Best Inverter/Controller location

JoeContiRC · May 2017

Good day. I am installing a 50W solar panel for my new hobby workshop. I have 2 12v 100A batteries which are connected in parallel. I have a couple of questions. At the moment I have tested Option A below which resulted in a 1.1v valtage drop, from 12.7v to 11.6v when I switch on some load (3 * 4ft LED strips). The LEDs are the only load at the moment. Voltage read at the distribution board. Not sure if that is the norm. The LEDs light up as bright as when powered with a 12v transformer using the mains supply. I am not sure which option in the drawing below would be best to have an efficient system with the least voltage drop possible. I am also aware that cable thickness plays an important role here. I am not sure what to use and am currently using car speaker wire which I had handy for this experiment. Personally I wish to go with Option C, to have everything at eye level in the same room. Any help would be appreciated and please excuse my crude drawing

Once I can put this behind me, I will move onto the next question, cable thickness and where. Thank you

Image: http://jcrc.ddns.net/images/shared/SolarPanelOptions.png

mcgivor · May 2017

Add some more information such as distance and wire gauge, this would be helpful in providing an answer.

BB. · May 2017

All things otherwise being done correction (wire gauges, electrical connections, etc.), Options A or B are both fine.

Option C is not a good idea. For battery bus connections to the solar charge controller and to the AC inverter, these connections should be short an relatively heavy copper wiring (the AC inverter typically has very heavy wiring). The wiring from the charge controller to the battery should be short and relatively heavy to keep voltage drop low.

For a 12 volt battery bank, roughly 0.05 to 0.10 maximum drop at maximum charging current--Too much drop will give inaccurate battery charging voltage back to the charge controller. This may be 6 AWG wire.

For the AC inverter, you want around 0.5 volt maximum voltage drop (for 12 volts) on your DC connection. This can be 2 AWG to 4/0 AWG copper cable (very thick)--Depending on wire length and amperage/voltage/wattage of the AC inverter.

Long, high current, low voltage DC connections require very large diameter copper cable to keep voltage drops low. 120/240 VAC wiring is ~1/10th the current and can have higher voltage drops (~3% drop or 3.6 volt drop at 120 VAC is typical maximum). This is usually easily done with 14 awg or 12 awg copper wire (for 15-20 amp 120 VAC circuit).

-Bill

JoeContiRC · May 2017

Thanks for writing back guys. Appreciate it

This is my controller

Image: https://scontent.fmla1-1.fna.fbcdn.net/v/t31.0-8/r270/18673071_1902015686706207_4618604215441041348_o.jpg?oh=fa53f64f9831f666481fe3dbcf8d3a99&oe=59A12F0E

This is my panel and my batteries

Image: https://scontent.fmla1-1.fna.fbcdn.net/v/t31.0-8/18699456_1902015736706202_1507782291270394907_o.jpg?oh=fe82de576330e2dd7fe5ff8f589b4523&oe=59E2799D

At the moment everything is very temporary until I decide what is going where. Yes the panel will not be there when its ready .. that's for sure and in case you didn't notice, the controller is zip tied to the rear of the panel, keeping it close to the panel but will eventually be far from the batteries

I used the word "inverter" - in reality I do not have one - and cannot really understand why I used it. I am rinnihg a pure 12v DC system where everything runs mainly on 12v DC, consisting of 12v DC LED light strips.

As for the wire gauge carrying the load of the LED strips it is some speaker wire I found in my garage, looks like 16AWG or 18AWG, distance about 20 to 25 feet.

The cable from the panel to the controller and from the controller to the batteries is the ones that came with the panel, that is 2.5mm cable

BB. · May 2017

Generally, the "long cable" is between the solar panel and the charge controller. Short/heavy cable between charge controller and battery bank (low voltage drop/accurate battery voltage to controller).

Note that speaker wire is, very likely, not UV (ultra violet) resistant. And after a year's exposure to the sun (and heat), the insulation will be in very poor shape. Keep wiring in conduit (away from sun) or use UV rated outdoor cable.

