Circuit breaker blew like a fuse

[JackofHearts]

7 dollars sounds good to me. So does 50A. Plenty of headroom. Do you know the breaking curve/type for it?

Tiny linear glass fuses mightn’t be as voltage agnostic, I don’t know, but blade fuses won’t sustain an arc with any voltage I’ve tested up to 84V. The “v” shape between posts probably helps. I use the larger “maxi” versions, which might also make a difference.

There aren't any brand name stuff available here so researched best I could hoping a 7 buck breaker will do. I wasn't even trying to be cheap - everything available here is sketchy.

I will check the auto shops to see what they have available. Shopping for anything that isn't the norm here is not good. For example, I went to an ebike/scooter store to see if they had any breakers - nope, not one of them had any whatsoever.

 

[glennb]

If you’ve been using your old breaker as a switch it could be rooted.

The contacts are in all likelihood designed for very intermittent use. Think about their purpose. Data sheet for a regular relay or switch will list the number of rated “switching operations”.

I haven’t looked, but I doubt you’ll find any equivalent rating for an MCB, because they’re unlucky to be flicked twenty times in their lifetime.

There’ll be a thin layer of nickel or other corrosion-resistant material plated on steel. Certainly nothing fancy.

Perhaps expensive high voltage DC rated breakers are more durable, but on regular household types the arcs (audible pops) I’m confident will the plating will disintegrate in short order, after which the steel will corrode and you’re left with a high resistance contact.

If the resistance is high enough, I imagine the heat generated could trip the breaker by exceeding the thermal threshold (as opposed to instantaneous current threshold), which could explain the issue you’re experiencing.

I know that’s a lot of speculation, but it’s only wrong by degrees (or orders of magnitude if I’m way off base). It makes a hell of a lot more sense to use smart BMS’ shutdown/sleep functionality than using breakers as switches.

I’m sure I’ve said this more than once in this thread … the breakers should be regarded as resettable fuses. The incorporated switch is a bonus, and very handy if you want to do some downstream wiring alterations.

The reset function might be useful to get you home, or to the electrical department to buy a replacement breaker, but beyond that, it ought to be treated like any other fuse that is discarded once it blows.

I’m happy to be wrong about this and discover that $5 AC rated MCBs are far less destructible than I imagine. Measure the contact resistance on new vs worn contacts. Crack one open to inspect the contacts. Delve into the datasherts. I won’t bother because of how I use them, but I if I intended to switch them semi-often I would, and you should if you do.

Auto shops are guaranteed to stock blade fuses. If I suggested 40A earlier, I shouldn’t have. Again, I haven’t examined data sheets for them, but IME they’re a fast blow, meaning little headroom above their rating for current spikes, and you might as well seek out an 80A fuse if the purpose is defense against clumsy accidents and stupid lapses of reason.

(Edit: electricity is destructive and dangerous etc etc. Manufacturer guidelines should obviously be followed. Cost cutting by using under-rated equipment is inadvisable. But you’re going to do it, because the 100VDC rated gear costs an arm and a leg. At least test it for your application, before you test it in your application.)

 

[nicobie]

If you’ve been using your old breaker as a switch it could be rooted.

electricity is destructive and dangerous etc etc. Manufacturer guidelines should obviously be followed. Cost cutting by using under-rated equipment is inadvisable. But you’re going to do it, because the 100VDC rated gear costs an arm and a leg. At least test it for your application, before you test it in your application.)

This is the correct answer

 

[JackofHearts]

If you’ve been using your old breaker as a switch it could be rooted.

The contacts are in all likelihood designed for very intermittent use. Think about their purpose. Data sheet for a regular relay or switch will list the number of rated “switching operations”.

I haven’t looked, but I doubt you’ll find any equivalent rating for an MCB, because they’re unlucky to be flicked twenty times in their lifetime.

There’ll be a thin layer of nickel or other corrosion-resistant material plated on steel. Certainly nothing fancy.

Perhaps expensive high voltage DC rated breakers are more durable, but on regular household types the arcs (audible pops) I’m confident will the plating will disintegrate in short order, after which the steel will corrode and you’re left with a high resistance contact.

If the resistance is high enough, I imagine the heat generated could trip the breaker by exceeding the thermal threshold (as opposed to instantaneous current threshold), which could explain the issue you’re experiencing.

I know that’s a lot of speculation, but it’s only wrong by degrees (or orders of magnitude if I’m way off base). It makes a hell of a lot more sense to use smart BMS’ shutdown/sleep functionality than using breakers as switches.

