Solar panel to power gate alarm

Forums › Gadgets, robotics, home automation, electronics (including wearables) › Solar panel to power gate alarm

1 | 2

frankv

5705 posts

Uber Geek
+1 received by user: 3666

Lifetime subscriber

#2693661 16-Apr-2021 10:11

PaulL:

I do think I get an issue with current if I'm not careful - a lead acid battery can deliver a lot of current, and I think I fry the batteries in the units if I drive too much current into them. Is that a legitimate concern?

No. You drive current into batteries with voltage. If the voltage is less than the battery's maximum charging voltage, the current will reduce until the battery is fully charged, at which point the current is zero, regardless of how much energy is left in the lead acid battery.

Think of voltage as pressure and current as flow. If you have too much pressure, it causes too much flow. But if the pressure is less than the receiver can manage, the receiver limits the flow. If you have a swimming pool connected to a firehose (i.e. able to deliver a lot of flow) connected to an ordinary ballcock, filling a bucket, you only get as much flow as the ballcock allows. When the bucket is full, the ballcock stops the flow.

trig42

5889 posts

Uber Geek
+1 received by user: 2094

ID Verified

#2693662 16-Apr-2021 10:13

If your panels are shaded, it will affect voltage output. ie., if half the cells on your solar panel have no sun, and the other half do, then you may only get 5-6V out of your panel, therefore never charging the batteries.

You need to get them out of the shade.

Once you get the panel into some sun, then add that controller and either a car battery, or 12V SLA battery (~9Ah). Run the charging port for your gate sensors off the load output on the PWM controller.

I have this setup (90W panel, mounted vertically, but north facing), PWM controller, 12Ah SLA battery at our bach. It is to run lights and a couple of USB sockets in a caravan sized outbuilding. It works perfectly well during summer. Hanging a couple of phones off it at this time of year will drain the battery in about 4 hours. Phone charging can draw quite a bit of current though - about an amp each.

PaulL

91 posts

Master Geek
+1 received by user: 16

#2693663 16-Apr-2021 10:16

No, I'm not worried about the car/motorbike battery. I'm worried about the batteries in my break beam sensor. THey're made to be charged at 0.5A. The motorbike battery can probably deliver 20 or more amps.

PaulL

91 posts

Master Geek
+1 received by user: 16

#2693664 16-Apr-2021 10:20

frankv:

No. You drive current into batteries with voltage. If the voltage is less than the battery's maximum charging voltage, the current will reduce until the battery is fully charged, at which point the current is zero, regardless of how much energy is left in the lead acid battery.

Think of voltage as pressure and current as flow. If you have too much pressure, it causes too much flow. But if the pressure is less than the receiver can manage, the receiver limits the flow. If you have a swimming pool connected to a firehose (i.e. able to deliver a lot of flow) connected to an ordinary ballcock, filling a bucket, you only get as much flow as the ballcock allows. When the bucket is full, the ballcock stops the flow.

Ah, this is what I was hoping - the theoretical current that can be delivered doesn't relate to the actual draw of the device. Which makes sense, otherwise a car battery would fry the light bulb in the internal roof light, for example.

So in theory I can just add a 12v battery to the setup I already have, and move the connection to the sensor charging port to be on the load. Then it will give a bit of buffer in that larger battery, and both the battery being charged and the load will be limited by the charge controller to a max of 12v (i.e. it won't over drive them).

timmmay

20858 posts

Uber Geek
+1 received by user: 5350

Trusted

Lifetime subscriber

#2693667 16-Apr-2021 10:22

PaulL:

No, I'm not worried about the car/motorbike battery. I'm worried about the batteries in my break beam sensor. THey're made to be charged at 0.5A. The motorbike battery can probably deliver 20 or more amps.

My understanding is current is effectively drawn in, not pushed in.

tripper1000

1648 posts

Uber Geek
+1 received by user: 1176

#2693678 16-Apr-2021 10:49

To answer your question, you can add solar panels in series, but it might/might not blow up your regular. I can't say for certain if it is safe or not because Jaycar doesn't list the max PV voltage in the regulators spec's, which is a very poor oversight because it is a pretty standard/necessary figure to know when building a solar system. Additionally the regular may not be passing any current at all to the unit because it is designed to charge a battery, and without seeing a safe in-range battery voltage at their battery output terminals, many regulators will not even start up. But this is highly unlikely to help you anyway, so read on.

Short story: You need to provide 12v and a minimum of 0.5 amps to the unit (think wall-wart power supply levels of power), so your solar panels are only just barely sufficient to charge the battery in ideal sun shine conditions (which seldom occur in N.Z) and there is no way they will ever charge your unit with any kind of shade on them.

