Using 32V car fuses in 24V PV systems

HI

I've been using simple blade fuses (http://www.evilution.co.uk/info/3fuse.jpg) in 12V systems for cheapness and easiness for replacement in the DC parts of the systems. This has been working fine.

- and i am thinking of doing the same for 24V systems.

However, the rated voltage for these types of fuses is 32V, and on the PV to Charge Controller side the Vmp of the panels can reach 35V or so.... what will happen to these fuses?

  1. Will a few volts above the rated 32V not really matter?
  2. or will I just need to put in a fuse slightly higher rating, eg 12A instead of 10A
  3. or will the fuse explode?


Thanks for any insights

Larry

Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Using 32V car fuses in 24V PV systems

    In my opinion a few volts won't make a lot of difference. I know of one case where they were used on a 1Hp 240 VAC motor that didn't have internal overload protection. Added after having motor re-wound several times. After that, only the fuse blew if the motor got stalled. That said, the current was already limited to what the windings would pass before burning up. On a more serious note, I nearly had a fire with the combination of one of those 30A fuses and it's plug in holder, where there was continuous 20A or so current. Seems a resistance built up between the fuse blade and the holder clip. Melted the holder, blackened the fuse leg, ate part of the blade away with arcing, still the fuse didn't blow! When I found it by accident when checking voltages and discovering a drop where there shouldn't have been any, the whole mess was welded together. Had to cut it open to see what had happened. After that, I soldered the wires directly to the fuse blades and have had no more problem. Used to have similar electrical problems with 12 volt motorbike systems years ago, at points where the wires were crimped into connectors. Just something to consider.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using 32V car fuses in 24V PV systems

    Many times, it is difficult to tell if the rated voltage is nominal (i.e., 32 volt battery bank expecting 40+ volts for recharging/equalization) or it is a never to exceed voltage. A few volts will not make a real difference in any case.

    But as Wayne states, these are not really bullet proof devices. And can overheat with "rated current", especially if there is not a lot of cooling air flow (tight wiring box).

    If you can test them for your needs (loaded to rated current and a dead short) to see if they are behaving correctly--It probably would make you feel better.

    Otherwise, I would avoid these types of fuses. The really are not appropriate for some place where a fire could really hurt somebody or property (home, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using 32V car fuses in 24V PV systems

    Voltage ratings on fuses are mainly about being able to safely and effectively interrupt that Voltage when current is exceeded (by 'X' amount for 'Y' time). 24 Volt solar panels can run Vmp @ 35, and Voc above that. If a problem occurs the fuse may "blow" but not actually cut the Voltage; there could be arcing through the fuse.

    Since fuses are safety devices in case something goes wrong, it's best not to use one that could be something else to go wrong after the first failure.
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    Re: Using 32V car fuses in 24V PV systems

    Thanks for your replies on this subject

    Taking these points into account,
    what fuses would you recommend then, that dont have this problem?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using 32V car fuses in 24V PV systems

    One of the guys here from Spain/Europe can probably give you better local suppliers/options.

    If you have any marine stores in the area, you should find some good fuse holders/wiring systems. Out here, you may also find some good solutions for people that install high end car stereo systems.

    Also fuses/wiring solutions are very current specific... Much above 15/20 amperes, you may be looking at entirely different fuse/breaker/bus components.

    Blue Sea makes some very nice distribution units that use Automotive Type fuses... For the most part, it is the holder/wiring connections that seem to be the weak point for automotive type fuse installations.

    They also make some nice larger fuse blocks too (some are even direct bolt to battery lug types).

    Regarding sizing of fuses/breakers... Take the maximum expected/supported continuous current and multiply by 1.25 and size the to the next larger available fuse/wire diameter. Fuses (at least in the US/North America) are designed to blow at rated current (may take minutes or hours). You need that 1.25 "safety factor" to reduce the chances of false tripping.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    Re: Using 32V car fuses in 24V PV systems

    On vehicles I like to stick with the plastic blade fuses.
    http://en.wikipedia.org/wiki/Fuse_(automotive)
    Those automotive fuses are good for up to 32 volts.

    But on everything else I use glass tube fuses, I always see them rated for 32v up to 30 amps, 125v @ 10 amps or less and 250v @ 5 amps or less.
    (That is what I use at work, there may be a larger selection out there)

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.