Chassis and house batteries voltage

[garyb1st]

Just took the Pace Arrow out for an hour and a half run.  First time we've had it on the street in almost 9 months.  The primary reason for the run was to see how the alternator performed while charging the new Lithium batteries.  I believe they were between 80 and 100% charged when we started.  I know the lithium batteries will pull a lot of amps from the alternator so expected the volts to be high.  But based on the readings while we were on the highway I'm wondering if they were possibly too high and maybe a problem with the charging system. 

The motorhome has a voltage indicator on the dash.  It was reading about 14.1 - 14.2 for the entire trip.   The motorhome also has a voltage meter in the cabinet that houses the tank and propane meters.  DW checked the main and aux batteries while on the road.  The main was showing 15.1 - 15.2 and the aux batteries just under 15 at highway speed.  So the dash meter and the meter in the cabinet were showing significantly different voltages. 

A couple hours after shutting down, I checked both the house and chassis batteries with my multi-meter.  Both looked good.  The chassis about 13+ so likely still had some surface charge.  The new lithium house batteries were at 13.27 and increasing.  That's also what my Victron Battery Manager read.  Prior to taking off, they were at 13.3.  They had been at that level for several days.  The Victron also shows the batteries at 100%.

I've read that if the voltage output of the main battery is 15v or more, it could mean there is an issue with the charging system. 

So my questions. 

Does this sound like an alternator issue?   

If not and still a charging issue what could it be?

Anyone with a Fleetwood product know what the typical dash voltage reading is? 

With a difference between the dash reading and the reading in the cabinet which one is likely more accurate?

[Henry J Fate]

First impression is that the charging is probably within the limits of the lithiums which can handle 15 volts or about.

The difference in the readings from the dash meter to the meter in the cabinet should be resolved by using a reliable volt meter at both the chassis and the house lithiums while the engine is running.

In your post you mentioned the voltage readings of both the house and chassis batteries 2 hours after shutting down the engine. Both those readings seem fine except for the mention of the voltage still increasing at the house lithiums. Was that a mistake in your post or maybe you were plugged in?

[garyb1st]

Henry, I'm going to check them again tomorrow.  That way any surface charge should be completely dissipated.  I'll also check them with the engine running.  Don't know why the lithium batteries continue to increase in voltage but they've done that several times before.  Possibly something to do with the way their BMS, battery management system operates.  Lithium batteries have an interesting SOC chart.  They read about 13.3 volts until they are almost 80 to 90% discharged.  That's why a battery management system is important. 

[Domo]

Charging voltage is higher than battery voltage.


When your are driving, the batteries are charing - the voltage will be higher than 12.6 volts - even to the 15+ you mentioned on the (less than accurate) panel meter.


If you want to measure the battery voltage wait until you've stopped - haven't plugged into shore power, don't have a generator running and have had a beer. Then measure the voltage - each bank should be around 12.6 assuming you aren't running your refrigerator through your inverter...


IMO - anything more than 12.6 means you are charing - less than 12.6 means you are discharging.


Use a real analog meter so you know what you voltate really is.


In OP's case - it looks like all is well.

[garyb1st]

Charging voltage is higher than battery voltage.


When your are driving, the batteries are charing - the voltage will be higher than 12.6 volts - even to the 15+ you mentioned on the (less than accurate) panel meter.


If you want to measure the battery voltage wait until you've stopped - haven't plugged into shore power, don't have a generator running and have had a beer. Then measure the voltage - each bank should be around 12.6 assuming you aren't running your refrigerator through your inverter...


IMO - anything more than 12.6 means you are charing - less than 12.6 means you are discharging.


Use a real analog meter so you know what you voltate really is.


In OP's case - it looks like all is well.

Thank you.  I'll recheck tomorrow after they've been at rest over night.  I've turned everything off so there won't be any discharge other than the typical phantom stuff. 

[Ex-Calif]

The alternator voltage is predominantly limited by "acceptance" - Lithuium will accept a high charge rate so alternator voltage will be higher with other types.

That's one reason people go to lithium. Higher voltage + higher amps = faster charge.

[Mark_K5LXP]

It might be useful to know what the charging system will do under different conditions.  In the olden days where there was little charge control, the alternator basically maintained a fixed voltage set for a compromise of operating conditions.  But as systems became more sophisticated there was some temperature and current monitoring thrown in.  Today it's literally down to coulomb counting and parameters adjusted on the fly.  Put in a different chemistry battery and a less sophisticated system may not charge it correctly, and a more sophisticated one may not accept it.  No matter what the actual system in place, using a DC-DC converter solves all the problems because now the converter is managing the lithium charge and is merely a simple load to the stock vehicle charging system.

