Paralleling Battery Banks [RE-wrenches]

[Ray Walters]

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I noticed this in many "code" systems. Some controllers like the RV-50 
from Blue Sky can actually be damaged if the batteries are disconnected 
before the array current is removed. I believe they've fixed this issue 
now. I've also noticed that if the inverter load is close to array 
output, that the inverter can continue to run array direct. Its funny to 
pull the main battery disconnect, and still have everything on. Some day 
maybe we'll have an automated disconnect system, that will disconnect 
charging sources first and then the batteries. Until then, we can label 
away, but my customers don't seem to actually read all those labels we 
stick on everything.

I'm working on an electric vehicle with 4 parallel strings of batteries. 
I'm adding all copper interconnect resistances up to balance the bank (I 
had to add 5 ft of #4 to one string for instance) The problem is that I 
don't know where to put the fuses. A fuse at each battery positive would 
protect the sometimes long runs under the vehicle, but the other 3 
strings could back feed a potentially dangerous short without blowing 
their fuses. So, do I put fuses on both ends of each cable, or just live 
with the problem, as we do with most solar systems, where the main 
battery cables are unprotected all the way into the DC load center. 
Personally I would like to see batteries with integral fuses to protect 
any short, even the classic "dropping a wrench across the terminals" 
move. My kids' Barbie Jeep had sealed batteries with an ATC  fuse that 
plugged right into the top of battery.
We go crazy protecting systems from sometimes very improbable dangers, 
while blindly ignoring the most dangerous source of fault current that 
I'm sure all of us dealing with batteries have experienced personally.

Anyone smell something burning?

Ray Walters

 William Miller wrote:

>
> Hugh:
>
> This is a very significant point you have raised.  In the past I might 
> have been a bit cavalier about opening battery breakers, but no more!  
> I have drafted a warning sign that will remain in memory in my label 
> printer.
>
> I always find something illuminating in your posts.  Thank you.
>
> William Miller
>
>
> At 12:02 AM 12/31/2006, you wrote:
>
>> Take care that pulling a fuse will not leave the charging sources 
>> connected to the inverter and controls without any battery.  I would 
>> use a separate fuse(s) for any charging sources, so that this is not 
>> possible.  A wind or hydro turbine that shares a fuse with the 
>> inverter can be a source of dangerously high voltage if the fuse is 
>> pulled.  Charge controllers may or may not be able to deal with the 
>> turbine output in the absence of batteries.  I am not sure about PV 
>> but I would imagine that the same problem would arise to a lesser 
>> extent (lower open circuit voltage).
>>
>> I guess if you put a separate inverter fuse on each battery string, 
>> then you need multiple fuses for the charging sources as well.  Or 
>> else place a conspicuous sign indicating the dangers of pulling out 
>> all the battery fuses.
>> -- 
>> Hugh
>>
>> Scoraig Wind Electric
>


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