Has anyone any thoughts on solar powered battery chargers to keep battery topped up in the winter,or is it better to use one of the new smart chargers?If so has anyone any recommendations on which one is best.Thanks to all for help with my previous questions
I can recommend an Optimate, mine as worked faultlessly for nearly ten years.
Unless you can aim it exactly at the sun, here in the UK we don’t receive enough sunlight, either bright enough or for long enough, especially not in winter, unless the panel is big, certainly much bigger than the vast majority of those offered for cars or boats. Buy a Smart mains charger.
See the Wiki article “Theory of Solar Cells” It is very relevant.
https://en.wikipedia.org/wiki/Theory_of_solar_cells
I have a nominal 2.5W panel and was very disappointed by it, so I checked out the physics and it is actually performing quite well, just not well enough to make up for 28mA dark current 24/7 in the NC. I was considering using the OBD2 socket as the feed point because the B+ is live there all the time.
My panel is this one below, it is not sufficient. I could only give it a 2* review because it was inadequate compared with its unrealistic (in the UK) claims (almost OK in the tropics). Also now the shipping cost is ridiculously high.
https://www.amazon.co.uk/NOCO-BLSOLAR2-Solar-Battery-Charger/dp/B00B7GC50Y/
If anyone wants to collect mine they can have it for free. Because the cells are so fragile (bitter experience on other panels) despite the glass and plastic covering I’m not prepared to risk posting it. {It came in a gigantic padded box, long since disposed of.)
Following this…
I live in an apartment with outside parking only, and no access to mains power for a charger, therefore I have been thinking of a solar charger.
I totally agree with Richard’s comments - I tried a commercially available solar charger ( bought from the AA). It worked to a degree, but never produced sufficient current to prevent the battery discharging slightly. After a while it gave up giving very much current at all (3mA was all it could muster), so I took it to bits to see what was what. Basically it was just a couple of cheapo panels amd a diode in a fancy package, and one of the panels was broken. I did consider making up a replacement by buying a much larger and substantial panel - but then decided not to bother and just make sure I use to MX5 once a week instead.
So in summary, to get sufficient umph to keep your battery topped up a comercial car solar charger won’t do, if you can get mains to your car then an Optimate is the way to go.
Colin
Why not remove the negative earth lead it only takes minute?
I think as someone mentioned earlier when disconnecting the negative battery terminal it is a pain to set up the radio again. I know I do this as well and spend ten minutes setting it all up again. I think it will be a smart charger for me in future … If I can stop my son stealing it and putting it on his motorbike!
Just a point of note. With the MK4 DAB radio it retunes itself anyway so in disconnecting/reconnecting the negative battery lead (which I’ve done a few times since September) I’ve not noticed any changes to the radio or any other system.
I have noticed several recommendations for an Optimate but they produce quite a number of versions, at least 6 I think. Any thoughts on what is the best one to keep a Mk.3.5 topped up during the winter?
Would be a nice simple solution, but the mk3 doesn’t like having it’s battery disconnected, the DSC needs a reset and the ECU can take a while to settle down, and then there’s no alarm without a supply.
Pointless disconnecting the negative terminal, the battery will still need charging if the car is left without regular use in winter, guessing this is the case.
If no electric point available the only solution I see is the boost pack if required but that doesn’t do the battery much good (keep leaving it to go flat) Alternatively take it out and charge in the home which is still a pain I guess.
In reply to Jaydoubleyou I have used an Optimate 4 for years and that has worked faultlessly. I expect there is a more modern version but I can vouch for the “4”. There are different connection methods but I’ve found the permanently fixed method the best…screw / bolt to the battery terminals and plug in when required.
I bought one of the cheapo £13 Chinese solar panel chargers off Ebay 3 years ago and can’t fault it. The panel’s stuck in the garage window and even though it’s never in direct sunlight it still keeps on top both the car and bike batteries, alternating between the two every few days.
They come with a cig lighter plug and crocodile clips. It’s no good using the car aux. socket because I don’t think they connect through to the battery unless the ignition key is at position 1. I fitted a fused marine aux. socket under the car bonnet with another on the bike fairing.
I don’t think these chargers actually charge the battery as such, if they do it won’t be much. What they’re very good for is keeping a fully charged battery topped up which would otherwise drain when unused over a few days.
Even though the bike’s been laid up for the last 18 months the battery shows 12.7 volts and starts on the first turn of the key.
If the panel is big enough, and the sun is bright enough, for long enough, and the dark current is low enough, then a solar panel will work.
This is when the Physics come into play.
In UK the midday summer sun is about a quarter the strength of tropical overhead sun (memories of taking subject light readings for my photography are 1600 in Africa vs 400 in UK on my old Weston Master), and in the winter the UK midday sun is down to less than half the brightness of the summer sun (a subject is typically 100 to 200 on the meter).
