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Hi all

Firstly, I must mention that I am not in the same league as the other members on this forum. Sometimes three really bad things can happen at once and it can take everything from you.

I'll spare you the details, but I ended up living in a caravan in the Karoo, isolated and helping on the farm in return for food and shelter. To be honest, I prefer this to society, but once covid is under control, I'll have to fight my way back.

For now, I have NO money, so what I have, I have to look after. No use suggesting I buy anything at this stage even if you mean well.

Someone donated a few rands so I can at least run my laptop, sound system, lights, be able to solder and keep a bunch of things charged, etc. I don't need more.

60A SLA (3x 20A motorized scooter batteries) 12mm X 300mm connector cables. I don't know the current rating, but it's overkill for sure. As thick as 300A jumper wire.

120W Panel (poly of course)

200W dinky "Alibaba quality" inverter (the only time I come near that output is when I use my 180W coffee grinder for 5 seconds in the morning) it's actually really okay for R550.

A now busted 10A PWM charge controller. The cheapest piece of cr*p on the market, but it worked well until I reverse polarised it on a starter battery this morning because I couldn't find my glasses. (I am middle aged and used to be middle class and understand electricity. I am livid with myself for this idiocy)

The controller started smoking immediately and was disconnected and the cranking battery is fine at least. Yet the controller still seemed alive. I took it back to my "home battery", connected negative and only touched the positive. The battery immediately started bubbling and I removed it within a second.

It was pumping 21.2v into the battery (the panel maximum short circuit current is of course about 6.5A). Idiocy #2, should've tested the battery out terminals first.

Could this have seriously damaged my SLA's within a second? They didn't get warm and the multimeter reading was still 13.2v as before the incident (I hardly manage to drop to 80% SOC and that's only after an evening of binge watching series with the sound system loud and using my soldering iron, AC and 12v lights on and recharging stuff)

The best load test I could do was the 180W grinder and the drop was down to 12.64v after 15 seconds and stabilised there. It has since recovered to 13v and slowly dropping to resting voltage as usual.

I'm sure it took a few cycles off, but that's okay. If they last a year, it's all I need.

Someone is giving me a more expensive, programmable controller which I'll receive next week, so it's me and the Magneto lamp until then.

Any opinions welcome.

Thanks

Johnny

 

 

 

 

 

 

 

 

 

 

 

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19 minutes ago, Johnny L said:

The controller started smoking immediately and was disconnected and the cranking battery is fine at least. Yet the controller still seemed alive. I took it back to my "home battery", connected negative and only touched the positive. The battery immediately started bubbling and I removed it within a second.

Bummer 😞 your "home battery" should be ok, I think, but you should certainly refrain from trying that again 🙂. Good luck with the controller to come next week...

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21 hours ago, Johnny L said:

it worked well until I reverse polarised it on a starter battery this morning

If the battery modules are from a motorised scooter, I would hope that they are not actually starter batteries, but rather deep cycle ones (but that can hopefully dish out decent current as well).

21 hours ago, Johnny L said:

The battery immediately started bubbling and I removed it within a second.

Bubbling means that water has been dissociated into hydrogen and oxygen. Are the battery modules sealed or flooded? If flooded, you may need to add water a little sooner than would otherwise have been the case. If sealed, that's not great, but some dissociation can be tolerated; as long as the vent didn't have to release pressure, the gases can combine back to water, and no great harm would be done.

I'm surprised that 6.5 A of charge current (just over 0.1 C) doesn't sound like too much charge current to me, so I'm surprised that the voltage rose to over 20 V, or sceptical that the current was only 6.5 A. With your 10 A solar charge controller (when it was working), you might have delivered more than 6 A, perhaps as much as 10 A. I would expect 60 × 0.15 = 9 A to be safe for almost any lead acid battery, and one designed for a scooter might possibly take even more charge current.

I hope your life comes together soon, and that you don't have any more electrical accidents.

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21 hours ago, Coulomb said:

If the battery modules are from a motorised scooter, I would hope that they are not actually starter batteries, but rather deep cycle ones (but that can hopefully dish out decent current as well).

