Battery protection - fuse or circuit-breaker?

[Zerogee]

Do most folks on here use traditional glass fuses for battery protection, or resettable circuit-breakers?

In my case, the battery is to run a Tam DRS receiver that is rated at 3A continuous, 5A brief peak, with its own cutout that trips at 5.6A (according to the instruction manual). The DRS Rx output will then feed a Massoth XLS which in turn drives the loco.

Should I use a 5A fuse or circuit breaker on the battery?

Jon.

 

[sparky230]

A Fuse will give roughly a 5 second disconnection time a Circuit breaker will be about 0.5 sec , but make sure the circuit breaker is rated for dc. many are rated for ac only.

 

[Zerogee]

Thanks Sparky! Sorry if this is an idiot question from a non-electrician, but what's the difference between a breaker rated for mains voltage AC, and one for low voltage DC? Will both still trip at the same amperage?

Jon.

 

[sparky230]

It depends how the trip coill is wound, you can usally find out in the specifications what a breaker will work on,

For example one i have at home is rated 230v ac or 50v dc.

 

[Zerogee]

Thanks again.
I asked the question of Rapid's tech team, as to whether one of their miniature circuit breakers rated at 230V AC and 5 amps would be suitable for use at 15V DC - their answer was yes.

I'm assuming that the tripping of a breaker (like the blowing of a fuse) occurs at the same fixed Amperage, irrespective of what voltage is being put through it? Otherwise, surely they'd have to specify an exact voltage it had to be used at, not just an "up to" range...?

Again, apologies in advance if these are stupid questions to a trained electrickery expert....

Jon.

 

[sparky230]

Not quiet

Usally a AC breaker will work on DC up to 1/5th of the Rated AC voltage, but some ac magnet trip coils will not trip with any amount of DC

Current Wise they are the Same, but the response time may differ, be interesting to see if rapid have the trip curve for the breaker on DC

 

[Rhinochugger]

Nah

Why use glass?

On my one two battery locos with a fuse, I use automotive fuses that plug in. You can buy the sockets on evilbay because you can get an in-line variety. Then you can choose your popping current - 1amp, 2 amp, 5 amp, 10 amp seemples

As to circuit breakers, you can get a variety of 12v circuit breakers from Maplin, again just choose your popping current.

The amperage is not that crucial if you're not protecting delicate electronics. In our case, we're only looking to protect against a short circuit which, with the power ratings of modern batteries, can be potentially catastrophic (don't ask me how I know - there was on article on Gscalemad :-X :-X )

 

[nicebutdim]

I use polyfuses, http://www.ebay.co.uk/itm/5x-RESETTABLE-FUSE-POLYFUSE-PTC-RADIAL-60V-ROHS-Compliant-900mA-2-5A-/181079501492?pt=UK_BOI_Electrical_Components_Supplies_ET&var=&hash=item2a292deab4

 

[spoz]

I would have thought a simple quick blow glass fuse would be ok for the TAM RX.

Agreed. I don‘t specifically know the TAM so I'll defer to those who do, but I do use RXs with integral
protection, and I've always found fast blow switches, automotive blade type in my case, to be more than adequate

 

[gregh]

It doesn't matter what you use. Just decide on price and the ease of resetting. The speed of operation really isn't an issue. The whole requirement is to protect the wiring from melting and the supply/transformer or battery from overheating.
Just choose something with a trip setting a bit above your load or the rating of your supply.

How often do you get a short circuit? If it's often, you don't want to be replacing fuses all the time. I prefer Polyswitch.

Also, circuit breakers come in two types - thermal type which are slower acting and magnetic which operate quickly.
With circuit breakers, you have to consider 3 things:
the trip or operate current ie about the same as your load
the current rating of the CONTACTS which break the current - for DC this is only about 1/5 of the AC current rating.
the VOLTAGE rating of the contacts - see Sparky230's comment