[RE-wrenches] Passive Battery Venting

Fri Oct 31 14:38:09 PDT 2014

.............a heck of a lot easier to water the darn thing.

----- Original Message ----- 
From: "Steve Higgins" <steve at surrette.com>
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Sent: Friday, October 31, 2014 2:07 PM
Subject: Re: [RE-wrenches] Passive Battery Venting

Hey Wrenches.

Looks like this came from Concorde, Allen S posted it in Feb of 2014...  I 
don't know how up to date it is..

It's got some good information about the different gassing rates of VRLA 
batteries.   Most all VRLA's are pretty close to these numbers.

The specific numbers on Surrette AGM is

When the battery is float charged at 2.3V/cell, the amount of the gas 
generated will be approx. 0.0187 cc/hr/AH/cell.  When the battery is charged 
above 2.4V/cell, the amount of the gas generated will be approx. 0.0366 
cc/hr/AH/cell.

Since I've been a Surrette, most of the inspectors I've talked with don't 
worry about the normal operation of the battery bank, they worry about if 
something goes wrong with the batteries, or the chargers.  They tend to like 
things to be designed so that their rear ends aren't in a sling if things go 
wrong. So to make them happy, it can be a good idea to design to when things 
fail, also adding a hydrogen detector sometimes will pacify them.

The issue I hear most is without moving the air out when there is too much 
Hydrogen, is if you have a loose connection, or it's in the same room as the 
inverter/controller and there is a spark/ignition source things tend to go 
"bang" and most people don't like that.

In most cases this will cause the top of the battery to blow off.

Steve Higgins
Technical Services Manager
P: +1.902.597.4020
M: +1.206.790.5840
F: +1.902.597.8447
Surrette Battery Company
Exclusive manufacturer of

-----Original Message-----
From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On 
Behalf Of William Miller
Sent: Friday, October 31, 2014 1:44 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Passive Battery Venting

You would smell it.

Miller Solar

> On Oct 31, 2014, at 1:20 PM, Phil Forest <pforest at southmountain.com> 
> wrote:
>
> Drake,
> Please explain what might happen if something went wrong with one battery, 
> when they are not vented to outside. How would we know it?  Thank you.
>
> Phil Forest
> South Mountain Company
>
>> On Oct 31, 2014, at 8:42 AM, Drake <drake.chamberlin at redwoodalliance.org> 
>> wrote:
>>
>> One big advantage of not venting AGM batteries to the outside is that 
>> when something goes wrong you will know it. A well vented system could 
>> have one bad battery ruin the entire pack before the problem was 
>> detected.
>>
>>
>> At 08:12 AM 10/30/2014, you wrote:
>>
>>> To do it totally passive you will need a long (tall) pipe up the
>>> side of the building, probably painted a dark color to have the sun
>>> help warm the tube to help encourage it to vent up, not draw into
>>> the building. Put a 180 on the top to keep the rain out and a screen to 
>>> keep out the bugs.
>>>
>>> With outside venting the batteries will just draw in room
>>> temperature air, if the room is 70 the battery min temp will be 70.
>>> If they are in a basement they will naturally draw in outside air,
>>> run the vent as high as you can to help prevent that. If you are
>>> using a Classic use the relay to turn the fan on and off at a
>>> specific battery voltage. Use a brushless fan and a voltage powered 
>>> relay if no other choice. Do not put the relay in the battery box!
>>> Sealed batteries do need to be vented. I have seen them gas when
>>> things go wrong, not pleasant.
>>>
>>> I wouldn't do it without a fan for LA batteries but it would work
>>> for sealed. If the home has a makeup air system or huge exhaust
>>> system all bets are off.
>>>
>>> Just some thoughts,
>>>
>>> Bob Ellison
>>>
>>> -----Original Message-----
>>> From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org]
>>> On Behalf Of Drake
>>> Sent: Wednesday, October 29, 2014 8:19 PM
>>> To: RE-wrenches
>>> Subject: Re: [RE-wrenches] Passive Battery Venting
>>>
>>> Hi Daniel,
>>>
>>> I typically vent them the way you do, which will allow any small
>>> amount of hydrogen out. The customer is absolutely adamant about
>>> venting these to the outside. I will cooperate so long as his method
>>> doesn't compromise the system through cooling the batteries 
>>> unnecessarily in the dead of winter.
>>>
>>> He is a lawyer and came to the conclusion of the need for venting to
>>> the outside from reading the NEC which says that sealed batteries
>>> "require the same amount of ventilation" as liquid lead acid
>>> batteries. The code also says to vent appropriate to battery
>>> technology, so the code says two conflicting things. On the other
>>> hand, it doesn't say that liquid electrolyte batteries need to be
>>> vented to the outside. They will sure stink if you vent them to the 
>>> inside.
>>>
>>> Drake
>>>
>>> At 09:54 AM 10/29/2014, you wrote:
>>>> I just re-read the original post Drake. These are AGM batteries. Do
>>>> you
>>> have
>>>> a "belt, suspenders,...then a rocket pack" type of client here?
>>>>
>>>> We typically vent our AGM boxes with small louver vents top and
>>>> bottom to allow the batteries to ventilate for cooling purposes, not H2 
>>>> concerns.
>>>>
>>>> With Regards,
>>>>
>>>> Daniel Young,
>>>> NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90
>>>> NABCEP Certified Solar Heating InstallerTM: Cert #SH031409-13
>>>>
>>>> -----Original Message-----
>>>> From: RE-wrenches
>>>> [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Ray
>>>> Walters
>>>> Sent: Tuesday, October 28, 2014 11:12 PM
>>>> To: RE-wrenches
>>>> Subject: Re: [RE-wrenches] Passive Battery Venting
>>>>
>>>> That's why we usually have the batteries in a garage, basement, or
>>>> out building that is not open to the living space.
>>>> I've seen some cases of very well sealed and insulated enclosures
>>>> allowing batteries to over heat, and also build up a lot of acid
>>>> damaged
>>> connections.
>>>> Boxes I've seen with more air space and less sealing don't get this
>>>> build up, but you're correct: they do occasionally allow H2S into
>>>> the surrounding area.
>>>>
>>>> R.Ray Walters
>>>> CTO, Solarray, Inc
>>>> Nabcep Certified PV Installer,
>>>> Licensed Master Electrician
>>>> Solar Design Engineer
>>>> 303 505-8760
>>>>
>>>>> On 10/28/2014 8:10 PM, Jerry Shafer wrote:
>>>>>
>>>>> We do what we can to seal the enclosure so if or when a battery
>>>>> fails and really gasses off the two vents on the same wall
>>>>> regardless of wind direction will vent the gas. If it is not
>>>>> sealed then the gas can travel through out the area this is not 
>>>>> advised.
>>>>
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