Bubbling means that water has been dissociated into hydrogen and oxygen. Are the battery modules sealed or flooded? If flooded, you may need to add water a little sooner than would otherwise have been the case. If sealed, that's not great, but some dissociation can be tolerated; as long as the vent didn't have to release pressure, the gases can combine back to water, and no great harm would be done.

I'm surprised that 6.5 A of charge current (just over 0.1 C) doesn't sound like too much charge current to me, so I'm surprised that the voltage rose to over 20 V, or sceptical that the current was only 6.5 A. With your 10 A solar charge controller (when it was working), you might have delivered more than 6 A, perhaps as much as 10 A. I would expect 60 × 0.15 = 9 A to be safe for almost any lead acid battery, and one designed for a scooter might possibly take even more charge current.

I hope your life comes together soon, and that you don't have any more electrical accidents.

Hi Coulomb

Ja, my "solar" batteries are VRLA deep cycle, or as my friend who's in a wheelchair calls them, traction batteries. It's OEM stuff, but his has lasted almost 3 years now in spite of having pulled them past 50% a few times. He prefers using his normal chair, but they are used regularly enough. He just puts them on charge immediately after use and on float when parked for a while.

What I was trying to do was to test my setup on a 415Ah flooded car battery to see if it could help maintain batteries on equipment in remote parts of the farm where they can stand for months before needed.

I can't see how a budget 120W poly panel could produce so many amps, but of course I'm no expert. All I know is that the controller had none of the protection features as stated in Engrish on the pamphlet. It destroyed the rectifier (or whatever those three transistors do to buck it to 14.4v) and the full voltage from the panel was output to both battery out and DC out when I measured it. Is overvoltage not dangerous in itself too?

Happy to report that my SLA's are fine. It really was a split second of touching the terminal. The VOC of the panel is always 21.2v under full sun. I've measured it a lot because I manually turn the panel and adjust the altitude angle a few times a day so I get 9 hours of optimal generation in order for my system to stay in float during the day so I "pull power directly from the sun" (I realise that's not how it actually works). By the time the sun sets, the system voltage is almost always close in the high thirteens.

I opened up the charge unit. I've never seen such a mess in my life. I'll take pics now and upload. No use trying to describe with my rudimentary electronics skills.

Thank you for the wishes re my future. I've picked myself up before. I had problems before lockdown, but things were coming together. In tourism and advertising, hahaha. No need to explain. There are many of us. I'm just grateful that I have no debt whatsoever. Most are not that lucky. That's a horrible mess. I just need to work hard and now know how to live off almost nothing.

This farming experience is invaluable. Food production is my future. I'm already building a reputation in the district for my work ethic. It's also in my blood. My forefathers are from here. I know what to do, just have to wait a bit longer. 

 

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Posted (edited)

I thought it was cheap because it didn't have a digital display. Hey, it's just a transformer, right? That was 3 months ago.

The thing failed because it got the slightest tap.

 

IMG_15032021_120752_(1080_x_1920_pixel).jpg

Edited by Johnny L
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On 2021/03/15 at 7:46 PM, Johnny L said:

I opened up the charge unit. I've never seen such a mess in my life.

It looks fine to me from the photos. Nothing charred, nice 1% metal film resistors (or copies thereof). The mounting of the three transistors looks a little strange though. It looks like the main PCB (phenolic, loses points for that) was wave soldered, and the three transistors soldered on later by hand.

Good old through hole components! Ah, those were the days.

I wonder if it might be repairable.

On 2021/03/15 at 7:46 PM, Johnny L said:

Is overvoltage not dangerous in itself too?

Yes, overvoltage is bad. It's just that solar panels are current sources with a voltage clamp, so they are inherently current limiting.

On 2021/03/15 at 7:46 PM, Johnny L said:

the full voltage from the panel was output to both battery out and DC out when I measured it.

So the battery had 20+ volts across it? That doesn't sound right. Is it possible that the battery was disconnected somehow? Is there a fuse that could have blown? Though usually the panel doesn't have enough current capability to blow a fuse. Maybe the fuse or wiring was loose? You mentioned a tap; could the tap have disturbed the wiring rather than the charge controller?

It may even be that the charge controller is still working (if you can get it back together successfully).

