Different voltage reedings between remote and battries

[63Hotrod]

Installed new inverter and remote and 4 new house batteries. I am seeing a good bit of difference between what I read at the batteries and what the remote indicates  varies a bit in a range of .15 to .40 .The battery reading being more than the remote. How much difference is normal

[Frank McElroy]

12 minutes ago, 63Hotrod said:

Installed new inverter and remote and 4 new house batteries. I am seeing a good bit of difference between what I read at the batteries and what the remote indicates  varies a bit in a range of .15 to .40 .The battery reading being more than the remote. How much difference is normal

They should be the same but, if you have high current draw and/or a loose connection, the reading on the remote can be lower than actual readings at the batteries.

[63Hotrod]

Everything is clean and tight. Charges as expected and Inverter works well. No major drain on the system When un pluged all that's running is the fridge drawing 9 amps

In the next day or so I plan to disconnect from shore power. Take readings at both places a couple of hr apart and will post them

[Tom Cherry]

Not to contradict Frank, but I see a difference in voltage readings between my remotes, and it is less than 3 years old.  I get about 0.15 - 0.20 volts.  I asked Magnum and they said that it was normal due to the run from the inverter to the remote.  I have verified this under several different conditions.  Under load when I was running down the batteries;  then after I removed the load as well as other times.  However, I never got 0.30 to 0.40.  I would start to check things out.  The first would be to check the voltage from the positive to the chassis ground.  I might even trace the grounds under the battery box to the ground stud.  Loosen the nut and move the cables back and forth or pull off and clean.  Do the same for the Chassis.

The other test would be to put a load…maybe 300-400 watts on the batteries and see the difference.  I made sure that the remote was reading a solid number like 12.5 and not flashing between 12.4 or 12.6 and 12.5.  Then go quickly and read the battery terminals.

If you are getting the 0.40, call Magnum and discuss.  My differences were half of yours.  I didn’t ask them what was excessive, but they said my readings were “as expected”

[Frank McElroy]

That reminds me, years ago I was seeing a delta but that was under heavy load with voltage drop between the batteries and the inverter.  To solve that problem, I ran a separate wire between the AGS module and the battery terminal.  That way the AGS and the remote display would see the actual battery voltage vs the voltage drop feed from the long battery cable under high amp draw conditions.  A +/- 0.1 volt is rounding.  Anything more is either meter calibration errors or voltage drop from long cable runs with high amp draw.

[Dr4Film]

Would a Magnum Battery Monitor Kit (if installed) give a more accurate reading of the House battery bank at the remote?

[Ivylog]

Even after cleaning and tightening multiple connections I still have a difference in voltages. Just use the differences on the note below.

Side note: While on shore power I use the AGM2 setting to charge my Lithiums as it doesn’t recharge until about 40% SOC.

Edited April 19, 2023 by Ivylog

[cbr046]

6 hours ago, Frank McElroy said:

To solve that problem, I ran a separate wire between the AGS module and the battery terminal.  That way the AGS and the remote display would see the actual battery voltage vs the voltage drop feed from the long battery cable under high amp draw conditions.

If I took that approach it's just as hard to run two wires as it is one, so I would run two wires - one for +12V and one for ground to eliminate any ground issues. 

Maybe even run a separate ground test wire outside the coach to confirm / eliminate ground drops.  That would tell you if have an issue without the fishing through the coach. 

- bob

[Tom Cherry]

12 minutes ago, Ivylog said:

Even after cleaning and tightening multiple connections I still have a difference in voltages. Just use the differences on the note below.

Side note: While on shore power I use the AGM2 setting to charge my Lithiums as it doesn’t recharge until about 40% SOC.

I had one of those “I WONDER” thoughts.  I would suggest the following.   Run this test and since my MH is in storage I can’t. 

While charging, measure the voltage at the batteries.  Then immediately measure the voltage on the terminals of the inverter.  I totally agree with Frank, there should be minimum voltage drop and the 0.1 VDC should be the rule.  I BELIEVE that the 08 Nav & Dynasty are like mine, that the inverter is cabled directly through a 300 or 400 A fuse.  Turning off the House Disconnect switch does NOT remove power from the batteries to the invert.

