DC Help
Measuring
DC I started this thread as an off shoot of the refrigerator
exhaust fan thread. Most of the comments in the other thread
were related to the battery losing power. To restate, I ran
the fridge on DC Friday night for 3 hours while driving. We
stopped to find we had a dead trailer battery ( no lights or
anything in the trailer). This was after rewiring the DC to
go directly from the battery to the fridge. I did not run it
on DC for the rest of the trip. I returned home yesterday. Last
night I measured the DC with one of those meters from CW that
you stick in the DC outlet. It measured 12.4v (25% discharged).
This morning it measured 12.1v (over 50%) discharged. I measured
it tonight and it was 13.2V. I borrowed a digital multimeter
today. Measurements in the trailer were 12.38v.This was at the
battery, at the fridge, at the converter and in the DC outlet.
Since I did not measure last night with the multimeter I don't
know if I had this variance last night. The trailer was not
plugged in today so why would the reading goup? Are these plug-in
voltage meters inaccurate? Should I buy a digital multimeter
if I want to monitor the battery or should the plug-in model
give correct readings? Mary - Per Interstate documentation "If
the battery is operated in a high heat environment, (consistently
above 90 degrees F) the typical number of cycles could be drastically
reduced."
Yes, those
plug-in meters aren't very accurate, but your battery voltage
might also have gone up. It isn't unusual for a battery's voltage
to rise after it has "rested" from a heavy current
load. (Don't ask me why, something to do with the chemicals.)
Also, the voltage at the DC outlet may drop when the fridge
is running if it's on the same circuit. This is caused by voltage
drop in the wires due to resistance. That's why you want heavier
wire for higher-current loads, and why you want to measure battery
voltage at the battery. I think it would be a good idea to get
a multimeter to back up your plug-in meter.The plug-ins are
good for spotting trends and changes in voltage, but not so
good for accurate absolute voltage readings. And DVMs are pretty
cheap these days. 1. Yes, get a volt meter. Doesn't have to
be easier than a swing meter. 2. Yes, to some extent, batteries
have a "resting recovery rate" due to the acid action
on the plates but it usually is a false reading. Good example
of this would be a dead car battery. You grind and grind till
it won't go no more. You wait awhile, and then get another grind
out of it. One way to evaluate battery health is to fully charge
the battery and then disconnect it so that you know there is
no way it can be discharged by sneak loads. After are sting
period of 24-hours, measure the voltage across the terminals
with a good digital voltmeter. If the batteries aren't holding
12.6 Volts, (12.8 for gel cells),then they are in poor health.
Maybe I'm way out in left field, but it sounds to me that your
car alternator is not charging your house battery. You should
have around 13.x DC volts when you are driving and with the
fridge on. And that is where the plug in meter is a great "indicator".
if it is showing 13.x when you start up on your trip and 3 hours
later it shows 12.x, you know you got a big difference. Since
the fridge draws 15 amps when on and you ran it for 3 hours,
that would be about 45 amp hours -- enough to take a battery
down, especially if it is a type 24 (has around 80-90 amp hours).
Bob Steffen
I checked
the charge line today coming from the exact reading, but I think
it was 13.6v. I'll check it again later.
I use one
of those "plug-in" digital type,in my cig. lighter
when on the road just to monitor for the fun of it. With the
refrig. on 12v, and running down the highway with everything
settled down, it stays a steady 13.6v. Where this means anything
or not,just thought I'ed throw it in. If you ran the 12v line
to charge the trailer battery thru the connector, you need to
check the voltage IN THE TRAILER. A digital voltmeter will give
you a better reading if you are looking for voltage drops thru
connections, etc., and I have them for $10. Analog meters are
show changes easier, but for exact measurements, digital is
much better. (I have been looking at the Casita's for the last
year, and plan on getting one probably when the factory does
their end of season mark downs after Oct.) ... friz
* DF Electronics
Bill, Where
did you check the voltage from the truck: at the connector socket?,
at the trailer battery? If at the trailer battery, was the battery
(+) wire disconnected from the battery? If your truck alternator
is putting out 13 volts or more, I would suggest the wiring
is at fault. Are you sure you have a good ground through out
the wiring harness, or is the trailer being "grounded"
through the ball? This in not good. John
Bill, Couldn't
sleep thinking about your problem, thought I'd better send my
thoughts on so I could get some sleep!! I'm not sure where you
are on circuits and electricity, so if I sound rather "basic",
please bare with me. The battery voltage you are measuring is
the"no load voltage" or the "surface voltage".
