An RV Question...voltage when generator is on vs off

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An RV Question...voltage when generator is on vs off

December 04, 2016, 11:17:44 pm

With the monitor reading 13.5-13.6 volts while driving (i.e. alternator is charging systems), what causes that voltage to then go up to 14.2-14.3 volts when turn on the generator?

I have the feeling I have no idea how the charging, electricity, supply/usage works! Is something getting too little when the alternator alone is charging the batteries....or too much when the generator is running?

Re: An RV Question...voltage when generator is on vs off

Reply #1 – December 05, 2016, 12:31:01 am

My dash volt meter usually reads low. I suspect some questionable connections causing a higher resistance somewhere, but don't have the time to trace them down just yet. So i purchased two digital voltmeters that plug into the cicarette lighters. One for coach batts the other for start batts. Takes all the stress out of an inaccurate analog gauge. Keeps my cell phones charged too. I aslo noticed some of my dash gauges vary with the gauge lighting intensity. Again, probably a connection issue.

Re: An RV Question...voltage when generator is on vs off

Reply #2 – December 05, 2016, 12:41:48 am

Most likely you are fine, Mike. I don't have the time to explain at the moment, but will take time to show you how to prove that your readouts are normal, tomorrow.
Or give me a call and I'll walk you through it.
Neal
603 seven seven zero 7459

Re: An RV Question...voltage when generator is on vs off

Reply #3 – December 05, 2016, 12:45:22 am

I may be mis-remembering, but I seem to recall reference to our alternators as a 14.2 volt class alternator. I would expect your alternator to put out about 14.2 volts.

Trent

Re: An RV Question...voltage when generator is on vs off

Reply #4 – December 05, 2016, 01:15:35 am

By monitor, I am referring to the camera, tank monitor and voltage readout. An electronic screen.

I understood that the dash volt reading gauge is one battery bank, I think the engine batteries, and I was taught by some tech to watch it when cranking. If the voltage falls too low, then the batteries are going bad or something. I think I was told to watch to be sure this did not fall below 10.5 volts as cranking? It normally reads about 13.5 or so as driving, kinda hard to read better than that.

Then I think the monitor (screen) voltage had to do with the house batteries and their charging. It is this voltage reading I was seeing change.....being about 13.5 without the generator running and 14.2 with the generator running. (nothing about the dash voltage meter (the round gauge).

Interesting, when I first crank up, the monitor screen shows lower voltage but quickly climbs as the engine runs....I guess because the alternator being to send it some juice.

It is plainly obvious I need electrical education and the right terminology so I can help you folks help me. Mainly at this point it is a curiosity.....why does the voltage showing on that monitor screen change with generator running, and does that mean I have a pending failure in some switch or alternator or other?

I may have that totally backward....as to the purpose of the two voltage meters (dash gauge and monitor)...so dear reader be sure to see what the experts say on this.

I think we wait until Neal has time to explain this before you file this a good information, a reference source.

Re: An RV Question...voltage when generator is on vs off

Reply #5 – December 05, 2016, 08:45:32 am

Mike,

When you start the generator, the inverter/charger comes to life. Since it is just starting, it starts in BULK MODE as it always does.

That is why you see the higher voltage. But it should taper off if generator is on long enough for the inverter/charger to progress to FLOAT MODE.

Re: An RV Question...voltage when generator is on vs off

Reply #6 – December 05, 2016, 09:16:46 am

Mike, those numbers are OK. The alternator is probably charging both sets of batteries at about 13.5 volts (alternator voltage - 0.7 volts for the drop through the isolator) maybe a bit more just after starting. At 13.5 volts it will take quite awhile to fully charge the house batteries.

When you start the generator it powers the inverter/charger which senses that the batteries are less than fully charged and will start charging at low 14 volts. I see this as well while driving and the generator is on. So with the generator running the inverter/charger must also be charging the start batteries as if the boost solonoid is closed (boost switch on). But I don't see how that can happen. I am waiting on Neal as well.

With the engine and ignition off (no alternator) does the generator charge the house batteries with the boost switch off? I haven't measured that so I don't know. If it does then how?

Re: An RV Question...voltage when generator is on vs off

Reply #7 – December 05, 2016, 09:41:43 am

Roger and Brett, thanks very much. Will wait see what Neal says Roger as you say. Just quick reply to say thanks lots. I seem to never run out of things to learn....wish I could retain it all without notes!

P.S. I think I recall that my alternator charging voltage was a bit higher and Mike Rodgers of MOT turned it down...not sure how, D2? It seems max 13.7 now but soon settles to 13.5. (Thanks too to John...see next response below)

Re: An RV Question...voltage when generator is on vs off

Reply #8 – December 05, 2016, 09:47:32 am

On the 96 270 the charging voltage is set at 13.8.

