Solar Panel trickle charges car battery - or does it?

Small solar panels which sit on the car dashboard, under the windscreen, and plug into the cigarette lighter socket, can be purchased from car accessory shops.

The marketing spiel leads the unsuspecting purchaser to believe the solar panel, when placed in the sunlight under the car windscreen, will keep the car battery topped up by trickle charging, while the car is parked.

Sounds like a good idea, BUT does it work?

With every car I’ve ever owned, the cigarette lighter socket is DISCONNECTED from the vehicle electrical circuit as soon as you remove the key from the ignition.
This means the solar panel CANNOT trickle charge the battery, no iffs, no but’s, period!

I think it is fair to assume this is the case for most cars on the road.
What this means is that the solar panel cannot possibly do what the marketing spiel claims, it is a hoax, and it is a waste of money.

You could get around the problem by leaving the keys in the ignition and on accessory setting, which would keep the cigarette lighter connected to the circuit, BUT besides the obvious risk of leaving the keys in the ignition whilst the car is unattended, the current being used by other accessories in the car would likely outweigh the charging current of the very small solar panel anyway.

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In my car there are three cigarette type sockets. Two are connected at all times to the battery via a fuse. Only the actual cigarette lighter is disabled when the car is off.
But if you were serious about charging your battery off a solar panel, I would connect using something direct with a regulator to prevent damage to either the battery or wiring.

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We have the same with our Subaru. But, all three are isolated when the ignition is turned off. But other manufacturers may be different.

I also suspect that some sockets may be unidirectional (from the battery to the socket) not bidirectional to allow flows back to the battery - to protect the electrical system. It might be worth checking with the car manufacturer that the sockets are bidirectional, otherwise plugging a solar panel into the socket will have no effect.

or damage to components hanging off the same circuit (sensors, computers, etc). While any damage would be claimable against the solar panel retailer/manufacturer under the Australian Consumer Law…when dealing with non-OEM accessories it can be a claim nightmare.

Edit: If one plans to use for a EV, then they might be misguided on the real benefit. A small dashboard mounted panel will have little (or no) effect on energy stored, unless the panel is rated to charge the battery system and/or the vehicle consumes less in standby that the panel produces (and the vehicle is parked for a very long time).

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Are you able to post a link or copy of an add for these products? It would be useful to read the fine print with the instructions.

It varies with vehicle whether 12V accessory and cig lighter sockets are disconnected from the battery when the key is removed (off position). Note: some vehicles do have always on accessory sockets (OEM or added after market) for powering portable fridges etc. Some vehicles keep power on to the sockets for a time (60mins or longer) after turning the key to off.

One product from Jaycar and user guide.

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I bought a solar panel trickle charger from Jaycar when we had a Ford Transit. When I had it connected to the accessory socket (cig lighter) and the vehicle was turned off, the radio would continue working, which completely defeated the purpose as it probably used as much power as the trickle charger provided.

I ended up connecting it to the battery via the clips. To do this, I had to find a way to pass the connections through the firewall. In the Transit this was easy, but in the replacement vehicle, it is a monumental task as there is only one very circuitous and torturous path through the firewall to the engine bay.

Using the battery clips it did work without issues.

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Connecting it directly to the battery via the firewall is one way to solve the problem. As you said, a difficult route through the firewall. Using a trained mouse :computer_mouse: might be helpful here :blush:

It may also be possible to connect it to a live terminal in the fusebox, if said fusebox is inside the cabin.

But the main point I’m highlighting here is that with many, perhaps most cars, the cig lighter is out of the circuit when the keys are removed so the panel is a hoax.

The type of panels sold for this purpose are the cheaper style which has a low power output anyway.

I used to have a larger polycrystalline panel mounted under my rear window, connected direct to the battery via a current meter so I could see how much current was charging into the battery. Also with a series connected diode for reverse polarity protection when the panel is dark and the alternator pushing the battery up to 14volts.
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It’s a valuable point concerning the marketing of the product. Whether it’s a ‘hoax’ might be one for the ACCC and a bunch of lawyers to agree. The Jaycar kit example comes with both a lighter/accessory connector and clip on cable options? If the packaging indicates both isn’t it up to the purchaser to know their vehicle?

In the instance of the Jaycar product the user guide makes it clear not all vehicles have lighter outlets that remain connected once the ignition switch is turned to off. Is this information repeated on the packaging?

Another retailer well known by those interested in geeky stuff, and product, and a higher capacity unit.

