Thread: Batteries
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[email protected] pfjw@aol.com is offline
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Default Batteries

On Monday, October 10, 2016 at 1:29:43 PM UTC-4, Phil Hobbs wrote:


Sure, but if it ever had enough torque to start up against the load,
that amount of current wouldn't blow the fuse. Of course it might be a
super slow blow variety that eventually went, but saying that the
current went up because the voltage went down makes no sense unless it's
using a SMPS.


Phil:

Here is the scenario:

a) Go-Buggy has what passes for a full charge, and off the rider goes.
b) At some point, the battery starts to "run down". Voltage drops.
c) There is a magic moment when the battery *cannot* put out enough current (combination of voltage *and* amps) to start the motor under load. Say, a small hill.
d) As this very cheap device has a brush-type DC motor, the battery is now dead-shorted across the fuse. As you suggest, that fuse is likely a very slow blow device, also rated well over the actual 'normal' operating current. It is designed to protect real-estate vs. the device.
e) *POOF* goes the fuse, along with, effectively, the battery.

It is not so much that the current went up. The battery DEAD SHORTED.

Try it yourself. Get an inexpensive 12V DC brush-type motor. Feed it with a sealed lead-acid battery and measure the current. Get a fuse at 3X that rating. Clamp the motor shaft so that it cannot turn. Turn on the power. *POOF*. Even if the battery is on its last legs, making say.... 9V, the amount of current a lead-acid battery can put out is pretty massive even then...

Again, this is a BRUSH-TYPE motor.

http://www.monsterscooterparts.com/m...-motor-brushes

Nor are the controllers much of anything.

http://www.monsterscooterparts.com/2...MG7RoC42bw_wcB

I pay more for my R/C submarine control devices - which do have current limiters and also high-temp shutoff capacity. And a fail-safe that blows ballasts tanks and 'floats the boat'.

Peter Wieck
Melrose Park, PA