Panel to controller fuse sizing

dchristodchristo Registered Users Posts: 5

Hi and thanks for the Forum.

I’m getting ready to hook up my first “real” panel of any size, and want to make doubly sure I am sizing the fuses between panel, controller, and controller to batteries correctly. I’ve owned this old inverter since it was new, but have previously only charged it with shore power, or a generator. All the main battery cables are #2AWG and the positive cable between the batteries and Heart is fused correctly. I searched your site for fuse sizing info, and to find out what ISC stands for, (now I know it stands for short circuit current). I plan on using #10AWG  blade type automotive fuse holders for these fuses.

Now, I’m adding the panel and controller below to the system. The guide with the panel gives this formula for sizing the fuses for the positive leads from panel to controller, and controller to batteries:

# of panels in parallel (I have only one), X panel ISC (5.75 amps), X 1.2 

I came up with 6.9 amps.

Does this sound like I am on the right track? I would rather undersize than oversize, as I live in an extreme fire hazard area, and this system is in a shop a mile from my home.





Heart Freedom 25 Inverter/charger

(one)Renogy 100 Watt 12 Volt Monocrystalline Solar Panel

WindyNation P20L LCD 20A PWM Solar Panel Regulator Charge Controller


Two 6volt golf cart batteries. (Costco)


  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Yes, you are advised to start the way you mean to continue. Carling or CBi DC breakers. Available right here for only a few bucks. Midnite big baby box or something to keep things tidy.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,

  • dchristodchristo Registered Users Posts: 5

    Thank you for the information, and the especially the cautions vtMaps. When it comes to DC power, I am an electrical novice. The controller is rated at 20 amps. How much higher should I size the fuse than that 20amps? I am using 10 AWG wire for panel to controller and controller to battery connections. How do I figure the ampacity of that wire? Is there a guide, formula, or table I can use to determine this?  I have been waiting years to finally hook up a panel to my system and I'm anxious to do it, but not so much that I want to risk a fire! 

     I will throw the blade type fuse holders I ordered in the tool box to be used elsewhere.

    Thanks again,


    Heart Freedom 20 inverter/charger, (1) Renogy 100 watt 12v panel, WindyNation P20L PWM 20 Amp controller, (2) Costco 6volt golf cart batteries, Honda EU2000i, Kubota 6500 Lowboy.                                                                                      



    • P.S.

  • dchristodchristo Registered Users Posts: 5
    Thank you zoneblue, I will go with DC breakers, as soon as I can figure out/learn what size to use.
  • dchristodchristo Registered Users Posts: 5

    I appreciate everyone who has taken the time to chime in on my post in an effort to help me install this system more safely! Obviously, I'm doing this on a shoestring. I purchased a very inexpensive controller, that had good reviews on Amazon. The golf cart batteries I just purchased were to replace the very old Trojans I had, and I miss their performance comparatively. These new batteries were half the cost of new Trojans or equiv., and while not the same quality, do not seem to be half bad. The 100w PV specs show "optimum operating current" as 5.29 amps, so I'm going to order a 7 or 8 amp breaker (if I can find one) as a switch between PV and controller.

    I'm using 10 AWG wire for that, and from the 20 amp controller to batteries.  10 AWG is rated at 30 amps, so I am going to order a 25 amp breaker for controller to battery run.  

    If any of this sounds unsafe (or just a bad idea) to anyone, I would welcome your comments.


    Heart Freedom 20 inverter/charger, (1) Renogy 100 watt 12v panel, WindyNation P20L PWM 20 Amp controller, (2) Costco 6volt golf cart batteries, Honda EU2000i, Kubota 6500 Lowboy.     

  • dchristodchristo Registered Users Posts: 5
    vtMaps, I was hoping the 100w PV I have would at least maintain the golf cart batteries, and I was counting on topping them off, and equalizing them with a generator. I hope to add more panels as finances allow.
    The 10 AWG cable runs will be as short as I can make them. 12 feet to and from PV/controller and 6 feet from controller to batteries. Trying to make the most with what I have.
    Thanks again!

Sign In or Register to comment.