RE: [Electric Boats] emergency disconnects

 

Tom,

 

Good luck with your project, it sounds very interesting!

 

An emergency disconnect switch is a necessity, not an option, in any EV traction system whether it resides on land or water (or potentially air).  It is a first-line safety device and anyone who has ever experienced a power runaway situation, such as when main contactors weld themselves shut, will inform that they are absolutely necessary.  This happened to me once in my homebuilt electric car and I was grateful I had the presence of mind to heed these instructions.  Mine was a ”big red switch” made by Albright, a UK company, but there are many firms who build suitable disconnects.

 

One may be tempted to think that there exists less potential for mayhem in the water than on our roads but that belief is false.

 

Another point well worth raising is the subject of overcurrent circuit protection.  I am particularly fond of products made by Blue Sea, which seem uniquely and ingeniously designed specifically for our marine purposes.  For my preferred nominal voltage (48 volts DC), Blue Sea carries a brilliant and professional looking product line called the MRCB 187 http://bluesea.com/category/3/10/productline/overview/14 which is available in both a panel mount (on the helm) or a surface mount (inside the battery box).  It is available in a range of amperages from 25 to 150 (for those using a Torqeedo Cruise 4.0R, use the 100-amp unit).  It is designed (and rated) to be safe in the marine environment we are working in, unlike most other circuit protection systems.  The price for these is very reasonable (well under $100) and they are readily available from most marine suppliers.

 

Another benefit (keeping to the main premise of this discussion) is that there is a reset switch built into the unit.  While I still would not recommend negating the “big red button”, the MRCB 187 reset switch (small yellow lever) does offer the opportunity to disconnect the batteries in a pinch, especially if it is a panel-mount and mounted at easy reach on the helm.

 

Blue Sea offers DC circuit breakers in other voltages as well, as do other manufacturers.

 

As a final caution, I would never recommend using fuses on an electric vehicle of properly-rated circuit breakers are available.  Nothing worse than being caught out with a dead motor and no fuse.

 

Monte

 

After 17 months of part-time building my 21' launch, I'm wrapping up construciton and starting to work out wiring details.
I try to glean all I can from this group and the EV folks. Something I see in the cars, but not so much in boats is an emergency disconnect switch in case of powertrain runaway.
It seems that it might be really handy in the event of a failure to be able to totally disable the battery bank without leaving the helm.
The EVs sometimes use "big red switches" within reach of the driver, and sometimes use a mechanical cable to actuate a switch remotely.
Since I want to keep the battery bank wiring as short as possible, I'm leaning toward the latter method.
This disconnect would be in addition to the keyswitch actuated battery bank contactor and typical fusing.
Any thoughts?
-Tom

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