SOLVED: Blown Fuse on New Stealth Bomber Clone

[igashosparks]

I just received my Stealth Bomber Clone from an outfit in China called Coolfly Bikes.

8000W QSMotor
SVMC72V100(M) Sabvoton sinewave controller
72V 41.6AH(China Battery)

On the trial run, going about 35MPH / 56 KPH, after riding for about 20 minutes.. all power died to the bike, display went dark after posting a 30H error code. After some initial troubleshooting, I saw that the fuse had blown on the outbound battery positive lead (between the battery and controller).

The response from the supplier is to replace the fuse.. I'm guessing about 120 Amps? My question back to the supplier was why did the fuse blow in the first place. (still waiting for the response, so I got up the courage to post the situation here, I'm pretty new to this.. and do not have a lot of electrical experience)

I was concerned that the controller at 100Amps is under spec'd, and I should have at least a 150Amp.. The supplier assures me, that the controller is not under spec'd.

Any advice, feedback, suggestions are most welcome. Thank you to any responses!

 

[SlowCo]

What is the peak amp draw that the controller is programmed to take from the battery pack?
What is the peak amp draw that the BMS will allow?
What is the peak amp draw that the battery can provide?
Those are the most important values you need to know before replacing the fuse with a higher amp rating.

 

[igashosparks]

SlowCo,

thank you for the response.. I don't have the answers to any of these questions at the moment. I guess my first step is to install a new fuse, similar rating for now so I can power up the controller, login and see what the amp draw is programmed at. I'm not sure how I can get the peak amp draw of the BMS or battery.. I'll do some research on those two, and also see if I can get the manufacturer to provide.

I'll post back when I have those numbers..

 

[SlowCo]

I think that is best. And see if you can program the peak amp draw of the controller under the max rating of the blown fuse. Are there any numbers on the fuse?

 

[igashosparks]

I pulled the fuse, it's 80 AMP.. I would have thought larger, given a 72V battery and 8000W motor.. (if it's really 8000W, or am I thinking about that wrong.. I know there's lot's of variables)

 

[SlowCo]

Is your controller 100A peak or continuous rated? Can you find any info on the battery pack? You should carefully remove the pack out of the bike and check for manufacturer info on it. Especially the continuous and peak amp rating of the battery pack.
Then first start with a 100A fuse before going higher. Normally the battery BMS should have a higher continuous and peak rating then the controller.

 

[amberwolf]

I pulled the fuse, it's 80 AMP.. I would have thought larger, given a 72V battery and 8000W motor..

The voltage and wattage don't have anything directly to do with the fuse amp (current) rating.

Only the current thru the fuse matters to the fuse A rating, and that rating needs to be higher than the maximum expected current thru it. The fuse is there to protect the wiring beyond the battery, and to protect the battery from any short circuit, so you don't get fires in wiring or in battery, so it should be as close to the battery terminal as possible, and should be rated below what the wiring it protects can handle, but above what the system will draw thru that wiring.

(if the wiring is not sufficient for that current, then the wiring should be replaced with some that is)

If the battery isn't designed to handle the 100A (or more) of the controller, and they are using the fuse to protect it, then the answer is to reprogram the controller to a lower current to be below the maximum the battery can handle (or replace the controller with one that has that lower current limit). Or to replace the battery with one that can handle the current the controller will draw. Then either way, use a fuse with a current rating appropriate to protecting the wiring and battery from shorts.


The voltage of the system does matter to the fuse used, as if the rating is not high enough the fuse may not stop the arc created as it blows, and can start a fire in the wiring from the continuous arcing (like a welder)...and the RF from the arc can damage electronics in the system (BMS, controller, etc). So with a 72v nominal system, that's usually 84v full (20s x 4.2v/cell) should have a fuse with a voltage rating higher than 84v to truly be safe. A fuse with too low a voltage rating will still blow when the current is exceeded, but if arcing occurs it may not extinguish and so not actually stop the current flow of the overload.

Fuse manufacturers have charts for their fuses to show which is applicable to a particular set of conditions at which it would blow to protect the system, including how long it should tolerate the overcurrent before blowing.

There are a few threads about fuses and breakers and such, with more detailed information about these things.