I’m sure I’ve said this more than once in this thread … the breakers should be regarded as resettable fuses. The incorporated switch is a bonus, and very handy if you want to do some downstream wiring alterations.

The reset function might be useful to get you home, or to the electrical department to buy a replacement breaker, but beyond that, it ought to be treated like any other fuse that is discarded once it blows.

I’m happy to be wrong about this and discover that $5 AC rated MCBs are far less destructible than I imagine. Measure the contact resistance on new vs worn contacts. Crack one open to inspect the contacts. Delve into the datasherts. I won’t bother because of how I use them, but I if I intended to switch them semi-often I would, and you should if you do.

Auto shops are guaranteed to stock blade fuses. If I suggested 40A earlier, I shouldn’t have. Again, I haven’t examined data sheets for them, but IME they’re a fast blow, meaning little headroom above their rating for current spikes, and you might as well seek out an 80A fuse if the purpose is defense against clumsy accidents and stupid lapses of reason.

(Edit: electricity is destructive and dangerous etc etc. Manufacturer guidelines should obviously be followed. Cost cutting by using under-rated equipment is inadvisable. But you’re going to do it, because the 100VDC rated gear costs an arm and a leg. At least test it for your application, before you test it in your application.)

The current breaker is 40A 72VDC. The breaker I ordered is 50A 100VDC. I haven't been using the current breaker to turn the scooter on and off - the scooter has a key switch to turn on and off. The breaker is under the seat so not easy to access. I have flipped it off then on to reset it 5 times at the most and flipped it off then on when I disconnect a battery to connect the other battery.

The DALY BMS I'm using is 100AMP and through bluetooth I set over current to just 30A yet it is the 40A breaker that flips first. If the new 50A break doesn't flip and I leave the BMS settings the same, maybe the BMS will shutoff. I'm not sure for how long DALY must experience over current before shutting off. I know the general specs of the DALY BMS, but not how long it will take over current before shutoff.

When I set it to 30A, I was just starting low and if necessary going high. It is easy to change.

Attached is what I have coming. It is the best I could find. It is a B curve breaker. I tried to find a D curve breaker, but couldn't. I asked ChatGPT about D curve DC breakers and was advised they are rare. When I search Amazon for D curve breakers, only AC breakers are in the results so ChatGPT appears to be right.

 

[glennb]

That’s good, you’re not abusing the equipment.

I’d still say to treat the new breaker like a mislabelled AC one though.

The Chinese ratings are complete fiction.

For example, the highest DC voltage rated MCB available from RScomponents is 500VDC, and the prices start at 100 dollars. (100VDC ones are also all >$100).

From aliexpress you can buy a 1000VDC rated MCB for fifty cents, with shipping a whopping two dollars. See here:

https://www.aliexpress.com/item/1005005616584575.html?spm=a2g0n.detail.1000014.3.28118jzT8jzT67&gps-id=platformRecommendH5&scm=1007.40000.326746.0&scm_id=1007.40000.326746.0&scm-url=1007.40000.326746.0&pvid=1aa48a39-1ef6-4da8-8c6f-95d6a4e01d6d&_t=gps-id:platformRecommendH5,scm-url:1007.40000.326746.0,pvid:1aa48a39-1ef6-4da8-8c6f-95d6a4e01d6d,tpp_buckets:668%232846%238116%23925&pdp_npi=4%40dis%21AUD%2113.42%217.93%21%21%2162.09%21%21%402101effb16960411825197661e7977%2112000033761527457%21rec%21AU%212061826290%21&search_p4p_id=20230929193302549714713143225059575_1

 

[JackofHearts]

That’s good, you’re not abusing the equipment.

I’d still say to treat the new breaker like a mislabelled AC one though.

The Chinese ratings are complete fiction.

For example, the highest DC voltage rated MCB available from RScomponents is 500VDC, and the prices start at 100 dollars. (100VDC ones are also all >$100).

