Friday, March 2, 2018

Re: Possible SpamRe: [Electric Boats] Re: Electric motor Grounding locations

 

Very well said James. Balancing the safety of an isolation transformer against suddenly Spikey hair and pain seem to bring the cost down. Not to mention the other advantages of variable inputs of an isolatin transformer when plugging in to the grid.
Cheers,
Ric Sanders

On Thu, Mar 1, 2018 at 4:19 PM James Lambden james@electroprop.com [electricboats] <electricboats@yahoogroups.com> wrote:
 

The best piece of equipment that can be installed in a boat for protection from Galvanic Corrosion and Electric Shock Drowning is an isolation transformer.


It is the only piece of equipment that gets the job done right.     

We put them in a majority of our builds.    

The shore power cord and input breakers can then all be GFCI protected without the possibility of nuisance tripping because there is no leakage current on the primary side of a transformer based isolation transformer.

Everything downstream of the isolation transformer should be protected at the GFCI level,  for each individual circuit to prevent nuisance tripping.   

All the metal objects on board the boat including the case of the isolation transformer should be tied together and grounded.   This prevents any one metal surface having a different potential than any other surface and stops the possibility of shock.   

The most important thing is to isolate the boats grounds from the shore grounds.   

If you can't afford an isolation transformer, then get GFCI outlets for every outlet on board the boat and then you will have a fairly decent form of protection for the occupants.    

its only 10 to 20 milliamps to have a fatal shock of AC current, so please, be very careful.   In my opinion AC is the most dangerous component on any boat which is why we treat it so vigilantly.   All of our AC is housed in waterproof PVC non-conductive boxes.    We don't take any chances on AC at all.    

Its easy to become complacent with AC because we use it all the time.   But AC around water is a completely different story and necessary protections should be in place to keep it safe.    






On Mar 1, 2018, at 10:49 AM, Carter Quillen twowheelinguy@yahoo.com [electricboats] wrote:

 

I would concur the best course is to avoid higher voltages and stay below 48V. There is a good reason why the standards change dramatically above 48V and if you're operating in a salt spray environment on a vehicle with a lot of relative motion that could easily promote wire chaffing scenarios you have a formula for disaster and death with high direct current voltages. IMO (Not to mention what could happen if you're boat is sinking)

My understanding is the problem with chassis grounding your higher voltage systems, especially 120VAC, on your boat is the potential for galvanic corrosion if you develop a partial ground fault in ANY of your equipment or appliances that's not big enough to trip the breaker. This allows current to leak from your boat and can ruin anything bonded to your ground thruhulls, prop, shaft, etc.  That's why I would prefer the use of a dedicated dyna plate for a high voltage ground. Another good but also expensive solution is a GFI protected main breaker but the objection to this is often nuisance trips. 

While I do NOT recommend it to others, my high voltage systems on the Arc are not grounded because of a fear of galvanic corrosion within the steel mesh of the ferro cement hull that might slowly dissolve my boat from the inside out.  If I had the extra cash I would definitely install a dyna plate and that is my intention at some point in the future.

Capt. Carter

On Thursday, March 1, 2018, 10:11:36 AM EST, James Lambden james@electroprop.com [electricboats] <electricboats@yahoogroups.com> wrote:




The Resistance monitor provides any necessary bleed path.

Its my understanding that any differences in potential between the 48 volt bank and ground have very little energy and are at most static buildup charges.   Even in a lightning strike that hits the grounds of the boat,  the potential difference is very small.

What is more of an issue is if the 48 volt charger fails and puts AC line voltage onto the battery pack.   At that point, the Ground Fault Monitor should disable any AC charging source.   Since AC is grounded, the Resistance monitor will pick up this fault.   








On Mar 1, 2018, at 6:10 AM, Chris Morriss chris.morriss@ouroboros.myzen.co.uk [electricboats] wrote:

 

Certainly float the ground, and use double-pole breakers, but I suggest you add resistive bleed paths from the + and - feeds to the boats hull or other metalwork to prevent a potential difference building up.

You could also use symmetrical transient absorbers (Transorbs or similar) to ensure that any PD doesn't exceed SELV safe limits.


On 01/03/2018 13:12, king_of_neworleans wrote:
Good answer, makes sense. I know you have repowered quite a few boats, James. Have you tried doing any with grounded banks, and actually seen electrolysis become a problem?


---In electricboats@yahoogroups.com, <james@....> wrote :

At 48 volts, The reason why we float the ground is to prevent possible corrosion of the through hulls and propeller.  At higher voltages, the ground is floating for safety and reliability purposes.

Floated ground systems can be monitored for ground faults, whereas grounded systems cannot.  

Floated Ground Systems require double pole breakers throughout.   The negative is treated as a live wire requiring circuit protection.   

I like isolating the 48 volt battery (floated ground)  because it makes it easier to troubleshoot and to monitor..    When you add a Resistance Monitor, you end up having an on board megger for every circuit.    














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