1.5 Watt panel supplying power coffee grinder for my coffee grinder every morning but I need a small controller

As the title says. I am saving some energy dollars. Maybe only a few pennies every day but it works, so far.

It all started with a Harbor Freight 1.5 Watt solar panel. I disconnected the blue LED that I believe was for a sort of battery over-charge protection and anti-discharge diode. I hung the panel on a south facing wall of the house. Ran wires into the pantry where I have a 12 volt riding mower battery, sealed lead acid. A freebie Harbor Freight digital multimeter, remains connected. I turn it on to check battery voltage. The volt/multimeter is off the rest of the time.

Every morning I fill the coffee grinder, turn on the voltmeter and inverter. Then grind the coffee beans. Shut off the inverter and voltmeter. During the summer months I was seeing 12.9 volts just about every morning before grinding my beans. As the days grew shorter I was seeing lower voltage as the battery was being discharged more during the increasing hours of darkness.

I tried one of the 5 amp charge controllers with LED indicator lights. It seemed to have too much quiescent draw. It would discharge the battery more at night, than the panel did by itself. Is there a charge controller known for the least amount of quiescent draw ? A diy kit I can solder/assemble ? Anything that will work with such a small PV panel ?

For now I am connecting the incoming wire from the panel to the battery when I grind. Later in the day I have to remember to disconnect it so it doesn't overcharge the battery. I wasn't doing that in the summer and probably took some useful life out of the battery already due to my neglect. I am being more careful now but I'd much rather have a controller do the watch-dogging for me.

In case anyone is wondering, this system trickle charges the battery all day. The one-use per day of the coffee grinder takes only a little charge out of the battery. I'm not trying to run the coffee grinder off of the panel. It's running off the battery/inverter. The panel recharges the battery is all it does. Apparently more than enough to do the job ... if I could only get a charge controller that didn't take so much power to operate.

It's a very small solar system, yes.

This is the way every DIYer should start. I'm surprised to leard that the charge controller is using any power at night. Is there a backlit display?

Is 1.5 a typo? I've never seen a panel that small.

I think I had one of those panels, sold to put on the dash of your car and keep the battery up when a car might set for weeks without driving it. I am a bit of a hoarder but I threw that thing in the trash because it would not even charge a 12v pack that I could put in my shirt pocket. Get something like this that is real.

Ahhh, I just saw it on harbor freight. I'm sure the OP is aware of "real" panels, and wanted a firm grasp on how it all works before taking the plunge. I wish I had done it that way.

DThames, I appreciate your frustration but in fact I have used this panel before now for a year or two for the specific reason it was marketed.

It took care of a car with an old battery that was very iffy in cold weather. On very cold days, it would not crank fast enough to start. With the panel, it always started, regardless how cold it was outside.

Since a new battery was installed, I've used the panel on a tractor battery that sits for weeks and months at a time. It kept it charged very well.

I read somewhere that by cutting the LED you can get more power. I wanted to at least see how useful it can be for something more domestic. Everywhere I look all the talk is about bigger and bigger. Makes sense if you are trying to go off-grid. I'm not. I'm just trying to save money and eventually keep adding "units" so that maybe someday most of my power will be derived from PV.

I'm looking to use the smallest panels I can and run small intermittant power users. Hopefully less of an intrusion on the appearance of the property.

My solar powered coffee grinder is the first "unit". Since it runs only once a day for about 20 seconds I figured 1.5 watts would replenish the charge even in my southern New England Winter latitude. The grinder uses about 150 Watts continuous. It's a 500 Watt pure sine inverter. The battery voltage has dropped by about a half a volt after each grind.

The 1st inverter I tried was one of the so-called "pure-sine wave" named converters. It was putting out in fact a modified sine wave which made the grinder run about 70% speed.

The charge controller I bought off Ebay and waited until it arrived from China (YEs I'm cheap too). CMPT02 is the model number. 10 AMP. Some of you are probably familiar with it. No back lighting. An LED for panel activity. Another 3 LEDs for battery charge. Another LED for load. 3 pairs of connections.

When I connected it, all 3 battery charge lights were on brightly. Indicating full a fully charged battery. I checked the owner manual/download to verify. The PV panel light was also on and I assume the load light would go on as soon as I turned on the inverter. It has three pairs of +- terminals for panel, battery and load/inverter. The load inverter/pair had nothing connected to it.

I wired the battery straight to the inverter. I am not concerned with trying to run the grinder when the battery was discharged too much or overcharged because I check the voltage first every morning before grinding the coffee.

After one night, the battery charge LEDs had only one lit brightly and the middle one dim or maybe splash from the lit one. I verified that the controller limited the voltage/charge rate so I assume it was working. I remind you it had all 3 battery charge lights lit even after dark on the 1st day I wired the controller into the system.

