60 amp 12 volt fuse = 150 amp 32 volt fuse? Roughly?

Trying to confirm this equation a bit. #MyDodgyMath
First Bank:16 180 watt Grape Solar with FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
Comments
Keep in mind that fuses need to be sized for the smallest wire size in the circuit that it is protecting, so if you have a piece of #12 feeding into a box and coming out with #14 the correct fuse size is 15 amps for the #14 not 20 for the #12. There are exceptions for 120 vac plugin devices with limited cords, like lamps that are wired with #16 and even #18 wire. That said, the classic fire situation is a lamp cord coiled up under a rug, so it runs warm. Branch circuit fused with 20 amps, but the warm wire keep heating up with the load and lights itself on fire. Old fashioned standing lamps may have had 3 or 4 hundred watt bulbs around the perimeter with one large 150 watt bulb in the centre, drawing maybe 5 amps from 110 vac, add the light weight lamp cord, a bit of resistance in the connectors, and pile a rug on it an voila...fire!
Tony
Now - they mostly seem too large for almost any realistic application. It is also harder to find them in less than 100 amp sizes. Here is an example: https://www.ebay.com/itm/Blue-Sea-5105-MEGA-AMG-Fuse-200AMP/352795910688?epid=1000083973&hash=item5224466220:g:JyMAAOSwTW1dg8Mq
I'd hazard a guess that 200 amps is the average size.
Then again - I suspect most cautionary purchases fail to pan out. Though we may never know if such a purchase silently saved the day.
Proper prepping is almost unlimited in potential expenses. Especially considering that a thorough prepper must consider a couple dozen different disaster scenarios. Which lead me to the conclusion that I can give 50 reasons to prep and 100 reasons not to. But if one if ideally situated for prepping - then why not? I guess.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
The fuse blows from HEAT = I^2 x R, over a period TIME.
From an overload point of view, the fuse has no idea what Voltage is across the load.
The fuse could care less about the voltage, until it is time to break the current flow and extinguish the arc.
You should never use a fuse in circuit that exceeds the Voltage rating or the Amp rating of the fuse.
Typically, a 40 amp fuse should never blow with only 38 amps flowing.
In fact, a 40 amp fuse should never blow at 40 amps either.
Where did you get 20 seconds?
On average, it take about 16 Minutes to blow a 40 amp automotive fuse with a whopping 50 amps flowing.
A 40 amp fuse is not designed to blow at 40 amps,
it is designed to allow 40 amps to flow,
and at some amperage above 40 amps, with enough time, it will eventually blow.
This is called the i2t time-current characteristic of the fuse.
a) The voltage rating of the fuse must never be exceeded.
b) The amperage rating of the fuse must never be exceeded.
Suggestion otherwise is very bad engineering.
Both the voltage rating and the amperage rating of a fuse, is important when trying to break a DC arc, even at 12 volts.
The AC and DC rating voltages for a fuse are there to ensure that an Arc will not be sustained if a fuse (or breaker) pops. "Arc Flash" (basically explosive arcs in higher voltage/higher current situations that releases heat in the ~30,000F+ and hard UV radiation for AC voltages at ~400 VAC and above???).
And there is the current a fuse will pop (which is a current vs time--High current, the faster a fuse will pop). And the minimum current at which a fuse will not open (I use 80% of rating for "typical" devices--Although, there are different rating methods for different products).
The AIC Amp Interrupt Current is the maximum current from the "supply" -- If you exceed that source current, then the fuse/breaker cannot manage that energy and will self destruct/sustain an arc/etc.
This link has (probably) more than you would ever want to know about fuses/breakers/overcurrent protective devices:
https://forum.solar-electric.com/discussion/353232/oversized-wire-and-breaker
-Bill
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,