BIM Worked Properly Today

[Boxster1971]

Started trip to dealer for 80,000 mile service early this morning, just before sunrise - no solar charging. Checked my battery voltages before starting. Coach batteries were down to 12.6V and about 2% (~9 AH) from full. Then I started the van and saw that the BIM had connected the battery systems and the coach batteries were getting the charge they needed. (note: I know when BIM relay connects batteries because I changed the "Battery Boost" switch from a momentary ON push switch to a regular Toggle ON switch with indicator light.) This made me happy to know the BIM was working properly - great!

I've observed a problem with my modified 400 watt solar system; when the sun shines the BIM will not automatically connect the batteries to get a charge from the Sprinter alternator even when they are discharged significantly. The problem is caused because when the sun shines the solar panels apply 13-14V to batteries depending on their state of charge. Then even when the batteries are down 20% the BIM will not connect because it only measures voltage. Solar alone will not recover 20% (88AH) during a normal daylight cycle. The fix for me was changing the Boost switch to a manual toggle so I can control when to charge the coach batteries while driving.

Suspect this can also be a problem for Interstates with 100 watts of solar. When the sun shines you get no battery charging from the Sprinter while driving. Then the limited solar charging leaves your coach batteries less than fully charged even after a long drive in daylight. This leads to a slow death spiral of the coach batteries unless they get a full charge when plugged in to shore power.


- - Mike
2013 Lounge EXT on 2012 Sprinter

[FlyFishinRVr]

Interesting!

So, I've been thinking about it, and while your coach may work this way, I'm not sure mine does. My observation has been that when my solar alone is providing a charge, my house and chassis batteries read approx. 13.1v (checking via the tank monitor panel). I can then start the engine, and both banks read 14.1-14.2v. To me this says 1) the BIM is working as it's connecting both banks together (obviously this is with somewhat depleted batteries, which mine typically are ), and 2) when the engine is running, the alternator is providing the charge source even when the solar is "on". I've seen similar behavior when turning on the generator (i.e. the batts read 14v+ even with the solar "on").

Maybe on the 17's they added some logic that allows it to work this way?

[Boxster1971]

Originally Posted by FlyFishinRVr

Interesting!

So, I've been thinking about it, and while your coach may work this way, I'm not sure mine does. My observation has been that when my solar alone is providing a charge, my house and chassis batteries read approx. 13.1v (checking via the tank monitor panel). I can then start the engine, and both banks read 14.1-14.2v. To me this says 1) the BIM is working as it's connecting both banks together (obviously this is with somewhat depleted batteries, which mine typically are ), and 2) when the engine is running, the alternator is providing the charge source even when the solar is "on". I've seen similar behavior when turning on the generator (i.e. the batts read 14v+ even with the solar "on").

Maybe on the 17's they added some logic that allows it to work this way?

Good to know. Yes the newer BIMs may have the ability to charge batteries properly, sounds like yours certainly does.

[Camerons]

Boxster. What stitch did you replace so that you can see if the bim is working. I have a momentary one by my left knee but no light on it. Have to ask my gf to get up and see if the tank level switch says it is charging. Would like to have a light on it so that I know if it is working. Curious to know what switch you used. Thanks. Cam

[Boxster1971]

Originally Posted by Camerons

Boxster. What stitch did you replace so that you can see if the bim is working. I have a momentary one by my left knee but no light on it. Have to ask my gf to get up and see if the tank level switch says it is charging. Would like to have a light on it so that I know if it is working. Curious to know what switch you used. Thanks. Cam

I replaced that momentary switch by your left knee. Attached photo of panel removed and final switch installation. Also installed an indicator light just above the tank monitor panel. Added another switch near the DC fuse panel to disable the BIM when I want to be sure the batteries don't get connected.


Sent from my iPhone using Airstream Forums

[gghayes]

What is BIM?
Gloria

[73shark]

Originally Posted by gghayes

What is BIM?
Gloria

Battery Isolation Module

It keeps the house loads from draining the chassis battery but allows the alternator and/or solar to charge both the chassis and house batteries. At least it did on my 2011. It doesn't seem to function that way for some any more.

[FlyFishinRVr]

Originally Posted by 73shark

Battery Isolation Module

It keeps the house loads from draining the chassis battery but allows the alternator and/or solar to charge both the chassis and house batteries. At least it did on my 2011. It doesn't seem to function that way for some any more.

On my '17 EXT Lounge, the BIM will connect the house and chassis batteries together any time a charge source is available (solar, engine, genny, or shore) and the chassis battery is below 12.6v.

The issue Mike is running into is when his solar is active, the BIM doesn't seem to want to connect the battery banks together because it's detecting the 13.1v that is coming from the solar and thinking that's the chassis battery voltage. Since it's below the 12.6v threshold, it thinks all is fine.

To me, it seems like something is wonky with Mike's coach because that is NOT how the BIM should function. It should look at the chassis battery voltage and then check for a charge source. If the chassis battery is below 12.6v and a charge source exists, it should close, regardless of the source of the charge.

The only thing I can surmise from his situation is when his mods were done, something got reconnected wrong and now his BIM is looking at the voltage across the house batteries to determine whether to open or close vs. the chassis battery. Very odd......

