Solar charger for car battery?

[David Thomas]

If you park any modern car, but Priuses (Prii?) more than most, at the trailhead for a long time, the 12-volt battery can discharge.  There are 5- and 10-watt solar panels to sit on the dashboard and keep it topped off, but I’ll be leaving it parked for months at a time and so I fret about the solar panel’s voltage regulation.  Do any of the more techie BPLers have a recommended make and model of charger for that application?

Backstory: I so enjoyed bringing Casey’s old Chevy Bolt EV up the Alcan from Berkeley to Kenai last month (Fall colors, no motorhomes, no road construction, free Canadian electrons), now I want to see the OTHER side of the same trees and drive the 3200 miles south, in my 2005 Prius, and leave it in the SFBA, PHX, etc, so when I come south to hike, 1) avoid rental car fees and 2) there’ll be my hiking stuff, basic tools and clean underwear already there allowing me to travel lighter and not check bags.

Oh, and like Dick Cheney, the Prius will be in “safe, undisclosed locations” so I’m conscious of but not too worried catalytic converter theft in the big city.

[Ray J]

I’ve got no input on a Solar Charger for a car battery.  If you are parking for very long, there are all the other systems that need attention.  Fresh oil.  Tires about 4 pounds high.   Disconnect the battery.  Trickle charger on it.   Clean fresh brake fluid.

Can you park it someplace where you can place it on a charger?   Or, park it someplace and allow the person to use the vehicle about once a month.  NOT just “Start it and let it run for a few minutes”.  That does more harm than good even in just a few weeks.   Someone drive the car about 30 minutes to burn off the condensation and let the car recharge the battery, knock surface rust off brakes.

[Richard Nisley]

To trickle charge a 12V car battery without using a voltage regulator, the solar panel should not exceed the battery’s voltage significantly. Generally, a solar panel with an output of around 15-18 volts is common for charging a 12V battery, but to avoid overcharging without a regulator, it’s safer to use a panel with a maximum current output of about 1-2 amps.

A panel with a wattage of about 10-20 watts is typically used for this purpose. This provides enough power to maintain the battery charge without risking damage from overvoltage.

[Thom]

You can’t fit a very big solar panel on a dashboard and get anywhere near full power . Yes charge controller for larger panel. My lithiums battery’s at home would shut off the power and not overcharge. I live off grid since 1985.

[David Thomas]

Ray:  Agreed, ideally, someone would run an errand in it every few weeks.  For the benefit of many of the systems.  I may end up just disconnecting the battery where I don’t have someone to use it occasionally.

Trickle charger?  That’s probably better than a PV panel at one location where 120 volts is easy, so I could just leave a trickle charger on it.  I’d lean towards putting it on a lamp timer, say 15 or 30 minutes each day, so it wasn’t charging 24/7/30.

[Jerry Adams]

You could just leave on the small solar charger.  Measure the voltage occasionally to make sure it maintains the voltage.  I forget, what is it, 12.5 volts or something for a fully charged battery?

And monitor the fluid level in the battery.  If you over charge it can convert water to hydrogen and oxygen which blow away, leaving the fluid level less.  If it goes too low it will kill your battery.  Like I’ve done in my RV.  That was more when I left on a 110V charger though.  Good idea about putting it on a timer.

Some trickle chargers automatically keep it charged without over charging.

[Jerry Adams]

Wait a second.  You live in Alaska.  I thought there’s no sun there:)

[Jerry Adams]

You still have to run the engine every once in awhile.  I did 2 months with my RV which seemed to work.  They said to run it every 1 month.

[Ray J]

Something like this.

https://shorturl.at/n6ROF

Do you have a “Batteries + Bulbs” near you?   the one by us has great advice on all things battery related.

I’ve got two old cars.  They get driven only a few times a year.  So they sit for months at a time.  They stay on their battery minder chargers round the clock and year round.  I pull off the car covers, open the garage door and start cranking.  Old carburetors take some time to get some fuel and fire.  Once the car is running, I go pull the quick disconnect on the battery minder.   After my drive, back on the minder, check all the fluids.  Once the car completely cools, on goes the cover.

But the trick is to drive the car for 20 minutes minimum.  Works the shocks, the suspension, gets the exhaust hot to burn off moisture.  I work the heater for a few minutes, even in the middle of summer, to circulate the coolant through the heater coil.

So, I’m not sure why you need any timer.

Letting it sit also presents other issues, namely varmints making a nest in the car or eating on the wires.

[Ray J]

and my paste failed.  Just look for Battery Minder on Amazon, your local auto parts store….

[David Thomas]

Jerry:  I live in Alaska, but I propose to park the car near OAK and PHX.

I’ve let some cars sit for 4-5 months through the winter and that was too long, certainly for the starting battery.  On the Prius, with its dinky little starting battery (to save weight, I believe) and a moderate amount of always-on electronics; we’ve had issues after just a few weeks of parking it at the Anchorage airport.

[Jerry Adams]

good points Ray J

I’ve put “sta-bil” in my gas tank.  Mixed it around by driving.  Let the gasoline with sta-bil get into the carburetor.  Then it was a couple years before I used up the tank of gas.  The sta-bil reduces fouling in the carb and so forth.

[Jerry Adams]

A battery minder charger won’t over charge.

Some chargers do, so you have to turn them off when the battery is charged.

I bet it’s cheaper on amazon than batteries+bulbs :)

Maybe it would be better to just rent a car in OAK and PHX :)

[Terran Terran]

There is sun in Pheonix. I’d be concerned with mice.

