Solar charge controller recommendations, anyone?

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hank
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Solar charge controller recommendations, anyone?

I find I’m accumulating lead-acid batteries in the 3AH-7AH range as my several household UPSs declare them unacceptable.
They still show 13 volts or better; I presume there’s some algorithm the UPS uses to test them. They’re still entirely adequate for 12V LED lighting for several hours.

So I’d like to stick small 12v solar panels and charge controllers on them, to have them charged and handy when the earthquake happens.

I find a LOT of solar charge controllers out there for sale under $10 or so, and a lot of skeptical take-apart videos, but no good summary and recommendation.

One distinction I found online that’s probably worth knowing:

Quote:
A 7 Ah battery can generally be safely charged at 0.5 C or less (3.5 A). The battery manufacturer may have other specifications (e.g. a lower rate to prevent overheating) which should be available on their data sheet. You should use that as a guideline.

MPPT controllers will give you a maximum charge rate of 2.5 A (12 V x 2.5 A); considering that this is the maximum possible it would be fine for your battery. They aren’t cheap though, relative to PWMs.

PWM controllers are cheaper but would give you less power because they pull the panel voltage down to battery voltage (rather than converting the voltage/current like MPPT), so it depends on what you’re using the battery for. In your case, it might make more sense to get another 30 W panel (which costs less than a MPPT controller) to give you added power.

https://www.quora.com/What-size-solar-panel-should-I-use-for-a-7AH-12v-b...

(Some of the online reviews/cautions are about people mislabeling PWM controllers as MPPT controllers, apparently a common problem out there.)

Edited by: hank on 04/18/2020 - 21:10
hank
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One and only bump, hoping someone out there has thought about this question already.

hiuintahs
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Pardon me if I didn’t quite grasp what you are trying to do but I put some thoughts down.

Based on what you quoted, a 7Ahr battery that is going to get charged at a maximum of 3.5 amps means you are talking a 50w panel (3.5 amps x 13v = 45.5 watts). That seems a bit over kill for a 7 Ahr battery because we’d be talking about a full charge taking only 2 hours if the battery was empty and most likely you don’t want to run your batteries all the way down. My guess is that you don’t need that fast of charging. So a lot smaller panel per battery would suffice.

Are you going to parallel any of the batteries or are they all going to be single entities. The reason I ask is that the 100w panel is probably the best value for the money (most amount of watts / $ )

On that small of a solar panel I wouldn’t worry about whether you go MPPT or PWM. You will lose a little bit of power accumulation with PWM over MPPT and its something like 10 to 20%………I can’t remember. But its insignificant for a small solar setup.

If wanting to keep a separate solar panel / charger per battery, then I’d go for something around 20 to 25 watts max……….or whatever is the best value for the money in that area.

I suppose there are a lot of cheap PWM solar charge controllers, and I haven’t played around with any, but I think that would be best for what you are trying to do. Just go off of the reviews and see if the majority of buyers are happy.

You may even be able to get by with a low wattage solar panel that has some type of controller built on it that says that its basically a trickle charger. I guess it really depends on how fast you want to be able to replenish a battery.

So my conclusion based on what I understand from your post is:

1) no solar panel bigger than 50 watts and preferably in the 20 to 25 watt area if you don’t parallel any of the batteries
2) just go with an inexpensive pwm charge controller……….maybe even one that is already built onto the back of the solar panel.

gravelmonkey
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Watching this thread with interest as I’m in a similar situation (no earthquakes here in SW UK though :P).

I’m also considering a mains powered charger as I don’t have that much space available for solar panels.

I do currently have a 20W panel to hand right now, and a few salvaged electronics components including a LM317.Google shows a few links with tutorials for building a charging circuit, might have a go this week.

ChrisGarrett
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8 years ago I put together a small portable 60w (2×30w) 12vdc system for my hurricane preps. I’m in a condo and needed to lug it down to the ground, by the lake/canal, so it had to be fairly light in weight.

I went with the 10A Morningstar SS-10 PWM controller, since my charging needs are on the smaller side of things. In perfect conditions, I might get 3.5A of current.

MPPT controllers are better, but since they contain a processor that utilizes some of the power to run themselves, they ‘might’ not be the best option for some applications on the lower end of the scale.

