How Do MH Engine Batteries Receive Their Charge?

[wolfe10]

Assuming you have an RV absorption refrigerator, probably not for two reasons:

In most coaches, the 120 VAC plug for the refrigerator is NOT fed by the inverter.  Easy to tell-- with the refrigerator on automatic, unplug.  It should switch to gas (propane).  If so, the load due to the refrigerator is very small and would not significantly drop house bank voltage.

Even if the inverter was supplying the refrigerator heating element, it is not a huge draw.

But, let us know whether your inverter does power the refrigerator outlet.

[manholt]

BB.  I have a 23cu. ft. Whirlpool and it will draw 6.5 A at start, then drop to .6A.  AC units spike when first starting. AC heat pump or strip, same spike...However the only one I can run on Inverter is fridge, some 120V lights, 12V, and computers.  I have run also my microwave on inverter...I have 8 AGM 6V house batteries.

[bburns8]

When I disconnected from shore power and tested the voltage on the house banks I did see 12.8v then started dropping and stopped at 12.02v.  Just confirming this is not normal correct?

 

[wolfe10]

14 minutes ago, bburns8 said:

When I disconnected from shore power and tested the voltage on the house banks I did see 12.8v then started dropping and stopped at 12.02v.  Just confirming this is not normal correct?

 

Depends on how fast this occurred and with what load on.  But, unless very heavy load and/or long time with moderate load, no that is not normal.

Again, suggest fully charging and taking to a battery shop where they can be load tested.

Certainly age is related to battery condition/life, but very deeply discharging them materially shortens their life.

[kaypsmith]

If there was nothing pulling any power from the house batteries, the drop should be almost none. But you must factor in any posiblity of a parasitic drain. Best way to test is use the disconnect switch after a full charge. Then you can watch for the drop, as stated earlier by others, 13.2 to 13.5 should be available on both banks immediately after unplugging. If the drop happens within 30 minute to close to 12 volts, then that could be the sign of a bad battery in the bank, that's why a good current test device needs to happen right after the batteries have been completely charged.

[bburns8]

Ok, I will get them charged and load tested and go from there.

Could the charger on my Inverter/Charger be bad and not charging the house batteries?  Is there a way to test the charger?

 

[wolfe10]

With a reading of 13.9, your inverter/charger is working.

[kaypsmith]

Your inverter/charger is working as Brett just said, if you have a bad cell in any one of your batteries, the charger may be overcharging because of this condition, ie. staying in bulk mode because of the bad or weaker battery. 

[bburns8]

I have not taken the house batteries to have them load tested yet.

I tested the chassis and house batteries with the volt meter again this morning.  This time I had everything in the MH turned off and unplugged.  Only appliance turned on was the refrigerator in AC mode.
 

Here is the voltage readings I am getting now.

Plugged into Shore power

Voltage at chassis batteries tested in series:  14.01v
Voltage at house banks batteries tested in series:   14.00v

Unplugged from Shore power

Voltage at chassis batteries tested in series:  12.82v
Voltage at house banks batteries tested in series:   12.04v

 

QUESTION:  Is the voltage reading for the chassis batteries normal?

That is a big drop in voltage on the chassis batteries from plugged in vs unplugged.  The chassis batteries are brand new and installed last week.

[wolfe10]

12.82 is a fully charged 12 volt battery AT REST (no charging and no discharge). Anything above that is surface charge and is quickly dissipated.

 

It is the drop to 14.0 to 12.04 that causes all of us to suspect a house bank major issue.

[bburns8]

1 hour ago, wolfe10 said:

12.82 is a fully charged 12 volt battery AT REST (no charging and no discharge). Anything above that is surface charge and is quickly dissipated.

 

It is the drop to 14.0 to 12.04 that causes all of us to suspect a house bank major issue.

Thanks wolfe10.

[bburns8]

I tested the volts on the house batteries individually (disconnected) and two of the batteries read 6.39v, one reads 6.38v and one read 6.40v.

QUESTION:  My understanding is a 6-volt battery that is charged should read 6.25 to 6.37.  So wouldn't this indicate the house batteries are ok?

