Richard,
Each battery requires a fuse within 6 inches of the 48 volt battery terminal though sometimes this is not practical. If the battery has a lug terminal, the fuse can be bolted directly to the lug which is preferable. If the fuse has a fuse holder, then often it will be more than 6 inches. In any event it is very important to further protect the battery cables with split loom or other form of insulation.
The overall fuse value should be slightly more than the peak current of the system. Peak current of the system occurs when the boat is at full boat speed and full reverse is engaged. This only happens for several seconds and a Class T fuse is a slow blow fuse so you don't have to have much extra. We typically fuse our systems at 225 amps which is plenty.
If you have two battery packs and want to be able to run on either battery pack you would use a 225 amp fuse on each battery pack, but when the batteries are combined this would then increase the total fuse rating to 450 amps which is excessive, so where the two wires join together you should place a third fuse.
Quite often we don't use the fuse that is located on the controller because the controller has already been protected at the battery level.
Be creative with the split loom. You can buy large split loom up to 2 inches. The overall objective is that there is no bare current carrying metal in the system and as much as possible all current carrying metal is doubly insulated. You can split apart the split loom to cover the entire battery terminal, fuse and all.
The purpose of a fuse is to limit the short circuit current potential of a battery. As batteries increase in energy density it becomes even more critical. Consider a 400 amp hour Lithium cell. It has a short circuit current potential of 4,000 amps. Multiply that by a system voltage of 48 volts and you now have a short circuit power potential of 192 KW! With Lithium it is advisable to fuse at the 12 volt level bringing the potential of 48 KW (12 x 4,000 amps) down to 2.7 KW ( 12 x 225 ).
Although we have never seen a fuse blow in one of our systems, it is advisable to carry an extra fuse along anyway. The big reason why we don't see blown fuses is because the controllers are current limited.
Ignoring safety issues creates issues we don't want to contemplate. If we concentrate on the safety issues, then we can make our electric boats the safest boats on the water!
James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
jlambden: Skype
On Jan 3, 2014, at 7:14 AM, R&M <fullkeel2000@yahoo.ca> wrote:
Both packs come together before the contractor. Thought about 2 fuses but in parallel this would change the protection value. To James The shore power is separate and operates as if plugged into an outlet. In fresh water now with no isolator. In the frozen north won't be a concern till Spring.RichardSent from Samsung mobile
boat_works@yahoo.com wrote:
Hi Richard,
Only one main fuse?
Looks as if you should have one for each bank.
-Tom
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