Chassis and house batteries voltage

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Henry J Fate

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I would guess it is possible that the computer may be seeing battery voltage that is high due to the lithium bank but I do not know enough about that to say one way or the other.

I can suggest to keep the switch you are using to combine the banks in the position that keeps the bank separate when the engine is running. That way the engine alternator and computer will not be affected by the lithiums because of the isolators but the alternator will still charge both banks.  Resetting that error code becomes the next problem. If you can reset it, keep that switch in the separation position and maybe the error code will not return.
 

Henry J Fate

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In reference to the switch.....

You indicated in an earlier post that you "disconnected the house batteries from the chassis battery and then checked the voltage".

How were the house and chassis batteries connected and how did you disconnect them?
 

garyb1st

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Henry J Fate said:
In reference to the switch.....

You indicated in an earlier post that you "disconnected the house batteries from the chassis battery and then checked the voltage".

How were the house and chassis batteries connected and how did you disconnect them?

As far as I know, the house batteries are not connected to the chassis batteries.  All I did was replace the house batteries. 
 

Henry J Fate

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This was your post below...............


Just checked the chassis and house batteries.  After sitting overnight, the chassis battery was reading about 13.2v.  That's too high for an at rest reading.  The house batteries were reading about 13.16v.  That indicates a discharge which doesn't make sense since almost no load.  After disconnecting the house batteries from the chassis battery, the chassis battery voltage dropped to about 12.65v and the house batteries increased to 13.26v.  So what's happening?

 

Gary RV_Wizard

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I believe the engine alternator in a modern vehicle operates between 12.6 and 14.5v, but typically in the range 13.3-14.4.  I don't think its worth agonizing over 0.1v on either end.  The old adage applies about measuring with a micrometer when cutting with an ax.


Disconnecting a battery from the charging source doesn't make the surface charge go away, whether in an hour or even overnight.  Self-discharge doesn't happen quickly.  It usually takes a few minutes under load to do that, e.g. 5 minutes with a 1.0 amp light bulb connected.
 

garyb1st

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Henry J Fate said:
This was your post below...............


Just checked the chassis and house batteries.  After sitting overnight, the chassis battery was reading about 13.2v.  That's too high for an at rest reading.  The house batteries were reading about 13.16v.  That indicates a discharge which doesn't make sense since almost no load.  After disconnecting the house batteries from the chassis battery, the chassis battery voltage dropped to about 12.65v and the house batteries increased to 13.26v.  So what's happening?

Henry,  I have always assumed that the positive and negative cables to the house batteries are from the chassis battery.  If not, then I have no idea how current goes from the alternator to the house batteries. 

When I say disconnect I'm simply talking about removing the battery cable from the positive and negative posts of the house battery.  Once I've done that, I believe I've broken any connection and a reading of the house batteries is simply that.  Likewise, the chassis batteries are no longer connected to the house batteries so any reading is strictly from the chassis battery.  However before removing the cables, current seemed to be flowing from the house to the chassis battery or visa versa.  Is this normal or is something else causing this? 
 

garyb1st

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Gary RV_Wizard said:
I believe the engine alternator in a modern vehicle operates between 12.6 and 14.5v, but typically in the range 13.3-14.4.  I don't think its worth agonizing over 0.1v on either end.  The old adage applies about measuring with a micrometer when cutting with an ax.

Agree.  But it's not 0.1v, it's .5v or more. 


Disconnecting a battery from the charging source doesn't make the surface charge go away, whether in an hour or even overnight.  Self-discharge doesn't happen quickly.  It usually takes a few minutes under load to do that, e.g. 5 minutes with a 1.0 amp light bulb connected.
  But how do you explain the voltage drop from 13.2 to about 12.6 by simply disconnecting the two sets of batteries as explained in my reply to Henry? 
[/quote]
 

garyb1st

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Just read an article that may explain part of the puzzle.  The article describes the difference between a battery isolator and a battery separator and how a battery isolator can allow current from a fully charged battery to flow to a less charged battery.  The Workhorse manual suggests my motorhome has a battery isolator.  This could explain why my lithium batteries appear to have drained a bit over night while the voltage in the chassis battery increased to about 13.2v.  Guess I'll find out next week when I have the engine light diagnosed. 
 

Heli_av8tor

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Gary,
I'd imagine that your coach has the same or similar setup as mine. The alternator, house, and chassis batteries are connected to a "black box" that lives under the hood. The box contains a circuit board with several relays. It provides several functions. I haven't tried to totally figure out exactly what it does (and when) but here's my understanding.

1. It serves to (mostly) disconnect the house +/or chassis batteries with the "salesman" switches.

2. When the engine is off the house and chassis batteries are not connected to each other.

3. Connects the house and chassis batteries together for jump starting the engine with a dead or low chassis battery by depressing the momentary switch.

4. Sends alternator output to both house and chassis batteries for charging after engine starts.

The control board had been replaced by my selling dealer just before I purchased the coach. So this control board can and does fail which could affect any of these functions.

You mentioned that it appeared that the house lithiums discharged and the chassis charged while not running or connected to shore power. Indicates to me that the two systems are still connected. Perhaps a failure of the black box. If so, the voltages should equalize over time. (Expect small differences due to parasitic loads drawing from different points along the circuit.)

I've not found the DVM readout of house and chassis batteries to be very accurate. I don't rely on it. If I have a voltage readout on the dash it's part of the speedometer display. I've never used it.