It seems this controller draws battery juice all night to keep the LEDS lit. Apparently that is enough to cause more discharge than I would like. Battery voltage had fallen down close to shutoff voltage. Although, it was able to run the coffee grinder that morning, I'd rather have the battery kept fully charged. Or at least closer to 13.5 V by the end of the dark hours.

So far the system cost :

1.5 watt PV panel $10
12 Volt battery $30
24 gauge X 50 feet, X single strand wire - leftover from some communications wiring project. Probably $10 worth max, more like 1$ probably
digital multimeter/voltmeter free, retail is about 10$
500 Watt sine wave inverter about $100
150 Watt 110 Volt coffee grinder already had maybe 30$-40$ to replace with a new one
CMPT02 10 AMP controller $15 the lowest rated power controller I could find

total :
Approximately 200$ for 20 seconds of 150 WATT usage daily. 1st use was 01012019. It's been almost one year, trouble free.

I bought the 5w version to keep my truck batteries up when unused. Did nothing but show a flashing blue LED denoting the sun was shining.
Threw it in the tool box to gather dust.
The 10w panel DThames suggested is a much better idea for trickle charging.
I doubt it would over charge a lead acid battery that sees daily, or even weekly use.

The Genasun controllers are the smallest (in form factor, charge current, and self-consumption) that I'm aware of -at least, in reputable, proven-performance SCCs. They're OEM in solar-powered parking meters and stuff like that... tiny, useless for most of us because they're one-per-panel and very low charge current, but may be perfect for you - they're basically designed for exactly what you're trying to do.
...ehhhh they're not cheap though, in general. We've been looking into carrying them, but keep hemming and hawing because they're such limited functionality that, for the price, I don't think there's much market for them among our customers. Worth looking at though, and maybe it's a starting place for you at least... here's a listing for an open box one that might work for you - I don't know the seller, tho, so I can't speak to their service/knowledge/products etc.

tirebiter said:

As the title says. I am saving some energy dollars. Maybe only a few pennies every day but it works, so far.

It all started with a Harbor Freight 1.5 Watt solar panel. I disconnected the blue LED that I believe was for a sort of battery over-charge protection and anti-discharge diode. I hung the panel on a south facing wall of the house. Ran wires into the pantry where I have a 12 volt riding mower battery, sealed lead acid. A freebie Harbor Freight digital multimeter, remains connected. I turn it on to check battery voltage. The volt/multimeter is off the rest of the time.

Every morning I fill the coffee grinder, turn on the voltmeter and inverter. Then grind the coffee beans. Shut off the inverter and voltmeter. During the summer months I was seeing 12.9 volts just about every morning before grinding my beans. As the days grew shorter I was seeing lower voltage as the battery was being discharged more during the increasing hours of darkness.

I tried one of the 5 amp charge controllers with LED indicator lights. It seemed to have too much quiescent draw. It would discharge the battery more at night, than the panel did by itself. Is there a charge controller known for the least amount of quiescent draw ? A diy kit I can solder/assemble ? Anything that will work with such a small PV panel ?

For now I am connecting the incoming wire from the panel to the battery when I grind. Later in the day I have to remember to disconnect it so it doesn't overcharge the battery. I wasn't doing that in the summer and probably took some useful life out of the battery already due to my neglect. I am being more careful now but I'd much rather have a controller do the watch-dogging for me.

In case anyone is wondering, this system trickle charges the battery all day. The one-use per day of the coffee grinder takes only a little charge out of the battery. I'm not trying to run the coffee grinder off of the panel. It's running off the battery/inverter. The panel recharges the battery is all it does. Apparently more than enough to do the job ... if I could only get a charge controller that didn't take so much power to operate.

It's a very small solar system, yes.

Click to expand...

Back to your original question about charge controller. I think if it were me, I would connect a 14volt zener diode across the battery. 14.4 volts is a common charger cutoff voltage for lead acid. As the battery gets to 14v the zener to turned on and limit the voltage to the zener's value. If the diode watt rating is much larger than your panel, it can short the power allowing the power to bypass the battery. So it will never be higher than 14v.

I bought a 1 watt (yes, one watt) 100mah solar panel from a yardsale for a buck a few years ago. Looks very similar to yours but was made by some marine company (Seasense, Seachoice...something like that). I use it to keep a dead riding lawnmower battery charged enough to start, and it works great. I periodically check the battery voltage and never see it above a safe level (floating at about 13.1v or so max, usually less). $1 solar panel vs buying a new crappy battery every 2 years? I'm happy.

So, with a panel that small I don't think a charge controller is necessary, and would surely waste too much power. 1w @ ~17v is just not enough power to bust through bulk stage and overcharge a lead acid battery...but lithium would be a different story.