Chris

hank
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Thanks guys! Yes, the small panels are what I was thinking of — I’d wondered if anyone made what hiuintahs describes:

Quote:
a low wattage solar panel that has some type of controller built on it

as that would be just about what I want to build. I’d be delighted to find them premade. I want to be able to set these rigs in sunny windows and forget about them until the earthquake happens, and then find the batteries fully charged. That would be using the typical batteries rejected by my APC UPSs (12V 3Ah) which still hold charge; I’m assuming the UPS thinks their capacity has diminished.
hank
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Oh,and

Quote:
there are a lot of cheap PWM solar charge controllers

Agreed, several dozen for around $10 apiece, blue rectangles — the only difference is black buttons or clear buttons, and whether “PWM” is painted on the front.
Here’s a typical takeapart video (nobody does text reviews anymore, ya gotta watch videos)
https://www.youtube.com/watch?v=9fjeYi3SwLc

But the takeaparts I’ve seen on that sort suggest they’re unreliable and that the sellers have no idea what they’re selling.
It sounds like the early days of the China flashlight lottery, with lots of stuff but nothing known reliable to order.

I gather just putting a little solar panel directly onto the battery is never a good idea because panels can hit 18v output and stress the battery. Thus the need for a controller, even for trickle charging which is what I want to be doing.

ChrisGarrett
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hank wrote:
Oh,and
Quote:
there are a lot of cheap PWM solar charge controllers

Agreed, several dozen for around $10 apiece, blue rectangles — the only difference is black buttons or clear buttons, and whether “PWM” is painted on the front.
Here’s a typical takeapart video (nobody does text reviews anymore, ya gotta watch videos)
https://www.youtube.com/watch?v=9fjeYi3SwLc

But the takeaparts I’ve seen on that sort suggest they’re unreliable and that the sellers have no idea what they’re selling.
It sounds like the early days of the China flashlight lottery, with lots of stuff but nothing known reliable to order.

I gather just putting a little solar panel directly onto the battery is never a good idea because panels can hit 18v output and stress the battery. Thus the need for a controller, even for trickle charging which is what I want to be doing.

My initial thought was to buy quality stuff back then and be done with it, with what I could afford at the time, even though money was tight.

The Morningstar is a quality PWM controller which can handle up to 10A, so I can add bigger panels and keep the controller in place.

There are lots of cheaper things you can get…but buy once, cry once is how I handled it.

Chris

hank
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> Morningstar

Yeah, the one controller I’ve had for a couple of decades is a Morningstar SG4, their smallest. No fiddling, no worries, costs around $30 nowadays.
More than I’d prefer to pay apiece to trickle charge little 3Ah SLA cells though. Plus solar panels.

Sigh. Maybe the universe is telling me to set up a proper big solar installation and home battery bank, economy of scale.

hiuintahs
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hank wrote:
Thanks guys! Yes, the small panels are what I was thinking of — I’d wondered if anyone made what hiuintahs describes:
Quote:
a low wattage solar panel that has some type of controller built on it

as that would be just about what I want to build. I’d be delighted to find them premade. I want to be able to set these rigs in sunny windows and forget about them until the earthquake happens, and then find the batteries fully charged. That would be using the typical batteries rejected by my APC UPSs (12V 3Ah) which still hold charge; I’m assuming the UPS thinks their capacity has diminished.
You should be able to find one. Most of those charge controllers that are already on the back of the solar panels……….well just say, I haven’t the best impression of them. They are also in the category of $10 or so controller.

Another thought is that if you are not going to use the batteries until there is a crises, that maybe you only need one decent charge controller and about once every few days move it to another battery. The batteries shouldn’t discharge very much on their own if there isn’t any load on them.

For me what I do is have a bigger portable setup (without battery) and use the battery of my vehicle as the battery means. Then with the rechargeable batteries that fit your flashlights make sure your chargers for them can be powered via 12v. My main interest is in powering a 12v portable compressor refrigerator when I go camping or if we get into a power outage at home. Every car has a battery and they are around 50Ahr or more. And thus I have a couple hundred watts of solar panels. Though if you do not live in a residential area where you can keep an eye on your vehicle and stuff that may not work so well.

will34
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Have you tried victron controllers? They are very efficient MPPT controllers with Bluetooth support to use with an amazingly well designed phone monitoring app.

I had mine for years with a vmaxtank AGM in a diy emergency UPS. Even without input power the Bluetooth module drains minimal current and it can stay powered for 6 months+ without the battery dropping to critical voltages. I charge it with both solar and 24V DC adapter via a switch.

hank
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> Victron Energy SmartSolar MPPT 100/50 Charge Controller
> $323.85 from 50+ stores

Nope, not even close.
I’m sure Victron is nice, but I’m looking for someone’s recommendation of one of the $10-ish cheap controllers, one that I can attach to a 3Ah battery and cheap 12v solar panel, as a trickle charger.

