Batteries, Inverters, Generators & Charging,

[Long Spur]

First time post. I am a Mechanical Engineer and have no problem with understanding technology and logic ... when "well done" and well thought out.

I searched for some similar threads ... but came up empty with my specific issue and observations.

About 14 months ago ...I purchased a new 2018 Interstate GT 4x4, and had the dealer upgrade the battery/inverter package to: four 6 volt AGMS batteries (GPL-4CT), and a Magnum MS2812 Inverter/charger.

I was told that I was going from 210 ah (105 usable) on batteries and from 1000 watts to 2800 watts for inverted 110vac power. They also reconfigured the 110vac outlets so that all but the AC unit was working from battery bank.

From reading past threads - it is pretty obvious that Airstream has much room for optimizing the: battery/inverter/solar/generator/shore power configuration, and besides the above upgrades - I am eager to incorporate some more improvements as oft discussed here. I would really appreciate a shopping list of sorts on that front... but first I need some insights...

Here is my observation and issue. I now have only about 9000 miles on this unit and have yet to use shore power when on a trip. In fact - until this weekend ... I had never used the AC unit, nor the generator. It was blazing hot in the Nashville area last weekend, and we were in need to cool down the unit inside upon arrival and walking around. I did not have access to shore power. I start the generator and it proceeds to charge my house batteries which were at about 12.2 volts. I turn on the AC unit ... and it starts ... but then "nothing" and I hear the generator "unload". After some preliminary trouble shooting - I crawl underneath the unit (on hot gravely pavement), locate the very "touchy" circuit breaker on the 2500 watt generator. It was tripped ... but I swear that it was so sensitive that I felt the vibrating generator may have "jiggled it open". Go through same process 3x ... and repeat the circuit breaker tripped mode. Believe me when I say that it is not enjoyable to be crawling under the Airstream in 96 degree heat, and I wished I was 25lbs lighter for better clearance.

I call the dealer the next morning and they tell me that the battery bank needs to be near fully charged before I can use the AC. Yikes! my wife is hot and sweaty and we need comfort NOW ... why wait for batteries?

Here is what I observe: at a house battery status of 12.2 volts, and upon starting of the generator - the Magnum Invertors controller goes into "ABSORB CHARGING" mode at about 13.8volts and 100 amps. (*note - this current seems very high ... is that normal?), and as the battery bank charge is built up ... the ABSORB CHARGING voltage increases to about 14 to 14.1 volts and the amps start to decrease.

Neglecting: power factors and efficiency factors - ABSORB CHARGING is using 1380 watts of generator power under the above scenario. Neglecting "start current" - the AC unit is using 13 amps ... which is 1430 watts. It is very obvious why my 2500 watt generator CB kept tripping. After about 45 minutes of ABSORB CHARGING ... the AMPs decrease to about 60a at 14vdc (about 840 watts). At this time my AC starts and runs just fine.

Is something out of whack with my system or the controller settings? Do you folks have a similar issue?

I am NOT happy with the above. We can NEVER cool down the unit "on demand" with such a scenario. I would think that one should be able to put an "override" or priority on AC for when it is truly needed fast. A larger generator would obviously mask the issue ... but I think things could be made to work with some brain power and perhaps optimized settings.

I appreciate any and all insights.

Thanks,
Mike H
Wisconsin

[PSchw]

Hi Mike,
Yes this is what happens when you upgrade the inverter/charger. You should install also the Magnum ME-ARC50 controller. This allows you to reduce your charge rate or stop charging completely until cooled down.
Hope that helps.
Peter

[wachuko]

Someone with more knowledge will chime in... and I will try to find it to link to it...

But I remember reading that there is a priority on what the AI will shutdown when the generator is used... I might be mixing things...

I believe that the problem you are having is that the inverter/charger has higher priority to charge the batteries over the A/C... something like that...

I have been able to use the A/C with the generator without issues... standing still or while driving... but I have not had a situation similar to yours where the batteries are low...

Like I said, someone with more knowledge will sure chime in...