Justin, Thanks for the link. The specs say it uses 125 Ma at night. That's about half of what I think the controller I have, uses. Better but I was hoping for less than a 10th of an amp.

SolarRat,
I have recently seen as high as 16.4 Volts even after disconnecting the PV panel. The voltage seems to drop extremely quickly back to nominal 12 something to 13.5 when I use the grinder. Short winter days however. I am worried about what happens in summer.

I was not checking voltage after hours of daylight before so I was ignorant of how high the readings would have been. Now that I am watching, I am worried. I guess your point is probably more valid than I would have thought. It did work all this past year without ruining the battery. I just figured I got lucky but you maybe are explaining it more accurately ... although I do not exactly understand the chemistry that allows a lead acid battery to not over charge with low current even at high voltage.

The 1.5 Watt PV panel with the blue LED limiter bypassed will read over 20 volts when it's sunny out and disconnected from the battery, no load. I think I've seen it go to 27 volts by aiming the panel better. Right now it's just hanging vertically. Not aimed at all really so 20 is about it.

I was hoping I could get it to read 13.5 every morning when I go to use the grinder. I suppose if I keep seeing 11.9 due to overnight drain and as high as 16.4 due some (false) surface charge, it will not shorten the battery life too much. I just feel if the voltage was controlled better it could only help the battery lifespan increase.

I bought 2 more panels on sale the other day. $20 more dollars. One last question. If I connect 2 in parallel (not that I want the extra PV panel hanging on the side of the house) is there anything else besides a couple of half amp fuses I need to incorporate ?

It seems to me that there should be some way to prevent overcharge and the nightly discharge that goes on. The zener will not prevent the nightly discharge will it ? I'm thinking maybe another smaller battery to power the controller might be the ticket. It would be cheaper to replace and if I can configure this system properly, the main battery would be kept at optimum charge most of the time.

If possible I'd rather be using a smaller battery than the riding mower battery but being unable to find a low night time drain controller has me stumped. I believe the battery I have now is way overkill for a 20 second use of 150 Watts at 110 Volts, daily.

Am I barking up the wrong solar tower ?

The zener diode would be used in place of the charge controller. Any discharge would be inside the battery, or if the inverter is connected, inside the inverter.

Look at this page. Rseries is not needed as the power is so low and the zerer is so large compared to the power. Rload is your battery. The zener will short to ground any power once the voltage is as high at the zener rating. It is an voltage regulator. If you are charging without a charge controller and are happy with the results, this will protect your battery from higher voltage and keep everything the same.

Maybe just use one of these?:

I I 2nd the simple Diode, 1.5 watt in full sun shouldn't be able to overcharge the battery if its lead acid. I think i remember something along the lines of 2 watts per 50 AH of battery doesn't need a controller. You could also hook up your meter and measure how much amperage the controller is drawing during standby by running it through the current meter. Then calculate how much it is using over 24 hours and see if its even worth it. If its PWM modulation it will be cutting out power by switching current on and off, something that also uses a small amount of power to calculate. You are dealing with such a small amount of current here I think the best way to deal with this would be to have an under volt warning. flashing led when undervolt condition exists or an inverter with voltage readout. Just my .02

A cheap ups SLA 7Ah battery would be 91Wh and your demand is only 30... but your 1.5W panel can only produce 9Wh per average day... so... you need a bigger panel to power even the small demand you have.

a 5 watt panel will JUST barely handle he load. I would get a 10 or 15W panel to be sure you cover the load of your inverter.

and you would need a charge controller for that. The cheapo one you have should suffice. Still around 1amp with hat small a panel.

I hope this doesn't upset you, but I am considering buying a manual hand-grinder - have you considered that? They sell them on Ebay or elsewhere? Seems a little therapeutic to me, LOL.

SoalrRat,
I can see how something like the buck converter might address the need for preventing overcgharging but I don't know enough about them to know if they would buffer the battery to prevent drain during the dark hours. Also, I did not see any info regarding how much drain they impose. I assume since there are no LEDs, then there would be less drain than the CMP102 controller I have, when in use but is it also less at night ?

Supervstech,
Can you walk me through the math? I think I understand what you are saying but if I see it in the form of arithmetic symbols followed by an equal sign and number, it would probably be easier for me to see how it pertains.

Please understand this has been keeping the battery charged for a couple of days over a year now. I imagine the 1.5 Watt PV panel is rated on the low side so maybe it's adding more than 1.5 wats in direct sun.

Another thing to keep in mind is I disabled the circuit to the blue LED. My intent was to eliminate the typical 0.7 Volt drop going through the diode silicon and I assume some amount of current is not lost to power the LED.

