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Old 06-08-2022, 05:07 PM   #1
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The truth about "house battery" alternator charging

I've read so much info lately and it's clear as mud.

I have a 2005 Winnebago Adventurer 35A, W24 workhorse chassis, 8.1 gasser, standard factory wiring, 145 Amp alternator, batteries and solenoids/relays located under the entry stairs.

Everything works, house batteries are perfect, chassis battery is perfect. Everything stays charged perfectly.

The questions I have:

On this model and year motorhome:

Should the engine alternator charge my house batteries?

If so, what are the conditions? Do the house batteries need to have a low charge before the alternator will kick-in and charge them?

Why do I have a 145-amp rated alternator if the house batteries don't get charged?

Tech data: Converter output = 13.5 VDC
Alternator output = 14.5 VDC
Trombetta relays have checked out OK
Wring appears to be correct
Boost switch works on (motor off) no operation (motor running)
With motor running = chassis batt 14.5 VDC
With motor running = house batts 12.7 VDC

Please, please, please no guessing, no references to other model years, don't cloud the issue. I would love the informed straight answers from someone who knows exactly what those answers are. Thank you and I hope y'all have a great RV season.
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Old 06-08-2022, 05:48 PM   #2
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Well, someone may know your exact coach and BIM (battery isolation manager), but here is how our 2021 Thor Axis works with its Precision Circuits BIM 160, a modern equivalent of the older Intellitec BIM/Trombetta relay:

The BIM disconnects the house from the starting battery unless one of them is charging at about 13.5+ volts and the other is discharged to about 12.5 volts. Then it will connect the two for 1 hour. It then disconnects the two and monitors the voltages. When the above 13.5 and 12.5 criteria has been met again, it reconnects them for another hour. FWIW these connections draw no power after they have been made, like a latching relay.

This start and stop connection algorithm protects the batteries from over charging.

The older relay based BIMs work similarly as I understand it. Your coach probably has the Intellitec BIM or maybe another manufacturer's equivalent that i can't remember the name of.

David
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Old 06-08-2022, 06:06 PM   #3
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Definite yes, but as always, there are limits and things to know in the details!


With some very basic knowledge, we can explain why?
Do you know how electro-magnets work from the old scout or science class?

There is a Mode solenoid in your year, mkae and model as in many of the older RV. That solenoid is simply an electromagnet having a coil of wire that when it gets power, it pulls contacts inside the solenoid together.

It's that power fromtwo methods. The one you are asking about is when we have the ignition of the RV on, there is a line that carries the positive battery down to the coil, through the coil and to ground. On most Winnebago, that wire is labeled LR to the coil and the ground is FM and on your specific RV, FM is also tied to the mounting screw of the solenoid and gives ground from there also.

When LR gets power, it pulls the solenoid contacts together inside and the big lug on the left is connected to the big lug on the right. Kind of like slapping the two battery cables together!

If we look at the drawings for your RV, we see there is a big cable from the start battery to left side and a big cable from the coach batteries on the right side and they do get connected together inside when we start the engine!

As long as the enigne is running, the engine alternator is charging the start battery as well as the coach batteries but the thing to keep in mind is that battery charging is a slow chemical reaction and it does take hours to get a really low battery brought up to normal again.

The thing that blows the idea for many is that it takes hours to recharge but if we put that charge on for 20 minutes and take it off to read the voltage, we may see more than 12 volts and think it is charged.WRONG!

That is "surface charge" and will quickly go down when the chemicals become stable again and you may only see 10 volts!

Second use for the solenoid is when you have a weak start battery and there is a switch in the drivers area that you can push which also puts power on LR and makes the solenoid connect them together to "jump start" the RV. But that goes away when you turn loose of the switch as it is a momentary switch! You can feel it doesn't click like most switches but bounces back?

DEIT:
Bim is the newer solid state replacement for the mode solenoid setup and that makes it somewhat harder to work as we don't have any way to look and feel things as they move.
For the mode solenoid, one way to tell it is trying to work is to listen when it is quiet and you push the dash button. You can often hear it "clunk" as the solenoid works!
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Old 06-08-2022, 06:27 PM   #4
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More info on where to find the solenoid is here:
https://www.winnebago.com/Files/File...ire_146761.pdf

You may have already seen the labels!!

The reason for the big alternator is just to makesure you DO charge them all---even if you are driving, running the wipers, lights and honking while the wife and kids have all the vent fans,lights, and water pump running plus playing video games or recharging the toys!

