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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Honda EU2000 and ceramic heat combo OK?
Message-ID: <>
Date: Sat, 07 Dec 2002 14:55:22 -0500

On Sat, 07 Dec 2002 09:54:39 -0600, Allan <> wrote:

>>Unless you set the generator some distance from your truck and run a cord
>>you're probably going to have more exposure to CO from the engine than you
>>ever would with a ventless or catalytic heater.  I know because I tested it,
>>that the Coleman Black Cat catalytic heater produces essentially zero (below
>>detectable with my equipment) CO.  It makes 6k BTU which is a little more than
>>a ceramic heater.
>But do you sleep safely with the Black Cat & CO detector running and
>window cracked? I'm not arguing just asking because I like safety.

I'm not one of those folks who goes to extremes so I simply run the black cat,
have a CO detector and sleep very well.  I did test the Black Cat to determine
that it makes essentially no CO.  I don't open a window simply because my rig
has sufficient air infiltration to keep it nice and fresh.  So does my mom's
MH and I suspect so do most of 'em.  A cold draft on the floor is a good clue

>Now I actually have thought about the CO from the generator engine
>getting into the truck. I considered a generator storage box under the
>floor, even running it in there but the exhaust would rise and enter
>and fill the truck! Could I pipe it out and up safely? Lots of issues
>I know. Brazed, welded or threated pipe fittings I think. Out and up
>where exactly? What do enclosed generator rigs do?  All that truck
>engine exhaust just vents down low at the rear. That doesn't kill
>anyone sitting at idle, though sleeping in an idling vehicle is

In my Itasca the generator box is a heavy steel box that is completely sealed
from the passenger compartment.  The bottom and one side are open to cooling
air.  Even the wire penetration is caulked.  The exhaust is run out the back
of the rig past the bumper.  On my mom's rig, the generator is slung low on a
steel frame but no box.  The exhaust simply exits the body right behind the
driver's side door.

Both setups work.  I've never seen more than a 10 ppm reading inside the rig
from either setup.  I HAVE seen higher readings from the furnace and much
higher readings from the cook stove.  I was in my rig last night and it was
cold enough that both the ceramic heater and the Hydroflame had to run a lot.
This morning I had a peak reading of 17 ppm on the NightHawk.  This was an
extremely calm night when a heavy blanket of frost settles.  Probably worst

When I use my stove I run the Maxxair fan in the bathroom.  This pulls air
from the stove across the NightHawk.  It's not unusual to see 200 ppm or more
after boiling water for coffee.

Point I'm making is, you simply can't rely on rules of thumb.  Relatively
minor changes in ambient conditions can greatly change the CO level in an
enclosed space like an RV or pickup shell.  The only reasonably safe (I'm
beginning to hate that word) method is to have a good CO detector and then
take reasonable precautions.  Set the genny away from the truck.  Or if you
mount it on the truck, seal it airtight from the living spaces and pipe the
exhaust outward, preferably pointing away from the rig so that inertia can
carry it farther away.

>Agreed. Cheap insurance. Got one already. The 12v direct is a good
>idea. Little RC filter for transient protection? Perhaps you didn't
>put it on the starting battery circuit like I'm thinking of.

I opened the thing up and analyzed the circuit.  It looks fairly robust, with
a full wave bridge and then a surge suppressor on the incoming line.  I put no
protection on it.  It's on the house battery which is connected to the
cranking battery when underway and which cranks the genny.  No problems so
far.  Of course, NightHawk would have a shitfit at this mod, I'm sure, but it
works for me.  If you wanted some isolation, one of those tiny 120 volt
inverters meant to power laptops would do the trick.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: CO Detectors revisited again
Date: Thu, 02 Jun 2005 01:34:21 -0400
Message-ID: <>

On Wed, 1 Jun 2005 18:08:21 -0400, "Steve Wolf" <> wrote:

>In addition to a battery operated device, I have a plug-in Nighthawk, with
>no battery, so that I will always have some protection when running the
>generator.  With the right breeze I can back my car up to the window nearest
>the detector, and sense the CO entering the motorhome.  It alarms properly
>and quickly.  Sitting in a traffic jam, with cars belching CO on all sides,
>might not be the correct environment for a super-sensitive detector.  I'm
>not sure I want to chase whiffs of CO.
>Anyone not connected to CO detector sales care to suggest a more balanced


My mom's rig came with an RV CO alarm that would go off every time the
genset ran.  It was promptly disabled.  I've never been interested
enough to determine at what level this thing is designed to alarm but
I do know that it is too sensitive by orders of magnitude.

I have installed NightHawk detectors in both rigs.  I use the one sold
by Sam's Club for $29 ($45 everywhere else including wallyworld).
This is a plug-in unit with a 9 volt battery backup and the two digit
CO level indicator on the front.  It has a built-in wall wart that can
be removed and a coil of wire deployed so that the detector can be
either plugged directly into an outlet or hung on the wall and cord
extended to an outlet.

I at first ran it on a small inverter but that seemed kludgy.

After disassembling a unit and analyzing the PCB, I found that this
model can be run directly from 12vdc, eg, the RV system, simply by
cutting off the built-in wall wart and connecting 12 volts directly to
the wires - polarity doesn't matter.

To make sure that they haven't changed the design, before you do this,
examine the wall wart to make sure that it is labeled for 12vac
output.  The input voltage doesn't matter much, as the first thing it
goes to after the bridge rectifier is a 5 volt 3 terminal regulator.