I tried the two new 1.5 Watt panels I picked up recently. Parralleled them. As soon as the sun went behind the roof, open circuit voltage dropped to just above 5 Volts. Reading the open circuit Voltage on the one with the disabeled blue LED yeilded over over 20 volts, still.

It seems the panel can get through the LED only in direct sunlight so it turns on and turns off by itself according to available sun. It is somewhat of a control and now I can see why some people did not have success with it. I didn't notice anything on the packaging that said it only charged the battery when in direct sunlight.

Someone asked about using an ammeter to see if I can get an idea of actual current coming out of the PV panel. I have a 10 amp Fluke which has an accuracy of 0.001 amp dc. I also have the el-cheapo I can select up to 2 amps.

I also have a clamp meter with hall effect supposedly accurate to a few decimals also. It's newer and I have yet to learn to trust it 100% yet. The positioning of the clamp around the wire has a lot to do with it.

I'm not sure how to go about it though. Do I measure with some other type of load resistor than the battery? I'm uncertain what happens if the battery is in a low state of charge as compared to when it is reading 13.5 volts after sitting all night. I plan to measure when the sun is shining directly on the PV panel and again when it the sun has gone behind the roof.

Any other suggestions ? I think I'll stick with the solar grinder for now Santa, but thank you for the opportunity to gracefully bail out ... if I decide to give up on it. Not likely though. Especially with all the helpful suggestions and ideas people have been posting.

I am correct that without a charge controller this is working as desired? (other than your concern about overcharging the battery)

tirebiter said:

SoalrRat,
I can see how something like the buck converter might address the need for preventing overcgharging but I don't know enough about them to know if they would buffer the battery to prevent drain during the dark hours. Also, I did not see any info regarding how much drain they impose. I assume since there are no LEDs, then there would be less drain than the CMP102 controller I have, when in use but is it also less at night ?

Click to expand...

The buck converter would just prevent overcharging. One of the reviews claimed it had a 8ma draw. As for drain during night...well, you might have caused that problem by removing the LED. LED = light emitting DIODE. The function of that diode was probably more than just a pretty indicator light.

Supervstech said:

A cheap ups SLA 7Ah battery would be 91Wh and your demand is only 30... but your 1.5W panel can only produce 9Wh per average day... so... you need a bigger panel to power even the small demand you have.

a 5 watt panel will JUST barely handle he load. I would get a 10 or 15W panel to be sure you cover the load of your inverter.

and you would need a charge controller for that. The cheapo one you have should suffice. Still around 1amp with hat small a panel.

Click to expand...

A 150w load will use 2.5w per minute. He's only using it for 15-20 seconds...that should be fine with that little panel.

SolarRat said:

A 150w load will use 2.5w per minute. He's only using it for 15-20 seconds...that should be fine with that little panel.

Click to expand...

150 W divided by 5 (20 seconds of a minute) is 30W/minute I skipped a step... my bad. 1.5W outputting for 6 sun hours is 9Wh, or 540Wminutes... plenty of power.
Carry on. Ignore me.

Another issue is your free Battery may have slowly sulphated to death. I mean at this point we have spoken on more solar, solar charge controllers, Diodes (including LED diode) and checking the actual current. Just to add something else to the mix I think you should upgrade the battery to LTO... (thats a joke) But really if battery voltage drops off right after the sun goes down or quickly after the panel loses sunlight the lead acid battery might be heading out to pasture so to speak. I personally hate motorcycle, lawn tractor and all those other expensive low capacity batteries that fail every winter on my motorcycles, sometimes even with a tender. I also think that the LED might have been whats called a "blocking Diode" they are used in solar panels so your panels don't become resisters overnight. I think someone was alluding to that above.

Supervstech said:

150 W divided by 5 (20 seconds of a minute) is 30W/minute I skipped a step... my bad. 1.5W outputting for 6 sun hours is 9Wh, or 540Wminutes... plenty of power.
Carry on. Ignore me.

Click to expand...

And my math still sucks...

Should divide by 3... so 50 W/minute... still nowhere near what the 1.5W panel should produce in an average day.

150wh/60 minutes = 2.5w/m /3 = 0.83 watts per 20 seconds. I think he's over-paneled .

TheDroidsYouAreLookingFor said:

I think someone was alluding to that above.

Click to expand...

Good catch.

DThames, Yes, with no controller and no Blue LED, I have used the grinder every day with adequate battery power. No sign of it slowing down in the 20 seconds it is running.

What I'm worried about in fact is the way the battery is being "Exercised". I think it's running through deeper discharge cycles than necessary with the steady night-time drain and then pushing the enevelope so-to-speak as far as overcharging during peak hours.

Battery life is my main concern. The system has proven so far to be reliable. No sign of slowing down after one year of operation. I'd like to be able to run a smaller battery.