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Old 04-23-2016, 11:20 PM   #1
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Location: Northern SC
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DC Power Issue understanding

To start, I have a Rockwood 8289WS fifth wheel. I took out the single 12 volt battery and instlled 2 6 volt Trojans in series (240 AH).

Everything has been fine until this extended trip my CO/Propane alarm started sounding the alarm when my furnace was running. Very scary! I looked at the details however and the alarm signal of Red-Green-Red-Green... Indicates a low voltage default (not CO or Propane detection). I got to thinking and I have a new DC power supply for my CPAP. I realized the alarm is going off only when I am using the CPAP and the furnace at the same time. Sure enough I slept without my CPAP last night while boondocking, used the furnace and no problems.

I am an amateur electrician but I was surprised my voltage is dropping that low. Batteries are fully charged. I would love to post the voltage coming off but I am having problems with my multi-meter and on the road. Everything is working perfectly fine with the exception of this situation.

I am looking for your thoughts on how I can improve my voltage situation. The first thing that occurred to me was the cables. I noticed when I put in the dual 6 volts the cables installed by OEM were tiny. Not sure what guage but I used a 2 guage to connect the two batteries together and it is many times thicker than the OEM cables (which I did continue to use on the new batteries for ground and positive feed). Would lower guage cables reduce voltage loss likely correcting my problem?

Thanks for your thoughts.


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Old 04-23-2016, 11:26 PM   #2
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How do you know your batteries are fully charged?

Where is the powerconverter/charger located in relation to the battery? The two should be nearby no further than 3 feet apart.

Is the CPAP 12 volt? If so, what gauge wire and distance from battery are you running?

Do you have an on/off switch? If not, your propane detector is draining the battery and will kill it in 2-3 days.

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Old 04-23-2016, 11:33 PM   #3
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Are you running the CPAP off AC or DC? It's more efficient to run it off DC if you can. Second, are you running the humidifier on your CPAP, or just the air pump? Adding humidity to the CPAP air takes quite a bit more power than just running the air pump.

One more thing that will help your voltage situation is solar panels or a generator. You mentioned that it was an extended trip, but you didn't say whether you were daily putting juice back into the batteries after taking juice out overnight. You can only go so far on the charge you got from the drive in.

As far as the OEM cables, yes, those little cables they install will give you more voltage drop than thicker cables, but they are likely not the problem. The problem is your power budget -- How much you consume, versus how much you put back in.

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Old 04-24-2016, 07:19 AM   #4
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If your batteries were fully charged, the furnace should only draw something like 7 to 9 amps, not that much for what you have. CPAP humidifier is a good thing to turn off. If you are using an inverter, you should check all of your connections first for corrosion and tightness. Low voltage at the detector sounds like a bad connection or that your batteries were never actually at full charge, which is common unless you were connected to shore power for a couple of days before you left. It takes a long time to get to 100% SOC but I would be surprised if your batteries are really that low. Multimeter on the posts while the CO detector is complaining should tell you what's up.

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Old 04-24-2016, 12:35 PM   #5
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My wife uses home dialysis and I am running into a similar problem, Hers draws about 500 watts off and on through out the night from the AC convertor. The trailers inverter doesn't seem to put a full charge on batteries. I am looking at either using the trucks alternator system to charge the trailers batteries, or make a gas battery charger from a automobile alternator and a small motor and charge the batteries directly separate from the trailers system. This way I am only going from DC to DC instead of an ac to ac to dc.
If I go with the truck alternator as a charger I will use a low voltage battery isolator so I can use the 2 truck batteries as a dc source also.
Either one I will be able to have around a 139 amp system to charge the batteries.
You are correct on the cables, I made my cables out of 1/0 awg welding cable. Since dc needs the large cables to conduct efficiently. I may have to either put in a dual alternator system or a larger 240 amp alternator in the truck.
I still haven't decided which way to go at this time.
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Old 04-24-2016, 12:40 PM   #6
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I know there is simple answer, but I have been RVing for over twenty years and can't figure out what the acronym CRAP refers to, other than something my dog does.
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Old 04-24-2016, 01:16 PM   #7
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The most likely thing to me is that you don't really have fully charged batteries to begin with. You can't rely on "down the road" charging to put or keep a full battery bank. How do you know they are full?? If you are using the "idiot lights" OR if you are charging and measuring with a voltmeter immediately... you are getting false readings.

You need to use a charger (suggest minimum 20amps..maximum 50 amps...preferablly 3 stage or 4) overnight to put a full charge on. Then WAIT 24 hours and disconnect the negative wire when you do so. THEN measure with a voltmeter and you should see 12.6 or 12.7 volts. Alternatively you can do the reading with a "turkey baster" hydrometer.

Your battery voltage WILL drop under load and if the load is sufficient, it may drop to the trigger point for the alarm solenoid even with fully charged batts...but it is more likely with semi charged ones. This is NOT an indication that you have a dead battery. You can kill the loads and watch the voltage climb right back up. I've had completely full new batteries read under 11.5 under a big load and be back up to 12.5 a couple of hours later. ONLY the voltage of a battery that has been static for 24 hours with no load or charging can be accurately read. ( cables were 000! )
If you're gonna be boondocking a lot you really should get a true battery monitor that can tell you what is going on in REAL time like the Victron or Trimmetric. Alternatively, you could put in a dedicated CPAP battery & socket and charge that separately so as not to influence the voltage cutoff of the CO/propane monitor.
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Old 04-24-2016, 01:25 PM   #8
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Originally Posted by Edmund View Post
I know there is simple answer, but I have been RVing for over twenty years and can't figure out what the acronym CRAP refers to, other than something my dog does.
CRAP = Dog dodo
CPAP = continuous positive airway pressure

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Old 04-24-2016, 01:28 PM   #9
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Originally Posted by Edmund View Post
I know there is simple answer, but I have been RVing for over twenty years and can't figure out what the acronym CRAP refers to, other than something my dog does.
What Is CPAP?

CPAP, or continuous positive airway pressure, is a treatment that uses mild air pressure to keep the airways open. CPAP typically is used by people who have breathing problems, such as sleep apnea.
CPAP also may be used to treat preterm infants whose lungs have not fully developed. For example, doctors may use CPAP to treat infants who have respiratory distress syndrome or bronchopulmonary dysplasia (brong-ko-PULL-mun-ary dis-PLA-ze-ah).
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Old 04-24-2016, 02:00 PM   #10
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Check connections. Nothing will cause voltage drop quite like a loose or dirty connection. I like the idea of trying it with the humidifier off also

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