You need a charger controller with the panel. I wouldn’t trust a timer.

solar charger

[David D]

My motorcycle would sit idle for 6 months every year and that Battery Tender Plus linked by Ray was the go in that community to keep it’s battery topped up all winter.  I get years from a battery using it.  I also use it to keep my boat battery trickle charged, the last one lasted 15 years.  Good choice for the starter battery

[Brad W]

Why not disconnect the battery all together? Is that feasible with your car? They also make battery post disconnectors that make this easier. I keep a jump pack in my car all the time as well.

[Ray J]

Jerry, Excellent point on Sta-Bil.   Yes it is added each time I add fuel to the old cars.  And all the lawn equipment also.  It seems to work very well.   For others with old cars, I’ve started paying the price for alcohol free fuel for them also, and the lawn mowers.  I was ecstatic when “Buc-Ee’s”  (a huge convenience store, if you know, you know) opened a few miles away.  Each of their 100 gasoline pumps can deliver Regular, Mid-Grade, Premium, Diesel and Alcohol Free!  Alcohol free has made a huge difference in the mowers already and probably the gas cars.

Brad W, yes I would disconnect the battery if the car is going to sit.  But the battery will still discharge all by itself.  The Minder/Tender solves several issues.

[Rob Lee]

That $65/25W set will work fine. It has a simple charging profile. The brand is not uncommon in van systems. The 10W is half price but you will not have ideal positioning of the panel that greatly reduces output. May need to lengthen some wires but you are a handy guy with tools.

 

[David Thomas]

BradW: I was concluding that just disconnecting the battery was probably the easiest, most rigorous way to maintain the starting battery voltage for months on end.  I can’t open the dang hatchback where the battery is (in the LR fender) when it has no power (the key fob won’t work without power) and only the driver’s door has a physical key lockset.

I think the positive wire from the battery runs untapped to the main fuse box under the hood, so if I effected a single-pole switch under the hood there, I know I can mechanically release the front hood from the driver’s seat.

RayJ: Oh, right, alcohol in the gasoline!  We don’t have that here in Alaska (and I’m not going to make it down there on one tank).  Pooh.  That does make the fuel less “shelf stable” and increases the desire to burn through most of a tank periodically and replace it with “fresh gasoline” (if anything made from 30-million-year-old oil can be considered fresh).

[Nick Gatel]

I won’t be able to check back on this thread. We’ve been camping for 3 weeks without cell/internet access. Drove to a spot so I could do some online banking.

A fully charged car battery is 12.6 volts. They are designed to be charged at around 14.2 – 14.4 volts. You don’t want to exceed this. For long term “battery minder” you want around 1-3 amp charge rate.

You can disconnect the battery (remove the negative cable). But the battery will still self-discharge. A new battery will self discharge at around 4-6% per month — older batteries more — and in high heat even more. I used to sell tons of auto batteries. In the summer with batteries that weren’t fast movers, they would drop down to 12.3 volts in a few months, so we tested all batteries that had been in stock for 3+ months and recharged as necessary.

A few years ago Volkswagen had a discharge problem with their new cars. The electronics would draw down the battery if it sat for extended periods. Keep in mind a car might be built in Germany, sit at a storage lot, sit at the dock, sit on a ship, then sit at the destination dock, and finally sit at a dealership for 90-120 days.

Volkswagen came up with a solar panel that plugged into the cigarette lighter and it worked well for them. You can buy them on eBay for around $20 used. A couple caveats:

If you car has a cigarette lighter or power point, make sure it is live with the key OFF. Some ports only work with the key ON. Also, you might need to adapt the connector to your car . . . make sure you do not remove the diode bridge in the wiring; this prevents the panel from drawing current when the panel isn’t charging. The panels come with suction cups to attach the panel to the windshield or other window, but I would not trust them to hold in Phoenix during summer. Industrial strength Velcro is another solution.

We’re retired and have three vehicles, and often one of them will sit for months on end. Palm Springs is generally hotter than Phoenix and we don’t have problems with critters, etc. Biggest problem is the sun is hard on them, especially the paint. So I wouldn’t worry about storing in the heat — other than cracking the windows open a bit. Not uncommon for a sealed vehicle to have a window explode when it is 115° F and up.

Hope this helps.

Time to go back to our camper and back to our technology free life ;-)

[jscott]

David, I’m in Berkeley and would be happy to drive your car out on the freeway once a month or more.

You guys are amazing! Richard goes from volts to amps to watts with presumption that I at least  can easily follow along  easy as pie. but I assume that takes a capacity for math…?

in my own defense, I can move from Latin to French to Spanish in three sentences, as Richard does in his own way above.

[Terran Terran]

V x A = W

[Ray J]

David,

Read your owners manual carefully, or download it and search it.   Many manufactures have several ways to access these new vehicles that only have one physical lock.  Maybe call a local dealer, ask for Service, and ask to speak to the person most familiar with your model.   I saw on a YouTube video that a car repair shop does, how Tesla has a hidden panel where you can access the battery, without actually accessing it.  “Ever wondered about this cover back here?  Looks like just trim?  Yeah, find a coin and pop it open.  Reach in and pull out these wires.  You can hook up a 12 volt battery!  It will do two things.  One, it activates all the doors, so NOW you can get in to where the battery is….Two, you can jump it”.   Gee, they thought about access when a battery is DOA.   Maybe there is some hidden latch to open that area where your batter resides.

[Terran Terran]

You can open the hatch from the inside. There’s a latch. Probably covered with carpet.  Crawl back there.

[David Thomas]

Terran:  Yup, I found instructions in a user’s group to crawl through the car, lift the carpet and release the hatch from the inside when there’s no battery power.  Good to know, tedious to perform.

My teenage driver had the battery die in the remote fob and she didn’t know that you can unlock a car door with a physical key because she’d never done it nor seen it done.

I was once warming a key fob in my nether regions to revive its battery before I remembered the same thing, and I have no excuse.

[Author]

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