T-Pain Is On A Boat: [Electric Boats] Fuses, Circuit Breakers and Switches

Sunday, March 13, 2011

[Electric Boats] Fuses, Circuit Breakers and Switches

Jim,

Another thing to remember is the voltage ratings of fuses.

Many fuses are being used that are 32 volt, 48 volt, even 58 volt fuses. I am changing the battery pack out on an electric truck right now and they employed 32 volt fuse on a 96 volt truck. Not a good idea.

But it's not just the rating that matters. Fuses need surface area otherwise a hot spot will be created on the fuse surface that ends up tripping the fuses.

The next set of ratings for these fuses are at 175 volts, which is what we are now recommending and supplying with our drives.

DC power is very inductive and does not want to stop flowing. If an arc is created, the length of the sustainable arc is proportional to the voltage. Using a fuse that is under rated, or even one that has no headroom is not a good idea. We are building and designing systems that are using huge currents on a continuous basis so everything will build up heat and even more so if it is not designed to dissipate heat.

The ultimate in safety of a system is to have a circuit breaker capable of breaking under load for a system shut down, and fuses on each battery bank. An aluminum boat should have fuses on every battery that is near an aluminum structure.

Most switches are rated at 48 volts but the electric drives regularly see 58 volts when charging so these 48 volt switches are under rated. 48 volts maximum is different from 48 volts nominal. Most Switches are not capable of switching under load, and they should be termed isolation switches and marked not to be switched under load.

The safer we can make these systems, the better off we all will be, as a group and an industry.

A comprehensive look at safety systems on boats would be a good idea, because the amount of electrical power stored in one of our large battery banks is huge.

It does not cost that much more to incorporate adequately rated components in our systems.

James

On Mar 13, 2011, at 11:38 PM, luv2bsailin wrote:

Thanks Tom.
I had a feeling I was missing something LOL. Looks like I'm a couple years out of date. That's the "over 50V" one right? Now I have to go find a copy of that one. Guess I should have asked my brother Scott, I'm pretty sure he's an ABYC member and has all that stuff. Too bad he's 2000 miles away or I'd go steal his copy.
Anyhow, I was shooting from the hip as usual, now I feel like a dumb-ass, as usual.
Those AWG sizes still seem way big to me, though my background is in aircraft wiring where they cut things a little finer due to weight concerns and also use higher-temp insulation. I'll be interested to see what TE-30 says and what is their rationale for such conservative wire sizing.
Anyhow, another "for what it's worth"...
I put together a little spreadsheet that shows various allowable wire lengths that would give a 3% of 48V drop at 100A. You can scale it up or down as it's just simple Ohm's law.
awg ohm/ft len amps drop
6 0.0003951 37 100 1.46
4 0.0002485 58 100 1.44
2 0.0001563 92 100 1.44
0 0.0000983 146 100 1.44
00 0.0000779 185 100 1.44
What I take away from this is that voltage drop in the wire is NOT the main driver in wire gauge selection for the lengths we typically deal with in our boats.
I think I'll read up on what the current standards say about fuse sizing before blathering on about that in detail. Suffice it to say, the fuse needs to be sized to protect the wire from meltdown in the event of a dead short.
I hope somebody finds this useful.
Regards,
Jim McMillan

--- In electricboats@yahoogroups.com, "Tom" <boat_works@...> wrote:
>
>
>
> It looks like James used TE-30 Table 1.
> -Tom
>
> --- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@> wrote:
> >
> > For what it's worth, I've been reading ABYC E-11 "AC and DC Electrical Systems on Boats", and the way I read it, E11.14.2 "Conductors for DC Systems" is what we should go by in this case.
> >
> > 11.14.2.7 "Conductor Size" refers to "Table VI" which gives the following conductor sizes for wire with 105 deg C insulation:
> >
> > Table VI-A "AC & DC Cirsuits - Allowable Amperage of Single Conductors NOT Bundled, Sheathed, or in Conduit"
> > AWG Amps
> > 6 120
> > 4 160
> > 2 210
> > 0 285
> > 00 330
> > Also, these are the figures for wire outside engine spaces.
> > The "inside engine space" numbers are around 30 to 40A lower than those listed above in this size range. One could argue that they don't apply unless it's an ICE engine or similarly warm space. The ratings vary considerably depending on wire insulation temp rating, inside/outside engine spaces, inside/outside conduit or sheathing, and whether or not it's bundled with other wires. The point is to prevent the insulation from being compromised by heat.
> > Some wire has a much lower insulation temp rating, so it's important to factor that in.
> > The second wire sizing consideration is voltage drop. ABYC 11.14.2.6 is a bit ambiguous on this. It basically says 3% is the max acceptable on circuits where drop must be kept to a minimum, and 10% where drop is not critical. Not sure where to draw the line here. I guess I'll work some examples and see how it comes out.
> >
> > The third wire sizing consideration (and probably most important from a safety standpoint) fuse or breaker size.
> >
> > Jim
> >
> >
> > --- In electricboats@yahoogroups.com, "luv2bsailin" <luv2bsailin@> wrote:
> > >
> > > James,
> > > Can you please reference which specific "chapter and verse" of ABYC you're looking at? Your numbers look awfully conservative to me. Not that there's anything wrong with being conservative, but I think it is possible to overdo it. For instance putting big stiff cables on too small terminals can cause problems.
> > > Anyhoo, I think it could be a worthwhile excercise to work through a "test case" scenario here on the forum, listing specific pertinant ABYC guidelines along with operating assumtions and such, with the goal of arriving at what would be considered an "approved" installation.
> > > From what I've seen of the ABYC guidelines there is room for interpretation in a lot of areas.
> > > What do you think?
> > > Jim McMillan
> > >
> > > --- In electricboats@yahoogroups.com, James Lambden <james@> wrote:
> > > >
> > > > Richard,
> > > >
> > > >
> > > >
> > > > According to ABYC code:
> > > >
> > > > 00 cable with 105 degree C insulation temperature
> > > >
> > > > - in an engine space 162 amps
> > > > - outside engine space max 30 degrees C ambient temperature: 182 amps
> > > >
> > > > 000 cable with 105 degree C insulation rating
> > > >
> > > > - in an engine space 187 amps
> > > > - outside an engine space max 30 degrees C ambient temperature : 237 amps
> > > >
> > > > 0000 cable with 105 degree C insulation rating
> > > >
> > > > - in an engine space 209 amps
> > > > - outside an engine space max 30 degrees C : 266 amps
> > > >
> > > >
> > > > As a general rule of thumb we are even more conservative, recommending 100 amps on a 2/0 cable.
> > > >
> > > > What is very important to consider is the crimp, and the contact area of the lug, to avoid hot spots.
> > > >
> > > >
> > > > James
> > > >
> > > >
> > > > http://www.propulsionmarine.com
> > > >
> > > >
> > > >
> > > >
> > > > On Mar 13, 2011, at 3:53 PM, Richard Mair wrote:
> > > >
> > > > > Just wondering what wire sizes people are using to set up the series connections on the batteries and connect them to the motor..
> > > > > 48 volt system with a max draw of 100 amps. Most times I expect to be in the 20 amp range from the anticipated figures
> > > > > Thanks Richard
> > > > >
> > > > >
> > > >
> > >
> >
>