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Solar Generator Fuses and Switches


Tiaan
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Hi,

First of all, this is a great forum which i have visited many times in the past as n guest and have received lots of info and answers as a result. It is because of this that i have decided to join in the hopes that more knowledgeable people out there can help me with a little project i would like to do.

In order to "ease into" solar power, i have decided to build myself a little Portable Solar Generator. Youtube and the internet are full of examples of people who have build similar generators that they install in a plastic tote/Pelican case/ammo box. Basically a container that holds the battery, charge controller and inverter with various plugs on the side to accommodate one's power needs. All this gets replenished with a portable/camping solar panel that also plugs into the side of the box.

Since I intend to use this for both camping and power outages i would like it as versatile as possible, and im contemplating to also add a automotive battery charger should the solar panel not keep up, or during extended periods of use (i.e. longer camping trips where the PV panel might not keep up)

I am including a crude wiring diagram to better explain my intention.

My question is regarding the placement of fuses and switches.

Assuming all the equipment and wiring have been sized correctly, were would one put fuses and switches?

I was thinking 3 switches, 1 switch to switch the inverter on and off independantly (to be able to switch it off if i only use 12 volt appliances)

Another switch for the charger

And a third "Master cut-off switch" to use when the unit is transported to and from camping sites, and should i wish to store it for extended periods of time.

I have not yet bought the inverter or battery charger, and i assume they come with their own switches and fuses. Is this assumption correct, and would said fuses/switches be sufficient, or would i need additional switches/fuses in my wiring?

So, to re-capp

1. Could I use the existing switches and fuses in the battery charger and inverter, and if not, where in my wiring diagram should i place these?

2. Where in my wiring diagram would i need to install a "master cut-out switch" and fuse?

 

 

 

 

Wdiagram.JPG

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Hi Tiaan, welcome to the forum.

I know there will be many replies to your topic and many ideas by other members, so I'll start off with the following:

  • The charge controller might not have a secondary 12V output (if that is what you've tried to indicate) to connect the 12V outputs and USB sockets to - I'd rather also connect that directly to the battery, but maybe via its own switch and fuse of lower rating, depending on the load you intend to connect to those sockets.
  • I will add a changeover (SPDT) switch with the common to the battery Positive and then one of the other two terminals to the AC charger and the other terminal to the Solar charge controller to select to use either one of the two at a time and to prevent power from flowing into the one not being used at that point in time. (maybe also with fuses in each charger's line)
  • I'll add another switch between the battery Positive and the inverter to isolate the inverter (and also with a fuse in that line)
  • then I'll put a "master cut-out switch" and a fuse between the battery positive and all the rest

Depending on what other suggestions might pop up I might change my thoughts.

 

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Welcome Tiaan.

I started with the exact same idea back in 2008/2009 ... man it was fun and you are going to learn a lot and have a lot of joy.

This project of yours, for camping, is going to grow as you get into it.

So to add onto superdiy post, if you have not bought a charge controller yet, consider a small MPPT one that has a light function that you connect the lights directly to it, if you want, one that switches off in mornings. All programmable.

And the chances are quite good that after a few trips you are going to want to add a panel or two more. Still a small easily transportable system, but you are going to want more. ;)

Then the inverter. Get pure sine wave if you can. Why? Once I got my project working it grew because with camping you are inevitably going to come across those camp coolers / small fridges that you want to power, daytime, and that is where the pure sine wave comes in very handy, with the additional panel or two. :D

See, if you can power a small camp fridge / cooler, the rest first like a glove like small TV, decoder, cell chargers etc.

 

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Thanks for the quick reply superdiy,

Regarding your first point (secondary 12v outputs on the charge controller), I already have a temp setup minus the battery charger and the inverter as a "proof of concept", and my CC (charge controller) have the additional 12v outputs, so no problem there. Also, the wiring and my current equipment (PV panel, CC, battery and wiring) have been correctly sized for each other, although i should mention that im considering a larger battery with a bigger AH rating - hence my intention to add the battery charger (at least until i have acquired n bigger PV panel to keep the bigger battery topped up). But even if/when i DO get a bigger PV panel, the charger is a nice addition to get the battery topped up quicker if and when conventional power is available

Regarding all your other points... thank you VERY much - that was exactly the answer i was looking for. Your suggestion about a SPDT switch between the Battery charger and CC is an excellent idea that i have not thought of. This will ensure that one can never (by accident) have both switched on.

