Paralleling Battery Banks [RE-wrenches]

[Michael Welch]

Hi gang. I have been working with Rick to get him back on the list, but in the meantime he asked me to post the following about his products, relevant to this discussion:

>All of the Solar Boost charge controllers can have battery or PV connected or disconnected at will with no ill effects, with the exception of early SB6024H's. In the SB6024H there is a protection circuit to protect against very high PV voltage being applied to the battery terminals by mistake.
>In early 6024's if the battery is disconnected while the unit is delivering output it is possible (but not assured) that a voltage transient on the battery terminals due to the sudden removal of load may trigger this protection circuit which results in a secret fuse blowing. The protection circuit was modified (PCB Rev E ~6/2004) to prevent this from occurring.
>Even though I believe the problem is fixed we still include a warning sheet in the box to say disconnect PV first. Again this only applies to early SB6024H's, and all other products can have battery or PV connected or disconnected at will.
>
>Richard A. Cullen
>Blue Sky Energy, Inc.
>760-597-1642 x102
>fax 760-597-1731
>rick at blueskyenergyinc.com
>www.blueskyenergyinc.com


Ray Walters wrote at 11:16 AM 01/01/2007:
 
>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?

  
------------------------
        
Michael Welch
Submissions Coordinator
Sr. Research Editor
     Home Power magazine
     www.homepower.com


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