If you get almost the same, less than 0.1, then use your correction.  I wrote a Magnum 101 setup White Paper or How To file that we have as a resource,  I stated exactly what Magnum told me.  That there “will or maybe…usually is” a lower remote reading than what you see on the batteries.  Thus, when you set the AGS to come on, you can go lower than the 11.9/12.0 recommended 50% SOC set point.  The voltage on the remote is what controls the AGS.  So, I keep mine lower.

I can’t speak for your Lithiums, but I also know and commented, that the “REAL” setpoint to run the FLOODED cells down to, would be maybe 11.7/8 VDC UNDER a load (say 350 watts for my 4 bank).  I discussed that with Trojan and they agreed.  My understanding is that the “under load” voltage will be lower that the “recovery voltage”.  So, if you drain the batteries to say 11.8 VDC reading at the batteries.  Then, you remove the jumper and let them “pop back and recover”, the battery will read around 11.9/12.0 VDC and be at 50% SOC.  In other words, if you use your remote, then you need TWO correction factors.  First is the “real” reading of the fully charged batteries (after you remove the surface charge) compared to the meter reading.  Next is the recovery voltage drop, which is inherent to the batteries and when Trojan or any battery manufacturer lists a voltage, it is the “recovery voltage” after the load is removed.  So, in theory…you could go down to 11.7 (dare I say) 11.6 VDC at the remote.  Then remove the load,  remove the jumpers and then let the batteries sit for 30 minutes and check the voltage.  On mine, they would be close to 11.9/12.0.

SO MUCH FOR THE THEORY….real world…

Make some measurements during “charging”, under load and also with NO Shore.  Read the batteries and then the terminals on the inverter.  If you get more than 0.1 VDC drop, you have a “high resistance” connection between the batteries and the buss, where the Fuse is and batteries.  By doing that under load, you may have a higher voltage drop….than at rest. If so, that is a dead giveaway that you may have some hidden corrosion in a cable.  For the “heck” of it…measure to ground.  If, under load, you measure the voltage between the Negative cable terminal and a GOOD Bare ground….if you get more than 0.1 VDC, then you need to clean the ground stud or you have a bad cable.

I think checking the voltages at the battery as well as at the inverter is going to show that there is  a connection issue.  Your drop is twice mine….and mine is “expected” by Magnum.  Once you do these measurements….you can also compare them to what the remote says.

My “Logic” is that the remote is DUMB and can’t be measuring voltages….the Magnum is doing that.  So…if you have NO voltage drop from the batteries to the inverter, then, indeed, there is an inherent drop within the remote….and you use your correction.  

BUT…be aware….if you made your readings during load or draw down, you need to find out what the recovery voltage is….and then THAT correction factor is what you use for the AGS.  That essentially is what Frank did…but I don’t think he adjusts for the recovery voltage…..as that really protects the batteries.  Trojan says to do so…..but not get under 50% after you measure the recovery voltage.

A little long….but the theory and the real world and each MH has to be known…

 

[Frank McElroy]

2 hours ago, Dr4Film said:

Would a Magnum Battery Monitor Kit (if installed) give a more accurate reading of the House battery bank at the remote?

The biggest advantage of a BMK is that you get a state of charge (SOC) reading on the amp hour capacity of the batteries used.  So, say you have a 900 amp hour battery bank.  When the BMK says your used up 450 amp hours, you're at 50% battery capacity and time to recharge.  The problem with BMK is that to completely reset to 100%, the batteries must be fully recharged.  If dry camping, using the generator to recharge to say 90%, small errors will creep in so that after say a week of daily generator recharging the BMK battery SOC capacity could be way off.  When that happens, you need to look at resting battery voltage to determine the SOC or completely recharge batteries to 100%.

[jacwjames]

Voltage readings on my Trace RC7 remote, especially when I was boon docking, were all over the place.  Usually at night I'd charge my batteries by starting the generator and the remote voltage display was all over the place, so I'd run the generator for ~1=1.5 hours and call it good.  The batteries would never show an accurate charge on the display at that point but if by chance I got up in the middle of the night it would show higher voltage.  Drove me crazy.  No idea how the Trace knows when to go through the different stages of charging if the display was that erratic.

