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Old 02-06-2020, 01:42 PM   #1
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Exclamation Dead Batteries - Catch 22 - Solved

I just had a real Catch-22 with my Newmar. -- Sorry a bit long.

Without me noticing, the landscaping guys had knocked the AC cord out of the socket that was keeping my stored MH charged up in the back yard.

By the time I noticed a couple of weeks later, the batteries had gone completely dead. I plugged the AC cord back in but even after a couple of days, the charger in the MH still read "Fault - Dead Battery".

Now here's the catch. I have power locking baggage doors and all doors were locked and wouldn't open even with the key. Chassis batteries, House batteries and access to the manual cutoffs, charger/inverter etc are all behind locked doors that won't open without power. Awesome design.

I realized I probably needed new batteries at this point but I couldn't even get to anything to troubleshoot.

THE (beginning of the) FIX:

After pondering what to do for a couple of days, I realized that I could get to the inside of the latch on the chassis battery door from underneath. I removed the two screws holding the latch on and was able to open that one door. I turned the chassis battery disconnect switch off to isolate it from the rest of the system and put the chassis batteries on a separate trickle charger. After two days, the charger reported the batteries were fully charged.

I was now able to start the MH. As soon as I started it, the charger/inverter panel Fault light cleared and reported that the house batteries were fully charged and in float state! Even after sitting a day, engine off, AC cord plugged in, the house batteries report they are fully charged and in float state.

I'm going to replace the chassis batteries (they are 5 years old) since they were definitely drawn down to 0 volts. But I'm wondering about the house batteries. As soon as the chassis batteries were charged, the house batteries (all AGM) reported they are fully charged. They were not on the external trickle charger since I had the chassis battery manual disconnect shut off while I was charging it. So did they get drawn down or did something shut them off when the chassis battles went dead and the charger/inverter was in that fault state?

Any ideas??
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Old 02-06-2020, 02:00 PM   #2
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I’m still wondering why your storage doors wouldn’t open with the key....they should unless you have the wrong key
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Old 02-06-2020, 02:09 PM   #3
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1; Is your chassis battery switch a complete cut off of all cables ? Could the isolation solenoid, boost start, cables still be connected ? If yes, then,

2; Did you leave the shore cord plugged in while you were trickle charging the chassis battery ? If yes, then,

3; If the chassis batteries charged up above 13. 3 volts, the Isolation solenoid would have closed, sending a charge to the house batteries.
Once the house batteries reached 8 volts or more, the inverter/charger would have kicked back in and charged the house batteries, but only if you still had shore power to it.
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Old 02-06-2020, 03:48 PM   #4
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I think twinboat got it right. On my MADP on a Spartan chassis, the chassis battery side of the bidirectional isolator / relay is connected directly to the positive post on the chassis battery. So if the chassis battery was being charged and the charge voltage exceeded the relay activation threshold (which it probably was since you are charging the battery at a higher voltage), then the charge level voltage would also pass to the house battery side of the bidirectional isolator. Of course the BIRD would have to have power to send the signal to activate the relay. I’m not sure how it is wired up such that the BIRD had sufficient power (assuming the house batteries were dead).
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Old 02-06-2020, 04:31 PM   #5
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Quote:
Originally Posted by twinboat View Post
1; Is your chassis battery switch a complete cut off of all cables ? Could the isolation solenoid, boost start, cables still be connected ? If yes, then,

2; Did you leave the shore cord plugged in while you were trickle charging the chassis battery ? If yes, then,

3; If the chassis batteries charged up above 13. 3 volts, the Isolation solenoid would have closed, sending a charge to the house batteries.
Once the house batteries reached 8 volts or more, the inverter/charger would have kicked back in and charged the house batteries, but only if you still had shore power to it.
I think you got it. Yes the shore cable was still plugged in while trickle charging the chassis batteries. I just assumed that the mechanical cut off switch in the chassis battery compartment would have completely isolated those batteries from the coach. Apparently not.

Of course that scenario would dictate that my house batteries really were drawn down to zero and probably should be replaced as well.
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Old 02-06-2020, 04:46 PM   #6
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I’m still wondering why your storage doors wouldn’t open with the key....they should unless you have the wrong key
I had the right key and now that the power is back, the key works again on all doors. I'm not about to kill the batteries again to test, so another mystery.
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Old 02-06-2020, 05:07 PM   #7
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Good detective work.

