What type of resistor material and tolerance should i use? - Page 1
Forum section: electronics / beginners

author: artvandalai
author_rank: Regular Contributor
timestamp: May 29, 2024, 03:59:16 pm
content: The resistor on my waterpik WP-100W burntout. I know the type of watts and ohms I need to replace the resistor with (47Ohm 2Watts) but im not sure what resistor material and tolerance I should buy for this component. Do i need a resistor with 1% or 5% tolerance and with the material should i get metal film, metal oxide, or carbon-film resistor?Picture of waterpik pcb and resistorhttps://ibb.co/JcXzFSM

author: TimFox
author_rank: Super Contributor
timestamp: May 29, 2024, 04:00:42 pm
content: Please specify the resistance and power rating for the resistor that needs replacement.

author: Zenith
author_rank: Frequent Contributor
timestamp: May 29, 2024, 04:17:15 pm
content: Quote from: artvandalai on May 29, 2024, 03:59:16 pmThe picture didn't appear in the post and I picked it up when I replied with a quote.The colour code looks odd, but I suspect it's a 5% tolerance resistor.I can't imagine it's critical. I'd steer clear of carbon composition and go for a metal film type because they are not much dearer and give less problems. The main thing is that the power and voltage ratings are adequate or better than adequate.An interesting question is why the resistor burned out in the first place. It could have been marginally specified, or there may be another fault.

author: artvandalai
author_rank: Regular Contributor
timestamp: May 29, 2024, 04:36:50 pm
content: Quote from: Zenith on May 29, 2024, 04:17:15 pmIm not really sure why the resistor burnt out. The voltage in my bathrooms outlet measured out at 125v. Searching on forums on repairing Waterpiks I see the resistors getting burnt out is a common problem.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 29, 2024, 04:45:53 pm
content: photo seems at least an 2watt resistorsome burn resistant IE: still able to read the color if they burnas why it toasted you have to find the cause, even if you say it can or could happen, or it's an common problem ...this pcb seems to be a very cheap power supply once filtered and the resistor seems in serial to protect against current overloadQ: what does it feed and at what voltage this small psu generates, it could be substitued with a more modern smps with wider voltage input etc ....

author: Zenith
author_rank: Frequent Contributor
timestamp: May 29, 2024, 05:55:29 pm
content: You might find this usefulhttps://newscrewdriver.com/2022/07/11/waterpik-wp-150w-teardown/It looks as if this is a DC supply which rectifies the mains supply directly and feeds a 125V DC motor. It's not clear what the resistor is for, but the circuit is simple and should be easy to trace and create a schematic for. If the motor bearings are becoming stiff through corrosion, (which would be understandable given that it's likely to be used in environments with a lot of moisture around) that would explain why it demands more current, maybe causing the resistor to be overloaded. It's not unknown for resistors to be used as a sort of fuse.I'm sure this has passed all sorts of safety requirements, but just looking at it and considering the sort of intended use, I have an uneasy feeling about it. I'm inclined to say you shouldn't mess with it, just throw it away and get another, or a better one.

author: Gyro
author_rank: Super Contributor
timestamp: May 29, 2024, 06:14:44 pm
content: Be aware that the final Blue/Violet band could well indicate that it is a fusible resistor, designed to safely open to prevent fire risk due to other faults. You should at least check the rectifiers, motor, mechanism etc. before replacing with exactly the same type. Some examples from a collection of various resistor manufacturers...https://electronics.stackexchange.com/questions/675737/color-code-for-fusible-or-flame-retardant-resistors-data-sheets-standardsP.S. Looking again at the OP photo, it certainly looks to have failed due to sudden fusing rather than long-term overheating (very small area discoloration and no signs of PCB damage).