Do you use a fuse or circuit breaker?

[BIG BEAM]

This is something I never thought about because we never used to use them in the R/C world years ago.Most of the wires are out in the open so I just didn't use one.What say you.
DON

 

[neptronix]

Both. I noticed my connectors would try to weld to each other ( plus ya know... giant blue spark ) every time i connected my battery so i knew i had to go with a switch!

If you are next to a harbor freight, and you are not using crazy amperage, check this out:

http://www.harborfreight.com/battery-cut-off-switch-92688.html

This will work good for mid-low power setups.

As a bonus, the key is removable from the switch... so it gives you a bit of security also.

 

[boostjuice]

I use a contactor (one of these) operated by a kill switch on the handlebars, together with an inline fuse.

 

[Alan B]

Quite a contactor! Do you precharge the motor controller to avoid welding contacts?

I plan to use maxifuses, 6 gauge wiring and Anderson SB-50's, at least up to the controller.

 

[boostjuice]

Quite a contactor! Do you precharge the motor controller to avoid welding contacts?

I do use a precharge resistor, but being as the EV200's are hermetically sealed with Nitrogen gas to avoid oxidisation of the contacts during arc-over, it is only to maximise the cycle life of the contactor, which is in hindsight not a concern for my battery voltage (16S LiFePO4) as it should be good for ~10,000 make/break cycles @ 1000A. (Without measuring it, I'm pretty sure the inrush into my motor controller capacitors is <1000A :lol: )

Here's my setup;

 

[deVries]

Quite a contactor! Do you precharge the motor controller to avoid welding contacts?

I plan to use maxifuses, 6 gauge wiring and Anderson SB-50's, at least up to the controller.

Hi Alan, I see you are one of the advanced elec-experts on ES having read just a few of your posts...

Hope you will have time to post pictures and a diagram of this set-up if possible. I'm going to build a few home brew ebikes, so I'm looking for the best ideas to use. Unfortunately, I'm not an expert at any of this!

Are you also doing some form of design to do an LVC on-board protection for your battery set-up or using someone's design(s) here on ES? Same question for a BMS or HVC/LVC CMS set-up?

Thanks for pointing me to any posts you have done, or could recommend, or could pass on your ideas in a reply here or elsewhere.

 

[johnrobholmes]

I stopped using precharge resistors a while back, they are just annoying to me. Instead I have a small sacrificial plug that gets plugged in first with spark, then the bigger plug.

 

[deVries]

I stopped using precharge resistors a while back, they are just annoying to me. Instead I have a small sacrificial plug that gets plugged in first with spark, then the bigger plug.

Hi John, could you explain this in more detail please. Not sure what you mean by sacrificial plug and how you connect in (parallel or ?) by putting in the bigger plug in 2nd, & these plugs are what?

Thanks!

 

[johnrobholmes]

Example, for my negative battery to controller lead I have both a 75a and 45a andersons plug. First I plug in the 45a pair, with a nice spark. Then I plug in the 75a pair that does the real work and the capacitor is already charged with no waiting.

 

[deVries]

Example, for my negative battery to controller lead I have both a 75a and 45a andersons plug. First I plug in the 45a pair, with a nice spark. Then I plug in the 75a pair that does the real work and the capacitor is already charged with no waiting.

So one can just go with a low-amp connector, say 20-30 amps for first connector with capacitor, for less than 60v DC and get a small spark... but with what size capacitor for that voltage?

Thanks!

 

[johnrobholmes]

Since the smaller plug is sacrificial and will get ruined over time anyway, it really doesn't matter what voltage or capacity. I have used 45/30 amp andersons, 4mm bullet plugs, and even just plain wire.

 

[amberwolf]

On CrazyBike2, I use a big CB of a type used on some powerchairs, but it is mostly a kill-switch in case something goes wrong. That was a necessary thing with my previous brushed motor setup, as a failure in a brushed controller is likely enough going to short full throttle. On CB2's setup, that meant enough instantaneous power to taco chainrings, break chains, and rip the wheel out of the rear dropouts with the chain as it folded up into the chainrings. So, kill switch.

It's the big gray thing on the toptube in the middle of the pic, right between where my knees end up so I can just reach down and flip it should all else go wrong, if it doesn't pop by itself from overcurrent (would take over 100A sustained to do that).

There's also fuses in each of my packs (2x 24V NiMH at the moment) in series between each of the pack halves, so that if something were to short across cells or something, in theory the pack fuse should blow and save the rest of them, depending on how it happens. It's a 30A fuse, and so far it doesn't blow even when pulling up to 42A for a few seconds at a time, and 31-33A for about 10 seconds or so (though I think it probably ought to). But those fuses are only there to save the packs, not the system as a whole.

 

[Jeremy Harris]

I hate the way contactors, big switches etc take up so my space on the bike. My solution to being able to disconnect the battery from all the high power wiring is a simple pull cord link:

The keyswitch on the left of the dangling key turns power on to the controller (the low current feed), the 'fuel gauge' (which gives me an indicator on the bars that the power is on) and also applies power to a pre-charge resistor that takes under a second to charge the controller capacitors up. The main power link is just a small Deans Ultra connector wired as a shorting link. These are rated at 70A so this works fine for this bike. I tied a bit of string to it and put some heatshrink around it to isolate the terminals. It's a tight fit, so won't drop out, yet can be disconnected quickly by just tugging the string (which makes a handy key ring). The string could be fitted to a safety lanyard clipped to your belt, so that if you fell off the main power would disconnect.

This gives me a high power switch, an easy emergency disconnect and a pre-charge switch that stops the sparks when I plug things in. It also makes for a reasonably good anti-theft/accidental operation device, as it's unlikely anyone would have both a key and a Deans shorting link with them.

