Options for Replacing Magnum Inverter/Charger

[InterBlog]

The other word for "porpoising" is phugoid, one of my favorite words in the English language.

I will forever be able to fetch this thread via the forum's search function now that I've written it there.

[Boom23]

I summarized our conclusions and sent them to Magnum tech support, together with the AI schematics, to confirm the scenario...

If that is the case, the solution is simple.

[Boom23]

Magnum tech support confirmed our assumptions. I will include the complete email conversation here.

My original email to Magnum tech support:

"I am the owner of a new 2018 Airstream Interstate Tommy Bahama RV. It has come to my attention that the Magnum MMS1012 inverter/charger installed in my RV may overheat and start smoking or catch fire, even under normal use.

I bought my RV to travel with my family and an inverter accident or fire is the last thing I want. I would like to know what you plan to do to correct this problem so that I can enjoy my new RV."

Magnum tech support replied:

"The issue is not with our inverter but with some connections made on the dc side during installation. If proper maintenance is performed on the battery cables to and from our inverter to the dc loads there should be no problems. All battery cables should come with a fuse that will blow if there is a short or overcurrent causing thermal runaway installed from the manufactuer."

I attached the Magnum recall information and asked:

"Can you be a little more specific? What should I check or change? Can you provide a diagram?
I just want to avoid problems.

I am concerned because another 2018 Airstream Interstate, same year as mine and with presumably the same wiring, had inverter problems…"

Magnum tech support replied:

"Crestline coach and Airstream do not wire the systems the same. Make sure the batteries are always connected when ac is applied to the coach. (shore or generator) You would not want to have shore power to coach with an open dc circuit that could cause ac ripple inside the inverter. No one should ever be plugged into shore with the battery cables off the inverter or have a battery switch open between house bank with shore power applied to input of inverter. If you need to work on batteries do not have the coach plugged into shore until batteries are connected to inverter. The battery B+ cable will have a fuse inline so that if there is a short on the battery side it will trip before the cables get too hot and cause thermal runaway. We have been making these units for 12+ years and never had any fire related problems because of overlapping protection inside unit and installation protection on the dc and ac side with proper breaker or fuse sizing."

Finally, I asked:

"If I understand correctly, on the Airstream Interstate, the problem can happen when one connects to Shore Power, Charger is ON and the House Battery, and possibly the Engine battery, is disconnected (switch is OFF). It is very easy to have the House Battery disconnected as the disconnect switch is by the side door with the light switches. Also, people may disconnect the battery, by habit, when they have the RV stored, even if connected to Shore Power.

This can cause the problem you are describing. Correct?"

And the Magnum tech support reply was:

"Yes this is only on the Airstream applications that they found a way to damage our unit during some testing. If you follow all our instructions for installation and operation it will work fine with no fire issue at all."

The solution to this problem is to NEVER disconnect the House batteries, when connected to Shore Power or running the Generator.

[felixkagi]

Originally Posted by Boom23

Magnum tech support confirmed our assumptions. I will include the complete email conversation here.


And the Magnum tech support reply was:

"Yes this is only on the Airstream applications that they found a way to damage our unit during some testing. If you follow all our instructions for installation and operation it will work fine with no fire issue at all."

The solution to this problem is to NEVER disconnect the House batteries, when connected to Shore Power or running the Generator.

............yeah right! How many times has the Admiral hit the battery disconnect switch when reaching behind the seat to grab a broom she stores there. Then closes the side door, rv on shore power. Would it not be possible for Magnum to have charging disabled when no batteries are connected!?!

[Alex AVI]

JOHN - glad your replacement has temp sensor. I can confirm mine did from factory.

MIKE - my practice was to have Battery Disconnect ON all the time because it was always plugged into shore power when in the garage. The only time I turned OFF Battery Disconnect was when no shore power to prevent house batts draining. Now that does not mean I have never done so before, especially in my early days of learning the AI systems. In fact, AS Manual specifically states charging happens regardless of Battery Disconnect switch position. This would be a fundamental shift in how many use the Battery Disconnect switch, if this has that detrimental effect on the inverter

[Boxster1971]

Originally Posted by Alex AVI

JOHN - glad your replacement has temp sensor. I can confirm mine did from factory.

MARK - my practice was to have Battery Disconnect ON all the time because it was always plugged into shore power when in the garage. The only time I turned OFF Battery Disconnect was when no shore power to prevent house batts draining. Now that does not mean I have never done so before, especially in my early days of learning the AI systems. In fact, AS Manual specifically states charging happens regardless of Battery Disconnect switch position. This would be a fundamental shift in how many use the Battery Disconnect switch, if this has that detrimental effect on the inverter

The Interstate manual is wrong. This is a chronic Airstream problem. Their manuals are not keeping up with wiring changes made by production. The way the 2017 & 2018 models are wired the only charging sources with battery disconnect OFF are solar and the Sprinter alternator. The disconnect disables the Magnum charger function as it disconnects the positive cable to batteries. If you then have the external power connected you run the risk of smoking the Magnum inverter/charger.

[Pahaska]

Originally Posted by felixkagi

............yeah right! How many times has the Admiral hit the battery disconnect switch when reaching behind the seat to grab a broom she stores there. Then closes the side door, rv on shore power.

I have often switched the disconnect switch when sliding the 2nd row seat back or just raising the armrest. In fact, I did just that about the time my charging problems started.

I think I will relocate the disconnect switch higher on the gray cover it is currently mounted on or put some protection over it.

[Boom23]

Maybe something like this (https://www.amazon.com/Plastic-Toggl...s=switch+guard) will do the job?

