Why exactly does forgetting to disconnect batteries kill the KDS/Nartron?

[TOBASH]

I believe you guys 100% and I'm glad I read this BB prior to working on certain issues.

But it still does not make any sense to me.

Why does working on electrical systems without disconnecting the battery in this vehicle kill the KDS/Nartron?????

What exactly is going on in the system.

ALSO, is there a preferred way to reconnect the battery? I doubt it, but now I need to do some work and I'm getting paranoid. Do I connect positive or negative first?

TIA,

T

 

[papakb]

All of the PCBs and ESSS systems have always had issues connecting and disconnecting with the batteries connected. The original PCBs were fairly foolproof because they were mainly relay based systems. With the advent of the replacements they started getting more and more solid state devices internally and they're the components that tend to fail.

Kurt
KG6KMJ

 

[NormB]

You disconnect from GROUND.

 

[TOBASH]

All of the PCBs and ESSS systems have always had issues connecting and disconnecting with the batteries connected. The original PCBs were fairly foolproof because they were mainly relay based systems. With the advent of the replacements they started getting more and more solid state devices internally and they're the components that tend to fail.

Kurt
KG6KMJ

Thanks, but what exactly is going on? Where is the overload? Where is the current imbalance? Where is the reversal of polarity?

Thanks,

T

 

[wheelspinner]

It's because of connections. If the batteries had a real disconnect you wouldn't need to. The disconnect is in the box, so the box is always powered. When the connectors are removed or plugged in you can have "jumps" or minuscule arcs happen between the connectors and boxes. These can jump to other pins until fully seated. These pins may be connected to parts of the system that shouldn't see power until designed to. Hence the potential failure points

 

[frank8003]

You disconnect from GROUND. View attachment 671045

It is good to heed this caution even on a Deuce. There is electronics in the alternator.

 

[springbok]

I was told a long time ago when working on airplanes that you never "hot swap" electronics.. Just a little surge when reconnecting and poof you have a paperweight..
I actually have changed a few and when I disconnect the batteries I actually then turn the switch to on to make sure anything solid state that holds power will discharge...
Better safe then sorry .

 

[kc5mzd]

Disconnect the ground first if you will be disconnecting both. The only reason for this is because the wrench may bump a nearby metal object when turning the bolts on the connectors. If the wrench bumps ground when removing the ground terminal nothing happens. If the wrench bumps grounded metal object removing + if - is already disconnected nothing happens. If you bump grounded metal removing + when - is connected all the magic smoke gets loose and is very difficult to get back into the wires.
When reconnecting connect + first for same reason...

 

[TOBASH]

If you bump grounded metal removing + when - is connected all the magic smoke gets loose and is very difficult to get back into the wires.
...

I'm old fashioned.. "Magic smoke" is for Hippies and Commies. LOL

Best,

T

P.S. - You're absolutely correct though.

 

[dmetalmiki]

It is good to heed this caution even on a Deuce. There is electronics in the alternator.
View attachment 671086

With Diodes to prevent reversal.
Modern cars (presumably these trucks as well can be disconnected..(From the main set of batteries), When a live jump lead is connected to the cable clamps. And batteries changed. etc?.