Does a 20 watt, 24 volt system have enough amps to charge?

[swiftk77]

I am a VERY newbie to solar, although I have been consider it for my RV! A few weeks ago I had a driveway gate installed and it came with a solar kit, but it just isn't charging the batteries and I don't know if it's the panel or the charge controller. The panel is a small 20 watt @ 24 volts, but the max power current (Imp) is only 0.56 amps. Everything tests out with my multi-meter, I get anywhere between 36-41 volts during peak sun and the amps remains pretty close to 0.56, but my two 12 volt small seal lead acid deep cycle batteries aren't getting charged. I called the gate company and it was clear within 5 mins that I knew more about solar than they did, and that was after an hour of googling. So the question I have is, "will 0.56 amps enough current to charge the batteries"? Do I need to get an extra solar panel to double the amp output? Should I just get a larger 24 volt panel; such as 100 watt to get ~5amps instead?

Thanks and sorry for the novice question!

 

[Vigo]

So, if your two 12v batteries are wired in series to make a 24v nominal system and you hook a 41v (open circuit) solar panel to it, the batteries will pull the solar panel output down to battery voltage, which may be as high as 28-29v. If you had 0.56amps at that voltage, you’ve got more like 15watts of true output. If you wanted todo better youd have to use an MPPT charge controller and i highly doubt your system includes one.

I dont know anything about what hardware is typical in a solar gate opener setup but i suspect two main issues:
1. You’re simply outpacing the charging system by using the gate too much, or not having enough sun hours to compensate for your gate use. More solar panel could fix this.
2. Whatever charge control scheme is in place is harmful to the batteries. For example, if there were NO charge controllers the solar panel may eventually push the batteries to too high of a voltage and damage them in fairly short order. Or, it may just be that the voltage setpoints of the controller arent appropriate for the batteries that are hooked up, or the temp at which those batteries are being stored in, etc.


Either way i suspect installing more batteries, or more battery capacity, is not a real solution. Symptom would probably reoccur. So you’ll have to figure out the root cause before devising the fix.

 

[swiftk77]

Thanks for the quick reply and I think you’re right, bayberry capacity won’t fix the issue. As I test, I disconnected the load on my controller to see if having no load on a sunny day would charge but that didn’t work either. The gate company went with pretty cheap components and I have the 20 amp version of this controller on Amazon:

PWM controller

Wish I could know if this is a controller issue or if I should get a different panel with a little more power.

Thanks again

 

[Tomthumb62]

Thanks for the quick reply and I think you’re right, bayberry capacity won’t fix the issue. As I test, I disconnected the load on my controller to see if having no load on a sunny day would charge but that didn’t work either. The gate company went with pretty cheap components and I have the 20 amp version of this controller on Amazon:

PWM controller

Wish I could know if this is a controller issue or if I should get a different panel with a little more power.

Thanks again

While that's a cheap PWM controller, it's extremely popular (cuz cheap). While PWM controllers aren't as good as MPPT, for your use case, the expense of a MPPT doesn't make sense. Get a 100W panel and I bet it'll make a huge difference.

Here's a cheap but probably way better than what you currently have 100W panel:

https://www.amazon.com/HQST-Efficiency-Battery-Charging-Applications/dp/B08SWJK87H/ref=sxin_18_pa_sp_search_thematic_sspa?content-id=amzn1.sym.6fd80408-71b6-44da-b059-082bba9089d3%3Aamzn1.sym.6fd80408-71b6-44da-b059-082bba9089d3&cv_ct_cx=hqst+100w+solar+panel&keywords=hqst+100w+solar+panel&pd_rd_i=B08SWJK87H&pd_rd_r=9c26a45c-4eec-41b4-ba7b-57991462d0aa&pd_rd_w=DU6S9&pd_rd_wg=FWnLu&pf_rd_p=6fd80408-71b6-44da-b059-082bba9089d3&pf_rd_r=R6N3JEG26T971MRWPJXH&qid=1688792902&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sprefix=hqst+100w%2Caps%2C207&sr=1-2-364cf978-ce2a-480a-9bb0-bdb96faa0f61-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9zZWFyY2hfdGhlbWF0aWM&psc=1

 

[swiftk77]

Thanks, I’ll grab a 100 watt panel and give that a shot! I am assuming that I’ll need to get a 24 volt panel rather than 12 volt since I have a 24 volt system? Or get two panels and wire them in series?

