Technician requires some insight ( Energized frame w/ batts off )

Smile........your on Candid Camera!!!

I don't recall you mentioning working in a steel plant up front in the thread. I have had to do inspections of that vary model in a steel plant in my area and I have to say those machines really look like hell when they are done with them. These units pull hot slag out of the plant and then dump it into a pile where water is continually sprayed on the stuff until it is cool enough to load on a truck and hauled out back to finish cooling. All that slag stuff coats the entire machine and the heat with water requires extra guarding and the sealing measures Nige has spoken of above. If your machine is operating in the same type of environment I feel for you and your job. Sounds like you have all the straight forward answers covered and I don't have anything to add except let us know what you find out.
Good Luck!

John C: Thank you. As far as feeling for me goes, no worries there. I`m the working foreman here and get to delegate the grimey jobs. We have about 20 pieces in the steel plant, under contract. The rest ( about 50 pieces ) are earth moving, toilsoil handling, etc... Along with screening plants, tractors, trucks, tri-axles, pickups, classic cars, blah... blah... blah... Makes for a busy crew. Of THREE...

Your frame is showing positive charge measured against the negative battery terminals, right? and you have a ground cable disconnect? You'll have to disconnect the positive harness and reconnect one by one to show what's leaking.

For one, I've used a power probe and don't find it more useful than thinking the problem through and testing with a $2 multimeter.

I didn't notice any mention of the alternator? the alternator is typically attached directly to the batteries with a fusible link somewhere in the wire. The rectifier leaks voltage, more or less.

TEX32 said:

Cmark: I did this as well. The energized frame continues, even when all the NEG terminals have been removed. This is what lead me to believe that I had a POS cable or circuit rubbed through somewhere in the machine. Upon checking and rechecking my harnesses, I determined them to be in good working order. As earlier stated, I`ve even pulled all fuses, circuit breakers, bus bars and relays, to systematically isolate any problem component or circuit.

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Delmer: Original post indicates my alternator was found to be GOOD. No internal shorts & rectifier bridge in good working order.

``For one, I've used a power probe and don't find it more useful than thinking the problem through and testing with a $2 multimeter. `` - CONGRATS... .. .

This is getting weird. All four battery negative terminals disconnected and an LED between positive and frame still lights, correct? And no physical damage to any of the batteries allowing current leakage to the frame? Doesn't seem possible.

Steel mill you say? Does it have fire suppression fitted? That will have an internal backup battery, probably in the box in the cab. Could be a possibility.

Okay, now you have got me laying awake at night thinking about this too. If I understand correctly, you have connected the frame to unswitched +24 v through an LED (diode), creating a circuit that goes from (+)battery to LED to frame to disconnect switch to (-)battery. When the battery shutoff switch is opened or the batteries are disconnected you now have an open circuit with (+)battery, LED, and frame on one side and (-)battery on the other. Since no current is flowing in the circuit, voltage across the LED goes to zero. Diodes have very small but measurable forward leakage current so it shouldn't be surprising that the frame eventually floats to the same voltage as (+) battery.

As to the Power Probe, the published spec for input resistance to ground is 350K ohms, while the input resistance of the Fluke DMM that lives in my truck next to the Power Probe is 10M ohms. When I measured the input resistance to ground of the Power Probe this morning with the Fluke I got 120K ohms, much less than what is supposed to be and makes me wonder what yours is. When you clamp the power probe to (-)battery and probe the frame you have just closed the circuit. The Power Probe is not the best tool for investigating this problem and may be introducing some unintended effects.

As to the LED being on with only one battery connection (and presumably the Power Probe not completing the circuit), I see more sleepless nights ahead. Steel dust? Parked next to the electric arc furnace in the mill? Grounded to earth through steel tire chains common in steel mills? ???

brianbulldozer: You are correct. Simply put, LED hooked up to a constant 24v supply ( not keyed ) and ground. When bats ON, the LED is illuminated, when bats OFF, the LED dims, but still stays on. This is what started all the confusion... It was at that point I discovered that the frame sports a +24v when the batts are off. No tire chains. No external voltage supply from another source. Just the machine sitting in my shop.
As bad as this sounds, thanks for the sleepless nights... I'm glad I'm not the only one....

Back to the subject of the wiring harness connections, I recall major issues on 992Gs where the main power feed (4 SWG cable) to the electronics compartment/fuse/circuit breaker box was routed in with a machine harness containing a load of 12-16 SWG cables. There was one particular connector that often came "loose" because of the weight of the harness with that big heavy cable in it. If the problem was not spotted the power cable would burn up because of the arcing in the connector. Maybe a similar problem could be happening on your 980G with the harness being of similar design...? Not necessarily the burned cable, but maybe the arcing inside the connector.