So I took the advice of others and installed a Victron BMV712 which is mounted very close to the batteries and remote is mounted near the RC7 display PLUS it has a Bluetooth function.  So now I simply look at on my phone very accurate and very convenient. 

[MyronTruex]

IR drop/loss across the cables between the batteries and the inverter. 

However, your description is a bit puzzling to me.

With the inverter charging almost full tilt at 100 amps, the voltage at the inverter should be a bit higher than at the battery terminals. Even though the cables are very short and hefty (technical term for having very little resistance, they do have some resistance so there should be a tiny bit of voltage dropped across the wires, thus leaving less voltage for the batteries.

When the charging current is low, the IR drop is much less and nearly unreadable by most cheap meters. (consumer models). 

 

[96 EVO]

10 hours ago, Frank McElroy said:

That reminds me, years ago I was seeing a delta but that was under heavy load with voltage drop between the batteries and the inverter.  To solve that problem, I ran a separate wire between the AGS module and the battery terminal.  That way the AGS and the remote display would see the actual battery voltage vs the voltage drop feed from the long battery cable under high amp draw conditions.  A +/- 0.1 volt is rounding.  Anything more is either meter calibration errors or voltage drop from long cable runs with high amp draw.

They wired my AGS module wrong. It was getting it's sensing voltage from the chassis bank!

Imagine my confusion during testing when my house bank was down to 11.6V, and the gen still hadn't started 🤔!

[63Hotrod]

At full charge indication on the remote zero amps 12.8 and the same at the battery. New style remote which I think shuts down charging once it reaches full charge   Will unplug leave the fridge on and see later. But I have seen at the meter a drop to 12.2 in a couple of hours
Ground runs from battery to junction block then one wire to frame Seeng .20 at battery and junction block

On start batteries zero ground voltage 

On inverter zero ground voltage

Ok now I am charging confused 

[Frank McElroy]

1 hour ago, 96 EVO said:

They wired my AGS module wrong. It was getting it's sensing voltage from the chassis bank!

Imagine my confusion during testing when my house bank was down to 11.6V, and the gen still hadn't started 🤔!

Yes, that sure would be a head scratcher.  And on top of that, the remote monitor was reading the lower house battery voltage. 

I bet there are techs out there that would just replace the AGS module thinking it must be bad before first testing to be sure the input voltage was correct.

[63Hotrod]

Clarification no voltage at the inverter copper wire 

[Tom Cherry]

1 hour ago, 63Hotrod said:

Clarification no voltage at the inverter copper wire 

Ok…some times it is good to repeat back for clarity.

you established a good Chassis Ground.  You measured, using the voltage scale, the voltage to ground from the negative terminal (cable) for Chassis, House and on the Negative terminal of the Inverter.  That is good, but may not be 100% verification of a high resistance connection.

The next steps are this.

Use a quartz halogen work light or if you can find REAL 100 W bulbs, maybe 3, of them to start discharging the house.  NOTE…this is not just a test, Trojan says to exercise the batteries for 3 cycles about every 4 - 6 months to keep them happy and folks are getting 8 - 10 years out of them.  NOW with your Lithiums, you must figure out how to discharge.  One way is to find some hair dryers, but they might overheat.  A normal (not heavy duty or contractors) 3/8 drill pulls about 800 watts.  You could run that drill for maybe 5 minutes (clamp or taped trigger)….then wait 5 minutes.  Repeat.  You want to get the batteries “under inverted load” voltage down to say 12.2 or so….measured at the batteries.  Note the remote voltage also.  
 

NOW….leave the load on the inverter.  Repeat your voltage tests (Ground to Chassis).  This will then tell you that there is no “high current” or load resistance. IF ZERO VOLTS….the cables are good.

