[RE-wrenches] Fuse sizing in battery circuits

[boB]

Those 250 amp and 175 amp breakers we have used for many many years now
have an AIC of 50,000 amps at 125 volts and if you look at the curve, at 
48 volts
they are around 100,000 amps.  I think that this information is on the label
of the breaker.

How many problems have you had with the Carlings or any other type of
those large breakers ?

boB


On 4/9/2013 10:40 AM, Michael Welch wrote:
> If anyone would like an Acrobat version of this article, you can find 
> it here:
>
> ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdf
>
> <ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdf>William Dorsett 
> wrote at 07:00 AM 4/9/2013:
>
>> This topic comes up often enough that we ought to mention a yellowed 
>> article in Home Power, (1992 Issue 27, pg 26). Christopher Freitas 
>> wrote /Overcurrent Protection for Battery-Powered Systems /where he 
>> describes experiments he did back when he was with Ananda. He put a 
>> 2000 A Big Switch to initiate a short (4/0 cable) between the 
>> terminals on a set of four golf cart batteries (2 strings @ 12V). In 
>> series, he put in a 500A Shunt so he could measure current passing 
>> and various fuses and breakers. "For comparison, we decided to 
>> directly short the battery...the meter read 6960 amps peak current 
>> (three seconds) ...during each test the 4/0 cable lifted off the 
>> ground 4 inches into the air by the forces generated by the extremely 
>> high current.." They videoed the 250 A ANN buss fuses arc and smoke; 
>> the 200A Heinemann Series AM breakers (paralleled ones that maybe Roy 
>> mentioned) went 3 seconds without breaking and the video showed a 
>> flash and blue smoke.
>> 175A ITE breaker with 42,000 AIC "simply tripped...but still allowed 
>> a peak current of 2960 amps
>> 200A Class T Littlefuse "opened promptly with no external signs of 
>> stress...1920 amps peak current"
>> Christopher's recommendations:
>> "Every AE system must have overcurrent protection able to interrupt 
>> the maximum current available from the batteries. For most systems, 
>> the main protection should use current limiting high AIC fuses, such 
>> as a Class T or Class R. A disconnect switch which allows the fuse to 
>> be safely changed should be included. A lower cost alternative is to 
>> mount the fuse in a fuse holder without a disconnect. Although the 
>> fuse would always be electrically hot,  it normally would not be 
>> changed during the life of the system. The fuse holder should be 
>> mounted outside the battery enclosure. Fuses should not be bolted 
>> directly onto the battery terminal, as they are not designed to 
>> handle the physical stresses that can occur without the protection of 
>> a fuse holder.
>>
>> Fuses which have exposed elements, such as ANN fuses, should not be 
>> used because they are not current limiting and have only 2500 amps 
>> AIC. They also may be a significant hazard when installed near 
>> batteries.
>>
>> High AIC breakers, like the Heinemann Series CF (25,000 Amps AIC @ 
>> 65VDC) can provide overcurrent protection for individual items. They 
>> cannot be used to protect lower AIC breakers. This eliminates their 
>> use as a main disconnect in most systems.
>>
>> Low AIC breakers, like the Heinemann Series AM (5000A AIC @65 VDC) or 
>> the Square-D QO (5000A @ 125 VDC) can be used in load distribution 
>> centers and components, but must be protected by a current limiting 
>> fuse. Using low-AIC breakers alone will not provide sufficient 
>> protection with a battery system and may be a significant hazard 
>> during short circuit situations."
>>
>> It won't pull up anymore on HP's article search but probably Michael 
>> has a copy he could post for those interested./
>> /
>> Bill  Dorsett
>
>

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