Chassis Batteries Discharging

[Edward Buker]

Rod,

I'm not sure which charging system you have for the chassis batteries that usually utilizes the main charging system in some manner. If it is a 10 amp output Echo Charger it will take a long time, probably several days. I do not know for your coach year and model if you have the ECU load issue or some other load causing your batteries to discharge. Usually the main charging system charges just the house bank. If you do not have a maintenance charger or a small coupling charger you can take a set of jumper cables and connect the positive post from the house bank that has the main wiring lead on it that powers the coach and connect the other lead to the main positive post of the chassis bank. If you have any doubts check with a voltmeter that you have +11 to 13.8V on the connection points before you connect them just to be sure that you are not connecting to a 6V post in the house bank or a ground post. That should charge the chassis bank in just a couple of hours. The grounds of the two banks are in common so you just need to use a positive jumper cable.

The battery switch will solve your problem but if there are several leads that head out into the coach wiring going to the chassis battery positive post you will need to sort out which lead has the load on it that is causing the discharge before you add the switch. If there is just one positive wire on the battery post then this is easier. If more then one lead you will need to get hold of a DC current meter that will measure up to 10 amps and put it in series with each lead and record the loads with everything in the coach chassis wise that uses 12v in the off position (like head lights etc.) You would add the switch into the wiring that is connecting the load. Hope this helps.

Later Ed

[Mike Groves]

1996 36' Beaver Monterey. First, this is a recently purchased motorhome. It is not plugged into a 110 source. After 3-4 days, the chassis batteries are at about 10-11. I have had the batteries checked and they are not the problem. (1) If I plug into a 110 source, how long would or should it take to charge up the batteries enough to start the engine?  (2) For my year and model, should I put a diesel battery kill switch in the battery compartment as discussed previously? (3) Will the battery kill switch eliminate any and all the drain on the chassis batteries?

Rod,

Based on my experience with my pre-2000 Beaver, the reason your battery ran down was because the ECM does draw from the battery IF THE BATTERY DISCONNECT switch is not set to disconnect.  So, as stated, your issue is the same as most SMC owners experience and the issue has been typically the parasitic drain on the battery cause by the ECM.  It should take no more than a couple hours with a charger to charge the battery back up (with high charge).  That being said, I think in all RVs typically you want to disconnect your battery(ies) from the rest of the coach while charging so as not to cause an issue with the coach's normal charging features.  When mine ran down after a couple days of sitting the first time I experienced this issue, that's what I did.

In the future, when you know the coach will be sitting, with no shore power, my recommendation is that you do as I do now, and use the battery disconnect switch to turn off that battery connection.  In my coach that has been sufficient to prevent the batteries from discharging to a worthless condition.  As previously stated in this thread, even after 6 weeks of this condition, my chassis batteries are still at 11.7V as indicated on the silverleaf computer in my coach.

Of course, if you model beaver has no battery disconnect, then certainly you might add one even a simple one.

Just my opinion.

Mike

[Edward Buker]

Mike and Rod,

There is no need to disconnect anything from the coach when you are charging, there are no interference issues.

Mike, the only way you will ever know if shutting off your battery disconnect eliminates the ECU load is to actually measure it with a current meter with the switch in the on position and then again in the off position as I have mentioned before. You should also check for a smaller lead coming off of the starter solenoid post on the starter that has the large lead coming from the battery as a clue to see if a possible ECU wire is connected as Gerald eluded to.

 Until you do that, telling others that just turning off the switch fixes the problem is misinformation. The fact that your battery voltage decays to 11.7V, which is basically dead leads me to believe that you have the ECU load issue like others, and if not the ECU, then some other load with the switch off. I'm not trying to be difficult here, it is just that you have to take current measurements to know the loads and what is happening before you can say that turning off the switch disconnects the ECU load. Hope this helps.

Later Ed

[Mike Groves]

Mike, the only way you will ever know if shutting off your battery disconnect eliminates the ECU load is to actually measure it with a current meter with the switch in the on position and then again in the off position as I have mentioned before. You should also check for a smaller lead coming off of the starter solenoid post on the starter that has the large lead coming from the battery as a clue to see if a possible ECU wire is connected as Gerald eluded to.

Until you do that, telling others that just turning off the switch fixes the problem is misinformation. The fact that your battery voltage decays to 11.7V, which is basically dead leads me to believe that you have the ECU load issue like others, and if not the ECU, then some other load with the switch off. I'm not trying to be difficult here, it is just that you have to take current measurements to know the loads and what is happening before you can say that turning off the switch disconnects the ECU load. Hope this helps.

Ed,

And I'll politely disagree in that I've had the coach unplugged from electrical power now for 6 weeks at a time, as I've said previously.  If I had a parasitic drain from ANYTHING drawing 2 amps continuously I would have had a battery discharged way, way, way below 11.7V.

