T-Pain Is On A Boat: Re: Possible SpamRe: [Electric Boats] 48 volt system

Yes. in a floating system you simultaneously disconnect both positive and negative for every circuit. This is why troubleshooting is so easy. Because each circuit can be completely isolated from the system. In a floating system, both positive and negative are considered to be live wires. In a grounded system, only the positive is treated as a live wire because the negative is held at ground potential.

Floating systems have many advantages over grounded systems but they are more expensive and require insulation resistance monitoring.

A lot of people think that the system will float up in voltage away from ground. The resistance monitor prevents this by bleeding any static charge to ground, and provides a "loose connection" to ground. What is more worrisome is if any system gets 120 AC onto the battery pack from a failed charger. A grounded system will not know if this happens, whereas a floating system will give warning so it can be fixed.

It would be nice to float the 12 volt house battery too…..but that is not a practical thing to do with the equipment on today's boats. Alternators and starters are typically grounded. And most boats have water cooled refrigerators, VHF on the mast and other incidental ground points so it is just not practical on the house system.

But a propulsion system is already fairly isolated to the charger and the electric motor and is easy to keep isolated.

If you do ground the propulsion battery, and that shares the same ground as AC and the 12 volt house battery, then troubleshooting has just become a really long and tedious process of disconnecting every circuit until you find the one that is compromised.

I would rather know, by looking at my resistance monitor, that I have a healthy propulsion battery with no faults. This enables higher reliability and confidence in the most important circuit aboard and electric boat - the propulsion motor.

James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103

805 455 8444

james@electroprop.com

www.electroprop.com

On Mar 3, 2018, at 10:46 AM, bob jennings sabre281@yahoo.com [electricboats] wrote:

James, when you refer to double pole breakers on a 48 volt floating system, are you breaking both positive & negative from the battery bank?

--------------------------------------------
On Sat, 3/3/18, James Lambden james@electroprop.com [electricboats] <electricboats@yahoogroups.com> wrote:

Subject: Re: [Electric Boats] 48 volt system
To: electricboats@yahoogroups.com
Date: Saturday, March 3, 2018, 1:01 PM

Either way is acceptable. Grounded
systems are simpler and require single pole breakers.
Floating systems have complete on the fly diagnostics.

Floating systems
require double pole breakers and a ground fault monitor with
alarm.. You can build to E-11 or E-30 but follow all the
recommendations.
Be careful with your solar… to
build a solar array that charges at 48 volts, you need at
least 70 Volts Maximum Power from the panels if you are
using an MPPT charge controller. You will want to have
a ground fault breaker put on the solar array as that
voltage is higher than 48 nominal.
In either scenario, every conductive
metal component that is likely to be energized needs to be
tied into the bonding / grounding system.

Make sure that both
48 volt banks can be switched out and the switch is rated
for 48 nominal and not 48 maximum like all the basic marine
switches are. A switch that can switch under load
should be specified.

James
Lambden
The Electric Propeller Company
625C East Haley Street,
Santa
Barbara, CA
93103

805 455 8444

james@electroprop.com

www.electroprop.com

On Mar 2, 2018, at 3:00
PM, brucenoble@bellsouth.net
[electricboats] wrote:

OK
my head is spinning from all these electric ground post.
some say ground some say no ground.  im getting
dizzy      I am building a small solar boat with a 48
volt motor ,with two banks of 48 volt batteries and
three 270 watt solar panels and  NO hook up for
shore power.....ok chime in please   ground or no ground
to earth....Bruce

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Posted by: James Lambden <james@electroprop.com>

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