My first action though would be to use a known good meter to measure the terminal voltage of the batteries under the conditions in question.  Generally digital meters are pretty accurate but you have no idea at what point they're monitoring.  Where it matters for now is right at the battery, so even a set of alligator clips on the posts and some light duty zip wire out to put a known meter in a place you can see it underway would answer some questions.  You need this data to proceed, otherwise you're just guessing.

Mark B.
Albuquerque, NM

[Bobtop46]

My RV alternator puts out a constant 14.1v to the both batteries and through a charge line to my towed battery as well (6 batteries total 4 house, 1 chassis, and 1 towed).  I can't answer your question directly but after you stop for the day wait a couple hours you say the battery indicates 13.27v and increasing.  They were at 13.3 before you left.  My question is isn't this the converter or inverter charging of the batteries voltage?  You would need to turn either or both off wait the 2 hours and check the battery voltage.  Mine reads 13.3 while charging and 12.5 when not. I have the Trimetric battery monitor. My converter slowly discharges the battery (40w or so) for awhile then charges and repeats, and has a equalization schedule.

[garyb1st]

Just checked the start and house batteries.  Start was about 12.5v and the house were 13.25.  Then I started the engine and the volts increased to about 15.  So about the same as when out on the highway. 

I was concerned that maybe my new lithiums were pulling too many amps from the alternator so I disconnected the house batteries and started the engine again.  No change.  The on board meter was showing about 15v on the main battery.  Now the question is why my engine light came on.  I'll start a new thread on that.   

[Mark_K5LXP]

I started the engine and the volts increased to about 15.
...
I disconnected the house batteries and started the engine again.  No change.

OK, so you have a relative comparison based on an unknown change in load current but not an absolute value.  Until you correlate the dash meter to one that's known correct you could end up chasing ghosts.  Is it really 15.00V or something else.  A tenth of a volt difference in your result can mean a lot in this context.

Mark B.
Albuquerque, NM

[Henry J Fate]

Things seem to be normal. 15 volts is in the high end of things but as long as it stays where it is you shouldn't have any problems.

One issue I had several years ago was with a rebuilt alternator from one of the cheap houses. I installed the alternator in the mini van only to be faced with the battery going dead again. I put my volt meter on the alternator while it was running after recharging the battery and it read about 15 volts which was about a half volt higher than the bad one I exchanged. I left the meter on it for about 20 minutes and paid close attention. The voltage began to slowly increase and at one point went over 18 volts. The store said they needed to look at it so I drove it in. They put it on their analyzer and it came up fine. They said I should replace the battery because it was closing in on 80% capacity. Dis-believing all of what I was hearing, I agreed to buy a new battery because I needed another battery for one of my yard trucks. New battery died the same as the old. I called the store back to say that the alternator is bad due to the voltage readings I metered. They said they couldn't just replace it because they have not verified anything I was claiming and that if I wanted to replace the alternator I would need to buy another and if it worked they would refund the 2nd purchase. Being the upset customer I was at the time, I agreed to purchase a new one but a more expensive one and that if it worked I would get the refund of the more expensive one and basically pay for a standard alternator but have the premium one. The alternator was bad and we got the $380 alternator for $160.

Sorry for the long winded story but it was one of those alternator stories I will never forget. I kept the new battery in the staff mini van and used the old battery for one of the yard trucks.

My suggestion is to watch the the charge voltage. I constantly keep track of it on all my vehicles since.

[garyb1st]

My Victron battery monitor only looks at the house battery but it's spot on compared to my DMM.  I have a clamp meter that I'll use to verify the DMM. 

[Mark_K5LXP]

I know you have other distractions right now (CEL) but in my mind I'd want to know why I would read 14.2V on the dash and 15V with another meter.  That's about a 7% difference and in battery charging terms is a world apart.  It would be highly unusual for a system of this vintage to put out 15V unless it was broken, so I suspect something up with the 2nd meter or it's connection point. 

Multiple options for measuring alternator current.  Most direct is a clamp on current meter.  Or put in a shunt and ammeter.  Something I've done over the years to monitor currents in various things is to run a known amount of current through one of the existing cables, measure the voltage drop (millivolts) and from there you can measure the voltage drop of that cable during operation and with ohm's law calculate the current.  That way you're not adding in a shunt, you're using the existing cable as a shunt.

My personal take on this setup would be to let the alternator handle the chassis battery since that's what it's designed to do, then manage the house side with a dedicated lithium battery isolator or converter.  These systems were designed for a very specific set of operating conditions and when those are modified, you're off on your own and things may not work as desired.  Nice if it happens, but be prepared to become your own applications and field engineer.

Mark B.
Albuquerque, NM

[garyb1st]

Just checked the chassis battery again.  With engine idling, both my DMM and the meter in the cabinet were about 14.5v.  The dash was indicating 14.1-2.  So the same as it was reading the other day while driving at highway speed.  Based on this I can only conclude that when the meter in the cabinet was hovering around 15v while on the highway it was correct. 

