Car battery charging question

[aortiz268]

Hi guys brand new to solar was thinking about doing solar i park up my car in the street sometimes a month at a time and needed help before i made a purchase to be able to solar charge my car battery (d3400) since i dont have access to an outlet. I call my battery company (xspower) they suggested i trickle with at least 15 amps per hour. while googling i am seeing you need a decent size solar to get to this amount. Is this something i can diy and save some money. and can i get the 15amps from solar during the day.
what size panel (watts) would i need to invest in. i know i need a decent solar charge controller as well.

 

[DThames]

You can keep a 12v car battery charged up with a 10watt solar panel. Something like this.

 

[MrNatural22]

You can keep a 12v car battery charged up with a 10watt solar panel. Something like this.

That looks like it would maintain an idle car battery. ️️

 

[Hedges]

I have a horrible problem with car batteries because I don’t drive my car much. I drive every week but only for very short distances. On top of that I travel for work, so my car can sit idle for two or three weeks at a time. Bottom line— even a brand new battery will require a jump start in about six months time. And I have used the Sunway solar car charger, my problem is solved

A good AGM battery can sit for months and start the car right up.
I had such good luck with my first yellow-top Optima that I put them in all my cars.
They started dropping like flies.
The pair of full-size ones in my K2500 have been fine, also one in step-son's RSX.
But one in the Sable, a daily driver, went out. I suspect loads that don't disconnect due to gremlins.
In my Civic, I went through three of them, about 18 to 22 months each. Auto store kept replacing them regardless of manufacturer's warranty.

Now I have blue Bosch batteries in both those cars. OK so far, but not 5 years yet. Also put a small PV panel in the Sable.
I've carried a spare battery for years. That has served me well. Now, a clutch-sized lithium jump-start kit from Harbor Freight.

I've wondered if I could press a SunXtender into starting battery service. A set occasionally recharged over a decade is still kicking.

Panels can work, ideally with a voltage regulator keeping battery at float voltage. An unregulated panel puts in power, but isn't great.

 

[snoobler]

The linked panel should do it provided you can position the panel favorably.

One can simply disconnect the negative cable from the 12V. Cars pull 15-40mA from the battery all the time. That will flatten most batteries in a month or two. Most vehicle charging systems are pretty abusive to the battery and rarely get them truly fully charged, so that month or two could be notably less if the battery never gets fully charged. Fuel savings motivations have pushed manufacturers to pursue even less healthy treatment of the 12V for very tiny savings in fuel.

The key to buying a good battery is looking for the manufacturer. If it says "Made by Johnson Controls" or "made in Mexico," you can count on it being shit. Yes, Optima is made in Mexico. JC sold their battery division to Brookfield Business Partners - an investment firm. I'm confident they will only get worse as they try to enhance profits.

 

[chrisski]

I had a problem with batteries dying on my car after sitting four to seven days, parasitic draw I think, and when I traveled a few weeks a time six months a year, I would disconnect the battery on my car, and it always started fine. I just kept a 10 mm wrench in the dash. I'd tried a Pulsetech Solargizer panel with desulphate technology and a regulator, but it didn't work.

I took the same Pulsetech Solargizer panel and put it on my dual battery truck which had been dying when parked more than a month, and left it on for six months without driving it, and it started like a champ after sitting idle for so long.

So, I think if your battery is dying so quick, even when new, I'd suspect a minor parasitic draw, which you can troubleshoot, or its much easier to unhook the battery. An average smaller car charging panel may not keep up.

 

[Hedges]

I think I blew a fuse in my meter trying to measure how many mA the car drew from battery (different terminals on the meter for 10A vs. 150 mA). When you first complete the circuit with an ammeter, it charges capacitors, and maybe ECU powers up to check state of key switches.

The trick is to short out the meter (e.g. stackable banana plugs) while completing the circuit. Then unplug the shorting jumper so current goes through the meter.

Of course any car much younger than me has an ECU with tuning parameters stored in volatile RAM. Disconnecting the battery for a period of time is one way to clear error codes, also causes loss of data for mixture and other settings, which are re-learned while driving under a variety of conditions. Small price to pay for having it actually start those days you plan to use it. In the case of my Sable, also transmission shift settings. Presumably wireless key fobs are recognized using non-volatile memory.