Another set of batteries failed, almost catastrophically

[Bughunter]

I was thinking a bit differently but I see the point here. Fusing
between the series pairs would drop those batteries out if the fuse
popped. Is this correct?

Yes, if fuse 1 popped, String A would be disconnected from String B and the
load.
String B would still be supplying 12v to the load, same current, but at half
storage capacity.

Current flow would also stop in string A, even with a internal battery short
in that string.

If so this is the simplest method. But
again what value fuse to use? But if the battery, in the series pair,
before the fuse was to short will the fuse still pop? Isn't the
current being converted to heat in that battery instead of passing
through the fuse? Been too long since I've had to use any electronics
theory.

There still has to be a complete circuit for current to flow in any series
string. The fuse is in series with that circuit, so it would see any
increased current flow and pop as long as it was of the correct rating.

My thought was fusing the parallel connections. In this case the
fuses would see different current loads but would still leave the
series pair vulnerable.

I thought that my diagram WAS fusing the parallel connection between series
strings. Parallel goes from left to right, and series goes from bottom to
top in my drawing.

I can't see how it matters whether it's in a series of a parallel leg, but
most discussion talks about putting it in the parallel leg, which I believe
I have done in my drawing.

I'm running 8 L16's in series parallel so the current through the fuse
closet to the load connection could be quite a lot. I've already got
a 400 amp T fuse for the total load but that doesn't protect the
batteries in a situation like mine.

That fuse would be to protect the wiring between the load and the battery
and the battery bank as a whole. But, it does nothing to protect individual
strings.

I have to admit to being a bit rusty on theory myself. There has to be some
trick in understanding this, and I think that is an understanding of
internal battery resistance.

Somebody out there has to have done this before. I'm hoping they will pop in
and set us straight.

 

[Bughunter]

Depends on how you connect it. The way I'd connect it, each would only
need to carry 1/3 of the 3-parallel battery bank.

A smaller diagram:

+out
+++F+++++++++F++++
+ + +
B1 B2 B3
- - -
------------------
-out

But that would allow B2 to get fried by B1 and B3 acting together (ie,
B1 or B 3 shorting would be limited to F amps, but B2 shorting could get
2F amps), so the following would be better, and scales to as many
parallel strings as you have:

+out
++++++++++++++++++
F F F
+ + +
B1 B2 B3
- - -

I think I grok that. You have more fuses, but they can be at a lower rating
in the second diagram. If you go with dirgram 1, you need to increase the
current rating of the fuse as you add additional series strings.

Diagram 2 would also seem to simplfy the calculating the ampacity of the
fuse. Since you are fusing each series string, you want to select a fuse to
protect the weakest link in that series circuit, which would be a battery, a
cell, or the smallest conductor in that string. It would not matter how many
batteries were in series, because that only increases voltage and not
current.

So, I agree, diagram 2 simplifies the problem considerably.

Now, all that is needed is some form of battery specification, internal
resistance, or charge rate that allows you to determine how much input
current it can take before it catches fire
or otherwise endangers the rest of the bank.

In actual point of fact, some sort of thermal cutout which sensed
battery temprature might be a good plan, as well as the current limiting
of the fuses, but it can get quite complicated/expensive and could also
be inefficient. Temperature monitoring of the batteries and high
temperature alarms are probably well worthwhile, especially given cheap
temperature sensing devices. It argues in favor of fewer parallel
strings of larger batteries.

Trace SW series inverters (and others) have battery temperature sensors to
modify battery charging. I wonder if they can be used to trigger a some form
of safety device. I'd have to look to see if there is a overtemperature
fault. If there is it could be used to remove the load of the inverter, or
perhaps to trigger a fire supression system through one of the inverters
relay outputs. I agree that it seems to complex.

I don't know if I buy the fact that it argues for larger batteries. All that
larger batteres buys you is fewer interconnects. You loose some modulatity
and the ability to swap out a less pricy single point of failure.

Good discussion. I am learning a few things, and at least exercising the
brain a bit to make this all a bit more fathomable. I really want to
understand this before I go out and buy a whole bunch of pricy DC fuses and
fuse blocks.

The item that remains illusive is how to calculate the rating of each fuse.

 

[N9WOS]

I have always considered his second diagram as the only
logical way to do things.

I go a bit on the side of reliability.

