[PSUBS-MAILIST] Electrical Question

Tue Jun 30 05:02:26 EDT 2015

Hi Guys,

There is of course a fuse inline.  There is for all the electrical items.

But ive realised that even if I insulate the body of the compressor from
its mounting bracket, it wont make any difference as the pipework is still
grounded to the hull.   There's no way I can insulate that, so I cannot
isolate the earth unless I can find how its connected inside the motor and
isolate it there.

But in the meantime, I am going to put a switch on the negative lead as
Keith suggests and just click it on when I need it.

Regards
James

On 29 June 2015 at 21:43, via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> James,
>
> How about putting a battery switch in the negative lead of the compressor.
> Blue Sea makes high current units, that I use to connect/disconnect the
> battery banks on my boat. You can get tham at most marine supply stores
> (Westmaine, Defender, etc.).
>
> That way you can kill the compressor with the twist of the wrist,
> instantly.
>
> Keith T.
>
> Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
> wrote:
>
> >James,in the mean time, why not just put a suitable fuse betweenthe hull
> & - battery connection. The biggest issue, as Sean says, is if apositive
> contact comes off any electrical item on the sub, & makes contact with the
> hull.Then you are shorting the battery & can cause a fire or blow up the
> battery etc.Better still put the compressor switch, or an additional switch
> (or solenoid) in the wiring from the hull tothe negative terminal. Then if
> there is any shorts they won't happen continuously, onlywhen you have the
> compressor on.Alan
> >      From: James Frankland via Personal_Submersibles <
> personal_submersibles at psubs.org>
> > To: Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> > Sent: Tuesday, June 30, 2015 3:45 AM
> > Subject: Re: [PSUBS-MAILIST] Electrical Question
> >
> >Agreed, that would be better.  Not sure if its possible.  I suppose I
> could try and find the negative brush and insulate it.  I can only assume
> the negative brush is in contact with the chassis. This is the compressor
> here.. https://www.google.com/patents/US2450468
> >On 29 June 2015 at 16:00, Sean T. Stevenson via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
> >
> >
> >
> >Would it be possible to disconnect the compressor motor negative lead
> from its chassis, instead wiring it to your negative/common bus, and then
> ground the chassis? If it's easy to do, that would be the better solution
> as it preserves incidental contact safety.Sean
> >
> >
> >On June 29, 2015 8:52:58 AM MDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> >The battery negative is not connected to the hull.   But, the battery
> negative is connected permanently to the negative bus, which is then
> connected to the negative of all electrical items.  So far this has been
> fine as the electrical items are all insulated.  However, in the case of
> the compressor, as the compressor is connected to the hull, and the
> negative connects to the compressor chassis, its opening up a hull
> connection to the negative terminal.  I suspect that if I put my voltmeter
> across the positive battery terminal and the hull, I will get a reading.
> It still wont create a circuit as the positive is of course insulated, but
> I don't want any connections to the hull at all. Im going to insulate it.
> Ive ordered some nylon bolts which I think will do the job, along with some
> plastic washers.
> >On 29 J! une 2015at 15:38, Sean T. Stevenson via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
> >
> >Perhaps I misunderstand. Chassis continuity to hull is a good thing. You
> just don't want to tie your power supply common (battery negative) to
> it.Sean
> >
> >
> >On June 29, 2015 7:56:32 AM MDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> >Hi sean,
> >The battery negative is NOT connected to the hull.  Only the chassis of
> this new item. But thinking about it, I suppose it does create a permanent
> connection to the negative terminal.   The negative wire on the compressor
> is connected to the negative bus on the boat, which is creating a permanent
> connection to the hull via the mounting bracket.   Damn, i'll have to
> insulate it somehow, before Sat. RegardsJames
> >On 29 June 2015 at 14:46, Sean T. Stevenson via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
> >
> >Your electrical system should not be neg! ativegrounded, meaning that the
> battery negative should not be common with the hull / chassis as it would
> be in an automotive system, for example. The reason for this is in part to
> do with galvanic corrosion, since this avoids regular currents and nonzero
> potentials through structural elements, and in part to do with arc safety,
> since a single fault or operator error which connects either battery
> potential to the chassis will not produce a short circuit current through
> the battery in this case. That said, SAFETY grounds, which include AC
> ground and most chassis ground and cable shield connections which are
> confirmed not in common with the supply DC negative, should indeed be
> connected through the hull (either locally or through a dedicated ground
> point) in order to serve their intended function: providing a short path to
> earth-ground potential in the event of a fault that might otherwise
> energizeequipment / chasses that could be hazardous to personnel, and
> serving as a connection to an "infinite" charge sink to reference cable
> shields to for effective noise rejection.A negative connected chassis on a
> DC powered compressor can be accommodated, as you surmised, by isolating
> that chassis from the hull, and additionally should be isolated from the
> operator / cabin (via enclosure?), because the chassis in that case does
> not represent the safety ground potential, and is thus akin to a large bare
> conductor at the battery negative potential.  Alternatively, you could look
> at modifying the unit to break the negative-chassis connection, running
> that negative to the battery and grounding the chassis.Sean
> >
> >On June 29, 2015 6:48:15 AM MDT, James Frankland via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> >Hi All, Ive made a real point of making sure that nothing at all is
> electrically connected to the hull of my boat.  Everything is wired to and
> from the battery and insulated from the hull. However, ive recently fitted
> a new item, a Cornelius compressor which Hank gave me.  Ive realised that
> the negative terminal on the unit is the chassis of the compressor, which
> is bolted to brackets on the hull, so its actually connected to the hull of
> the boat as well.   The hull of the boat is not connected to the negative
> battery terminal. I don't think there is an issue there with galvanic
> corrosion, but im not sure.
> >I could insulate the compressor from the mounting bracket and hence
> insulate it from the hull, but it will be a bloody pain and im diving this
> weekend so don't really want to start changing it now. Thanks
> >James
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