Chassis Batteries Problem

[Larry Azus]

Our RV had been in storage for four months. While in storage we had it plugged into a 50A circuit and charging. When we went to start the RV the chassis batteries were totally dead - however the house batteries were kept charged fine. At the time, we were able to start the RV by holding the Battery Boost - but several weeks later the chassis batteries were dead again after being plugged in for several weeks.

I had always assumed the shore power charging circuit would also keep the chassis batteries charged - but this did not appear to be the case. Should the charger also be charging the chassis batteries while connected to shore power? Not sure if this is a problem with the charging circuit and/or the house batteries. Any suggestions?

On another note - I could start the generator by holding the Battery Boost switch to bridge the house and chassis batteries. However, the generator would stall as soon as I released the boost switch. This happened for the first five minutes or so (I assume until the chasis batteries held some charge). Does the generator require some level of charge on the chassis batteries in order to run?

[David T. Richelderfer]

You should have a bi-directional electrical device between the chassis and house battery banks that allows a charging current to charge both battery banks.  The typical electrical devices are a BIRD System or an ECHO Charger.  Do you know which electrical device you have?

Basically, if your coach is plugged in, then the inverter will charge the house battery bank.  After it gets to 13+v, then the bi-directional device will allow the charging current to cross-over to the chassis battery bank.  Conversely, when traveling, the engine's alternator will charge the chassis battery bank.  After it gets to 13+v, then the bi-directional device will allow the charging current to cross-over to the house battery bank.  It sounds like your bi-directional electrical device isn't working properly.

[Larry Azus]

My unit appears to be the BIRD system. Would this be the Battery Isolator Relay that is suspect (https://www.amazon.com/Intellitec-77-90006-120-Battery-Isolator-Relay/dp/B077YR1W55)? I didn't get a chance to make any measurements yet - I'll head over there tomorrow with a meter. What are some good checks to confirm the defective component (and not battery problem)?

Looks relatively easy to replace - anything to be wary of (obviously after disconnecting all power)?

[Joel Ashley]

Larry, at 13.4v your Bidirectional Isolator Relay Delay (BIRD) switches charging to the other battery bank.  When on the road, it switches from an alternator-charged chassis bank to begin charging the house bank, and when plugged in it switches from an inverter-charged or generator-charged house bank to begin charging the chassis side.

The BIRD has been known to fail from corroded or loose high resistance connections.  But as reported on this Forum recently, the Big Boy solenoid that does the actual circuit switching can fail from corroded internal contacts.  When on the road have you noticed whether or not your house batteries arrive fully charged?  If not, the Big Boy is suspect.  It could also be your Magnum inverter’s charger has failed, but not likely since your house set is getting charged when plugged in... and over time it goes from Bulk Charge to Absorb to Float Charge, right?

Use a voltmeter to see if when plugged in to 110v power and the remote reads Float Charge (at least 13.4 volts on the screen) that both large wire lugs on either side of the Big Boy indicate identical voltage readings.  Over your battery tray and between the chassis and coach Main Switches is a gray door behind which are both above mentioned devices, large-amp 12v fuses, and other components.  The Big Boy is front and center.  The BIRD is mounted on the inside of the door.

Others here have disassembled, cleaned, and reassembled their Big Boy.  Search the Forum.

I’ll leave generator commentary to others more familiar with that circuitry, except to say the genset may rely on fully charged chassis bats to stay running, and they aren’t at that point except via the alternator.  With a working BIRD/Big Boy, the genset would eventually go from charging the house set to doing the chassis set, thereby then supporting the generator.

Joel

[Larry Azus]

Now that you mention it, I do recall a few times that the house batteries were not charging while on the road. However after tapping the Battery Boost switch once or twice they would start charging. This sure sounds like the problem you describe.

I'll head over to take the measurements on the Big Boy tomorrow. How to best isolate the problem to the Big Boy or the BIRD? Can I clean the internal contacts or would it need to be replaced?

[Joel Ashley]

Search the Forum here for “Big Boy” and reference useful info.  I couldn’t find the photos I’d seen re. cleaning the device, but you may find something on YouTube, if Bill Lampkin or others don’t chime in here to assist.  I think Mike Schumack recently did something with his.

Joel

[Steve Huber Co-Admin]

Larry,
If you don't have approx. equal voltages on the 2 large terminals of the Big Boy (assuming one of the battery banks is at ~13v), check the "solenoid" output voltage at the BIRD. It should be about 3v or so if the BIRD is working. Dis-assembling the Big Boy is fairly easy. Clean up any corrosion and re-assemble. Be sure to inspect the 'O' ring. If you've got corrosion it is probably because the 'O' ring is allowing moisture in. Hitting the Boost Switch causes the big Boy to close, so sometimes that can get it working for a while if you are in a pinch. After hitting the boost switch a few times, check voltages on the large terminal of the Big Boy.
Steve

[Gerald Farris]

Larry,
There is nothing wrong with your generator. It requires at least a partially charged chassis battery for it to operate, and since your chassis batteries were dead, the only way it could operate is for you to hold down it boost switch so that it could run off of the fully charged house batteries. You just need to repair your "BIRD" system and everything will be OK if you have not damaged your chassis batteries by excessively discharging them.

Gerald   

[Larry Azus]

Quick Update: I went to the RV today and made the suggested voltage measurements at the batteries and Big Boy terminals. While plugged in the house batteries had a float charge of >13.4 volts, but the solenoid output terminal on the Big Boy (as well as chassis batteries) were reading low <8 volts. This seemed to confirm that the Big Boy was not operating.

I removed the Big Boy, took it apart and cleaned and burnished all of the internal contacts and reinstalled. After a few minutes, I heard the Big Boy energize and then started charging the chassis batteries. Hopefully the batteries will recover.

I greatly appreciate everyone's help on this (David, Joel, Steve and Gerald) - Many thanks!

[Joel Ashley]

I’m glad it worked out, Larry, and we appreciate your reporting back affirming our suspicions.

Check the chassis set regularly now, especially after drycamps or storage.  Unlike deep cycle house batteries, they don’t like being discharged even once.  And after dry camping, charge things up using the generator before hitting the highway;  it’ll save overheated alternator issues down the road.

Joel

[rick Kirchner]

I had battery issues for years.  Basically, with house-battery priority using an echo charger, once those things get a tad weak nothing ever goes to the chassis batteries, and the parasitic draw of the drivetrain computers eventually drains the start batteries to the basement.  Since the house batteries are deep cycle and the chassis are not, the house batteries are much more likely to recover from a discharge.

I re-engineered my system to be chassis-battery priority with an amp-l-start in place of the echo charger and an alternator designed to be used with a solid state isolator.  Haven't had an issue since. 

[Fred Cook]

I have been following this thread so I decided to do a voltage test.  My house batteries read 15.43 volts and my chassis batteries read 14.43 volts. The coach is plugged in to 50 amp service at my home.  Are these readings OK?

[David T. Richelderfer]

Turn off or unplug the shore power, give it 10 or 15 minutes, and re-test the batteries.

[Fred Cook]

Turn off or unplug the shore power, give it 10 or 15 minutes, and re-test the batteries.

Ok, just did that.  Reading on house batteries dropped to 12.67 volts and the chassis down to 12.49 volts.  After turning shore power back on house batteries went up to 14.45 volts and the chassis stayed the same at 12.49 volts.  Does this seem ok?

[rick Kirchner]

It probably means the follower charger is not passing anything to the chases batteries yet.  Prior to your test, the house batteries were high enough for the follower charger to kick in.  It will probably take a little while for the house batteries to reach the cutover point again.