Waking up from dead battery situation.

[Craig]

Ok so here is the problem my off grid system at times may have weeks of snow and no sun at some point. This year after 2 weeks of clouds and snow my batteries are now drained to nothing. Obviously this is not a good thing not to mention I have solar panels attached to 4 Charge controllers that are turned off because batteries are to low. My system is remote and I cant get there to clean panels and check on things often enough.

So my answer is to have at some point when the batteries reach a certain voltage to shut everything down. The problem with this is once the SCC is shut down the batteries will never be able to charge. How do I get the SCC to turn itself on and start charging the batteries on its own, so when the sun comes out things can start working again I would like this to be automatic so once I get there my batteries are charged and also to run my router and my security cameras.


I was thinking that if I took a spur line off of the PV array and added a voltage divider circuit that would never go over say 22 volts that I could charge my batteries without the SCC enough to get the SCC to turn on again and take over. I think I would need blocking Diodes to stop the panels from discharging the batteries while there is no sun. But if the voltage from panels never goes above 22 volts which would be plenty for SCC and not higher than the batteries limits what would be the real danger? I would use some sort of relay that would turn the SCC on once the battery reaches 20 volts or whatever. Could I leave the 20 Volt panel attached? or would I need to have it disconnect once the SCC turns on?


Thoughts please thank you.

 

[jasonhc73]

How about melting the snow off the panels when it gets cold?

Not exactly going to help if zero solar for two weeks though.

Is Cellular-signal data available?

And there is always the wind generator option. Do you have a weather station to monitor what your average wind is?

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[Craig]

How about melting the snow off the panels when it gets cold?

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Thats one part but sometimes we get no sun as well. I am going to add that capability on at least a few panels though.

 

[JeepHammer]

22v seems awfully odd, what's the nominal battery voltage?

Not recommend as a home game, but I might do this parallel to the charge controller.
Scavenges anything the panel produces, puts out a regulated voltage ("trickle charge") to the batteries.
It's only 2-5 amps (Vmp) to close the MOSFET and allow charging...

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These usually do like 28-30 volts on output when they say '24 Volts', and the adjustment isn't 'Clicks' on the ones I use for outdoor lights and electric fence chargers, it's a sliding scale.
I use a multimeter to set output voltage and forget them.

I do recommend a box with a gasket and some of those 10¢ each moisture absorbers or potting them in acrylic to keep moisture out.
If you are sneaky, glue some undersized 2¢ grommets in a box (or pill bottle) and snake a greased wire through them for a seal, throw some moister absorbers in and glue the lid shut.
When they fail, they are disposable.

----------------

Have you though about pulling the charge controller and simply using a voltage regulator?
Battery charger circuits are pretty stupid simple and they don't have an 'Off' mode, ANY power from the panel gets regulated and sent to the batteries.

Same deal as above, but heavier duty and might run close to $10.

 

[WoodsieLord]

Hello Craig,

My project requires a voltage divider reading the panels to know when they're producing and a two relays to connect or disconnect the solar panels from the PWM charge controller. I'm going this way and I'm betting this is doable. But I haven't finished it yet! So I guess it's up to ... trial and error ?

Regards!

 

[Craig]

22v seems awfully odd, what's the nominal battery voltage?



----------------

Have you though about pulling the charge controller and simply using a voltage regulator?
Battery charger circuits are pretty stupid simple and they don't have an 'Off' mode, ANY power from the panel gets regulated and sent to the batteries.

Same deal as above, but heavier duty and might run close to $10.

My cells are LTO they run from 20 to 30 volts I picked 22V as a random number but know its enough to get SCC running properly.

As far as the voltage regulator goes I wonder all the time why we need $400.00 charge controllers to regulate voltage.

If you have a battery that maxes out at 28 volts and you never let more than 28 volts in what is really the problem.

But you did give me a good Idea I have 20 of these rolling around

https://www.amazon.com/Converter-DR...er&qid=1579878081&sprefix=drok,aps,223&sr=8-4

These will come on with any power from the panels and kickstart my batteries. They only put out 12 amps but that would be plenty to trickle.

