I picked a Maplin 1.5W solar panel out of our fitter's waste bin, the sort you leave on the dash plugged in to the cigar lighter socket when you leave the car for a couple of weeks, except he left it on the roof and it got wet.
It's dry now but doesn't seem to generate much current, in moderate sunlight it gets up to about 17V but it fluctuates down to below 12V at about 2Hz. There are only black and red wires coming out of the panel to a very small pcb to which the + lead feeds a diode and then to the output - lead goes to earth. + lead also feeds a blue LED which has a 5.1k Ohm series resistor to earth. The diode flashes in synchronism with the voltage peaks. There are about 30 cells, is it likely to be recoverable in part at least?
Seems to be working as designed. The LED flashes 'cause the cells can't actually provide enough volts and current at the same time. Volts rise, LED starts to conduct and glow, volts drop, LED goes off, rinse and repeat.
I may have the same panel as you from maplin, PV cell area about 3
1/2" by 12". Cells 1/2" strips in the narrow dimension. Bought it to keep the generator battery topped up but disconected it as the battery wasn't kept topped up and I though it was leakage through the diodes at night/low light conditions.
Had a power cut this afternoon, dragged out generator, battery absolutely flat. Even after the generator had run for a couple of hours the battery still didn't have enough umph to throw the bendix into the starter ring let alone turn the engine over... May be that panel was keeping the battery topped up a little even in a north facing window.
What you are describing is how this unit works from new. They are useless, with almost no output. The output doubles if you disconnect the LED indicator!
But it is only a 1.5 W panel so "almost no output" is accurate. B-)
The flashing LED, gimmick or not? It breaks the charge current into pulses instead of pure DC. I have vague memories that pure DC is not really good for rechargeables, it enables/encourages finger growth were as rough or pulsed current doesn't.
See other thread about maintaining a lead acid battery with long standby times. This sort of panel *with good light* might be enough for that. Need to reread the suggestions made over there.
Well if I short the panel output with an ammeter it give 4 mA with a cloudy sky. I think the blue diode is a voltage regulator, the forward voltage and resistor conducting excess charge away because if I short the output to where the cigar lighter plug should be I also get 4mA. The output to the plug is parallel with the LED and resistor.
It strikes me it is a crude use of the 30 PV cells as they would be better used charging a capacitor and then discharging this through some sort of Joule thief voltage step up device, then they can continue charging even if the light is too low to provide 12V.
Does a schottky diode have good reverse resistance? If the leakage current at 12V during bad light exceeds the accumulated charge current it needs better isolation.
We have cars and vans in our fleet at work that get left for a fortnight while people holiday abroad, batteries often get discharged and I put it down to the alarm/immobiliser which may use 10mA, holiday for 14 days and that's 4 Ah plus any self discharge and it only takes
That sounds about right. I bought a couple of these from a local fleamarket stall (not at the same time) for about 4 or 5 quid apiece two or three years ago. In fact, I think the first was purchased the day I also bought a 12AH 12v SLA (from yet another stallholder in the same fleamarket).
The battery voltage looked ok on a *borrowed* DVM (about 13.5v or so) but turned out to be 12.something when I tested with my own DVMs - not quite fubard, just a little closer to being totally flat than I'd have liked.
I guess it mustn't have been in such a low state of charge for very long since it charged up just fine after a couple of weeks on the first of those solar panels during the intermittent summer sunshine that illuminated my west facing office window from which I had hung the panel out of (the double glazing noticeably reduced the panel's charging output of 80 to 90 mA to something like a mere 40 to 60mA afaicr - short cct current is only about 10 to 15mA greater).
The first panel was a new item (old stock) whilst the first must have been a customer return due to the blue indicator led not working. I guess I managed to get this one even cheaper than the first. :-)
The problem turned out to simply be a faulty self-flashing blue lED which I replaced with an ordinary blue LED also replacing the 5K1 ohm resistor with a 10K ohm to match the average current draw of the original (less than 2.5mA peak when charging, slightly higher on no load 22 volts or so).
The led is simply there to indicate that the panel is producing voltage, The charge current is uninterrupted DC. A single such unit, optimally exposed to 12 or more hours of direct summer sunshine could manage to provide an ampere hour or so's worth of charge into a 12v lead acid battery which is ample to keep a typical 36 to 42 AH car battery in sound condition nicely maintained without any great risk of overcharging.
