BAC Forum
General Boards => Technical Support => Topic started by: Joel Weiss on January 10, 2016, 10:53:52 PM
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The other day I noticed that the house and chassis battery voltages on the CMP were about half a volt lower than those displayed on the Magnum MS2812 remote panel. I played with this for several hours before trying something simple--flip the salesman's switch off and then on again to find that everything was fine--the Magnum's voltages were correct. That was last night. I checked the voltages again only to find the same problem. Flipped the switch again and everything was fine. My guess is that the relay's terminals are introducing some resistance. I guess I'll need to replace the relay.
Since the actual battery voltages are normal, what's the effect of the relay issue on the MH? Are the 12V systems seeing the lower voltage shown on the CMP or is that an artifact?
Does anyone know what the relay's specs are before I tear the old one out to look at it? Any particular precautions other than disconnecting battery banks and shore power?
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Joel,
No precautions beyond what you mention. Just measure the terminals at the solenoid to be sure it is not seeing voltage before you work on it. There are versions of these solenoids with better alloys for resistance to corrosion and pitting. They will state that if they are an improved version. A lot of the solenoids will be rated at 100amps or more which should be fine.
If you are like me Joel, I have never used this solenoid or the feature. I would probably get a short wire cable, same gauge or larger as is already in place and jumper the two large terminals on the salesman switch solenoid. It will ultimately be a better connection and more reliable if you do not have or use the switch.
Later Ed
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Joel I did replace the relay for no reason other then I was at BCS and it was covered under out EW plan. Everyone at BCS indicated that jump the relay is fine I also got this same info from many members and from Monaco.
I had enough wire to just move the wire to the same post. I ran like this for about 3 weeks with no problems.
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On my documentation, this device is simply a manually operated high current switch not a solenoid.
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John,
The coach battery cutoff is a high currant (200A) switch. The "salesman switch" inside the coach controls a 200A solenoid located just after the cutoff switch.
See page 4 of this 95 service manual. https://www.dropbox.com/s/us15putll0k09xg/Beaver%20Service%20Manual%20%28Electrical%20Diagrams%29.pdf?dl=0
Steve
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John,
The coach battery cutoff is a high currant (200A) switch. The "salesman switch" inside the coach controls a 200A solenoid located just after the cutoff switch.
See page 4 of this 95 service manual. https://www.dropbox.com/s/us15putll0k09xg/Beaver%20Service%20Manual%20%28Electrical%20Diagrams%29.pdf?dl=0
Steve
Steve:
Those electrical diagrams you posted appears to be for a 1995 Patriot which, I assume, was based on the Gillig chassis. You wouldn't happen to have the equivalent drawings for the Magnum C chassis on which my MH based, would you?
Joel
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Joel,
No. I used the 03 Marquis electrical dwgs located in the Links to Coach Assist thread in the Private BAC Members Only area. They were very helpful on both my 01 Contessa and 00 Marquis. My observation was that since they are for the top of the line Marquis they will contain teh info generally needed for the other models and seem to be fairly accurate for all SMC era Magnum chassis units.
Steve
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I was all set to jumper the relay when it occurred to me that a voltage drop across the relay shouldn't have any effect on the displayed chassis voltage because there's no current path through the relay for that measurement. Furthermore, every time I reset the relay the displayed voltages came back up instantly. If there were actually issues with the relay contacts I would assume that some resets wouldn't resolve the problem.
Anyway to make a long story short, I let the house voltage displayed on the CMP drop down to ~12 volts and then I measured the house voltage at a light fixture with a digital voltmeter. Even with other lights on that circuit drawing power the measured voltage was always within 0.2V of the reading on the Magnum's remote display. So my conclusion is that the CMP is "drifting" and losing its zero reference point. Any other explanations?
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Joel,
If you turn off the salesman switch does the CMP still display? I am not sure where the CMP picks up its voltage for measurement but that would tell you if the CMP supplied power goes through the relay.
I think the easiest thing would be to make a temporary short jumper and see what happens to the CMP display. You could spend more time trying to figure this all out by tracing and measuring. If you jumper the relay and see that the CMP behaves itself voltage measurement wise then change the relay or leave the jumper.
Resetting the relay mechanically remakes the contact points on the disk which are probably pitted and oxidized at this point. There is some reduction in resistance expected when you do that but it tends to be temporary.
Later Ed
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The CMP is powered by the power going through the relay but that's the house batteries. If the CMP displays a reduced voltage then you would expect that all 12V circuits going through that relay would also have a reduced voltage, but they aren't.
There's absolutely no reason for the chassis battery voltage to display incorrectly even if the relay is pitted and worn. The CMP is essentially a voltmeter that is getting its internal power from one of the circuits it is measuring (the house batteries). But to the chassis batteries the relay is just a voltmeter and they should read correctly regardless of whether or not the relay contacts are dirty or not.
Yes, I do have the wire needed to make a jumper and was about to try it today until I discovered that my terminals wouldn't go over the relay's lugs. I'll get some new terminals and try again tomorrow.
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Joel,
See https://www.dropbox.com/s/iizggmnsuewfcdt/Bat%20Cutoff%20Box%20Mrq%20Part%2042003.pdf?dl=0
It shows the CMP power coming from the battery boost relay. I'd take a hard look at the connections at the relay and fuse as well as the integrity of the butt terminal. The diagram is from the 2003 Marquis schematics, part 4, page 4. I'm fairly sure your coach is wired similarly.