(if it's really 8000W, or am I thinking about that wrong.. I know there's lot's of variables)

The motor itself doesn't determine the wattage of the system, if that's what you mean. That is determined by the battery current limit of the controller (100A in this case) and the voltage of the battery (72v nominal in this case). So that is 72v x 100A = 7200W nominal power that could be provided to the motor. At full charge it might be a bit more, but voltage sag under load will usually mean less power than you could potentially have if the battery, wiring, etc were all perfect and didn't have any resistance.

If you are interested in the relationships between the various factors on the bike, as well as the conditions you ride in, and the power you get out of it, you can use http://ebikes.ca/tools/simulator.html to see how it all works.

 

[igashosparks]

@SlowCo

Here are the parameters that I've been able to find on the Sabvaton SVMC72100 controller, they appear to be adjustable Parameter settings, I haven't logged in yet to verify that these are what they are actually set at:

Rated Phase Current: SVMC72100 is about 100A
Max Phase Current: Setting is no more then 200A
Protected Phase Current: Setting is no more then 300A



Not much to go on from the battery itself (mostly in Chinese):



@amberwolf

thank you for all the information, I've read it about 5 times so far.. I'm still digesting all that.

So far the only response from the bike builder (Coolfly bikes) is to replace the blown 80Amp fuse with a 150Amp fuse. I've requested the other information..
What is the peak amp draw that the controller is programmed to take from the battery pack?
What is the peak amp draw that the BMS will allow?
What is the peak amp draw that the battery can provide?
but no response as of yet.

(I may be over my head in all of this! thank you for the support!)

 

[SlowCo]

Although not entirely sure, it seems the controller is indeed limited to 100A peak/max DC amp draw from the battery pack. And a 41.6Ah battery pack should be able to sustain a 2.5C or 3C discharge for a while. So I suspect that a 120A fuse would be fine and should be strong enough.
You could try to contact the battery manufacturer directly and ask them if they can let you know what type of battery cells and BMS are in the battery pack. And what the continuous and maximum discharge rate/amps the battery pack can handle. Send them the photos of the pack with the numbers: https://thinked.en.alibaba.com/contactinfo.html?spm=a2700.shop_pl.88.dcontact

 

[igashosparks]

Great suggestion.. I'll do that!

thank you!

 

[amberwolf]

The bottom label translates (with the Yandex image translator) as

which indicates the BMS is rated at 80A max (assuming it's labelled correctly and the translation worked), and is probably saying the cells are 2900mAh each. I don't see anything that says how many cells, but you could divide up the pack Ah by the cell Ah to find that out, if you ever need to know. The 20# probably means 20s, whcih would be a 72v pack.

If the BMS is 80A max, then it's being overloaded by a 100A controller, and is probably why they used a smaller fuse than they should have, because they were trying to protect the improperly sized battery / BMS.

If the current limit of the BMS is exceeded, and it's a well-designed BMS, it will just turn it's output off and won't need a fuse to protect it against this simple issue (the fuse would be used to protect against a "real" short circuit). It's probably not a well-designed BMS, as that is not very common, and as has been shown in various troubleshooting and testing threads (like the recent DALY threads by Methods), the FETs may fail under this condition, and a common way they can fail is stuck on, so the BMS cannot then stop discharge for overcurrent, overdischarge, overheating, etc, and in some design cases the charge FETs may also be damaged the same way, and be unable to stop charge in case of an overcharge / etc situation.


So in this case, the appropriate fix is to reprogram the controller to less than 80A max (peak or momentary or continuous) battery current, so it never exceeds the capabilities of the BMS and battery.

Or replace the BMS (or entire battery) with one that is capable of handling what the controller is able to draw from it.

Note that if you just replace the BMS with a higher current version, and the battery cells, wiring, or interconnects are not actually able to handle the higher current, various potential problems can happen; the most minor of which is excessive voltage sag under load and faster aging of the cells (so shorter pack lifespan), the worst of which is a fire.

It is unfortunately not uncommon for builders/sellers to provide mismatched components that can't actually support each other properly, most especially to provide a battery that is truly capable of providing the power that the system needs to do the job it's advertised as being able to do.


