Garden Solar Lights - Page 1
Forum section: electronics / beginners

author: Utdfederation
author_rank: Newbie
timestamp: August 03, 2020, 10:51:29 pm
content: Hi Guys.First off, thank you for letting me join this forum.Ok....where to begin...I have 30x1.2v garden solar decorative lights, i also have a "Special High Efficiency 12v 50w Solar PV Panel"All my solar garden lights have their very own individual solar panels built into the lights itself.Considering the location that i have placed many of them, they don't seem to get the full charge, so i was thinking on a way to link them all up via my solar panel so they all charge from the one solar panel.this is what i was going to do....Disconnect the built-in solar panel wires on ALL the lights and join all those wires so they ALL charge from my solar panel on my shed.Or do i have to do it a different way?Any help on getting this to work from anyone would be greatfully appreciated..

author: Dabbot
author_rank: Regular Contributor
timestamp: August 04, 2020, 02:57:04 am
content: Have you looked at the circuit in one of these lights?With such a large panel, you will also need to consider appropriate current limiting to ensure you don't damage the batteries.

author: Ian.M
author_rank: Super Contributor
timestamp: August 04, 2020, 06:54:58 am
content: You'd need to keep the built-in solar panels because they are also used as the photosensor that switches the lights on.Bucking nom. 12V down to nom. 1.2V would loose a lot of efficiency, converting them would be a big mess, there's no provision for connecting water resistant wiring to them,so all-in its just not worth doing.I'd relocate them to get good sun and think about my options for a wired 12V lighting system for the shaded areas.Your 50W panel will only deliver its rated output when square on to direct noon sunlight in a cloud-free sky which is pretty rare in the UK. In the winter with the usual succession of Atlantic depressions rolling in, you'd be doing well to get a few percent of that averaged over daylight hours, for days or even weeks at a time. Depending on how long you want the garden lights on each evening, you may well only be able to power 5W of lighting reliably eight months a year. In the winter, you are basically screwed for solar powered garden lighting as excessive discharge and freezing temperatures will kill the system battery stone-dead unless you minimise the load on it so the panel can keep it well topped up.

author: eblc1388
author_rank: Frequent Contributor
timestamp: August 04, 2020, 07:15:23 am
content: I would buck the 12V down to a few volts using a single switching converter and feed this voltage to each solar light battery via individual Schottky diodes. BTW, what is the battery voltage of these solar lights?

author: Ian.M
author_rank: Super Contributor
timestamp: August 04, 2020, 09:39:52 am
content: Quote from: Utdfederation on August 03, 2020, 10:51:29 pmNiCd batteries in consumer devices have been banned in the EU for over a decade, so they've got to be single cell NiMH batteries. As NiMH batteries don't tolerate overcharging or simple voltage based float charging, and once charged can typically only tolerate a C/50 or lower trickle charge (Duracell recommend C/300), any distributed charger system is going to be far from simple.Each light would need its own charge controller board, at which point you might as well replace the light with three series white LEDs with a dropper resistor for 12V operation off a central battery. It doesn't even make sense to gut the solar lights for the housings as you'd still have to sort out water resistant cable entry and termination, which would be easier without the physical constraints of a typical solar light housing.

author: Zero999
author_rank: Super Contributor
timestamp: August 04, 2020, 09:44:15 am
content: Solar garden lights tend to be built to a low price and don't last long. You'd be better off using the 12V solar panel to charge a large 12V battery and using that to power an array of 12V lights.

author: Utdfederation
author_rank: Newbie
timestamp: August 08, 2020, 01:44:20 am
content: okso if i get a car battery and charge that from the 50w solar panel i could remove all the batteries from the lights and run a linked live and neutral to connect to all the batteries, so in effct all 30 garden lights would run from 1 battery.but would i need something else to reduce the voltage considering the lights are only 1.2v?I really appreciate all the help you guys are willing to help me withthank you very much guys.

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2020, 09:30:56 am
content: Quote from: Utdfederation on August 08, 2020, 01:44:20 amMy advice would be to scrap the lights altogether and replace them with 12V lights, but you probably won't want to do that.You could convert the lights to work from 12V. Remove the circuit board and connect the LED to 12V, via a suitable resistor, try 1k. The problem is they won't turn off, when it gets dark, but a light sensitive switch circuit could be added to solve that problem.

author: Ian.M
author_rank: Super Contributor
timestamp: August 08, 2020, 09:51:04 am
content: Converting single white LED lights is rather wasteful as >3/4 of the power will go to heating the 1K resistors. That's why I said to use three white LEDs in series, for a total Vf of about 9V. Assuming 13V from a well charged Lead Acid battery, the series LEDs' resistor will only waste 30%. Try three series LEDs with a 270R resistor, which will give about 15mA at 13V but will tolerate up to 17V without exceeding 30mA through the LEDs so will survive the lights being turned on while the battery is being given an equalising charge. If 15mA is too bright, increasing the resistor would save power.

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2020, 10:46:15 am
content: Quote from: Ian.M on August 08, 2020, 09:51:04 amYes that's true, but I'm guessing he wants to keep the existing solar lights and there won't be enough room for three LEDs in the enclosure. Power could be saved by connecting them in ten strings of three in series, with a suitable series resistor.http://idielectronica.blogspot.com/2015/03/led-circuit-design.html

author: RJSV
author_rank: Super Contributor
timestamp: August 08, 2020, 09:08:39 pm
content: So far, these replys are giving you some good tips, allow me to chime in with my thoughts:Forget the individual charging, you are going in circles there, consider a 12 V lead acid batt often used in burgular alarms and electric scooters. Use Ian.w suggested strings of three.Now the use of panel (voltage) for sending, maybe you would be better to have just one sensor, perhaps salvaged from one of those little stand-alone units, it's certain those work, in a sunny / open spot. So far, that looks like PANEL - BATTERY - Sensor, but you next will put the switch. Heck, a 2n2222 NPN can switch your entire yard (and shed inside). Just don't charge, only charge that medium sized battery, on your covered porch.By the way, I've been trying to make up an optical - electronic oscillator, blinky light, by pointing an LED at the little solar cell, in my stand- alone unit. You may have noticed: frequently without hysterises some garden lights may blink, as dusk comes.You're on the right track, for those replies look good.More questions / feedback as you go, looking fwd to that. - RJHayward

author: james_s
author_rank: Super Contributor
timestamp: August 08, 2020, 10:49:11 pm
content: Just dispense with the internal batteries in the solar lights and wire them all to a single central battery/photo-control/solar cell unit placed in an optimal location. Personally I would probably just toss the cheap solar lights and get some good quality low voltage outdoor lights and wire them to a solar charged power source instead of using the traditional transformer.

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2020, 03:04:35 pm
content: Here's a circuit which switches on the LED, when the solar panel stops generating current, which will be when it's dark.

author: Dabbot
author_rank: Regular Contributor
timestamp: August 09, 2020, 03:22:02 pm
content: Quote from: Zero999 on August 09, 2020, 03:04:35 pmDon't do that. You'll smoke the transistor.Instead, connect the base to the solar panel +ve via that 10K resistor.

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2020, 03:53:06 pm
content: Quote from: Dabbot on August 09, 2020, 03:22:02 pmOh, I forgot, that schematic is for a solar panel which has a built-in diode, to prevent reverse current.Your suggestion will only work, if the solar panel doesn't have a built-in diode.If you don't know whether the solar panel has a built-in diode or not, use two resistors.