A more accurate reading is the "loaded voltage" (turn
on something, the greater the "load" the more the
voltage will drop). Another thing about batteries: temperature
increases, voltage increases; temp. decreases, voltage decreases.
Let them rest, the "surface voltage" increases, but
there is no reserve. If the alternator charges your vehicle
battery, it will charge your trailer battery, if the wiring
is OK. Now to circuits. To charge the trailer battery and run
the 12v appliances from the car, electrical current must travel
from the car battery, to the trailer battery and 12v circuits,
and back to the car battery. From what you describe, this is
not happening. Trouble shooting: You will need a multi-meter
for this, it doesn't matter if it is digital or analog (swing
needle), just make sure you understand the function and range
selections before using it. You will need a wiring diagram of
the connector,also. Check for 12v (+) at the connector: Set
the multi-meter to DCV with a range that is above 20 volts (DC)
Red lead to the connector 12(+), black lead to something metal
on the car. Is voltage present? (it doesn't matter how much)
Y: move on. N: check the car wiring. Check for "Ground"
at the connector. If 12(+) is present, touch the black lead
to the"Ground" terminal. Is voltage present? Y: move
on. N: The ground circuit is open (not connected). Rewire the
ground. Check for 12v (+) at the trailer battery: Disconnect
wires at the battery, check on top of the battery for (+) and
(-). Plug in the trailer connector. Connect the multi-meter,
red to the (+) wire, black to the (-) wire. Is voltage present?
Y: reconnect the battery wires and move on N: there is a problem
in the trailer wiring, possibly the converter. I have not determined
if there is a fuse in the battery charge circuit on the Casita,
if there is, it might be blown. Check for ground continuity
at the connector: (Note: This is another method to check for
a ground. If a "ground" was present using the voltage
method, this step is not necessary.) Unplug the connector. Set
the multi-meter for a resistance reading (Ohms), it doesn't
matter which one. Touch the leads together and set for "0".
Touch one lead to something metal on the car, the other to the
"ground" terminal in the connector. Be sure to check
which terminal is the "ground", have a helper hold
the flap open, for if you should connect to a voltage while
in a resistance function, you will be replacing a fuse in your
meter or purchasing a new one. Reading (it doesn't matter what)?Y:
this is good; N: the trailer is not being grounded through the
wiring harness, only through the ball. Rewire the ground. I
have said this in other threads, the ground must be 10ga. (Factory
wiring is most likely 14ga.) The small wire will not carry the
load. This is why the 12v(+) wire must be 10ga. also. 30 amp.
protection (circuit breaker) is needed. I have suggested a relay
in other threads, also. Give this a try, let me know the results.
If you still have problems, I'll put on my "thinking cap"
again. John Hamilton
Hi John!
Boy, everyone should print out your last post and carrying it
with them. Good explanation of how to trouble shoot electrical
wiring in any trailer! According to an old factory wiring diagram
of a 16 footer, the black (+) direct charge line is protected
by a 20-amp fuse. But in the back of my mind, it's one of those
auto reset able breakers, believe it's attached to the back
(inside the trailer) of the battery box. Don't quote me on any
of this ... and as Isaid, my diagram is an OLD one, so may not
be current. You said it should be a 30 amp fuse.Wouldn't a 20
amp be better? Showing my vast ignorance here, but if there
was a problem, a 20 amp would blow faster, correct? I still
think he ought to have the battery tested. John,
Thanks for
the detailed response. You can't be too basic for me. This will
take a couple of days before I can look into all of this.In
the meantime I think I will take the battery in to be checked.
I plugged the trailer into house power last night. The reading
this morning was 12.73 on the multimeter and 12.7 on the plug-in
meter. I'll let you know what I find out. I am always amazed
by the knowledge and helpfulness of the people on this forum.
Bill
I took the
battery to NTB today. The battery tested fine. Hello Charles,
The amperage rating of circuit protection (either fuse or circuit
breaker) is determined by the wire size. IE: 10ga. wire can
safely carry 30 amperes = 30 amp.protection; 12ga = 20 amps;
14ga = 15 amps.;16ga = 10 amps. It is safe to put small protection
on a large wire; 20 amp protection on a 10 ga. wire; but not,
say,30 amp protection on a 12ga. wire. I say this, because some
individuals will replace a 15 amp fuse with a 20 amp fuse, not
safe.So, I am saying 30 amp circuit breaker on the 10ga. wire,
but a 20 amp breaker will give an extra margin of safety on
the 10ga wire, if it will carry the load. All wire has internal
resistance, long wire runs and small wire ga. increases resistance.