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Thank you terrible triplett, as you said, this is a "learning project" for me, a point to "get started" and learn while at the same time expanding both my knowledge and equipment as my experience and knowledge broadens... an MPPT controller and pure sine wane inverter is definitely on the bucket list, but for now, i would like to build the most cost effective (read: cheapest) system up and running so i can test and play and learn

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lol... OK, consider me tempted - job well done. On the topic of fuses.. What size fuse would i be looking at next to the "master cut out switch"?

For the inverter and A/C charger it would be pretty self explanatory, since each of those components would already have a fuse of the correct size, but im a little unsure what size fuse i should be looking at that protects the whole system right at the battery's positive terminal.

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25 minutes ago, Tiaan said:

On the topic of fuses.. What size fuse would i be looking at next to the "master cut out switch"?

For the inverter and A/C charger it would be pretty self explanatory, since each of those components would already have a fuse of the correct size, but im a little unsure what size fuse i should be looking at that protects the whole system right at the battery's positive terminal.

You'll have to calculate the maximum current draw when you use everything you want to. Say you have a 600W inverter which might draw up to 60A from the battery and you want to use a camp fridge on the 12V output which draws 8A and you want to charge 2 x tablets @ 5V 1A each, which would be approximately 1A @ 12V, you will have a total power draw of 60+8+1 => 69amp.  You have to add about 25% to that to prevent nuisance blowing so you would require a 69A + 25% => 86.25A fuse, but since you cannot buy a 86.25A fuse off the shelf, you have to get something close to that and that would be a 100A fuse - if you put a fuse of less than 86.25A in that line it might blow under normal usage and you don't want that to happen, therefor you need to get a higher value than 86.25A.

BUT, and here is the BUT: You still have to add fuses with lower A ratings in other individual lines in case something in any of those goes wrong. e.g. between the battery and inverter you would put a 60A + 25% => 75A fuse in case something inside the inverter goes wrong and between the battery and each charger you would need a smaller fuse - typically the maximum current that might flow in each of these lines + 25%.

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2 minutes ago, viper_za said:

I think more it is to protect both ;)

Lets focus on the wire, length, amps and the required fuse before we go off track? ;)

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13 minutes ago, The Terrible Triplett said:

Lets focus on the wire, length, amps and the required fuse before we go off track? ;)

You need to have a load in that equation too and that is normally limited to the device or am I missing something? 

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Thanks for all the replies regarding fuses, again, it gives me a "starting point" from which to experiment further.

Last night another thought crossed my mind though...

I was thinking that instead of a "built in" charger, it might be better to install "remote battery terminals" that leads to the outside of the box. This solves a number of problems. First, it "free's up" the charger, allowing me to either connect the charger to the remote terminals should i need to charge the box, or i could use the charger elsewhere, like on my car if ever that needs recharging. Secondly, it gives me the option of connecting different chargers, like a trickle charger for example during long periods of non-use. There are also other advantages like weight reduction and the ability to connect ANY appliance through the use of crocodile clips. (i cant tell you how many times i wanted to pump up my air mattress, just to find that the flimsy cigarette socket was stepped on or damaged in some other way. Truth be told, ive long since replaced the air mattress pump's socket with crocodile clips)

Speaking of weight reduction, i have wondered around the geewiz site (thanks to Terrible Triplett's tempting) and came across this:

http://www.geewiz.co.za/geewiz-inverters/6019-500w-inverter-built-in-8a-battery-charger.html

Not a pure sine wave inverter-i know, but maybe a good "stepping stone" inverter before i decide to trough serious money into this project. i love the fact that its so small and light. Plus, the fact that it has the ability to charge (albeit probably a very basic charger), is what turned my thoughts towards remote terminals...

