MEngr, I think what you may be calling "interesting" I might consider a "problem". but I do agree with all your points other than what is 'interesting'*.
I try to use some concepts that may be easier to grasp; "Low resistance is only telling the tech that there is a potential path for current to flow" I may say as 'testing the ability of a circuit to carry 1000 watts with a tool that only checks the circuit with milliwatts may not be all that accurate" or that "The real problems are created by current flowing in systems and areas it shouldn't be happening" I might have expressed as "sometimes the path of least resistance at.01 watt may not be the same path of least resistance at 1000 watts", but I kind of think we are making the same points, more often than not.
I do take your point about the more modern trucks having greater egress ratings, and therefore not being any where as susceptible to frame leakage.
I also wonder if our audience recognizes the apples and oranges of your comparison about A/C trucks then your comment about an IGBT. (or is there an A/C truck somehow using IGBTs, that I just have never heard of or considered exactly how that might work out?)
I also hope everyone catches on to the idea that the frame leakage testing is not done as a specific repair for a specific problem, but is more a check in case proper maintenance has not always followed the unit you are working on.
Proper maint. would include battery removal and cleaning, as well as cleaning and keeping clean the battery compartment.

*=?did you watch too much ot the original Star Trek series, and decide you wanted to be just like Mr. Spock? He always thought things that were problems to be solved were "interesting"?
;-)

Ed;
Resistance of a trucks chassis to it's electrical and/or electronic systems is a valuable tool to use in the determination of a truck's electrical cleanliness. A truck can have no or low resistance readings and still be electrically clean. The real problems are created by current flowing in systems and areas it shouldn't be happening. On todays AC vehicle, when they are being used to work in all weather conditions outside may fall short of the 100K ohm you are looking for yet still perform and do their job well. This is often the case in Europe. Low resistance is only telling the tech that there is a potential path for current to flow. What is interesting is when a truck stops working and the chassis has a higher resistance reading then 100k but the current flow is above say 45 mA and the electric steer drops out or transistors blow, particulary an IGBT.

An option to the mud flaps as an insulator, is a mat made for the bottom of pick up truck beds. Last time I bought one from a parts store like Auto Zone was ~$50.00 for a Ford Ranger class. One can cut to fit & probably have enough material for two.
Just a "no charge" for a back yard engineering suggestion.

I almost always go by the 100K ohm short to frame as max allowable, and with the battery disconnected, check ALL power cables (this gives a check of the insulation sheets between heat-sinks and recs etc...)
As far as how to avoid the battery problems, other than fixing and keeping the battery clean, there is no "correct " repair, only ways to rig it, and in that path, I have found used mud flats from 18 wheelers to have some value as a cushion/insulation, but you MUST remove -all- the old corrosion first, and any power cables that are saturated with corrosion must be replaced too.

Hi duodeluxe;
What the concern should be is the amount of current leakage going through the truck by way of the truck's chassis. Basic electrics, for current to flow from a battery it must have a path from the positive plates to the negative plates. Using a volt meter to determine leakage will only tell you that there is a potential for current to flow and the likely source of the flow. GE in their SCR speed controllers state that current leakage of 100 mA or more is excessive. With the introduction of CAN networks and AC drive systems I've noticed that the tolerence level for current leakage as being less than half the 100 mA. In keeping with the thought of current leakage the source originates at the battery but wiring, insulation breakdown, dirt, dampness, etc. can be the route taken.
By now you are wonder how to determine if leakage is occurring and how much? With the battery in the truck and the battery's electrical connector disconnected from the truck. Using an amp meter placed on it's highest amp scale and the BV+ (POS) of the meter at the positive post of the battery and the BV- of the meter in contact with a cleaned surface of the truck and touching it's bare metal measure the amount of current flowing. Dialing down the amp scales of the meter to the lowest readable scale. IF YOU SEE 120 mA DO NOT GO TO THE 100 mA SCALE or LOWER. Current flow in the states in the industrial truck industry is positive to negative but the others say flow is from negative to positive for other applications. We have one half of the questioned answered. We now know what the flow of current out of the battery is. Now if we were to place the BV- (NEG) probe of the meter on truck battery's negative terminal and the BV+ on a clean bare metal surface of the truck and the amp scale read the amount of current flowing.

Thanks Ed. Is there an answer of what the maximum resistance can be no matter what controller the truck is outfitted with?
What have you done or what do you recommend to do to correct it?


In the past where excess voltage bleed through to the frame has caused issues with a truck we have removed the battery, cleaned it and painted the area of the truck where the battery sits and never had another problem.

Voltage is not a good measurement for battery (power cable) leakage to the frame of the truck, nor is positive to negative at the battery connector.
The correct answer and method to check depends on the controller manufacturer's spec, GE usually calls for no less than 100K ohm resistance between frame and any power cable (not just the battery cables).
I am pretty sure that if you can light a 12 volt test light between the battery post/cable and frame of truck, you have too much short, but reading the voltage only has the ability to clue you into which cell on the battery has the most short to the case, not really how much current that short may carry, nor if there may be some other short that is not showing at that moment, since the path of least resistance* at that point in time is the voltage short you are looking at
* the path of least resistance for a.001 watt current may not be the same for as for a 1000 watt current