Chassis Batteries Discharging

[Jerry Pattison]

I am having a new problem with my 98 Marquis.  My chassis batteries are discharging with the coach in storage, while the master switch is off.  I took the batteries out and re-charged them fully at home, then re-installed and ran a test with a simple ammeter, and the current draw vaporized a 1/2 amp fuse.  Again, this with the master switch off.  I think the engine sensors remain connected with this switch off, but drawing more than 1/2 amp?  Any suggestions will be welcome!!

[Jeremy Parrett]

When my Echo charger stopped working (it charges the chassis batteries from the coach batteries)
  I just disconnected the ground from the chassis batteries to stop the engine computer from running the chassis batteries   flat  in 3 days.  Hope this helps.

[Mike Groves]

Jerry, I'll relate my experience with my '99 Beaver Marquis.  It's been discussed on the forum before but I did get some new findings.  I also store my coach and leave it with both Chassis and House isolation switches turned off.  I have left it in storage up to 6 weeks without a visit and my Chassis batteries have never shown below 11.9V on the Silverleaf when I've come back, simply turned to key on, and check it..  That part I've mentioned on the forum before.  I also mentioned that the coach would start with this 11.9V showing. 

What I've learned since is that when I removed all the batteries when I repainted the battery sliding rail system, I also took them all home and when I checked the chassis voltage on a volt meter it showed about 12.3V (vs the 11.9 on the Silverleaf), so it might be that the reason the coach started is that the Silverleaf is simply reporting lower than the batteries actually are.  Some on the forum told me that 11.9V was a dead battery according to definition and I disputed that because my coach started.  Therefore assuming both of these statements are true, then an obvious conclusion is that my batteries WERE NOT at 11.9V but rather above 12V.

I said all of that to say this, evidently when my Chassis switch is off, my chassis batteries are not being drawn on for if they were then there would be no way I could start the coach after 6 weeks of storage. 

My conclusion, therefore, given that our two coaches should be similar and probably more so even than when comparing them to the 2000 model, is that what you're seeing is not as it should be.  I do know that mine will be drawn down after just a couple days if the isolation switch is NOT turned off, so indeed the coach does draw that down probably due to the computer I imagine.

As to what is drawing yours down, I have no clue on that.

Mike

[Edward Buker]

Jerry,

As others have mentioned the typical wiring for this era Beaver coach was to power the Cat ECU continually which by my measurement pulls about 1.7amps continually. I discussed with Cat engineering in detail, if there was any fundamental benefit to leaving the ECU powered all the time, and other than a shorter start sequence there was not. There is write time for the ECU memory, if fully powered down, so it may take an extra 20 or 30 seconds from the time power is turned on to have the engine ready after the battery power is being supplied. Some electronics benefit from being on all the time, reliability wise like for keeping condensation at bay, but that does not seem to be an issue here.

Your choices are to disconnect the starting battery bank grounds, as Jeremy pointed out when stored, or to find the wire that supplies the feed to ECU power that bypasses the battery disconnect switch and rewire it to go through the switch, or put a separate manual switch on that lead. Once you supply power to the ECU you would leave it on until you again had no charging source. I do not know anyone that has made that modification but there should be no issue in doing so.

Later Ed

[Steve Huber]

Ed,
1.7 amps to power the ECU seems significantly higher than one would expect for a solid state device in a quiescent state. Did CAT explain why it draws that much?
Steve

[Edward Buker]

Steve,

If the ECU is powered up, it is probably clocking at some rate and looking for minimal data. This era of solid state design was probably developed in 1995 or so, probably some bipolar, and long channel fet devices, analog to digital converters, memory, voltage regulation, etc. I am guessing they were not worried at all about power consumption, just function and reliability given most of the time the vehicles being designed shut the power to the ECM off.

I cannot tell you why it draws that much power but we all have the same two to three days of use and the chassis batteries are dead experience. 1.7 amps at 12V is 20 watts which I do not find extraordinary for a clocked CPU and associated converter circuits even if they run the clock speed slow. I think they also probably run fairly high current for any analog sensor data coming in to stay out of the electrical noise ranges. Just some guesses here...