 

[nwillitts]

i love DROK.
i have that regulator.
your gonna love it.

 

[JeepHammer]

My cells are LTO they run from 20 to 30 volts I picked 22V as a random number but know its enough to get SCC running properly.

As far as the voltage regulator goes I wonder all the time why we need $400.00 charge controllers to regulate voltage.

If you have a battery that maxes out at 28 volts and you never let more than 28 volts in what is really the problem.

But you did give me a good Idea I have 20 of these rolling around

https://www.amazon.com/Converter-DROK-Voltage-Regulator-10V-75V/dp/B071LGTTRN/ref=sr_1_4?crid=3RUR1XE49KN5K&keywords=drok+buck+converter&qid=1579878081&sprefix=drok,aps,223&sr=8-4

These will come on with any power from the panels and kickstart my batteries. They only put out 12 amps but that would be plenty to trickle.

Why we pay? Convince.
Nice case, set of instructions, no parts collecting, no soldering, etc.
And you get micro components on a PCB so it's compact.

At my shop, R&D testing might involve a melt down since *I* did the design and assembly, and I'm NOT a trained engineer, so COMPLETE FAILURE IS A VERY REAL POSSIBLITY!

When I say I've burned my eyebrows off, I am not kidding...

Still, when I want to charge a weed wacker or power drill battery off the battery bank instead of the inverter loosing 150-200 Watts to charge a battery at 50 Watts, I use a regulated converter instead of DC-Losses-AC-losses-DC again...
And for the price I will break out a pill bottle to protect the converter and do the wiring, since the DC to DC units are like $100+ from the manufactures, IF they are available at all...

"YOU'LL SHOOT YOUR EYE OUT KID!"
My solution was good safety glasses cause I'm STILL going to try it...

 

[Craig]

Im seriusly thinking of connecting my batteries to a panel array with a switch and a blocking diode once full charge is reached I will turn panels off with a voltage switch. My LTO bank is 120 AH so that means they can suck 1200 amps at 24 volts so thats 28kw they could absorb at one time
I only use 2000 watts of panels so Im 14x under their specified charge rate.



This is what I talk about by dangerous activities not reccomended by the manufacturer. But if you are willing to take some licks in an effort to learn, its only money...

 

[JeepHammer]

Im seriusly thinking of connecting my batteries to a panel array with a switch and a blocking diode once full charge is reached I will turn panels off with a voltage switch. My LTO bank is 120 AH so that means they can suck 1200 amps at 24 volts so thats 28kw they could absorb at one time
I only use 2000 watts of panels so Im 14x under their specified charge rate.



This is what I talk about by dangerous activities not reccomended by the manufacturer. But if you are willing to take some licks in an effort to learn, its only money...

It's only YOUR money, I say go for it!

If the converter has the capability to pass enough Amps, then it *Should* work...

Your diode will have to handle the amperage, but if the converter is adjustable you can compensate for the voltage drop through the diode.

I would check to see if you get conductivity backwards through the converter before adding a diode, it's probably already isolated by the power MOSFET which doesn't have the line Resistance/voltage drop a big diode would.

Since I don't own and haven't messed with what you have, I can't say anything as fact...
Just spit-balling what runs through my brain thinking about it, and what I've run into with other stuff.
Glad we don't have a 'Salesman' in here to tell us what we can, and can't do with our own ideas/stuff...

Maybe an engineer type will stumble along and throw down an idea or two...?

 

[SolarRat]

So my answer is to have at some point when the batteries reach a certain voltage to shut everything down. The problem with this is once the SCC is shut down the batteries will never be able to charge. How do I get the SCC to turn itself on and start charging the batteries on its own, so when the sun comes out things can start working again I would like this to be automatic so once I get there my batteries are charged and also to run my router and my security cameras.

Why would you ever shut off the controller? Why not shut just the load off at a certain low voltage???

 

[Craig]

I don't think I'm clear, what I'm proposing is a direct connect from PV to Batteries with a switch to turn off PV when voltage reaches a certain level. To avoid overcharging.

