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Old 11-13-2017, 03:46 PM   #1
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Keeping House Batteries Charged

In the spring I replaced the house batteries on my 2012 AI with 2 Lifeline GPL-6CT's. At the same time I added 2 volt meters (one for the chassis and one for the house batteries within sight of the driver's seat). When reconnecting the Atkins Sunexploer, i clipped the blue jumper as reccomended. The threshold with the blue wire clipped is on at 12.4 V and off at 13.9 V vs. the unclipped on at 12.7 V and off at 14.2 V. I am more interested in getting a boost from the solar panel than keeping the batteries from being depleted. Would it be a good idea to add a manual switch to the jumper so I can change the threasholds as needed?! I also am curious about the house batteries charging from the alternator. With the motor running the chassis volt meter typically showers 14-14.2 Volts. The house batteries are doing great and are about always fully charged or close to it (12.8 V). I hear the BIM click when I start the AI but the volt meter does not move. How do I confirm that the alternator is charging the house BATTERIES?

By the way, the new batteries are great and everything seems to be functioning properly. I just wish to understand the system better.
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Old 11-13-2017, 06:37 PM   #2
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Re. the Atkinson, I see no reason why you would want to wait until your batteries are down to 12.4v before it does something. I suggest you reconnect the blue wire and let your solar work more often.

If you're really concerned about maintaining your batteries via solar, I highly recommend replacing the Atkinson with a MPPT charge controller. They are all 3 (or 4) stage chargers and will keep your batteries in better health than the Atkinson.
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Old 11-13-2017, 07:19 PM   #3
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Originally Posted by FlyFishinRVr View Post
Re. the Atkinson, I see no reason why you would want to wait until your batteries are down to 12.4v before it does something. I suggest you reconnect the blue wire and let your solar work more often.

If you're really concerned about maintaining your batteries via solar, I highly recommend replacing the Atkinson with a MPPT charge controller. They are all 3 (or 4) stage chargers and will keep your batteries in better health than the Atkinson.
I agree with the 12.4 ON setting being too little and too late. I will switch it back. I also understand the concept of replacing inferior components. My honest concern with this is the slippery slope of replacing more and more and more components because they are not the best. In the case of my AI I prefer to wait until I have no choice but to replace something that is broken.
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Old 11-13-2017, 09:27 PM   #4
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Originally Posted by CAS138 View Post
My honest concern with this is the slippery slope of replacing more and more and more components because they are not the best. In the case of my AI I prefer to wait until I have no choice but to replace something that is broken.
Understood. Are you maintaining your batteries via solar when the coach isn't being used? If so, you'll likely extend the life of the batteries by enough to offset the cost of the MPPT controller. Pay now or pay later....

Re. charging from the alternator, that's the job of the BIM, and frankly it does it poorly. The trouble is in the BIM's logic. It needs two conditions in order to close (which connects both battery banks together). First, it needs to see a charging source at either the house or the chassis bank of at least 13.3v. That part is fine. The part that is not is it ALSO needs to see a voltage below 12.6v at the other bank. So if you're driving and the chassis is getting charged by the alternator at 14v+, the house batteries need to be LESS than 12.6v or the BIM won't close and your house batteries won't get charged. What was the reading on your house batteries when you were driving? I'm betting it was at or over 12.6v....
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Old 11-14-2017, 06:37 AM   #5
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Per the lifeline specs, 12.6 volts (BIM closing voltage) is about 85% charged if the 12.6V is measured with the battery in an 'at rest' condition. Driving on a good sunny day with 200W of solar will get me to 100%. Driving while the sun is not shining does not. Many other posts bemoan the BIM and offer solution that enable the Sprinter alternator to charge the coach batteries to 100%.
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Old 11-14-2017, 07:16 AM   #6
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Since I replaced the batteries and (I think) learned to dillegently keep tabs and not completely trust the automatic systems I have had no problems with the house batteries. The house batteries are just about always at 100%, 12.7-12.8 Volts and the inverter/charger is rarely on. I do see the value of the solar system should the voltage drop significantly in the house batteries while the AI is resting in my driveway but so far they have not been needed. My main desire for the solar system is that it augment my electrical usage when boondocking. So...I will reconnect the blue wire and add a manual switch.

Regarding the the alternator charging, i guess I need to drain down my house batteries to below 12.6 volts then go for a drive and see if my house batteries recharge (or monitor my volt meters)?

Like everyone else, my objective is to make sure that at the end of each and every day traveling, I am starting with the most electricity in the bank I can possibly have.
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Old 11-14-2017, 07:37 AM   #7
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Per the lifeline specs, 12.6 volts (BIM closing voltage) is about 85% charged if the 12.6V is measured with the battery in an 'at rest' condition. Driving on a good sunny day with 200W of solar will get me to 100%. Driving while the sun is not shining does not. Many other posts bemoan the BIM and offer solution that enable the Sprinter alternator to charge the coach batteries to 100%.
I certainly have noticed that I am far from alone with my questions and that the same issues get rehashed over and over again. I also believe that many AI owners are perfectionistic and problem solvers. That is a good thing But perhaps a curse as well!