If you have ten batteries in parallel,
and you want to pull a maximum system load of 200 amps.
You pick a size of fuse that will total to 400 amps.
(ie) 40A each, and each carries 1/10 of the load.

Maximum that can be pulled of the banks is 400A.
That will stop things from melting down if the wires to
the main inverter cutout/(over current protector) short.

And the system will still operate nominally with half the
batteries removed, for maintenance, by fault, or what ever.
That allows you to pull maintenance on a string by just removing
the fuse for that string, to isolate it from the system.

If you have only two or three strings in parallel, you should probably go
with 150% of the rated maximum load on the system.
(ie)300A for a 200A system.
150A on each of the two strings.
100A on each of the three strings.

And my opinion for batteries under 200AH is that the fuses that are widely
available
in stores that is rated at 10,000A ISC for about a $1.50 a piece, should be
adequate.
The maximum they have to handle is the current through one battery,
in their intended protective mode.
If the batteries are over 200AH, I would go with the bigger 20,000A ISC or
larger fuses.

 

[SpiderG]

Seems to me that you could get a relatively inexpensive non-contact infrared
digital thermometer (point & shoot), and aim it at each battery in teh
system. Record the measured tempereatures during different cycling periods
(charging, standby, discharge), and see if there is great variation over
time.

Probably takes longer to describt than to do the measurement...
I think I have seen them for sale by Exeltek for under $75USD.

Just a thought...

SpiderG

*************************

 

[Gordon Richmond]

Yes, I was speaking of soda solution, not the powder.

I believe the caveat against using water on an electrical fire is
mainly for protection of the person holding the spray nozzle; they
could get a jolt of juice via the stream from the hose.

But here we are talking of relatively low-voltage DC current, and an
automated sprinkler. Do buildings with sprinkler systems have an
interlock to over-ride the sprinklers in the event of an electrical
fire?

I figure if you have a bank of lead-acid batteries in which things
have gone so wrong that the smoke is getting out, there is little risk
of further harm by wetting them down with soda solution. An intact
battery would likely get very little in through the vents, but one
that had burst would benefit from the neutralization, as would any of
the surroundings that had been acid-sprayed.

Gordon Richmond

 

[daestrom]

Yes, I was speaking of soda solution, not the powder.

I believe the caveat against using water on an electrical fire is
mainly for protection of the person holding the spray nozzle; they
could get a jolt of juice via the stream from the hose.

But here we are talking of relatively low-voltage DC current, and an
automated sprinkler. Do buildings with sprinkler systems have an
interlock to over-ride the sprinklers in the event of an electrical
fire?

No, but areas where electrical fire is most likely (UPS battery rooms,
switchgear rooms, etc...) are usually *not* protected by sprinklers. Halon
or CO2 banks are used there.

Water on electrical fires can create more shorts and sparks. Best way to
fight electrical fires has always been to de-energize the circuits then
combat it as a simple class A fire. But batteries can't be de-energized, so
that makes fire-fighting a problem.

Best way is to avoid them in the first place. Keep everything out of the
battery compartment that isn't strictly needed. Use 'sawed-off' or
insulated tools that are too short to bridge between terminals. Always
open-circuit a battery before working on inter-connections. Prefer
series-parallel connections over parallel-series connections.

And as this discussion has pointed out, fusing each series string is a good
idea.

I figure if you have a bank of lead-acid batteries in which things
have gone so wrong that the smoke is getting out, there is little risk
of further harm by wetting them down with soda solution. An intact
battery would likely get very little in through the vents, but one
that had burst would benefit from the neutralization, as would any of
the surroundings that had been acid-sprayed.

Like you say, at that point, you've got little to lose by dousing it with
soda water. Just make sure your system is reliable enough that it doesn't
go off on a false alarm, or that it can be 'disarmed' when necessary. If
you use a set of typical fire sprinkler heads, and you happen to knock one
hard while doing maintenance, you may want a quick shutoff to prevent a
minor thing getting major.

daestrom

 

[Steve Spence]

We aren't allowed to use Halon anymore. It was too effective, on computer
room personnel ......

--
Steve Spence
Renewable energy and sustainable living
http://www.green-trust.org
Donate $30 or more to Green Trust, and receive
a copy of Joshua Tickell's "From the Fryer to
the Fuel Tank", the premier documentary of
biodiesel and vegetable oil powered diesels.