Regarding  your comment about the vintage of my motorhome, what do you think the appropriate voltage output should be?  My clamp meter doesn't measure DC current. 

[Mark_K5LXP]

A "dumb" alternator like the one you and I both have (My WH is the same year as yours) shouldn't go much north of 14.2V, 14.4V would be the max I would ever expect under any circumstance.  My dash meter and actual measure within half a tenth of a volt (dash is one decimal place so not sure where it rounds).  To see north of 15V is far outside any normal operating condition.  A lead acid battery is under hard charge at 14.4V and would be damaged if left there for extended periods, so more would not be better.  If your chassis battery is actually seeing 15V under normal operating it's going to be boiled out and shot in relatively short order.  I'd be poking around that system with a meter starting right at the alternator output and tracing around to see why the voltage is elevated.  Could be a wonky regulator but it could also be a compromised ground connection somewhere, which might explain the disparity between your two meters.

There are clamp meters that measure DC current.  They tend to be a bit more expensive than an AC ammeter but not tremendously so.  Shunts are cheap so that would be one option, or using an existing cable as a shunt with an inexpensive voltmeter.  You don't need precision here, just enough to give an idea of a lot or a little.

Mark B.
Albuquerque, NM

[Gary RV_Wizard]

Modern alternators don't really have a "regulator" per se; there is a built-in feedback loop where the system voltage is used to bias the alternator magnetic field, which causes a voltage change in the output. There is no regulator component to adjust or replace.  However, loss of the connection to the ignition switch for the voltage feedback will cause the alternator voltage to rise. So will corrosion on that connection. Anything that reduces the feedback voltage causes the alternator output voltage to increase.

[garyb1st]

Mark, you may be correct.  Two things.  First, when I noticed the 14.8v on the house and 15.1v on the motorhomes meters, I assumed it was because of the new lithium batteries I just installed.  Before installing the lithium batteries the highest readings on both the house and chassis that I recall seeing was around 14.4v.  Second, the first time I started up the engine after installing the lithium I smelled an odor.  That was while the engine was idling for maybe 15 to 20 minutes.  I wasn't sure but it made me think something electrical was heating up.  I turned off the engine thinking there was a problem and the smell dissipated.  I didn't smell anything unusual on our 90 minute run the other day. 

Gary RV_Wizard, you didn't say but are you agreeing with Marks comment on maximum voltage for these older alternators? 


 

[garyb1st]

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?

When I installed the new lithium batteries, I simply replaced all the wires in the same order as I had them connected to the FLA batteries. 

Looks like the chassis battery was pulling volts from the house batteries.   

Aside from connecting an inverter and Victron battery management system more than a year ago, nothing has changed since connecting the lithium batteries. 

An hour later the voltage on the start battery dropped a bit to 12.5. 

The Alternator continues to put out about 15v.  I verified that with my DMM. 

 

 
 

[Henry J Fate]

Individual battery banks (house and chassis) should be metered when they are separated. Connecting them together then taking readings will result in a medium reading of each bank depending on charge state and load.

The isolators keep the battery banks separate basically for same source charging and do not combine the banks for usage. The switch you are using to combine the banks is bypassing the isolators and in fact combining them.

The drop in voltage at your house lithiums would be partially due to the fact that your lithium house bank was sending current to the chassis battery while you had them combined with charging off because of the difference in voltage between the lead acid and the lithium. This is also the reason your chassis battery is over 13 volts.

[garyb1st]

Individual battery banks (house and chassis) should be metered when they are separated. Connecting them together then taking readings will result in a medium reading of each bank depending on charge state and load.

I believe they are.  Unless I managed to do something wrong when replacing the old FLA house batteries with the new lithiums the wiring has always been this way. 

The isolators keep the battery banks separate basically for same source charging and do not combine the banks for usage. The switch you are using to combine the banks is bypassing the isolators and in fact combining them.

I haven't added a battery isolator, a dc to dc charger or any other switch so not sure what would be connecting them.  My Victron BMS only reads the house battery and is not connected to the chassis battery.  In fact the only way I know of connecting them is with the momentary switch.  So if that has failed in any way, perhaps that's an issue. 

The drop in voltage at your house lithiums would be partially due to the fact that your lithium house bank was sending current to the chassis battery while you had them combined with charging off because of the difference in voltage between the lead acid and the lithium. This is also the reason your chassis battery is over 13 volts.

Agree, but why?  As far as I know, that didn't happen when I had the old FLA batteries connected.  And I've wired the lithium batteries the same way as the old FLA batteries. 

While it could be coincidental with another problem, I'm inclined to believe it's connected with another issue since the engine light is illuminated.  It through a PO332 code which doesn't really narrow it down.  Thought maybe a mass flow air sensor but it could be a ECM.  But since the engine light illuminated after installing the lithium batteries, it makes me wonder if somehow it's related. 

[Henry J Fate]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.