The basic promo on their site mentions the package comes with a 12v vehicle plug. It’s in addition to the supplied clip on connectors. In retrospect it would be appropriate to mention not all cars have live lighter/accessory sockets, and it is up to the purchaser to determine how their vehicle is wired. Whether this is mentioned on the packaging I don’t have a pack shot. The 14 day money back guarantee would be a worthwhile protection if it did not perform as expected

Other thoughts:
There are aspects of how these products are intended to be used that we might question.

  • Which products come with a protection diode?
  • Which products might include a basic regulator?
  • Is the output of a particular brand and model adequate to meet the needs of a typical battery, given it is not on at night, PV output varies with time of year, positioning and weather?
  • Is there any benefit if the battery is not fully charged and conditioned?

Some of the promoted products of this type may be effective in meeting the needs of a user to maintain a battery which is in use intermittently. They may or may not be the best for a battery out of use for many months. That is compared to a smart charger designed to be permanently connected to a lead acid battery.

The technical questions of fit for purpose would appear a more pressing concern. It’s not evident all such products are being falsely promoted.

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In order for a Solar panel to operate correctly it must meet certain requirements?
1 The open circuit voltage from the panel needs to be about 18 to 21Volts.
A regulator set to 14.2 Volts is required to allow it to charge the battery. The regulator needs to be connected to the battery directly.
Most Solar panels incorporate a Shotkey diode to prevent the battery discharging during periods of low light.
It is doubtful if any meaningful charge due to the small size of the panel.

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Would it also be wise to have a qualified auto electrician run the cable to avoid potentially (pardon the pun) compromising the firewall?

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Paying an auto electrician to install the panel would, in my opinion, only add to the money wasted on this “sham” product.

My initial contention was that in most cars the cigarette lighter is disconnected from the car electrical circuit when the keys are removed from the ignition, and this being the case, the product cannot do what is claimed - ie trickle charge the battery via the cigarette lighter socket.

Some responders have pointed out that in some vehicles, the cigarette lighter remains in circuit even after the keys have been removed, thus the panel may indeed trickle charge the battery.

The panels that I have seen in auto part shops are only small - about 20cm x 8cm or thereabouts, and they are the amorphous silicon type, (not the polycrystalline type that rooftop solar panels are mode from). An amorphous silicon solar panel of this small size is only going to produce a very small amount of power, even under direct sunlight.

Earlier in this article one responder put a link to the Jaycar product of this nature, and it quotes an output of 1.5watts or around 90milliamps.
This is rather insignificant for topping up a car battery and puts more question marks over the products viability.

The addition of a voltage regulator would also be a superfluous waste of money as this amount of current will not damage a car battery.

The agenda of marketing and advertising is to:-
Get us to feel something.
Get us to imagine something.
Get us to think we are getting something for nothing.
Lead us into thinking the product will do things which it clearly will not.
And thereby sell us the product.

A person who walks into an auto shop, and has very little technical knowledge about car electricals and solar technology, will see this item and think “wow, I can install this and get free energy from the sun and keep my battery topped up”
And they will feel good about that, and perhaps buy the product.

Thus the marketing people have won.

But unfortunately the product is worthless and is not really going to do what they have been led to believe it’s going to do. It’s a waste of money.

Technically, in some cars the panel might trickle charge the battery when under direct sunlight, but the amount of current is very small and will not make any significant difference to the car battery condition.

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There has been a trend with European cars to have at least one socket live when the key is removed so the owner can charge their phones and tablets. All the latest vehicles from the VW group, Skoda, Audi for example have a live charge socket and lately the the USB C type are live. I use a Cetec charger to trickle charge my MG as it can be a while until I use it. MOst Cetek chargers come with an attachment that connects to your battery and had a waterproof plug that you can connect to the charger. There are much larger PV panels designed for off road use that will work, but they also have a wired in plug system. A small PV panel would not work in most modern cars as the amount of power needed to run your alarm system would be more than the tiny panel could produce.

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I have two solar trickle chargers, one for a classic car that isn’t driven much, and one for a ride-on mower. In each case, the charger is connected directly to the battery. No problem. The packaging emphasised the cigarette lighter function, but the mower doesn’t have one, and I park the classic with the bonnet open to discourage habitation by mice, so the battery is easily accessed.

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It’s great to have some alternate feedback.

Are you able to share the model/brand details of the solar trickle chargers you use?