Resistance reduces voltage and will produce heat as electrical
current flows. Long wires need to be large to have electrical
energy at the end. Wire also needs to be large enough not to
over heat as current flows. Bottom line- if in doubt, go big.
This also applies to house wiring and extension cords. If your
skill saw seems to have little power at the end of a long extension
cord, it is due to the wire size of the extension cord being
too small for the length and the load. This in another way to
think of current flow: Electrons moving easily in a large wire,
like a 4 lane highway. Then the electrons come to a smaller
wire and must squeeze together to get through, like traffic
merging from 4 lanes to 3 lanes or to 2 lanes. Traffic slows
down, radiators and tempers overheat. In electricity, wires
over heat or can not carry the load. Therefore, the recommendation
to add a larger ground wire between the connector socket and
the chasis. Most trailer wiring, including factory wiring, is
for lighting only and uses 16ga. or 18ga. wire, which is not
large for the added load of a refrigerator or battery charging.
Case in point, I check the trailer lights by turning on the
running lights and the 4-way flashers at the same time. When
I did this, I noticed the clearance lights would dim when the
turn signal/brake lights came on. The lights no longer dimmed
after adding a larger ground wire. John
"Not
all who wander are lost."
John,
I tested
the voltage coming from the truck (at the connector) and it
was 13.8v. I then disconnected the wires at the trailer battery.
The current from the wires was 13.4v. Hello Bill,
So far,
everything sounds good. What is the voltage at the refrigerator?
Is the polarity correct at the refrigerator? ( negative to negative,
positive to positive) You said you ran new wires directly from
the battery to the refrigerator, did you put a circuit breaker
in the (+) wire? If I remember, it was 10 ga. wire, a 20 amp
breaker should work. I love challenges, keep me posted, something
has got to work! John Hamilton
I have 10g
wire from the battery to the fridge. I put a 15 amp fuse on
the line. I will check the power going to the fridge. Interesting
note (maybe), I had the battery charged at NTB on Tuesday. After
the charge it registered 12.73v. Yesterday it was 12.43. This
morning it was 12.3. Last nightI turned on 5 lights and the
Fantastic. The reading was 11.8v. All of this was done with
no connection to shore power. NTB said the battery was good.
I'm not so sure. I bought one of those Vector Start-It things
that Target has on sale just in case.
Hi Bill
... as I posted before ... a 24 hour test is a better test of
a battery's ability to hold a charge. One way to evaluate battery
health is to fully charge the battery and then disconnect it
so that you know there is no way it can be charged by sneak
loads. After a resting period of 24-hours, measure the voltage
across the terminals with a good digital voltmeter. If the batteries
aren't holding 12.6 Volts, (12.8 for gel cells), then they are
in poor health I will disconnect it and check it after 24 hours
to see what happens.
Since I
have moved to the heat of Texas, I have never had a battery
last through the warranty period. I now replace vehicle batteries
after 3 years rather than risk a dead battery late at night,
etc. Our Explorer battery failed after 2 years. If I have doubts
about this battery I will replace it before we head out to the
Grand Canyon. I've had enough trailer related problems already.
I don't want to risk pulling over and not having power. Especially
if we decide to dry camp. Bill, not familiar with the vector
... does it have a 12-volt torpedo plug-in spot? If so, make
yourself a "connector" with a torpedo plug and two
alligator clips which you can use as an "emergency"
power source for the trailer by disconnecting the leads to the
house battery and clipping on the alligator clips. Another was
to do it is to make a "double" torpedo plug (making
sure the polarity is correct), and then disconnect the house
battery, plug one torpedo into the vector and the other into
the 12-volt-plug on the rear deck. Have a great time at the
Grand Canyon! I agree, batteries are cheap and I, too, replace
before they fail. Charles,
The Vector
has the DC torpedo outlet. I read your post in another thread
about making a connection cord. I don't remember the thread
but someone mentioned the Vector and you mentioned using the
Prestone Jump It. I plan to build the cord this weekend. Where
did you buy your torpedo plug? At $45 the Vector was hard to
pass up. I guess I can also buy an inverter and use the combination
of the Vector and an inverter to run some small power tools
in the field. Bill
Walmart
sells them in the auto department The Walmart connectors used
to have wires attached, but replaced with 12 gauge wire. Didn't
fuse my wires since I was attaching the alligator clips to the
Casita house battery leads which lead to grounds and fuses ...