Now…still under load….measure the Inverter cables.  Then measure the batteries.  You MIGHT have a drop on the Inverter.  Frank and I talked.  Your rig may have 30 -35 or so feet of cables (total of positive and negative).  Under load you can see the REAL voltage drop.  That voltage drop might be what you observed or your “correction factor”.  The reason it is different (0.15 - 0.40) is dependent on the load.  The higher the load, the more the difference.

I am on hold with Magnum…and I will report or give more information.  When Magnum told me that my 0.15 - 0.20 difference was normal…the did not go into too much detail.  The voltage that the remote is reporting is, most likely, a multiplexed voltage reading from the inverter’s terminals.  There is NOT a voltmeter in the remote.  If your batteries were cabled say less than 5 or 10 feet….odds are, under load or being recharged, there would be NO difference in what you read on the batteries compared to the meter.  THAT is what both of us concluded, independently, and what I tried to convey earlier.  But, when you have longer runs of cables, you DO get a voltage drop.  For example, using a reliable Voltage drop calculator….a CONTINUOUS run, no connections or going through the 400 (300?) Amp Fuse, here it the specs…for just 4/0 Stranded Cooper Cable.

12 VDC (can’t use decimals)   In 21.5 Ft……with 50 Amp (half the charging amps) or a 600 Watt Load….you will have a voltage drop of 0.12 VDC.  

13 VDC              In 23.t Ft … ….with 50 amps (charging load )….you will have a voltage drop of 0.13 VDC.  

OK…..based on the above…..and doing the math.  If you have around 34 feet (total negative and positive), then you will have a 0.19 VDC DROP.  

To preface another way….when you measure the voltage under load of 50 amps charging or 600 watts of load, you will have almost 0.2 VDC DROP in voltage from the batteries to the inverter.  That is NORMAL…..nothing is wrong.  

NOW, if you measure the voltage with NO LOAD or current draw, then the voltage drop would be far less, or at least I think it would.  Therefore, we need to know whether you are charging or inverting and the DC Amps.  We need the voltage at the Batteries.  We need the Voltage at the terminals on the Inverter.  We need the voltage reading on the remote.  ODDS ARE….whatever the voltage is on the Inverter terminals, that should be the voltage that the remote is displaying….

OK….after being #8 on hold, Magnum tech support confirmed that the Inverter terminal voltage is what is being displayed.  I went over the entire issue and what I have posted is correct.

BUT HIS CLOSING COMMENT.  The Remote is ONLY PLUS OR MINUS 5%…which is about 0.6 Volts.  He said to use a VOM and test under load, the cables. If the calculated voltage drop is what you are seeing between the batteries and the terminals…..then don’t get hung up on trying to compare that to the meter…due to the accuracy of +/- 5% (+/- 0.6vV) that they guarantee….

 

 

 

2 hours ago, 63Hotrod said:

At full charge indication on the remote zero amps 12.8 and the same at the battery. New style remote which I think shuts down charging once it reaches full charge   Will unplug leave the fridge on and see later. But I have seen at the meter a drop to 12.2 in a couple of hours
Ground runs from battery to junction block then one wire to frame Seeng .20 at battery and junction block

On start batteries zero ground voltage 

On inverter zero ground voltage

Ok now I am charging confused 

Can you be a bit more specific about the 0.2 VOLT and where you measured it??

[Ivylog]

It’s been 4 years since I ran a voltage drop test. Today I have battery voltage meters inside and 2 Lithium banks 20’ apart. The voltage difference between the 2 is higher than I’d like…0.3 at 50 amps. The readings below are at the batteries closest to the inverter. Unfortunately the inverter display is only in 1/10 of a amp. Charging Amps is 118 but only 55 into the first battery bank.

Amps.     Display.   Difference    Battery 

0 amps         12.9       0.2              13.08

-145.             11.5        0.8              12.33

+55               13.6        0.1              13.46

Going to run a longer test tonight and try finding the bad connections using a IR temp gun.