To give you an idea... Say that panel has an Imp current of 5 amps. Using 18 awg wiring and 25 feet, you will have a voltage drop of:

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=20.95&voltage=12&phase=dc&noofconductor=1&distance=25&distanceunit=feet&amperes=5&x=67&y=13

Voltage drop: 1.60
Voltage drop percentage: 13.33%
Voltage at the end: 10.4

Not good at all... If you have 25 feet between 17.5 volt solar panel and charge controller, 5 amps and 3% maximum drop, playing with the numbers:

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=5.211&voltage=17.5&phase=dc&noofconductor=1&distance=25&distanceunit=feet&amperes=5&x=53&y=10

12 AWG
Voltage drop: 0.40
Voltage drop percentage: 2.29%
Voltage at the end: 17.1

And if you have 3 feet between the charge controller and the battery (14.5 volts charging) and a 0.05 volt drop:

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=5.211&voltage=14.5&phase=dc&noofconductor=1&distance=3&distanceunit=feet&amperes=5&x=77&y=19

12 AWG
Voltage drop: 0.048
Voltage drop percentage: 0.33%
Voltage at the end: 14.452

So some 12 awg (UV rated outdoor) wiring and placing the charge controller next to the battery bank would look to be a good fit here.

-Bill

JoeContiRC · May 2017

Spoken like a pro - thank you for the advice above. Makes 100% sense. Just so you know, that "speaker wire" is a temp thing, wanted to see it work

Now that it does I want to start putting everything in the right place, using the right wire gauge for a safe and efficient solar system for my new workshop

I will follow the advice you gave me and will upload pics and if need be a video of the finished system, but until then I might come back for some more advice. Thank you so much for your help and for your quick replies.
BTW, I'm in Malta

mcgivor · May 2017

The batteries in the photo are automotive starting type, not the best choice, deep cycle are the preferred type with fewer, thick plates designed for lower discharge current, deeper discharge cyclical applications. Automotive batteries are designed with more thin plates, designed to supply large currents for short durations and do not perform well in cyclical deep discharge applications. In case you weren't aware of the difference.

Also included some fuses in the system, battery to charge controller, solar panel to CC. a 12V battery can pack enormous amount of current, suggest 20A max at battery + terminal if using 12 AWG ( 2.5 Sq mm) . For the solar side, panel information, on the back, should suggest maximum fuse size.

https://en.m.wikipedia.org/wiki/Deep_cycle_battery

BB. · May 2017

Welcome to the forum Joe!

We have had a few posters over the years from Malta.

Regarding the wiring--Yes, I know that this was a temporary setup with the speaker wire--But we aim for safe/reliable installations here and can get a bit repetitive about these safety/reliability issues.

One thing we have not discussed--I am guessing you can have some pretty good lightning storms in Malta? Grounding the solar panel/array properly (run 6 AWG or heavier cable down the outside of the building to a ground rod/plate next to the wall/foundation (do not bring lightning ground cable inside the home/building) and possibly grounding the negative battery post to cold water pipe/ground rod too...

Another suggestion--In general, the "alligator clips" are not reliable. Replace those with bolted up battery lug connectors as soon as you can. Use some sort of good quality "plug" to make your DC connections if you need to have a portable system.

I don't know if Anderson Power Pole Connectors are common/not too expensive for Malta/Europe--But they are pretty common in North America for HAM radio connections (you only need the smallest .

https://www.andersonpower.com/us/en/products/powerpole/
http://www.westmountainradio.com/kb_view_topic.php?id=ST166

They are nice, rugged connectors, that can be stacked and polarized to prevent backwards connections (solar panel, LEDs, and such do not like being connected backwards to a lead acid battery bank--Lots of current available to fry reverse polarity devices).

And, get a small (DC rated) circuit breaker or several to protect you wiring and turn stuff on/off. Size the breaker/fuse to protect the wire from short circuits (breakers/fuses are to protect wiring from starting fires--not to protect the loads themselves).

-Bill

JoeContiRC · May 2017

mcgivor said:

The batteries in the photo are automotive starting type, not the best choice, deep cycle are the preferred type with fewer, thick plates designed for lower discharge current, deeper discharge cyclical applications. Automotive batteries are designed with more thin plates, designed to supply large currents for short durations and do not perform well in cyclical deep discharge applications. In case you weren't aware of the difference.

Also included some fuses in the system, battery to charge controller, solar panel to CC. a 12V battery can pack enormous amount of current, suggest 20A max at battery + terminal if using 12 AWG ( 2.5 Sq mm) . For the solar side, panel information, on the back, should suggest maximum fuse size.

https://en.m.wikipedia.org/wiki/Deep_cycle_battery

Thanks for that

Yes, the whole system came off different projects I had going here - panel came off a camping trailer which was connected to my car battery and the batteries came off an offroad vehicle powering a 24v winch, so yes, you are right in many ways about what you said .. they are not the correct batteries to use but rather than throwing them out or selling them for peanuts, I thought I'd use them until they are of no more use. Appreciate your input

JoeContiRC · May 2017

mcgivor said:

Also included some fuses in the system, battery to charge controller, solar panel to CC. a 12V battery can pack enormous amount of current, suggest 20A max at battery + terminal if using 12 AWG ( 2.5 Sq mm) . For the solar side, panel information, on the back, should suggest maximum fuse size.