[Boxster1971]

Originally Posted by FlyFishinRVr

On my '17 EXT Lounge, the BIM will connect the house and chassis batteries together any time a charge source is available (solar, engine, genny, or shore) and the chassis battery is below 12.6v.



The issue Mike is running into is when his solar is active, the BIM doesn't seem to want to connect the battery banks together because it's detecting the 13.1v that is coming from the solar and thinking that's the chassis battery voltage. Since it's below the 12.6v threshold, it thinks all is fine.



To me, it seems like something is wonky with Mike's coach because that is NOT how the BIM should function. It should look at the chassis battery voltage and then check for a charge source. If the chassis battery is below 12.6v and a charge source exists, it should close, regardless of the source of the charge.



The only thing I can surmise from his situation is when his mods were done, something got reconnected wrong and now his BIM is looking at the voltage across the house batteries to determine whether to open or close vs. the chassis battery. Very odd......

Actually when solar is available and the chassis (Sprinter) battery is below 12.6V it will keep the batteries connected and charged while parked in my driveway. The problem I was referring to is when you are driving the van in sunlight. Then there is 13+ volts on the coach batteries and 14 volts on the chassis battery. Since my BIM only senses voltage it will not connect the batteries under these conditions, even if the coach batteries are significantly depleted and need more charging than solar can provide. This problem may be unique to my modified systems so can't be considered a universal problem as I may have implied in my original post.

Stay safe,

- - Mike
2013 Lounge EXT on 2012 Sprinter

[FlyFishinRVr]

Originally Posted by Boxster1971

Actually when solar is available and the chassis (Sprinter) battery is below 12.6V it will keep the batteries connected and charged while parked in my driveway. The problem I was referring to is when you are driving the van in sunlight. Then there is 13+ volts on the coach batteries and 14 volts on the chassis battery. Since my BIM only senses voltage it will not connect the batteries under these conditions, even if the coach batteries are significantly depleted and need more charging than solar can provide. This problem may be unique to my modified systems so can't be considered a universal problem as I may have implied in my original post.

Stay safe,

- - Mike
2013 Lounge EXT on 2012 Sprinter

Sorry Mike, I messed that up. Thanks for clarifying.

So either the old BIM worked differently from the new ones, yours is faulty, or as you say, something changed in your configuration when your system was modified to make yours work the way it does currently.

This does bring up an interesting question though. In the detailed operation of the BIM, it says the relay will remain closed for a max of 60 minutes, then it will open for 2 minutes (apparently to avoid overcharging the batteries and allow the relay to cool). After that it will test the batteries again and if either bank is still below 12.6v (and there is still a charging source), it will close for another 60 minutes, otherwise it will remain open. Is there any chance you just happened to check yours during that 2 minute "rest" period? I know it's a long shot, but I thought I'd toss it out there.

Also, there is something in the BIM owner's manual that's a bit cryptic which says "If the charging system is drastically overburdened, the batteries will be isolated". It doesn't say anything about the conditions that would cause this however. Could there be something in your new config that's making the BIM think this is the case so it's staying open?

[Boxster1971]

Originally Posted by FlyFishinRVr

Sorry Mike, I messed that up. Thanks for clarifying.

So either the old BIM worked differently from the new ones, yours is faulty, or as you say, something changed in your configuration when your system was modified to make yours work the way it does currently.

This does bring up an interesting question though. In the detailed operation of the BIM, it says the relay will remain closed for a max of 60 minutes, then it will open for 2 minutes (apparently to avoid overcharging the batteries and allow the relay to cool). After that it will test the batteries again and if either bank is still below 12.6v (and there is still a charging source), it will close for another 60 minutes, otherwise it will remain open. Is there any chance you just happened to check yours during that 2 minute "rest" period? I know it's a long shot, but I thought I'd toss it out there.

Also, there is something in the BIM owner's manual that's a bit cryptic which says "If the charging system is drastically overburdened, the batteries will be isolated". It doesn't say anything about the conditions that would cause this however. Could there be something in your new config that's making the BIM think this is the case so it's staying open?

I'm aware of the 60 minute limit and that is not an issue. The basic problem is the simple voltage logic in my BIM controller. Mine seems to work as advertised in the older technical documents I downloaded in 2013. The newer models may have different logic that better handles the solar input. Also I noticed the newer technical documents on the BIM logic to not specify specific voltages as the older versions. That hits that things were changed.

Interesting comment on the overburdened charging system. This is the entire sentence from the manual:
"If the charging system is drastically overburdened, the batteries will be isolated, however, if the BIM sees a long term charging of both

batteries it will allow the batteries to remain connected and allow the charging system to do its job."

Yes a very confusing statement - don't know what it means. Perhaps it has logic that when in its 2 minute checks of the voltage after 60 minutes of connection it looks for a level of voltage recover on the charged system. If it doesn't show recovery it could judge the charging system to be overburdened. What ever the logic I don't think it plays in my setup.

From my observations the BIM systems in my van performs as specified. It just cant measure the battery state of charge.

The only factor that could improve the system performance of the BIM would be current measurement. Airstream chose not to provide a current measurement of the coach batteries; the only way you can accurately measure the battery state of charge.