You have plenty to do all those things and still have plenty to charge batteries-- but it takes time, so atwo hour drive home may still leave the coach batteries a little weak when you get there.
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Old 06-10-2022, 11:30 AM   #5
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Richard, which one of the wires comes from the Alternator or chassis battery, is it the RED (PUR) from the isolated stud? it would appear the BLACK KKG (same lug) feeds three breakers from the chassis battery. LR and FM power the solenoid and I get continuity through the contacts, the contact is closing. My alternator output is 14.5VDC, but I'm not seeing it applied on the house batteries.

Test: Disconnect shore power
Check engine battery and house battery voltages, 12.7 and 12.5
push "boost button" no change in voltage (not even a flicker)
Start motor, no change in voltage on "house batteries" with the solenoid
energized.

Like I said earlier everything works except alternator voltage applied to the house battery, batteries are fully charged, the battery disconnect, and the mode solenoid energize when operated.
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Old 06-10-2022, 11:39 AM   #6
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I might be dealing with an intermittent issue with the solenoid. I'm going to measure voltage at the "isolated stud" with and without the motor running, if I see a voltage change at the stud 1-RED (PUR) from 12.7 to 14.5, I'll have my answer.

Is there a fuse or breaker between the chassis battery and the stud?
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Old 06-10-2022, 01:19 PM   #7
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There is a tag of tape put on when the RV is new and if still there, this "code" may help ID the cables? But tape has a bad habit of getting old and falling off!

I don't know of any fuse, etc between the alternator and "isolated stud" and when we deal with the part that come on the stripped chassis before it gets to Winnebago, we don't get much info as they call that somebody else's problem??
So where that stud even is, is really a big question, short of pulling cables to find it.

That solenoid tends to be a problem for many as it does take a beating as it closes every thime we start the engine and that makes an arc that eventually corrodes the contacts or burns them to the point they don't make good contact.

The contacts inside that I have seen are the ends of the big studs that look like they put them in a press and mashed the stud flat and then the part that moves is something like a big washer about the size of a half dollar on the end of a metal rod. When the solenoid operates, the big washer gets slapped against the contacts/ studs ends and that ties start and coach together.

I think your solenoid is behind the fuses and hard to get to on many RV, so one way to test it working is to hear or feel it move but it can move and if the contacts are corroded, it still doesn't pass current, so I go to the battery ends of the cables as I know where they are and easy to reach.

If you what the start battery cable, start the engine and see the voltage go from 12+ up to maybe 14 if we rev the engine.we know the alternator is good and the battery cable to that point is good, so if we switch the meter to the coach battery and don't see that voltage go up and down, we have to look back from the coach battery connect, toward the solenoid.

Sounds like you have the right ideas and it does sound like a very common problem we hear about on the forum. And it can be come and go type thing as the washer may land on a good spot now and then but fail at other points.

If you are an old poor boy, you may have had a car that you had trouble gettingto crank at times but if you hit the switch enough times it might jump up and start? That's because a starter solenoid and this solenoid are nearly the same, except the mode solenoid is rated "continuous duty" and the starter solenoid might not. From the outside and older cars they both look just the same!

I had to get out and hit the solenoid with a wrench when I first got married!
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Old 06-13-2022, 09:54 AM   #8
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I have a good working solenoid if you need it - just pay for shipping.
Removed it to install lifepo4 system - now have a Victron Orion instead.
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Old 06-14-2022, 05:40 PM   #9
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Quote:
Originally Posted by CJBROWN View Post
I have a good working solenoid if you need it - just pay for shipping.
Removed it to install lifepo4 system - now have a Victron Orion instead.

Chris, can you post a detailed schematic of the battery to battery install and how it relates to the alternator and genset when it's running? Will it interfere with the onboard converter when the genset is running?