Provided the vehicle electrics don't burden the battery with an excessive 'vampire' loading, I reckon it would serve its intended purpose, assuming the battery itself is still in reasonable condition.
Incidentally, I've only ever charged my 5 quid bargain SLA from solar power. I bought it as a 'UPS spare'/test supply voltage source, so it's very rarely used. However, I do check it on a 4A lamp load every 6 to 12 months and the indications suggest that it remains in very good health despite only receiving a 'freshening charge' once a year.
The last time I charged it, a couple of months ago, I was using both panels so it only took just over a week to raise the voltage from 12.76 to a 14 volt end point before I parked the panels in a filing cabinet drawer for the next 50 odd weeks.
The off-charge voltage swiftly declines to 13.5 volts or so, dropping to
12.80 volts a day or two later, where it more or less remains for the rest of the year. Indeed, a quick voltage check just now shows a reading of 12.80 volts.
I rather think Dave Liquorice will find this particularly interesting. I find it *very* interesting in that this experience suggests that the 'sulphation problem' due to insufficient float voltage level may be being overstated in the extreme by the battery and UPS manufacturers.
Owners of APC UPS kit will be only too familiar with the dismayingly short life of these rather expensive 'consumables'. A problem that's quite evidently due to excessive float voltage settings (often, in a lot of cases, aggravated by a lack of temperature compensation in the charge control circuitry).
When I first got hold of my SmartUPS2000 (sans battery unit - it was a
2nd hand purchase at a Radioham rally), I used a set of four 36AH car batteries (60 quid the lot from my local friendly car spares dealer). Unfortunately, these only lasted about a year before it became rather expensive in replenishing the electrolyte with de-ionised water. Lesson
*still not learned*, the second set of car batteries started going the same way in only a matter of 6 months or so.
The set of 25AH SLAs (and the couple of banks of 7AH SLAs in parallel) fared much better but nowhere near the 5 or 6 years they were supposed to last, maybe just two or three years. In the end, I gave up on feeding the UPS's battery habit and bypassed it (it was providing a 'protected supply' to a dedicated circuit feeding a few sockets in strategic locations around the house).
In view of my experience with that 'everlasting' 12AH SLA and the observations of others, I'm now inclined to re-commission that SmarUPS2000 with another set of batteries (either another set of 25AH SLAs or a bunch of car batteries) but this time dropping the float charge voltage to the equivalent of 13.5v per 6 cell SLA (or even lower) rather than the specified 13.80 volts per 6 cell SLA.
When I was monitoring the float voltage, it was just a tad on the high side at 55.4 volts (it should have topped out at 55.2v but the extra 50mV per 12v SLA didn't seem significant... at the time). I'm hoping that setting it to a max of 54.0v will avoid the problems I had with the early demise of all those car batteries.
I suspect the only penalty of the lower voltage setting will, like the case of Li-Ion batteries, be a reduction in usable capacity per charge cycle (80 or 90 percent compared to the "100%" claimed capacity by the battery manufacturers?).
There has to be a reason why the UPS manufacturers are increasing the risk of premature battery failure and the only one I can think of is that such a choice very likely offers an extra 10 to 20 percent run time out of any given rating of battery pack capacity.
If the reason for the piss poor battery service life in UPSes is simply to max out the autonomy for a given nominal battery capacity, I'd rather accept the lower effective capacity and use a larger nominal capacity battery pack to compensate and save a small fortune in replacement battery costs.
Many modern vehicles run a lot of the electronics all the time, e.g., ECUs of various kinds, so the consumption may be a lot more than 10mA. I tried to measure it once on a car that was prone to flattening its battery at speed, but it blew the fuse in my ammeter!
My VW Touran is prone to a dead battery if undriven for 3 weeks. The battery is only 2-3 years old so I reckon it is because of the sheer amount of junk that is powered all the time.
I've checked the battery in my car is 60 Ah so I guess it will still start the car if half discharged, on that basis it would take nearly
10 weeks so either the discharge is greater, the self discharge is more significant or the battery is just old but having had to jump start them I can assure you a couple of weeks is often enough.
The thing is that it seems likely the little 1.5 W (peak) Maplin panel as configured is not likely to be able to keep up the charge.
I have twice left (different) cars parked for 14 days and they started first time on day 15. (The only time recently I had a car battery go flat on me was around 10 years ago, when I had only been using it for going to work, 2 x
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