From aliexpress you can buy a 1000VDC rated MCB for fifty cents, with shipping a whopping two dollars. See here:

https://www.aliexpress.com/item/1005005616584575.html?spm=a2g0n.detail.1000014.3.28118jzT8jzT67&gps-id=platformRecommendH5&scm=1007.40000.326746.0&scm_id=1007.40000.326746.0&scm-url=1007.40000.326746.0&pvid=1aa48a39-1ef6-4da8-8c6f-95d6a4e01d6d&_t=gps-id:platformRecommendH5,scm-url:1007.40000.326746.0,pvid:1aa48a39-1ef6-4da8-8c6f-95d6a4e01d6d,tpp_buckets:668%232846%238116%23925&pdp_npi=4%40dis%21AUD%2113.42%217.93%21%21%2162.09%21%21%402101effb16960411825197661e7977%2112000033761527457%21rec%21AU%212061826290%21&search_p4p_id=20230929193302549714713143225059575_1

I agree - the labels mean near nothing and we can't trust the certificates they sometimes post with the products. The one soon to arrive is labeled 50A but there is no telling what it really is. If it works, grea - I will still have the BMS set low as possible so to a degree I will have double protection.

 

[glennb]

I’m confident you’ll get your 50A, and a good product at a good price. It’s the contact ratings that are unbelievable. If they thought there was a market for lightning conductor MCBs they’d label them as 500,000,000VDC.

 

[E-HP]

If you’ve been using your old breaker as a switch it could be rooted.

The contacts are in all likelihood designed for very intermittent use. Think about their purpose. Data sheet for a regular relay or switch will list the number of rated “switching operations”.

As I mentioned in my earlier post, after using a breaker as a switch for maybe 7k-8k actuations, and doing a tear down, there was no indication of any wear and no wear of the contacts. I don't routinely switch power on or off under load (nobody does).

Circuit breaker blew like a fuse

This is on my Fly 7 E Scooter/ moped that I bought new about 2 years ago. It has a 1500W motor and 60V 29 AH battery. No problems for 2200 kilometers till last week when I was 2 blocks from home going down hill making a turn and lost power, dash instrument display went dark. Recycled the key a...

endless-sphere.com

 

[nicobie]

If you are using the breaker to activate the controller (initial charging of the controller's capacitor's) You will be causing a big arc at the contacts. On my bike running at 96V if I don't use the precharge switch the contacts on my 100V US made contactor will weld together every time. With voltages under 60V it's not quite so bad.

 

[Zambam]

If you are using the breaker to activate the controller (initial charging of the controller's capacitor's) You will be causing a big arc at the contacts. On my bike running at 96V if I don't use the precharge switch the contacts on my 100V US made contactor will weld together every time. With voltages under 60V it's not quite so bad.

Can you show a schematic of your precharge switch, how it's wired to your breaker and battery? Thanks!

 

[Zambam]

As I mentioned in my earlier post, after using a breaker as a switch for maybe 7k-8k actuations, and doing a tear down, there was no indication of any wear and no wear of the contacts. I don't routinely switch power on or off under load (nobody does).

Circuit breaker blew like a fuse

This is on my Fly 7 E Scooter/ moped that I bought new about 2 years ago. It has a 1500W motor and 60V 29 AH battery. No problems for 2200 kilometers till last week when I was 2 blocks from home going down hill making a turn and lost power, dash instrument display went dark. Recycled the key a...

endless-sphere.com

Interesting! What voltage is your battery? The first time I disconnected/ reconnected the battery (60V lead acid), the loud spark scared the sh*t out of me since I didn't expect it and thought I blew something. If I get a replacement MCB, I will do an autopsy on my old MCB and see what the contacts look like.

 

[glennb]

Earlier in this thread eee291 raised the subject and described their precharge circuit.

Instead of punishing a heavy duty main switch …

You could punish a contactor engaged by a smaller switch.

You could use a separate switch and resistor in parallel to the main switch to avoid that punishment.

You could use a multi-pole rotary switch with the first position open, the second engaging the precharge resistor, and the third position a contactor coil. Again, avoids punishment.

You could use a single switch that simultaneously engages the precharge resistor and a time delay relay (that in turn engages a contactor after the appropriate delay). Also avoids punishment.

You could forego the switch (and even resistor) and have a “Hotwire” setup with two loose hot wires that you tap together to charge the controller caps. Again, in parallel with the main switch. The sacrificial Hotwire terminals take the punishment. I wouldn’t recommend it … just trying to be thorough in outlining your options.

That’s off the top of my head. If you racked your brains there’s likely other possible configurations.

Another way to avoid arcs altogether is to leave the main switch closed and instead put the BMS to sleep. You can forego precharge in this configuration, but in doing so the controller capacitors take the punishment. The inrush current will stress the controller capacitors. Whether that’s to a damaging degree, I couldn’t say … you’d need to run that past some of the resident electronics experts here, or perform your own research and form your conclusions.

I believe HP uses the breaker as an isolator after system shutdown. I don’t know their exact circuit though. It sounds interesting.