Long story:

The way your gate alarm charges off of it's inbuilt solar is likely to be quite different to the way it charges off the DC input. It will use voltage limiting only on it's internal solar panel as the solar panel is pretty small and it's size means it can not provide excessive amps - this means it will be able to use any energy available from inbuilt solar over 4.1 volts. On the DC input plug the charging methodology will be quite different. This plug will feed a lithium Battery Management System, and it won't start up until the input reaches ~10-12 volts (which your regulator may be stopping your panels from providing to the unit). If/When it does start, it will be trying to charge at a constant current (remember the minimum input is 1/2 an amp!) which will pull your shaded panel voltage down below the min voltage, so it shuts down and the cycle repeats, with the result being the batteries don't get charged sufficiently or at all.

Your only option is to supply the required 12 volts, 0.5 amps.

1) Increase the panel capacity (bigger panels, face toward the sun etc) so that in the short time it has sun shine, it can get as much charge as possible.

2) Move panels to a sunnier spot (and increase the panel capacity because your current panels are scraping the bare minimum for a sunny day!) and make sure your regular is not blocking the power.

If you panels aren't achieving their rated voltage they aren't starting up properly so their behaviour is unreliable and you are on a hiding to no where. No amount of electronic reconfiguration/trickery is going to create more charging (aside from doing open heart surgery on your unit and charging the internal batteries with a custom built charging solution). You simply need to build a system that can supply the required 12 volts, 0.5 amps.

Don't waste any money on a voltage converter. The lack of voltage is a symptom of a lack of energy. A voltage converter converts excess amps to make more volts - you clearly don't have excess amps (your 2 panels in full sunshine only just barely provide the minimum amps your unit requires), so it will not/can not help.

Edit: Above I thought you had two solar panels. If you only have one your system would never achieve the 1/2 amp minimum required to charge the unit.

Dyson

Shop now for Dyson appliances (affiliate link).

PaulL

91 posts

Master Geek
+1 received by user: 16

#2693679 16-Apr-2021 10:51

I see this DC-DC step up unit: https://www.jaycar.co.nz/dc-to-dc-step-up-voltage-converter-module/p/AA0237. The documentation is poor, but from looking at pictures and the manual, I don't think you can pick what voltage it delivers. It basically is applying some fixed multiple of the input I believe. So that would be useful when the voltage is low, but when the voltage is high that would be a problem. In effect it would do a similar thing to having a second panel - it would give me higher voltage but no limiting of the total voltage.

I feel like the charge controller might/should solve that, but again the documentation is poor.

It seems that I should be able to have:

Solar Panel x 2 (10-30V) ----------- Charge Controller ------------ Battery (12V)

| Load circuit

Sensor unit (12V)

And that the charge controller should prevent the battery from being over charged or delivered over voltage, and should make sure that the sensor unit is only seeing 12V. But is that actually what happens?

Thinking even further - now that I've had help to pose my questions better, the answer is that I can buy the second panel and test it - these are all things I can empirically verify using my multimeter.

tripper1000

1648 posts

Uber Geek
+1 received by user: 1176

#2693740 16-Apr-2021 11:11

Many affordable solar regulators such as those blue digital ones on trade me have a load output control option that disconnects the load when the solar system battery gets too low (and some also have options to only supply the load during daylight or darkness (for lighting)). I recommend you use one of these, (also set to only supply the load in day light if possible) otherwise your unit will over discharge your battery, which will drastically shorten its life and also mean the (non-load controlling) regulator doesn't see a safe battery voltage so won't recharge the battery the next time the sun is shining.

frankv

5705 posts

Uber Geek
+1 received by user: 3666

Lifetime subscriber

#2693793 16-Apr-2021 13:15

What @tripper1000 says makes sense... the solar panel voltage is sagging because there's too much load. There's no electronics-provided free lunch here... you need more energy from somewhere.

A step-up converter of any sort wouldn't help... to output the demanded current at 12V, the converter would be demanding over twice the current at 6V, which the panels wouldn't be able to supply, so the solar panel voltage would just sag further.

Putting your two solar panels in parallel could work just as well as putting them in series, since each panel would see half the load, which would mean the voltage wouldn't sag (as much), and would/might stay up near enough to 12V to charge the battery.

Something to think about... instead of a lead acid battery, use a LiPo USB powerbank and 5-12V step-up converter. Get two of them... whilst one is down at the gate powering the system, the other can be charging. Swap them over whenever you go out the gate.

Another thought.... I'd guess the most power-hungry part of the system would be the RF transmitter that signals when someone's at the gate. Check that that isn't triggered on all the time. It might also be that there's a momentary transmission as the system starts up. When the battery is flat, that transmission could suck so much power that everything shuts down again. The voltage recovers, the system starts up, and the whole cycle repeats.

PaulL

91 posts

Master Geek
+1 received by user: 16

#2693912 16-Apr-2021 17:01

All useful info thanks team. I will think harder on this, and more importantly, how I can measure what's actually going on to determine the truth of much of this. Weekend job.

1 | 2