Solar Panel Car Battery Chargers - Any Good?

Nicely explained. GA vote from me.

The only problem with those plug-in solar chargers is that people expect that they will REcharge a dead battery. Technically they will, but if your life depends on that battery charging in under a week, make sure your affairs are in order...

I've had mine charge the battery from a click to starting in 3 days.....

Will this work on cars that do not "activate" the cigaret lighter unless the ignition is on?

Yes. You just need to leave the key in the accessory position while parked. Now that may add to the battery drain, so buy a bigger solar charger.

I had been using one when a solar ellipse occurred, at first I thought that I had ruined the sun!

Seriously, I have one that has a VW symbol on it (accessory?) it serves to keep a charge on the battery during storage.

My '05 VW Jetta had one in the windshield as delivered from the factory. The guy at the dealer wasn't going to include it because I think he was selling them on the side. When I pressed the issue, I got the one that came with my car. They do a nice job of making sure the battery doesn't go flat if the car is unused for longer periods. I think the max charging current on the VW unit is 75 mA. Certainly not useful if your battery is already dead.

First you need to know what the parasitic drain on the battery is by all the electronic devices it maintains when off. By testing it you may find that there is a problem some where. Like the trunk light is staying on or the light under the hood.

Also these short trips. If the draw on the battery from the starter is more then what's being replenished to the battery during the trip. Then the float charge may have to compensate. The solar charger will need to be sized so it has the time to do so.

the parasitic drain should be less than 10-20 MA

at 20 ma = 15 amp hours per month = dead in 3 months, sooner if parasitics are high. The article gets into it

Here is an article on it

It might be more economical to dispose of it and use a bicycle instead.

?????

I use 20w chargers with battery tenders....I disconnect positive side of battery and wire directly to the battery post for long term....works great....just place panel on the dashboard....

That is about 1.5 amps, 24/7 = 36 amp-hours per day. Might cause water loss unless you have the platinum catalyst covers that re-combine the electrolyzed water?

<...1.5 amps, 24/7 = 36 amp-hours per day...>

_{Er, it is widely accepted by the Engineering community that solar panels don't work at night...}

so true. I was not sure what his battery tender was, I assumed a plugged in source

That's the reason for the battery tenders....a device that controls the charging/maintenance mode...

Now that is a neat unit and seemingly correctly monitors/controls the charge for almost any 12 volt LA battery that I have seen!!! Thanks for your great post, one of the best if not the best here....from me many thanks!

I saved up and bought enough solar panels from Halbor Fleight to power my ciggy lighter. *Cough*

Why solar panel to add to your cost? Just do same 100mA trickle charging from mains supply. Just use a mains supply to 15-0-15 V trasnformer, rated say 500mA, buy 1N4007 diode , 2 nos, to convert to full wave rectified output, a 1 3 watt rated 33 ohms wire wound resistor in series. No capacitor needed too!!!!

It assumes that battery is not fully dead, but is closer to say 12V. May be cheap chargers like this may be available off the shelf. In India it would cost Rs 300/- and if you make for less tahn Rs 100/- Note Rs 63/- = $1/-. I used to charge my car battery with tis and run 10 to 20kms/year for 5 years. Recently sold off teh car- as I was really not using it.

This is a very durable solar charger. They were given to buyers of Volkswagen cars in 2003 and a couple years later. It's a solid, well made charger - not the newest technology, but it works. http://www.ebay.com/itm/Vw-12-Volt-Solar-Panel-Auto-Battery-Charger-Maintainer-1c0-915-687-OEM-/171406709351?hash=item27e8a2d267&vxp=mtr

To the OP:-

Those "uncontrolled" units using a solar panel, as a few have already said, could cause the battery to gas over long periods, shortening an already possible short battery life even more!!! As I always say, it simply depends on.......... lots of things!!

The gas produced is quite dangerous and needs to be safely vented to the outside. Also, it means that battery fluid will be lost, a further complication for many women.....