 

[E-HP]

Interesting! What voltage is your battery? The first time I disconnected/ reconnected the battery (60V lead acid), the loud spark scared the sh*t out of me since I didn't expect it and thought I blew something. If I get a replacement MCB, I will do an autopsy on my old MCB and see what the contacts look like.

72V, 20S. I use it to switch battery supply to my controller (every time I switch the bike on or off; its in series with the P+). I added a pre-charge circuit when I replaced the breaker, but after taking apart the old one, it was clear that the pre-charge wasn't needed. I'm going to remove the pre-charge circuit the next time I'm working on my connection box in order to simplify and reduce the clutter.

 

[Zambam]

72V, 20S. I use it to switch battery supply to my controller (every time I switch the bike on or off; its in series with the P+). I added a pre-charge circuit when I replaced the breaker, but after taking apart the old one, it was clear that the pre-charge wasn't needed. I'm going to remove the pre-charge circuit the next time I'm working on my connection box in order to simplify and reduce the clutter.

Does your controller make a big spark when connected to the battery? If so, wouldn't that spark cause deterioration of (cheap) MCB contacts? I am sure there are MCB contact materials that won't deteriorate but those are probably found in much more expensive breakers.

 

[E-HP]

Does your controller make a big spark when connected to the battery? If so, wouldn't that spark cause deterioration of (cheap) MCB contacts? I am sure there are MCB contact materials that won't deteriorate but those are probably found in much more expensive breakers.

The breaker was cheap (a few bucks), used for several thousand actuations, and had no deterioration to the contacts. I'm not sure why you want me to speculate or theorize on what you think should have happened, just presenting the actual results. Connecting an XT90 directly will fry it after a few times, so yes, a big spark.

 

[Zambam]

The breaker was cheap (a few bucks), used for several thousand actuations, and had no deterioration to the contacts. I'm not sure why you want me to speculate or theorize on what you think should have happened, just presenting the actual results. Connecting an XT90 directly will fry it after a few times, so yes, a big spark.

I am not doubting what you said, that your cheap MCB did not have deteriorated contacts. Aren't you curious why? Maybe there is anti spark RC or LC circuitry built in?

 

[E-HP]

I am not doubting what you said, that your cheap MCB did not have deteriorated contacts. Aren't you curious why? Maybe there is anti spark RC or LC circuitry built in?

You can review the photos, just an ordinary Square D single pole. No separate arc contacts. I probably still have the parts in a box somewhere. The discoloration in the photo isn't pitting, but due to alignment, but the surfaces are smooth. Maybe how breakers use sintered metal for the contacts makes them more durable compared to brass or silver plated brass contacts (or brass to brass for an XT-90)?

 

[glennb]

The spring mech in MCBs also seems pretty good. Perhaps the design prevents contact bounce.

Whatever the reasons, it seems they can cope with the controller inrush current. Good to know.

Breaking a short circuit is far harsher on the contacts though, and I’d stick with the recommendation to discard them after such events.

Section 3.1 in the below link briefly discusses the contact damage.

https://electrical-engineering-portal.com/the-design-basics-of-motor-protection-circuit-breaker

 

[JackofHearts]

The current breaker is 40A 72VDC. The breaker I ordered is 50A 100VDC. I haven't been using the current breaker to turn the scooter on and off - the scooter has a key switch to turn on and off. The breaker is under the seat so not easy to access. I have flipped it off then on to reset it 5 times at the most and flipped it off then on when I disconnect a battery to connect the other battery.

The DALY BMS I'm using is 100AMP and through bluetooth I set over current to just 30A yet it is the 40A breaker that flips first. If the new 50A break doesn't flip and I leave the BMS settings the same, maybe the BMS will shutoff. I'm not sure for how long DALY must experience over current before shutting off. I know the general specs of the DALY BMS, but not how long it will take over current before shutoff.

When I set it to 30A, I was just starting low and if necessary going high. It is easy to change.

Attached is what I have coming. It is the best I could find. It is a B curve breaker. I tried to find a D curve breaker, but couldn't. I asked ChatGPT about D curve DC breakers and was advised they are rare. When I search Amazon for D curve breakers, only AC breakers are in the results so ChatGPT appears to be right.

Refresher: I tried changing LA battery to LI 72v battery. 40a MCB trips, bought a 50a MCB, it trips, bought a 100a MCB and it trips.

Daly 100a BMS is not tripping. After tripping, I reset the MCB, all works until I give the scooter a tiny bit of throttle on flat ground. BMS has no time to trip since the MCB trips so fast.

