Changing Electrical componet sizes

[nod]

Hello, Its been a long time since I've done electronic troubleshooting. I was wondering about changing resistors & Caps that are bad with some that are larger. I have a 15 ohm 1/4 watt resistor thats bad & was wondering if I could use a 15 ohm 1/2 watt. Also I have a .1 mf 100 volt cap and wondered if a .12mf 600 volt cap of the same kind would work. Its a little physically larger but not to big.

Thanks Don

 

[melone]

The resistor is a no brainer (yes), but depending on what the cap is doing, it isn't so easy. Figure out what it is doing, and then determine whther changing the capacitance will affect circuit performance.

 

[Lewish]

Just make sure the circuit doesn't require a non-inductive resistor. A larger wattage doesn't affect performance.
As to the capacitor, 0.1 mfd caps of all kinds of voltages are readily available. Check digi-key if you are in North America.

 

[buzzp]

Resistors are not necessarily no brainers. Generally it is, but you need to look at tolerances/material types for temperature drift and related items. Capacitors are generally no brainers but can have a significant affect on circuit performance (capacitance and type, not voltage as long as voltage is higher than the original). What is the capacitor doing? Coupling, bypass, etc..

 

[melone]

The old 15Ohm 1/4Watt resistor is notorious for being a highly specialized component. You couldn't possibly find one of those in any resistor kit. I'll even go out on a limb and say it is probably a leaded component.

OF COURSE there are circumstances that require special resistors, but by the sound of the orignal post, I don't think bumping the power will cause too much problem. However, just dot your i's and cross your t's and make sure you know exactly what the circuit is doing.

With regards to caps, those are definitely NOT no brainers (not + no = is???). Even keeping that same values (C, %Tol), can have hugh circuit implications. Try changing a cermaic cap to a lytic in a timing circuit. (might work at room, but wait till it gets hot). That is exactly why I told him to figure out what the cap is for.

 

[Lewish]

Hi melone, I will agree with you that it is a leaded part, but maybe not specialized. 15ohms is a standard resistor value for a 5% part. I happen to have a bunch of 15ohm carbon comp resistors left over from meter shunts.
If I knew exactly where they were, I would send him one.
As to capacitors, try making the mistake of putting a 10uF ceramic on the output of a linear regulator, and see what frequency it oscillates at. It had better be a tantalum or electrolytic. Just the point you made.

 

[buzzp]

Yeah, use a carbon film in place of a wirewound in a high temp environment where the TC and noise properties can play games with any measuring circuit, especially older ones. Or nevermind the widely varying high frequency characteristics of each type of resistor. You simply made my point, figure out what the circuit is doing. Or if the equipment is not doing anything important that could hurt life or limb, put it in and see what happens. Chances are nothing, it very well could be fine. If I tell my purchasing agent to buy any resistors with only a resistance and wattage spec, who knows what he will deliver.
BTW: His component is probably a thru hole part but most resistors made are not thru hole parts. Also, I was not disagreeing about the statements made about capacitors. Obviously ESR values, polarity, and frequency of operation can have a significant effect on circuit performance, again depending on the application.
Breath melone breath.

 

[nod]

Thanks to all who replied to this thread. I found the 15 ohm 1/4 watt resistor 5% tol. at Radio shack. It was a carbon resistor. Sorry I had a typing error, I said I had a .1 mf cap at 100 v and was wondering if a .12 mf at600v would work. It should have been a .1mf at 600v. As far as what the cap does, I will pull the print out and look at it again. I've been waiting on some other componets to come in so I can install them all on the board at one time. Just so everyone knows I'm repairing a Star Castle arcade video machine.

Thanks again
Nod

 

[buzzp]

This certainly is not critical so I would drop them in and see if they work. If you are getting paid for this you may want to spend a little more time evaluating the circuit for the parts replacement. If you use the same material parts, you should have no problems. Good luck.