Our solution on the 992G was to route a new main power cable outside the machine harness and take it through the firewall into the Electronics Bay/fuse box on its own separate connector..

Nige: Since the [your] inception of kish filled dirty connections came about, I am in full agreement with this latest analysis. I believe that a bad connector within the machine MUST be the source of the back feed. The main connectors shown are a problem area for the 980's and will be re-examining them in the New Year.

Hi been following this with interest had something similar but with fire suppression years ago .Just for giggles disconnect the hydraulic and transmission ECM's behind the seat and see what happens
Mark

Cmark said:

• Disconnect the ground lead from the master switch and remove all four battery negative terminals. The problem SURELY must be gone by now.
• Start reconnecting things one at a time until the problem reoccurs.

That HAS to lead you somewhere.

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If you’ve done this and still have power to the frame it can’t be a positive cable problem unless there is an alternate power source like fire suppression back up power.

Why do you want your operators to shut the master switch off? So the batteries don’t go dead? The batteries couldn’t go dead if there wasn’t a path for current to get back to the batteries, right? What I’m saying is you don’t have a problem. Use an ammeter instead of your power probe between the frame and negative post, you probably have very little current flow. I believe any newer machine with ANY electronics will do the same thing. That’s why you always get a spark when you connect a battery cable.

379Pete said:

Why do you want your operators to shut the master switch off? So the batteries don’t go dead? The batteries couldn’t go dead if there wasn’t a path for current to get back to the batteries, right? What I’m saying is you don’t have a problem. Use an ammeter instead of your power probe between the frame and negative post, you probably have very little current flow. I believe any newer machine with ANY electronics will do the same thing. That’s why you always get a spark when you connect a battery cable.

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Because on these new machines, even though it would be logical to think that you should be fine by just turning off the keyswitch, in reality it does not work that way. My excavator is a 2014, and I have not added anything or modified the electrical system in any way. If you do not shut the master switch off, it is an absolute certainty that your batteries will be dead within a month, the only unknown is if they will be dead within a week, or four, I've experienced both. It caused me to have to replace the batteries after 3 years, when they should go 10 or more. The last time they were killed, one refused to take charge, and the other reversed polarity so thoroughly that I couldn't even hook a charger to it, that was a new one for me.

Shimmy1 said:

Because on these new machines, even though it would be logical to think that you should be fine by just turning off the keyswitch, in reality it does not work that way. My excavator is a 2014, and I have not added anything or modified the electrical system in any way. If you do not shut the master switch off, it is an absolute certainty that your batteries will be dead within a month, the only unknown is if they will be dead within a week, or four, I've experienced both. It caused me to have to replace the batteries after 3 years, when they should go 10 or more. The last time they were killed, one refused to take charge, and the other reversed polarity so thoroughly that I couldn't even hook a charger to it, that was a new one for me.

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I can see you only read the first sentence of what I said

As for why turn off master switch, where I worked it was mandatory company policy. It was instituted after a few plants around the country had fires related to an electrical problem that started while machines were parked over night. Some to the point that the fire involved equipment parked near them. That lead to a policy of also not parking two machines within I believe it was 20 feet of another machine.

And any equipment that did not come from factory with battery disconnect switches those had to be added to the equipment. I believe the only exceptions were pick-up trucks.

kshansen said:

As for why turn off master switch, where I worked it was mandatory company policy. It was instituted after a few plants around the country had fires related to an electrical problem that started while machines were parked over night. Some to the point that the fire involved equipment parked near them. That lead to a policy of also not parking two machines within I believe it was 20 feet of another machine.

And any equipment that did not come from factory with battery disconnect switches those had to be added to the equipment. I believe the only exceptions were pick-up trucks.

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I guess it’s normal here to only read the first sentence of a post and then reply?

379Pete said:

I can see you only read the first sentence of what I said

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No, I read your whole post. And answered your question as to why *most* (in my opinion) people want the master switch turned off. But, hey, if ya want to argue or contradict, have at it.

379Pete said:

I guess it’s normal here to only read the first sentence of a post and then reply?

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No I read the whole post but was just mentioning why we were required to use disconnect switch for the benefit of anyone who might not see a reason for doing that. Sorry if I wasted everyone's time I'll shut up now!

379Pete said:

I guess it’s normal here to only read the first sentence of a post and then reply?

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What kind of a response are you looking for, because obviously we aren't giving it to you? You want to debate whether or not current draw is an issue, because that's all there is left? The bigger question is why the attitude??