As for the fuses you recommended, I also agree 100%

JoeContiRC · May 2017

Welcome to the forum Joe!

We have had a few posters over the years from Malta.

Thanks you

Regarding the wiring--Yes, I know that this was a temporary setup with the speaker wire--But we aim for safe/reliable installations here and can get a bit repetitive about these safety/reliability issues.

Could not agree with you more. Safety is a priority. I am not alone in this building and would not be able to live with myself if I put anyone in danger.

One thing we have not discussed--I am guessing you can have some pretty good lightning storms in Malta? Grounding the solar panel/array properly (run 6 AWG or heavier cable down the outside of the building to a ground rod/plate next to the wall/foundation (do not bring lightning ground cable inside the home/building) and possibly grounding the negative battery post to cold water pipe/ground rod too...

I have another 12 panels installed on a metal structure. I'm pretty sure that one is grounded. Will grounding this extra panel to the same metal structure be any good? They will be within inches of each other eventually.

Another suggestion--In general, the "alligator clips" are not reliable. Replace those with bolted up battery lug connectors as soon as you can. Use some sort of good quality "plug" to make your DC connections if you need to have a portable system.

Agreed. Batteries already have the proper lugs but nothing is connects as it is supposed to be as yet, but will be by the time I'm finished

The system will be a permanent one so will need no plugs.

And, get a small (DC rated) circuit breaker or several to protect you wiring and turn stuff on/off. Size the breaker/fuse to protect the wire from short circuits (breakers/fuses are to protect wiring from starting fires--not to protect the loads themselves).

I have an automotive fuse box will will be installed on the distribution board. Main power cable will come into the room and distribute via this fuse box. Will have a fuse on the + side of the battery and on the + side between the

BB. · May 2017

Grounding your single panel to the rest of the (hopefully properly grounded) array will be fine.

-Bill

mcgivor · May 2017

JoeContiRC said:

mcgivor said:

The batteries in the photo are automotive starting type, not the best choice, deep cycle are the preferred type with fewer, thick plates designed for lower discharge current, deeper discharge cyclical applications. Automotive batteries are designed with more thin plates, designed to supply large currents for short durations and do not perform well in cyclical deep discharge applications. In case you weren't aware of the difference.

Also included some fuses in the system, battery to charge controller, solar panel to CC. a 12V battery can pack enormous amount of current, suggest 20A max at battery + terminal if using 12 AWG ( 2.5 Sq mm) . For the solar side, panel information, on the back, should suggest maximum fuse size.

https://en.m.wikipedia.org/wiki/Deep_cycle_battery

Thanks for that Yes, the whole system came off different projects I had going here - panel came off a camping trailer which was connected to my car battery and the batteries came off an offroad vehicle powering a 24v winch, so yes, you are right in many ways about what you said .. they are not the correct batteries to use but rather than throwing them out or selling them for peanuts, I thought I'd use them until they are of no more use. Appreciate your input

Totally understand, no point in throwing away, if lightly discharged, they may have value, actually when I started I used a similar battery with one led strip light drawing 1 amp for 4 hours per night and got 2 years of service using a similar PWM controller, we all started somewhere.
By the way, good to hear you are talking precautions with fusing and such and protecting yourself and others around you.

littleharbor2 · May 2017

Your 50 watt panel , in perfect conditions , will put out less than 3 amps. This is far to low to charge 200 amp hours of battery. At the minimum recommended rate of 5% you would need 10 amps of charging power. If you are going to use this system for 24/7/365 duty you would need more like 20 amps of charging power (10%)..

Perhaps you need to define you loads and base your battery size accordingly, then figure out how much solar charging power that will require. At least that's how it's usually done.

JoeContiRC · May 2017

mcgivor said:
By the way, good to hear you are talking precautions with fusing and such and protecting yourself and others around you.

Yes, I've seen a few near death disasters in my time - don't want to go that way. I believe that if you are going to do something you do it right or go fishing and forget everything

JoeContiRC · May 2017

littleharbor2 said:

Your 50 watt panel , in perfect conditions , will put out less than 3 amps. This is far to low to charge 200 amp hours of battery. At the minimum recommended rate of 5% you would need 10 amps of charging power. If you are going to use this system for 24/7/365 duty you would need more like 20 amps of charging power (10%)..