 

Gary RV_Wizard

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Henry,  I have always assumed that the positive and negative cables to the house batteries are from the chassis battery.  If not, then I have no idea how current goes from the alternator to the house batteries.
Your chassis and house 12v systems are normally separate (isolated) but get connected together by a relay when appropriate.  That relay gets closed (connected) when the engine is running (alternator producing output) or when you press & hold the Aux power switch on the dashboard.  Your Fleetwood coach will also have a Battery Control Center (BCC) that will close that relay under certain conditions when shore power is actively powering the house converter/charger. That allows the chassis battery to be charged while on shore power.

The Workhorse manual suggests my motorhome has a battery isolator.
Not sure what you read, but Workhorse does not provide any sort of battery isolator or BCC with the chassis. The chassis comes with the chassis 12v system in place but there is no house 12v system at all, so nothing to isolate from.  All the house-related stuff, including the isolation relay and BCC, is added by the coach builder (Fleetwood in your case).
But how do you explain the voltage drop from 13.2 to about 12.6 by simply disconnecting the two sets of batteries as explained in my reply to Henry?
Whenever two batteries are connected, the voltage reading on either battery's terminals represents their combined voltage, which is roughly the average of the two of them.  As soon as they are disconnected, each battery will show the reading of its independent voltage rather than the combined reading. Apparently one of the batteries was much higher voltage than the other, so when you separated them, one showed a lower voltage (12.6) and the other presumably increased by some amount.
 

Heli_av8tor

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Gary RV_Wizard said:
That allows the chassis battery to be charged while on shore power.

Gary, do you know how the BCC senses that shore power is connected and charging the house batteries to connect them to the chassis batteries for charging?

Do you know of a schematic source for the BCC that would likely be on Garyb1st's and my coach?
Thanks,
Tom
 

garyb1st

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Heli_av8tor said:
Gary,
I'd imagine that your coach has the same or similar setup as mine. The alternator, house, and chassis batteries are connected to a "black box" that lives under the hood. The box contains a circuit board with several relays. It provides several functions. I haven't tried to totally figure out exactly what it does (and when) but here's my understanding.

1. It serves to (mostly) disconnect the house +/or chassis batteries with the "salesman" switches.

2. When the engine is off the house and chassis batteries are not connected to each other.

3. Connects the house and chassis batteries together for jump starting the engine with a dead or low chassis battery by depressing the momentary switch.

4. Sends alternator output to both house and chassis batteries for charging after engine starts.

The control board had been replaced by my selling dealer just before I purchased the coach. So this control board can and does fail which could affect any of these functions.

You mentioned that it appeared that the house lithiums discharged and the chassis charged while not running or connected to shore power. Indicates to me that the two systems are still connected. Perhaps a failure of the black box. If so, the voltages should equalize over time. (Expect small differences due to parasitic loads drawing from different points along the circuit.)

I've not found the DVM readout of house and chassis batteries to be very accurate. I don't rely on it. If I have a voltage readout on the dash it's part of the speedometer display. I've never used it.

Tom, I've got the same set up.  One of the Youtube video's I've looked at by another Fleetwood product owner removed the board to get at a relay or some device that is housed behind it.  So they do fail.  I have all the service records on this motorhome and there has been a history of battery issues including several problems with the BCC which was replaced at one point. 

Gary, you are correct.  The Workhorse chassis manual also says the isolator is installed by the body manufacturer.   
 

garyb1st

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Heli_av8tor said:
Thanks Gary. Have a great Thanksgiving

You're welcome.  Hope you and Theresa are well and enjoying the Thanksgiving holiday. 

FWIW, I don't read these schematics.  So if you're going to be in the desert January, maybe you can give me a short tutorial. 

 

garyb1st

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Decided to reconnect the house batteries today.  To my surprise everything went back to normal.  The dash voltage read about 13.7v with the engine running.  Previously it was reading 14.2v.  The chassis voltage meter in the cabinet was about 14.5v.  The house battery meter in the cabinet was about 1/2v higher than my Victron BMS and my DMM.  So it appears the voltage meters in the motorhome are both high. 

The only thing I can think of is a bad connection to the house batteries when I first put them in.  The lithium batteries do not have normal battery terminal.  They have size M6 bolts that screw into the battery.  That's a very small post and on top of that, they can only be torqued to about 12 lbs.  Not having a torque wrench I was concerned about over tightening them and possibly ruining a rather expensive battery.  So I'm guessing I didn't have good contact the first time.  Hopefully it's as simple as that. 

The engine light is still on but it's probably coincidental rather than related.  I'll find out Wednesday. 

 

garyb1st

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Scratch my earlier post.  After doing a bit more research on the voltage issues, I think they are related to the Intelletec BCC.  In a previous post, when I mentioned the two batteries were connected I was referring to the chassis and house batteries, not the two house batteries. 

The chassis battery appeared to be pulling amps from the house batteries after I turned off the engine.  With nothing connected, my Victron BMS indicated the house batteries were discharging at about 2 amps.  After turning off the aux and main batteries at the BCC, the discharge dropped to about .10-.15 amps.  It appears the the Intelletec Bi-directional Isolator Relay Delay (BIRD) sensed the house batteries were being charged and opened a relay.  If I understand it correctly, when the BIRD senses more than 13.2v at the house batteries it assumes the system is being charged and begins charging the chassis battery.  Since the lithium batteries are always more than 13.2v, I'm guessing there will be a constant discharge of the house batteries attempting to charge the chassis battery.  This won't hurt the lithium batteries but suspect it could shorten the life of the chassis battery.  So my question is how do I defeat or alter the BIRD system? 
 
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