In any case the fuse is still intended to protect the system as previously described (not to do the job of the BMS which is to limit pack overcurrent by shutting off entirely, or do the job of the controller which is to limit pack overcurrent by scaling back current draw under load to not exceed what the BMS and cells can handle).

 

[igashosparks]

@amberwolf

I'm humbled by the effort in your response.. I will definitely be making a contribution.

I'm willing to purchase a new sufficiently sized Battery with a properly configured BMS. Would it be in bad form to ask you for a recommendation based on what you know about my bike.. would it be better to PM about this?

While I'm at it, should I also be looking to upgrade to a 150Amp Contrller?

 

[amberwolf]

I'm willing to purchase a new sufficiently sized Battery with a properly configured BMS. Would it be in bad form to ask you for a recommendation based on what you know about my bike.. would it be better to PM about this?

Public is always better, so the knowledge is shared with any other readers (many people read ES but never post, at least not until they have a question not answered well enough already).

I don't have a specific battery recommendation, as I haven't researched what *good* batteries are out there. Just seen lots of bad ones posted here with various problems, or someone asking if a particular ad for one is any good or not for their purpose.

I know there are some sellers (EM3EV, or Ebikes.ca, for instance) that can be trusted to at least be honest about what they sell, and to take care of problems when they arise, but since it's not safe/legal/etc for the end-user to ship "defective" batteries, it's tough to ship them back for warranty work....

What I use are ( >decade old) large-format EV-grade cells; there are places like Batteryhookup that periodically get modules with various cell types, that can either be rebuilt into a battery for a bike or even used as-is in some cases. I prefer the EV stuff because it's designed to handle higher currents with less voltage sag, and as larger cells there are less interconnects to go wrong, etc.


You can also build a battery from scratch with bare new cells, but depending on what you use, that's usually going to require some equipment that will cost a fair bit (and only likely be used once for the build), and knowledge that takes time to acquire. There's a lot of threads here about building batteries of various kinds, if you are interested in this option.

While I'm at it, should I also be looking to upgrade to a 150Amp Contrller?

That depends on what job the system has to do for you and under what conditions.

I'd recommend making yourself a list of the worst-case conditions you will ever ride in: weather, winds, road conditions, terrain (hills slope and length), etc. And how far you have to go under those conditions, and at what speed.

If you go to http://ebikes.ca/tools/simulator.html you can put in your riding conditions and the parts of your bike you know what they are (wheel size, weight (including you and anything you carry), etc), and then use different setups (batteries, cotnrollers, motors) until the simulator shows it can do what you want.

For instance, riding on the flats with headwinds up to about 10mph, at road speeds up to 20mph with a several-hundred pound trike (including myself as rider, and some cargo or a St Bernard in the back), I can still accelerate at around 4-5 seconds zero to 20mph, using two hubmotors in ~22" wheels with ~40A controllers at 52v, for about 4kW of momentary power. I can also maintain that 20mph with no winds up a long fairly steep hill (going up 7th street on North Mountain from Dunlap to the top on the way up to Thunderbird). I don't recall the power used for that as I had other things on my mind at the time but nothing overheated. Only cargo was a spare ~40lb battery.

 

[igashosparks]

I believe some of this is starting to click.. please let me know if I need to course correction in my thinking here..

With a 41.6 AH / 72 V battery with a max discharge rate of 80Amp.. I still use an 80 AMP fuse with my existing china battery, and limit at the controller for max peak of 80amp, I should avoid blowing the fuse, breaking the battery, and causing any internal melt downs. I believe the fuse blew when I hit about 40 MPH or so..

If I run full throttle in this configuration.. i.e., running at 80Amps, I'm only getting 30 minutes or so of ride. so if I want a longer ride, I either ride slow manually or further limit the controller down to say 40 Amps max peak.. then get an hour at full throttle, and potentially suffer going up hills? I'm likely never to push that 8000W motor from a speed/RPM perspective. My intention with the bike was to take it on fire roads for 1 - 2 hour rides or longer. So probably could have gotten away with a much smaller motor.. (oh well). Also, my thoughts on needing a larger Amp controller were misguided, as I don't care so much about acceleration or torque. I'll likely average 20-30mph, max speed of 40MPH.. is fine with me.

So plan as it stands is to replace the fuse with a quality 80Amp fuse, limit the controller to max peak of 80 amps.. see how it goes.

