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I have an Ecoflow battery to be used in a Volkswagen Caddy and which I'd like to keep connected to the Caddy's 12V accessory port (unless the car is OFF for more 1 or 2 hours). The Caddy has the 12V accessory ports always live. The Caddy manual gives the following warning regarding 12V accessories:

To avoid damage from voltage fluctuations, switch off connected electrical equipment before switching the ignition on or off and before starting the engine.

This means I'd have to (remember to) constantly plug and unplug the Ecoflow battery, which would be a tremendous hassle.

What's the reason for the warning in the Volkswagen manual and does it really need to be followed?

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  • Welcome to Motor Vehicle Maintenance & Repair! Sep 26, 2023 at 11:51
  • They are probably just protecting themselves against any blame. What is the Ecoflow battery for?
    – HandyHowie
    Sep 26, 2023 at 14:04
  • Is the Ecoflow battery able to supply power back into the socket, or is there protection against that?
    – HandyHowie
    Sep 26, 2023 at 14:08
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    The battery management system in the unit should be able to handle the expected fluctuations in automotive electrical systems. You might want to consider a low-voltage cutoff switch to keep the Ecoflow from continuing to charge from the battery if the main battery voltage drops too low.
    – Jon Custer
    Sep 26, 2023 at 14:57
  • Check if there's a "Klemme X" contact / whether your vehicles has a "Entlastungsrelais" / "X contact relief relay". Its code at Volkswagen should be J59. Everything that's connected to this rail will be disabled while starting the engine. You could hook up your battery to this contact, perhaps with an additional relay.
    – towe
    Sep 27, 2023 at 5:43

1 Answer 1

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The reason for this warning is, when you start the engine of the vehicle, there is a large power draw. This drops the voltage which the Ecoflow battery will see from the charging port. When you shut down the starter draw at the end of the starting process, there is what's called a load dump. The load dump causes the spike. According to the Wiki article, the spike from a load dump can be in the range of 120 vdc in the 12 vdc system. This large fast fluctuation in voltage from low to high can cause damage to electronic equipment.

Probably the easiest way to protect your equipment without needing to plug/unplug it all the time would be to install a surge protector. A cursory glance at such units shows most of them are not plug-n-play, but rather need to be hard wired. This would be a one time installation, though, so once installed, life would be easier.

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  • Surely the "fluctuation in voltage from low to high" can't be any faster than when the device is first plugged in to the socket. It will be going immediately from 0 volts to 13.8 volts.
    – HandyHowie
    Sep 26, 2023 at 14:07
  • @HandyHowie - Updated the answer. Sep 26, 2023 at 14:40
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    In addition to a voltage spike, there can be a brief reverse voltage as well. I have a scope trace from a personal project that shows a very brief (~2ms) negative six volts on a nominal +12V car battery that happened at the moment that a high-torque starter stopped cranking. Reverse EMF from the starter motor. Some electronics don't react well to reverse voltage, lending support to the reason for the warning, though the OP's device is probably fully protected as a mass market product should be.
    – MTA
    Sep 26, 2023 at 15:13
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    As I understand it, shutting down the starter should not cause a "load dump". That term (and extreme voltage spike) is reserved for the event of disconnecting the battery while the alternator is charging it at the full rate. My understanding is that it is never seen to occur in modern vehicles, but automotive electronics are still certified to withstand it just in case. Sep 26, 2023 at 22:52
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    The circuitry which protects the solid state control systems in modern cars will clamp voltage spikes to a lower level than might have been found on some older cars. A typical device designed to plug into a cigarette lighter should be able to survive the voltage excursions that would be found in a typical modern car, but it would be a bit awkward for a device maker to tell people they need to unplug their device if they're using a 1974 Buick, but not if they're using a 2022 Tercel., but the warning would let the manufacturer off the hook fi they leave the device plugged into the Buick.
    – supercat
    Sep 27, 2023 at 18:00

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