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> I was thinking that instead of a "built in" charger, it might be better to install "remote battery terminals" that leads to the outside of the box.

I have installed Brad Harison Connectors on my box. for the solar panels (grey) and for the inverter and charger (2x Red) and that way I can mix and match inputs (including and option to connect the box to my National Luna solenoid (Dual Battery) in my bakkie.  Small solar charge controller is inside the box.  I also have 2x 12V sockets and 2x Hella sockets for other bits like lighting.  All fused!  50A for National Luna Connection and rest are Automotive 12V 10 to 20A fuses. 

2015-12-21 11.25.38.jpg2015-12-21 11.25.32.jpg2015-12-21 11.24.58.jpg2015-12-21 11.24.34.jpg2015-12-21 11.24.18.jpg

 

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If you have a 12V fridge and only ever intend to connect lights / TV / cellphone charger to this solar generator, then a modified inverter would be more than sufficient. Many smaller inverters and battery chargers have a built-in fuses and switches. So, first see what you can get your hands on and then see if you need extra fuses and switches. 

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Mark, that is a very nice example of what i intend to do with this project. Your photos are an inspiration for me to get started!

Silvernodashi, The idea is to start small and cheap. hence the modified sine wave. I would like to build a unit, and use it before i throw more money into it. By using it, i would be able to determine how many times a month/year it has helped me, and also how much of a necessity/luxury it is. by using it, i would best be able to determine if it is worth spending extra money to "upgrade" it with more/better features.

I said in the beginning that this is going to be a "learning project" for me, to allow me to "ease into" solar. Im hoping that through using (and later expanding) this project, i would gain enough knowledge to maybe later have a more permanent off-grid system in my small house.... one has to start somewhere..

Thank you to everyone that has replied to this thread - it is most valuable, i feel that i have learned something from every post. All very positive tips and suggestion. Many threads that i have read in the past (on other forums relating to other topics) quickly turns into negative comments where each poster is trying to show (in his mind) his superior knowledge, and doing so through derogatory comment. My experience on this site has been very positive thus far

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So, I finally will have a few hours available on Saturday, and im planning to buy the thicker wire, switches and fuses i might need for this project. Just a quick question. Superdiy suggested right at the beginning that i put a SPDT switch between the A/C battery charger and the solar charge controller, to ensure that both cant be switched on at the same time by accident. Since im substituting the a/c charger for remote terminals, i am wondering what route some of you might take. Would you still install a SPDT switch? It would be a good idea, since i would still use the remote terminals to charge the battery. The one drawback is that if i want to use the terminals to DRAW power from (like connecting an air mattress pump for example), i wont be able to draw power from the terminals and charge via the solar panel at the some time.... what to do, what to do....

Im curious as to what route you guys would take.

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I saw a video once (somewhere on youtube i suppose) of a guy who stripped the wires off a laptop charger and screwed them into a solar charge controller. Those "laptop bricks" (as they are called) puts out anywhere between 13/14 up to 19 volts depending from which laptop it comes from - typically what a 12volt solar panel would put out during peak sunshine. End result is he kept frying the laptop bricks. He had quite a few spare and kept replacing them, but they wouldnt last. I cant remember the video, but in the comments section someone explained why the solar charge controller would keep on frying the laptop bricks. For whatever reason the charge controller can distinguish between 12-19 volts coming from a solar panel and 12-19 volts coming from a laptop brick, and it didnt like the latter.

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4 minutes ago, Tiaan said:

I saw a video once (somewhere on youtube i suppose) of a guy who stripped the wires off a laptop charger and screwed them into a solar charge controller. Those "laptop bricks" (as they are called) puts out anywhere between 13/14 up to 19 volts depending from which laptop it comes from - typically what a 12volt solar panel would put out during peak sunshine. End result is he kept frying the laptop bricks. He had quite a few spare and kept replacing them, but they wouldnt last. I cant remember the video, but in the comments section someone explained why the solar charge controller would keep on frying the laptop bricks. For whatever reason the charge controller can distinguish between 12-19 volts coming from a solar panel and 12-19 volts coming from a laptop brick, and it didnt like the latter.