[kidjedi]

It sounds to me like you will be doing some serious reconfiguring of how the electrical system is layed out, but in the meantime, couldn't you just unhook the batteries (install a shut off switch if there isn't one) so that the generator would only be powering the AC (you mention the AC is the only thing on a direct circuit not routed through the battery bank)? True, nothing else in the camper would work, but the "blackout" would only be necessary for a cool down period (you could also run a bypass circuit so things would still work with the generator on). Obviously there are more steps to take to "fix this right," but perhaps this could be a workable "bandaid" for now? Also, I'm sure there is a higher end controller that would let you choose the type of charging, or even turn charging off completely while running the generator.

[rowiebowie]

Is your new Magnum Inverter/Charger configurable in this regard?

If you could program it to not prioritize battery charging so much, you should have enough generator capacity to run your air conditioner. You'd think the new "smart" inverter/chargers would be configurable. Heck, my old stock Tripplite has dip switch settings for higher or lower charge rates.

Another option is installing an easy-start to reduce the load when your compressor kicks on.

Good luck, and let us know when you find out what works for you.
.

[Boxster1971]

Originally Posted by PSchw

Hi Mike,
Yes this is what happens when you upgrade the inverter/charger. You should install also the Magnum ME-ARC50 controller. This allows you to reduce your charge rate or stop charging completely until cooled down.
Hope that helps.
Peter

LONG SPUS (aka Mike H) - this is good advice for your setup. That Inverter/Charger that the Airstream dealer installed is a 2800W unit with capacity to charge the batteries up to 125A. In my view that is a bit of overkill for the batteries your have. I have the same battery setup, but only a 2000W Magnum inverter/charger that is very adequate.

The generator has just enough power to run the AC, but not much else. So the heavy load to recharge your batteries is exceeding the generator's capacity. Normally an Intestate with the 1000W inverter/charger does not place such a heavy load on the generator and is protected by the Energy Management System.

[Boxster1971]

Originally Posted by kidjedi

It sounds to me like you will be doing some serious reconfiguring of how the electrical system is layed out, but in the meantime, couldn't you just unhook the batteries (install a shut off switch if there isn't one) so that the generator would only be powering the AC (you mention the AC is the only thing on a direct circuit not routed through the battery bank)? True, nothing else in the camper would work, but the "blackout" would only be necessary for a cool down period (you could also run a bypass circuit so things would still work with the generator on). Obviously there are more steps to take to "fix this right," but perhaps this could be a workable "bandaid" for now? Also, I'm sure there is a higher end controller that would let you choose the type of charging, or even turn charging off completely while running the generator.

This won't work as you need 12DC to control the AC unit.

[Long Spur]

I checked my installed inverter controller... it is indeed the Magnum ME-RC50, and not the ME-ARC50. They are both exact same look and dimensions from outside. I assume that differences are just software related.

I need to do some research... but if the ME- ARC50 has set up or programming features that allow me to limit ABSORB CHARGING to a value of say ... 50 or 60 amps, I believe that will solve my problem. If anyone has first hand experience - I would appreciate the insights.

I also want to upgrade the solar controller. Suggestions on that front are very welcome and most appreciated.

Thanks.
Mike H

[wachuko]

Originally Posted by Long Spur

...I also want to upgrade the solar controller. Suggestions on that front are very welcome and most appreciated.

Thanks.
Mike H

I installed a Victron solar charger controller... I am very happy with it.








The new version (Victron SmartSolar Charger Controller MPPT 100/30) has built in Bluetooth so you can check everything with your smartphone... In mine (photo above), I had to buy the additional dongle to get the Bluetooth option... so if you go with a Victron unit, get the latest version...

[Boxster1971]

Originally Posted by Long Spur

I checked my installed inverter controller... it is indeed the Magnum ME-RC50, and not the ME-ARC50. They are both exact same look and dimensions from outside. I assume that differences are just software related.

I need to do some research... but if the ME- ARC50 has set up or programming features that allow me to limit ABSORB CHARGING to a value of say ... 50 or 60 amps, I believe that will solve my problem. If anyone has first hand experience - I would appreciate the insights.

I also want to upgrade the solar controller. Suggestions on that front are very welcome and most appreciated.

