Circuit Breaker

[dontsendbubbamail]

Has anyone tried using a circuit breaker like this? http://www.affordable-solar.com/apollo.90.amp.circuit.breaker.htm I know that it might blow the my CC 85 esc if it trips, but I think it would be useful for two reasons. Would 90 amps be right or 100 be better?

1. It would keep the bike from going up in flames.
2. It would act as an emergency cutoff. Tie a string to the switch and to the back of the seat. Then pull string to disconnect when needed.

Bubba

 

[oofnik]

That's not a bad idea. I didn't know they make DC breakers of that size. Not cheap though.
Now if I could find one from a surplus outlet or something...

What's the difference internally between an AC and a DC circuit breaker?

 

[michaelplogue]

Those look similar to the mini circut breakers by Blue Sea:

http://bluesea.com/category/3/12/produc ... verview/21

I got a few of the 100 amp versions of the Blue Sea breakers. Just so you know, the 'spring' that holds these in the 'on' position is pretty weak, and a good jar can cause them to close. I've found that they are less vulnerable to shutting off if they are in a horizontal orientation (conducted some un-scientific drop tests).

 

[PaulM]

Here's a much cheaper option although it is limited to 48 VDC: surplus center

They come in 90, 120, and 150 amp sizes.

 

[northernmike]

I'm using a 58V, 100A BUSS fuse, instead of a breaker.

I wouldn't trust a circuit breaker to protect my equipment unless I was really sure it was built for what I was going to throw at it = high current spikes, vibration, mechanical shock and widely variable humidity and temperature.

A marine grade one might do the trick, but they're not designed to be used as an main power switch. A breaker, by design, is supposed to be a protective element - repeated switching can actually damage them. The idea is if the breaker trips, you figure out WHY before switching it back on.

As for a dedicated main power switch, Blue Sea Systems makes a great selection of battery switches, I'm using a 48V 300A continuous rated one. $32 CDN.

Think about it, cheaping out on the most important thing in your system - the main protection element - probably won't help you sleep at night.

I KNOW that if something shorts, I won't get a plasma arc. I know that repeated switching won't diminish the reliability of my fuse. And I can just look at the fuse and know if it's OK.

 

[Link]

What's the difference internally between an AC and a DC circuit breaker?

There is none, from a technical standpoint.

However, the contacts on equivalent-rated DC ones are more heavily built, since AC tends to snuff itself out within a cycle. DC holds an arc, damaging the contacts more and increasing the chances of them welding together.

 

[TPA]

Square D series QO breakers are rated for 48VDC as well as AC

 

[An average human]

What would happen if you put 2 or 3 30A rated circuit breakers in parallel?

http://www.technobots.co.uk/acatalog/On ... s_426.html
they are cheap (if you live in the uk)

human

 

[northernmike]

What would happen if you put 2 or 3 30A rated circuit breakers in parallel?

http://www.technobots.co.uk/acatalog/On ... s_426.html
they are cheap (if you live in the uk)

human

I'm sorry ... what?

 

[Link]

What would happen if you put 2 or 3 30A rated circuit breakers in parallel?

They'd trip at around 60 or 90A.

But all at slightly different times, and the ones tripping later take more damage.

 

[biohazardman]

I thought about that also but fuses take up less space, are easier to mount and weigh less. They are also inexpensive easily upgradeable and easy to replace when they blow.

 

[rhitee05]

What would happen if you put 2 or 3 30A rated circuit breakers in parallel?

As Link mentioned, the problem here is tripping them at the same time. This would probably work a lot better if you used a two- or three-pole breaker. Those are intended for two- or three-phase AC use, the individual breakers are connected together so they all trip together. Paralleling to get more capacity is not exactly what they're intended for, but it'd probably work. The biggest problem would be that all poles wouldn't be perfectly matched for DC resistance. That would cause the current to divide unevenly, and the breaker is going to trip based on the highest-current pole. You'd end up with a parallel breaker that's rated for somewhat less than the sum of the individual poles, but it'd be nearly impossible to predict exactly what the de-rating would be.

Probably okay for applications where you have a fairly large margin of safety in your breaker size, but not so good if you need a more exact cutoff.

 

[An average human]

i have ordered a few 30a circuit breakers to play about with, but how could I simulate a 60a load ?
(I still haven’t had time to build my bike)

 

[rhitee05]

The biggest problem would be that all poles wouldn't be perfectly matched for DC resistance. That would cause the current to divide unevenly, and the breaker is going to trip based on the highest-current pole.

