Need help with panels

[dashboy979]

Recently came into possession of three Uni-solar 136 watt panels and a Midnight Solar Kid charge controller. The controller is rated at 150 volts/30 amps.

Hoping for recommendations on what circuit breakers to use for the pv panels. The previous owner of the panels replaced the pv wires with new 8 gauge wire. I tested the panels with a meter and they were pushing 43.2 volts so they seem to be in good shape despite being 7 years old.

My hope is to use this system to power a small frigerator freezer combo with a 3000 watt inverter. The frg is a combo 12 or 24 volt DC/ 110 volt AC type (run on 12 volt battery or plug into AC outlet) and pulls 70 watts total input power with 5.8 amps.

The panels are 136 watts, (33 vmp), (4.1 imp), (5.1 isc), and (46.2 voc). I currently have a 200AH lithium Iron phosphate battery, but will be acquiring a second one in a couple weeks.

Just can't figure out what b size breakers go between charge controller and the panels. I plan on using a 30 amp breaker between the charge controller and battery, but a little unsure about that as well.

Any help is much appreciated.

 

[GMB]

I assume these are your panels? https://www.solarelectricsupply.com/unisolar-pvl-136-solar-laminate-solar-panel-550

It says, "Maximum Series Fuse Rating: 8 A (near the bottom of the page).

With that said, I've seen it posted that you do not 'need' a fuse/circuit breaker between the panels and the solar charge controller - just some means to turn off that connection, like a Blue Sea switch.

I personally use a combiner box with each series on a 15 amp breaker for my array (the fuse size it says to use), then a Blue Sea switch from the combiner box to the solar charge controller. I like to be on the safe side...

 

[dashboy979]

GMB, your heaven sent. Thank you for the info. I will try to find a 8 amp breaker and use the blue sea switch. Amy idea what breaker to use between the battery and charge controller?

 

[gnubie]

Don't forget that anything that breaks the PV side has to be rated to open the Voc of the array, and of course handle the short circuit current. If those 3 panels are in series that means about 140v.

 

[GMB]

GMB, your heaven sent. Thank you for the info. I will try to find a 8 amp breaker and use the blue sea switch. Amy idea what breaker to use between the battery and charge controller?

Usually it's about 20% above the amp rating of the charge controller. In your case, for the 30 amp controller, I would put a 35 - 40 amp fuse between that and the battery bank. To be 100%, you could look up your solar charge controller manual online and it should state that info there.

Also, this is a good article on panels and fusing. https://www.windynation.com/jzv/inf/how-properly-fuse-solar-pv-system

 

[dashboy979]

Don't forget that anything that breaks the PV side has to be rated to open the Voc of the array, and of course handle the short circuit current. If those 3 panels are in series that means about 140v.

Gnubie, with at said about the 140v, what amount of amps should I see, so that I don't destroy my Kid Charge controller? I believe mine is rated at 30 amps top.

 

[GMB]

This is the user manual for your charge controller. It mentions using a 30 amp fuse on page 17. I would read this front to back, over and over. And it has wiring diagrams as well. I just browsed it quickly, but I'm pretty sure it said a 500 watt system at 12 volts was it's max. So you should be good there with your panels.

https://www.altestore.com/static/datafiles/Others/Midnite_Kid_Solar_Manual.pdf

This is a good video on the math behind connecting solar panels. If you series connect those panels, you will be sending 4.1 amps to the controller at 99 volts, for 405.9 watts.

 

[dashboy979]

This is the user manual for your charge controller. It mentions using a 30 amp fuse on page 17. I would read this front to back, over and over. And it has wiring diagrams as well. I just browsed it quickly, but I'm pretty sure it said a 500 watt system at 12 volts was it's max. So you should be good there with your panels.

https://www.altestore.com/static/datafiles/Others/Midnite_Kid_Solar_Manual.pdf

This is a good video on the math behind connecting solar panels. If you series connect those panels, you will be sending 4.1 amps to the controller.

Simply awesome. Let me start reading. You guys are the best!

