1.2W+ per resistor networks? - Page 1
Forum section: electronics / projects

author: TbirdMan
author_rank: Newbie
timestamp: November 11, 2016, 08:14:24 pm
content: Hey all, I am working on a circuit for my grad project and I am hoping there is such a thing as a resistor network (8 resistors) that can tolerate >=1.2W per resistor. I was fooled by Mouser's rating of theBourns 4116R-1-471LFas "2.25W per element" into thinking that meant per resistor not per entire package. If I need to I can fashion a replacement out of individual resistors, but I would like a cleaner solution. Thanks in advance.

author: Paul Price
author_rank: Super Contributor
timestamp: November 11, 2016, 08:40:16 pm
content: No way, only an initially expensive custom made device bought at 10K pieces min, or just use individual power chip resistors..in fact, this is the clean solution but you still must worry about getting all that heat away from your PCB.

author: TbirdMan
author_rank: Newbie
timestamp: November 11, 2016, 09:23:10 pm
content: I see your point about the heat. I could have up to 6 of these active at any time, 6.6W is not a trivial amount of heat. To back up, what I am doing is building a 4 floor elevator trainer that is controlled by an Arduino interfacing with a 24V PLC. the PLC handles the major aspects of the elevator function, the Arduino takes inputs from the limit switches in the trainer and the control signals form the PLC and handles the elevator car motion.These resistors are current limiting resistors for Opto-Isolators (50mA 1.2V). I neglected initially to account for the power a 470Ohm resistor will dissipate at 22.8V. I designed it to use an SIP-9 8 resistor network and an SIP5 4 resistor network. I was able to sub in the DIP package networks with minimal modifications. I think I will make a sub-board with 2W resistors spaced out and if necessary I can add a small fan to cool them (though hopefully this won't be necessary).

author: Floyo
author_rank: Regular Contributor
timestamp: November 11, 2016, 09:35:40 pm
content: If you have a supply rail available somewhere that isn't isolated you could get one of those isolated switching regulator modules, and use that much lower (5/3v3) rail to drive the optos and do the level shiftingwith some fets/transistors running at a much lower current and thus dissipation. 6+ watts of heat is quite a bit and getting around the problem in an alternative way might be more elegant, but if that is a possibility depends on your other requirements.

author: The Soulman
author_rank: Super Contributor
timestamp: November 11, 2016, 09:46:05 pm
content: Quote from: TbirdMan on November 11, 2016, 09:23:10 pmSeems a lot to me, what part number are they?

author: Paul Price
author_rank: Super Contributor
timestamp: November 11, 2016, 09:46:35 pm
content: Unless your elevator trainer is toilet training your elevator for power dumps, I don't quite understand why you need 50mA to do anything. In any case, a single chip buck converter (or module) could efficiently and easily lower the 24V voltage to drive whatever you are dumping all that power into so that 1/4 watt resistors could do the job.

author: darrellg
author_rank: Unknown
timestamp: November 11, 2016, 11:30:18 pm
content: Quote from: TbirdMan on November 11, 2016, 09:23:10 pmMost optos will turn on with a much lower current than that.