 

[Bughunter]

I think you can still use Halon for fire supression in boats.

 

[Dale Farmer]

We aren't allowed to use Halon anymore. It was too effective, on computer
room personnel ......

there were two forms of Halon commonly used in firefighting. One was
extremely deadly to people, the other was merely very bad for you. *grins*
Neither of them is being produced anymore, as both of these chemicals
were banned under the CFC treaty. If you have an existing halon system,
you can still have it. I'd suggest hanging on to it, as it will become more
valuable for the halon in the tanks as time goes on.
To take this back to battery fires. Why soda water? If the goal is
to neutralize the acid, dry baking soda in a metal pan underneath the battery
tray would be a better solution, I think. Adding water to an electrical fire
is frowned upon. Fuse all the strings with appropriate sized DC fuses,
and construct your battery tray so that a fire in one string of batteries
won't spread to another still live string of batteries.
One could construct narrow tanks of water to sit between the battery
strings. This water could serve multiple purposes. A distilled water supply
for the batteries, fire barrier, and thermal mass for the battery compartment.

--Dale

 

[Bob Peterson]

the main reason halon went out of common use was that insurance companies
found that the reason it was being used (less damge to the equipment it
protected) just was no longer an issue as computer equiment got cheaper.

 

[daestrom]

We aren't allowed to use Halon anymore. It was too effective, on computer
room personnel ......

Only those not smart enough to get out when the 30-second pre-discharge
alarm goes off ;-)

But you're right, it isn't approved for new installations. And buying a
refill for an existing installation includes a heavy government fee.

daestrom

 

[daestrom]

the main reason halon went out of common use was that insurance companies
found that the reason it was being used (less damge to the equipment it
protected) just was no longer an issue as computer equiment got cheaper.

Well, as far as that being the 'main' reason, I'm not so sure. Refilling
the tanks has become a very expensive proposition. Even those installations
that still have expensive computer equipment are having problems maintaining
it. Last year at work, we 'canabalized' the halon tanks from a computer
room that no longer had computers in it, to restore halon protection to
another, nearly empty computer room. It would have cost us on the order of
~$30 000 for those two tanks if we had to buy the halon and pay the govt
fees.

And the only reason we did this was because without the halon, the insurance
on that 'nearly empty' computer room would have gone up sharply.

daestrom

 

[N9WOS]

there were two forms of Halon commonly used in firefighting. One was
extremely deadly to people, the other was merely very bad for you. *grins*
Neither of them is being produced anymore, as both of these chemicals
were banned under the CFC treaty. If you have an existing halon system,
you can still have it. I'd suggest hanging on to it, as it will become more
valuable for the halon in the tanks as time goes on.

100% correct.
The ban on ODPs(ozone depleting substances)
is the only reason that halon is being phases out.

It's use on airplanes, and on the ground was banned.
I still don't know if they came up with an effective replacement for
airplane use.

Before they put government ODP fees on it, halon was a very cheep for all
uses.
We had a couple handheld ones for putting out gas fires, and engine fires.
Still have one old empty halon extinguisher setting around here.
It would put out any fire ASAP.

 

['Captain' Kirk DeHaan]

100% correct.
The ban on ODPs(ozone depleting substances)
is the only reason that halon is being phases out.

It's use on airplanes, and on the ground was banned.
I still don't know if they came up with an effective replacement for
airplane use.

Before they put government ODP fees on it, halon was a very cheep for all
uses.
We had a couple handheld ones for putting out gas fires, and engine fires.
Still have one old empty halon extinguisher setting around here.
It would put out any fire ASAP.

So I should hide the halon extinguisher I have in my truck?



Kirk

"Moe, Larry, the cheese!", Curly

www.sandpoint.net/captkirk
www.stormyacres.com

 

[N9WOS]

So I should hide the halon extinguisher I have in my truck?

It is perfectly legal to use it, but don't let any environmentalist see you
use it.
He will have a green peace march out infront of your house ASAP. :-O

 

['Captain' Kirk DeHaan]

It is perfectly legal to use it, but don't let any environmentalist see you
use it.
He will have a green peace march out infront of your house ASAP. :-O

This is logging country. It would be interesting.



Kirk

"Moe, Larry, the cheese!", Curly

www.sandpoint.net/captkirk
www.stormyacres.com