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SWharton

Still having b attery problems

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We have installed 4 new AGM batteries for 420 amp hours. We have set our Magum ARC for 400 hours. We have a steady overnight draw of 2 amps according to the ARC which best I can tell is normal for the MS 2000 inverter.

We start overnight with “full” batteries 13.2. We have turned off the residential refrigerator. In the morning our batteries are down to 12.3-12.5. We just can’t figure out what is going on overnight. We are thinking of turning off the inverter for one night and seeing what the numbers are.

Temperature outside is down to the 30s in the AM.

Anyone have any ideas…………...

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Assuming the 13.2 volts is the reading when you stop charging (turn of generator or solar or ???) that is the voltage the charge source was trying to charge to.  The battery will drop to 12.6 - 12.7 within minutes of stopping the charge - this is the fully charged level of a battery after the surface charge has dissipated. 

To accurately measure the voltage you would have to disconnect the batteries and take a reading AFTER they have had a small load (light bulb?) on them for a few minutes to dissipate the surface charge.  Not a very practical solution.

Also, when your invertor is ON it will cause the voltage to read lower than it truly is.  Again, disconnecting them will show correct voltage.  I typically see voltage reading in the 12.3 range when my batteries are still at 90% simply because there is a load on them.

If your static draw is only two amps your maximum drain overnight (10 hours??) would only be 20 amphours or 5% of the total capacity.  Again, the 12.3 to 12.5 your seeing in the morning may well be 95% full reading depending on the load at the moment.

Best solution is to install a battery monitor that will monitor amps in and amps out and tell you the state of charge.  Relying on the voltage is not an accurate method.

Lenp

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We have a battery monitor Magnum-ARC and the BMK. We were happy to see the SOC but it just doesn't seem to be correct, to the point we don't trust it. Next week, when we are not traveling we will be able to better determine the numbers without as many variables(unless the grandkids mess all that up). We want to better understand all this(first Mh and generator, had 5th before) and determine if something is mis-wired or if everything is correct.

All of you, as usual, have given us ideas.

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A full battery is about 12.6V after dissipating the surface charge.

12.5V at the end of the night would not overly concern me, but 12.3V would, assuming your starting voltage was truly 12.6V after dissipating the surface charge.

Also be sure the monitor is showing 100% charged and the AH reading is zero so you have a known starting point to document your nightly discharge. 

Since it was cold, were you running your furnace?  It pulls lots of current when the fan is running. 

One more thing to check if you haven't.  Look at your battery bank, the negative post.  Is there only ONE cable attached to the negative post and that lead goes directly to the shunt for the monitor?  Also on the other negative battery posts the only cables there must only be going to other battery posts.   On my 2003 DP we had, the factory had a second cable on my bank of 4 batteries going to frame ground.  I didn't think much about it when I installed my Trimetric monitor.  But I discovered, after feeling the batteries were being discharged quicker than I thought they should be, that there was load in the MH which had its negative connection going to the frame and not a negative return wire.  The mfg saved a few dollars by not running a negative return cable. 

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We may have a delay in testing all this. Ttemps in Phoenix, our winter home, are still fairly high. Need to wait for the weather to cool down a bit.

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A minor load of 10amps on a 400AH battery pack should not drop the battery voltage more than a half (0.5) amp if that much, if the batteries are in good condition.  You have new batteries so you should not see a 1V or 2V voltage drop with that low of a load. 

Turn on the microwave to heat some water and you can expect to see the voltage drop 2-3volts when you see a 100 to 130 amp load in the battery monitor. 

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4 minutes ago, SWharton said:

We may have a delay in testing all this. Ttemps in Phoenix, our winter home, are still fairly high. Need to wait for the weather to cool down a bit.

A little to warm to turn off the A/C so you can disconnect from shore power for several hours?  :D

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2 minutes ago, SWharton said:

Need to wait for the weather to cool down a bit.

If you visit this link, there are charts for a wide range of ambient temperatures that list batteries from Exide at full charge and other levels of charge. It has both voltages and specific gravities. Specific gravity is a far more accurate method of evaluating charge levels. 

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Temps in Phoenix right now are in the mid 90s during the afternoon. Temps are suppose to be in the 80s next week and we have time available. We only have one thing scheduled for next week so we think we can work on the electrical then.

