Inverter charging

[jeffbrown1]

Hello folks!
I've been a motorhome owner for almost 15 years and mostly a lurker here. I couldn't find my answer poking around so I'll post.

I've had 3 previous motorhomes mostly Fleetwood from the built in Riverside era. (2002 and 2004 Models) I now have an 05 Itasca Meridian. That means this is my first time with an inverter vs a converter charger. I think there might be an issue but I want to ask if maybe this is normal?

If I leave the coach in storage for too long obviously the house batteries get low. When they are low the Inverter wont kick on at all, that means that plugging in the coach doesn't charge anything, if the batteries are already low. If I start the engine and run it for 15 to 30 mins then turn off the engine and plug in the 110 then everything works exactly like you'd expect.

Is this normal or is something wrong?

Second related question: Can I run the engine while it's plugged in? Previously I have been told to only have one power source at a time. Don't start the generator while plugged in to shore power. Is that true for running the engine with an inverter?

Thanks,
Jeff Brown

 

[rvlifer]

what make and model of inverter do you have? Is it an inverter only or an inverter and charger?

The inverter may have a safety built in to not pull power from the battery bank when the voltage is too low. My magnum inverter charger has an autocutover switch built in so i dont have to worry about power from multiple sources but i dont have it installed in a motorhome either.

yours may work differently. If you can post which inverter you have there are probably folks here who can provide details about how it works

 

[Gary RV_Wizard]

"One power source at a time" refers to 120/240 VAC, not DC. It's perfectly OK to have multiple 12VDC sources active and it's actually common if you have a solar panel. So yes, it's OK to run the engine while connected to shore power or running the generator. Also, your coach has built-in protection that prevents multiple AC power sources from interfering with each other. Generator & shore power are isolated from each other in one of two ways: (1) an Automatic Transfer Switch (ATS), or (2) manually plugging the shore cord into the generator outlet instead of the site power outlet. Your Meridian has the ATS. The inverter (probably Dimensions brand) also has an ATS that prevents it from supplying inverter AC when either generator or shore power is active.

As for the inverter vs converter concern, this is not a matter of inverter vs converter - it's just a design difference between your previous chargers and the one built into the inverter. Newer models of chargers incorporate circuitry to avoid any attempt to charge a shorted battery because that has a high probability of causing a battery fire. This is particularly important when the charger has a high amp capacity, as the one in the Meridian surely does. The charger in the inverter can't tell the difference between a deeply discharged battery bank and one that has an internal short, so it simply refuses to charge at a very high rate. The engine alternator has no such safety limitation, so it can do the initial charging of the discharged battery and bring it up to where the inverter charger can take over. However, the alternator output is limited by a fusible link that will open the charging circuit if the amp rate gets too high, i.e.the fuse will blow. But that is typically at a higher amp rate than whet an inverter/charger or converter/charge would use.

The bottom line is that your Inverter charger is "working as designed" and is not broken.

 

[jeffbrown1]

Gary,
Thank you again for your sharing your wisdom.

Follow-up question. You seemed to imply that it will charge but very slowly on shore power. Or would it be safe to assume no power will go to the batteries because the system thinks they are shorted?

Thanks again,
Jeff Brown

 

[Gary RV_Wizard]

Follow-up question. You seemed to imply that it will charge but very slowly on shore power. Or would it be safe to assume no power will go to the batteries because the system thinks they are shorted?

I didn't mean to imply anything like that. Low cost electronics have enabled the chargers used in newer RVs to substantially improve their design quality, adding digital logic for multi-stage charging, monitoring charge rates, and otherwise avoiding damage that was all-too-common in older models. These "smart charging" improvements began to appear in inverter/chargers around 2000 and in lower priced converter/chargers by around 2005. The previous dumber chargers were prone to overcharging, causing shorter battery life and occasional battery melt-downs or fire.

Or would it be safe to assume no power will go to the batteries because the system thinks they are shorted?

Yes. If the charger sees an unusually high amp rate flowing into the batteries, it will limit the flow. And if that rate doesn't quickly taper off on its own as the charge builds up, the charger cuts off altogether for safety reasons. This would be true of most any smart charger, whether part of a converter or an inverter.

 

[Kirk]

Gary has already covered the issues quite well so I'll simply say that you are getting good advice. Gary and I have a lot of the same background so I'd have said pretty much the same thing, but possibly with slightly different words. Us old guys know a lot of "stuff!"

 

[John From Detroit]

In my life I've used many charger/converters
Some Just charge., then they over charge and destroy the batteries (Very old Not seen one in decades)
Some have electronics that sense the battery
Some will send a LOW current to totally dead or shorted batteries and if they see the battery start to "recover" will up it to their rated output

Some will see zero or "less than x volts" as "no battery" and simply refuse to do anything.

Most limit current to protect themselves.

Inverter/chargers tend to be very high grade chargers They are also expensive and thus protect themselves either by sending a very low current to a totaly dead battery or nothing at all.

One solution and I highly recommend it for other reasons is a small Lithium Jumper pack about 75-100 dollars at horrible (Harbor) Freight. Some of these however also "Sense" the battery "

Or the older Lead Acid type (much larger and heavier) These do not usually sense but they will put enough into your house batteries to get the inverter charger to kick in .

OH and they come in handy when the car battery is dead as well. >Used my LI unit twice (Other peoiple's cars) and the old Lead Acid types many times.. NOT always for cars. and rarely mine.