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| Re: Battery Cutoff switch [message #370762 is a reply to message #356474] |
Wed, 16 November 2022 07:45   |
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RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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On the topic of battery disconnects, I just want to bring up a warning about "Alternator Load Dump". This is a very high voltage spike (typically >100V lasting several hundred milliseconds) that can occur when you disconnect the engine battery while the engine (and alternator) is running.
I understand the battery disconnect is intended to be used when the engine is OFF, but sh*t happens!
Our coaches (normally) have two batteries connected to the output of the alternator, so the House battery(s) may absorb any spike IF they are in-circuit. If the House batteries are disconnected or missing, the 12VDC side of the house wiring will also get the "Load Dump" spike.
Those of us with fancy modern radios, EFI, electronic ignition (HEI or ESC) and other electronic 12VDC devices are more susceptible to damage than those with points ignition, carb, and the OEM Delco radio/heater.
Anyway, I just wanted to toss that out there in case anyone was not aware of the risks of disconnecting the battery from a running engine.
https://en.wikipedia.org/wiki/Load_dump
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Battery Cutoff switch [message #370763 is a reply to message #356474] |
Wed, 16 November 2022 11:15 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Very good point Bruce.
It can get worse. I worked on a coach where a DT dual terminal battery was installed. 2 positive battery cables were used, a top terminal and a side terminal. One to original boost spot and one to starter. This was a real head scratcher with sudden no crank electrical gremlins. Long story short, the battery internal connection had failed to one of the + terminals. This odd arrangement created a situation where the alternator sense was not seeing it’s own output. I could start the coach only with boost switch but as soon as it started hear the alternator whine screaming very loud. Immediately shut it off! Not until I put the battery on the bench and metered all terminals did it all make sense. Be careful with electrical mods. Though they seem a good idea at first, you can create unforeseen problems if the fail conditions add up right. If stock, this particular one could not happen. No one expects one + terminal on a battery to be good and the other + open.
John Lebetski
Woodstock, IL
77 Eleganza II
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