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I am copying my reply from your other posting about your battery charging problems, so that information can be consolidated in one place.

Quote
 
On 10/24/2017 at 6:53 AM, SWharton said:

We are unhappy with how long it takes to charge our batteries when boondocking. We have a Magnum MS2000 and an Onan Gold 5000w generator. When we run the generator can I add an additional battery charger to speed up the charging? Any special charger needed?

 

The Magnum MS2000 IS a 3 stage (actually 4 stage if you count the equalize stage) charger.  The charger is also rated at 100amps.  If memory serves me correctly you have about 400AH of battery.   Also you have AGM batteries.  You don't want to charge the batteries at more than a 100amp rate. So you don't want a second charger, unless it is solar.

About the charging time.  Some actual numbers from your process would give us something to work with.

I have a MS2000 inverter, although the vast majority of my charging comes from 650 watts of solar.

In general, these are some rough numbers from memory (all assuming 400AH of battery):

--  If you have discharged 25% you are down about 100AH

--  At that amount of discharge level the inverter will probably start charging at around 50-70amps.  After about 10-15 minutes of charging the amps will drop 10 or more amps.

--  At the end of an hour the charging amps will be quite a bit lower, maybe 20amps

--  At the end of 1.5 to 2 hours you will probably be at somewhere around 90% full, give or take 4-6%. and your charge amps will be down to less than 10, probably 6 ams.

--  To get to 100% full you will need to run the generator for 4-8 hours.

It would really help if you replicated my above description and provided your actual numbers taken from your battery monitor.  Be sure to start at batteries 100% full and the monitor AH reading at "zero".  Then let the batteries discharge 25-30% (70-75% full)

Once you start charging be sure to record from the battery monitor about every 10 minutes, the  % charged, battery voltage, AH's, amps going into the batteries.  Also, very important, before you start charging record the battery voltage.  When you record the voltage be sure to check the amps on the monitor to be sure you are discharging less than 2-4 amps.

I have more details to add later.  I have an appointment to go to. 

NOTE to others, SWarton has a residential fridge which puts a significant power usage over 12-24 hours on the batteries. He also has about 400AH of AGM batteries. 

To summarize my recommendations for testing:

--  Have your batteries at 100% charged.  Being on shore power for 24 hours or more is good.

--  Dissipate the surface charge and be sure your voltage is reading about 12.6V.  Use the voltage info supplied by others for a reference.  If the batteries are not at 12.6V, say maybe 12.5V or lower something is not right and start your troubleshooting from there.  You could have a single cell in one battery causing a problem.  I believe you have AGM batteries so you can not check the specific gravity reading, which is much better than trying to go by voltage.

-- On your battery monitor be sure the AH reading is reset so it is reading at or close to zero.  This will give you an exact reading of the number of AH's you have used.

--  Unplug from shore power and use 100 to 150AH's of your capacity.  Monitor and write down the following every 15  minutes as the batteries are being discharged. 

  • AH reading
  • Number of amps being discharged each time you take the readings
  • Voltage reading
  • % of battery capacity (State of Charge SOC)

Once you get down to the 100-150AH's used (or a SOC of 60-75%) start up your generator and run it for about 2 hours.

Now that you are charging your batteries document the readings, like you did while discharging.

Some additional information, which will be very helpful to you, is to document how many amps your fridge is using at different operating conditions.  These reading will give you an excellent idea of just how much power the fridge is using

--  unplug the fridge or turn off the CB feeding the fridge and document the amp reading on the monitor.  This is your background or phantom power usage.  All these reading will be the DC amps being used through the inverter.

--  Listen or feel for the compressor running and document the number of amps.

--  When the compressor is off document the amp draw.

--  This is harder to do, but it would be interesting to know what the amp draw is when the fridge is in a defrost cycle.  Kind of hard to determine when the fridge is in the defrost cycle though. 

A thought, is there an energy saver switch or setting on the fridge?  Some fridges have a heater wire going around the door seals to keep condensation from building up on the surface around the seals.  I would assume it pulls quiet a bit of power.

Bottom line here is: With 400Ah of battery you should be able to boondock with the residential fridge.  It does take some work to monitor your usage and to know how long you need to run the generator to recharge your batteries. 

 

 

Edited by Al F

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For what it's worth....