 

[gnubie]

Gnubie, with at said about the 140v, what amount of amps should I see, so that I don't destroy my Kid Charge controller? I believe mine is rated at 30 amps top.

Often the current rating of a MPPT controller applies to both the PV input and battery output. I looked at the spec's PDF for the Kid but it doesn't explicitly say the PV input current rating. Assuming it is like all the rest, it's 30 amps, ie the unit is built to handle more current on the PV input than your panels could ever supply, so no damage is possible. No need for a fuse on the PV input to the controller, IMO, but definitely a breaker/isolator to disconnect the panels.

On the battery charging side, a fuse is appropriate. If something goes horribly wrong with the controller, the batteries would be quite happy to throw 100 amps at it.

Probably all covered by GMB's clip

 

[tictag]

Usually it's about 20% above the amp rating of the charge controller. In your case, for the 30 amp controller, I would put a 35 - 40 amp fuse between that and the battery bank. To be 100%, you could look up your solar charge controller manual online and it should state that info there.

Whilst I totally agree with you, @GMB, for the OP's information, it's best to think of fuses/breakers etc protecting the cable, not the device the cable is connected to, which means fuse/breaker selection should always be the LOWER of:

1. Expected load +25% (20% is fine).
2. Ampacity of the cable.

There is not point fusing at, say 35A, then installing a cable only rated to carry 20A.

My hope is to use this system to power a small frigerator freezer combo with a 3000 watt inverter.

I appreciate that you might want such a large inverter (3,000W) to power other things, but please note that the higher the rated power of the inverter, the more losses that inverter will introduce. Your fridge is only 70W! Without knowing your other AC needs, I would be powering this fridge by DC and thereby avoid the need for an inverter entirely.

 

[dashboy979]

Tictag,
Thank you for your input. I do have the option to power the frig with DC, since I have 12 volt cigarette lighter adapter for it, so I will certainly do that. I am utilizing 2/0 gauge wire for most of my connections, including the inverter to the battery and 8 gauge for panels to charge controller and battery to charge controller.

The inverter is for small smaller appliances such as my CPAP machine, small air tank for oxygen and air purifying machine should I go through the problem of power outages again. Unfortunately I have lost a full regular sized frigerator/freezer full of meat and food because power was out for several days so I needed to come up with some way to prevent this from happening again.

Thanks again.

 

[nogridhome]

Recently came into possession of three Uni-solar 136 watt panels and a Midnight Solar Kid charge controller. The controller is rated at 150 volts/30 amps.

Hoping for recommendations on what circuit breakers to use for the pv panels. The previous owner of the panels replaced the pv wires with new 8 gauge wire. I tested the panels with a meter and they were pushing 43.2 volts so they seem to be in good shape despite being 7 years old.

My hope is to use this system to power a small frigerator freezer combo with a 3000 watt inverter. The frg is a combo 12 or 24 volt DC/ 110 volt AC type (run on 12 volt battery or plug into AC outlet) and pulls 70 watts total input power with 5.8 amps.

The panels are 136 watts, (33 vmp), (4.1 imp), (5.1 isc), and (46.2 voc). I currently have a 200AH lithium Iron phosphate battery, but will be acquiring a second one in a couple weeks.

Just can't figure out what b size breakers go between charge controller and the panels. I plan on using a 30 amp breaker between the charge controller and battery, but a little unsure about that as well.

Any help is much appreciated.

I use 3 panels in an array to generate ~120VDC, at 9A these are fused with 15amp fuses. Four of these arrays are combined to generate 36A at 120VDC. They are fed through a breaker to the charge controller. This protects the circuit and also provided the disconnect you are seeking. The charge controller output has the same type breaker. The charge controller output is rated up to 90A so I use this breaker. You can get them here:

Midnite Solar MNEPV100 100A, 150VDC Din Rail Breaker

Midnite Solar MNEPV100 100A, 150VDC Din Rail Breaker

www.hurricanewindpower.com

Many sizes to suit your needs.
I hope this helps. ALL THE BEST!