On the off chance that the voltage to power the CMP and the voltage it displays are from 2 different sources, another diagram in section 5 shows the following getting 12v on Circuit #9 through a 10a fuse: Datron satellite, CO detector, Monitor Panel (CMP??), Kitchen T'stat, LP detector, and antenna boost. Ineitehr case I'd also verify that the connections at the back of the CMP itself are clean and tight.
Steve
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Steve:
I appreciate your efforts to help. But in the five years I've been a BAC member I've become convinced that those of you with "Monaco era" Beavers have no idea how many changes were made in the 2000-2003 period. The BAC manuals repository has 2003 Thunder wiring diagrams, all 85 pages of them, but on every one I can identify many differences between the coaches depicted there and what I own. Yes, something like my isolation board bears "some" resemblance to the one in the schematics but the operative word is "some." The Magnum chassis Beavers were a very different breed from what was being built in 2002-2003.
But help is always appreciated. I have only one large relay on the isolation board which I assume is the "salesman's switch" relay. I'm not at all sure where the battery boost relay is located.
Joel
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Joel,
Just trying to help. They worked fine for my 00 and 01 SMC chassis coaches.
Good luck! Steve
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Don't get me wrong; help is always appreciated, but by 2003 the Patriot Thunder was powered by a Cummins ISL and had all sorts of Monaco features on it which my "primitive" SMC coach didn't have. As I said, there are some similarities but the specific schematics are very different from the "as built" that I'm staring at.
Not much can be done about it, IMO Monaco did all of us SMC-era owners a terrible disservice when it destroyed all as-built drawings prior to its acquisition.
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Joel,
It isn't just the CMP current draw here, it is any current draw through the contactor dropping voltage through the relay/solenoid contacts and then the CMP sensing lower voltage somewhere (god knows where) on the output side. If you reset the relay/solenoid contactor and get a different result on the CMP and the issue is that it seems repeatable, that is it alleviates the low voltage result each time, then I think it is worth jumpering to see if the CMP issue is resolved.
I'm not saying for sure that the CMP measurement module is stable, but if all other measurements by the unit seem correct then there is reason to consider that it may be correct in its DC measurement also. Unless you can find the actual DC measurement point that the CMP is using and then verify that point with an independent voltmeter measurement then the you do not know if you are measuring apples and oranges being they are different DC locations, wiring paths/loads....
Later Ed
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Ed:
If the 12V devices in the coach are seeing voltage significantly ABOVE that displayed on the CMP then I can't think of any explanation other than the fact that the CMP is wrong especially when the voltage I'm measuring at light fixtures is roughly the same as the Magnum inverter is reporting. These are lights that are among the many things that are turned off by the salesman's relay. Therefore, they're seeing the same voltage as the CMP is seeing.
I think Steve's suggestion to check the connections at the CMP itself makes a lot of sense. It's possible that a slightly bad connection gets temporarily "better" when the switch is turned off and then back on again. The same kind of "corrosion" that could affect relay contacts could also build up on a terminal of any other device. We're only talking about <1V in voltage drop so a connection might be "almost Ok."
Joel
Joel
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Joel,
Assume for a moment that there are two legs coming off the salesman switch, one to the lights and one to another load that has some current draw on it going somewhere, say the circuit board in the fridge and the solenoid valve safety device for the propane system and that is the CMP sense line. In theory you are right that there can be just one voltage on the output side of the relay and if you have no load on the light circuit and measured it, it would read the same as the relay terminal. If there was load on the other circuit that the CMP measurement point would see then it would have a lower voltage at its measurement point. It is hard to diagnose compare the two voltage wise without knowing the loads. The issue that adds some "fog" to this is that the CMP readings change as you reset the relay and seem to recover and I see no way that the wiring path to the CMP would coincidently heal itself for a resistive wiring path issue going to the CMP because of resetting the relay. There is no doubt that the hand held voltmeter reading coinciding with the inverter panel is incorrect. Just not clear how resetting the relay can cause the CMP to recover. It is probably not worth a lot more effort on this.
The voltage supply line that is the sense line for the CMP is probably what supplies the unit 12V in the cabinet. You could find that and measure that point with your voltmeter and see what the voltage difference is between the two and have your answer as to the accuracy of the CMP and what voltage the line is seeing with relay resets.
Later Ed
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I think Steve's suggestion to check the connections at the CMP itself makes a lot of sense. It's possible that a slightly bad connection gets temporarily "better" when the switch is turned off and then back on again. The same kind of "corrosion" that could affect relay contacts could also build up on a terminal of any other device. We're only talking about <1V in voltage drop so a connection might be "almost Ok."
Steve gets the prize for the correct answer! I removed the CMP from the cabinet this morning, "pushed" all the wire connections to ensure that they were in tightly and Voila! it now works perfectly. House battery voltage displayed on the CMP is within 0.1V of the Magnums's display.
Thanks to Steve and Ed for helping me puzzle this out!
Joel
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Joel,
Glad you found it. One less item on the fix it list...
Steve
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Joel,
The large solenoid in your battery bay should be the boost solenoid, and the salesman's switch solenoid is normally the size of the old Ford starter solenoid.
Gerald
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Joel,
Glad it is fixed.... The mysteries of poor contacts and where they lie is a lot like where did I leave my car keys? You know they are out there somewhere....Steve, good sleuthing :-)
Later Ed