[RE-wrenches] Fuse sizing in battery circuits

boB boB at midnitesolar.com
Tue Apr 9 21:14:54 PDT 2013


After 100's of thousands of  inverters having been shipped in the last 
many years
and thousands of inverters broken and shorting the battery terminals, 
there has
never been (to our knowledge) one breaker that has not tripped.

The Midnite site lists the AIC rating of all our breakers I believe.

The Carling F series of Magnetic-Hydraulic breakers poop sheet is here...

http://www.carlingtech.com/sites/default/files/documents/F-Series_Details_%26_COS_0.pdf

I guess there isn't a graph of AIC vs. voltage on their F series web 
page but we remember
them showing us figures or a graph that says those breakers have an AIC 
of more than
100,000 amps at 48 volts.  We'll try to find that info or you may be 
able to get that
from Carling.

I have, many times, directly connected these breakers across good L-16 
battery strings
to demonstrate the left-hand rule to people where the 4/0 cable jumps 
apart or towards each
other when very high current passes through those wires when they are 
near each other.

It always trips.  Never tried it at anything above a 48V battery banks IIRC.

Robin would like to mention that anyone that wants to use T-Classc 
fuses.... Welcome back to the 1990's

boB


On 4/9/2013 1:23 PM, Ray Walters wrote:
> Hey Bob;
>
> Can you share that AIC vs Voltage chart?
>
> Thanks,
> R.Ray Walters
> CTO, Solarray, Inc
> Nabcep Certified PV Installer,
> Licensed Master Electrician
> Solar Design Engineer
> 303 505-8760
> On 4/9/2013 1:46 PM, boB wrote:
>>
>> 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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