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On 2021/03/16 at 3:11 PM, Coulomb said:

It looks fine to me from the photos. Nothing charred, nice 1% metal film resistors (or copies thereof). The mounting of the three transistors looks a little strange though. It looks like the main PCB (phenolic, loses points for that) was wave soldered, and the three transistors soldered on later by hand.

Good old through hole components! Ah, those were the days.

I wonder if it might be repairable.

Yes, overvoltage is bad. It's just that solar panels are current sources with a voltage clamp, so they are inherently current limiting.

So the battery had 20+ volts across it? That doesn't sound right. Is it possible that the battery was disconnected somehow? Is there a fuse that could have blown? Though usually the panel doesn't have enough current capability to blow a fuse. Maybe the fuse or wiring was loose? You mentioned a tap; could the tap have disturbed the wiring rather than the charge controller?

It may even be that the charge controller is still working (if you can get it back together successfully).

When I removed the controller from my wall to take the kit to the starter battery it fell about 2 cm onto the table. It was fine before that.

Thinking about it now, the controller lights shouldn't even have lit up when reverse connected. It was the top transistor in the pic that was smoking and the unit got burning hot (metal backplate).

This is where my experience fails, but this little knock seems to have caused both the reverse current protection and PWM action to fail.


I didn't read 21.2v across the battery terminals, but OC from the unit terminals afterwards. This is why I assume that this unmodulated 20+ volts must've caused my solar batteries to bubble.

Another thing I forgot to mention was that my PV junction box got warmer than usual. I immediately checked everything and even though the box gets quite hot at times in the Karoo sun, this was warmer than it should've been on a day below 30° with a nice breeze blowing.

Again, I don't know what I'm talking about, but it would seem that amps from the battery maybe flowed to the panel for a second or the panel shorted as well.

It's all very confusing. Like the unit did all the opposite things that it should've done.

Must mention that one of the display LEDs failed on the first day I got the unit. That's why I suspect it's all rubbish. Not touching that thing again.

Getting a proper PWM controller tomorrow from a qualified electrician who uses the same type for his load-shedding setup, just with higher amp rating. It's SMD with microcontrollers that look like mobile phone chips. He uses batteries from phone towers and forklifts and mentioned that these need special programming which include critical temperature settings and ridiculously low voltage cut-offs and timers. (I'm talking out my behind now, but will still learn about this). He does this with these controllers, so I'd rather use this one than go near that other thing again. It's actually awesome because it's a gift probably worth 10x more than what I can afford.

PS. I'd prefer to set my cut-off a bit higher than default. Does this affect both SOC as well as load? I can only think that it would be universal.

Thanks for the input! Getting better info here than the mess Google search had become.

 

 

 

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2 hours ago, Johnny L said:

Thinking about it now, the controller lights shouldn't even have lit up when reverse connected. It was the top transistor in the pic that was smoking and the unit got burning hot (metal backplate).

That could be a dual diode, and would have failed shorted. Most semiconductors fail shorted when they overheat like that.

I finally figured out why you thought it was so messy under there, with what looks like bare solder over some PCB tracks. That's actually a standard technique for increasing the current carrying capacity of printed circuit tracks. It's easy to do with standard wave soldering, where a wave of molten solder is passed at a carefully controlled speed over the bottom of the board.

2 hours ago, Johnny L said:

This is where my experience fails, but this little knock seems to have caused both the reverse current protection and PWM action to fail.

It wouldn't have been the knock, but the reverse connection. It obviously doesn't have reverse protection, or if it does, it relied on a fuse that wasn't there, between the MPPT output and the battery.

2 hours ago, Johnny L said:

I didn't read 21.2v across the battery terminals, but OC from the unit terminals afterwards. This is why I assume that this unmodulated 20+ volts must've caused my solar batteries to bubble.

Ah. No, the 21.2 V is probably you somehow reading the open circuit voltage of the panel, which will fall with load. The bubbling was probably the battery being short circuited by the MPPT, with no fuse to limit the current. 

2 hours ago, Johnny L said:

Another thing I forgot to mention was that my PV junction box got warmer than usual. I immediately checked everything and even though the box gets quite hot at times in the Karoo sun, this was warmer than it should've been on a day below 30° with a nice breeze blowing.