Even if my BMS Sucks, and does not limit to 80 Amps to protect the battery, I should be good to go if I have a quality 80Amp Fuse between battery and controller, and set the controller to 80amps max peak. Long term, I'd like to replace the battery.. if I can find a reputable battery with higher Amp Hours that fit in the bike.. I don't need to go too fast, fast enough.. but I'd like to go on longer rides without having to swap batteries mid ride.

Does any of this make sense?

thanks for all the help, @SlowCo & @ amberwolf

 

[amberwolf]

With a 41.6 AH / 72 V battery with a max discharge rate of 80Amp.. I still use an 80 AMP fuse with my existing china battery, and limit at the controller for max peak of 80amp, I should avoid blowing the fuse, breaking the battery, and causing any internal melt downs.

Realistically it depends on what the items in question can *actually* handle--if the battery can really supply 80A continuously with no trouble, it'll be fine if the controller only draws that much...as long as the wiring from battery to controller (and any connectors, crimps, switches, etc on the way) can also handle that, continuously.

You'll probably need a fuse rated higher than the current you'll actually be drawing, just so it won't blow while you're using the system normally. Doesn't have to be much higher, but a little higher would help ensure it doesn't blow under normal operating conditions, rather only when there is a fault causing excessive current.

There are various kinds of fuses, that blow fast or slow, etc. How long a fuse takes to blow depends on it's design (each manufacturer has charts/etc on what each fuse is meant for). If you use a fuse rated for the same amount of current that you will actually be drawing under max load, then you probably want a slower blowing fuse so that it won't blow for just a burst of the max load current....but if the fuse is designed / rated to blow at the marked current, then even a slow blow fuse would still blow eventually, just while riding under max load normally when there isn't actually a problem.

I believe the fuse blew when I hit about 40 MPH or so..

The best way to find out the current that is actually being drawn under whatever conditions (and to do other troubleshooting with if necessary, such as finding out actual system watts, or measuring voltage sag (to know how well or poorly the battery is performing under that load) is to use a wattmeter between battery and controller. There are a lot of them, and most are fairly inexpensive. I use the Cycle Analyst v3 on my SB Cruiser trike, but that's because it also has a lot of other functions I need. For just testing, I've used cheap RC wattmeters like the old Turnigy Watt Meter; it doesn't do the voltage you need but there are versions that will. There are also panel-mount types you could permanently install on the bike if you like; I have one from Amazon that I have not yet tested (maybe get to that this week if my yard fence work goes as planned...but you know what they say about plans...) that should work on your system, and there are a bunch of versions like it out there:
https://www.amazon.com/gp/product/B013PKYILS

If I run full throttle in this configuration.. i.e., running at 80Amps, I'm only getting 30 minutes or so of ride. so if I want a longer ride, I either ride slow manually or further limit the controller down to say 40 Amps max peak.. then get an hour at full throttle, and potentially suffer going up hills? I'm likely never to push that 8000W motor from a speed/RPM perspective. My intention with the bike was to take it on fire roads for 1 - 2 hour rides or longer. So probably could have gotten away with a much smaller motor.. (oh well). Also, my thoughts on needing a larger Amp controller were misguided, as I don't care so much about acceleration or torque. I'll likely average 20-30mph, max speed of 40MPH.. is fine with me.

If you limit the controller to less current, then you get less power. If you need that power to go the speed you want to go under the conditions you'll be riding in, then it won't be able to do the job you want it to. Let's say there is a hill you need to go up that takes 8kw to go up at whatever speed you need to go there...if the current is limited below that, you won't be able to climb that hill at that speed. There can even be situations where going too slow up a hill at too high a load can burn out the motor (even though you're not at it's power limit).... Not very likely, but it has happened.

It will limit your acceleration just as it limits the slopes you can climb and the speed at which you can climb them, for the same reasons. If you need quick acceleration, then limiting the current severely is probably not the best solution (but you can test it easily enough if you have easy access to changing the limit in the field).

