wildbillwildbill Registered Users Posts: 5

opinions on comparing anl type fuses to class t type fuses for a 3000w inverter with peak @ 5000w



  • BB.BB. Super Moderators, Administrators Posts: 30,184 admin
    Re: fuses

    Fuses have two different ratings that people frequently overlook and which are sometimes buried in the original technical documents.

    First is working voltage... Typically, as fuses get larger (and are DC rated), their rated interrupt voltage falls... You might find a "small" fuse rated to 120 VDC, but the high current version of the same fuse rated at 32 VDC.

    Second is maximum interrupt current... Basically the maximum current the fuse/breaker can withstand a "dead short"... Lead Acid batteries can output 1,000's to 10,000's of amperes into a dead short--You want to make sure your fuse/breaker has a chance of interrupting that current flow instead of becoming a huge arc in its own right.

    Here is a nice post from Jim years ago that talks about the details and has a couple of links:
    crewzer wrote: »

    OK… I think I see what’s going on here. In short, a 250 A ANL fuse with the right AIC spec should work for you.

    The 250 A fuse rating looks OK to me. Assuming full power (1750 W), minimum battery operating voltage (10.0 V), and the low end of Xantrex’ efficiency range spec (85%), the inverter will draw 1750 W / (10 V x 85%) = 206 A from the battery bank. Applying the typical 80% derating factor (or 125% multiplier), the fuse should be rated at 206 A / 80% = 258 A. A fuse rated at 250 A is probably “close enough”.

    I suspect that Xantrex’ discussion about CCA specs and fuse AIC is derived from ABYC standards. The basic issue is that the fuse (or circuit breaker) must not only be able to open at its nominal rating, but it must do under extreme current conditions and open wide enough (fuse) or nor suffer internal damage (fuse block or inside of DC breaker) so that the device remains “open”. Blue Seas and Home Power magazine have further discussions on this issue.

    See: http://bluesea.com/viewresource/98
    and: http://www.homepower.com/article/?file=HP101_pg128_Letters_3

    So, what’s your proposed battery bank’s CCA? I agree that such specs for golf cart batteries appear to be impossible to find. But, we might be able to develop a reasonable cross-reference.

    Specifically, the Trojan SCS200 deep cycle battery is rated for 12 V x 115 Ah. Its CCA spec is 620. A pair of these batteries wired in parallel would be rated at 12 V x 230 Ah, with a combined CCA spec of 1240.

    A series-pair of Trojan T-105’s are rated for 12 V x 225 Ah – pretty close to the parallel-pair of SCS 200’s described above. So, let’s assume the series-pair of T-105’s would also have a CCA spec of ~1240. Continuing on with this model, a series-parallel combination of four T-105’s (12 V x 450 Ah) might have a CCA spec of ~2480.

    The ABYC table in Xantrex’ manual indicates that a fuse (and fuse block) rated at 5000 AIC is required for a battery bank of this specification. Blue Seas’ ANL fuses and fuse block are rated at 6000 AIC, so they should do the trick for you.

    See: http://bluesea.com/category/5/22/productline/overview/135
    And: http://bluesea.com/category/5/21/productline/129

    Finally, Nigel’s recommendation to use heavy cable is well founded. The manual recommends 1 AWG cable for runs up to five feet, which is pretty short. 2/0 would probably be a better choice, and the Blue Seas fuse block can handle cable and lugs of that size.
    Jim / crewzer

    So, we would, at the very least, need to know the working voltage of your inverter to insure that you find the correctly rated fuse/breaker.

    Finally, you need to also look at the mounting of the fuses/breakers... One of the neatest (small/easy to use) I have seen are these:


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: fuses
    wildbill wrote: »

    opinions on comparing anl type fuses to class t type fuses for a 3000w inverter with peak @ 5000w


    Welcome to the forum.

    It is said that confusion reigns supreme. We try to over-throw the dictator! :p

    There's information missing from your question. Namely the system Voltage. That will make a difference in what current is being drawn at the peak Wattage, which will (along with distance) determine the appropriate wire size and that in turn the fuse size.

    For example: 5kW @ 48 Volts = 104 Amps. 5kW @ 24 Volts = 208 Amps. 5kW @ 12 Volts = 416 Amps. What's worse is that the calculations should be based on peak output at minimum input Voltage to determine the maximum current potential. A 3kw inverter on 12 Volts is a very bad idea for this reason.

    Standard inverter fuses: http://www.solar-electric.com/infubr.html

    Fuses types: ANL and AGU. ANL is used for inverters. Class T is a case style.
  • wildbillwildbill Registered Users Posts: 5
    Re: fuses

    Ah ha !
    so much for impulse buying . . .
    got a deal on a 12v, 3k inverter

    The distance is < 4 feet, and I'm using dual cables to the dual conections on the inverter.
    My idea was to use 0 cables and run both cables thru one fuse. (?)
    An anl 400 amp was one recommendation or a 350 amp class T was another.
    This is for a small mountain retreat and the cost difference between them is significant.
    However, the cheaper one, anl, needs to be safe.
    I thought that it might, in fact, be safer since there is no delay as there is with the more expensive class t fuse.

    I was told that this was a good forum but my friend was wrong - it's excellent.
    I haven't had time to read all the references yet but certainly will do soonest.

    Thank you and cheers
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: fuses

    Oh no. AIMS inverter alert! :p (Guessing.)

