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Author Topic: How does an inverter/charger work?  (Read 1296 times)

rrfpacker

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How does an inverter/charger work?
« on: July 11, 2013, 05:18:00 PM »
We are having issues with the inverter/charging system in our 09 Fleetwood Discovery. Right now it will not charge in any capacity and will only invert when connected to shore power or while running the generator. The house batteries will charge a bit when the engine is running (or we think so because the information panel reads over 13 volts instead of 8). I think it is broken and will hopefully find out on Monday when someone can look at it. We have been getting numerous suggestions as to what could be the problem and I'm really tired of the "Could Be This".

I would like to know how the system works in a motorhome and would be grateful for any links, books, etc. suggestions. I want to know how/when/why the charging/inverting system works. Does it just work and we can't do anything about it without changing parts until it finally works? That's what most repair shops want to do. They want to change the batteries ($400), change the inverter (it's a magnum and over $2000-an expensive guess at what the problem is). Isn't there any way to put a meter on different outputs, like the batteries, the inverter/charger, and KNOW what is wrong?

We've also been told that when the batteries reach a certain low voltage, somethings will not work even when connected to shore power; this has been verified as the air conditioners will not come on when voltage is low. I've also been told that everything is run by the batteries even when connected to shore power. What exactly happens when connected to shore power?

As you can guess I'm pretty ignorant about this and it seems to be pretty important in a motorhome. Anything will help. Thank you.
2009 Fleetwood Discovery

SeilerBird

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Re: How does an inverter/charger work?
« Reply #1 on: July 11, 2013, 05:35:29 PM »

I would like to know how the system works in a motorhome and would be grateful for any links, books, etc. suggestions. I want to know how/when/why the charging/inverting system works. Does it just work and we can't do anything about it without changing parts until it finally works? That's what most repair shops want to do. They want to change the batteries ($400), change the inverter (it's a magnum and over $2000-an expensive guess at what the problem is). Isn't there any way to put a meter on different outputs, like the batteries, the inverter/charger, and KNOW what is wrong?
The whole problem is there is not just one way for your RV to be configured.
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We've also been told that when the batteries reach a certain low voltage, somethings will not work even when connected to shore power; this has been verified as the air conditioners will not come on when voltage is low. I've also been told that everything is run by the batteries even when connected to shore power. What exactly happens when connected to shore power?
When you are connected to shore power there are some items, like your refer, that runs on 110 volts but still needs 12 volts to operate correctly.

Everything is not run by batteries when connected to shore power. Your microwave oven does not 12 volts for anything.

To start to troubleshoot your problem you should start with the batteries. If they are the original then at 4 years of age they are getting long in the tooth. Start by getting your batteries tested. I would take them out and take them to Walmart or to an auto parts store and verify that they are operating properly. One dead cell can cause the problems you are looking at.

Gary RV Roamer

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Re: How does an inverter/charger work?
« Reply #2 on: July 11, 2013, 09:27:58 PM »
The question is so broad I don't know where to start, but there are some articles in the forum library that should help get you started. Meanwhile, let me hit some highlights.

When no shore power or generator is active, the inverter function of the inverter/charger produces 120v power from battery 12v to power some (not all) 120v circuits in the coach. 12v power still comes direct from the batteries, but physically passes through the inverter's battery cables on its way to the coach wiring.

When shore or generator is available, the Magnum inverter ceases inverting and becomes a battery charger, taking 120v power in and pouring 12v back into the batteries and the rest of the coach 12v system as well. However, and this is a big one, the 120v branch circuits that are serviced by the inverter still get their power that way. The inverter/charger passes through shore/generator power to the same circuits it handles by inverting. So it is possible that a failure in the inverter can cause a loss of power to branch circuits, even when power is coming from shore or generator.

Yes, it is possible to measure whether the inverter/charger is charging batteries from shore power, and whether it is putting out 120v when inverting. It is also possible that a really bad battery can muck the system up to the point where nothing works right, but a skilled technician ought to be able to figure that out too. But not all RV techs are skilled in electrical systems diagnosis. Nor do they want to spend a lot of time on diagnosis at $100+/hour, since they know you will complain bitterly about that too. So they tend to make a educated guess and throw in some parts.
Gary
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Gary Brinck
2004 American Tradition
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Homebase: Ocala National Forest, FL

John From Detroit

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Re: How does an inverter/charger work?
« Reply #3 on: July 12, 2013, 05:51:11 AM »
Might be the batteries that are broken. Not the inverter.