I'm stumped. If there was a short in the battery or anywhere else, it would trip immediately after connecting it to the scooter. Keep in mind, it works fine with the LA battery so if there was a short, it would be there when the LA battery is connected too and would not work.
Why would the controller/motor pull vastly more AMPs from the LI battery than the LA?

I'm about to give up, because I don't know what to do next. Dang it. I really wanted to increase travel distance.

 

[glennb]

That sucks. Sorry to hear that.

You’re spot on in your assessment.

Do you have a way to measure the current?

Fattening up the wiring for the li-ion install would make a difference, and it’s possible your LA batteries had high internal resistsnce.

Still shouldn’t happen, B curve should’ve been fine. But you might have to use a c curve breaker all the same - that’ll buy you twice the headroom for current spikes.

 

[JackofHearts]

I'm going to see if I can get inside the controller so I can replace the 12 gauge wires with 8 - I might double up the 8 gauge wire. It is worth an experiment since I've watched a lot of youtube LA to LI conversions that's usually just a simple swap that works.

 

[amberwolf]

The controller may be pulling more current with the Li if the LA was sagging in voltage a lot during the peak, and the controller responds by not drawing that much to reduce the sag, if the Li doesn't sag under the same load.

The other difference between LA and Li is that the LA with no BMS is a different kind of "load" to the controller input, and the voltage and current response between them under the same motor loads will be different. The specific response depends on the characteristics of the actual packs being used. You can see some of the response differences using an oscilloscope on the battery leads (with a suitable probe to scale the voltage down to the scope input level), and loading the system in different ways.


If it's actually an overcurrent trip issue, then to fix the problem, you need to *measure* the *actual* current that is being drawn, peak, during the conditions the problem occurs.

A regular multimeter won't usualy do this, but a wattmeter that can record very short peaks will, as long as it has it's own battery to power it (otherwise the data will be lost when the breaker trips).


A 100A breaker wont' trip at 100A, it will trip at a higher current. To trip instantly the current must be much higher than that 100A--check the datasheet for your specific breaker to find out what it's instant trip current is, and compare it to your actual measured current. Then you will know what breaker you have to get to handle that momentary current without tripping, but that will still protect your wiring, whether that is a different trip curve or a higher rating.



Note that the controller to battery wiring being too small will not affect the breaker operation. Upgrading it to thicker wires will probably actually make the problem worse as current will be less limited by wiring resistance.

 

[glennb]

That’s a better answer than mine.

Sorry, I wasn’t clear. I was suggesting that beefier wiring with the battery upgrade could account for higher current peaks. That and high resistance LA.

But if you stuck with the same gauge wiring for the li-ion install, that’s not a factor.

The cheapo wattmeters are good up to 150A. You’ll need something more capable, with a clamp or shunt.

 

[JackofHearts]

AmberwoQUOTE: "Note that the controller to battery wiring being too small will not affect the breaker operation. Upgrading it to thicker wires will probably actually make the problem worse as current will be less limited by wiring resistance."


What is a breaker for then? I've read on diysolarforum.com (screen shots below) that CBs are to protect the wire only. No one argues on the solar forum about this. Does the ebike forum have a different opinion?

I'd like to know what the CB is for on an ebike? Is it to limit current, protect wires, protect devices or protect against a short? Which is the CBer's primary purpose - the one that's above all else?

BTW, if you are reading this glennb, I do keep wondering about bypassing the CB while being very careful not to short the wires. Go easy on me if you reply. Thanks.

If I bypass the CB, will the controller survive? Do ebike controllers have their own built-in protection? Or is it generally not known if they have their own built-in protection from overcurrent? Has anyone tested this or verified it? Any subject matter posts about such tests?

While the LI battery doesn't work, the LA battery works so there is no short in the system.

 

[glennb]

The fuse/breaker offloads short circuit protection from the BMS.

Your BMS provides overcurrent protection functionality. The purpose is to prevent cells from discharging more than they can comfortably cope with, but it affords the same protection to the wiring by default.

You don’t need to duplicate this overcurrent protection, and attempting to do so via a MCB is problematic, as you’re discovering.

A short circuit is an overcurrent event, but a bit too extreme of one for a BMS. It could damage the BMS, so it’s a task best handled by a different dedicated device - fuse or breaker.

Wiring you want as thick as possible to minimise resistance. If you size it at least a gauge up from the BMS’ overcurrent limit, your BMS is protecting it.