[Pahaska]

Originally Posted by Boom23

Maybe something like this

Thanks. I like it.

[Boom23]

Originally Posted by Pahaska

Thanks. I like it.

I am not sure if it fits... but the concept is correct.

I may have to make something with thin metal (raised sides) and double sided tape.

[Alex AVI]

Originally Posted by Boxster1971

The Interstate manual is wrong. This is a chronic Airstream problem. Their manuals are not keeping up with wiring changes made by production. The way the 2017 & 2018 models are wired the only charging sources with battery disconnect OFF are solar and the Sprinter alternator. The disconnect disables the Magnum charger function as it disconnects the positive cable to batteries. If you then have the external power connected you run the risk of smoking the Magnum inverter/charger.

MIKE - Not on 2018. FLYFISHINRVR and I had this discussion on the Fusion draining batts thread. On 2018's there is an ACE line (AC ENABLE - red circle) and diode that keeps the Magnum inverter connected to batts. in the presence of shore power. The ACE and diode was non-existent prior to 2018. ACE & diode essentially renders the Battery Disconnect a non-factor in charging operation, regardless of Battery Disconnect switch position. The only thing Battery Disconnect does is disconnect it from the DC Distribution Panel. I can confirm this by behaviour of charging activity even whilest Battery Disconnect is set to OFF (again 2018's only, so the NEW practice still should hold true for units without ACE line & diode)

[Boxster1971]

Originally Posted by Alex AVI

MIKE - Not on 2018. FLYFISHINRVR and I had this discussion on the Fusion draining batts thread. On 2018's there is an ACE line (AC ENABLE - red circle) and diode that keeps the Magnum inverter connected to batts. The ACE and diode was non-existent prior to 2018. ACE & diode essentially renders the Battery Disconnect a non-factor in charging operation, regardless of Battery Disconnect switch position. The only thing Battery Disconnect does is disconnect it from the DC Distribution Panel. I can confirm this by behaviour of charging activity even whilest Battery Disconnect is set to OFF.
Attachment 314748

OK I stand corrected. That also implies that Airstream was aware of the problem caused by disconnecting batteries from inverter when connecting AC power to the inverter. The 2018 setup could then be the model for recall design change on earlier models.

[Alex AVI]

Originally Posted by Boxster1971

The 2018 setup could then be the model for recall design change on earlier models.

Exactly. Except they still fried my Magnum . Ugh!

BOOM23 - read my prior post. Should not need to do on 2018's with Firefly. If you want to be sure, just check status of Magnum is in one of 4 charging modes when plugged in when Battery Disconnect is OFF.

So the moral of the story is if your unit is pre-2018, when plugged into shore power, keep Battery Disconnect switch to ON so that Magnum inverter is always connected to batts. and does not get fried. But my unit is 2018 and Magnum is always connected to batts. when on shore power . . . and my Magnum is still fried. Is there 3rd choice ?

[Boom23]

Originally Posted by Alex AVI

BOOM23 - read my prior post. Should not need to do on 2018's with Firefly. If you want to be sure, just check status of Magnum is in one of 4 charging modes when plugged in when Battery Disconnect is OFF.

Will do. Thank you for the info. I hope you get your situation resolved soon...

[LB_3]

The solution to this problem is to NEVER disconnect the House batteries, when connected to Shore Power or running the Generator.

This is a terrible solution. Operational controls for catastrophic hardware hazards is what fill binders full of industrial case studies. I stated it previously, but it’s worth repeating: Charging circuits should be separate from your electrical loads. I don’t understand why otherwise competent system designers don’t understand this. Do this simple thing and you can put a big fat switch on all your loads and never worry about your RV draining down when the power goes out in your storage unit or a circuit breaker trips. Do this and you don’t burn up your RV by accidentally disconnecting your battery. Do this and you don’t lose both your charger and inverter when the other one breaks....

[Alex AVI]

Originally Posted by LB_3

This is a terrible solution.

I don’t understand why otherwise competent system designers don’t understand this.

LB_3 - Yes, VERY terrible solution. But necessary at this point. Kinda like the Apollo13 Kevin Bacon sticky note reminder on control panel (if that's accurately depicted in the movies).

Just postulating - If they don't understand, maybe they were not competent system designers to begin with??

[LB_3]

Originally Posted by Alex AVI

LB_3 - Yes, VERY terrible solution. But necessary at this point. Kinda like the Apollo13 Kevin Bacon sticky note reminder on control panel (if that's accurately depicted in the movies).

Just postulating - If they don't understand, maybe they were not competent system designers to begin with??

[Alex AVI]

LB_3 - As you said earlier , "Do this simple thing . . ."
The simplest fix is sometimes the best.
As Bill Engvall would say . . .


This is my yellow sticky, I just printed one up that said 10' 0" and stuck it to my dash, easier than 9' 8" , no subtractions for this engineer while driving

[Air99]

Worth noting that with this new knowledge, a procedural change for me prior to shore power hook up is to take a quick glance at the Magnum remote panel, to confirm there is power there (12v to the inverter), or else a blown battery fuse will also put the Magnum at risk when 120vac is applied ⚠️

[wachuko]

Originally Posted by Boxster1971

....Wachuko - don’t replace your Magnum inverter. It is one of the best on the market. Just don’t have the batteries disconnected when plugged into external power and you will be fine.

That is the plan. It was good to research alternatives, but will stay with what I have now and just make sure that I do not make the mistake of turning off the House switch when plugged to shoreline or while the generator is running.

Thank you all for your contribution!!!