Fuse for SPM-48500 Controller

kobx

In anticipation of receiving my new SPM-48500 Controller, 2AWG Wires, and HD F/R switch I ordered from ScottyB, I've been reading/prepping for the install.

I noticed the SPM-48500 Controller calls for a fuse to be installed at the battery. Couple of questions:

1. Does anyone know if Scotty supplies this fuse with the kit?
2. If not, where can I buy this fuse (ANN400) ?
3. If the controller is rated at 500A, with 576A peak (I think), why does it call for a 400A rated fuse? In other words, if the controller will allow 500A to pull from the battery, why wouldn't the 400A fuse blow?

BGW

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scottyb

The fuse is included along with the mounting hardware.


As for why the fuse is sized the way it is you need to ask an engineer. I suspect it has to do with the fuse burn rate being very slow & given the cart motor can will only draw MAX amperage for seconds before it increases rpm and reduces draw.

kobx

Volt_Ampere

That fuse is not going to protect the controller. It may prevent a meltdown though.

JohnnieB

The ANN400 Fast Acting Fuse will pass 400A forever and it will pass 4,000A for about 0.1 Seconds, 3,000A for about 1.0 Seconds, 1,000A for about 150 Seconds and 600A for about 1,000 Seconds.

Unless you try to push a brick wall, uproot a tree or do something else that keeps the cart from moving, the motor (and I mean any type DC traction motor likely to be used in a golf cart) isn't going to be electrically capable of drawing anywhere near 600A for more than a few feet off the starting line, which shouldn't take anywhere near the nearly 17 minutes it would take to melt the fuse element in an ANN400 with 600A of current flow.

Also, a SMP48500 won't pass 575A more than a few seconds at most, 500A for 2 minutes and 420A for 5 minutes without shutting down.

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The thing to remember about fuses is that they are fire protection devices, not equipment protection devices.
In fact, electronic devices, such as a controller typically protects the fuse from blowing. (Don't ask how I know. )

Also, The "Fast Acting Fuse" in description of an ANN type fuse, doesn't mean they act fast, only that nothing has been added to delay the fuse element from melting open.

kobx

Thanks Johnnie. Can't help but wonder why have the fuse, or in other words, what event would cause it to see the amps at the time needed to blow it?

JohnnieB

The aftermarket controller companies probably recommend using them for liability reasons since golf carts have started fires that have burnt down barns, garages and houses.

It depends on where the fuse is physically located in the series loop.
If in the main B- or B+ cable from battery pack to controller, it would take a catastrophic failure of the MOSFETs in the controller, or catastrophic motor failure, but the MOSFETs usually burn open before the fuse element does.

If the fuse is inserted into one of the interconnecting cables within the battery pack, a dropped wrench or a shorted battery might blow the fuse before anything caught on fire.

FWIW: I exploded the armature of a stock PDS motor, which took out the DCX400 that was feeding it, but the ANN250 fuse in the B- cable stayed intact.

BTW: I was looking at the wrong Time-Current chart. The numbers I posted were for the AJT family of fuses, which are time delayed. The Amps vs Time for the ANN family is about half of what I listed.

Attached is the chart for the ANN family from 35A to 800A ratings.
Looks like 0.01S is 4,500A. 0.1S is 2,000A. 1.0S is 950A and so on.

Attached Images

Average Time-Current opening current for ANN fuses.jpg (148.9 KB, 0 views)