Re: An RV Question...voltage when generator is on vs off

Reply #9 – December 05, 2016, 09:57:25 am

Hey Jet Doc...how to do that? Where to buy what? Do you have to change wiring to the cigarrette lighters for I do not think of one lighter going to one set batteries and the other going to the other batteries? Maybe there is separate thread on this?

Thanks

Re: An RV Question...voltage when generator is on vs off

Reply #10 – December 05, 2016, 10:37:38 am

Michael,

If your 2001 is the same as my 2001 320 the LH Cigarette lighter socket is for the Engine batteries and the RH is the House ones. there is a separate post on this where questions were asked re plugging in a solar panel inside to keep the engine batteries charged.

Speedbird 1.

Re: An RV Question...voltage when generator is on vs off

Reply #11 – December 05, 2016, 02:45:18 pm

Michael:
I understand that electronics is confusing to many owners and also, that (often) explanations make the confusion even worse. Improvements to understanding are often lacking because written dialogs (such as on the Forum) are more difficult to process because the "face to face" feedback/corrections/improvements in understanding are missing.

That being understood, there are dozens of variables associated with the battery voltage/current readouts in our coaches that make it difficult for owners to understand what is what and how accurate it may or may not be.

So point by point, here is some explanation, and if you remain confused, please call me because written conversation is cumbersome and there is a wealth of bad information out there as well as good.

Your Question: With the monitor reading 13.5-13.6 volts while driving (i.e. alternator is charging the batteries), what causes that voltage to then go up to 14.2-14.3 volts when I turn on the generator?

Ans:
Every coach and every inverter/charger will (possibly) be a little (to a lot ) different. Brett touches on the most common issue. In OEM design, when your coach is running and the batteries are being charged by the alternator, DC current is being supplied from the alternator, through the isolator to both sets of batteries. But when the engine is shut off and AC is introduced to the coach (inverter/charger) by either shore power or the generator set, the charger immediately starts a three step charge process, to the HOUSE battery bank alone (which assumes the Boost Switch is open):

Bulk charging first,

Then absorption charging second and

Finally float charging at the end.

Equalizer Charging applies almost exclusively to Flooded Batteries and is a manually controlled process that I won't address.

Typically, the inverter/charger will initiate the three step charging process every time AC is introduced to the coach, so even if one just cycles the shore power breaker, the process will start all over again.

Directly to your question, because, when your engine was running, the alternator was trying to charge your start battery bank to a set voltage, let's say an alternator setting of 14.0 Vdc (through inaccuracies, shown as 13.5 to 13.6 on your dash voltmeter). When you start the generator, the Shore Power/Generator Automatic Transfer Switch contacts close to admit AC to the coach, the inverter/charger senses AC available and it starts the charging process which immediately goes into Bulk Charge Mode. Depending upon how your charger is configured, Bulk Charge Mode starts at a constant maximum current, with a target of achieving anywhere from 14.1 to 14.7 Vdc output at the HOUSE battery terminals. The charger will continue in Bulk Charging Mode until the HOUSE battery bank reaches the target Bulk Mode Voltage setpoint for your battery type, or a time limited setpoint is reached. At that point, the charger will shift to Absorption Charge Mode, which is a constant voltage, decreasing current mode. Depending upon how fully charged your HOUSE battery bank was to begin with, as well as several charger settings, your battery type, any temperature compensation, etc., the Bulk Charging Mode and Absorption Modes timeframes may vary from a few minutes to well into hours to complete. And, your initial dash voltage indication may vary from the high 13's to the low 14's, depending upon your HOUSE battery State of Charge.

I've attached some TYPICAL diagrams to this thread (the horizontal axis is TIME), but you must understand that we have already covered multiple variables that are going to change the REAL answer to your question, on a coach by coach basis:

What Inverter do you have?

What Charger do you have?

What Alternator voltage setting do you have? Alternators (OEM) are not temperature or current compensated. Because I want only GEL cell batteries, I have always run mine at 14.0 Vdc maximum, as sensed at the engine start battery set terminals. AGMs and Flooded batteries have different needs and need to be tailored to match the actual components that you have installed in order to maximize life (see attachments for TYPICAL applications).

What type (Flodded, Gel, AGM) of battery/battery sets do you have?

How are the inverter/charger control settings configured and what charging current limit settings (if any) are imposed?

Is the charger temperature compensated and then what is the compartment ambient and battery temperature?

What was the initial battery (SOC) State of Charge?

What is the battery capacity, age and condition vs. initial design parameters

Is the Boost switch open or closed?

Are you OEM? Do you have an isolator or manual battery switches?

What engine battery maintainer is installed and how does it operate?

