Phantom volts

[pcatterall]

While doing a bit of wiring I thought it prudent to switch off the batteries I tested the cable I was working on and noticed about 0.4 volts was still present.
The batteries are straight to the on off both switch and there were no extra wires or batteries. I tested accross the main bus bar and got nothing but testing across the main connections under the instrument panel gave the same voltage. I disconnected both battery banks but still had 0.4 volts. Have I discovered free energy??

 

[richardabeattie]

Nobody prepared to kick off but as an Ex R Signals officer I cannot resist.

Your voltmeter is not zeroed.
You are moored downwind of Jodrell Bank/under a power cable and are being irradiated.
You have a short circuit between your system and your iPod
You have overpaid on your last electricity bill and they are smuggling volts into your boat to avoid paying you a rebate.
You have recently combed your dry hair and generated static.

 

[fishermantwo]

Common fault using a digital meter. I can get a similar reading by putting the probes onto timber bearers in the engine room of my fishing vessel. I got panicky and had my mate who is an aircraft electronics engineer explain and demonstrate to me. Analogue meter wont show these false voltages.

 

[jwilson]

One of the bits of electronics might have a smoothing capacitor on the power input circuit with a bit of charge still in it ???

 

[jimbaerselman]

A salt solution between dissimilar metals, one each side of the circuit, creating a battery?

A salt solution bridging the 'off' switch?

ps - check for zero error by reversing your meter connection, looking for a negative where there was a positive.

 

[whipper_snapper]

Try setting your meter to 'Amps' and measuring the current straight across where you measure 0.4V.

If it is a 'real' voltage you will probably blow up your meter! But it isn't, so you won't! If you see a true sustained current then something is going on. But I predict you will see nothing, or possibly a flicker the instant you make the connection and then nothing. In which case, forget about it.

(But do make sure the battery is off or you certainly will melt your meter)

 

[pcatterall]

Thanks guys for your suggestions.
The meter is zeroed, as I said I am getting zero in many places but this voltage on other parts of the circuit.
Yes, I thought there may be leakage ( dirty salt water etc) but my final test was to completly remove all the battery connections. Will try the recommended test and see if I can blow up my meter!!
Thanks again.

 

[30boat]

My multimeter won't blow up if used that way,it just displays a battery sign.I've made that mistake before,that's how I know.