[wolfe10]

6.40 VDC plus 6.38 VDC (two six volt batteries wired in series)= 12.78.  That is just fine, but a LONG way from the 12.04 posted above.

Double check that the connections are clean and tight.

[bburns8]

Ok, I checked the connections. 

I'm unplugged from Shore Power.
I checked two house batteries in series and I'm now getting 12.41 VDC

I checked the other two house batteries in series and I'm getting 12.38 VDC

Everything is turned off/unplugged in MH accept refrigerator in AC mode.

 

[wolfe10]

Both those readings are a lot better than the 12.04, but show they are still not up to full charge.

Interesting that individually they test at 6.40 VDC plus 6.38 VDC (two six volt batteries wired in series)= 12.78  yet connected they show 12.41??

That is why I asked about the connections.

[bburns8]

QUESTION: 

Can the battery cables be bad and need to be replaced?

I had the inverter is turned on with a steady light and the charger is turned on with blinking green light.  Does having the inverter/charger turned on make a difference in the VDC reading.

[wolfe10]

If the charger section of the inverter/charger is on, absolutely, voltage will be higher. If just plugged in, the inverter/charger will be in BULK MODE and around 14 VDC. After batteries fully charged voltage in FLOAT MODE will be in the 13.2-13.5 range.

Sure, battery cables can be bad-- have seen some of them turn to copper oxide (green powder)!

[bburns8]

Ok, if it's not the battery cables what else could cause the low VDC reading I'm getting?

[dickandlois]

4 hours ago, bburns8 said:

Ok, if it's not the battery cables what else could cause the low VDC reading I'm getting?

There are a number of items.

Corrosion build up at the connections. This is caused by the off gassing of the acid and water through  evaporation. Coating the connections with terminal grease or oil protects the materials from the acid that is off gassed.

Wrong charging  current and or voltage level.

This process over time decreases the percentage of acid to water, but by that time if the batteries are charged properly, there internal materials totally brake down. Known as wet Cells.

 Use only distilled water to replenish the lost water.

Charging AGM,  Gel,  or lithium based batters with the wrong voltages or current rate will shorten there life time.  Referred to as dry cells. 

Should the water level get low(exposing the  internal structure to the air) the plates will shed material that drops to the bottom of the case and builds up shorting out one or more of the cells.

Hope this helps.

Rich.

[kaypsmith]

Staying above 12 volts in most cases kindly eliminates a bad cell in one of the batteries, but a bad cable or corrosion on the terminal end (or ends) can cause the lower voltage or even a poor ground to the frame (chassis) can cause a lower voltage. The cable that crosses from positive to negative could be either corroded or even too small to properly carry current from battery to battery. There are many scenarios that may or may not be a factor. You stated that you checked the battery terminals and the reading went from 12.04 to 12.41 on that bank, so there is progress there, maybe recharge then recheck, if no better, then look for more terminal corrosion, and check the copper wires right where the terminals are connected for that green colored corrosion, if this has occurred, then the cable needs to be replaced.

[bburns8]

Thanks for the info.  I do have some green colored corrosion.

Would a bad battery control circuit board cause house batteries to not charge?

[wolfe10]

Shiny copper is an excellent conductor. Dull copper is an OK conductor.  Green (copper oxide) is NOT! If you even suspect a bad cable, ohm it or just replace it.  VERY cheap compared with ruining batteries.

Because you do see correct charge voltage at the batteries, I would not suspect a battery control circuit board. 14 VDC is what you said you saw (yesterday 1:07 CST) when plugging in (both battery banks).  That is perfect bulk rate voltage.

[bburns8]

I am going to replace my battery cables on my 4 house batteries, 6v deep cycle.  What size cable should I use?  What is proper gauge in wiring these in series?  Is 2 or 4 gauge OK for house batteries?

[wolfe10]

Wire gauge for interconnects should be the same as the primary cables.

What size are they now?  Remember, an inverter can put a huge load on the batteries/cables.

[bburns8]

I have no idea.  The only information I can find on the cables is Essex 1/0GASEJ1127TYPESGT105C.

Doing a little research online it's a 1/0 wire size so I'll probably stay with that or go to a 2/0.