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Old 11-18-2018, 07:05 AM   #1
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2015 Interstate Grand Tour
Lake Oswego , Oregon
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Battery Charging - Monitoring & Strategies

The stock AI equipment for monitoring battery charging is not very handy to see while driving and does not tell the whole story.

I replaced my Magnum monitor with the Magnum ME-RC for more control over charging. I also have the Victron BMV-712 and can watch the charging details on my iPhone.

With the ME-RC, you can change the Charge Rate. This affects how many amps are being delivered to the batteries. Conventional wisdom says use 50% (also called .5C ) because batteries love to be pampered and not taxed (don't we all?). But I saw in the Magnum paperwork a recommended default of 80%. So it sounds like we have some flexibility there.

With the Victron BMV-712, I'm getting a reading of how many volts/amps/watts are actually entering the batteries. Really handy because my ME-RC is only reporting how many amps are passing through the Magnum inverter, then the house takes its cut (Vegas humor for Alex) of about 4-10A to run the fridge and the freezer and charge the laptop, and most of the the rest goes on to the batteries.

The Victron also tells me many Amps consumed since the last full charge. Since I have 220Ah of house battery capacity, I can use 110Ah before hitting my recommended minimum 50% state of charge (SOC) level. If I'm taking a short trip after using up all 110Ah, and my alternator is putting out say 30A net to the batteries, then I'd have to drive 3-4 hours. Longer actually... since the charge profile for AGM (and lead acid) batteries keeps dropping the delivered amperage after the Bulk stage and transitions through the Absorb and Float stages.

What if I'm not going to drive that long? Well, back to the ME-RC... I can change the Charge Rate to 80% (and I've even done 100% a couple of times). The Amps being pulled from the alternator and passed on to the batteries go way up. Now I'm pushing 50-60A and only need a two hour drive.

We have, what is it, a 200A alternator? I'm a long way from taxing it and burning it up, right?

The same battery charge strategy applies when you are plugged in for short periods or, heaven forbid, have to run that awful generator. The generator is the same decibel level and fuel consumption whether you have A/C running or not. Same for if you are charging your batteries at Bulk or Float stage, or 50% Charge Rate vs 90%. If you want to reduce the pain of running that genny, then amp up your Charge Rate to get more utility out of it in a shorter period of time. When you're done shoveling Amps at breakneck speed you can always throttle back the Charge Rate to 50% afterward.

I'm not here to say you should always charge much above .5C, that can degrade your batteries if constantly used. But it's sure a handy tool to use from time to time.
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Old 11-18-2018, 07:17 AM   #2
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Old 11-18-2018, 07:33 AM   #3
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Tronadora,
I don't think that your analysis of the stock AI takes into account the BIM. If I understand correctly, it has a cut-off voltage that causes it to cycle on and off and thus keeps the batteries from reaching 100% as quickly as you analysis suggests. I think the use of a Blue Sea ACR fixes this problem.
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Old 11-18-2018, 08:06 AM   #4
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Titus,
I'm glad you brought that up. I don't know much about the stock BIM except that everyone says it's crap, so I replaced that item too, with the Blue Sea ML-ACR.

It's been working well, but there have also been times I've used it to manually interrupt the connection so that I'm not sharing my incoming energy from solar or whatever with the chassis battery and can direct it all to the house batteries.
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Old 11-18-2018, 08:24 AM   #5
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I use a Trimetric battery monitor to monitor SOC, what's going in and out. It is also very handy to see exactly how many amps each electric drawing device uses. It would be nice to have the Victron, but my system works well, and if it ain't broke....
As far as charging, I rarely plug in, maybe once a year if air conditioning is needed, I rely almost 100% between solar and alternator.

Charging Scenarios:

Sitting with engine off- charged by solar panels, controlled by Trimetric solar charge controller.

Engine running (this is my belief, I could be wrong) - if BIM is closed then charged by alternator, controlled by same charge controller that charges the engine battery. At this time, my house bank is at the mercy of the MB charging system. If BIM is open, nothing from alternator, all solar. My BIM only stays closed for 1 hour then cycles off.

Plugged in - charged through Magnum, controlled by Magnum

Generator running- charged through Magnum, controlled by Magnum.
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Old 11-18-2018, 10:31 AM   #6
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What is BIM?
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Old 11-18-2018, 10:44 AM   #7
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BIM - Battery Isolation Module


Here's a good thread that talks about it.


http://www.airforums.com/forums/f240...ie-151481.html
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Old 11-19-2018, 06:00 AM   #8
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Old news here, but for the benefit of any readers who may come across this thread without reading previous ones, our DIY lithium system incorporates an Electrodacus BMS. It is not a conventional choice, but it has worked very well for us (knock wood).