Later Ed

[Jerry Pattison]

This is interesting, because it has not happened until this/ late last year, and I have owned the coach since 2000.  For about 10 years, we kept the coach in storage for months at a time without power, and never had to jump or charge the chassis batteries. It seemed to have started after we had a couple of freezing nights in Dec/Jan.  I visited the coach in storage after that, and started the gen to charge the house batteries, no problem.  Then recently, as in early March, I could not start the gen.  Both chassis and house batteries were below 8V!  That is why I removed the chassis batteries and charged them, then attempted to check the current draw after re-installing, and vaporized a 1/2 amp fuse.  So, I am thinking something is "hung", or in an "on" status and should be "off".  Very strange indeed.

[Mike Groves]

Jerry,

Your experience for 10 years then would jibe with mine, although I've never left mine sitting more than 6 weeks without visiting and starting the generator or starting the coach.  In other words, like I said, by using the rotary solenoid to disconnect my chassis battery they didn't run down, so perhaps our coaches are wired differently than the 2000 and beyond.  Sounds like something has now happened to change all that and has nothing to do with what Ed and others are saying about the ECU and that it is normal for our batteries to expire within 2-3 days.

A mystery, obviously, but having nothing to do with the ECU.

Mike

[Steve Huber]

Jerry,
Have you checked your solar panel output? If it is not supplying a voltage the batteries will discharge in short order with the ECU draw. With a 1.7 amp ECU draw, a 1/2 amp fuse doesn't stand much of a chance.
Steve

[Edward Buker]

Jerry,

I think your ECU is probably not on with your battery switch off, given you have gone long periods since you have owned the coach without this issue. That is an assumption and it seems rare that these coaches do not have the ECU on all the time but yours and Mikes are similar vintages and do not seem to discharge sitting.

I think you need a way to monitor the DC current flow out of the chassis battery bank with a DC amp meter and start turning off DC breakers if they are the resettable type, pull DC fuses, and in the electrical bay below the drivers seat is a row of breakers on the left buss that you could unbolt the wire one at a time and lift it off. These are the branches of loads that could be using current. Hopefully one of those will eliminate the current load and give you a clue where your problem is.

Later Ed

[John Olsakovsky]

I am having a similar problem with the chassis batteries discharging quickly. I am a new owner of a '97 30ft Monterey. I added a 15 watt solar panel connected to the house batteries and that keeps them high enough to start the coach. I have not been able to physically locate the chassis battery cutoff switch.
Also, still trying to figure out how the factory solar panels are wired and connected....no idea if they are active.

I appreciate all the comments here.

[Edward Buker]

John,

Not all Beaver models and years had battery switches. If it is not near the battery bank you do not have one. You could add a marine version for diesel which has good alloys and capable contacts. Something like this would work wired as a simple switch. Just off and on....

http://www.overtons.com/modperl/product/details.cgi?pdesc=Blue-Sea-Systems-Add-Battery-Dual-Circuit-Battery-Switch-Only&i=87327

Later Ed

[John Olsakovsky]

Thanks Ed,

I found a switch for a semi at Napa. It looks identical to the house battery switch by the steps and it looks like I can mount it on the side of the queen bed frame right above the battery box. I'll also mount a switch on the dash for the ECU monitor and that should take care of the current draw. Appreciate the suggestion.

John Olsakovsky

[Edward Buker]

John,

I am not sure what is drawing current on your year and model Monterey. Once you add the battery switch for the chassis batteries, see what happens with the switch off. It should be fine for holding charge then. When we talk about the ECU drawing current, it is the engine ECU mounted on the Cat engine that has been wired to bypass a Beaver installed chassis battery switch on some models and years. The dash monitor system is usually not powered up until the ignition switch is in the on position at least in my coach. If not, as long as it goes off with the new main chassis battery switch you should not need to provide separate on/off switching at the dash for the monitor.

Later Ed

[Jerry Pattison]

Jerry,
Have you checked your solar panel output? If it is not supplying a voltage the batteries will discharge in short order with the ECU draw. With a 1.7 amp ECU draw, a 1/2 amp fuse doesn't stand much of a chance.
Steve

Steve, the coach is parked under cover, I don't expect the panels to put out much power.