Fuse blew, no reason?

[Sunder]

Hi guys,

I shouldn't say no reason, but maybe just that I don't know what the reason was.

I fitted a new Q100 on the weekend, after I stripped the gears in my old one about 3-4 months ago (Yeah, been a bit busy). I rode it today and did about 4kms before I blew the main fuse between my battery and controller.

The controller is a 48v, 1000w model, running 12s, 10Ah. After only 4km, that should have been about 4.0 per cell. I haven't traditionally had sagging issues, but the battery has been "lying fallow" for 3-4 months.

The fuse I was running was 25a, which means power surged past 1200w for at least a second to blow the fuse.

The controller shouldn't have been able to draw this much without a fault. I couldn't find anywhere that looks burned or shorted, so I'm at a loss as to where to look.

Any suggestions on where to diagnose would be helpful.

Thanks.

 

[r3volved]

What's the max amperage of the controller?
If it's above 25a then the fuse would have blown before any damage to the controller.
I'd start by checking all your harnesses and connections for wear or any sign of a short. Good luck and keep updating

 

[Sunder]

The controller was sold as a 1000W model, and I've done several thousand kilometres on it with a 25A fuse with no problems before. I used to run 20A fuses, but I kept blowing fuses if I didn't pedal up hills. I figure the limit of the controller must be about 21-22A...

My wife is dropping me a pack of fuses tonight. I'll see if it blows again, or if it was just a freak occurrence.

 

[dnmun]

try using a 40A fuse. that should solve the problem.

 

[Sunder]

try using a 40A fuse. that should solve the problem.

So would a solid piece of copper... but if there's a problem, I'd rather not start a fire or kill anything that I don't need to kill.

 

[dnmun]

use a 20A then if you like replacing it more than not.

 

[dogman dan]

I would try a 30 amps fuse, if more 25's keep blowing. A 40 amps fuse will still protect fine from the major hazards, such as a shorted wire.

Exactly same motor? A faster winding would amp spike a lot more. Sounds to me like your controller is quite capable of spikes in the 30 amps range, but should ramp down to lower than 25 amps pretty fast. Maybe you just had a fuse that blew at less than 25, and other fuses will work fine.

But again, I see no hazard in going to a 40 or 50 amps fuse. A major short will still blow one very fast.

 

[teklektik]

I would try a 30 amps fuse, if more 25's keep blowing. A 40 amps fuse will still protect fine from the major hazards, such as a shorted wire.

+1
Remember that the fuse rating is the 'carry current', not the current at which it will blow. Depending on the fuse type/style you may have to apply a fair bit more current for a long time for it to let go. This suggests that your setup may be dragging down some pretty good amps.

It's unclear what kind of controller you have or what it's doing, but it would not be surprising if it delivered considerably more than 25A on getaway - perhaps by design.

• For example, the classic EB2xx/EB3xx Xie Chang (Infineon) controllers will deliver essentially unlimited (still limited but very very large) current during the 'block time' which is in play if you go WOT off the line. The 'rated' current limiting only comes into play after the block time has elapsed. The idea is to give motors a boost to get things rolling.
  
  Your controller may or may not have this exact behavior, but without special knowledge to the contrary, you should be viewing the 'rated' current not as the maximum current, but as a limiting value used for normal operation at speed. That may make a fuse value equal to the rated current a marginal selection - which seems to be the case here.

So - as dogman indicates, view the fuse as protection from catastrophic failure and go larger to get some headroom for normal controller operation. In cases of catastrophic failure, the currents will be very large and the difference in delays between 25A and 40A fuses will be of little consequence from the perspective of preventing additional damage.

 

[wesnewell]

The controller was sold as a 1000W model, and I've done several thousand kilometres on it with a 25A fuse with no problems before. I used to run 20A fuses, but I kept blowing fuses if I didn't pedal up hills. I figure the limit of the controller must be about 21-22A...

My wife is dropping me a pack of fuses tonight. I'll see if it blows again, or if it was just a freak occurrence.

The 1000W on the controller specs is not the max wattage draw. It's the rated max draw for 24/7 operation. Max amperage could be anything and is likely more than 25A. Even my old 500W controller has a 45A draw, modded from original 30A, which at 60V is 2700W.
It could be the fuse holder is bad. A loose fitting fuse will heat up and blow fuses fast. DC voltage requires a wider gap fuse than AC voltage. A 1 inch glass fuse is a good cheap fuse for this, but many times the holder is crap. For high voltage DC, an ANL fuse is probably the best solution, although I use cheap 40A ATC blade fuse on my 40A controller because it was cheap and I had a 40A fuse for it. If a direct short ever happens though, it will blow not only the fuse, but the holder too. My battery pack is rated for 200A, so not a problem.