So, all I am saying, politely, is that until others with SMC era coaches actually test theirs to see if their battery disconnects actually do (as mine does) disconnect the battery from this mysterious ECM, I believe you are misinforming other owners by giving solutions to problems that may not even be problems.  I was certainly misled and have been up until very recently when I found that my coach doesn't have this issue.

Why on earth would I put a meter on my battery to measure anything when I don't perceive a problem at all? Or crawl under the coach to find the starter solenoid? 11.7V may merely indicate that my batteries were not fully charged with I left the coach, who knows?

Ed, since you're an electrical engineer by trade, let's assume when I left the coach at T0, it was at 12V.  What would the current draw be if T1 is 6 weeks later and its at 11.7V.  That simple, I guess, calculation, would save me the trouble of attaching a meter to my battery.  But as I've said in the past, it always shows about 11.7V (its never shown lower) even when looked at after 2 weeks, or 3 weeks, or a month.  So I think its certain that for my specific 1999 there's not this ECM issue.  And that's all that I am saying.  I am not, as you and others are saying that one size fits all.  I am merely giving evidence to what is actually a fact for my 1999 Beaver Marquis. 

Others can try the battery disconnect as I did and see for themselves.  Mine works so I'll continue to add my 2 cents worth and suggest that other owners charge their battery and use the disconnect when parking more than a couple of days, and if that still drains the battery they can then look further to find out what the issue is.  That's pretty simple advice I think.  I am never giving misinformation to anyone, I am merely sharing my experience as I hope everyone here is. 

I must admit I was a bit disappointed by your detailed solution of rewiring the ECM circuit when you admitted you've not actually done it.

Thanks,
Mike

[Edward Buker]

Mike,

If you go to page 5 in this reference you will see that at 11.7V a lead acid battery is 100% discharged. It will not give up any significant current at that voltage level so I am not sure how rapidly the voltage continues to drop at that point but I know it will continue to drop. The next thing, the only way to know the true voltage state of the battery is to get a meter out and measure it at the posts, not the Silverleaf, given we do not know exactly where the voltage is being sensed by the Silverleaf.

http://ecee.colorado.edu/~ecen2060/materials/lecture_notes/Battery2.pdf

I believe you have a pair of group 31 batteries in parallel and if you look at this Trojan reference at 2 amps a single group 31 would have discharged in 3000 minutes, so say 6000 minutes for two in parallel as a reasonable approximation. That is 4 days. So if you are truly at 11.7V in 4 days at the battery posts that would represent about a 2 amp load. You do not know without measurements what kind of current load you have and where it is going which is the whole point.

 http://www.trojanbattery.com/pdf/datasheets/31AGM_Trojan_Data_Sheets.pdf

I will try this one last time, the reason you would put a meter on the battery is to measure the voltage, or in series with a positive lead is to read the current so that you actually know what is happening load wise on your coach. You have made a bad assumption that you do not have a problem because your batteries only get down to 11.7V. That voltage represents complete discharge and the current is going somewhere with the chassis switch off. The idea that your batteries are at 11.7V because they were not fully charged to begin with is out of the range of partially charged batteries, more like 12.4V might be a rational expectation representing a 75% charge level, 12.2V is 50%.

Mike the whole issue is you do not perceive that you have a problem and my point is that if you did not have a load, ECU or otherwise, you would be able to measure the voltage at the battery and it would stay in the 12.5 or 12.6 V range for several weeks or longer, so you have an issue whether you want to do anything to understand it or not is up to you.

I understand the current loads on my batteries with the battery switches in both the on and off positions because I have measured it. I know where the current is going with the chassis switch off, it is going to the engine ECU. I know that load is 1.7amps and I have chosen to not address that issue because my coach is always plugged in. If my batteries were decaying charge wise to 11.7V in 3-4 days, I would rewire my coach in a heartbeat because at those discharge levels the plates sulfate much more rapidly and you are basically destroying the batteries.

I am very comfortable with the information I have provided about rewiring this ECU circuit because I have done the research with Caterpillar on the downsides of not powering the ECU all the time and because I have done the measurements to characterize what the loads are and what needs to be done wiring wise to eliminate this issue. This info is to help those who want to follow a path to see if they have the issue and based on how they use their coach provide a suitable path if they find they need to correct this design flaw.

I do not understand you being disappointed if I have elected not to make this change based on how I use my coach, that seems irrelevant to me, but so be it... I will be happy to answer specific questions if there are questions but I will probably end the long explanations here given this subject has been fully discussed.

Later Ed

[Mike Groves]

All,

I'll let everyone know on 9th of June, if my "dead chassis batteries" start my coach.  If they do, then I'll have to believe in miracles.  And, as Forest Gump was fond of saying, "and that's all I have to say about that".

