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Old 01-20-2021, 06:34 PM   #1
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House Batteries Dead

Well, I screwed up! Took our 2019 DS 4018 out for a ride Sunday and forgot to plug it back in to 50 amp when I pulled into the garage. Today is Wednesday and I went out to the motorhome and noticed door light didn't come on. Checked and sure enough batteries dead. My question is will just plugging it back in to 50 amp recharge by leaving it charge them back up? If so how long or should I start engine ?
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Old 01-20-2021, 06:43 PM   #2
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Plug it in. That would be too much of a job to give to your alternator.

Time depends on how big of a converter and how much battery capacity you have. As an example: If I ran 400ah of batteries completely dead and had a 55amp converter, I'd give it a solid day plugged in.

And the sooner you start, the better chance you won't kill the batteries.


(Oh, and: check the water level of your batteries and top them off before you start charging if you have flooded lead acid batteries.)
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Old 01-20-2021, 07:40 PM   #3
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Your inverter /charger may not start charging, if the house batteries are very low.

If it doesn't start charging on shore power, and you can start the engine, start it up with shore power connected, and let it run for 15 minutes or so.

That should bring the house batteries up to the point when the inverter/charger will kick in and take over charging.
Then you can shut down the engine.

If the chassis batteries are dead too, you may be able to jump the house batteries. That may bring them up to have the inverter/charger take over.
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Old 01-21-2021, 08:24 AM   #4
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Plugged it back into 50 amp overnight but that did not make any difference.
Also let it run for 15 min. to see if I could get the charger to kick in.

Magnum is showing low battery.
Red fault light on.
Charger lite flashing green.

What do I need to do to get the charger to start to kick in?

8 AGM all in great shape before my brain freeze . Thanks
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Old 01-21-2021, 09:06 AM   #5
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I believe I got it charging. Started the MH up and hit the battery boost and generator start.
Generator didnít have enough umph to start, but this process did reset the magnum, fault light went out, charger shows charging and displaying properly. Iíll let run 15 min. , keep it plugged in and keep my fingers crossed.
It appears they were so dead It just needed some kind of a reset to start back up.
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Old 01-21-2021, 09:57 AM   #6
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Magnum inverter/chargers will not charge dead batteries.

Pushing the boost switch probably sent it enough volts to wake it up.
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Old 01-21-2021, 11:05 AM   #7
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Quote:
Originally Posted by twinboat View Post
Magnum inverter/chargers will not charge dead batteries.
Dumb question: Why not?
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Old 01-21-2021, 11:09 AM   #8
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I'd like to know what completely drained your less than 2 year old batteries in less than 3 days.
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Old 01-21-2021, 11:22 AM   #9
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Quote:
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Dumb question: Why not?
Don't know, but as chargers, not converters, they need a battery to operate.
A dead battery could be a missing battery.
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Old 01-21-2021, 11:22 AM   #10
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Quote:
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Dumb question: Why not?
They need to sense a battery being present before starting the charge cycle. There are a lot of chargers/converters that now do this. Most chargers are of the smart technology era and won't charge a completely dead battery. I've seen this before and all you needed to do was push the emergency start switch to feed some voltage to the house batteries. Once the Magnum saw voltage it sensed batteries were present and started the charge cycle.

Avoid charging a dead set of batteries from your engine alternator if you can. They are not designed to recharge completely dead batteries.
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Old 01-21-2021, 11:45 AM   #11
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The bi-directional isolator with not automatically close the relay...one, it still needs the minimum voltage to operate...and two, it's designed not to try to charge a bank that has shorted out cells. Why would you want to continue to send massive amps to shorted out batteries. It's designed to operate within a bracket.

The boost switch probably did it. By overriding the brains...and you obviously still had the minimum voltage to operate the boost function...once the Magnum saw the voltage was okay, it kicked in again. It won't attempt charging if there is no battery or the voltage is too low on the bank...for the same reason.

So, boost may work...or hooking up a stupid battery charger to trick the system is also a technique. You just have to let these devices see a certain minimum voltage for them to start working. It's a protection.
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Old 01-21-2021, 11:55 AM   #12
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Since you let them go dead...you may want to do a recovery charge...

I would throw this out for consideration...

Changing

SETUP > 03 Absorb Time > Absorb Hours = 6

You probably have an absorb time of 3 hrs or less. Giving it a bit more time for one charge cycle may help. Remember to return the time to your original setting when completed.

If you notice a loss of capacity and have Liflines...do an equalization charge to help aid in recovery. If you don't have Lifelines...you're SOL...most other AGMs prohibit equalizing charges.
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Old 01-22-2021, 08:27 AM   #13
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Conclusion here: So actually the Magnum was smarter than me.
In the Magnum setting I had it set to shut down at low voltage of 11.
By not having it plugged in, once the voltage dropped to 11 it shut everything down.
Hitting the boost brought everything back to life, electronics came back on, fault light went off the Magnum and the Magnum came back on and started charging .
Within a few hours all was good and charged back up.

I read and re-read the Magnum book, checked all settings and it did exactly what it is supposed to do.
Save your batteries when they hit a particular set point .
The tricky part was resetting the fault and getting it to come back to life.
Learn something every day with these things.
Thanks all for the suggestions.
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Old 01-22-2021, 10:20 AM   #14
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Quote:
Originally Posted by Granite17 View Post
Conclusion here: So actually the Magnum was smarter than me.
In the Magnum setting I had it set to shut down at low voltage of 11.
By not having it plugged in, once the voltage dropped to 11 it shut everything down.
Hitting the boost brought everything back to life, electronics came back on, fault light went off the Magnum and the Magnum came back on and started charging .
Within a few hours all was good and charged back up.

I read and re-read the Magnum book, checked all settings and it did exactly what it is supposed to do.
Save your batteries when they hit a particular set point .
The tricky part was resetting the fault and getting it to come back to life.
Learn something every day with these things.
Thanks all for the suggestions.
Yes, the Magnum will shut down, but any other 12 volt parasitic loads will remain on.
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