First I want to verify that the alternator does recharge the house batteries as engineered. After that I want to explore the least invasive way to fine tune the system to ensure the batteries are always fully charged at the end of the day.

I greatly appreciate the education and understanding of theses systems that I get from this forum.
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Old 11-14-2017, 09:12 AM   #8
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At what voltage does the BIM open up again to prevent overcharge when charging from the alternator?
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Old 11-14-2017, 09:31 AM   #9
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Per the BIM sheet:
Once the battieries have reached a Float Charge state for one hour, the BIM will isolate the batteries to prevent overcharging, and will only reconnect the batteries for charging if one of the Battery drops to approximately 80% charge, and the other is being charged.

Not clear to me how they define 'float' since the battery type is not known to the BIM (and coach and chassis batteries are different types!)

From a BIM document:

Trouble Shooting of Battery Isolation Manager is complicated. It is much easier to check the proper operation.

Operational Testing:
Press Dash (Battery Assist) Switch. Relay should audibly click and Voltage from Chassis Terminal to Coach Terminal should be <0.2V. If Not, Check for 12V power from Dash Switch to Ground Terminal directly on Relay. (Do not use a Chassis Ground) If 12V present and Relay does not click or bring Chassis and Coach Battery Voltage close, replace Relay.

Release Dash Switch Start Engine & Turn on Coach Lights (or other coach load)
Wait between 20 seconds and 2 minutes and Relay should click. Voltage from Dash Switch Terminal to Ground Terminal should be between 3.5Vdc to 6.0Vdc. If not check that Chassis Terminal >13.3Vdc, Coach Terminal <12.6Vdc, Ignition Terminal >12Vdc. (Check that Chassis and Coach Battery connections are not reversed)

Turn off Engine Plug in Shore Power & Turn on Battery Charger Turn on Head Lights Wait up to 10 minutes and Relay should click. Voltage from Dash Switch Terminal to Ground Terminal should be between 3.5Vdc to 6.0Vdc. If not check that Coach Terminal > 13.3Vdc, Chassis Terminal <12.6Vdc, Ignition Terminal <2Vdc.
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Old 11-14-2017, 09:38 AM   #10
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CAS138
I agree with your blessing and curse comment about forum posters. If only Airstream had a couple of people on staff who were equally anal about things. Many of the things we are doing would cost little if done by Airstream in the first place: decent valve stems, non-rats-nest wiring, well-thought-out refrigerator venting, eliminate low spot in plumbing system just before the macerator, front wheel re-alignment after adding 2000+# to the chassis. etc. etc. etc.
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Old 11-14-2017, 09:52 AM   #11
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CAS138 - I was in a similar state of confusion last summer about whether I was getting coach charging with engine on and determined it was not happening. I had the fridge and freezer going while driving on a bright sunny day for an hour and the coach voltage kept dropping. Dealer checked and found my 125A (or was it 150A?) fuse was blown. Replaced and now it works, but one of my batteries was toast so replaced them with 6V 220Ah.

You probably already know this but a 100w solar panel will only keep a stored coach battery level up if you have the 12v power switch turned off, or if it is left on and there is no load that you've turned on, like lights or refer. Kinda depends if you're under rainy skies and short days, too, so I'm checking it about once a week.

Oh, and when the batts are being charged, the voltage will appear artificially high because that reading is being influenced by the infusion of high voltage. Once the charging stops, the voltage will settle down a lot at first, then gradually over the next many minutes so watch for that.
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Old 11-14-2017, 09:59 AM   #12
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Better, of course, is the sworn enemy of "good enough"...

However, the definition of "good enough" tends to be a bit slippery. Many Airstream designs and installs seems to be, in the opinion of the owners, "inadequate" for the task. That's the frustrating bit.

As a rather anal engineer, my tendency is to go for 'overkill' on too many of the functions f my Airstream. My cross to bear...
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Old 11-14-2017, 10:17 AM   #13
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Keeping House Batteries Charged

With exception of Advanced RV - none of the B-van manufactures install systems to properly monitor the health of your batteries. They likely see it as a cost-benefit trade. To do it properly you need a system that actually measures the power going into and out of your batteries. A good solar controller that includes proper battery health monitoring is the most significant change you can make to your Interstate. IMHO it has more value than bigger batteries and more solar panels.
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Old 11-14-2017, 11:50 AM   #14
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I have always wondered how things work if you have two (or three) smart chargers - say the Magnum, a 3 stage MPPT solar controller, and a better-than-BIM controller for the Sprinter alternator. Since each of the three has its own separate cable feeding the batteries, it seems as if the three are in parallel. So how do the three smart controllers work together (extreme case of being plugged in to AC, sitting in a sunny campsite with the engine running) to give proper charging current & absorption time?

Forgive me if that is a stupid question, as I am a mechanical engineer, not an electrical engineer. In my mind it is three people trying to quickly but precisely fill but not overfill a tub (quick = bulk charge, precisely fill but not overfill = absorb charge) with each person knowing how much water they are adding but not how much the other two are adding.
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