Hi John,
I'm betting I have the same one, just the 30AH version. Typically I'm not a fan of pre-packaged "black box" but this one has served me well. It capacity tested to exactly 30AH. While I don't recommend doing it often, if pushed to the limit, the BMS cuts power for a few seconds and automatically comes back on. Being its only a 20AH battery, for maximum cycle life of the battery I wouldn't push the 50 amp continuous limit for too long. That's a 2.5 C rate.
Personally, I wouldn't worry about a fuse for testing.
Matt Foley
Sunlight Conversions
Perpetual Energy, LLC
201-914-0466
On Wednesday, May 6, 2020, 04:37:36 PM EDT, john via groups.io <oak_box=yahoo.com@groups.io> wrote:
Thomas,
Below are some details of the application:
Boat: The test platform is a home build plywood boat.
Length: 13'
Beam: 5'8"
Weight: (guess) under 400 pounds
The boat has been re-powered with a Torqeedo Cruise 4R outboard. 48V, max input 4KW.
The first experiment was to power the Torqeedo with a bank of four Group 31 Deka AGM 12V batteries.
It worked, but the batteries were excessively heavy, took up a LOT of space, and provided no backup in the event that the primary bank died or suffered any kind of technical failure.
For the next experiment, I'd like to try running the boat on a lithium battery bank, for improved power density, depth of discharge, and overall weight/space.
Since I have zero prior experience with lithium batteries - the first step will be to use an Ebike battery from Amazon. This is a bundled system:
48V Nominal
20AH rating
Sustained current drain: 50A
Peak current: 100A
The battery pack has a built in BMS. However, there are no details about what happens if the BMS trips. It may permanently disable the battery to prevent a catastrophic failure.
In this setup - the motor can pull up to 4KW, but the battery can only provide half that on a sustained basis. If the operator accidentally or carelessly pushes the throttle to full speed, I would expect the battery BMS would trip - possibly permanently "bricking" the battery.
Therefore, I would like to put a fuse or breaker after the battery to gate the max drain of the battery to no more than about 40A. The thought was that if I used a fuse or breaker of about 30A, it would blow before the battery BMS kicked in - giving me the opportunity to either replace the fuse or reset the breaker, and move on.
Protecting the battery with a 30A fuse or breaker should be a very conservative step. All other wiring is being sized to support the current drain potential of the motor - which far exceeds what the battery can supply at this time.
From other responses - it sounds like the fuse/breaker must be rated for DC usage, and that the voltage rating should comfortably exceed the 48V system (with a max charging voltage of about 55V).
John
On Wednesday, May 6, 2020, 09:32:53 AM CDT, THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:
John,
Can you clarify what your application is please? You mention an electric motor that "can pull up to 100A" to be used "in a proof of concept type experiment".
Are you putting the motor aboard a vessel or testing on the bench? [More specifically, what's the potential degree of loss in the event of a fire? If you're running your system on a bench in a controlled environment where the loss might be a burnt wire, that's one thing. But taking people aboard a vessel on the water requires an entirely different standard of care!]
Do you know what motor (nominal rating in watts) the battery pack was intended to power? And what concepts are you looking to prove?
Ampacity of a wire is a function both of diameter/gauge *and* length. In some situations, a 12 awg wire might safely carry 50 amps for brief periods, but it would not be prudent to create such a situation where there's meaningful risk of property or life.
I'm not an engineer or expert by any definition, but I would take the cautious approach, and size my load wires for the maximum expected load and required length of wire. For 100 amps, over a few feet or so, that would mean 8 awg to me. [I'm using 150 amp ANL type fuses and 7 awg wire to my motor that could pull 150 amps.]
Will there be any other loads on your battery? Ideally, each load would have its own fuse, and your battery fuse sized to allow for the entire system.
Take a look at <https://newwiremarine.com/circuit-protection/> for a useful illustration [no endorsement of the vendor intended].
Good luck, and have fun!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, MI
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