It might be short circuiting the panels as well, which would cause the extra current. But short circuit current for a panel is usually only a little higher than MPP current, so that's a little weird. Maybe you have thin cables or a high resistance connection somewhere. Worth checking after the new unit is installed.

2 hours ago, Johnny L said:

Must mention that one of the display LEDs failed on the first day I got the unit. That's why I suspect it's all rubbish. Not touching that thing again.

LEDs commonly fail either at high age, or very low age (first week or so of operation; the "bathtub curve"). Cheaper parts are not burn-in tested.

2 hours ago, Johnny L said:

Getting a proper PWM controller tomorrow from a qualified electrician...

That is lucky. I note that PWM controllers are generally inferior to MPPT ones, but with single panel 12V systems, they can perform well. Some people even claim that they are more efficient than MPPT controllers for that situation.

2 hours ago, Johnny L said:

PS. I'd prefer to set my cut-off a bit higher than default.

If you mean the low battery voltage cut off, yes, that's good for battery life. See if you can set it as high as 12V. This will affect run-time. The ideal is about 50% SOC for lead acid batteries. This is a little over 12V no load and rested, which is often roughly 12.0 V under load (depending on many factors).

2 hours ago, Johnny L said:

 

 

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5 hours ago, Coulomb said:

That is lucky. I note that PWM controllers are generally inferior to MPPT ones, but with single panel 12V systems, they can perform well. Some people even claim that they are more efficient than MPPT controllers for that situation.

 

Just to chime in. PWM is always inferior to MPPT, except in perhaps a very specific case, and will only be so for a small part of the year (or day). PWM has no storage component - it really is just what it says PWM. It will connect the solar panel to the battery with a mosfet until the battery voltage exceeds a setpoint and then disconnect until it goes below setpoint minus hysteresis. So it also cannot output more current than the panel current. The big loss in efficiency is the fact that you lose all the power in the voltage mismatch between panel and battery. So if you have a panel that delivers 20V and 5A (at peak power in this example case), and a 12V battery, you will only be able to deliver [email protected] to the battery, which means you lost out on 40W.

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3 hours ago, P1000 said:

Just to chime in. PWM is always inferior to MPPT, except in perhaps a very specific case, and will only be so for a small part of the year (or day). PWM has no storage component - it really is just what it says PWM. It will connect the solar panel to the battery with a mosfet until the battery voltage exceeds a setpoint and then disconnect until it goes below setpoint minus hysteresis. So it also cannot output more current than the panel current. The big loss in efficiency is the fact that you lose all the power in the voltage mismatch between panel and battery. So if you have a panel that delivers 20V and 5A (at peak power in this example case), and a 12V battery, you will only be able to deliver [email protected] to the battery, which means you lost out on 40W.

Thank you Coulomb. I'm learning a lot from you.

The busted unit is actually PWM. I read up on on MPPT and that's definitely the way to go when I upgrade, but for now too expensive and the PWM is enough to keep my little 60Ah bank floating even on overcast days. Even when I draw a bit more at night and it goes into saturation mode, it floats again before 11am.

That's because I manually set the panel up at 60° and pointing east just before sunrise, turn it North East at 45° around 10am, dead North at 30° between noon and 1pm, North West at 45° around 2:30 and then dead West at 60° for the stretch between 4pm and sunset around 7pm. I've also been adjusting this as the season changed since January. So I'm my own MPPT for now. Most of my work is within a 500m radius from my caravan and I have a 30 minute break every two hours, so it's just part of my routine.

I have a 180° horizon and in Jan/Feb I easily got 11 hours of my panel pointing straight at the sun. Plus the sun here I'm sure puts out way more than 1kW/m². I used to be a ginger, but now look like a Spaniard after 3 months!

I taught myself to solder and to me that would not have been acceptable because it looks dangerous and messy and I didn't trust the masking, or anything on that.

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8 hours ago, Johnny L said:

Apologies P1000, was in a hurry and had an emergency. Thought you were Coulomb.

Thanks to everyone for the help and info

Well, I think the advice from Coulomb is worth a lot more than my input, so you really should be thanking him 😉

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