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Old 11-14-2017, 12:06 PM   #15
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2013 Interstate Coach
Raymond , Iowa
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rmkrum
Don't feel bad, I suffer from both overkill and overanalyze. Overanalyze in deciding whether or not to do something and then overkill in doing it.
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Old 11-14-2017, 12:11 PM   #16
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Originally Posted by CAS138 View Post
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.
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At what voltage does the BIM open up again to prevent overcharge when charging from the alternator?
The only way to ensure ALL your batteries are fully charged at the end of a day of driving is to replace the BIM with something like the Blue Sea Automatic Charging Relay (do a search on this forum and you'll see some discussion about this). The Blue Sea ACR will stay closed any time there is a charge source above 13v at either bank, regardless of the state of charge of the other bank. To prevent overcharging, you rely on the current limiting function built into the Sprinter alternator (lots of discussion about this too that shows the Sprinter alternator does indeed current sense and limit) and ideally the 3 stage charging function of a MPPT solar charge controller.

With these two changes (Blue Sea ACR and MPPT solar charge controller), you will have a very robust system that should work well under all conditions and will keep your batteries topped up when driving and when stored (assuming you store it outside in the sun or leave it plugged in).

Frankly, if Airstream wants to continue to market their motorhomes as "Best in class", they really need to make these two changes. I realize pop-up TV's, LED lighting under the coach, and remote locking storage bays are great visual selling tools at shows and on sales lots, but spending a bit more time tending to the SYSTEMS that make these expensive beasts more useful and less frustrating for owners would go a long way towards meeting their stated goal.....
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Old 11-14-2017, 12:31 PM   #17
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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?
Each will do it's job, and that's why it's best to use "smarter" devices vs. the blunt instruments that Airstream has been using. If you want the "smartest" system possible, each charging source would current sense vs. voltage sense. Will the batteries accept any more current? No - then go into "rest" mode and keep monitoring.

As is, the Atkinson solar charge controller is a single phase charger and limits it's operation by setting a really low "on" voltage together with a timer (120 minutes). Are the batteries really low? OK, turn on for 2 hrs and hope for the best. Oh, the sun already went down? Bummer....

The Magnum is actually quite good and follows the 3 stage charging algorithm that battery manufacturers want to see, complete with preset "tables" for different battery types. Yes, it could be better and smarter if it current sensed instead of voltage sensed, but it's still usable.

The BIM is just a wart. Like the Atkinson, it's a holdover from the days of wet cells where the biggest concern was boiling off the electrolyte due to overcharging. Well, welcome to the new millenium, AGM batteries, and electronics that no longer rely on vacuum tubes. With a MPPT solar charge controller, current sensing alternator, and smart (ish) inverter/charger, the BIM can now go the way of the woolly mammoth and be replaced by something that allows smarter devices to better manage the charging system(s).
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Old 11-16-2017, 07:55 PM   #18
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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.

Titus- My 2012 rig does not have a dash (battery assist) switch. But I did try something like your 3rd procedure and it did show that I was getting current from the inverter/charger or house batteries to the chassis
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Old 11-16-2017, 08:08 PM   #19
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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.
Tronadora- I do know that I am getting some charging but I am just not certain from what because it is so subtle. The solar seems to be working. Once I am certain I may just disable it and see if the batteries charge from vehicle operation. If not, my next step will be to check that fuse.
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