Perhaps you need to define you loads and base your battery size accordingly, then figure out how much solar charging power that will require. At least that's how it's usually done.

This is for a hobby room. It is full of natural light. In summer I rarely put any lights on and as the moment it gets dark at around 8:30pm and switch on the lights at around 7:30pm - it is not in use on a daily basis - there are days I don't even open the room. It will be maybe a max of 20 hours a week with the lights on and I'm thinking BIG here ......

BB. · May 2017

As LittleHarbor2 said above, you will only have enough solar panel to "float" the battery (bank). It will sort of work in the short term, but you will probably have less battery life.

As the battery cycles/ages, self discharge will slowly increase to 1%-2% self discharge... At that point, the battery will be discharging more AH than the solar panel can keep up with.

-Bill

littleharbor2 · May 2017

Without proper amperage coming into your battery you will get stratification of the electrolyte. You need to get the electrolyte mixed and this is done with a proper amperage ratio and periodic equalizing. What I am saying is you either need a larger panel, or less battery.

Anybody else care to chime in?

JoeContiRC · May 2017

I see, so the batteries will not be being to to work hard enough so to speak? - I can disconnect one of them as I am only using 2 batteries because I happen to already have them. What would be an ideal battery for my kind of use? 3 LED strips and the occasional mobile charge.

littleharbor2 · May 2017

Sounds like a light , intermittent load. A single battery should be MORE than sufficient. What is the watt rating of those lights?

A better sized battery for that panel would be something like a 30 to 50 amp hour AGM type. Then again as mentioned you usually start with your load requirement and build from there.

Estragon · May 2017

That panel would support around 30-50 amp hours of battery. Even 1 battery at 100ah is pushing it.

Do you know what the lights draw? If they came with a wall wart there may be in/out current ratings printed on them.

Estragon · May 2017

An ideal (but expensive) type of battery for this is probably lithium based system. They're fine with sitting partially charged, but could run 5-10x more money.

Next best might be AGM as they generally have low self discharge and don't stratify, but need a controller that will charge at appropriate voltages. They run around 2x the price of flooded lead acid.

JoeContiRC · May 2017

I am beginning to understand I think - so the batteries I have are really meant to be drained quick and recharged quick too (what they were doing on my offroad truck working a 24v winch) - my load is very small and since I don't drain enough to "work" the battery like the winch did and top it up even slower - which is not what the batteries were designed for.

So you are suggesting I remove one battery to have less to volume to drain and recharge

but ideally a properly sized battery intended for this kind of use would be a future solution, something around 50A (compared to the 2*100A I currently have)

and a second panel will help recharge if I used the battery faster than the 1 panel can cgarge at .. depand is larger than supply!!

The working current of the 5m LED strip I have is a MAX of 2A - but I am only using about 3.5M of it. Will have another 3M long strip put in in the future - or at least that was the plan!!

Estragon · May 2017

A starting battery is built differently than a deep cycle. It has more and thinner plates, which increases surface area and allows the chemical reactions involved in charging and discharging to happen fast. That's what you want for starting or a winch. That feature becomes a bug for a deep cycle application. Because the reactions happen faster, leaving it sitting in a deeply discharged state for long will damage it.

A second panel would certainly help.

If you add the second strip, and use the lights for say a couple hours a day, that would be ~2x2x2=8 amp hours/day (assuming the 2a is 2adc@12v). On a 100ah battery you could go about 5-6 days to 50% charge, although leaving a starting battery that low for that long is a bad idea.

JoeContiRC · May 2017

There is no need for the battery to go down to 50% since we are blessed with an abundance of sunshine here

Estragon · May 2017

If you consistently get 5-6hours of full sun (no wire shadows etc) and the panel is properly angled, it might work out ok then. A second panel still wouldn't be a bad idea.

JoeContiRC · May 2017

Thank you. I will concentrate on the correct wire gauge and the fusing and hope to get the most out of the batteries while I have them

Estragon · May 2017

Good plan!

Lumisol · June 2017

Keep the DC wiring as short as possible and make the long runs in the 120 AC wiring to keep costs down and lessen the current loss.

JoeContiRC · June 2017

Lumisol said:

Keep the DC wiring as short as possible and make the long runs in the 120 AC wiring to keep costs down and lessen the current loss.

Thank you for that - but I am running a 100% 12v system. No inverter here

Lumisol · June 2017

What's the thing in the diagram labeled inverter/controller then? Just a mislabeled controller?

Best Inverter/Controller location

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