But also letting a normal car battery "sit" for long periods below 12.5 volts, is already shortening its life quite dramatically.....usually, the running engine replaces any lost capacity and the problem happens then seldom in a car regularly in use...

Why not teach your wife how to attach a quality small charger, one with proper charge control that will not over charge the battery, as it appears that the car "sits" at home, so mains will be available!!! It really only needs to supply say a max of 2 - 4 amps to a low battery.....so will not be so expensive either....

If she is not technical, get a plug/socket fitted so that she cannot accidentally swap leads. You really don't need solar.....but do make sure that it is fully charge controlled....few are!!

For example, there is a lot of rubbish spoken about trickle charging or floating a battery, just to keep the charge where its is. Which you actually do not need or want in most cases anyway, as I am of th opinion, this over time reduces the battery capacity. My opinion only!!

You need a unit that when the battery is really down, does a reasonably job of recharging. Then when some level of charge is reached (better low rather than high, I always aim for around 70% of full charge myself), either maintains it with no increase, or even disconnects till the charge has decreased to a specific point, when it starts charging again!!

BUT, THIS "TRICKLE/FLOATING " THAT MANY BANDY ABOUT, IS NOT A FIXED AMOUNT OF CURRENT AS MANY APPEAR TO THINK IT IS ( and some charger manufacturers too!!).

The amount of current need to maintain a LA battery at a fixed charge level is affected by at least some of the following factors just for a start:-

1) Size of battery (AMP/Hours)

2) Age of battery

3) Type of battery

4) Manufacturer of battery

5) If connected to vehicle, the extra charge needed to balance any loads the car has when not switched on, sometimes I believe called parasitic loads, though I do not know why!! From car manufacturer to manufacturer it can vary....

Also, some GPS/Audio/Bluetooth/Telephone units on modern cars can "forget" to completely switch off occasionally, and discharge the battery completely in a day or less....

6) Temperature of battery

Thats just for a start, I expect to have completely forgotten a few factors as well!! (but someone here will delight in mentioning them!!)

Which means that without some form of charge control, the battery will MOST LIKELY either over or under charge, but it is most unlikely to stay at a set level!! If it does, what a surprise!!!You just won the state lottery!!!

So even if this optimal voltage (whatever that is, I have my own opinions on what that is!) or charge level is reached, it is MOST unlikely that a cheap solar cell alone will actually maintain it correctly....

Also, as several people have already said, some Cigarette Lighter/Accessory sockets are not connected to the battery when the key is removed. But there are some easy ways to find that out and several ways to fix it so that a charger will work,

Use the cigarette lighter with ignition key removed, did it heat up? If YES, then you can use it for charging in most cases.....

If it did not charge, then there are basically two easy methods (if you are technically a tiny bit competent) to fix that:-

Either simply add a fused accessory socket, just for charging solar or charger, and wired across the battery terminals, but placed inside the car for the solar panel/charger to keep it out of the weather, or rewire the original one to do just that!!

Using that unit the "Battery Tender" that Solar Eagle posted, will make the whole business a lot less fraught assuming it is as good as it says it is....I have not used one myself....

Best of luck....

"The gas produced is quite dangerous and needs to be safely vented to the outside. Also, it means that battery fluid will be lost, a further complication for many women"....

A tad sexist, but I guess you are referring to a flooded battery here as even a man can't replace the fluid in an AGM or GEL battery.

"But also letting a normal car battery "sit" for long periods below 12.5 volts, is already shortening its life quite dramatically...."

12.5 volts for a flooded LA battery is equivalent to a 90% SOC, and you're correct in that leaving it there for any long period is detrimental.

"For example, there is a lot of rubbish spoken about trickle charging or floating a battery, just to keep the charge where its is. Which you actually do not need or want in most cases anyway, as I am of th opinion, this over time reduces the battery capacity. My opinion only!!"

A bit more rubbish there. Whilst an uncontrolled high charge rate can erode the plates and cause fluid loss in both AGM and flooded batteries, or drying and channeling of the electrolyte in GEL batteries, a true trickle charger will be unlikely to cause any problems, and it is always better to keep batteries fully charged, this is why standby batteries last 20 years plus.

