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Old 04-25-2016, 11:57 AM   #21
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larryandamy gave you one of the best responses to help you isolate the problem. There are a number of factors that are causing the problem you're having and I suspect that the alarm is a combination of more than one, which will make it very difficult to troubleshoot. The immediate problems that come to mind are:
1. Battery is not fully charged - possible but likely a minor contribution to the problem
2. Battery output is effected by temperature, when cold, batteries exhibit less capacity
3. Batteries have internal resistance. The higher the current load on them, the lower the output voltage from them. Adding the CPAP and furnace motor current draws is likely a major contributor to the problem.
4. Voltage drop in the wiring from the battery to (in this case) the propane detector.

In my 2011 Georgetown, the propane detector is wired directly to the house battery, giving it the maximum possible voltage. Your rig may not have heavy enough wire from the battery and the CO detector is connected at the distribution panel where the fuses are located. In this case, voltage drop in the wire from its resistance will exacerbate the problem, as mentioned by larryandamy in their prior post.

I solved the idiot light charge level problem by installing a digital voltmeter (~$10) that reads down to 1/100 of a volt in my Georgetown. I have a set of 2/0 wires from the kitchen area to the battery and just attached the meter to them. These heavy wires feed an inverter that's never used when we're not travelling so they made a convenient attach point for the meter. I also recalibrated the purchased voltmeter using my calibrated meter because very few of these low cost meters are accurately calibrated when manufactured.

Phil
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Old 04-25-2016, 03:15 PM   #22
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A thought occurred to me while I was in the Dr. waiting room. One of the advantages of two 12 volt deep cycle batteries (vs two 6 volt batteries) is the ability to share the load across two electron generators with relatively thinner plates; thus much less Peukert Effect (the reduction in apparent capacity under load) on the battery system.

At lower amperage draws on equal AH systems, 2 6 volt deep cycle batteries will see nearly the same performance as a pair of 12 volt deep cycle batteries.

However at higher amperage demands, the ability to share the amperage load between the two 12 volt batteries reduces current demand from each battery; thus lower capacity penalty.

In the example below with a dual 12 volt 100AH setup the 35 amp at 12 volts (420 Watts) demand would be shared equally (with proper interbattery wiring) at 17.5 amps each. The Peukert Effect penalty would be reduced from 50% of rated total capacity to 35%. Since only the voltage and not the generation capability is doubled by putting two 6 volt batteries in series; each 6 volt battery "sees" the full 35 amp demand and the full 50% penalty.
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Old 04-25-2016, 11:33 PM   #23
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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.
Thanks.
CPAP Continuous Positive Airway Pressure

BiPAP Bi level Positive Airway Pressure

Breathing machine for those of us with a bit of Sleep Apnea.

To keep us from stopping our breathing 10-30 times an hour and causing our self brain and heart damage
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Old 04-25-2016, 11:55 PM   #24
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I forgot to mention that I do have 2 Honda 2000W generators and run them about 2-4 hours when boondocking with the 30 amp plug connected to charge and to run the coffee post etc...

I just went through the menus on my CPAP and found an option to set the humidity level to off. I will try it tonight. Not sue how much I'll need the furnace tonight though. We pulled off in the Mojave around Barstow CA to sleep.

Thanks again. I really enjoy and learn so much from this community.
Where you at and were are you going. We are in Chino Area about 90 miles South of Barstow. I have a bad itch to work on an RV since we sold our TH a month ago and still have not gotten delivery of our new FR TH. I also have a friend who is something of an automotive electrical GURU who lives about 40 miles down the 15 from you who would always be up for a challenge. Pm me is you are frustrated enough to reach out for help.

Tom
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Old 04-26-2016, 08:26 AM   #25
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A thought occurred to me while I was in the Dr. waiting room..
That is a really interesting thought. Have to mull that over but it seems to indicate that any installation that has multiple parallel batteries would derive a benefit from a lower Peukert penalty by keeping the load current on each individual battery to a minimum.

