Looking to make a solar charger/maintainer for car

[jzmtl]

Complete solar noob here, I'm entertaining the idea of making a charger/maintainer for my car and have some ideas, lemme know if this is feasible.

The situation is I would like to keep my car battery charged even in dead middle of winter (-20 is common) when I will be parked for many days at a time, maybe even run the electronics/lights with engine off without worry about draining battery too much.

I'm looking at a 20W panel, which is the biggest that will fit under the sunroof glass (or would a 10W be better?), and a PMW charge controller from amazon:

https://www.amazon.ca/ALEKO-20-Watt-Monocrystalline-Solar-Panel/dp/B00XOITM90/

https://www.amazon.ca/XCSOURCE®-Intelligent-Controller-Regulator-LD296/dp/B00KWVRIW0/

My fear of the whole system originates from using one of those crappy 2.5W panel sold for cars years ago. I wired it to battery directly since that's what the instruction said. However several days later when I tried to start the car, it cranks just fine but wouldn't run, after finally starts it barely able to idle. What I suspected is the high voltage from panel (measured to be 17~19V) somehow messed up the ECU, luckily without any permanent damage. I threw the panel out and it has never happened again.

How well do these charge controller work when other sensitive electronics are running off battery all the time? If the output is same as vehicle charging system then I suppose it won't be a problem, but if it just send full panel voltage to the battery and cuts off when battery is charged then it's a serious problem.

Thanks!

[Sunking]

OK first thing you have to figure out is where the panel will be installed because behind any glass in the car is not going to work. It will turn you 20 watt panel into a 1 watt panel which is completely useless. So until you get that figured out, do not proceed. Keep in mind the panel has to be in direct sunlight all day with no shade issues. At least for most of the day Not easy to do in a vehicle.

Next is keep in mind there is a big difference between a Charger and Maintainer. Both are exactly the same thing except how much current they provide. To charge a Car Battery in any usable amount of time would require 200 watts or more of power to generate 15 amps. A Maintainer is low current for a given battery size. Depends on how you want to play the numbers game. A 2-amp charger is is a Charger for a 10 to 20 AH battery, but a Maintainer for Auto Battery.

Now for some good news. All you need is 10 watt panel, 1 amp diode, and a Cigarette or Power Port to plug into your vehicle 12 volt Power Ports. You do not need a controller for low power especially in winter. A 10 watt panel is only around 0.6 amps. Make sure the Power Port it is not operated by the Ignition Switch and is Hot when key is removed. Plug it in and walk away. Or use clips and connect to the battery. You just gotta figure out how to keep the Panel from Walking Away. They have a tendency to grow legs.

[bcroe]

Now for some good news. All you need is 10 watt panel, 1 amp diode, and a Cigarette or Power Port to plug into your vehicle 12 volt Power Ports. You do not need a controller for low power especially in winter. A 10 watt panel is only around 0.6 amps. Make sure the Power Port it is not operated by the Ignition Switch and is Hot when key is removed. Plug it in and walk away. Or use clips and connect to the battery. You just gotta figure out how to keep the Panel from Walking Away. They have a tendency to grow legs.

I would make sure there aren't any drains on the battery; even a 24/7 clock might be enough to cancel out your sun only panel. I
tried to pull the fuse on my clock for this situation, but it also disconnected the lighter socket I was going to use for a maintainer.
Check it out. Bruce Roe

[jzmtl]

OK first thing you have to figure out is where the panel will be installed because behind any glass in the car is not going to work. It will turn you 20 watt panel into a 1 watt panel which is completely useless. So until you get that figured out, do not proceed. Keep in mind the panel has to be in direct sunlight all day with no shade issues. At least for most of the day Not easy to do in a vehicle.

Next is keep in mind there is a big difference between a Charger and Maintainer. Both are exactly the same thing except how much current they provide. To charge a Car Battery in any usable amount of time would require 200 watts or more of power to generate 15 amps. A Maintainer is low current for a given battery size. Depends on how you want to play the numbers game. A 2-amp charger is is a Charger for a 10 to 20 AH battery, but a Maintainer for Auto Battery.

Now for some good news. All you need is 10 watt panel, 1 amp diode, and a Cigarette or Power Port to plug into your vehicle 12 volt Power Ports. You do not need a controller for low power especially in winter. A 10 watt panel is only around 0.6 amps. Make sure the Power Port it is not operated by the Ignition Switch and is Hot when key is removed. Plug it in and walk away. Or use clips and connect to the battery. You just gotta figure out how to keep the Panel from Walking Away. They have a tendency to grow legs.

Even clear glass? That's a total surprise to me, consider most small panels sold for car battery maintenance are instructed to mount inside the cabin.

I guess it's more of a maintainer, but I wanted a bit higher wattage so I can leave the lights/radio on a bit longer without worry about won't be able to start the car later.

I would make sure there aren't any drains on the battery; even a 24/7 clock might be enough to cancel out your sun only panel. I
tried to pull the fuse on my clock for this situation, but it also disconnected the lighter socket I was going to use for a maintainer.
Check it out. Bruce Roe

Having a solar panel to counter all the drains is actually my goal. There are so many drains in modern vehicle it's not worth it pull fuses for me, besides it would reset the ECU which I don't want.