    When you run parallel wires on the DC supply to this turkey inverter, you must be sure each wire has its own fuse. Yes, it will probably say the inverter has built-in circuit protections. If it does, find out how much. You want external fuses blowing first because changing ones inside the inverter is a pain in the anatomy.

    12 Volt inverters often have a 10.5 Volt low-Voltage shut down. That's near enough to 500 Amps current at surge Wattage that it isn't even funny. That's a couple of runs of 0 gauge at least and 300 Amp fuses each.

    Easier work-around is to limit your loads to something a 12 Volt system is actually capable of handling. Say 1 kW with a 2 kW surge. If you can shut down at 12 Volts or 11.5 Volts even better. There you're looking at a peak of 175 Amps, which can be handled by one set of cables. If you use one of these 150 Amp breakers http://www.solar-electric.com/mr60ampdccib.html then any over-current will trip that instead of frying wires or multiple parallel connectors.
  • BB.BB. Super Moderators, Administrators Posts: 30,184 admin
    Re: fuses

    I don't know how big your battery bank is or how much solar/genset charging you have... A problem with "big" inverters is that they have fairly high "idling current"--Yours may be 20 watts or more--just sitting there 24x7 with now load--and for many small cabin power systems, that can be >50% of your daily system capacity (battery+solar).

    I would suggest that you look at the MorningStar 300 watts 12 volt TSW inverter. It is pretty efficient and has several features that you rarely find on small AC inverters... From what others have said, it is built like a tank and larger than the picture would suggest.

    Besides being a True Sine Wave inverter, it has both a remote on/off switch (just a simple 12 volt signal) and a "search mode" (uses very low power on standby, pulsing the AC line ~1 per second looking for >6 watt loads).

    And for measuring your AC loads (Watt*Hours/kWH)--A Kill-a-Watt type meter is very handy (and cheap).

    For many people they can run most of their small loads on this one inverter (some lighting, radio, laptop, cell phone/battery chargers, etc.).

    And you can use the "big guy" to run your hand tools when needed.

    A couple of important FAQ's to read:

    All About Inverters
    Choosing an inverter for water pumping
    Deep Cycle Battery FAQ

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wildbillwildbill Registered Users Posts: 5
    Re: fuses

    Well guys - thanks a bunch !
    I think that I have some things figured out, at least for the time being.
    An anl fuse block with an AIC of 6000 should work safely with the 4 x 6 volt gc batteries that I have.
    I just hope that the 400 amp fuse is sufficient for my 6 amp water pump, if not I feel comfortable going to a higher amped fuse, or I might get 2 smaller, 250amp fuses in parallel.
    I was told initially that 2 fuses in parallel would not work.
    You confirmed my intention to use parallel 0 cables.
    I'll run both of them through the one fuse, at least initially.
    I'll use the big inverter for my 6 amp water pump, the freezer (the hotter the day, the colder the beer) and various tools and get a smaller, pure sine wave inverter for the cabin.
    Thank you again so much.
    Happy trails
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: fuses

    This "6 Amp" water pump. 120 VAC or 240 VAC? At 120 it's a tiny 720 Watts running. At 240, it's a significant 1440 Watts running. Then there's the start surge, which will be much higher than that. Five times higher, perhaps. What's worse; it's a water pump. It starts and runs against a significant load. You may find it actually draws more than 6 Amps running and the start-up is tremendous.

    Even if the inverter could technically handle it on a Volt * Amp basis, the battery bank may "collapse" (electrically, not physically) when asked to supply so much power all at once. A 12 Volt system will be hard-pressed to power this.
  • wildbillwildbill Registered Users Posts: 5
    Re: fuses

    It is 115v booster pump on a gravity feed.
    I was told the initial draw should be under 15a.
  • BB.BB. Super Moderators, Administrators Posts: 30,184 admin
    Re: fuses

    To show a little math on the project:
    • 115 watts * 15 amps * 0.6 Power Factor (guessing) = 1,035 watts surge
    For a 12 volt battery bank, assuming 85% efficient inverter and 10.5 volts cutoff:
    • 1,035 watts * 1/0.85 inv eff * 1/10.5 inv cutoff = 116 amp surge (12 volt bank)
    A good working number for the maximum surge reliably supported by a flooded cell battery bank is C/2.5 or C*0.4:
    • 116 amps * 2.5 surge derating = 290 AH battery bank minimum
    Your batteries are probably around 220 AH and a bit on the small side (with all of my guesswork above).

    Have you looked at 12 volt DC booster pumps instead? Usually much more efficient (typically less than 10 amps @ 12 VDC) and will last 3-5 years or so on clean water with usual household usage.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wildbillwildbill Registered Users Posts: 5
    Re: fuses

    You are correct about the batteries, 220ah each, except that I have 4 of them.
    I'm expecting ~440ah. No?
    I considered a dc pump.
    Even tried one but the distance from the solar setup to the pump house is too far for dc.

    I appreciate that you took the time to go through the math.
    Thank you very much.
    Happy trails
    Bill (2)
  • BB.BB. Super Moderators, Administrators Posts: 30,184 admin
    Re: fuses

    Sorry, I missed the 4x6v in your earlier post.

    Yes, sending power any distance--You almost have to use 120 VAC or higher. 12 and 24 DC just does not cut it.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.