I’ve found that providing I use the ride on mower once every 2-4 weeks it is not a problem. The big mower (farm tractor) only comes out once a month. Both live in sheds where there is no power. The battery in the tractor is nearly 6 years old. The mower batteries seem to have a shorter life 2-4 years, which I’ve put down to the rough riding and conditions on our crude block.

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There is no branding on the items, but the packaging says: Jaymax part No. JM942. Then it gets interesting: “How to use - plug into cigarette lighter. Ideal for ATVs, boats, motorbikes, jetskis and ride-on lawnmowers.” The only indication of an alternative is a picture of a pair of battery clamps beside the lighter plug.

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Possibly this product. (Warranty 3 months)
JAKMAX 12 Volt Solar Charger - JM942 | B.W. Machinery
12 Volt Solar Charger | JAK Max

It’s listed as a product on a number of large Aussie yard equipment suppliers web sites. Scant technical details to assess whether the typical output is sufficient to maintain float or make up for self discharge over an extended period of time.

The well known Arlec brand offer 5W, 10W and 15W products, promoted as Maintenance Chargers. Bunnings sells the Arlec 5W version for $26.14 and a ‘Projecta’ branded 1.5W that looks much like the JakMax JM942 charger sold for $34.99.

Note:
Several retailers of power accessories for boats, caravans etc indicate that the larger panels should not be used without a charge controller based on the size of the connected battery. One offered a quality 5W panel for $24.95 and with an up to 3Amp charge controller for $15.95.

Just a product range with many choices, big name retailers and potential uses. It does need further investigation and possibly testing to sort the wheat from the chaff, IMHO.

There is amongst the promotional material for some brands/models potentially misleading content that implies a vehicle lighter/accessory plug can be used (unconditionally) to charge a vehicle. The claim however is not universal looking across a number of brands and sites. The OP did not provide any specific brand or model details.

The lack of specific advice on the use of each model or actual performance under differing conditions, leaves it to the end user to guess at the products suitability.

@BrendanMays, Worth a Choice product test to bust the poor marketing of some of the products, assess performance and provide some guidance on what to look for or avoid?
For products intended either as a low powered maintenance charger, or capable of recharging a partial discharged battery.

I’ve updated the topic category accordingly.

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Yes, a closer examination would seem to be warranted, to look at specifications and function.

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This is not my call to make, but I suspect Choice might better invest their time in evaluating everyday high volume products that every household uses, rather than this specialist miscellaneous item.

Perhaps Choice might consider doing a short write up basically setting forth what can and cannot be expected from Solar panels and give enough information for potential purchasers to have some knowledge.

I’m about to do another write up about small solar panels attached to Power Banks and small electrical items. Another gimmick that doesn’t really work and exposes the marketing BS :cow: :poop: that is employed to sell products to the unsuspecting.

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Is it worth considering that not all such products are marketed with BS and a good percentage can do the job asked of them by the purchaser?

Accepting many consumers are as you put it

Would it be a greater service to identify by brand and model which are not effective and which are?

Back on the current subject matter. Have you purchased any of the products in question, what was asked of them and what testing was performed? Where is the evidence by brand and model?

Choice can add objectivity if it chooses to do so. I’d not discourage a follow up. At which point we can all agree on the outcome.

I have never purchased one of these products as I knew enough about car electrical systems, electronics, and solar panels to realise the product was either not going to do as it claimed due to the cigarette lighter being out of circuit in many cars when ignition off, and also due to the small size of the amophous silicon solar panel having such a low power output that it would not produce enough power so make a significant difference.

I did end up however, purchasing a polycrystalline solar panel 250mm x 300mm approx, and hard wired it into the car battery via a current meter and protection diode. The solar panel was fixed into the back parcel shelf of the car to get max sunlight. I no longer have that car or the setup but from memory in full direct summer sunlight it could push around 450mA into the battery.
That figure would of course change throughout the day as the angle of the sun changed with reference to the panel.

The reason behind the installation was because the car was frequently parked for long periods without use, and thus the panel was installed to help keep the battery topped up.

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The subject is about using a solar panel trickle charger. The purpose is to maintain the charge in an already charged car type battery. As long as the battery is kept near fully charged, it will last well, and that is where these devices are very useful.
As long as the power produced is more than any drain on the battery, and diode protection ensures oneway current only.

On the other hand, if you were looking to recharge a car battery from a depleted level, then the power required is in the hundreds of watts over many hours that would blow the fuse in any cigarette lighter type socket circuit.