Edited April 19, 2023 by Ivylog

[63Hotrod]

Tom I miss spoke I followed it for 3 hr and there is only a .10 difference example 12.3 Vs 12.4  Sorry I miss spoke I changed to a more reliable meter my error

I was measure from the ground on the house battery to a solid chassis There I think I have a problem  When inverting it shows 2.5 every time I check it. Un bulk charge I see 7 .2 at the same place

 Is this a bad ground issue

[Tom Cherry]

1 hour ago, 63Hotrod said:

Tom I miss spoke I followed it for 3 hr and there is only a .10 difference example 12.3 Vs 12.4  Sorry I miss spoke I changed to a more reliable meter my error

I was measure from the ground on the house battery to a solid chassis There I think I have a problem  When inverting it shows 2.5 every time I check it. Un bulk charge I see 7 .2 at the same place

 Is this a bad ground issue

From the top.  I would not chase a ghost….so….do this.

Discharge (drain) your battle with 300 - 600 watt load.  See past post.  If no Load like that, then leave on all lights and fans and TV’s and HEC amps.  Run them down to 60% or so.  Take a 3/8 corded drill and tape the switch. let it run.  Measure the voltage on the House Bank and at the inverter.  If you have less than 0.3 - 0.4 VDC drop at inverter….all should be OK.

Next.  Plug in and start to recharge.  Same deal….except in reverse.  You should have a higher reading on inverter terminals,  again, less than 0.3 - 0.4….I’d not go any further.

If HIGHER, then while charging, you are going to have to start measuring VOLTAGE at every connection.  You have short leads, I think, going to terminals that go through the battery boxes. You can have a cable with a bad internal corrosion….that you can’t see. The only way to test is to use a big alligator clip on the stud or bolt…and attach a length of # 14/16 stranded copper and run to the other end of the cable.  Then you use an alligator clip to attach to a meter lead,  Then measure under the high current charging load.  If more than 0.1 VDC….the cable is bad and needs to be pulled and new terminals crimped on with a hydraulic crimper.  You MIGHT have to order the terminals from Amazon and take to a Welding supply shop.  Or, you can order a hydraulic crimper and then be equipped to do it yourself.

You have to test under load each cable or connection.  If you have a good cable….then move on.  

please explain….were you measuring Volts or ohms.  It has to be VOLTS.  Unless a cable is really flaky and you get lucky, voltage under load is best.  I would also, before my test on recharging or load drain, just clean the GROUNDS a on the ground studs.  I had a problem.  Genny wouldn’t start.  Jumper cable up to it.  NO ISSUES.  I kept playing around with the meter on ohms and found that when I closed the battery tray, sometimes Zero ohms….some not (to ground from negative).  Chassis was always negative.  I never opened the battery tray again until I got home….as it closed with zero ohms.  When I got home….cleaned and retightened….that was in 2015….nay a bobble in Genny starting for rest of trip or since then….some 20K and maybe 6 months on road.

[63Hotrod]

Tom it is volts I am testing. Going to clean the cable where it attaches at the frame. Really in Tuff place to get at. Then clean all connections at the junction block. Then run the test as described 

Question could I add an extra ground cable if there is room on the junction block stud. Any harm in that 

[Ivylog]

5 hours ago, Ivylog said:

Going to run a longer test tonight and try finding the bad connections using a IR temp gun.

Ran the microwave on the inverter for 5 minutes. Negative cable at the inverter went from 80* to 100*… 5 other connections had no change in temperature. Will try soldering the connection before cutting it off.

 

 

[63Hotrod]

Tom recheck this new meter the readings were Ohms not volts

This is clearly not my best area

Still planning to clean the chasis ground 

[Tom Cherry]

1 hour ago, 63Hotrod said:

Tom recheck this new meter the readings were Ohms not volts

This is clearly not my best area

Still planning to clean the chasis ground 

That was my thought.  But the real test is the load voltage.  So do that.

3 hours ago, 63Hotrod said:

Tom it is volts I am testing. Going to clean the cable where it attaches at the frame. Really in Tuff place to get at. Then clean all connections at the junction block. Then run the test as described 

Question could I add an extra ground cable if there is room on the junction block stud. Any harm in that 

NOPE….you only need one ground.  If a cable is bad, have the ends clipped and check the condition on the cable.  IF NO corrosion, then reterminate.  Cheaper and better.