Thanks.
Mike H

Here is a copy of the ME-ARC50 remote manual. On page 20 in setup section the parameter "01D Max Charge Amps" is explained. It can be set from 20 - 990A, the default is 200A.

Good luck,

[InterBlog]

Originally Posted by Long Spur

First time post. I am a Mechanical Engineer and ... I call the dealer the next morning and they tell me that the battery bank needs to be near fully charged before I can use the AC. ...

Thanks,
Mike H
Wisconsin

Welcome to Air Forums. You will find yourself in good engineering company here.

This whole situation just sounds wrong on its face. We have a 2,000 watt inverter (installed by us), and an Onan generator (installed by Airstream). I run the generator at truck stops to power the roof a/c, and not only does it work, I have juice left over to top off our 300 AH lithium battery.

We have a 2007 Interstate with an 11,000 BTU roof a/c but IRRC, the generator on the newer Interstates put out more power to remain in lockstep with the up-sized a/c units on those rigs... someone correct me if I'm wrong.

I'll ask my husband (also a MechE, with extensive EE) to comment when he wakes up (he designed and installed our system).

[TheGreatleys]

Originally Posted by Long Spur

I checked my installed inverter controller... it is indeed the Magnum ME-RC50, and not the ME-ARC50. They are both exact same look and dimensions from outside. I assume that differences are just software related.

I need to do some research... but if the ME- ARC50 has set up or programming features that allow me to limit ABSORB CHARGING to a value of say ... 50 or 60 amps, I believe that will solve my problem. If anyone has first hand experience - I would appreciate the insights.

I also want to upgrade the solar controller. Suggestions on that front are very welcome and most appreciated.

Thanks.
Mike H

The ME-RC remote has a button on the left that says ON/OFF CHARGER. Use it to disable the battery charging function. That should stop the draw.

I suspect Interblog may be correct that there's something else going on here. But turning off the battery charging function should allow you to eliminate that variable.

[Boxster1971]

Originally Posted by TheGreatleys

The ME-RC remote has a button on the left that says ON/OFF CHARGER. Use it to disable the battery charging function. That should stop the draw.

I suspect Interblog may be correct that there's something else going on here. But turning off the battery charging function should allow you to eliminate that variable.

This is a good solution - the ME-RC remote is more capable than the basic ME-MR remote that Airstream installs.

[Long Spur]

Update:
My MS 2812 Inverter/Charger has software Rev 5.9. This makes is a "level 4+" compatible device (per ME- RC controller manual)

I see now how I missed the "charge amps" function... this is only available when the battery selection at setup is : CC/CV. With my initial battery selection of AGM1 ... that function is disabled.

In the mode associated with CC/CV battery selection ... I have a Max Amps setting option of: off, 20-990A ... with default of 200A. I set mine to 60A, with the following additional settings: Chg Volts - 14v, End Charge - time, Done Time - 2 hours, Max Time -12 hours, Recharge - 12v

I tested the above. AC works fine while by batteries do an Absorb Charge at 60amps to start

Note: Rather than using time - It also gives me an EndChg option of: DC Amps.

Not sure which method ( time or current) is optimal for my battery bank ... 1020 total amp-hours (510 usable) with my 4 AGM's ... but one would think that DC amps would be most precise. Any opinions?

Alternative to CC/CV:
I see that if I select battery type = AGM1 .... I can modify the "Charge Rate". I suspect that this would also provide the ability to run my AC right away ... because the amps to battery would be limited. Question for those with experience... any downside to using CC/CV as battery type? I have not tested this... but the MS2812 manual says Charge Rate: this setting can be used to limit current that charger uses (leaving more current available to power loads).

The dealer really should have set up these parameters properly ... and at the very least- been in a position to discuss these options with me while I was on the road "sweating and swearing".

Using my existing ME-RC seems to be my preferred approach. A list of optimized setup parameters would be appreciated. This would save me some trial and error.
Thank for all the insights,
Mike H

[PSchw]

Check page 32 of them manual there you can adjust the max. Charge rate by % . Default setting is 100% but you can go adjust it down to what works for you.
Peter