How is the dash (engine start battery bank) voltmeter wired (from what exact sensing point) and how accurate as well as precise is the dash voltmeter itself (accuracy and precision are NOT the same).

Same for the "Monitor" (Javelina/VMSpc) HOUSE battery wiring and accuracy/precision variables?

Same for all of the other various "plug in" devices used in power outlets and EMS applications.

What other large Vdc electrical loads are being operated when the charger starts and runs through its functions?

[/list]

Speculating as to what is normal or acceptable is not very productive until all of the above (and any other pertinent parameters) are established.

So how does one sort all of this out reasonably and with any degree of accuracy?
It isn't hard. It is just time consuming. First, answer and write down the answers to all of the above questions (and most importantly, read all of the corresponding owner's manuals).

Then, make sure that all of the settings on the inverter/charger are properly configured for your particular batteries and expectations.

Then, if you don't have one already, get yourself a good DVM.

Then get ready to run a timed test by making a table of the components and readouts that you want to understand: e.g. - each battery set, the dash voltmeter, the two dash power outlets, the inverter/charger readout, VMSpc/Javelina Monitor display, etc. etc.

Next set up and document your test "conditions": e.g. - just driven the coach for more than 50 miles, shut down the engine, headlights off, interior lights and climate controls off, etc, etc, whatever repeatable state you want to set up that is realistic.

Open the breaker from the AC source of power

Take an initial set of readings at all of the above points of interest; NOTE: battery readings must be taken directly at the + and - battery set of input/output posts.

Then close the AC supply breaker and take an initial set of voltage/current readings

Then repeat and record the set of voltage/current readings on a periodic basis (10 minute, 15 minute or 30 minute intervals — whatever timing is appropriate to the rate at which parameters are changing)

Then you will have the information necessary to plot a graph for your actual configuration and a repeatable set of conditions.

Most importantly, from the good DVM readings taken directly off of the battery set load terminals, you will know just how accurate and precise your various readouts are and will be able to adjust the condition accordingly. You may want to adjust or change out some of your components if the compensations that you have to apply are too cumbersome.

Some readouts may be improved by improving connection integrity and by moving sensing points to better locations. The various FT designs ,over the full range of years and model numbers, have been notoriously weak in terms of dash instrument accuracy being influenced by various load and sensing point variables.

[/list]
So, I think that is about as easy to understand as I can make it. I could go on ad infinitum with nuances, but this covers most, or at least many, of the major influences.

As I said, call if you want to talk it through more.
HTH,
Neal

Re: An RV Question...voltage when generator is on vs off

Reply #12 – December 05, 2016, 07:35:04 pm

Just want to add another data point to this discussion, for comparison purposes.

Mike's question made me curious, so while driving today I paid close attention to my voltage meters. I have the factory analog volt meter in the dash, plus the Audit screen which shows "coach" voltage, plus a lighter plug digital volt meter which reads the "start" battery voltage (we only have one lighter socket).

Today, while driving at 65 mph, head lights off, my voltage readings were:

dash gauge: 14.0
Audit (coach battery) gauge: 14.4
plug-in (start battery) gauge: 14.3

I tried turning on my headlights, still at 65 mph, and got the following:

dash gauge: 13.8
Audit (coach battery) gauge: 14.4
plug-in (start battery) gauge: 14.1

When we got parked for the evening, I plugged into shore power, which of course powers up the inverter/charger, and got:

dash gauge: no reading
Audit (coach battery) gauge: 14.2
plug-in (start battery) gauge: 14.3 (We have a Trik-L-Start)

The Magnum panel shows (coach) batteries at 100%, "absorb charging" and battery voltage = 14.6 volts.

Re: An RV Question...voltage when generator is on vs off

Reply #13 – December 05, 2016, 08:46:18 pm

Chuck, my monitor may be fancy, I do not know what is or is not higher tech.....my monitor has a little rocker switch on the dash. In one position it shows the camera to the rear. In another a compass and temp. In the third position it shows three tanks, the LP and the voltage. Is this an upgrade over original? I think it says Javelina that I believe Clide told me is the tank level reading mechanism. Thanks for your data.

Neal......I do not know how to thank you. I have read your education twice, will print it out so I can study further, then take to coach and look at things. I THINK, hope, I have it from doing that but if not I will call. Most likely a call to be sure I understand it correctly. I hope everyone that cares about this topic finds this thread.....your write-up is invaluable. Thanks for sharing and taking the considerable time.

I can only begin by saying that I have ProSine 3.0 charger/inverter (2010). My alternator is original 2001 as far as I know. The batteries are all fairly newish (coach and start). But that is not even close to all that I need to know. Too much rain tonight to go out and check, will do tomorrow.

