Blowing fuse while charging battery for small solar shed light

[pothos]

I put togethe a shed light as a first project (specs below). However my 7.5A fuse keeps blowing while charging and not using the light. Is it safe to incrase the fuse size to 10A or is there somewhere else I went wrong? The panel isn't in full sun but I figured that it would be sufficient to only use the shed light for several minutes per week. I find that after the fuse blows, the display on the charge controller shows EO1 which means the battery is over dischaged.

12.8V 6Ah LiFePO4 battery

LiTime 12V 6Ah LiFePO4 Lithium Battery

LiTime 12V 6Ah LiFePO4 lithium battery is perfect for fish finders, kid's scooters, LED lights, alarm systems, security cameras, game machines, outdoor camping, hair curlers, etc.

www.litime.com

Renogy 10W 12V solar panel

10 Watt 12 Volt Monocrystalline Solar Panel

Renogy 10 Watt 12 Volt Monocrystalline Solar Panel is perfect for small plug-and-play projects! Renogy sells the best Solar Panel perfect for your solar application.

ca.renogy.com

Renogy 10A PWM Charge Controller

https://www.renogy.com/content/RNG-CTRL-WND10/WND10-Manual.pdf

5V USB light strip connected to the 5V 2A usb output of the charge controller

https://a.aliexpress.com/_msSxZNA

18 AWG cable with a 7.5A mini inline fuse close to the battery on the positive/red wire to the battery.

 

[ericfx1984]

18 gauge wire will not hold 10 amps especially if it's over any distance

Is this the fuse between the solar panel and the charger or between the charger and the battery?

Also you really shouldn't use a PWM charge controller with a lithium-iron phosphate battery

 

[pothos]

Hi Eric, the fuse is between the solar charge controller and the battery on the positive/red wire.

Why should I avoid a PWM charge controller with a LiFePO4 battery? Are there any small MPPT charge controllers that you would recommend for this battery?

Thanks for the help.

 

[ericfx1984]

Hi Eric, the fuse is between the solar charge controller and the battery on the positive/red wire.

Why should I avoid a PWM charge controller with a LiFePO4 battery? Are there any small MPPT charge controllers that you would recommend for this battery?

Thanks for the help.

You should consider increasing the wire size to something a little more manageable... 10 or 12 gauge would be just about right

Generally speaking PWM charge controllers simply Don't have enough programmable options to be set up properly for lithium iron phosphate... Not to say that they can't be used, but that they just simply are not ideal...

Additionally the vast majority of them are based on a unit that can be purchased on Amazon for about $12... Yes even the one that you've listed

It's also important to realize that MPPT will charge your batteries significantly more efficiently

Keep in mind, PWM is going to take whatever amperage the solar panel is providing and pass that on to the battery... Well simultaneously lowering the voltage to the appropriate charge voltage

So with PWM it is extremely important that you are as close to charge voltage as possible

For instance if you were using a solar panel to put out 16 volts and 6.25 amps(100 watts), then it might come down to say 14.4 volts and 6.25 amps... Which is about 90 Watts.. so not a huge deal

But let's instead say that it is a 28 volt panel at 3.58 amps... Still 100 W panel

But that turns into 14.4 volts at 3.58 amps or about 51 Watts... So 51% of the power actually passes through... And it's even lower than that by the time you account for cable losses and other such things

For the most part you would expect any MPPT charge controller to be somewhere in the mid to upper 90s on conversion rate... To be honest I have units where I'm running 10 times the voltage of the battery and still seeing around 98% conversion rate.. But more importantly than that I'm able to program the batteries to charge exactly as I want them


As for unit that is affordable that is MPPT
PowMr 12V 24V AUTO 20Amp solar charge controller, MPPT charge controller Intelligent Regulator w/LCD Display for AGM, Gel, Flooded and Lithium Battery Charging https://a.co/d/6W8lznT

 

[mikefitz]

You have a very low power system. A 10 watt panel will be current limited well below 1 amp.
The fuse you have will protect any circuit collected to the controller load outputs and USB outputs. Something in your circuit is making a short across the positive and negative wires. Can you provide a rough diagram of the system? What length of led strip are you using?
For a simple basic experimental system there is nothing ' bad' about using a PWM controller, its just not ideal. A 10 watt panel wont deliver much power , especially if its shaded. Its possible the battery wont be charged enough to power the load for long enough to be useful. 18 awg is good for 15 amps so fusing at 7.5 is OK. With the very small charge current, the panel maximum is around 0.5 amps, and the USB circuit will be a few amps, so everything is within the capacity of 18 awg.
The very low cost PWM devices are not well made, 1 so there could be a fault In the unit.
To be honest your system doesn't justify a expensive MPPT controller. However if you decide to build a larger system then a MPPT is justified. The best value for a reliable MPPT is the victron smart range.

 

[Suijkerbuijk]

Hi Eric, the fuse is between the solar charge controller and the battery on the positive/red wire.

Why should I avoid a PWM charge controller with a LiFePO4 battery? Are there any small MPPT charge controllers that you would recommend for this battery?

Thanks for the help.