 

[beast775]

Q100...
What amps are you pushing to this motor with youre controller?

 

[Sunder]

Actually, now that you mention it. I think it's the faster winding one... Didn't realise that a faster winding motor would draw more amps...

Q100...
What amps are you pushing to this motor with youre controller?

Yeah... Now that's a good question, isn't it? I never finished building my ammeter, so I never found out. I always assumed it was just circa 20a. Last time it lasted about 5 months before the gears striped up a steep hill when I was carrying 10kg or so more than usual without pedaling. Figured I'd try again and if I stripped another gear, I'd go the SWXH.

 

[dogman dan]

Boo Ya. I definitely suspected a faster winding. It will for sure pull a much bigger amp spike on startup. Get some 40 or 50 amps fuses and be done with it.

The fuse is not to limit amps, it's just to cut the circuit when you short out and try to pull 500 amps.

 

[Sunder]

Boo Ya. I definitely suspected a faster winding. It will for sure pull a much bigger amp spike on startup. Get some 40 or 50 amps fuses and be done with it.

The fuse is not to limit amps, it's just to cut the circuit when you short out and try to pull 500 amps.

Will do. Thanks for your help.

 

[Sunder]

Just did 10km with a 30A fuse. All good, nothing blown.

Really worried about burning the windings now though. I've been babying it up hills, letting my legs do more of the work, and pulsing the throttle rather than keeping it on.

Hopefully it only needs to last until my 1.5kw SWXH motor is built anyway.

 

[teklektik]

Really worried about burning the windings now though. I've been babying it up hills, letting my legs do more of the work, and pulsing the throttle rather than keeping it on.

Good to see issue is resolved.
Since the whole Amps/temperature thing tends to be a way of life with ebikes, you might consider getting a watt meter or Cycle Analyst for your present rig to keep tabs - it will continue to be useful with the new motor.

Here's a thread about adding a temp sensor to your present motor without too much fuss. You could low-ball it with a Taylor cooking thermometer if you wish. This isn't as good as a tear down and re-run of wiring with the sensor on the windings, but it should work pretty well for your small diameter motor. In my case it showed I was being too conservative on some local hills, and I was able to safely lean on the bike quite a bit harder.

 

[beast775]

Good news,anything over 20amp on a hill will saturate that q100 with heat.pulsing throttle will help.good luck,sounds like you need a hub upgrade anyways.

 

[dogman dan]

Just pedal briskly up the hills, and use partial throttle, just enough to keep it painless. The pulses just make heat from most of top end of the pulse. Slow and steady at half to three quarter throttle, plus brisk pedaling will heat the motor less.

No need to pedal your guts out, just put out a comfy but brisk effort.

 

[Sunder]

Good news,anything over 20amp on a hill will saturate that q100 with heat.pulsing throttle will help.good luck,sounds like you need a hub upgrade anyways.

Yeah, I was happy with the Q100 for a while, getting me to high 40s (km/h) on flats, but the irritating part was even on minor hills, I would drop to high 30s. The speed drop didn't bother me, but it just so happens on a part of a road where it's unsafe to overtake. In a 50 zone, most drivers won't overtake someone doing high 40s, even if it mildly annoys them. However, they will pass someone doing high 30s, so I either need to aggressively block or completely pull over to avoid some idiot doing a pass with only 30-50cm to spare.

My goal for the new motor is to keep high 40s up a fairly mild but long hill (5% grade over 600-700m?) The bad news is that my wife just had a car accident, and so the insurance excess just ate into our budget, so I'm going to delay this project.

 

[alsmith]

Sometimes fuses just blow, possibly age. Replace it with the same value and if it blows again then start looking for an issue. If it lasts another few years then you can budget to buy one every few years......

 

[TheBeastie]

You can try and buy a slow blow or "time delay" fuse.
http://www.ebay.com.au/itm/Microwave-Fuse-32mm-20A-Time-Delay-20-Amp-x-10-Pack-/360768883971?pt=UK_Home_Garden_Kitchen_Ovens_Hobs_Cookers&hash=item53ff804d03
My BMSbattery battery uses a 20A fuse. It blew going up a hill. I replaced it and it kept blowing because it was easy to go past 20Amps on take off of the bike.
I bought a few different types of fuses some slow blow some normal and I think the one in there right now is normal and I see on my watt meter I go past 20amps now and then but not for too long and it has stayed good.
I don't know why but the 5th fuse I put it just stayed good and hasn't blown no matter what I have done. I recommend just shoving some fuses in there and see if it just settles and stays good.

I think most controllers and pull more then 20amps. I am using a S12S controller now that has 21amps sticker on it but I seen the watt meter go up to 25amps.

 

[alsmith]

I wouldn't use a slow blow fuse- it gives more time for damage to happen. Stick to fast blow.