If the controller is limited to 40A, then at 72v that's about 72x40=2880W. Best guess without simulating that is that it might get you to 40MPH on flat paved roads with no winds. this post might help you see how to use the simulator to compare settings/etc
https://endless-sphere.com/forums/viewtopic.php?t=95465#p1398639


Using the throttle to regulate the system just as you normally do would work better, and more safely as far as riding itself goes, letting the system draw whatever it needs to to accomplish the job you're telling it to do with the throttle.

I don't know if the controller you have has presets or levels you can change while you ride, that also can be programmed to change the current limit rather than the throttle percentage (which is often what they do, though some controllers use the throttle to control motor current, which means that such presets would still effectively do the same job, whereas controllers that use throttle to control motor speed won't).


Something to think about, though: if you're having to run full throttle to get the ride you're after, there's no limiting you can do that won't decrease the ability of the system to do what you want.




A bigger, more capable battery, once you know what you need, would probably be the best solution to the potential problems you have ATM. But I'd test the bike out under all the conditions you need to use it in, the way you want it to be, before replacing parts--you might find there are other limitations to address that merit a different bike entirely, and then you could sell this one to help pay for the more appropriate one.

 

[igashosparks]

@amberworlf..

Thanks again for all the useful information!.. just a couple of follow up questions.

I love the idea of the wattmeter between battery and controller... looking at the wiring diagram on Amazon, is that shunt exposed circuitry? or do you insulate around the shunt as needed?

Regarding limiting the controller to 40Amps, or some other number below the max of 80.. I guess I can play around with it, and either leave it at 80-Amps for the hill climbs, or find a happy medium that provides enough power to get the job done..

I don't know if the controller you have has presets or levels you can change while you ride, that also can be programmed to change the current limit rather than the throttle percentage (which is often what they do, though some controllers use the throttle to control motor current, which means that such presets would still effectively do the same job, whereas controllers that use throttle to control motor speed won't).

I have an all terrain electric skateboard that has this... on the throttle/remote you can set it to 4 different levels in increments of 25% of full power.. Level 4 it goes 35MPH on flat paved ground which is pretty insane on a skateboard, but off road and up hills the extra power comes in handy. Something like that would be useful on the bike, but no.. I don't believe my controller/display has this feature.

But I'd test the bike out under all the conditions you need to use it in, the way you want it to be, before replacing parts--you might find there are other limitations to address that merit a different bike entirely, and then you could sell this one to help pay for the more appropriate one.

I love the frame, and look of this bike.. it's as close to a DIY that I'll likely get for a while.. If anything, I'll pull and swap components as I go along.. but for now, I'm determined to get this one to my liking.

I just received my 80Amp replacement fuse (so I can at least get power to the controller), now just waiting on the blue tooth adapter to log in and take a look at the settings and adjust accordingly. Hopefully that goes smoothly, seems like quite a few out there have trouble connecting.

thanks again! I really appreciate the support!

 

[amberwolf]

I love the idea of the wattmeter between battery and controller... looking at the wiring diagram on Amazon, is that shunt exposed circuitry? or do you insulate around the shunt as needed?

The best way is to bolt it to a mounting spot on the frame, ensuring it is insulated from the frame. Then it can't float around and wear thru whatever insulation is used, if it happens to bang or rub on something.

Otherwise, you can just do it the same way the fuse is installed (except it goes in the *negative* battery lead instead of positive), and insulate it however you need to.

BTW, I recommend the heatshrink insulation rather than electrical tape, mostly because tape tends to unwrap itself over time as heat/humidity/etc degrade the adhesive. Some tapes are better than others (like the 3M brand stuff usually works better than most generics, and there are automotive grades intended for more abusive environments, etc).

If using heatshrink I would get the thickwall stuff, so when shrunk it will better protect. Or use two or three layers of thinner stuff. HS usually shrinks to half or less of the original diameter, so get a size that will easily slip over everything involved. If the wires to the items are way smaller than the items, you might need two sizes to make a water-intrusion-resistant covering, but if you only need to make sure the contacts of things cant' touch anything else, just the one size should work fine. (meaning, all the fusing / wiring / etc you're working with is inside a box or other already-water-resistant containment).

Just cut a couple inches longer than you need to entirely cover the entire fuse and bolt connections including the crimped areas of the wiring lugs, slip the HS over the wiring with the fuse (or shunt) unbolted, then bolt down and slide one layer of HS over the area to be protected. Heat just that piece till it's fully shrunk, but not enough to melt it, and wait for it to cool. Then do the same with any additional layers.