Jeremy

 

[knoxie]

Nice!

Yes I agree Jeremy I don't like to see big contactors on bikes either, it depends on the bike of course some bikes on here its not a bad thing
as there are some bikes which you wouldn't want to take your hand off the bars to pull out the lanyard if your throttle stuck.

Its funny as I have had a throttle failure on the BMX (Cheapo hall throttles) and I had a kill switch, it happens so damn fast when it goes
the few seconds I had to react weren't enough to stop me before I hit something! ha ha.

I still think if properly implemented the brakes are a pretty safe option, after years of riding bikes its the most natural thing to do but
not easy to implement of course without extra switches switching big contactors.

I suppose a cable operated version of your system would be ideal maybe using an old gear shifter? however you still have to rely on
your reactions.

We don't see a lot of safety measures taken with a lot of builds so I am all for it mostly even if they are a bit on the ugly side
I like your design nice and simple and suitable for nearly all but the most powerful machines on here.

Knoxie

 

[Jeremy Harris]

To kill a brushless controller if the throttle got stuck you don't need to switch the main power feed at all. All you need is a switch to turn off the controller power, usually that's around 60mA or so, so a tiny, handlebar mounted, switch will do the job just fine. This is the switch I have on my bars (the red one at the right of the photo):



It is easy to turn off by flicking your right thumb and kills the power to the controller.

Unlike a brushed motor controller, where failure can result in full motor power, a brushless controller failure will always stop the motor (often with some sparks, magic smoke escaping, etc, too). Pretty much the only failure mode where you could get stuck at full throttle with a brushless motor is throttle failure, most probably the thing jamming mechanically.

Jeremy

 

[Kingfish]

Jeremy,

RE: Power Switch & Meter

Yours is as elegant of a solution as I have ever seen. Clean & simple. 8)

Thanks for sharing, KF

 

[vanilla ice]

For the low power guys, you can pull circuit breakers off of dead toysRus electrics maybe. I know one of my kids bikes came with one. Even amped and volted up he never trips it. I do though! Or there's car audio breakers, or home depot AC breakers too if they will work?

For the high power guys, you can get dead man switches where you have to plug in a coiled arm cord to the handlebars to ride. That way you always have it right there to rip the cord out if the controller sticks wide open. And it won't run away and hurt somebody if somehow it does manage to dump you..

 

[amberwolf]

or home depot AC breakers too if they will work?

Ah; don't use AC-type breakers to cut DC power; they can be designed to require the zero-crossing of AC to extinguish the arc, which won't happen with DC, so the arc could continue across the gap and burn the contacts or even set fire to the breaker itself if it arced long enough to get hot enough.

Well, probably wouldnt' actually set *fire* to it, but it would certainly damage it to the point where the plastic would turn to ash and crumble--I've seen *that* happen on a breaker even in AC use, when it did not seat properly into the breaker box, and it continued to arc across the gap to the busbar under load (on an air conditioner's power line).

 

[vanilla ice]

Ah good to know.. I might have tried it! Here is a pic of one car audio breaker I have that says "140a." They are pretty affordable.

 

[amberwolf]

Just remember it was meant to break 12-15VDC, most likely, so going higher voltages is progressively going to be harder on the breaker, trying to extinguish the arc. I suspect for most of our pack voltages it won't be much of an issue, but getting up at and beyond 100V it might be.

 

[Ricky_nz]

Just remember it was meant to break 12-15VDC, most likely, so going higher voltages is progressively going to be harder on the breaker, trying to extinguish the arc.

This goes for any device (switch/fuse/breaker/relay) that opens a DC circuit. You must obey its rated voltage and current or it will likely fail to open.
Likewise do not use AC devices unless they have specific DC ratings ( often much lower lower than AC ones).
I have witnessed blade fuses (32V rated) fail to open the circuit in a measly 48V. I took a calculated risk at 36V but when I swapped to 48 I didn't have a better fuse handy and as is usually the case it was working and I hadn't got round to changing it when I fried a controller.
Of course there are issues with reliably connecting blade fuses too.

It was strange to look at the fuse arcing until it heated enough for the holder to fail!
My wiring held up easily as I over sized it by a large margin.

 

[docnjoj]

I dunno about all this A/C D/C stuff but I have been using a 20 amp wall light switch for over 3 years on up to 54 volts nominal without a problem. Sometimes ignorance is bliss.
otherDoc

 

[Ricky_nz]

I dunno about all this A/C D/C stuff but I have been using a 20 amp wall light switch for over 3 years on up to 54 volts nominal without a problem. Sometimes ignorance is bliss.
otherDoc

The problem comes if you try and turn it off with significant current flowing. It will cause an arc that will not be extinguished so the current keeps flowing through the plasma! At very light loads the switch is probably fine (0 throttle etc) as the arc is too small to sustain itself.

This fact is extremely important for a circuit breaker which needs to be relied on to disconnect a load which may be greater than normal full load.

Look at a jacobs ladder at the top the arc is travelling over a far greater distance than air can normally break down but the arc is conductive so it keeps flowing. Once an arc is formed across your switch contacts it will not stop until something else opens the circuit or the arc is blown away by airflow or magnetic blowouts etc. in a sealed or semi sealed switch the arc will sit there as did the arc on my blade fuse.

 

[docnjoj]

Thanks for the warning, Ricky_NZ. I guess I never needed to turn the bike off under load. I have an Anderson connection that I would pull in an emergency and a fuse so I guess I'll just keep on trucking.
otherDoc

 

[Ricky_nz]

Ok, just figured I would highlight some of the risks for those on the forum that might not realise the problems.
When something goes wrong it is a bad time to find out you backup plan or protection doesn't work :lol: