How Do MH Engine Batteries Receive Their Charge?

[bburns8]

I have two 12v engine batteries on my diesel MH.  I understand the engine batteries receive a charge when driving, but I have a few questions.

1. Are the two 12v engine MH batteries receiving a charge when I am plugged into shore power?

2. Are the two 12v engine MH batteries receiving a charge when I run the generator?

3. Can the two 12v engine MH batteries receive an overcharge? If yes, what would cause this (a bad board, etc.)?

I appreciate any help/advise you may have. Thanks. 

 

2001 Fleetwood Discovery 37'
330 CAT HP, Freightliner XC

Edited December 2, 2017 by bburns8
Added make, model of RV

[rossboyer]

It depends. If we knew your make, model and year of your RV, more factual information could be provided. But you chassis batteries are charged while driving and usually the coach batteries are also. My motor home charges the chassis batteries until charged and switches to the coach batteries. When plugged in or on generator, the chassis batteries are charged and then switches to the coach batteries. The problem on my motor home is that as the chassis batteries discharge, the land line or generator charge does not switch back to the chassis batteries to top them off. There are devices to utilize a portion of the current used to charge the coach batteries to charge the chassis batteries. Your RV may not have one of those devices or it may automatically switch back to top off the chassis batteries. 

[wolfe10]

Yes, we need more information.  But answers to generator and shore power will be the same.

Let's do this-- have YOU tell us what is going on with your coach.

With digital voltmeter (start under $10):

With shore power off and generator off, check voltage at chassis and house banks.

Plug into shore power or start generator.

Check voltage at both banks again.

Post here.

And, unlikely it could be overcharged from shore/generator unless both banks are being overcharged, but your readings above will give us "bulk rate" voltage.

 

[bburns8]

19 hours ago, wolfe10 said:

Yes, we need more information.  But answers to generator and shore power will be the same.

Let's do this-- have YOU tell us what is going on with your coach.

With digital voltmeter (start under $10):

With shore power off and generator off, check voltage at chassis and house banks.

Plug into shore power or start generator.

Check voltage at both banks again.

Post here.

And, unlikely it could be overcharged from shore/generator unless both banks are being overcharged, but your readings above will give us "bulk rate" voltage.

 

My two engine batteries were just replaced.  The service repair man said that my engine batteries are getting a overcharge because my battery control circuit board is bad and needs replaced.  The service repair man turned my inverter/charger off so I checked the voltage at the chassis batteries and house banks both with my inverter/charger turned OFF and with it turned ON.

With SHORE POWER OFF and GENERATOR OFF (with inverter/charger OFF)
Voltage at chassis:  12v
Voltage at house banks: 12v

With SHORE POWER OFF and GENERATOR OFF (with inverter/charger turned ON)
Voltage at chassis: 11v
Voltage at house banks: 10v

Plugged into shore power with generator off (with inverter/charger OFF)
Voltage at chassis:  11v
Voltage at house banks:  11v

Plugged into shore power with generator off (with inverter/charger turned ON)
Voltage at chassis:  12v
Voltage at house banks:  12v

[wolfe10]

Every one of those readings means neither battery bank is receiving ANY charge from your inverter/charger. And, all are dangerously low.

What inverter/charger do you have.  On most, you can not turn off the charge circuit or the pass-through feature. Said another way, on most only ability to "invert" from battery is a normal on/off function. Without knowing what inverter/charger you have we are GUESSING.

The only other explanation I can think of is that when the smart inverter/charger sees 11 VDC, it (properly) says, that is a dead battery, I am not going to try to charge it.  This can be overcome by plugging in a "stupid"/old technology charger to get it up to 12 VDC or so to where the inverter/charger will take over.

[manholt]

Brett.  He could shut down both sides, via the CB?

[abyrd]

On my Magnum charger/inverter you can turn the charger and the inverter OFF you cannot turn the pass-through off.

It might be helpful if you could change the scale on your volt meter so you can read you volts with in 1/10 volt.

 

Jim

[bburns8]

2 hours ago, wolfe10 said:

Every one of those readings means neither battery bank is receiving ANY charge from your inverter/charger. And, all are dangerously low.

What inverter/charger do you have.  On most, you can not turn off the charge circuit or the pass-through feature. Said another way, on most only ability to "invert" from battery is a normal on/off function.

The only other explanation I can think of is that when the smart inverter/charger sees 11 VDC, it (properly) says, that is a dead battery, I am not going to try to charge it.  This can be overcome by plugging in a "stupid"/old technology charger to get it up to 12 VDC or so to where the inverter/charger will take over.

The inverter/charger on my MH is a Freedom 458 Series COMBI inverter/charger model 81-2022-12(214) dated 01/05/01.

[bburns8]

1 hour ago, abyrd said:

On my Magnum charger/inverter you can turn the charger and the inverter OFF you cannot turn the pass-through off.

It might be helpful if you could change the scale on your volt meter so you can read you volts with in 1/10 volt.

 

Jim

I will take a look at my volt meter.

[bburns8]

3 hours ago, wolfe10 said:

Every one of those readings means neither battery bank is receiving ANY charge from your inverter/charger. And, all are dangerously low.

What inverter/charger do you have.  On most, you can not turn off the charge circuit or the pass-through feature. Said another way, on most only ability to "invert" from battery is a normal on/off function.

The only other explanation I can think of is that when the smart inverter/charger sees 11 VDC, it (properly) says, that is a dead battery, I am not going to try to charge it.  This can be overcome by plugging in a "stupid"/old technology charger to get it up to 12 VDC or so to where the inverter/charger will take over.

Wolfe10 my digital volt meter is set in DC mode and I connected red lead to the positive terminal and the black lead to the negative terminal in series to get volt reading.

[wolfe10]

With the difference between a fully charged 12 volt battery and one that is 50% discharged being only about .6 VDC, you need at more accurate measurements-- that is the point being made here.

[bburns8]

1 hour ago, wolfe10 said:

With the difference between a fully charged 12 volt battery and one that is 50% discharged being only about .6 VDC, you need at more accurate measurements-- that is the point being made here.

My volt meter that I always used went out and this one I'm using was a gift.  It turns out that this voltmeter unit only outputs whole volts which is useless.  I will pick one up and redo the volt readings.  Thanks.

[manholt]

Jim, I also have that on both of my Magnum 2800's!

[wayne77590]

"With SHORE POWER OFF and GENERATOR OFF (with inverter/charger turned ON)
Voltage at chassis: 11v
Voltage at house banks: 10v

Plugged into shore power with generator off (with inverter/charger OFF)
Voltage at chassis:  11v
Voltage at house banks:  11v"

I have a problem understanding these two conditions. With both Shore and generator off there will be twiddle-winks for a charge. (Read that as zero amps/zero volts.) The reading is the condition of the batteries and they are "dead."

Plugged into shore power with the Gen of AND the inverter/charger OFF should also render no charge and the 11v is a seriaos condition for batteries.

Be curious to know what the voltages are when you get a voltmeter that reads the 10th's of a volt when plugged into shore power and inverter/chrarger turned on.

Questions: Do you have your battery disconnects turned on or off?  If off, turn them on and see if there is a difference in the reading with the new voltmeter.

[kaypsmith]

15 hours ago, bburns8 said:

My volt meter that I always used went out and this one I'm using was a gift.  It turns out that this voltmeter unit only outputs whole volts which is useless.  I will pick one up and redo the volt readings.  Thanks.

The giver must shop at one of those dollar stores where everything is $1.. I have used one in the past while in a bind for lack of my tool bag one that cost less than $6.00 that read in tenths. Hope you get this resolved soon, the repairman stated that the batteries were being overcharged, the alternator on the coach may have been charging in bulk mode to try to overcome the weak battery situation, or may mean that the voltage regulator on the coach system has gone bad, it may be built into the alternator or an external depending on make and model.

[bburns8]

18 hours ago, wolfe10 said:

With the difference between a fully charged 12 volt battery and one that is 50% discharged being only about .6 VDC, you need at more accurate measurements--

that is the point being made here.

Here is the voltage readings I am getting now.

Plugged into Shore power

Voltage at chassis batteries tested in series:  13.98v
Voltage at house banks batteries tested in series:   13.99v

Unplugged from Shore power

Voltage at chassis batteries tested in series:  12.93v
Voltage at house banks batteries tested in series:   12.02v

[manholt]

Without external power it should not drop 1A, unless the reading was done later.  With nothing on, you will get a parasitic drop from computer boards that you can't shut off.  13.9A on shore power is a little high, but good....what did you use to test the batteries with?  Was your charger/inverter on/off?