The early model units would periodically alarm if the 9 volt battery
was not installed.  This seems to have been corrected in later models.
For the early models, a jumper around a diode connected to the + lead
of the 9v battery connector solves this problem.

The reason I don't want the 9v battery in the unit is that when I kill
the 12 volt power on the rig, the detector fairly quickly discharges
the 9v battery and then I have to dismount the detector to replace it.
Since I'm already on battery power, the 9v battery is redundant.

When I got the first unit I purchased a tank of 100ppm CO calibration
gas and tested the unit by putting it in a plastic bag and filling the
bag with the calibration gas.  It agreed within 5% which is more than
adequate for the intended purpose.

The display is more or less instant (about 10 seconds) in its response
to atmospheric CO but the alarm follows the UL time weighted average
model.  This model is designed to mimic the human response to CO and
alarm before the accumulated level becomes hazardous while minimizing
false alarms on transient concentrations.

The NightHawk will display the peak reading since reset if one of the
buttons is pushed.  At the end of a drive I usually find 15-20 ppm
indicated from CO that enters the cabin from the exhaust.  Under
normal conditions, running the genny in calm air will produce a peak
CO reading of about 25 ppm.  Occasionally in a semi-confined area
(such as parking next to a retaining wall) or a temperature inversion,
the CO will build up enough to cause the first level alarm at about
100ppm.  When I anticipate those conditions, I run my Maxxair fan on
suction at the lowest speed which pulls in air off the roof.

The alarm proceeds in increments, from a periodic chirp at the
threshold of concern to a continuous LOUD alarm when the level is
dangerous.  It seems to take 3-5 minutes to clear out and reset when
the detector is brought to fresh air.

IMHO, this is the perfect RV CO detector.  When it alarms there is a
problem.  The display is accurate and quite useful.  Of course, it
hasn't been officially approved for this application.  If official
approvals matter to anyone then this unit is not for you.  The rest of
us will enjoy its competent performance.  The only complaint I have is
that the alarm is TOO loud for a confined RV.  I solved that problem
by partially taping over the horn hole.

The one thing I have not tested is its durability when un-powered.
The instructions say not to leave the unit un-powered for long periods
once the sealed package is opened.  Something about the sensor being
hydroscopic or something like that.  My 12 volt system is always
powered up except when I'm working on it so that hasn't been a


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: CO Detectors revisited again
Date: Thu, 02 Jun 2005 02:01:43 -0400
Message-ID: <>

On Thu, 02 Jun 2005 05:32:30 GMT, "The Airman" <>

>I talked with a mechanic at work about CO detectors (I am an Airline Pilot)
>He told me that CO is CO is CO.  All the detector has to do is alarm.  There
>is not a "rate of rise" factor like heat detectors as far as he knew.  So
>the argument about smaller volume such as an RV is baloney.

Incorrect.  CO detectors respond to a time weighted average defined in
the UL spec, designed to duplicate the body's response while
minimizing false alarms.  A pretty good bit of info on this is
available on the net, although the spec itself isn't, AFIK.

>He did mention that the module inside the CO detector should be replaced as
>necessary or whatever the time interval specified or indicated.  As I
>thought, a CO detector is a CO detector.

Again, incorrect.  There are two major types of consumer detectors -
photochemical and electrochemical.  The cheap detectors that require
periodic element replacement use the photochemical detectors.  This is
a module containing a chemical that darkens as it absorbs CO.  The
unit shines light through the cell and detects the reduction in light
transmission.  When the media becomes dark enough that the electronics
can't compensate, the cell has to be replaced.

The other type, electrochemical, is used in the better detectors such
as the NightHawk.  In this type, the cell's electrical characteristic
changes with CO.  Usually resistance but sometimes voltage out.  The
cell is not consumed during detection and has an indefinite life.
There are two types of these cells - moist chemistry and solid state.
The moist chemistry as used in the NightHawk is more sensitive but
will eventually dry out (or something like that) and have to be
replaced.  This is measured in years.  The solid state detectors,
while not as sensitive, last essentially forever.

It appears from simply removing the cover and looking at it that the
hard wired RV detector in my mom's rig uses the solid state detector.
Which is probably why it falses so often.  It's probably operating
near its sensitivity limit.

>The reply from the company about
>the Nighthawk regarding the disapproval for use of their product in an RV is
>because I suspect the company did not test the product and get UL or FM
>(read: test and pay UL or FM for their testing and approval) approval
>because there was no economic justification to get their product tested for
>a small market like RVs vs. Household or business stationary use. (which
>includes paying more liability insurance to sell it in each market)

Yes, I fully agree with this assessment.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: CO Detectors revisited again
Date: Thu, 02 Jun 2005 11:08:54 -0400
Message-ID: <>

On Thu, 02 Jun 2005 13:56:38 GMT, "The Airman" <>

>I will have to show this to my inspector buddy.
>Is there an electrochemical battery powered detector? or are these all plug
>in types with a battery backup....

I don't know but I suspect not.  The sensor in the NightHawk is
slightly heated, probably to keep out condensation.  If there is a
battery powered one it will probably be a solid state sensor version.

There are battery powered solid state sensor survey instruments
available so some probably has or will incorporate one into a consumer
instrument someday.

BTW, I'd imagine your buddy is right about aviation CO detectors.  The
UL standard strikes an explicit balance between what concentration of
CO becomes life threatening and avoiding false alarms.  Since
sub-lethal doses of CO dull the senses and slow response time I'd
imagine a pilot would want a much earlier alert.  The other factor is
probably that since the cockpit is up front in a fast moving stream of
air, the sources of CO are much smaller.


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