 

[littleharbor2]

What batteries are you using? Specs?

 

[swiftk77]

2 - 12 volt sealed 15ah deep cycle, like this:

12V 15Ah Battery. "Upgraded 12 amp hour battery"

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[littleharbor2]

At .56 amps charging you're a bit underpowered. and as mentioned may be over using the gate. Are you?

 

[swiftk77]

For an entire day I disconnected the load wires from the solar charger to see if the batteries would charge and their voltage didn’t increase at all. That left me thinking, is there an issue with the solar charger or is the .56 amps too low to charge these batteries. I debated this morning hooking the panel direct to the batteries for an hour this afternoon to see if I can determine if this is a solar panel or charger issue.

 

[littleharbor2]

As long as you can monitor the batteries that will work. I know that controller well. Have sold many dozens of them. They are really cheaply built. I had a few returns. Good chance it is faulty, or at least, not connected correctly.

 

[swiftk77]

I’ll give that a try after I get back home from my sons t-ball game and report back! Thanks everyone for your assistance!

 

[Tomthumb62]

Thanks, I’ll grab a 100 watt panel and give that a shot! I am assuming that I’ll need to get a 24 volt panel rather than 12 volt since I have a 24 volt system? Or get two panels and wire them in series?

Yes you either want a "24v" panel or simply wire two 12v panels in series. So to get 100W at 24v, you'd want 2x12v 50W panels, wired in series.

To tag on what @littleharbor2 has said, yeah the controller could be faulty, but something commonly overlooked is connections. Check all wiring connections, terminal screw downs, etc. Also we don't have a photo of your setup, so we don't really know what it looks like. I picture less than 2-3 feet of wiring, but maybe you've got 15+ feet of 16AWG copper-clad aluminum wire. Short wires is better and friend don't let friends use anything other than pure copper (or tinned copper) for solar wiring.

Case in point, I recently upgraded my solar system, which included replacing ALL the wiring. When I went to replace the BATTERY NEG- cables from the charge controller to the battery, I discovered that the terminal screw was pretty dang loose. We had a heck of a time keeping our lead acid batteries charged up and this may have been one of the problems, for over 3 years! Doh! Check those connections and use good quality copper wire! Now if I had a battery monitor shunt in the system, I may have seen that the SCC amps out was not matching up with the shunt's amps in to the battery and gone looking to investigate, but I didn't. I put all the blame on buying crappy lead acid batteries and not having enough solar to charge from (both of which were true, but perhaps not as much of the charging issue as I had thought).

 

[Vigo]

Well, i need more detail on what exactly this battery voltage was that didnt change for a whole day. If the controller thought the batteries were already at ‘float’ then with no load that voltage would never change even with unlimited solar.

Those charge controllers are fine for what they are. Also, you can buy a 30-40v solar panel and hook it through a pwm controller to a 12v battery, ive done it multiple times. Most of the super cheap ones have a 50v open circuit limit for the solar input. By extension, a 30-40v panel through a pwm controller to a 24v system is also fine. It will never make rated watts since it will always be way below Vmp, but the price benefit may outweigh that for some people since, for example, ive picked up 250w used panels for $35. Ok, maybe its a 140w panel or whatever at this voltage but i dont really care if the price is right.

 

[400bird]

Charging a 15 Ah pack at 1/2 an amp comes out to something like 30 hours to charge in round numbers.

What was the voltage when the batteries sat connected to the 20 watt panel for a day?

A larger panel may help. Giving the batteries a good charge from the wall to get them started could be helpful.
The 20 watt panel may me enough to keep up, but that depends on how much energy the gate uses and how many times a day it's cycled.

I don't know the system, but I'd probably go for that 100 watt, 24 volt panel. If that doesn't cut it, larger cells would probably be my next step. But, I'd want to do more testing.

 

[MichaelK]

One thing I can suggest you do right now, today, is disconnect those batteries, bring them inside, and get them fully charged with a bench-top battery charger. Since they are AGM, they will be very unhappy sitting there at a low state of charge, and might suffer some sulfanation by the time you solve the problem.

Typically, AGMs like charging in the 1/5th of C range, which for your battery would be 3A, not 0.5.

Now, just to be clear, this is a 24V gate, with two 12V batteries wired in series, not 12V with two 12V batteries wired in parallel?