A trickle charger is voltage regulated. As the voltage of the battery rises, then the output current of the charger is forced to reduce as the two voltages approach equilibrium - simple Ohms law. They are set at a sufficiently low output voltage that overcharging will not occur, this is also why they are pretty hopeless as bulk chargers

"Then when some level of charge is reached (better low rather than high, I always aim for around 70% of full charge myself),"

Hang on...A bit of inconsistency there!... Didn't you just say not to let the battery sit below 12.5v (which is 90% SOC)? Now you're advocating 70% SOC (which is about 12.35v).

While many automobile systems only charge the battery to around 70%, that is OK for daily driving, but useless if the vehicle is left standing for more than a few days and used for very short trips only.

If I quote you here:-

A bit more rubbish there. Whilst an uncontrolled high charge rate can erode the plates and cause fluid loss in both AGM and flooded batteries, or drying and channeling of the electrolyte in GEL batteries, a true trickle charger will be unlikely to cause any problems, and it is always better to keep batteries fully charged, this is why standby batteries last 20 years plus.

A trickle charger is voltage regulated. As the voltage of the battery rises, then the output current of the charger is forced to reduce as the two voltages approach equilibrium - simple Ohms law. They are set at a sufficiently low output voltage that overcharging will not occur, this is also why they are pretty hopeless as bulk chargers.

Sadly, many "so-called" trickle chargers, actually set a maximum voltage that can "eventually" overcharge some batteries, or a current value that does not reflect voltage....You should know that!!!. If the charger is intelligent, then what you say is true, BUT NEVER TAKE THAT AS A GIVEN...

"Then when some level of charge is reached (better low rather than high, I always aim for around 70% of full charge myself),"

Hang on...A bit of inconsistency there!... Didn't you just say not to let the battery sit below 12.5v (which is 90% SOC)? Now you're advocating 70% SOC (which is about 12.35v).

While many automobile systems only charge the battery to around 70%, that is OK for daily driving, but useless if the vehicle is left standing for more than a few days and used for very short trips only.

Due to tolerances in design and build of modern batteries, there is no line of absolute definition, you at least I had expected to know and understand that!!!WRONG!!

I found that this might help you better, you will notice the broad band of values:-

Would you have been happier if I had said say 75%? I doubt it.....A w***** remains a w******!!

Having already said that a voltage below 12.5 volts can over time damage a battery, I assumed, wrongly, that might ring a bell in your belfry!!! Obviously not!!

Spades, you come over as a singularly obtuse, picky individual, I hope that for a sane life outside of the web, its only here that your "black" side is demonstrated!Otherwise you must have surely screwed up a lot!!

Don't bother even correcting me, even if I am wrong, as you should remember the old saying "Methinks that thou protesteth too much!""

GOT IT?

The sail boat crowd for sure and maybe the power boat people like these devices. Not familiar with the good, bad and better units. Check it out I saw some informative comments.

I would take her car for a ride to the corner bar every week.

As an electricians mate on submarines, my father knew how to maintain LA batteries as if his life depended on them.

Funny how that is.

I have used a Battery Tender for years. Never had any issues, unless left unplugged.

Hi weijing3333,

Welcome to CR4. Chargers are usually rated in Amps, not Watts. For trickle charging for an automobile I recommend 200 mA, though an old battery may require more to stay up to par. This is with the battery out of the vehicle. Internal loads will need to be met before any charging occurs if used in the car as you are wanting. A 1A charging rate will probably not cause much water loss, and is typical of trickle chargers intended for 24 hour use. Higher currents will charge it faster. If a battery doesn't stay charged enough to start the car for 2 weeks after being fully charged, then it is most likely in need of replacement. I would say go ahead and get a solar charger anyway. It could pay for itself.

Ignore the bickering of the CR4 responders. This is normal.

I had this problem a few years back. A 1.5W solar panel proved sufficient to keep the battery topped up, even in dull winter weather.

Regards,

Tony Lee.