If you need to see the fuse window, you can just cut a small hole in the covering HS at that point; it wont' expose the conductors so would be fine as long as you're not looking for waterproofing there.

If you need better waterproofing, you can get adhesive lined marine-grade HS so it sticks to the wires/etc to better resist intrusion.

Regarding limiting the controller to 40Amps, or some other number below the max of 80.. I guess I can play around with it, and either leave it at 80-Amps for the hill climbs, or find a happy medium that provides enough power to get the job done..

Experimentation is usually the most certain way, but I do recommend the wattmeter to be sure what power draw you are actually getting in various use-cases.

Regarding the fuse itself: after some research on the manufacturer site, this spec sheet from Eaton for Bussman ANL fuses says that the series has versions that are good for up to 80v maximum:
https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/bussmann-series-supplemental-fuses/supplemental-fuses-limiters/bus-ele-ds-2024-anl.pdf
View attachment bus-ele-ds-2024-anl[1].pdf

Specifications:
Ratings
• Volts 80Vdc or less
• Amps 35-750A
• IR 2700A

So they should be safe to use with your system voltage, and still properly disconnect under load.

Interestingly, the chart on the second page

says that for this specific model, with an 80A version of the fuse, it will take about 150A to blow within about 100 seconds (a minute and a half). This is an "average" time, and they dont' state the range of min/max that is derived from, so some fuses could take a lot longer or shorter time to blow at any specific current...but I would guess from the chart that they should still all sustain under 80A indefinitely. The chart is exponentially drawn, so it's difficult to see exactly where the curve is intersecting when not near a line. Just a little bit more current than that would blow it in a tenth of that time. Twice that current would blow it in just a second or so.

A short circuit (like say, touching the positive and negative together, or a controller failure of FETs blown such that they short these) would probably draw many times that current, and so blow in an exponentially shorter time.

So....assuming the controller can be persuaded not to draw more current than the battery itself can take (the 80A it's marked as) you can probably continue to use the 80A version of this fuse, assuming that the manufacturer of the specific fuse you have followed the Bussman specifications, if they are not Eaton/Bussman-manufactured. If they didn't make them identically to those (fuse-metal alloy, size, shape, etc), then it would require the chart from that specific manufacturer, or experimentation, to find the actual limits of that specific fuse.

I have an all terrain electric skateboard that has this... on the throttle/remote you can set it to 4 different levels in increments of 25% of full power.. Level 4 it goes 35MPH on flat paved ground which is pretty insane on a skateboard, but off road and up hills the extra power comes in handy. Something like that would be useful on the bike, but no.. I don't believe my controller/display has this feature.

If the controller has a "3-gear" or "3-speed" switch input, usually just two wires and a ground, then if the programming software for it can change that to control the battery current limit vs the speed limit, or if the throttle percentage that it likely switches can be used to control the current limit (meaning a "torque" or "current" throttle rather than a "speed" or "PWM" throttle), then that can be wired to a switch like those used for turn signals with on-off-on contacts on the back, to give you three presets: whatever is setup in the programming software.

If it can only change the speed limit, it won't do what you need it to for the current limiting.


I'll see what I can find on how it does what it does if it has a 3-speed input. Is yours a V1 or V2? If it doesn't say, it's probably a V1. (just in case their functionality is different)

 

[amberwolf]

According to this
http://www.mqcontroller.com/upfile/202108/2021083061461253.pdf
for the SVMC series, it doesn't have a 3speed switch with the wiring I described, but it does have a speed limiter jumper (that could be used with a simple toggle or pushbutton switch). Page 25 has a chart and page 24 has a screenshot of the program with the FUNC tab showing where you set that "boost/3spd" presumably to "boost" for this wiring, or "enable", to use it to get a 30-second boost to higher current.


Or set it to 3spd to use a switch to change modes, per the chart at the bottom of page 25, and then the jumper wire instead acts to toggle between modes sequentially, IIUC.

 

[igashosparks]

So this is a little confusing on the topic of fuses...

