Sort of new at this and looking for advice/help

Blindowl1234

I've got 7 old Malibu Led landscape lights that were individual solar lights originally. They say they're 0.12 watts each I'm wanting to run with one solar panel. I've got a 25 watt solar panel and a 12 volt car battery (yeah I know it should be deep cycle). The lights were originally 3.2 volt and I'm currently stepping the voltage down from 12 volt on the battery to 6 volt. The output voltage is measuring 5 volts Dc and so far the lights are doing fine. I've not hooked the solar panel up yet do to cold weather here but I've experimented with running them off the battery all night. So far I've found I can run them for about 10 hours with the voltage at 12.4 but by morning the battery is at 10.5 volts. Then I trickle charge with a car charger. Two concerns so far I don't think a PWM controller will let the voltage drop that low so as to protect the battery is that correct? If that's true then I imagine the lights won't run anywhere near 10 hours before the voltage drops too low. The panel I'm guessing is big enough to keep the battery charged, perhaps a couple of decent deep cycle batteries are what I really need? Any tips or advice on what I'm doing wrong that I need to do differently I appreciate it.

BB.

With LEDs, they are "different" from filament bulbs. Basically, you need to control the current to an LED via a resistor (does cost energy) or an electronic current regulator.

Depending on how the LEDs are configured.. You should be able to put 3 or so in series (assuming they have a resistor/current regulator) to efficiently use 12 volt power source. If they are "raw" LEDs, you can put 3 or so in series, and figure out the size of resistor to limit current to the LEDs (we can help you with that). One resistor per string of LEDs.

Regarding the PWM controller--Most have 10.5 volts as they cutoff voltage. It is intended to protect the loads from too low of voltage (motors overheat, AC inverters over heat on low input voltage). It is not to protect the battery (taking a lead acid battery to 10.5 volts will shortly kill the battery).

You really want the low voltage disconnect to be around 11.5 to 12.0 volts (roughly 50% state of charge) -- And some charge controllers can be programmed for different LVD settings. Lead Acid batteries do not map well between terminal voltage and state of charge--So cutoff voltages are not very exact.

You need to figure out the Amp*Hours you are drawing from the batteries (per night). And how many Amp*Hours you are getting from your solar panels (and the battery capacity itself).

-Bill

Blindowl1234

Thanks Bill for the info. The lights were at one time a couple of sets of Malibu solar flood lights no longer made now. Both sets came with their own mini solar panels that put out about 4.5 volts each. After a few years the panels would quit so I was stuck with a few sets of LED lights to mess with lol. I'm stepping them down with a Drok Dc 12v to 6V/3A Step down voltage module etc....which puts out about 5 volts to the lights. At this point all 7 lights are connected together and running back to the 6 Volt output of the module. I figured I might be drawing a 1/2 amp total. The 25 watt panel probably produces 1 1/2 to 2 amp so basically a trickle charge. I've got the panel mounted today in 14 degree weather lol and it's charging so we'll see how long it runs tonight. The PWM controller is one of those cheap chinese units with nothing but a green light so I'm planning on upgrading it soon. If all works well I'll get some deep cycle batteries too. Didn't want to put too much money in it until I know it will work.

BB.

With a little DC switcher "Buck Converter", those are usually efficient enough that they are your best choice when you need low/different voltages. (there are losses in the switchers you need to worry about too).

Depending on the panel ratings, at best your panel will probably produce around 1.4 amps. If you have 4 hours of sun (very sunny winter weather):

• 25 watt / 18 volt Vmp = 1.4 amps (Imp estimate)
• 1.4 amps * 4 hours of sun * 0.80 battery eff = 4.48 AH per "sunny" day
• 4.48 AH of "useful energy" / 0.5 amps = 8.96 Hours of lighting per charge

The above numbers are probably "best case"--Put in some cloudy weather, less than optimum panel+charger+wiring+battery and it would not be hard to expect 1/2 (or ~4.5 hours of light per night) of "reliable" illumination.

