Re: Battery Boxes...What One Company Designed

[ddl@danlan.*com (Dan Lanciani)]

In article <7qcti1pqcg7enml3oijr9jtvao4rb0984f@xxxxxxx>, MFHult@xxxxxxxxxxxxxxxxxxxxx (Marc F Hult) writes:

[this is getting long, so big snip...]

| I wrote:

| >Perhaps.  However, I just looked at the hookup instructions and it appears
| >that the outputs are directly paralleled with the battery bank, i.e., whatever
| >over-current protection the devices offer does not actually protect the load
| >side.  That suggests that no matter the listing the output is going to have to
| >be treated like the output of any other battery bank which can deliver very
| >high current, requiring, e.g., (expensive) class T fuses.  And of course, the
| >wiring at that point isn't even class 1.  (I used to think that it could be
| >class 1 subpar (b) which goes to 600V with no power limitations, but that's
| >for signaling/control only...)
|
| Yes. See the ASCII circuit diagram in my previous post and at the end of this
| one. which I think makes this clear. Over-current protection is included.

Yes, you were clear.  I was confused by the description on the manufacturer's
site.  With all the talk of sophisticated over-current detection I thought the
supply had to interpose some electronics between the battery string and the
output.  I guess the protection is just for the wires to the battery. :(  In
case you care, I'm pretty sure that there do exist supplies that work the way
I thought these work.

| Where do I find out about class T fuses ?

A Google search seems to turn up quite a few hits.  One thing I noticed is
that they aren't as absurdly expensive as I remembered...

| Searching the 2005 draft NEC came up
| blank. Why do I need them?

To be honest, I'm not sure you do.  This came up some years ago when I
added a remote battery string to a UPS.  To my annoyance I found that while
inexpensive 100A automotive fuses could be used for similar applications in
cars, boats, mobile homes, and even internally to said UPS and its packaged
expansion batteries, I had to use a class T fuse because I was running the
circuit in a building.  This might have been a local issue and/or I might have
overreacted to some of the requirements.  After getting the correct fuse I sort
of stopped looking for additional problems because, well, the box I was using
wasn't a listed battery enclosure and the UPS wasn't actually listed for
connection to anything but their packaged expansion batteries (though at least
the string I used fell within the allowable range of capacities) and so on... :)

| Plain old Square D QO circuit  breakers are UL'd to
| 60vdc.

As I recall, a circuit breaker with the required DC arc interrupting capacity
(20kA?) and response time was even more expensive than the fuses.  But since
a lot of this is listing politics rather than genuine engineering it's
certainly possible that a commodity device would have been acceptable and
I just missed it.

| >If they have added a genuine class 2 supply requirement
| >I would think that many of the existing landscape lighting transformers are
| >now out of spec since even the multi-output ones typically exceeded 100VA on
| >each output.  It may be that there is now a specific (and different) type
| >of class 2 listing for such supplies that makes this all work out.  There
| >is an unfortunate trend in this respect to make listings extremely application-
| >specific, thus thwarting non-standard or unanticipated custom assemblies.
|
| Right. ABIK, it has changed and become more restrictive/ less useful. That was
| my point.
|
| Outdoor wiring low-voltage wiring was separated in the 2002(?). I haven't
| pursued what the draft 2005 has to say. but I didn't stumble across anything
| that clarified how to get from one t'other or made life easier.

I just checked the Juno Flex 12 system for which I happen to have a catalog.
It's one of those exposed-conductor indoor low-voltage track systems.  The
transformers go to 600VA per circuit, so I think even indoor systems are
going to have a problem with a class 2 supply requirement.  Unless those
were never under 411 to begin with (like your tracks?).

| >Here's the problem I had when I looked at the whole low-voltage DC distribution
| >idea a while back.  Whether you classify your circuits under 720 or 725's
| >class 1 you still have to use the same Chapter 3 materials and methods that
| >you would use for line voltage circuits.  Plus you have to keep the two
| >(or maybe all three) separate.  Plus you have to deal with non-standard
| >(and thus more expensive) ancillary components like DC-rated switches and
| >fuses.  Plus you have the inherent loss disadvantages of low voltage.  As
| >far as I can tell, the only thing you gain under class 1 is the ability to
| >use No. 16 and 18 conductors, not that I'd want to.  Am I missing something?
| >
|
| Yes and maybe not :-)
|
| Yes, from the perspective that you are analyzing the benefits as if the
| installation is something to be commercialized -- which it is not.

I was really trying to frame some simpler questions.  What is it that you
are allowed to do by remaining < 30V that you would not be allowed to do if
you used, say, 48V?  Similarly for using DC instead of AC.

| Yes, from social reality that in a system with multiple, distributed components
| that require electrical power, the conventional approach of providing that
| energy with Class 2 wallwarts quickly becomes untenable. Spousal factor -- the
| answer to "Can I put three _more_ wall warts over here so that the open-close
| and tilt drapery motors and the controller can be powered?"  is "No".  So what
| to do ? One part of the answer is distributed DC power in my case.

Don't the DC/DC converters take up about as much space as the wall warts
they replace?  Or do you have enough consumer devices that require neither
voltage conversion nor isolation nor class 2 current limitation that you come
out ahead?

				Dan Lanciani
				ddl@danlan.*com