The problem is that there are not many high-voltage, low wattage panels out there. Assuming panels usually put out only 85% of nameplate power, to get an honest 3A at >25V charging what you need is (3A X 25Vcharging)/85% = 88W. Maybe two smaller 50W 12V panels wired in series to get 36+volts going into the controller? Looking at the side of your battery, it appears that the max charging current is stated as 4.5A? Is that correct? It's a bit too fuzy with magnification to read. You might wire two 75W panels in series to get that much current.

 

[JWLV]

Most gate opener kits come with small batteries and a small solar panel, just like yours. And they all work just fine, unless you are opening/closing the gate dozens of times a day or it's been raining the whole week.

If the batteries are not charging, it's most likely a wiring error.

How did you come to the conclusion that the batteries are not charging? Does the gate actually work and then it dies eventually? Is that how you know the batteries are not charging? Using your volt meter, show us numbers and where you are measuring to get those numbers.

 

[Tomthumb62]

Most gate opener kits come with small batteries and a small solar panel, just like yours. And they all work just fine, unless you are opening/closing the gate dozens of times a day or it's been raining the whole week.

If the batteries are not charging, it's most likely a wiring error.

How did you come to the conclusion that the batteries are not charging? Does the gate actually work and then it dies eventually? Is that how you know the batteries are not charging? Using your volt meter, show us numbers and where you are measuring to get those numbers.

OP is just not getting enough charge. They should be getting at least a 0.2C rate (3 amps) but are only getting 0.035C (0.5 amps). They have a poor match of panel(s) to battery size.

I don't have one of these gate opener kits, but through my ignorance I have learned a few things about how to charge AGM batteries. OP says it came with a 20W panel, that operates at 24v and produces 0.56A at most. Assuming this panel actually produces more like 36V, the 36V x 0.56A = 20.16 watts. So the panel and output seems correct. They're using a 24V 15Ah AGM battery. My math is that AGM batteries prefer about a 0.2C rate and like a 0.3-0.4C charge about once a week. So 15Ah x 0.2C = 3 amps. OP is getting a whopping 0.56A from their up-to-spec solar panel. It doesn't seem like a wiring error, but an oversized battery with an undersized solar panel. 3A charge every day should be the bare minimum. A once a week charge of 15Ah x 0.3C = 4.5A would be ideal, otherwise the battery is going to die a quicker death.

I'm not sure how much juice it takes to power the gate and I suppose it depends on how often the gate is being used, but OP could get more/larger panels or a smaller 24v battery, 5Ah would give them a 0.1C rate, which would be far better than the 0.035C rate charge they're getting now.

 

[swiftk77]

Sorry for the delay, it was a very busy weekend. I ran out this morning and wired the panel straight to the batteries, which were at 22.1 volts and left them there for about 4 hours in direct sun, checked on them hourly. After 4 hours they were at 24.7 volts, so I think the panel is doing its job. I this this a good indicator that the charger is probably faulty? I’ve gone over the terminals and made sure everything was tightened down. I did hook up the charger late this afternoon and will check tomorrow to see disconnecting and reconnecting everything had any effect, but I’m not too optimistic.

 

[swiftk77]

Most gate opener kits come with small batteries and a small solar panel, just like yours. And they all work just fine, unless you are opening/closing the gate dozens of times a day or it's been raining the whole week.

If the batteries are not charging, it's most likely a wiring error.

How did you come to the conclusion that the batteries are not charging? Does the gate actually work and then it dies eventually? Is that how you know the batteries are not charging? Using your volt meter, show us numbers and where you are measuring to get those numbers.

I’ll try and snap a picture and label the wires tomorrow so everyone can see what’s going on. The gate company did bypass the load on the controller by wiring straight from the batteries to the control board. I called them and they didn’t really have an answer other than they wanted to bypass the battery low volt disconnect feature.

 

[swiftk77]

It’s been a couple weeks but I wanted to close the loop on this issue. I ended up hardwiring the solar panel to the batteries to make sure the solar panel was working and I was able to charge the batteries just fine. I checked and doubled checked all the solar charger wiring and it was fine, so that left me with the solar charge being the likely issue. It was Amazon Prime Day, so I ordered a new solar charger that showed up the very next day. I took 5 mins to swap out the chargers and everything has been working great the has week and a half.

Thanks to everyone for your helpful information!