Need advice on Fuses.....Fuses on DC or AC, or BOTH?

EverlongEverlong Solar Expert Posts: 36 ✭✭
hi guys,
my setup consists of a 2x12v batteries in series and a 2500w inverter, i understand that if im going to be running 1kw of load i should go with 1kw/24v= fuse amperage, so i get 41.xxx. I will be running LED ligting outside of my house(christmas lights + lighting for Halloween), few hundred LEDs. So, here is my question:
Should i also put a fuse between the inverter and the 110v load? if yes, what capacity? Lets assume my lights outside will draw 300watts, would the same formula apply 300w/120=2.5Amps, or 0.3kw/120=...... i guess i just answered my question :) anyway, any input is appreciated.... :)

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need advice on Fuses.....Fuses on DC or AC, or BOTH?

    Both the DC and AC side of the inverter should have circuit protection, although the inverter will usually fault before any fuse blows or breaker trips on the output.
    The manual that came with the inverter should recommend proper wire & fuse sizes for at least the DC side.
    Technically the circuit protection needs to be sized according to NEC regs in respect to maximum continuous current expected. For a 24 Volt 2500 Watt inverter that is 2500 / 24 (some same the minimum cut-off Voltage, which could be as low as 21) * 1.25 * 1.25 sized up to the nearest available, or 200 Amps. Although you can derate CP if you know you will not be using full power it may not be legal to do so depending on the installation. Never use smaller than recommended wire size, just in case.
    The output being 2500 Watts @ 120 VAC and subject to the same NEC calculation gives a fuse rating of 40 Amps. If this is not a hard-wired unit such protection may be impractical to install, or it may already have its own protection built in. Always check the manual.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Need advice on Fuses.....Fuses on DC or AC, or BOTH?

    You don't mention what you have for batteries, or what you have to keep them charged, but you should know that 1000 watts is a very heavy load, somewhat similar to cranking the engine in your vehicle. How long can you crank the engine before the battery dies? Won't be a lot of difference.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Need advice on Fuses.....Fuses on DC or AC, or BOTH?

    Note that the standard North American AC circuit is breakered at 15 amps for 14 awg wire or 20 amps for 12 awg wire (this are the standard household outlets).

    Your Christmas lights draw much less, but are "rated" to plug into 15/20 amp 120 VAC circuits/outlets.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EverlongEverlong Solar Expert Posts: 36 ✭✭
    Re: Need advice on Fuses.....Fuses on DC or AC, or BOTH?

    I have two 100amp 12v batteries, i have an mppt controller and 2 235w 24v sharp panels. This is just a starter project for a cabin that i will build next year on my property. For now i want to see how this is going to work out with LEDs and only two panels. During winter months i will be running these xmas LEDs, and possibly 6 par 16 lights under the soffit. The par 16s have three cree LEDs each, so im guessing around 10w each - not too much draw there.

    As i mentioned this is somewhat a temporary setup. Once this works out, in the summer i will be building a similar setup with 4 of these panels, mppt box, good inverter and 6V cells.

    The batteries that i am using now are automotive store "deep cycle marine" batteries.

    Any idea how much wattage is lets say a string of 100 leds +/- ?
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Need advice on Fuses.....Fuses on DC or AC, or BOTH?

    Note that deep cycle marine batteries are not usually very good for long term use in deep cycle applications (won't have a very long life if deeply cycled).

    There are so many variations in "Christmas Lights", I would not really want to guess what their power usage is...

    My suggestion is a Kill-a-Watt type meter (~$30 or so) for 120 VAC circuits, and a DC Current Clamp meter to measure your DC current/debug problems on the DC side of your power system.

    Note that a 300 watt constant draw for lighting is a lot of power. If you draw your batteries down by 1/4 capacity at night, then they would supply a 300 watt load for:
    • 200 AH * 12 volt battery bank * 0.25 discharge = 600 WH
    • 600 WH battery available power / 300 watts = ~2 hours of use per night (probably a bit less due to losses and other factors)

    Your lighting probably uses less power.

    I have ~21 x 8 watt LED Can fixtures (~168 watts) in my home (just doing some remodeling) [just checked, they are 13.7 watt LED modules so 21*13.7w=288watts total]... And they light up my living room/dinning room/hallway/bathroom like daylight if they are all turned on at once (I have multiple switches so I can just light sections of the rooms).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cruiser guycruiser guy Solar Expert Posts: 87 ✭✭✭✭
    Re: Need advice on Fuses.....Fuses on DC or AC, or BOTH?
    Everlong wrote: »
    Any idea how much wattage is lets say a string of 100 leds +/- ?

    The 100 LED Christmas light string that I have shows on the box as drawing 4.7 watts. These are 230v 50Hz lights purchased in Germany last year. I have not used them yet so no real life data yet. Ask me in a month or two!!

    According to BB's calculation and the wattage draw of my lights they should work for about 127 hours!! on a 600 watt/hour battery bank.


    We have standard 2 watt LED lamps in groups of up to 4 lamps per fixture throughout our house here in Sierra Leone and it works fine. Plenty of light and minimal power. I also have one LED "fluorescent" light that mounts in a standard fluorescent light fixture with the ballast starter and other bits removed and the line voltage to each end. 10 watts and more light than a standard 2' fluorescent tube.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Need advice on Fuses.....Fuses on DC or AC, or BOTH?
    The 100 LED Christmas light string that I have shows on the box as drawing 4.7 watts. These are 230v 50Hz lights purchased in Germany last year. I have not used them yet so no real life data yet. Ask me in a month or two!!

    According to BB's calculation and the wattage draw of my lights they should work for about 127 hours!! on a 600 watt/hour battery bank.

    sure if you want to drain the battery dead. you should not go beyond 50% on a battery's capacity.
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