Mike

[Edward Buker]

Mike,

Forest had a lot of good sayings, I did love that movie, one of Hanks best. That we can probably all agree on :-)  By the time this post is all done we will probably all learn something new...that is the way things normally go. Have a good Sunday.

Later Ed

[Gerald Farris]

Mike,
As a retired mechanic that has dealt with many Beaver coaches through the club and as a owner over the last 15 years, I can tell you that Ed is totally correct in every statement he made, including the one where he said that your batteries are dead (sufficiently discharged to be non-serviceable) at 11.7 volts. Even deep cycle batteries can not be discharged below 12 volts without shorting their life expectancy. 

Rod,
To answer your question about recharging time, you have to tell me if your coach is equipped with an Echo Charger or not.

If you are going to store your coach without it being connected to shore power, it would probably be beneficial to you to install a battery disconnect at the negative battery cable for the chassis batteries.

Gerald

[Mike Groves]

Gerald and all,

Well, I may be starting a church soon, as there will be lots of believers when I miraculously bring my C12 to life on June 9th with dead chassis batteries. 

"Do you believe in miracles....YES!"...that's another famous quote - Al Michaels this time.  Anybody remember?

Thanks,
Mike

[Mike Groves]

All,

I'll let everyone know on 9th of June, if my "dead chassis batteries" start my coach.  If they do, then I'll have to believe in miracles.  And, as Forest Gump was fond of saying, "and that's all I have to say about that".

Mike

All,

As promised, an update on my coach's condition POST STORAGE over the last 10 days. 

I store the coach under cover, and simply use the rotary switches in the battery compartment to shut off both batteries.  Since I am under cover, I get only reflective sunlight I guess on the 2 rooftop 75W solar panels.

Prior to this return, on June 9th, my last visit was May 30th.  I checked fluids, then turned on both battery banks via the rotary switches, and on the Silverleaf noted that chassis voltage as 11.9V.  As I usually do, I turn the key on, watch the Silverleaf come on, there is some sort of system noise (chunk chunk...chunk chunk - I think its the air valves perhaps), then I turn the key off, then on again.  This all according to my owner's manual. 

After this I started the coach.  At 11.9V, there was no hesitation, see Adam's Thread on Starter Hesitation.  There may have been an initial slower starter revolution, for just a split second, but it sounded pretty normal to me.  The engine started right up.

Now, as previously stated, over that 6 week period prior to May 30th, I'd left the coach stored under the same conditions an upon my return, noted the chassis voltage of 11.7V.

My conclusion, as offered previously, is that my coach, and perhaps other pre-2000 coaches DO NOT suffer from a separate circuit to the engine computer which draws a 2 amp (or even a 1 amp or even a .3amp) current in order to run this ECM computer.  If it did, my batteries would have drained over this constant draw for 10 days.  And I'll repeat that when the chassis batteries ARE connected, there is a huge draw, which I assume is the ECM, that will kill the batteries within a couple days if they are not supplemented - at least that's happened to myself and others.

So, while I can not "bust the myth" on 2000-2001 SMC Era coaches, I can certainly tell owners of 1999 Beaver Marquis that they can leave them stored for long periods (up to at least 6 weeks) in a "dry condition", ie not hooked to electric.  Since having the electric at my storage lot is an additional $20/month I believe (the covered is $171.00 without electrical hookup) you can certainly save money.

I haven't had the opportunity to start the coach using the 11.7V which Ed and Gerald both describe as a "dead battery", however, that voltage easily starts the generator, and by running the generator (which is a good idea anyway after 6 weeks) you can charge up the battery to 11.9V and then start the engine.  I am pretty sure mine would start at 11.7V as I just don't see a huge difference in 11.9V not being dead (which obviously it isn't since it started the coach) and 11.7V.

Enjoying Pacific Shores at the moment - Lot 53.  Any other BAC members here?   This is our first visit, so we'll be out and about.  This is by far the most maintained "RV Park" I've ever visited, but as I told Margaret, it is obviously the most expensive we've visited as well, having purchased our lot and with the HOA dues.  


Thanks,
Mike

[Edward Buker]

Mike,

Glad it started for you at 11.9V. I would guess one of the following, your ECU is not fed from before the chassis switch as you suspect, or your ECU is fed directly from the batteries but your battery banks are coupled by a change in wiring at the jump starter solenoid or a defective solenoid so you have extra battery capacity during storage. The only way you will know for sure is with measurements and a meter.

If you are happy and comfortable with your arrangement then that is all that matters. Obviously you have some charge or your C12 would not have started.

The problem is without a DC voltmeter measurement on the battery posts when you left the coach, and when you returned, it is hard to know what state of charge you started with and what it really was when you returned? Even better would be a current measurement with the switch off.

This reference has 11.9V as 0% charge. Like I say if you are happy then that is all that matters.

http://www.autoshop101.com/forms/hweb4.pdf

Later Ed