I need to put some resistors on my jeep. I picked up 2x 22ohm, 10watt resistors at a local electronic store. They do the job well, but are they waterproof? Can they hold up to the elements?
I put the resistors under the hood, so they should not get wet under normal usage - and I covered them in heat shrink. On the off chance that they get wet, will it chance their resistance?
I'm not talking about the striped cylindrical resistors, but the white rectangular ones.
On the off chance that they get wet, will it chance their resistance?
Unless they are sealed, yes. How much it changes depends on a few factors (impregnation depth, chemistry of the solution, volume, mass, and temperature).
They are made from a porous ceramic powder material so they will absorb moisture from the air and liquid in surface contact. However, if you run enough power through them, they will get hot and "bake" the moisture out. The bigger problem is the impurities left behind by the liquid.
For reliability, seal them with an automative-grade silicon sealant and derate their power rating by 2.
What are you using them for exactly? (just curious)
No they are not water proof. Three things you could do. You could seal them, but since the good Dr. Fried Parts says the power ratings should be halved, you might need to double up on each resistor. Or you can mount them in a automotive rated case, like under the hood car fuse boxes are.
Or you could get Load Resistors designed for automotive use. They are encased in aluminum, to provide resistance against weather conditions without affecting thermal conductivity.
You could also just deal with them as is. Unless you are off roading in river, or driving through flood prone areas, cars normally do not get much if any water under the hood, especially at headlight level. If they did, alternators, batteries, lightbulbs, fuses would all have serious risk of damage with the current state car design.
How about an alternative solution(s)? 1, Get a second set of led turn signal bulbs, hook them up in parallel. You instantly get twice the load on the line.
2, disable or trick the current sense circuit on the line. If people can trick emissions systems to remove o2 sensors that way, I'm sure a simple light bulb burnout sensor or circuit/system can as well. You might need a factory wiring manual for that.
Note also that the leads of this type of resistor are almost universally tinned copper wire, which is a combination that is not at all resistant to corrosion. They need to be kept clean and dry.
You also need to pay attention to how you connect wires (or whatever) to the resistor leads. A crimp connection will be more reliable than a soldered connection. But again, it needs to be kept clean and dry.