A charge controller cannot distinguish between different power sources.

Depending on the SOC of the battery the charge controller might sometimes draw very little power from the laptop PSU and on other instances it will draw a lot. Since it is a switch-mode power supply it will always try to keep the voltage constant, irrelevant of the amount of power being drawn from it. If the charge controller draws more power from the laptop PSU than what the PSU can handle (overload condition) or if the PSU is running at almost max output for extended periods it will eventually fail.

You will not have the same problem with a PV panel, because the panel will only be able to supply a certain amount of current and once you try to draw more than that the panel's voltage will start to drop (unlike the switch-mode power supply which will try to keep the voltage constant) and that is usually when the "maximum power point" (MPP) is reached. If the charge controller tries to draw more current the panel voltage will drop further and the charge controller will back off and draw less, the panel voltage will rise again and the charge controller will draw more current again, which will cause the panel voltage to drop again and the charge controller will back off again and that process will carry on and on and on without causing any harm to the panel.

 

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@superdiy covered it mostly. Basically, an MPPT is a variable resistor. Not for real, but in principle. Ohms law says V = IR, and a PV panel is a constant current device so I is mostly constant. By playing with R (actually X, because it uses an inductor), it can make the module run at a V that is close to Vmax.

A SMPS is not a constant current device. It's a constant voltage device.

The best thing to use is a current limited power supply. I know the demo portable kit used by Victron for training (it has a 24V Multiplus, a 150/70 MPPT, a BMV and two AGM batteries on it, with wheels so you can push it around) has a SMPS screwed to the back to simulate PV. I didn't look to see what kind of SMPS it was, but it looked like one of these off-the-shelf things you might buy at AC/DC :-)

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  • 4 weeks later...

Resurrecting this old topic. Tonight I wired a small current limited supply to a Victron 100/15 MPPT and then to a 7Ah alarm battery. The PSU has an LED that indicates when the current limiter goes active. The result: The current-limit LED blinks on and off as the MPPT runs it over the bend and then backs off, hitting precisely the voltage and current I set on the PSU.

So, if you need to simulate a PV panel, that's how you do it: With a current-limited supply like this one:

http://www.bidorbuy.co.za/item/239978553/DC_DC_Adjustable_Voltage_Step_up_Step_Down_Current_Driver_Charger.html

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Plonkster, how would you test the efficiency of a MPPT versus a PWM controller? Can it be tested?

And would one be able to see if a MPPT is a real MPPT or a PWM labelled as a MPPT for marketing purposes?

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29 minutes ago, The Terrible Triplett said:

Plonkster, how would you test the efficiency of a MPPT versus a PWM controller? Can it be tested?

Put a volt and amp meter on the input, do the same on the output. Measure power both sides. P_out/P_in times 100. There's your efficiency.

29 minutes ago, The Terrible Triplett said:

And would one be able to see if a MPPT is a real MPPT or a PWM labelled as a MPPT for marketing purposes?

Yes, easy. Measure PV voltage. If it's the same as the battery voltage (or close), it's not a real MPPT. Even better, measure the current. With a real MPPT, there is current gain, more current out than in. Some video material.

Example of a fake MPPT: https://www.youtube.com/watch?v=0lnShSebU4o

Example of a devious fake, an using an off-tune Transistor Radio to detect PWM (it makes a continuous tone if it is PWM): https://www.youtube.com/watch?v=la-gvy0DfJs

And here is one using a 555-timer to do a bit of DC/DC conversion, with no proper power point tracking, also just to fool people into thinking it's a real MPPT: https://www.youtube.com/watch?v=umRNiJ1oLwo

So that should keep you busy for an hour or so :-)

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8 hours ago, plonkster said:

So that should keep you busy for an hour or so :-)

I KNOW I have / had a PWM and now 2 MPPT's. 

Have a nefarious reason for asking.

Maybe someone will read the post and do a test on a Voltronic MPPT to see how efficient they are. :D

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