Thought provoking...but...that just seems to simple!
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Old 04-26-2016, 08:44 AM   #26
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That is a really interesting thought. Have to mull that over but it seems to indicate that any installation that has multiple parallel batteries would derive a benefit from a lower Peukert penalty by keeping the load current on each individual battery to a minimum.

Thought provoking...but...that just seems to simple!
There has to be a reason for the popularity of 12 volt deep cycle batteries where weight is a consideration. If you had room for 4 batteries and wired as indicated, the current demand per battery would be 1/4 of total load, while the 4 6 volt batteries would see 1/2 of the load per 12 volt cell.

When the PE in the previous example is taken into account, the longevity differential of the bank would be huge.

35 amp load @ 12 volts across 4 12 volt batteries would see only 8.75 amps per battery and the 100AH battery capacity would only be reduced by 15% or 85AH per battery. The longevity of the bank would be 340AH.

35 amp load @ 12 volts across 2 12 volt (2 6 volt in series) batteries would see 17.5 amps per set and the 200AH battery set capacity would be reduced by 35% or 130AH per battery set available. The longevity of the bank would be 260AH.
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Old 04-26-2016, 09:04 AM   #27
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Devil's advocate: The opposite view

Assumptions:

All Batteries (6 and 12 volt) are physically the same size and have the same internal construction. What varies is the thickness of the plates for more storage in 6 volt batteries. The 6 volt batteries have plates twice as thick for twice the storage, but there is only room in the container for 3 cells (not 6 like a 12 volt battery).

The electrons needed to produce current demand are only "available" at the surface of the plate and it takes "time" for electrons held deeply in the lead to migrate to the surface. The thicker the plates the more storage the battery has, but the less able that battery is to generate large currents.

Peukert Effect is the capacity penalty incurred when deep cycle battery thick plates are tasked to give up more electrons than they can immediately generate (without recovery time). Voltage (and available capacity) drops due to the increase in internal resistance when you try.

In a parallel circuit, the current is equally split through all branches provided the resistance is equal in all branches.

In a series circuit, the current is the same through both resistances, the only thing that could vary is the voltage drop across each resistor. The voltage (and available capacity) drop is identical if both resistances are the same.

Did I miss anything?
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Old 04-26-2016, 09:41 AM   #28
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In a parallel circuit, the current is equally split through all branches provided the resistance is equal in all branches
On paper that is true, but in the real world I have never seen a system where each cell had the same internal resistance or even end up with the same specific gravity. That is why we work in acceptable tolerances. Even the cables act as shunts and the batteries at the end of the lines have a slight current loss.
To most lay people they will never see or recognize this.
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Old 04-26-2016, 09:49 AM   #29
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Originally Posted by Herk7769 View Post
A thought occurred to me while I was in the Dr. waiting room. One of the advantages of two 12 volt deep cycle batteries (vs two 6 volt batteries) is the ability to share the load across two electron generators with relatively thinner plates; thus much less Peukert Effect (the reduction in apparent capacity under load) on the battery system.

At lower amperage draws on equal AH systems, 2 6 volt deep cycle batteries will see nearly the same performance as a pair of 12 volt deep cycle batteries.

However at higher amperage demands, the ability to share the amperage load between the two 12 volt batteries reduces current demand from each battery; thus lower capacity penalty.

In the example below with a dual 12 volt 100AH setup the 35 amp at 12 volts (420 Watts) demand would be shared equally (with proper interbattery wiring) at 17.5 amps each. The Peukert Effect penalty would be reduced from 50% of rated total capacity to 35%. Since only the voltage and not the generation capability is doubled by putting two 6 volt batteries in series; each 6 volt battery "sees" the full 35 amp demand and the full 50% penalty.
Herk makes valid point here, Good work.
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Old 04-26-2016, 09:52 AM   #30
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I may have missed this somewhere, I aplogize if so.


In series 6 volt string if one cell has bad plates this may very contribute to voltage loss quickly when a load is applied causing low voltage. It could be as simple as a bad battery with 1 cell bad.
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