According to the Bussmann data sheet.. their 80Amp fuse doesn't actually blow when it exceeds 80Amps of current, and it takes 100 seconds to 'melt' at ~150Amps.. let's say I mis-configure the limit setting on my controller, or for some other reason it fails to limit at 80Amps. And then I'm relying on the fuse to avoid potentially melting my battery which is only rated to discharge at 80Amps.. wouldn't I want the fuse to blow quickly once I exceeded 80Amps to protect the battery, and more importantly the rider?

Am I just not understanding this correctly?

 

[amberwolf]

I might have already said this, but:

The fuse is not there to protect the battery that way. It's really there to protect battery and wiring / etc against a short circuit (which will draw much higher currents) that could cause a fire; you don't want it to blow under "normal" usage. If you really want to use it that way (as the builders of the bike appear to have done), you'll need an "instant-blow" fuse that will blow (melt) as soon as current reaches the rated point. (I haven't found a bolt-on to fit where the ANL does that will do that yet; the ones you're already using are already non-time-delay types. I'll keep looking, though).

Doing that means that any momentary overload, etc., which could even include connecting the battery to the controller because of the current inrush to charge the caps, assuming no precharge circuit (probably doesn't have one, you can add if you like), could blow the fuse. So you would probably want to carry a bag of spare fuses and the tools to change it (and insulation to re-cover it) with you on every ride, just in case. There is also always a tiny bit of variation in fuses, so the fuse could blow a little sooner on one, the next a little later...


The controller current limit is there to protect the battery against overcurrent, so it needs to be set *and tested under high enough load to draw the max it could* to be less than the max the battery is intended / able to handle (presumably the 80A that is listed on that label). The builders did not do this, but they should have. They didn't do it because then they can't sell the bike as the higher watts it gets with the higher current limit...what they should do for that case is use a battery actually capable of continuously providing the current needed to do whatever it is the bike is advertised to do, but that would cost more, so....


The BMS in the battery, if properly designed, and if functional, should shut output off at the 80A limit, but since the fuse has already blown once in operation, it's possible that it's not designed to or not able to do this (for instance, the FETs may already have failed stuck-on--it's not an uncommon failure mode). If it's not able to do this but designed to, it also means it is probalby not able to shut off output *at all*, even if the cells drop below LVC, so it could overdischarge. That's another ball of wax, that should be tested and verified at some point once you have a wattmeter of some type to make capacity guesstimate/measurements from.


The battery is not likely to just burst into flame when current a little over 80A is drawn...it depends on *why* that is the limit (and how far over 80A you go and for how long). Most likely that limit is the BMS discharge limit, which means the max current it is capable of, which has to do with the FETs used, heat dissipation from them, etc. The BMS should be (isn't always) chosen for current provision based on how much the cells can handle, so that it will limit at less than that, so they aren't stressed. If the pack is correctly built, the cells will be able to handle more than 80A, at least for a short time (several seconds, probably longer, depends on how much more than 80A it is).

But the harder the cells are pushed, and the more often, for longer time, the faster they age. More current draw does mean more heating inside the cells (and the interconnects); how much heating depends on the specific cells and interconnects, etc; we don't really have any info on those, and probably won't be able to get any reliable info from the seller/builder. It's possible to measure the heating but you'd have to open up the pack and add thermal sensors and monitor this externally somehow, then do test runs of the bike to see how hot anything gets, which is a lot more work than it is worth, typically.


As noted above it's possible (I'd actually say likely) that the BMS FETs have already failed stuck on, so it probably doesn't matter about exceeding the BMS's own current limit (the 80A is more likely the BMS limit) by a bit. Exceeding it by enough for long enough could heat the FETs enough to desolder them which could cause other BMS damage from the solder shorting other things out, which has the potential to damage cells in various ways. How much is too much? How long is too long? depends on the BMS design, FET condition (and resistance), temperature at the time, where its' installed and how (for how fast heat will accumulate), etc. Essentially "unknowable" without testing to destruction or instrumenting and testing various conditions.

 

[amberwolf]

So, all that said....

Make sure the controller is setup to not draw more than the battery is capable of, then you don't have to worry about that part. It just needs to be verified under your worst-case test conditions that it obeys the limit.

Then use a fuse that protects wiring/etc against short circuits (so it can handle the current draw of the whole system without blowing (melting the fuse element). AFAICT the 80A ANL fuse should do that fine, as long as it conforms to Bussman's spec sheet.



