Load dump is when an inductive load in the vehicle is switched off, or in some cases, regenerates power back into the 12v bus. There are tons of inductive loads in modern vehicles that can cause this. Many are damped with freewheeling diodes, but not all. The 12v lead-acid battery acts like a big infinite power sink, so any excess voltage spikes on the bus are absorbed. This is especially true for EPS (Electric Power Steering) systems which use regeneration for damping. If you are in a parking lot maneuvering and let the steering wheel "snap" back after a quick turn, sometimes the EPS can dump a large spike onto the 12v bus. The 12v lead-acid battery will have no problem consuming it and keeping the bus voltage stable.
However, say you install a lithium replacement. It has a BMS that will typically have a MOSFET that will open once the battery is fully charged to prevent overcharge. Now any load dumps onto the 12v bus have nothing to consume them, so the bus voltage jumps up sharply. On an EV or hybrid with a DC-DC converter that's making power for your 12v bus, it doesn't like these at all, and can result in expensive damage. Does it happen immediately? Usually not. It's like handling sensitive electronic components without taking ESD precautions. You can probably not have any problems the first 50 times you do it, then you blow up something expensive. On Tue, Apr 20, 2021 at 10:00 PM EVDL Administrator via EV < [email protected]> wrote: > It appears that Lawrence has already made up his mind, so in a few years' > time we can ask him how that Leaf 12v lithium retrofit worked out. > > In the meantime, other folks here now have good, useful information and > advice from two knowledgeable and experienced engineers and EV builders, > Lee > and Phil. Thanks to you both. > > David Roden, EVDL moderator & general lackey > > To reach me, don't reply to this message; I won't get it. Use my > offlist address here : http://evdl.org/help/index.html#supt > > = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = > A good question is never answered. It is not a bolt to be > tightened into place but a seed to be planted and to bear > more seed toward the hope of greening the landscape of ideas. > > -- John Ciardi > = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = > > _______________________________________________ > Address messages to [email protected] > No other addresses in TO and CC fields > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/ > LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20210420/dde51d2d/attachment.html> _______________________________________________ Address messages to [email protected] No other addresses in TO and CC fields UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/ LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