and the torpedo plugs have fuses in them also. Use this set-up
all the time to extend dry-camping ... and also for winter camping
when the house battery's removed for safe winter storage. When
our 2000 model was new we put the that without the truck running
the battery dies in about 20 minutes (verified timing at Casita).
Also learned that when running with head lights on AND fridge
on DC the battery was slowly dying -- fix: turn off the lights.
Finally learned that the fridge seals so well that all food
stays cold a/o frozen for at least 12 hours driving or until
we go to either AC or propane (never drive with propane on).
We don't use DC any more for fridge. Additionally, our solar
panel controller keeps us apprised of the battery's status (Seimens).
Good point, Doug. Bill did say he was went dead. This would
indicate the alternator does not have enough capacity to keep
up. Some manufactures offer alternators with more output, and
are sometimes standard with trailer towing packages. If the
refrigerator is operated on propane while on the road, the unit
should be turned off, including the pilot flame, when in a gas
station. John Hamilton
Bill, Besides
the ability for a battery to hold a charge over time, as Charles
mentioned, it should be tested under a load. It is normal for
the voltage of a battery to drop as load is applied, the greater
the load, the lower the voltage. The usable capacity of a battery
is how long it will last under load. If a battery drops voltage
in a short time or doesn't last very long under use, it needs
to be replaced. "Doesn't last very long..." is subjective.
The wiring to your refrigerator sounds A-OK.I was going to suggest
a 15 amp. fuse, not the circuit breaker. Already done. Now I
am of the option that Doug S. has identified your problem, the
alternator could not keep up. I would still suggest a larger
size ground wire, if the one in your installation is small.
Good Luck,
John H.
I can't
tell the ground wire gauge for sure but it is the largest of
the wires going to the connector. I would guess at least 12
gauge. The truck is an F250 Superduty with all the heavy duty
tow stuff. I would think that it has about as powerful an alternator
as you are going to get without moving into the medium duty
trucks (F450/F550 and greater). It came pre-wired including
charge and brake wires. Re: The fridge holding temp. while driving,
my fridge has never been able to hold the temp when driving.
It's not so bad at losing temp in the winter but the Texas summers
are very hard on the fridge. Last week I lost 20 degrees in
3 hours. And that was not a particularly hot day. In the past
I have had trouble running the fridge on propane while driving.
The flame kept going out. Casita must have worked on it the
last time they had the trailer because it seems to stay lit
now. Also, it is the fridge that comes with the 17 foot trailer.
I saw a battery at Pep Boys. An Energizer made by Johnson Controls.
It has 120 amp hours and costs $59 with trade. One year full
replacement warranty/24 months prorated. Any comments. They
also had an Optima. It had 55 amp hours. The price was not listed
but I understand they are expensive. I took the battery out
of the trailer and checked voltage - 12.49v. I will check again
in 24 hours. While battery was out, I connected the trailer
to my truck to check power going to the battery. I had the following
readings. With radio on in truck 13.83v With radio and lights
on in truck 13.61v With radio, lights, AC and fan on max 13.43v
Lights and AC were on while towing the other day with fridge
on DC. The battery was dead in 3 hours. Bill, Ground wire size
is ok.
Connect
the trailer and check the voltage at the truck battery with
the full load; lights, A.C., frige, etc. It should be above
13 volts. with the engine running. John H.
Bill, if
it is the house battery you are buying a "Deep Cycle"
type. A regular auto battery can't handle all the discharges.
Bob Steffen
Bill: If
you're buying a battery, DEEP CYCLE for sure, might consider
whether you want a type 24, 27, or 29. I think they'll all fit
in the Casita, length differs and would require drilling a hole
for the angle bracket. I think the 27 gives you about 50% more
amp/hrs than the 24 and the 29 doubles a 24. All are at walmart
for under $70. Not to recommend walmart batteries, but to be
aware of the capacities according to the type, this holds true
regardless of the brand of battery. Don in OKC
