[Dprglist] [Dprg_roborama_committee] Circuit Breakers

John Swindle swindle at compuserve.com
Fri Nov 20 09:43:47 PST 2020

Ron and Carl make important points: Fuses and circuit breakers limit the overload, but the fault has occurred, and the fault likely caused some damage somewhere, maybe in a place that you can't see. As Ron said, with more experience and more care, there are fewer faults. Someone taught me long ago that if I felt that I needed a circuit breaker instead of a fuse, then maybe I was not being careful enough. And three more observations: 1) Some circuits, such as a LED light bulb that failed when it fell into an aquarium: When I tore into it, I found a sacrificial component that blew out much faster than either a fuse or a circuit breaker. Cheaper and faster than fuses. 2) Fuses always blow, at some point even when never passing more than rated current, since they work by heating and deforming the link. Circuit breakers that accumulate also trip even when there is not a fault. 3) As Carl said, active protection is always better, though more expensive. Voltage regulators, zeners, crowbar circuits, sacrificial semiconductor junctions, are all faster and safer than fuses and circuit breakers.

John Swindle

-----Original Message-----
From: Carl Ott via DPRGlist <dprglist at lists.dprg.org>
To: Ron Grant <deltagraph at aol.com>; dprglist at lists.dprg.org <dprglist at lists.dprg.org>
Sent: Fri, Nov 20, 2020 10:20 am
Subject: Re: [Dprglist] [Dprg_roborama_committee] Circuit Breakers

Keep in mind that    
   - some Lion and LiPo packs have protection circuits built-in.  Such circuits often protect against over-charge, over-temp and short-circuit events. I personally strongly prefer such packs, as they provide a layer of protection as close to the risk (energy source) as possible
   - Especially if you use batteries w/o such protection circuits, fast-blow fuses and circuit breakers can help prevent catastrophic battery events, in addition to load issues
   - But even if you DO use batteries with built-in protection circuits, fuses and breakers should help avoid damage to loads / circuitry / your-fingers / things-which-could-be-damaged-by-super-heated-wires-and-chips-acting-like-heating-elements-before-they-fuse
It's all about managing the unique benefit of Lithium chemistries compared to earlier chemistries - Lithium based batteries have relatively higher energy storage density per weight and volume -and can typically deliver considerably higher peak and sustained amperage...  So be careful about what you 'ask the battery to dump power into' - whether you 'ask on purpose' or 'by accident'...
Food for thought...


On Fri, Nov 20, 2020 at 9:48 AM Ron Grant via DPRGlist via Dprg_roborama_committee <dprg_roborama_committee at lists.dprg.org> wrote:

 Thanks for sharing -- they look pretty handy.
Funny thing is when I started using fuses on my robots was about the same time I 'stopped' having short circuits, overload conditions.Just me saying...  Maybe humor intended.
Would be nice to know if a lipo is concerned with duration of current surge from say accidental short. Just thinking fuse can blow quicker, but maybe not important.  Maybe having both fuse and breaker in series for ultimate safety?  Or just live on the edge?
Nice polarized power connectors sure are handy. In the early days I think things like screw terminals prompted me to use inline fuses to after popping a few lipo packs.

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