Incidentally and totally off-topic, this is one of several reasons why people use MOSFETs or IGBTs for these high-current drives, not BJTs. Try paralleling two BJTs and see what happens. They have a nasty thermal positive-feedback characteristic that makes a BJT's "on resistance" (technically the C-E voltage, but same effect) drop as it gets hot. It works fine with one BJT, but with two or more they'll get unbalanced and one will eventually go into runaway. One of my EE professors demonstrated this to great dramatic effect in class one day.

i have ordered a few 30a circuit breakers to play about with, but how could I simulate a 60a load ?

You'd need a really honkin' resistor. 60A at 24V is 1440W (obviously more at higher voltages). I've seen some resistors rated for 200W or so, they're ceramic tubes about a foot long that look like a relay baton. I assume you're only doing a very brief test, so they could take much higher peak power. Figure out the resistance you need and go looking with a multimeter. A space heater would work well, even an AC one (assuming you just use the resistance element). W = 1/2*V^2/R for AC, W=V^2/R for DC. Doing the math, though, you'll probably never find an AC space heater with low enough resistance. Using my above example (60A at 24V) requires 0.4 ohms. For a 120VAC heater, that would be 18kW. Yikes! That's more like a large furnace.

 

[An average human]

When I finish my bike I will try 3 circuit breakers in parallel with a 100a fuse in series and see what blows first. This may be in a few weeks time as I have lots of work to do
And also my motor will only draw about 75 amps so I may need to wire in a few 100w car head lamp bulbs to get to ~90a.
at least the will make nice bike lights
if all goes well the breakers will go before the fuse reliably.

 

[rhitee05]

Try to see if you can find trip curves for the breakers and fuses you will be using. Fuses and circuit breakers don't conduct at 89.9A and then turn off instantly at 90A. Every protection element has a current vs. time curve that tells you how long it will take to break the circuit for a given overcurrent condition. This is where "slow-blow", "fast-acting", etc terminology comes from. TPA previously mentioned QO-series breakers from Square D. Here is a link to their document with the trip curve on page 20:

http://ecatalog.squared.com/pubs/Circui ... 01R108.pdf

At rated current, the breaker will take upwards of 10 minutes to trip. At 2x rated, it will trip in about 10 seconds. At 10x rated, it will trip in milliseconds. Fuses operate on thermal principles (melting the strip), but circuit breakers usually have both thermal (bimetallic strip) and magnetic/inductive mechanisms. For the thermal-triggered regions, you get a curve with an I^2*T shape, based on how much energy it takes to heat up the strip to trigger temperature. Some manufacturers rate their fuses in terms of I^2*T. Different parts will have different curves, but the basic shape is the same.

The point of all this is that even at 90A it'll probably take a while to trip your breakers, unless the unbalance effect is really large. Unfortunately, there's really no getting around the gradual curve imposed by I^2*T. If you can, I'd suggest choosing a fuse based on what your batteries can handle. If they can handle a max of 200A for 15s, you probably want to find a fuse that'll blow in 10s or less at 200A. That provides a maximum rating, your continuous draw is a minimum, so pick something in between and you should be safe.

 

[JEB]

I paralleled 2 50 amp (1 240vac "dual" breaker) [100amp total] on 24vdc into a 132 perm motor (275amp controller) I draw about 250 amps~ for about 1/2 second at a full throttle take off, I have never tripped the breaker. I also use the breaker as a emergency turn off switch, pull cord activated.

 

[northernmike]

Then how do you know your breakers will protect your system in the event that they need to?

 

[JEB]

I don't know, but I also have a 200amp fuse in series with the system, I think the original thought for the circuit breaker
was that for around $11 I could not find a high current latching switch that cheap. I also had the thought that I could
add a 24vdc solenoid to bump trip it with a remote switch.

 

[northernmike]

You guys trying to use breakers as main switches are forgetting that they're not designed for this.

A SWITCH, with contacts designed for a few hundred thousand cycles, is what you need. Breakers are meant to be turned on and off only occasionally, and to interrupt currents at the voltages they're rated for...

Look at marine battery disconnects, I think you'll be pleasantly surprised.

 

[TPA]

Try having a look at Midnight Solar breakers...up to 150V 63A less than $20...meant for PV

http://store.solar-electric.com/mnepv.html

 

[michaelplogue]

I'll be using my mini-breakers primarily as cutoff switches (used in conjunction with regular fuses) for four independent packs running in parallel. That way, if one goes bad, I can easily shut it off using the breaker and continue on with the other three packs - without having to pull cable connections. They will also be useful when connecting/removing packs so I don't get a spark when messing around with the cables.