My panel is 200mm square, ie 8" by 8". In midsummer, at midday I could get about 75mA from it into a battery. If I arranged some mirrors around it (kitchen foil on hardboard) to increase the effective aperture, I managed to raise the short circuit output to 350mA, with an open circuit voltage of 27V. This gave me about 180mA into a 12V battery. But it is a bit impractical as the sun moves around, and what actually happens is the output peaks only when the panel is square on to the sun and drops off with all the other lower angles of incidence, simply because it is taking a narrower slice of direct light.
Remember that the NC is losing about 28mA all day (or mine is), which works out at about 2/3 of an Ampere-hour per day. A good full capacity 48Ah battery will therefore take about 70 days to become totally flat; smaller, older, less capacity batteries will be sooner.
My panel on bright hot sunny days in the summer would be able to produce almost 0.5Ah of charge over each 24hours, so it would be almost OK. But in mid-winter it will be about 0.09Ah per day, so not enough. And those figures assume unbroken sunshine, mere daylight is nowhere near enough, and overcast and rain is even worse.
If the vehicle has no dark current and the panel is only needed to combat self discharge in the battery, then it could be OK, especially on the more modern technology batteries.
However, to paraphrase Mr Bentley, “There is no substitute for area.” If you can increase the dimensions to quadruple the area, then it will probably just about keep an NC with a good modern battery topped up all year round despite losing the battle a bit in midwinter. It might even be too much in the summer, but the sun raises and lowers depending on time of year so shading out a high sun, and angling the panel for the low winter sun can help there.
It is all good fun, and something well worth experimenting with. Just don’t believe the hype. Read the Wki article to see how it all works.
Richard. All I can tell you is the solar panel measures approximately 12 x 4 inches, is sucker stuck to the garage window 4 ft opposite the house wall and facing North so it’s never in direct sunlight. The little blue light flashes as long as there’s light available, in fact it’s flashing right now even though it’s raining and very dull today). Whatever, it’s kept on top of both batteries for the last 3 years. The car battery is a 3 year old Varta and the bike still has the original dating back to 2009 which I find amazing.
Regarding the cheaper solar panels, they do not have a voltage regulator/ limiter and in a test I did the voltage output varied significantly with the amount of light the solar panel was exposed to. Bright sunlight could produce up to 18 volts. I’m sure that overvoltage is not good for battery charging.
Thinking way outside the box here.
It’s the 28mA permanent drain that lowers the battery voltage to the point that it won’t start the car that’s the problem.
Where is this drain coming from? I’m assuming that it’s the radio memory backup and alarm system that are the main culprits.
What if we could stop these systems draining the main battery?
Anybody who is into motorhomes or caravans will be familiar with split charger systems. The caravan or motorhome has an additional battery to power lights, fridges, TVs etc. This is connected through a voltage sensing relay so it is only connected in parallel with the car battery when the alternator is charging. Leave everything turned on and it will go flat but the main battery isn’t drained and you can still start the vehicle.
How about a small 12v 7Ah battery such as those used in home alarm systems stashed away in the glovebox. Sorry ND owners.
Connect this auxiliary battery via a split charger system and divert the radio memory and alarm feeds to the auxiliary battery. Should be enough to keep the radio presets and alarm active for a week or so but even if the auxiliary battery goes flat that’s all you lose. You can still start the car.
All slightly down the sledgehammer and walnut route I admit but something to get your little grey cells around.
Discuss.
Excellent! I guess that is one of the monocrystalline types, much better than the usual polycrystalline, and with a control module too (blinky blue light). Any charge is better than no charge, the question is; how little top-up can you get away with?
After my experiments with the 2.5W panel, the 10W mono panel I considered buying really needs a control module to protect the battery from midsummer overcharge, but (in theory) has just enough welly to do the winter job and will fit a windscreen or back window, and it was this one
https://www.amazon.co.uk/Solar-Panel-Premium-Quality-Photo-voltaic/dp/B016MMV8HS/
However I was then given an excellent Smart charger and promptly forgot about the panels. So I don’t have real life experience of this 10W one it was just next on my list and seemed to be big enough. I’d be interested to hear from anyone who has tried it.
On the USA circuit for Miata’s they have found that leaving the cruise selected on shutting the car down allowed 4x the drain on the battery than if it was deselected so I’ve adopted the deselect before I switch off or at least checking to confirm. I know that doesn’t help those that don’t have that facility.
My drain with everything switched off, all locked up, leaving everything to shut down for 5 minutes (ECU etc, cables trailing from under the front of the bonnet to the Fluke multimeter) showed only 20mA which is more than acceptable, leading me to question why my battery went flat.
Anyway bottom line is I will leave the battery on trickle charge on a timer when I go away. I’ve yet to decide whether I leave the negative cable connected or not. Trouble is paranoia sets in because if I leave the -ve connected and something goes wrong with the charger over the 10 weeks and it doesn’t fail safe the whole cars electrics get it or at least those circuits not connected via the ignition.
I think I’ve talked myself into what I will do LOL…