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I have been buying PSU DIY kits from eBay and I am learning a lot the PSUs that I've soldered together use the LM317 and the resistors used in R1 and R2 can change the outgoing voltage. The LM317 PSU should have no problem going from 1.25V to 30V. I have tried using two different power inputs: one is 12V AC and is only outputting 10.00V DC, then I tried a 15V DC adapter and still only get 10V DC out, so I suspect that the resistor combination between R1 and R2 needs to be changed.

So at this point I am considering getting a breadboard kit so that I don't have to solder in parts; I can just use the breadboard kit to get the parts working the way I want, then solder them in.

This is is a little background information telling how I arrived at the questions I am asking about in this post. I bought a lot of 5-band resistors, the seller penned in what the values are and some are unreadable and have separated from the strip. I went to an online resistor calculator and noticed that there are also 4- and 6-band resistors. This is when the question arose of what the differences are or if the values can even be the same. For example, is there a 4- or 6-band 1k resistor, and if so, what's the difference between them?

I also have put together an LM338 3A PSU module and it is basically acting the same way as the already mentioned LM317 PSU module.

Is the breadboard a good idea for this type of thing, and if so, should I also buy lots of 4- and 6-band resistors?

Any input is welcomed.

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    \$\begingroup\$ Please post the schematic for the PSU \$\endgroup\$
    – DerStrom8
    Aug 25, 2016 at 17:13
  • \$\begingroup\$ Don't have one and not sure what that would help with for my questions.This is a link to the item and what I used as a guide to put it together. I Have 4 different ones ebay.ca/itm/… \$\endgroup\$
    – KoolBreeze
    Aug 28, 2016 at 16:14
  • \$\begingroup\$ I have this kit as well ebay.ca/itm/… The issue with this one is the polaity is reversed poisitive is negative. I have been using the power meter to try and locate where it switches but I can't find the issue now I am considering unsoldering it all and then trying again but soildering and resoldering tends to ruin some of the pads forcing me to add wires, so I am hoping someone could give me a clue as to check before doing a full teardown. \$\endgroup\$
    – KoolBreeze
    Aug 28, 2016 at 16:21

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The difference between 4, 5, and 6 band resistors is (mostly) the resistance tolerance.

A four band resistor will have two bands giving two digits of the value, third band is a multiplier (number of zeros to follow the first two digits), and the fourth band indicates the tolerance - silver is +/-10%, and gold is +/- 5%

A five band resistor will have three bands giving the first three digits of the value, and will be +/- 2% or better.

A four band 1000 ohm 10% resistor may actually have a value somewhere between 900 and 1100 Ohms. (1000 +/- 10%)

Search for an LM317 datasheet to learn about the LM317 voltage regulator, and how to calculate the voltage adjustment resistor values.

Unless the power supply kits you have include a rectifier, you must not supply them from an AC source - the LM317 needs a DC input at least 2.5 volts higher than your desired output voltage.

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  • \$\begingroup\$ If the resistor manufacturer uses binning for the tolerances, then 10% resistors will not be within 5% of the rated value, 5% resistors will not be within 2% of the rated value, and so on. Except that tighter-tolerance resistors may be manufactured on a different line. \$\endgroup\$
    – Andrew Morton
    Aug 25, 2016 at 20:33
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    \$\begingroup\$ @AndrewMorton: I've often heard that rumor, but never experienced it. It may once have been true, for carbon composition resistors, but I don't recall seeing any evidence even then. I once measured 50 or so Philips carbon and metal film 10K 5% resistors - they were all within 1%,and a hair under 10K by my meter. I decided my meter was reading a bit low... \$\endgroup\$
    – Peter Bennett
    Aug 25, 2016 at 23:26
  • \$\begingroup\$ I am not sure I understand what your saying can a set of 5 band resistors cover all the needs I would have? Let me put it this way does 4 and 6 bands have equal values do they all have a 1k resistor value and if so whats the difference between them? Perhaps I should say it this way can a 5 band 1k cover all projects? \$\endgroup\$
    – KoolBreeze
    Aug 28, 2016 at 16:33
  • \$\begingroup\$ Yes, a 5 band 1K 1% resistor can be used anywhere a 1K resistor is called for (assuming it it the correct, or greater, power rating). A 1% resistor should be within 1% of its marked value, while a 5% resistor can vary as much as 5% from its marked value. There are some 5% standard resistor values that are missing from the 1% standard values, but using the closest 1% value will get you well within the grange of the "missing" 5% value. \$\endgroup\$
    – Peter Bennett
    Aug 28, 2016 at 16:44

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