But yes, it could be broken.
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Ken & Sheila

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Re: How does an inverter/charger work?
« Reply #4 on: July 12, 2013, 06:38:23 AM »
Here is a link to Magmun site for the manual on the ME series (modified sine wave)
http://www.magnumenergy.com/Literature/Manuals/Inverters/64-0002%20Rev%20B%20%28ME%20Series%29_Web.pdf

If you have the MS series (pure sine wave)
http://www.magnumenergy.com/Literature/Manuals/Inverters/64-0007%20Rev%20D%20%28MS%20Series%29_Web.pdf

You'll need to know which model you have as each manual cover a series of models.

ken
Ken & Sheila
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Gary RV Roamer

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Re: How does an inverter/charger work?
« Reply #5 on: July 12, 2013, 07:37:58 AM »
Problem is, the Magnum manual doesn't tell you how the inverter works in concert with the rest of the coach power system. One of major shortcomings of the "suitcase full of manuals" approach to owner documentation.
Gary
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2004 American Tradition
2007 GMC Acadia
Homebase: Ocala National Forest, FL

rrfpacker

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Re: How does an inverter/charger work?
« Reply #6 on: July 14, 2013, 09:02:57 PM »
SeilerBird; the batteries are eight months old.

Others; Thanks for the input...most of the answers are what I thought.

I am away from the coach right now, but the lady of the house has been asking questions from various techs in the small town where she is.

So far no-one has shown the least bit of interest/knowledge in checking the output of the Magnum. Seems to me you should be able to put a volt meter on its output and measure something. Doesn't it connect to the batteries in order to recharge them? Can't you just check there? If so, as I say below we are getting reading of below 12 volts.

My dad checked each battery, when we know they were low, and got a reading of 5.5 volts on each one, with a measurement of just less than 11 when measuring across all them. Sounds right to me and tells me it's not the batteries and tells me the charging system isn't working. Also, the lady has been charging the batteries by running the engine and they will charge to just over 12 they will hold to 10 or so for a day. Tells me again the batteries are ok...they just aren't getting a deep charge, only a "surface" charge. Am I correct in thinking this?

Tomorrow I will ask one other person in the town I'm in and drive 3 hours for an appointment with someone to check the batteries. If I drive the coach to the repair place can they check the batteries while connected?
2009 Fleetwood Discovery

Alfa38User

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Re: How does an inverter/charger work?
« Reply #7 on: July 15, 2013, 09:33:06 AM »
A voltage reading of 5.5 on a 6 volt battery or 11Volts on a pair in series (or a 12Vbattery) is not low, it is effectively DEAD. It sure sounds like they are not being charged properly. Charging by running the engine for a short period will not help as it takes many hours (12-24 or more) to fully charge a battery. A strong external charger is sometimes needed to at least bring a battery up before these built-in chargers can work effectively on a badly discharged battery.

The easiest way to check the battery charging output is to put the voltmeter across the battery terminals and plug the coach  in to 120V. The output across the terminals should be at least 13.2 to 13.4 Volts if the unit is functioning, a similar voltage should be seen while running the engine and charging is taking place. Be sure any battery cutoff switches are in the "ON" position (as opposed to a "Storage" position; although those may not be the exact terms used in that particular coach switch labelling!!). It would also be wise to check any output protection fuses or breakers on the unit itself. Many units have fuses that will blow should the batteries get hooked up accidentally in reverse or overload the charger.

A surface charge is the visible charge that can be measured shortly after disconnecting a charger. It usually disappears within an hour or so, but, if present, it does seem to indicate that some charging was taking place. What you are seeing is, effectively,  is a dead battery.

As far as thoroughly checking the battery while connected, I would say NO but it depends on what you expect to be done. They may be able to check the specific gravity and voltage (depending on accessibility) just as you can,  but, to do a load test they have to be removed, fully charged  and then load tested using specialized equipment for that purpose. An RV repair place is NOT the place to do that, your local battery seller, an automotive  parts seller etc can often do it at little or no cost. Once that is done, depending on the results, look again at the converter/inverter.
« Last Edit: July 15, 2013, 09:50:42 AM by Alfa38User »
Stu
Montreal, Canada
Snowbird, SW Florida
Alfa Gold 38 (2000) 5ver

jagnweiner

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Re: How does an inverter/charger work?
« Reply #8 on: July 15, 2013, 09:47:57 AM »
I know this sounds obvious, but I don't think it's been mentioned yet.  On my coach, the inverter/charger (Xantrex) has a control panel and the charger actually has to be turned "on" in order to charge off of generator or shore power.  I assume you've already checked to make sure the charger function is actually on.

With batteries that low, the inverter won't invert.  You would likely get a "low battery" message.

I had a similar problem with mine, where the battery wouldn't charge.  It turns out there was a fusible link between the battery bank and the charger that was burned out.  I had just about convinced myself my inverter was bad before we found that.
-Scott
2000 Itasca Horizon 36LD

rrfpacker

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Re: How does an inverter/charger work?
« Reply #9 on: July 16, 2013, 02:30:03 PM »
The problem ended up being the manual inverter battery disconnect was fried. No idea how that could happen, but it did. Replaced it and back to normal.
2009 Fleetwood Discovery

jagnweiner

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Re: How does an inverter/charger work?
« Reply #10 on: July 16, 2013, 02:41:44 PM »
Outstanding!  I was hoping it was something simple like that.  As you can guess from my previous post, I know the feeling of relief you probably have now that you won't need a new inverter.
-Scott
2000 Itasca Horizon 36LD