Why is There Still Power in My Electrics For a Short Period After I Disconnected?

[Shanaly]

Hi - I disconnect the batteries with the Cole Hersee - but if I turn on a lamp or the vhf they both light up for a couple seconds before (understandably) going dead. That seems to drain any excess power lurking in the system!

I s this normal?!

[daddle]

Some device connected to the circuit has a large bypass capacitor on its input. Not a perfect design in such a system but sometimes unavoidable. Common in boats.

[Paul Elliott]

You probably have some bit of equipment connected that contains a filter capacitor. This capacitor stores electrical charge, and is feeding the VHF, etc, until it discharges. This is completely normal, but it tells me that not everything is disconnected and/or switched off (in particular, the thing that contains the capacitor). This is probably just fine, but you should know what is and isn't connected.

[stevensuf]

a funny thing about capacitors , is they tend to self charge after a period of time, always beware of any high voltage ones, even if disconnected, they can be lethal.

[Redline452]

Definitely something with filter capacitors, likely something(s) electronic: VHF, AM/FM radio, etc.

Way back I worked on on a friend's boat that had a "battery eliminator" 12V supply intended for motor homes or trailers - it was basically a transformer-rectifier that put out about 13V RMS... when not filtered. Unfortunately connecting it in his boat added his radios' filter capacitors to the circuit, bringing the DC voltage up to nearly the 1.4 PEAK - something around 17-18 volts, which eventually fried his batteries (not for the first time).

He was looking for a cheap solution, but a regulator would have cost more than replacing the "battery eliminator" with a proper charger.

In your case, it's not a problem, just the way things work. You can figure out who/what is contributing the capacitance by switching off or disconnecting things one by one and repeating the battery-switch test.