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Old 06-01-2010, 02:33 PM   #1
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Electrical got me stumped!

Today as I was putting a disconnect on the chassis battery, I found a weird event. I disconnected the Neg. cable on chasssis battery, and everything still worked on ignition, including starter. Is it possible that the Aux. booster start switch could be bad and allowing a constant power to starter and dash? Don't know where to start to trouble shoot. When checking voltage on chassis battery, I put neg lead of meter on aux. batt neg terminal , pos of meter on pos of chassis battery, still got 13 volts. any ideas? Alleyman; 2004 Dolphin 3555
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Old 06-01-2010, 03:02 PM   #2
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Its a battery you will read 12v or 6v if you hook meter to pos & neg terminals.
You will have a ground on chassis frame from your house batteries and generator and if you are connected to house current you will have a ground from your house wiring system.
Heres a link explaning the world of 12volts may help you, I see no problem just a misunderstanding.
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Old 06-01-2010, 03:11 PM   #3
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Yes, somewhere you have the batteries connected together or else No, you have more than one negative connection to the frame.
You can check the solenoid that connects house & chassis easily (if you can reach it easily). Just check the voltage between the two large studs w/your meter. If you have battery voltage, then the solenoid is not connected; if you have zero then likely both sides are ground potential; if you have a coupla tenths volt then you are reading the voltage drop across the two studs due to greater than zero resistance of the solenoid contacts, and the solenoid is connected. You will probably need more info than this to do a complete diagnosis and answer your questions, but that should get you started. Post some more data for additional suggestions.
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Old 06-03-2010, 12:44 PM   #4
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That is one possible answer. Another is a bi-directional isolator

My coach has one of those

This device lets me charge house batteries off the engine or engine battery off the house.. Till the isolator realizes the chassis battery is "MIA" (missing in action) it will keep them hooked together.. Same for the house batteries.

Normally this means a serious voltage drop.. which won't happen till you hit the START position on the switch or turn on headlights.
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Old 06-06-2010, 02:29 PM   #5
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Mike; thanks for the info. I checked as you said, I have voltage on one stud & zero on the other. Are you saying, that the solonoid should read zero on both except when the booster button is pushed? The chassis battery is not charging from the 110 current when I am plugged to shore power. I can/t seem to locate a battery isolator. Not sure if Dolphin installed one. Thanks again for the help. Alleyman. 2004 Dolphin 5355
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Old 06-08-2010, 08:07 PM   #6
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Quote:
Originally Posted by EngineerMike View Post
You can check the solenoid that connects house & chassis easily (if you can reach it easily). Just check the voltage between the two large studs w/your meter. If you have battery voltage, then the solenoid is not connected; if you have zero then likely both sides are ground potential; if you have a coupla tenths volt then you are reading the voltage drop across the two studs due to greater than zero resistance of the solenoid contacts, and the solenoid is connected. You will probably need more info than this to do a complete diagnosis and answer your questions, but that should get you started. Post some more data for additional suggestions.
Mike could have explained this better, but he's describing an easy way to check a switch or fuse in the circuit with the power on.

We normally think of using a voltmeter to read volts to ground. Is the circuit on or isn't it.

a voltmeter actually reads the difference in potential between 2 points, it's not a rule that one of them is ground.

So... if you put a voltmeter across an ON switch, it will read zero. Both legs are at 12 volts, there is no difference in potential.

Same switch OFF has power on one side, none on the other, meter will read the difference, 12 volts or so.

Worls equally well with solenoids, or fuses. A good fuse will have the same voltage on both sides, zero on the meter. meter reads 12, fuse is blown.
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Old 06-08-2010, 08:29 PM   #7
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Actually I probably shoulda laid out the whole solenoid check sequence as follows:
1) is there voltage to solenoid to transfer: w/voltmeter check each large stud to ground. If one or both have 12v then there is voltage to transfer, if both then it is engaged & transferring.
2) if voltage to both, then check the difference between, i.e. large stud to large stud. If there is a difference, this is loss going thru the solenoid. Large contactor type solenoids have large arcing currents when they close or open. Arcing causes some level of burn of the contact material. Over time this can become a serious resistance to current flow, and the solenoid is reaching the end of its useful life. Some solenoids can be dissected & the contacts polished, reassembled and used again or as a spare; some are too cheap to make this a useful exercise. Once the contacts are losing more than about 0.2 volts the heat generated by passing current thru this high resistance will accelerate problems and the solenoid should be repaired or replaced. If voltage is critical, the threshold of 0.2 may be too high.
3) If there is voltage to one fat stud but not the other, check the small stud(s) to ground. If one has 12v then there is voltage to activate the solenoid but the 12v is not connected properly to ground, meaning either the ground side is switched and there is no "signal" to contact the large studs, or there is an open ground that should be closed; this last requires further investigation to determine the design of the circuit to say whether the condition is A-OK or there is a problem. Designs vary, so that investigation is beyond this discussion.

The important thing is to view large contactor solenoids as "wear" items, i.e. they wear out, pretty much definitely at some point, and need some look-see when the electrical problem circuit involves a contactor.
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Old 06-10-2010, 07:52 AM   #8
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Engineer Mike 68: Thanks for the additional info. I will follow your outline again for more testing. I have 12 volts to ground on each of the small studs. On the large studs, I have 12 volts (to grnd) on only one side. I didn't check with one lead on each large stud, as you mentioned. I will do that today. Thanks again, this helps to understand the system better. The schematic sheet on the cover is written in French, so, having a little difficulty translating all the right parts and wire tracing. They must have planned to ship to France. I'll get back to you tomorrow. Alleyman, 2004 Dolphin 5355.
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