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Old 11-21-2018, 07:35 PM   #9
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Tornadoes, thanks for starting thi thread. I still have the stock AI setup and after driving for 5hr both house and chassis bat read 12.4 with no fridge or freezer on. Is it not charging or is it because it is cold (15 deg F)? I will need guidance on the BIM when I switch to lithium. I called blue sea and the don’t recommend ARC with lithium
And I am concerned about over charging lithium batteries with existing stock BIM
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Old 11-22-2018, 07:47 AM   #10
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I am also researching a drop in Lithium project and have run into the BIM limitation. AM Solar has suggested the Cyrix-Li-Ct battery combiner like the one shown in this kit: https://amsolar.com/rv-battery-accessories/98-altcli230. It looks like it addresses the issue with the stock BIM with lithium. (overcharging and/or draining the house batteries). There are other options that I have looked at but the literature suggests this is a good solution. PS I was not going to change the Magnum inverter.
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Old 11-22-2018, 08:22 AM   #11
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I have been planning a lithium upgrade for a long time. One of the things delaying me is deciding how I want to deal with the BIM.

It looks to me you have a few choices. The Victron Cyrix-Li-Ct is what AMSolar recommends, but I'm not too convinced it would be the best choice. What it does is simply charge the lithiums (which can draw a huge amount of energy taxing the alternator), and then disconnects them for a period of time to cool things off. I'm concerned that the lithiums eventually will overheat the alternator, shortening its life since it does not limit the amount of current they can draw, only the amount of time it can draw.

Two alternatives I am gravitating to is a DC-DC charger that limits the draw along with a disconnect that can isolate the lithiums from the chassis when I don't need to charge, since I have 300 watts of solar to keep them topped off anyway.

I found two choices. The Sterling charger, and the Redarc 40 amp dc-dc charger.

What I like about the Redarc unit is you only have to tie in the positive from the chassis battery and then ground the unit. The Sterling requires a separate negative connection back to the chassis, which would be difficult to run. The difference in amp draw really doesn't concern me because we don't really need to fast charge them the way we camp.

If anyone has any other solutions other than these three, I'm all ears.
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Old 11-22-2018, 08:37 AM   #12
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Quote:
Originally Posted by DNM View Post
Tornadoes, thanks for starting thi thread. I still have the stock AI setup and after driving for 5hr both house and chassis bat read 12.4 with no fridge or freezer on. Is it not charging or is it because it is cold (15 deg F)? I will need guidance on the BIM when I switch to lithium. I called blue sea and the don’t recommend ARC with lithium
And I am concerned about over charging lithium batteries with existing stock BIM
Depending on the brand of lithiums overcharging isn't the issue as the two I'm considering (Battleborn or Lifeblue) have internal battery management systems to prevent overcharging and will cut the power when they are fully charged.

Depending on your choice of lithium batteries, overcharging may not be the issue, over taxing the alternator is a more serious concern with lithiums. But, I agree, it should not be used with lithiums.

As for the current BIM, to check if it is working, simply put a voltmeter on the positive side of the BIM from the chassis battery while the vehicle is running. If it is pulling 14 volts or so, then it's working. If not, the connection below the driver's seat to the right of the chassis battery where a dc bus is tucked down beside it and the BIM itself should be checked. A loose connection was the culprit when I bought my new AI and it took a trip to JC for them to figure it out (and it took the guy five minutes to do so as he'd seen the issue before). So, snug those bolts down on both the BIM side and the chassis battery side and check you voltage with the van running.
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Old 11-22-2018, 09:40 AM   #13
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There is more to checking the BIM than just making sure that 14V is getting to it from the Sprinter battery cable (though that can certainly be one problem). You need to check to see if it is switching right from both directions. (Or as 'right' as the poorly designed BIM can be.)

This is from BIM troubleshooting guide:

Press Dash battery connect 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
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 LightsWait 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 11-22-2018, 02:20 PM   #14
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Thanks for the feedback. Does it make sense that both chassis and house batteries were low if it was a BIM problem? I wonder if the cold, 15 deg F, to effect the reading or the alternator charging.
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Old 11-22-2018, 02:27 PM   #15
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If you were driving the alternator should have charged the chassis battery whether the BIM was working or not, cold temperature or not. And if you were plugged in the coach batteries should have charged whether the BIM was working or not (assuming the Magnum was set to Charge). Temperature would affect the Magnum charging schedule if you have the temperature compensation - which I think is standard now but was something that I had to add to my 2013. Low temperatures should not cause/allow the coach batteries to be low after a long (several hour) period of charging time.
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