Hey everyone,
I have a bit of a dilemma with my girlfriend's BMW—it's been draining batteries like crazy! We've replaced three batteries in just two years, and those things cost around $250 each. We've already spent about $2000 at dealerships trying to figure out the root of the parasitic draw, with no luck. As a temporary solution, I thought about installing a small solar panel in the back window to trickle charge the battery when the car isn't running.
However, I don't want to keep connecting and disconnecting the panel every time we start the ignition, as I'm worried it might damage the panel. I'm thinking of wiring a diode between the solar panel and the battery. Here's where I'm confused:
1. Should the diode be rated for the alternator's output (which is 180A)? I found some diodes rated at 200A, but I'm concerned they might restrict the current from the solar panel to the battery.
2. Do I need to install a diode on both the positive and negative wires?
We do intend to fix the car properly eventually, but for now, I just want to find a way to stop shelling out money for batteries!
3 Answers
It's frustrating that the techs can't find the battery drain. Honestly, a current sensor at the fuse box could really help pinpoint the issue.
As for your solar panel, don't worry about the ignition frying it. The diode you want to use will prevent the battery from discharging back through the panel when it's shaded. Most small solar panels actually come with a built-in diode already, so that might save you some hassle.
Why not just use a standard trickle charger when you're parked instead? You could connect that easily, and it would do the job without the hassle of wiring a solar panel.
Honestly, though, if you’re still set on the solar setup, it's best to use a cheap controller to avoid issues. Just hook the panel to the controller, and then to your battery, setting it for your battery type to keep everything safe and charged.
Good suggestion! Just wanted something convenient. Thanks for the advice!
Just to clarify, a solar panel won't produce 200 amps! Most smaller ones are in the 20-watt range, which translates to about 1.5-2 amps under ideal conditions.
But regarding your concern about backfeeding from the alternator, yes, a diode can help prevent that. You really don’t need to wire it on both sides—just the positive should do the trick. Also, consider getting a simple charge controller to manage the panel's output more efficiently!
I appreciate that! I want to leave the panel connected while driving but was worried about ignition surges. Might look into that controller!
Thanks for the tips! I'll definitely check if the panel has a built-in diode.