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Old 11-01-2017, 10:45 AM   #1
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Battery Charge Timing etc.

This past weekend was our first experience boondocking at Alumalina. 2017 30 FC Bunk

We keep heat on at 60 degrees. Furnace ran some through the night. Batteries were charged to 12.7 V on wall meter. When we woke up at 7 I checked battery meter and it said 11.6 V. Kind surprised. I ran generator for 5-6 hours. during the day.

Finally the questions.

At what voltage will systems turn off? 11.6V. Furnace and fan still worked.

How many hours of generator time will bring the batteries back to full charge? 6 hours was not enough.

Would a 4 stage converter charge the batteries much faster? My meter says 13.4 V while connected to shore power.


I purchased a Progressive Dynamics converter only to find out that it really does not fit. Modification to the chassis are required to allow the cover door to work.

Has anyone purchased an upgraded converter that fits a 2017 30 Bunk???

Thanks in advance!!!

Jim
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Old 11-01-2017, 10:59 AM   #2
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Q1....on our Classic they won't, it will drain 'til empty.

Q2....Don't know, never used the 2000i to fully charge the batt's from 12.4v, at least 12hr on the IOTA IQ4,(if below 12.2) and an hour a day on the Honda to bring it back. 12.4 is our max discharge point.

Q3...not necessarily, depends on the charger specs. 13.v is most likely the 'float' mode.

Does your Bunk have AGM batt's?

Bob
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Old 11-01-2017, 11:44 AM   #3
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We have the group 24 Interstate batteries. Continuing research indicates that it takes a very long time to recharge batteries back to 100% charged
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Old 11-01-2017, 02:13 PM   #4
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I would....fully charge both, let sit for at least an hour and, take them to your local NAPA and have them tested. It wouldn't be that unusual that they need replacement.

Our OEM Interstate 27's were ruined on the dealers lot.....24/7 un-attended on shore power.

Bob
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Old 11-01-2017, 02:32 PM   #5
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11.6v is 20% capacity. Should never let get below 50% (about 12.1v give or take). Your batteries sound like they are compromised.

It can take 36 hours to FULLY charge the batteries.

A good charger like a PD unit will start out in bulk charge at 14.4v...14+ volts is needed to really PUSH power into the batteries. Can stay there for up to 4 hours. Then 13.6 normal mode, then 13.2 float when fully charged.

The nice feature of a PD unit is you can manually put it into bulk mode, which is helpful when on generator and charge time is limited.

I'd suggest fully charging your batteries (couple days on shore power), let them rest an hour, and then getting a hydrometer and testing each cell. Did this for a friend who had fairly new batteries, they read 12.7, but that was just a post-charging surface charge. Both would tank overnight into the low 11s. He had a couple of dead cells in both batteries--specific gravity of zero, which is just water in those cells.
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Old 11-01-2017, 05:21 PM   #6
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Quote:
Originally Posted by jim6090 View Post

... Batteries were charged to 12.7 V on wall meter. When we woke up at 7 I checked battery meter and it said 11.6 V.

I ran generator for 5-6 hours. during the day.

Q1. How many hours of generator time will bring the batteries back to full charge? 6 hours was not enough.

Q2. Would a 4 stage converter charge the batteries much faster? My meter says 13.4 V while connected to shore power. ...
Answers:

A1. Even for a 45 amp converter (e.g. PD4645) the most that is used for battery charging is between 5-8 amps. Therefore, if your batteries were for argument sake 160 amp hours and you depleted the to 11.6 volts you would need to put back almost 160 amps. If you converter is putting out 8 amps then it will take at least 20 hours to charge them. Likely more because as the battery gets closer to 100 % charge the charging rate goes down.

A2. No a different converter would not make any difference if the maximum amperage they can direct to the batteries is 8 amps.

If you want a faster charge connect 4 gauge booster cables from your running TV to the house batteries. Depending on you alternator and engine rpm you can put in 40 amps per hour or more.
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Old 11-01-2017, 05:24 PM   #7
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Quote:
Originally Posted by pcskier View Post
...
A good charger like a PD unit will start out in bulk charge at 14.4v...14+ volts is needed to really PUSH power into the batteries. Can stay there for up to 4 hours. Then 13.6 normal mode, then 13.2 float when fully charged.
Voltage is only part of the equation. Most RV types of converter will only push 5-8 amps to the battery when connected to shore power. That is why it takes so long to charge your house batteries.
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Old 11-02-2017, 02:28 PM   #8
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When you check battery voltage on lead acid batteries the load must be removed for at least an hour. If you look at your house voltmeter, depending on load, you will see a much lower voltage. You really need to instal a battery state of charge system with an adequate shunt. That is the only way to determine remaining power during use. A good charging system that periodically, equalizes the batteries will make them last much longer. AGM and lithium batteries will also last longer with the above methods for increasing battery life, but cost more.
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Old 11-02-2017, 05:27 PM   #9
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Hi

We're getting into the time of year where it gets cold outdoors. If it got down in the 40's all night long, your batteries may have gotten a bit chilly out in the battery box. That will turn the 12.1V "magic number" into something a bit higher. Your batteries may effectively be "empty" at 11.6V if they are pretty cold. The magic 12.7V "full" number will get up to around 13.3V if it gets frosty out.

Best use practice is to never go below 50% on lead acid batteries. At 70F that would be 12.1V on a resting battery. Getting down to < 20% is not a good idea at all.

First question generally is - when did you last check the battery "water" level? If it's been awhile, check it now. Low water drops the capacity of the battery. It also increases the chances of damage when recharging.

Full capacity on a pair of group 24's is something in the 160AH range. That is based on the same 70F assumption. Capacity when cold can be much less. Since the full charge state is also off when cold, it's a double whammy.