Thanks
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Old 06-14-2022, 05:48 PM   #10
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Richard, do you ever run your generator while driving? If the "mode solenoid is energized and the genset is running, there will be two sources of DC power at the house batteries, one from the alternator voltage and the other from the converter. Does the converter have diodes to prevent an overvoltage from back feeding the converter? My alternator produces 14.7 VDC and converter produces 13.5 VDC and they would both be supplying the house batteries if the generator was running.
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Old 06-15-2022, 03:39 AM   #11
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Please, please, please no guessing, no references to other model years, don't cloud the issue. I would love the informed straight answers from someone who knows exactly what those answers are.
The wiring diagrams for your coach are here. The answers to many of your questions are there. Sheet 6 of the "Body, 12 Volt Wiring Diagram" (link here) is one place to start. The "Wiring Identification Guide" (link here) matches the circuit IDs to their purposes. Be sure to use the Workshorse wiring sheets in diagram sets that show both those and Ford wiring.
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Old 06-15-2022, 07:36 AM   #12
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Quote:
Originally Posted by Bob35A View Post
Richard, do you ever run your generator while driving? If the "mode solenoid is energized and the genset is running, there will be two sources of DC power at the house batteries, one from the alternator voltage and the other from the converter. Does the converter have diodes to prevent an overvoltage from back feeding the converter? My alternator produces 14.7 VDC and converter produces 13.5 VDC and they would both be supplying the house batteries if the generator was running.
Yes, it is common for many folks to run the generator as they drive as it is often needed for roof air to have AC as a second way to keep the whole RV cooled when the dash air is not enough.
But it is not a problem for either the converter nor alternator and I might guess at some reasons why. Not a field I really give much thought as it has always worked?

Two big first thoughts would be that both are designed with near the same voltages as output with some slack for difference in components, so slightly higher voltage on either is not a problem. They may put out a max of 14.5 but either may be good to stand 20? Or they may have something like you mention to avoid backfeed?? I've never looked and they are constantly improving/changing small points. With the newer solid state designs, we can't see what they've done nor will they tell you their trade secrets!
Magic in, magic out!

But the bigger thought is that both also will back down the voltage as it reaches near fully charged on the batteries. So the alternator putting out 14.5 will not stay at that level if it is finding batteries at 13 which it would if the converter was pushing that voltage! Same with the converter as they both have the same stages of output. I would assume one will be more prone to being higher than the other but both would quickly settle down to what is needed to charge and then float the batteries.

The current flows because there is a difference in voltage (potential) at two points. So there is no reason for current to flow from an alternator at 13 -14 volts to a converter at 13 if there are batteries at 10-11 or 12!

It is something like having a bunch of buckets of water connected together with pipes. Replace thinking about things like electrons with things we know like water!
One bucket starts with 14 inches of water and the others have various levels. The water runs pretty fast from the highest to the lowest but as those levels reach the same point, flow slows until they are all near the same.
At the same time we have hoses at the alternator and converter to put in more or less water as needed, we also have things draining the water out.
To make it all work, the flow going into the system has to vary as the need to charge and the drains vary.

I try not to think so deep as explaining/knowing why the chemical end works as I'm just happy that we don't have to constantly adjust something to get it to work.

The systems are both set up to turn the hose down when the buckets begin to get full or turn it up if we do something like run the jacks or slides.
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Old 06-15-2022, 08:28 PM   #13
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This is probably what controls the mode solenoid in your coach. https://www.amazon.com/Intellitec-00.../dp/B0721TL39Y or something very similar.
As far as the multiple charging devices, the battery does not care how many it has. You can have solar , alternator, converter and a portable charger all connected and the one with the highest voltage will deliver the current unless it does not have the capacity in which case the next higher voltage devise will kick in and so on. If the batteries are really low all of the charging sources might contribute current to the cause.

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Old 06-15-2022, 08:37 PM   #14
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"As far as the multiple charging devices, the battery does not care how many it has."

Yes, absolutely. You can have a charger, Alternator charger, 2 or more solar chargers, etc. all connected to the battery at the same time. If the battery resistance is low they may all charge at their maximum and as the battery charges and the resistance goes up the current from the devices will begin to drop. How much each and which is charging the most will depend on wire length and resistance, temperature, programmed charging etc.
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Old 06-16-2022, 03:30 AM   #15
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This is probably what controls the mode solenoid in your coach. https://www.amazon.com/Intellitec-00.../dp/B0721TL39Y or something very similar.
As it came from the factory, the OP's coach did not have a controller attached to the Battery Mode Solenoid. The solenoid activation signal, LR, comes from the BATT BOOST switch. In one switch position, the house battery bank supplies LR, and in the other the ignition supplies LR. This is common in Winnebago coaches of the era.
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Old 06-16-2022, 06:51 AM   #16
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Interesting that Winnebago had no means of charging the chassis battery from the converter while plugged in. I had a 2004 Damon with progressive dynamics converter and a B.I R.D. relay. The golf cart batteries lasted over 8 years and the original chassis battery was still with the coach when I traded it after 14 years.