It'd also be good to verify that the BMS does indeed shut it's output off if conditions occur that should do that. It ought to do it for overcurrent, but it's possible it's not designed to. It *will* shut off output if LVC on a cell is reached--that's usually around 2.8v, up to around 3.0v, depending on BMS design (some are programmable via BT, in which case there will be an app for your phone to do it with, which usually can also monitor cell voltages/balance, main voltage, main current, etc)), so that when the pack is empty (any cell at LVC) it will shut off output so cells are not overdischarged.

 

[igashosparks]

Last question, then I think we can put this thread to rest, at least until I am able to log into the controller and power back up the bike and start running some of these tests..

can you verify which controller parameter get's set to 80Amp, (the max draw that the batter is capable of)?



many thanks as always @amberwofl!

 

[amberwolf]

can you verify which controller parameter get's set to 80Amp, (the max draw that the batter is capable of)?

I am not absolutely sure because the wording they use is often not what I would use, but most likely it is the ones marked as "DC current". Some of the details for them are explained below the settings screenshot, but terminology is not always straightforward or well-explained.

Limit is apparently what it uses once battery voltage drops below whatever is set in the top field DC current limited volt.

Rated is probably the continuous limit, what you can draw at most for long periods.

Max is probably the peak that can ever be drawn, for some time limit not stated there.

For your purposes, I would just set both of them the same, to whatever the most you ever want to draw is; so if 80A is the max the battery is capable of, period, then Max would be at or below 80A. Rated is presumably always going to be the same or less than Max.

PHase current *should* refer to the motor phase wire currents, but their explanation of Rated phase current seems to be what I would expect for Rated DC current. Phase currents can be higher than battery currents (just the way controllers work), and controller models are usually named for what battery current they handle (with some exceptions, some of whcih use both the battery and phase numbers in the model number, like Fardriver does).

So their explanation of Rated Phase current may be right, or wrong, but you'll probably never get a clear answer from the manufacturers or sellers of bike or controller, between the language and the technical barriers. There *might* be a clearer explanation in one of the Sabvoton threads but I haven't found it yet.

 

[igashosparks]

I got this conversation back from the battery manufacturer, I can't tell if this guy doesn't know what he's talking about.. or he's just in a rush:

 

[amberwolf]

I got this conversation back from the battery manufacturer, I can't tell if this guy doesn't know what he's talking about.. or he's just in a rush:

Could be the technical language barrier, too--technical stuff doesn't translate very well or at all for most of the Chinese stuff I see. That on top of non-technical poeple answering technical questions can get some bizarre and/or irrelevant-sounding answers.

Some thoughts:

If this is the company that built the bike, and the answers they gave are actually the "real" answers to your actual questions, I would review everything that company says, does, or makes, before trusting any of it....If they *know* the battery they put in the bike is too small / incapable of handling the current the controller is going to draw, but do it anyway, that right there means they're deliberately selling stuff that can't work or won't work for long, or could actively fail in catastrophic ways that may include fire hazards.

If this is just the battery company, and their answers are actually real, and the 6A is not a typo for 60A (which it probably is), then that battery is probably made of recycled garbage cells (there are places that do this but may sell them as new, but in any case don't tell you they're recycled garbage...I'm not talking about just salvaging good cells from packs and reusing them, but taking the garbage that the people that salvaged the good cells threw away and making packs out of those, and selling them as if they were still good usable cells that aren't a fire hazard. I expect most of those packs are sold to end-users, not other companies, because the end users outside their country wont' really have much recourse after they get the pack, as they cannot ship it back for refunds....


If it's a typo for 60A (the most likely scenario), then that's reasonable for cheap noname cells--1.5C (1.5x the Ah for an A limit). But they say the continuous is 80A, then they say the normal is the lower number. This wouldn't make sense, so they probably mean 80A is the peak (usually for a few seconds), and the lower number (60A?) is continuous.


The part about the fuse is probably telling you to change the big fuse out for a smaller one that is closer to what the pack can handle, which wouldn't hurt anything as long as it's big enough to not blow under normal usage with correct controller limiting. However, the real answer is to change the controller current limit. One of their other answers also says this.