[bburns8]

2 minutes ago, manholt said:

Without external power it should not drop 1A, unless the reading was done later.  With nothing on, you will get a parasitic drop from computer boards that you can't shut off.  13.9A on shore power is a little high, but good....what did you use to test the batteries with?  Was your charger/inverter on/off?

When plugged into shore power, my two refrigerator and two TV's were turned on, laptop plugged in charging and bedroom lights turned on.

When unplugged the two TV's were off, laptop plugged not sure if it was charging and bedroom lights stayed on.

I used a multimeter by Klein Tools to test the batteries.

The charger/inverter was turned ON.

[abyrd]

Some what surprised to see the house battery voltage drop that much when disconnected shore power. 

I have some of the same questions that Carl had.

Was the inverter on?

How old are your house batteries?

How long was the shore power off before you took the battery voltage reading?

Jim

[abyrd]

Sorry for not seeing your response.  The load on the inverter when you interrupted you shore power explains for some of the voltage drop and we don't know the state of charge of the house battery when you started the test.

I have the same thoughts that Kay offered, if you chassis batteries are being overcharged I would check the charging circuit on you engine.

 

Jim

 

[bburns8]

4 minutes ago, abyrd said:

Some what surprised to see the house battery voltage drop that much when disconnected shore power. 

I have some of the same questions that Carl had.

Was the inverter on?

How old are your house batteries?

How long was the shore power off before you took the battery voltage reading?

Jim

Was the inverter on?  YES

How old are your house batteries?  4 MONTHS OLD.  THE DAY WE INSTALLED THE HOUSE BATTERIES WE ALSO TRAVELED THE SAME DAY.

How long was the shore power off before you took the battery voltage reading? 1 MINUTE

[wolfe10]

Clearly, the house batteries are either deeply discharged and need more time on the charger OR they are shot OR there was a very heavy load on them during the test (like inverter powering microwave for instance).

The "while plugged in" shows good bulk rate voltage.

12.02 if measured with batteries at rest is very close to completely discharged.

HOW LONG WAS IT ON SHORE POWER BEFORE YOU UNPLUGGED AND TESTED VOLTAGE?

[bburns8]

12 minutes ago, wolfe10 said:

Clearly, the house batteries are either deeply discharged and need more time on the charger OR they are shot OR there was a very heavy load on them during the test (like inverter powering microwave for instance).

The "while plugged in" shows good bulk rate voltage.

12.02 if measured with batteries at rest is very close to completely discharged.

HOW LONG WAS IT ON SHORE POWER BEFORE YOU UNPLUGGED AND TESTED VOLTAGE?

HOW LONG WAS IT ON SHORE POWER BEFORE YOU UNPLUGGED AND TESTED VOLTAGE?  We have been on shore power for 22 hours.

My MH has an inverter/charger.  Could the charger be bad?  If so, is there a way to test it?

Edited December 4, 2017 by bburns8
Added additional question.

[wolfe10]

You need to fully charge the house batteries and then have them LOAD TESTED.

So couple if indicators out of spec:

13.99 is just fine for bulk rate charging,  But, after 22 hours, you should be at float voltage which is 13.2- 13.5 VDC

Again, unless a significant load on the house battery (large appliance on inverter power comes to mind) that almost 2 VDC drop when disconnecting is a real issue.  When a battery bank is in good condition,  disconnecting shore power should show a pretty quick drop to around 12.8VDC, as voltage above that is just surface charge.  Then is should drop very slowly from there.

[bburns8]

12 minutes ago, wolfe10 said:

You need to fully charge the house batteries and then have them LOAD TESTED.

So couple if indicators out of spec:

13.99 is just fine for bulk rate charging,  But, after 22 hours, you should be at float voltage which is 13.2- 13.5 VDC

Again, unless a significant load on the house battery (large appliance on inverter power comes to mind) that almost 2 VDC drop when disconnecting is a real issue.  When a battery bank is in good condition,  disconnecting shore power should show a pretty quick drop to around 12.8VDC, as voltage above that is just surface charge.  Then is should drop very slowly from there.

Ok, when I disconnected from shore power and tested the voltage I did see 12.8v then started dropping then stopped at 12.02v

No appliances were on except the refrigerator was on AC.  Would the refrigerator cause the drop?