fuses

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: »

Barney,

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.
...
HTH,
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:



http://bluesea.com/category/81/21/productline/overview/378
http://bluesea.com/category/81/22/productline/overview/379

-Bill

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
www.batteryfaq.org

-Bill

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.

-Bill

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.

-Bill