Ali has dozens of people selling what looks like the same little cheap controller, but the video reports are that those are quite inconsistent.
Like this, and the comments to it: https://www.youtube.com/watch?v=9fjeYi3SwLc
Some work, some kill batteries, and as I said above it’s apparently like the early years of buying flashlights from China where nobody really knew what they were selling.

ChrisGarrett
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hank wrote:
> Victron Energy SmartSolar MPPT 100/50 Charge Controller
> $323.85 from 50+ stores

Nope, not even close.
I’m sure Victron is nice, but I’m looking for someone’s recommendation of one of the $10-ish cheap controllers, one that I can attach to a 3Ah battery and cheap 12v solar panel, as a trickle charger.

Ali has dozens of people selling what looks like the same little cheap controller, but the video reports are that those are quite inconsistent.
Like this, and the comments to it: https://www.youtube.com/watch?v=9fjeYi3SwLc
Some work, some kill batteries, and as I said above it’s apparently like the early years of buying flashlights from China where nobody really knew what they were selling.

SunPower, or SunForce makes a reputable 7A controller, similar to the Coleman branded jobbies for less than $30, IIRC.

Look there.

Chris

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Hmmmm.

From the SunForce page:

Quote:
A solar charge controller is needed when you have 15 Watts of solar energy or more.

Can I get by without one?

Quote:
Does a 5 watt solar panel need a charge controller?
Generally, there is no need for a charge controller with the small maintenance, or trickle charge panels, such as the 1 to 5-watt panels. A rough rule is that if the panel puts out about 2 watts or less for each 50 battery amp-hours, then you don’t need one.

Solar Charge Controller Basics | Northern Arizona Wind & Sun

Lessee, 2 watts for 50 Ah, and I’ve got a 3Ah battery …. I guess I’d be looking for a very small solar panel, if I went without a controller. Hmmm …

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The rule of thumb is <20w for the panel and you don’t need a DCC.

Chris

hank
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Hm, can my multimeter tell me what wattage a panel is putting out?

I’d worry about putting a 20w panel’s output through a 3w battery.
I’m almost sure I did that a couple of decades ago on a bright sunny day, and heard the battery bubbling after a while.
Cracked both ends of the plastic case, too.

hank
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Smallest cell I found looking was 250 mAh:
https://smile.amazon.com/Sunnytech-250ma-Module-Polysilicon-Charger/dp/B...

That oughta be about right to connect to a 3 Ah battery. I think. Kinda.

will34
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hank wrote:
> Victron Energy SmartSolar MPPT 100/50 Charge Controller > $323.85 .

$120 Victron SmartSolar MPPT 75/15 Solar Charge Controller 75V 15A with Bluetooth https://www.amazon.com/dp/B075NQQRPD/ref=cm_sw_r_cp_api_i_aeiNEbTXWGZ1J

This is the like one I got and it comes with the Bluetooth integrated, mine has a separated module. 75V 15A. Yeah It’s still expensive but an investment if you plan to upgrade your setup in the future.

hank
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How does the Bluetooth thing work? Needs a smartphone app (and if so which phone OS level)?

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I’ve been using this one for 6 years off a 30w panel into a 100ah deep cycle battery.
I’ve used it in very cold and very hot climates and have never had a problem.

!P4190275!

When you're up to your ass in alligators; it's hard to remember your original intention was to drain the swamp.

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You possibly have two different scenarios here.

Your question seems to be about keeping them charged and ready for an earthquake. A simple, literal answer to that problem would be to link them all in parallel and keep them at float voltage. The simplest PWM controller or even an adjustable buck module set to about 13.8V could do that. Panel size would be very modest; just enough to compensate for self discharge.

However….
Things get a whole lot more complicated if you plan to draw down on them and recharge. If you figure on staying in place for days or weeks after your emergency, then panel sizes and controller types have to be calculated based on you expected daily power consumption. Lots of good replies in this thread already.

One thing to note about the Victron controllers is that they need the panel voltage to be at least 5V over battery voltage to start charging. After that, +1V is sufficient. You may have trouble getting any charge at all on a heavily overcast day. I don’t know if other brands are comparable.

If you are serious about building a real emergency rig, take Chris’s advice and get good quality gear from the outset.