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Old 06-16-2022, 06:57 AM   #17
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For a solenoid replacement, we all may have differentideas but for my purposes, I often just go the easy way onsimple things like this. We are speaking of an item that has lasted nearly 20 years, so if the next one lasts that long, I call that good 'nuff!

That leaves me simply looking at minimum specs, price, and how easy to get it, rather than going for unltimate. Minimum specs on this would be that it is rated for continuous use with 85 amp or more rating and locally available in my area.
I also like to stay with the same wiring scheme on whether they use three wires or four but that is just my lazy side and there are so many available that I have never gotten into shipping to get one.
Brands do not effect my shopping as the company may have been bought out last year anyway! Most items are not made of parts and put together all in one place anyway. The folks who hammer out the metal are not usually the same folks who put the wiring in!
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Old 06-16-2022, 08:33 AM   #18
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Well, since I own a 2005 W. Sightseer, I've read this string with great interest, since it applies to me too. Richard, I always enjoy your wisdom and knowledge!

Bob, Clearly you're deep into all of this, from I read here. That's great. Have you read how our older inverters don't do a very good job of charging the batteries? It seems that we end up with shorter battery life, and less than a full charge on them too, because their voltage is below what lead acid batteries need to be fully charged. (Assuming I've read what they say correctly.)

As such, not mentioned in any of this that I can see, I'm wondering if you've fully charged your House batteries, with a charger, and then had them load tested for free at your local parts store; because sometimes the batteries only live a couple years. It's a good starting point to build from in your voltage testing. Surface charge voltages aside, a bad battery paired to a good one, should be eliminated from your list. And as an aside, unless the batteries are pretty new; you should replace the pair if one is bad.

I won't be installing a new style multi-stage inverter, that cycles a higher voltage to fully charger the battery; but I do hookup an external charger to the house batteries occasionally, to get them fully charged. I assume that the RV alternator also tops off to a full charge on a long enough drive.

Best wishes, in finding what's going on with your rig. As you well know, there's some real complexities in overlapping input voltage sources, safety lock-outs, and the like; that can boggle the mind.
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Old 06-16-2022, 09:14 AM   #19
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Quote:
Originally Posted by Rick 99037 View Post
Well, since I own a 2005 W. Sightseer, I've read this string with great interest, since it applies to me too. Richard, I always enjoy your wisdom and knowledge!

Bob, Clearly you're deep into all of this, from I read here. That's great. Have you read how our older inverters don't do a very good job of charging the batteries? It seems that we end up with shorter battery life, and less than a full charge on them too, because their voltage is below what lead acid batteries need to be fully charged. (Assuming I've read what they say correctly.)

As such, not mentioned in any of this that I can see, I'm wondering if you've fully charged your House batteries, with a charger, and then had them load tested for free at your local parts store; because sometimes the batteries only live a couple years. It's a good starting point to build from in your voltage testing. Surface charge voltages aside, a bad battery paired to a good one, should be eliminated from your list. And as an aside, unless the batteries are pretty new; you should replace the pair if one is bad.

I won't be installing a new style multi-stage inverter, that cycles a higher voltage to fully charger the battery; but I do hookup an external charger to the house batteries occasionally, to get them fully charged. I assume that the RV alternator also tops off to a full charge on a long enough drive.

Best wishes, in finding what's going on with your rig. As you well know, there's some real complexities in overlapping input voltage sources, safety lock-outs, and the like; that can boggle the mind.
Rick, your advice is good, but it's a "converter", not an "inverter" that's installed in most, especially older, motorhomes to charge the batteries. Actually, the full, correct terminology is "converter/charger". A converter/charger "converts" 120V AC shore power to 12V DC to run your DC appliances while on shore power and also to charge your battery.

An "inverter" inverts 12V battery power to run your 120V AC systems from your battery when disconnected from shore power. Some higher end inverters also have a charger built it that's operational when connected to shore power, but they aren't commonly installed, except as options or on high end MHs. Most of the inverters installed in our older MHs are relatively small devices intended to allow operation of our TVs and possibly other small appliances from battery power and have no built in charging function.

It's a new, "multi-stage converter" that we owners of older MHs are installing in place of our old, dumb converters.
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Old 06-16-2022, 09:24 AM   #20
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Thanks for the correction Bobc. I wouldn't want to confuse someone reading my post. You'll notice I know what it does, but I get the words "converter" and "inverter" mixed up. Getting old sucks!
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