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Old 05-21-2018, 08:29 AM   #1
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Brand: Thor Motor Coach
Model: Vegas 27.7
State: California
Posts: 289
THOR #10907
Stupid AC/DC converter wiring or Why Your Batteries Don't Charge.

Ok I've finally gotten a chance to move my attention to the charging and battery supply in our new Vegas. One of the things I wanted to "fix" is the fact that the battery isolator or "Store/Use" switch red light works wacky. I also wanted to install some volt and amp displays so I can better see what's going on.

So the "problem" (in quotes because I call this a problem, but all of these motorhomes are wired to operate this way...) is that you have no idea if the switch is in "Store" or "Use" mode when you're hooked to outside 110v power. The red light on the "Main Power" switch is on all the time when you're hooked to shore power. This is normal because the red light is monitoring voltage on the coach, and when plugged in to shore power the converter is powering the coach. So the problem is that if the switch is in the "Store" mode, meaning the batteries are isolated and not connected to the coaches electrical system, the 110 to 12 volt converter can't charge the batteries. And since the red light is on in both the "Use" and "Store" modes, you have no way of knowing you're not charging your coach batteries. That's stupid!

The other part that makes no sense to me (having spent my entire career working on automotive electrical systems) is why would you want to run 100% of your coaches 12 volt loads off of the converter alone? If you have your battery switch in the "Store" mode, every load you turn on in the coach is being fed by the converter. THAT'S why the fan on the converter turns on and off like crazy whenever you turn on or off a light. Again, stupid! lol.

This is how I believe it should be wired, and is the way motorhomes always used to be wired... The 110 to 12 volt converter should be wired directly to the coach batteries. This "fixes" the issue of possibly being hooked to shore power but not actually charging your coach batteries because the isolator is in "Store" mode. It also "fixes" the issues with changing loads causing erratic converter operation. If the converter is hooked directly to the batteries, the batteries will work as a natural voltage "damper" and will greatly reduce voltage variations when loads change. Voltage converters or chargers have capacitors in them to smooth the voltage output. A couple of big 12 volt coach batteries are about the best capacitors you can have for smoothing out voltage spikes. Why wouldn't you use them?

And yet another issue this fixes... Better battery charging. I put that in bold because this part is HUGE. It eliminates the need to use a separate battery maintainer to keep from boiling your batteries when hooked to shore power for long periods. These converters that are listed as "3 Stage" or "4 Stage" chargers are kind of a joke. They may be 3 or 4 stage chargers, but when they're wired the way they are they'll never fully use the different charging modes. That's because there will always be some amount of load on the batteries if you're charging them while connected to the coach electrical system. Multi-stage chargers work best when there are NO external loads on the batteries. That's impossible to obtain the way these coaches are wired. Actually, if there's even a little constant load, those 3 or 4 stage converters are now a single stage battery boiler.

Ideally when you're storing your coach for long periods, you want to isolate the batteries by putting the switch in "Store" mode. That way there will be no external loads on the batteries. The only way to charge them now is to buy a separate battery charger and hook it directly to the batteries, which is what many of you do. Why not just wire the converter to the batteries like it's supposed to be? That way you have a high amperage charger that will also properly maintain the batteries without boiling them. If the converter and batteries have any load on them when stored, they'll never be able to drop down to the float or low voltage mode.

Does any of that make sense? hahahahaha.

So here's what I'm going to do... I just ordered a 4 stage 100 amp converter/charger, mostly because I want to recharge dead batteries faster than the 55 amp stock converter/charger can do. I'm going to wire it directly to the coach batteries so when I'm hooked to shore power (or on the generator) I know the batteries will be getting good, strong high amperage charging that won't boil them as long as I have the isolator in "Store" mode. I MAY actually keep the 55 amp converter wired up to the coach side, I'm not sure about that yet. Keeping that converter wired in would mean if I want to keep the coach batteries isolated and charged, but still run loads in the coach itself, I can do that. And I would also have a total available charging amperage well over 100 amps for when the batteries are dead and I don't want to take all day to charge them back up. I like it!

Here's a picture of the "Store"/ "Use" or "Main Power" switch in case anyone has read this whole thing and not had any idea what the h*ll I'm talking about!...
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Old 05-21-2018, 10:12 AM   #2
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Brand: Thor Motor Coach
Model: Axis 24.1
State: Colorado
Posts: 5
THOR #11372
Thank for that great info I have an axis 24.1 and the coach batteries are always draining couldnít understand why when my rv was always connected on my house hold 120 volt . For a quick fix must my main power switch be in the off position before connecting the rv 120 volt ?
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Old 05-21-2018, 12:01 PM   #3
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Model: ACE 27.1
State: Florida
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THOR #7035
I've owned 5 different RVs over the last 20+ years. 4 of them had no way to isolate the battery from the charger, or the battery/charger from the running DC loads. All had 3 stage converters. The only time I had a problem with cooking batteries was when the charger went bad. Otherwise they all went into a 13.1 volt float mode even though DC loads were running like lights or the refrigerator control power.
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Old 05-21-2018, 07:25 PM   #4
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Model: Axis 24.1
State: Florida
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THOR #4366
While the problem description is long the fix is easy. Just move the plus converter charge lead to the battery side of the use/store isolation relay.
For us it doesn't matter as there is no indication of which position the use/store is in and the solar always charges the house batteries unless the solar system breakers are off.
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Old 05-21-2018, 11:30 PM   #5
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Brand: Thor Motor Coach
Model: 2017 Thor Vegas 25.2
State: Indiana
Posts: 297
THOR #7993
Our Vegas USE/STORE switch doesn't even have a light. Luckily it works as it should as long as my old, dead brain remembers to use it.
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Old 05-22-2018, 09:34 PM   #6
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Brand: Thor Motor Coach
Model: 2013 31L
State: Florida
Posts: 1,993
THOR #908
so if I understand what you're saying....
all loads are powered by the battery
the converter's job is only battery charging.

I've thought of that a few times myself. The only real hole I can see is in the case of a shorted or otherwise kaput battery... you're in the dark, no choice. Another similar example...I've read folks that are permanently plugged in asking if they even need a battery. Some folks just want it to be more like a house I suppose....
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Old 05-22-2018, 10:00 PM   #7
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Brand: Still Looking
State: Texas
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THOR #2121
Quote:
Originally Posted by blw2 View Post
so if I understand what you're saying....
all loads are powered by the battery
the converter's job is only battery charging.

I've thought of that a few times myself. The only real hole I can see is in the case of a shorted or otherwise kaput battery... you're in the dark, no choice. Another similar example...I've read folks that are permanently plugged in asking if they even need a battery. Some folks just want it to be more like a house I suppose....
Arenít they wired in parallel? Unless you ďonlyĒ charge when Coach/House is disconnected from batteries, you donít get to choose which way electrons flow. You can only control flow by where the switch is placed, but only when itís open. When switch is closed, it shouldnít matter.

Regarding second point, Iím not sure about newer converters, but on older ones if the battery is really dead, the converter wonít run the house properly. We spent a cold night once because of a bad battery in a motorhome, which was so dead that the converter couldnít power the furnace fan directly. Apparently it needs a stable voltage to regulate (at least on older converters).
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