Note that with a 1.4 amp charging current, we want 5% to 13% rate of charge (5% is good for weekend/seasonal, 10%+ is good for daily usage):

• 1.4 amps * 1/0.05 rate of charge = 28 AH flooded cell battery (largest recommended with "25 watt" panel)
• 1.4 amps * 1/0.10 rate of charge = 14 AH flooded cell battery (nominal size)

A car battery is probably closer to 60-80 AH typical capacity... So at best you would want 2-4x more charging capacity for a "robust" solar charging system. And "revisit" your battery choice after this battery craters.

At least, that is how I guesstimate from my side.

-Bill

Blindowl1234

Wow Bill thanks for all the info! I'd be happy with 4.5 hours per night or 8.96 I'm not greedy lol. So as far as a deep cycle marine type battery? or batteries, I'm looking for something with 56AH to 112AH is this correct? Any recommendations? Thanks again for all the tips

BB.

In general, for off grid system, we recommend 1-3 days of storage with 2 days "nominal" and 50% maximum discharge for loads. For example, if you want 9 hours per night at 0.5 amps:

• 9 hours per night * 0.5 amps * 2 days storage * 1/0.50 maximum discharge = 18 Amp*Hour @ 12 volt battery bank

If you want to charge the battery at a 10% rate of charge, then:

• 18 AH battery * 0.10 rate of charge = 1.8 amps charging

For a typical solar power system, the solar array would have to be rated at:

• 1.8 amps * 14.5 volts charging * 1/0.77 panel+charge controller deratings = 34 Watt solar panel minimum

And if the panel is rated at (typical) Vmp~17.5 volts, its Imp rating would be roughly:

• 34 Watt array / 14.5 Volts Vmp = 2.34 Amp Imp rating

Notice that if you want a large battery (56 or 112 Amp*Hour rating), we would be suggesting a larger solar array to make the 5%, 10% or 13% rate of charge, For example, a 56 AH @ 5% rate of charge would be:

• 56 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 53 Watt minimum array recommended
  

-Bill

Blindowl1234

Sounds like what I was thinking before I started all this I need to go with a 100 watt panel or so down the road. Today the panel charged the car battery all day probably 5 hours full sun. The rest of the day was partial sun. I turned everything on and within 1/2 an hour everything shut down on low voltage. I'm lost now lol but guessing the panel isn't big enough to even really fully charge the battery. I trickle charged them at 2 amps all day yesterday, and they lasted 6 hours without using the panel at all. Going that route I suspect I need a much larger panel, the right battery and the summer sun lol.
    Tonight I was thinking why didn't I use the Ni-Cad rechargeable batteries that were in the solar lights to begin with. They total 13.2 volt and I figure I could use them with the panel. I was thinking they charged fine for the last year or so as they were, but the individual panels attached to the lights had died. There's a 1000 MAH at 3.2v, (2) 400 MAH at 3.2v, and (3) 1500 MAH at 1.2 volt each for a total of 13.2 volts there. Am I losing my mind or am I on to something here? lol. Sounds like an easy way to make this work and save on the batteries, and a larger panel too. Thanks again for all the help! At almost retirement age I still enjoy learning new stuff but it's not as easy as it was long ago.

BB.

You should not put 1000/400/1500 mAH batteries in series. The small battery will charge first... IAnd you have to "overcharge" the small one to get charging current to complete charging the larger batteries.

If you look into how NiCad/NMH etc. batteries charge and terminate charging--It is not a simple/obvious DIY project.

-Bill

Blindowl1234

Bill, That's the batteries I had in the original mini panels. I was thinking of using a 2000 MAH 12 volt battery pack. Oh well maybe wait til spring it's to cold and no sun rest of the week lol. Thanks again

BB.

You can charge directly from solar panels--Use a resistor to limit current to typically 10% or less of the battery's AH rating. Note that this can be be vary dangerous for many Li Ion chemistry batteries.

Or, find/design a battery charger that run directly from a solar panel (charge when the sun is up).

Or, design a solar + 12 VDC battery system, and get a 12 VDC to battery charger. Advantage is you can quickly/fully charge your batteries at any time day/night/bad weather/etc...

-Bill

Blindowl1234

Well I can tell I need a much bigger panel to charge anything much. I think that will be the next move as weather warms up hopefully in March, then I'll look at batteries. My wife has learned all my projects involve cost over runs lol