[RE-wrenches] To insulate a battery bank -- sort of

Sun Dec 12 10:59:04 PST 2010

First of all, there is no one solution to battery selection, installation, operation, and maintenance. One size does not fit all. Allan and other wrenches with lots of battery experience have a good understanding about batteries in their regions for their customers.

Second, insulation is used to control temperature change. Insulation slows both heat loss and gain. Large battery banks tend to change temperature slowly due to their mass and may not need insulation in your region or in a specific installation. The goal is to keep the battery bank at its optimum temperature. Cold batteries have reduced capacity. 40 F (4.4 C) is too cold for almost all RE system batteries. Hot batteries have shorter lives. Heat affects both battery chemistry and materials. For example, the plastic around Absolyte terminals cracks if their temperature is repeatedly 90 F (32.2 C) which can happen in an uninsulated battery area in the southwest U.S. So too hot or too cold is not good.

Third, batteries need ventilation to safely remove hydrogen. Surprisingly, what most people consider a small amount of battery ventilation will suffice unless the battery bank is being charged excessively. For example, a PV system with eight 100 watt modules (rated 17.1 V, 5.88 A) and sixteen 6-volt batteries is wired for 24 volts DC. The required venting is 0.0135 x (5.88 x 4) x 12 = 3.81 CFM or 228.6 cubic feet per hour. Many, if not most, rooms are 8 feet in height with 2 air changes per hour. A room 8’ x 6’ x 6’ has 288 cubic feet volume and naturally vents 576 cubic feet per hour, almost 2.5 times the required 288.6 cubic feet per hour.

In general, a battery area, room, box, etc. should be kept at 70 F (21.1 C), have good ventilation, no open flames (heater, gas water heater nearby?), no electrical sparks (automatic igniters, etc.?), easy to maintain and inspect, tidy, out of reach of non-authorized personnel, and have an up-to-date fire extinguisher handy.

Batteries operate by electro-chemical process almost like living things. If they are too hot or too cold, they perform poorly and can die. If they are not fed properly (charged correctly), they will die. Interestingly, we use expressions like "die" and "end of life" to describe these non-living things. Most wrenches know people who party all weekend, don't eat well, forget to dress properly for the weather, and get sick. Likewise, if a battery bank is deeply discharged, not properly recharged, and too hot or too cold, it will perform poorly and die prematurely. You get the picture.

Lastly, we have learned a lot about batteries in the 200 year since physicist, Allessandro Volta, developed the first cells. Unfortunately, a lot of battery myths exist. Explode myths (but not batteries) by asking the "5 whys". See http://en.wikipedia.org/wiki/5_Whys

Joel Davidson
  ----- Original Message ----- 
  From: dan at foxfire-energy.com 
  To: RE-wrenches 
  Sent: Saturday, December 11, 2010 5:32 PM
  Subject: Re: [RE-wrenches] To insulate a battery bank -- sort of

  Ok, I'm a little reluctant to kick this critter much.. because I feel like I must be missing something here... but let me float this notion.. If we stuff flammable gas producing batteries in an enclosure (and proceed to button them up tighter than a bull's ass in fly season -- fan or no fan), Haven't we just created a Class I Division 1 location? (NEC 500.5).  then say we do rely on a $4. fan (OK -- $15.) to declassify as allowed in 500.5(A)fpn,  Wouldn't we still have a Class I Division 2 location? NEC 500.5(B)(2)(2)/(3). So my point is -- are fully enclosed battery boxes really worth the hassle? are they even A good idea? I can't seem to find where NFPA 70 "Requires" a battery enclosure.. 690 VIII  says you need to protect electrical connections (in dwellings) and kicks you back to 480, but makes no mention of "requiring" a battery enclosure.. 480.8 says basically that if you use racks or trays, they've got to hold up. 480.9 outlines ventilation and working space, but again doesn't "require" enclosures. (480.6 deals with Insulation of batteries.. But I'm thinking they're talking about electrical insulation)... But nowhere in the NEC have I found any mention of battery boxes or Enclosures being "Required"..  On the contrary, Seems to me they're suggesting that if by design you can provide for proper work space, adequate ventilation (both out and in) and protect the electrical connections, you're good as far as NEC is concerned.. In NFPA 70E, (Workplace Safety) 320.4 says batteries should be under lock and key (or require a tool for access), and that they be protected both physically and electrically.  also in NFPA 70E, 320.6 kicks around enclosure requirements some, but seems to focus more on protecting terminals and related equipment..  Now in OSHA 1926 (Subpart K), .441 seems to be where "required enclosures" originates, but again, it seems to be referring to commercial workplace safety... (i.e. also requires that "the charging apparatus be protected from damage by trucks" and "eye wash stations be provided within 25 feet" etc.).. I'll will tell you the majority of the failed / scummed out battery banks I've dealt with have been from poor ventilation, poor maintenance or defective / improperly designed or installed battery boxes.. If I can, one of the first remedy's I apply is to drill several large holes (and staple some kind of critter proofing over the holes from the inside). -or- if I can gracefully, I'll remove the sides altogether -- as long as the electrical connections are protected. also if I can, I try to find a way to route exhaust gases so they vent naturally -- so they don't rely solely on a vent fan... like maybe run 2" PVC up thru the roof -- inside the envelope of the house. at least try to make sure the fan is not competing with the furnace or exhaust systems... (like insure there's an adequate intake air supply for the whole house)...  as for protecting batteries from fluctuating temps.. the planet (some three feet down anyway) stays just over 48 degrees.. at least in these parts.. Just saying.. db

  Dan Brown
  Foxfire Energy Corp.
  Renewable Energy Systems
  (802)-483-2564
  www.Foxfire-Energy.com
  NABCEP #092907-44

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