Thanks again, very much.

mike

Re: An RV Question...voltage when generator is on vs off

Reply #14 – December 05, 2016, 08:49:53 pm

Speedbird1...thanks, did not know that. My coach is a close cousin of yours....build 5878....so bet my plugs are same as yours.

Now to find those plug in volt meters.

thanks

mike

Re: An RV Question...voltage when generator is on vs off

Reply #15 – December 05, 2016, 10:07:44 pm

Quote from: Michael & Jackie – December 05, 2016, 08:49:53 pm

Now to find those plug in volt meters.

Plug-in voltmeters area available from many sources. I received mine as a gift from the extremely handsome, charming and witty Bill Chaplin. With some purveyors, you have to wait 6 weeks for shipping from China.

I found the one (below) that at least ships from California. No guarantees as to accuracy. Buy yourself a couple Stocking Stuffers! Get extras for your friends!

LED Car Battery Electric Cigarette Lighter Voltmeter Voltage Meter Gauge...

Re: An RV Question...voltage when generator is on vs off

Reply #16 – December 06, 2016, 10:05:43 pm

Quote from: Michael & Jackie – December 05, 2016, 09:57:25 am

Hey Jet Doc...how to do that? Where to buy what? Do you have to change wiring to the cigarrette lighters for I do not think of one lighter going to one set batteries and the other going to the other batteries? Maybe there is separate thread on this?

Thanks

Hi Mike. I think others may have answered your questions already. I bought my voltmeter/chargers on Ebay. I have also seen them at Walmart and some auto parts stores.

Re: An RV Question...voltage when generator is on vs off

Reply #17 – December 06, 2016, 10:23:49 pm

Mike, you can get a Victron Battery Monitor from Bay Marine Supply. You can replace your dash voltage gauge with one. It will show both (the 702 model) the house and start batteries, much more data about the house batteries. And the really cool thing is that it can be bluetooth enabled and all of tha data is available on your phone.

Victron BMV-702 Battery Monitor

Re: An RV Question...voltage when generator is on vs off

Reply #18 – December 07, 2016, 12:24:49 am

thanks all for the sources of the meters.

I learned today at MOT that the monitor screen is the house batteries and the dash analog is the engine start batteries. They reported as some of you, that behavior and readings are normal.

The voltage is not the charging rate but the charge on the battery (I was not sure when I began this thread)

And the dash analog gauge did show a small increase in voltage when the generator was turned on.....not from the 13.5 or 13.6 move up to the 14.2 as on the screen monitor but more like up to 13.8 or .9 (hard to really know on that small gauge

I imagine this is already said by several of you but I was replying to a question of whether the analog gauge also showed a change when the generator came on.

thanks all..

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An RV Question...voltage when generator is on vs off

December 04, 2016, 11:17:44 pm

Re: An RV Question...voltage when generator is on vs off

Reply #1 – December 05, 2016, 12:31:01 am

Re: An RV Question...voltage when generator is on vs off

Reply #2 – December 05, 2016, 12:41:48 am

Re: An RV Question...voltage when generator is on vs off

Reply #3 – December 05, 2016, 12:45:22 am

Re: An RV Question...voltage when generator is on vs off

Reply #4 – December 05, 2016, 01:15:35 am

Re: An RV Question...voltage when generator is on vs off

Reply #5 – December 05, 2016, 08:45:32 am

Re: An RV Question...voltage when generator is on vs off

Reply #6 – December 05, 2016, 09:16:46 am

Re: An RV Question...voltage when generator is on vs off

Reply #7 – December 05, 2016, 09:41:43 am

Re: An RV Question...voltage when generator is on vs off

Reply #8 – December 05, 2016, 09:47:32 am

Re: An RV Question...voltage when generator is on vs off

Reply #9 – December 05, 2016, 09:57:25 am

Re: An RV Question...voltage when generator is on vs off

Reply #10 – December 05, 2016, 10:37:38 am

Re: An RV Question...voltage when generator is on vs off

Reply #11 – December 05, 2016, 02:45:18 pm

Re: An RV Question...voltage when generator is on vs off

Reply #12 – December 05, 2016, 07:35:04 pm

Re: An RV Question...voltage when generator is on vs off

Reply #13 – December 05, 2016, 08:46:18 pm

Re: An RV Question...voltage when generator is on vs off

Reply #14 – December 05, 2016, 08:49:53 pm

Re: An RV Question...voltage when generator is on vs off

Reply #15 – December 05, 2016, 10:07:44 pm

Re: An RV Question...voltage when generator is on vs off

Reply #16 – December 06, 2016, 10:05:43 pm

Re: An RV Question...voltage when generator is on vs off

Reply #17 – December 06, 2016, 10:23:49 pm

Re: An RV Question...voltage when generator is on vs off

Reply #18 – December 07, 2016, 12:24:49 am

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