[Sunking]

Even clear glass? That's a total surprise to me, consider most small panels sold for car battery maintenance are instructed to mount inside the cabin.

Not their job to educate the consumer. They will take anyone's money, that is their only job. As PT Barnum said; A sucker is born every minute.

At such low power levels the consumer is not going to know if it works or not. It would take test equipment to determine if it actually does anything. Auto glass is UV rated and filtered, almost no usable wavelengths can get through them. Sunlight would destroy the interior of your car and home interior. Same can be said about windows in your home and most other glass types.

I guess it's more of a maintainer, but I wanted a bit higher wattage so I can leave the lights/radio on a bit longer without worry about won't be able to start the car later.

No problem on paper. Any academic person can sing it praises. Now you have to figure out how. Seen it done on trucks, campers, trailers, and RV's where the panels (100 watt or more) are physically attached. so they cannot grow legs, but still have a problem with orientation and tilt angles. Panels need to face the sun, and be in direct sunlight. .

If you are going to go larger than 10/20 watts, now you need a charge controller.

[bcroe]

Having a solar panel to counter all the drains is actually my goal. There are so many drains in modern
vehicle it's not worth it pull fuses for me, besides it would reset the ECU which I don't want.

In that case you ought to measure the vehicle drains which are always present, then build a solar system with AT LEAST
10 times that output since it only works under good sun. Follow the guidelines from Sunking. Bruce Roe

[PNjunction]

You've seen this canonical video about small panels overcharging huge batteries right?

https://www.youtube.com/watch?v=z5RtZe9AW2E

Heh, my Noco 5w solar panel was already over-voltage, at about 25.5v ocv! Not a pleasant 18-22v. Put that on a fully charged gel, and you might as well throw your wallet down the highway.

*IF* your battery is large and heavily discharged, you may get away without a controller, but a solar maintainer is NOT to charge from any reasonable state of discharge anyway!

Keep the application in mind - a vehicular *maintainer*.

By definition, that means starting out with a fully charged vehicular battery, starting it so that it does not draw more than about 5% max capacity, and the vehicle charging system replaces that and a little bit more back to full.

The maintainer's job is to help with self discharge and very slight parasitic drains. Most importantly, from a fully charged battery!

So you are on the right track. Do not go without a controller. If you do, you are operating outside the application in mind, and in fact damaging a heavily discharged battery by prematurely aging it with a very inefficient charge. Most of that is plate-warping heat, even though you can't feel it. Heh, eventually you'll see it. You'll cry when your Enersys / Odyssey is a bulging freak show due to a directly connected panel with no controller. It will never fully charge it, but it will just slow-roast it trying to.

What you are talking about beyond this is no longer a maintainer application.

In that case, unless you ensure you get a full charge from your system (requires much bigger panel, especially in limited solar insolation times like winter!), your little 1A (20w panel) will only be doing a superficial PSOC to the vehicular battery.

Read some more here and do a rethink. Either that, or carry a fully topped off and well-maintained spare battery in your trunk, because you'll need it.

[jzmtl]

Thanks everybody, I'll have to thinking about it a bit more since not be able to place the panel behind glass really put a kink on things. Original plan is to put the panel below sunroof glass so it's easy to access, now I'll have to see where to put it. I suppose I could attach it to the roof rack, but driving around with it would be a bit tacky.

[PNjunction]

It makes a fun technical project, as long as you keep expectations in mind.

What was pointed out in the video was that not only was the lack of a controller damaging and costly for battery replacement, but most importantly, UNSAFE when a battery actually does reach full charge and goes beyond without any sort of control.

[jzmtl]

Yep a controller will definitely be incorporated, sending 18v to the various vehicle electronics isn't good.

[PNjunction]

In practice, it usually never reaches 18v, but hovers around 15-16v due to gassing - and that's the REAL safety issue:

Anatomy of an unregulated dinky solar panel safety issue:

1) Vehicle is driven long enough to fully charge a battery, or an external charger is used prior to storage in the sun. This is how maintainers are supposed to start out. If you aren't starting out from a fully-charged state, then the *dinky solar* maintainer will only maintain at the state of discharge it found the battery in. Which means eventual sulfation anyway. Larger chargers and panels (with controller!) excepted as they are going beyond maintainer status.

2) Unregulated panel on fully charged battery TRIES to bring the terminal voltages up to 18-22v, but due to gassing, only reaches 15-16v. Every day. Ridiculously low current, but plenty of voltage!

3) This endless high voltage corrodes and weakens the positive terminals, both inside and out of the battery.

4) User walks up to flooded battery that is gassing, puts voltmeter on it causing a spark, and boom. Battery explodes.

5) Or, perhaps in the case of a sealed battery that is not venting, all the void space above the cells is pure hydrogen.

6) User starts vehicle, and huge current draw of ignition violently melts the corroded positive material inside like a fuse with a spark. Battery explodes.

Yeah, it might not happen on day 1. Or day 30. Don't be the guy losing his eyes on day 35.