I have three 150 amphour Trojan 12 volt batteries (450 AH total), 750 watts of solar, Bogart Pentametric battery monitor,  residential Samsung RF197, AND a small 5 Cu Ft 120 VAC freezer. 

When camped in the Adirondacks in September (lots of trees so little solar) I would run the generator for about 90 minutes in the morning with initial charge rate of 90-100 amps.  It would taper off to around 20 toward the end of the 90 minutes.  Solar would (usually) finish the batteries to 100% but mid afternoon.

By dinner time the batteries had usually dropped to 90-92% (again, lots of shade) so generator ran another hour or so while fixing dinner.

By morning my batteries would be down to around 70% per the battery monitor. 

The battery voltage was a different story - with the "load" still applied they read in the 11.6 to 12.2 range.  CONCLUSION:  when there is a load applied you CANNOT go by voltage alone!

Lenp

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On 10/25/2017 at 7:51 AM, Kirk Wood said:

If you visit this link, there are charts for a wide range of ambient temperatures that list batteries from Exide at full charge and other levels of charge. It has both voltages and specific gravities. Specific gravity is a far more accurate method of evaluating charge levels. 

But impossible to do with AGMs.

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On 10/28/2017 at 7:34 PM, SWharton said:

I think this is part of our problem. We don't know what numbers to trust. SOC? Voltage?

Trust the SOC, but also monitor the "total AH" reading on the monitor.   The AH reading should match the SOC percentage.  That is a minus 100AH would result in SOC of 75%.  Voltage is always a guesstimate.  Some what accurate if you always remove all load and wait for some time for the battery voltage to stabilize.  But still the AH reading is the most accurate.

However somewhere you need to start with the batteries at 100% charged.

Edited by Al F

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Thanks Al. We are moving forward on this. Hope to get our research done this week. Odds and ends keep interfering(called Grandkids and doctor appts).

 

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The voltage or SOC question..... here again is the best argument for a battery monitor system from Bogart.  You set the "charged" criteria by entering a voltage and current combination that defines fully charged status.  While this may not be exactly equal to a specific gravity 100% reading, it sets a benchmark for your system and everything is them relative to that point.  I think mine is set for voltage >14.3 and current less than 9 amps.  Essentially these numbers reflect the point at which the batteries just don't want to take any more juice.  

The Pentametric system lets you enter other criteria such as battery efficiency and as you charge and discharge your batteries it will measure their efficiency for you (so you can re-enter their actual efficiency measured over multiple charge/discharge cycles).

It constantly measures the amperage going through the shunt (charge and discharge) so you always have an accurate SOC reading.

I have had my system for five years now and would never have another RV without something similar.  

 

Lenp

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 I would suggest that you test every single connection in the system.

 

 Now before you do anything you need to test every connection with a volt meter. Starting at the battery stud ,. +.  and  negative. Keep the negative test lead on the negative stud. Check both sides of every connection on the positive side of the system. As in same voltage on both sides of the connection. Then do the negative side as well.

 Then before you do any physical work. Use a DC ampmeter to see that all batteries are getting charged. And how many amps to each battery is receiving .

 

 Then separate each battery from the system and load test it.

 

 Then test the whole system charge amps and volts along with discharge amps and volts.

 I would even have a 110 volt meter on the supply voltage going to the charger while you are doing this work.

 Use a separate volt/amp meter than what you are using now.

 That should give us better info on what is going on.

 

 Safe Travels,.   Vern

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Al,

We started checking out our wiring today and found 2 ground wires connected to the batteries. I disconnected the one that was a ground to frame and a lot of the MH went dead which shows a phantom load. You mentioned your DRV had this, how did you resolve it? or did you not resolve it?

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21 hours ago, SWharton said:

Al,

We started checking out our wiring today and found 2 ground wires connected to the batteries. I disconnected the one that was a ground to frame and a lot of the MH went dead which shows a phantom load. You mentioned your DRV had this, how did you resolve it? or did you not resolve it?

I moved everything that went to the negative posts on the batteries to the house side of the shunt.  In the end you should only have one cable attached to the negative post of your battery bank, and that cable goes to the shunt.  

Any other cable on any other negative post on your batteries should only go to another post on the battery bank.  If you have batteries wired in series, some of the negative posts will go to a positive post on another battery.  However only one negative post on the bank should go to the shunt.

wiring1.gif

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