I'd try running the batteries through a few cycles before replacing them. Deep cycle batteries are designed to discharge flatter than regular ones.
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Old 02-06-2020, 05:11 PM   #8
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I think you got it. Yes the shore cable was still plugged in while trickle charging the chassis batteries. I just assumed that the mechanical cut off switch in the chassis battery compartment would have completely isolated those batteries from the coach. Apparently not.

Of course that scenario would dictate that my house batteries really were drawn down to zero and probably should be replaced as well.
I wouldn't write off the house batteries yet. A full discharge isn't a death sentence.

Give them a few days of charging and do a capacity test.

Find the total AH capacity of the bank, and divide by 20 hours.

Now, with shore power off, turn on things that add up to that calculated amp number and then monitor battery voltage for 20 hours.

Ex: A 400 AH battery bank should last 20 hours, with a 20 amp draw, until they drop to 10.6 volts.

If the voltage drops below 10.6 volts in 10 hours or less, that would indicate pretty weak batteries.

A longer time means you still have some decent capacity in them. Only your use will determine if that capacity is enough.

When people tell you that discharging deep cycle batteries below 50% damages them , just smile.
Deeper discharges only equal less discharges over the battery life.

Depth of discharge charts often show 500 100% discharges compared to 1000 50% discharges.Click image for larger version

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Old 02-06-2020, 05:41 PM   #9
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I'm not about to kill the batteries again to test, so another mystery.
Disconnecting the batteries is effectively the same as dead if you want to figure that out.

twinboat beat me to it, you can do a capacity test on your house batteries to know their merit. Only way to really know is a measured load test. One deep cycle like that won't take them out unless they were compromised already.

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Old 02-06-2020, 06:44 PM   #10
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Quote:
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...
twinboat beat me to it, you can do a capacity test on your house batteries to know their merit. Only way to really know is a measured load test. One deep cycle like that won't take them out unless they were compromised already.

Mark B.
Albuquerque, NM
Good to know, thx. I have always taken good care of them and never discharged them below 50% in the 5 years I've had them. So hopefully this didn't kill them.
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Old 02-06-2020, 06:52 PM   #11
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...
Once the house batteries reached 8 volts or more, the inverter/charger would have kicked back in and charged the house batteries...
@twinboat,

Is that why the batteries would not charge up initially from the inverter/charger and the Fault light was on -- because the voltage had sunk below 8 volts?

That is what had me in a bit of a panic at first. Even though I had plugged the shore power back in, nothing would charge up.
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Old 02-06-2020, 06:59 PM   #12
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Quote:
Originally Posted by Mark_K5LXP View Post
Disconnecting the batteries is effectively the same as dead if you want to figure that out.

...

Mark B.
Albuquerque, NM
Mark B,

I wonder if the door lock solenoids were somehow jammed up from the constant "chattering" that they undoubtedly went through as the chassis batteries discharged? When I tried the key initially, it was VERY hard to turn and I didn't want to risk breaking it off in the lock.

As soon as I attached the trickle charger, they started chattering like mad until I turned the disconnect switch off. I didn't re-try the key at that point since I already had the latch disconnected on the door I needed open.
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Old 02-06-2020, 09:14 PM   #13
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@twinboat,

Is that why the batteries would not charge up initially from the inverter/charger and the Fault light was on -- because the voltage had sunk below 8 volts?

That is what had me in a bit of a panic at first. Even though I had plugged the shore power back in, nothing would charge up.
Yes, most inverter/chargers need to see some battery voltage before they will start charging.

Unlike converter/chargers that serve as a battery substitute, inverter/charges need a battery to regulate charging voltage. That's why most of them do not have battery disconnects and are hard wired directly to the batteries..
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Old 02-06-2020, 09:47 PM   #14
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Quote:
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Yes, most inverter/chargers need to see some battery voltage before they will start charging.

Unlike converter/chargers that serve as a battery substitute, inverter/charges need a battery to regulate charging voltage. That's why most of them do not have battery disconnects and are hard wired directly to the batteries..
Thanks. The entire situation makes more sense to me now. Other than the power locks not opening with the key...
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