The Drop units work great as a SCC they just only support 12 amps so they won't work with a large bank. I use Drok's to charge individual cells for testing. So I know they work well.

 

[John Frum]

I wish they would add a feature to stop at a $n% current
or float

 

[Craig]

I wish they would add a feature to stop at a $n% current
or float

Can you elaborate on that more. I'm gonna use a Raspberry pi to monitor and control so I could use anything to turn on and off

 

[JeepHammer]

Hello Craig,

My project requires a voltage divider reading the panels to know when they're producing and a two relays to connect or disconnect the solar panels from the PWM charge controller. I'm going this way and I'm betting this is doable. But I haven't finished it yet! So I guess it's up to ... trial and error ?

Regards!

Not to side tracked the thread, but I'm already doing that...
My deal is first to open both battery and panel circuits in the event of a fire, simply shut EVERYTHING down and hose it with a fire extinguisher,

The second is Under volting my very expensive batteries.
Over volt came with the sensor, so I hooked it up, batteries get Under voltage they get disconnected from load so they can charge to a reasonable level before reconnecting.
Over volt from panels/charge controller, something went wrong with charge controller, and nothing shuts down a charge controller like disconnecting the panels from it.

SmoothJoey posted that DIN is like Legos for Nerds, and he's right!

It's just too stupid simple with currently produced DIN stuff, but you could surface mount also if that's your thing.
I can't guess at panel cost, but if I had to replace batteries it would be around $25,000...
So $100 thrown at protection isn't expensive insurance.

$10 off the shelf smoke detector, $2 thermal switch, $5 latching relay to convert 9V signal from smoke detector to kick bigger relays/solenoids/contactors.

$20 Over/Under voltage regular/sensor to disconnect panels or battery, or both.

Discounting the big contactor for the battery disconnect, under $150, one row on a DIN rail in a reasonable size box.
That box also has the circuit breakers, buss combiner bars, lightening protection, etc in it.
People poke fun saying it's over engineered and cobbled together...
Or just don't understand it.
I sleep where my system is, an enormous amount of power in the batteries, a little spent on safety doesn't seem like a bad idea to me.

Can't sell it as a home game since it doesn't 'Entertain' anyone like connectivity and colorful cell phone interfaces do, but I sleep better at night!

 

[JeepHammer]

I wish they would add a feature to stop at a $n% current
or float

Well... Not to put too fine of a point on it,
But that's why I pointed a voltage regulator instead of plain converters...

For an odd voltage like 22V, you would probably have to spend another $5 on voltage regulator & $5 on a relay, but it's very doable...

 

[John Frum]

Can you elaborate on that more. I'm gonna use a Raspberry pi to monitor and control so I could use anything to turn on and off

I want the buck converter to be more like a charger
it could be programmed to stop the current when the current flow drops to a configurable percent of CC
or optionally it could drop the voltage to a configurable value
Then if the battery is under load and the voltage drops enough the charger starts helping with the load.

 

[John Frum]

Well... Not to put too fine of a point on it,
But that's why I pointed a voltage regulator instead of plain converters...

For an odd voltage like 22V, you would probably have to spend another $5 on voltage regulator & $5 on a relay, but it's very doable...

A voltage regulator is just buck boost converter in essence, confirm?
Because there is overlap between the voltage of my supply and the range of the battery I use a buck boost for my goto charger.
I have also used a boost and buck back to back to the same effect.
But the current does not stop on its own

 

[SCClockDr]

@Craig
How are you monitoring your remote system?

 

[Craig]

@Craig
How are you monitoring your remote system?

Right now I'm not monitoring at all because batteries died and that shuts router off. Before when I had power I use Raspberry Pi's to monitor voltage and report back to me every 5 minutes. They send data to my home computer which I can then review. I can't get asynchronous communications yet as the Verizon hotspot won't let me ssh through it. Reverse tunneling works but I have problems keeping persistent connections. I'm now experimenting with websockets to see if that works better.