://www.fda.gov/ICECI/Inspections/InspectionGuides/InspectionTechnicalGuides/ucm072904.htm
Failure Modes
Resistor failures are considered to be electrical opens, shorts or a radical variation from the resistor specifications. The failure modes experienced vary with the type of construction. A fixed composition resistor normally fails in an open configuration when overheated or overly stressed due to shock or vibration.
Excessive humidity may cause an increase in resistance. A variable composition resistor may wear after extensive use, and worn away particles may cause high resistance short circuits. Wirewound resistors may experience open windings due to overheating or stress, or short circuited windings due to accumulation of dirt, dust, breakdown of the insulation coating or high humidity. Film resistors fail for the same reasons as wirewound and composition, but have also failed due to changes in resistive material characteristics resulting in reduction and increase in resistance value. |