The best mppt is the victron smartsolar 75/10 .
That unit you can adjust the max amp to the battery.
You can set it on 1-10a
And its fully program how you like to program

So you can set your lifepo4 on 6a charge profile what is the max of your battery

The problem its cost a lot .
But for the battery its really the best to have .
For the rest .
That renogy cost in my country about 50 euro.
The victron 75/10 cost 65 euro.

For the rest go for a 25watt solar panel.
That do about 1.7a charging on a mppt.
Personal i go for a 50watt panel that do about 2.7a

I know that i will thake that Victron any time.

 

[HRTKD]

As pointed out by mikefitz, with that solar panel the solar charge controller shouldn't have been able to generate enough amps to blow a 7.5 amp fuse. But if the wires are undersized and too long it might happen.

Use this wire size calculator to check to see what size wire should be used: https://https//baymarinesupply.com/calculator

The usual rule for fuse sizing is 1.25 times the expected amps. Worst case scenario is that your solar charge controller produces 10 amps, so a fuse rated for 12.5 amps is about right.

Still, something is out of what that you blew that fuse in the first place.

 

[chaosdsm]

Lets talk about the wire gauge.... I see misleading info posted here...

Basically, you need to know 4 main things when determining what gauge of wire works for your circuit:
+ Maximum amperage of circuit
+ Maximum allowable voltage drop
+ Maximum length of wire in the circuit
+ what type of wire you're using: solid copper > nickel plated copper wire > copper clad aluminum > solid aluminum
hint: > = greater than / better than

Also there's no way to say for certain that a given wire gauge is the wrong (or right) gauge if you don't know at least those 4 basics: i.e. a 6 inch long single conductor (solid or stranded) solid copper 18ga 450C insulator wire (commonly referred to as MG or Mica Glass insulator) at 100F ambient temp can support 31 amps DC continuous power handling, but at 10 feet that drops to about 9A DC continuous power handling. This is because: the larger the wire diameter, the lower the resistance. Lower resistance = lower the voltage and amperage capacity drop over distance.

 

[Bop]

The best mppt is the victron smartsolar 75/10 .
That unit you can adjust the max amp to the battery.
You can set it on 1-10a
And its fully program how you like to program

So you can set your lifepo4 on 6a charge profile what is the max of your battery

The problem its cost a lot .
But for the battery its really the best to have .
For the rest .
That renogy cost in my country about 50 euro.
The victron 75/10 cost 65 euro.

For the rest go for a 25watt solar panel.
That do about 1.7a charging on a mppt.
Personal i go for a 50watt panel that do about 2.7a

I know that i will thake that Victron any time.

Ridiculously oversized (and overpriced) for a 12v 6Ah battery being charged from a 10w 12v panel!!!
(even the Renogy charge controller is massively oversized and could handle up to 120w of panels at 12v)

The battery size is very small as well- but the Renogy has a very low (less than 10mA) self consumption- so it uses about 0.25Wh a day just sitting there, the battery has a 'actual' capacity of 77Wh of storage (but the panel would be lucky to get to 40Wh a day in most places so if you did flatten the battery, it might take a couple of days to recharge depending on your location), the Renogy controller 'can' output up to 10A, but with only 10w available, it would never get above about 1A from the panel- so thats not the issue, and same with the LED strip- its a 5vdc 2a limit (10w) on the USB outputs of the Renogy so a 10w led strip, so at the 12v nominal, it would never draw more than 1A from the battery....

So it makes no sense that a 7.5A fuse blows...
(short of an actual possible short circuit somewhere....)

 

[pothos]

Is there a smaller solar charge controller that you'd recommend? Ideally MPPT since it gets quite a bit of shade in the summer but I only really use the light for a minute or two most days.

I have switched to 12AWG copper clad aluminum wire between the battery and the charge controller, and upgraded the fuse from 7.5A to 10A. Fingers crossed the battery recovers from its over-discharged state.

 

[Rednecktek]

Is there a smaller solar charge controller that you'd recommend? Ideally MPPT since it gets quite a bit of shade in the summer but I only really use the light for a minute or two most days.

With a 10w panel you'd spend more on an MPPT than your entire system combined. At best you gain a watt. Until you're looking at 200-300w of panel a new SCC isn't going to do you any good.

You've still got a short in there somewhere, likely the USB port. Disconnect everything but the panel, SCC, and battery. If it starts taking a charge you can throw your 7.5a fuse back in and start reattaching your loads. When the fuse pops again, that's your problem child.

Expect it to take 8+ hours of good sun to get that battery filled back up.

 

[Bop]

I was just disagreeing with the Victron suggestion- that is a quite 'large' capacity controller (for this application at least) and at their price range, would be one of the most expensive parts of the entire system lol (in fact, it would be the most $$$ item...)- even the Renogy is a lot larger than is needed

Remembering that your battery is extremely small, and can't handle a panel wattage of more than about 75w anyway (that MAX charge current for that battery is 6A max- and that would be stressing that little battery)

Not a fan of the 'elcheapo' ebay/ali units, but this is the kind of stuff they are prime for- a tiny, cheap and rarely used setup- you wouldn't put in a $10k 48v 6kw system to run a 10w shed light- and the equipment prices should reflect the usage needs...