If the furnace pulls 5 or 6A (as some do), running for 12 hours is at most 72 AH. I'd start poking around for other loads that might be active. Leaving the inverter on is one classic mistake. Having a three way fridge that switches to 12V is another.

Unless something odd came in as a load, you likely have a battery issue.

Bob
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Old 11-02-2017, 06:46 PM   #10
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Quote:
Originally Posted by Adventure.AS View Post
Answers:

A1. Even for a 45 amp converter (e.g. PD4645) the most that is used for battery charging is between 5-8 amps. Therefore, if your batteries were for argument sake 160 amp hours and you depleted the to 11.6 volts you would need to put back almost 160 amps. If you converter is putting out 8 amps then it will take at least 20 hours to charge them. Likely more because as the battery gets closer to 100 % charge the charging rate goes down.

A2. No a different converter would not make any difference if the maximum amperage they can direct to the batteries is 8 amps.
This isn't true for any modern switch mode multi stage converter/charger produced since the late 90s-early 2000s. Let me help if I may.
While it's true that older linear and ferroresonant transformer type converter had a separate charge function that was often only 3-6 amps, all of the new switching converters are capable of charging at their full rated output.
Airstream as of late, has strictly used a 55 amp Parallax converter, (7455, 7355, 8355) and believe it or not, all 55 amps are available for charging and will deliver that under certain conditions but they are constant voltage and many complain about overcharged batteries because they don't step the voltage down. That's why you see folks opting for other brands that are multi-stage (voltage)
Since it's a shared load with the other DC accessories (lighting, furnace fan, igniter boards, water pump, radio, etc) that subtracts from the amperage available or left for charging. Because most DC accessories are not used all at the same time, there are ~50 amps available for charging most of the time.
So why don't I see 50 amps being delivered to my batteries by my on board, shunt equipped battery monitor? The answer is usually battery internal resistance, and sometime inadequate cable size or voltage drop.
Your batteries are in charge of the current being delivered to them, not the converter. The way multi-stage converters work (excluding Parallax, more on that in a minute) is by changing the voltage (force) so the converter can deliver more current (amps.) When the converter is first applied to the load, it samples the voltage and if it's low enough, it will enter the boost mode and remain there for a predetermined period, such as the PDI, Boondocker and Iota units to force as many amps into the battery in the shortest period of time. It can't determine the actual SOC (state of charge) of the batteries so it uses timers to estimate what the battery SOC is based on that initial voltage. After the time expires, it will enter the normal phase and remain there until the voltage drops again another predetermined low SOC, or if no voltage change is sensed, it will enter the float or storage mode after ~48 hours. If you sit there with a volt meter expecting something to happen at the same time or voltage reading every time, you will drive yourself crazy. There is more to the algorithm.
If you have a 55 amp converter and only see for instance 20 amps and tapering off, that is telling you the resistance in the batteries is increasing and preventing too much current from being delivered. There is nothing wrong with your converter. On the other hand, with very low SOC, it's not uncommon to see a few amps more than the rated output. I've seen 64 amps from a Boondocker 60 and 57 from a PDI 55 amp unit.
Expecting a FULL charge from a generator while boondocking for a few days isn't going to happen unless it's running all the time. It's usually 12+ hours to get the last 10% back into the batteries. No need to even try, just run your generator for 2-3 yours in the morning and you can repeat that 50-90% SOC cycle for several days or more and worry about that last 10% when you get home and have shore power. You won't shorten the life of your batteries doing that, just remember to get that full change when you get back. Solar will help for longer trips.
Parallax has a different charge algorithm . Airstream used their constant voltage converters and they now claim to vary the current, again I presume on a set of timers. They recently changed their literature to enter into the "multi-stage" charging market about the same time they lost the Airstream account but I'm not sure which came first. They will remind you to not leave your converter connected to your coach during periods of non-use or long time storage. I agreed to retest their equipment that I did 10 years ago and there has not been any change so far that I can measure but will report any new finding. Moot point for Airstream since they bailed on them this year anyway.
I prefer to have a 4-stage converter that I can leave plugged in indefinitely and not worry about over-charging. I've had my Lance camper plugged in since 2007 with a Progressive Dynamics 9245 that came with it and the batteries are still alive, although showing capacity loss. Pretty good track record I'd say.
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Old 12-03-2017, 11:30 AM   #11
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Quick question about converters and charging batts. If one is concerned about boiling batteries while keeping an AS plugged in all the time, why not just put the plug on a timer and say,have it go on once a week for say 6-8 hrs and just top up the batteries once a week. Wouldn't that prevent any problems, especially if your not sure what stage your converter actually goes to?
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Old 12-04-2017, 07:33 AM   #12
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Originally Posted by capt_ron777 View Post
Quick question about converters and charging batts. If one is concerned about boiling batteries while keeping an AS plugged in all the time, why not just put the plug on a timer and say,have it go on once a week for say 6-8 hrs and just top up the batteries once a week. Wouldn't that prevent any problems, especially if your not sure what stage your converter actually goes to?
Hi

... that has been suggested a few times

The gotcha with batteries boiling is that it happens from a shorted cell. We happen to run them in parallel and that's a bad configuration if there is a cell short. The second battery is there to boil the first one, even with no charger present. Yes, when you turn the charger on, the process will proceed. By then it's already to late.

Since most of us grow up with single battery setups, we don't get a lot of exposure to the weird stuff combination wiring can do. In addition, a shorted cell takes out both batteries. It's one of the "twice as likely" things with a combo. In a normal car, we'd just say ... battery dead ... time to replace. No drama, it's just a dead battery.

Bob
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Old 12-04-2017, 09:49 AM   #13
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"why not just put the plug on a timer?"

I know a number of people who do this when storing their rig. About an hour a day reportedly works well.
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