Sabvoton controller help?

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Eastwood   10 mW

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Sabvoton controller help?

Post by Eastwood » Jan 13 2021 3:03pm

Hello everyone!
First post here and I’m excited about joining this forum. There seems to be a lot of information on sabvoton controllers :) I’m fairly new to the E bike world as far as building E bikes. Everything is working great on my bike and I’ve learned so much info over the past several months.

I’ll get some specs before I ask my question.
I have a 1500w hub motor with a 48v 30ah 50aBMS.

So first off I would like to say how much I am loving this new controller over the cheap Chinese controller that came with this ebike kit. I gained over 10 mph on the top end without any boost or flux weakening. Also the acceleration is so much harder off the line where the stock controller felt similar to my 500W E bike off the line :lol: I can get up to speed much quicker now!! :D

So my first question is about flux weakening.,
Having a 50a BMS what is the maximum current I can use with the flux weakening?

My second question is how much boost can I use with this 50a BMS?

Both of these terms are new to me and I’ve been reading a lot on them but I’m just not clear on how much I can you safely with my limited BMS. I will be getting a 72 V battery with a higher be a mess but for now I will just be running the 48 V

I would greatly appreciate any feedback on those two questions, thank you in advance for any help!!

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MadRhino   100 GW

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Re: Sabvoton controller help?

Post by MadRhino » Jan 13 2021 3:09pm

A BMS is safe by definition, because it will cut off power if you ask too much. So you can play with you controller settings without worrying about damaging the battery.
Make it fool-proof, and I will make a better fool.
Current bikes
Street:
Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

Eastwood   10 mW

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Re: Sabvoton controller help?

Post by Eastwood » Jan 13 2021 3:35pm

MadRhino wrote:
Jan 13 2021 3:09pm
A BMS is safe by definition, because it will cut off power if you ask too much. So you can play with you controller settings without worrying about damaging the battery.
Yes that makes perfect sense thank you! I will play around with the settings now and do a test ride. That being said do you have any suggestions for those two settings? Thankfully I found the post on here where it was a breakdown of all the different settings and it seems like you can raise those numbers quite higher than what the BMS is rated for.

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MadRhino   100 GW

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Re: Sabvoton controller help?

Post by MadRhino » Jan 13 2021 6:23pm

Of course it is useless to set the controller above battery limits. A controller software breakdown has nothing to do with it though. This is a problem that is usually caused by communication interface, that this controller is known for, occasionally.
Make it fool-proof, and I will make a better fool.
Current bikes
Street:
Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

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amberwolf   100 GW

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Re: Sabvoton controller help?

Post by amberwolf » Jan 13 2021 6:30pm

MadRhino wrote:
Jan 13 2021 3:09pm
A BMS is safe by definition, because it will cut off power if you ask too much. So you can play with you controller settings without worrying about damaging the battery.
That depends on the actual BMS specs and how it works, vs what it is advertised as.

For instance, there is a recent thread where a BMS was advertised as a particular current rating, but it does not shut off even at several times that current. So that BMS's current rating is apparently (but not obviously) meant as a max that it *should* be used at, not a max that it will prevent use at.

This isn't all that uncommon, in ratings of various components in the ebike world, unfortunately, making it difficult to predict how a particular part will behave near or at it's "max" ratings.


So in this case I recommend testing your battery's response to high current, to determine where it's actual shutoff point is (since the seller or manufacturer may be unable or unwilling to give you the information you really need about this). Keep in mind it may be possible to damage or destroy the BMS or the cells in the battery by running currents past their maximum ability to handle it, if that ability is less than the point at which it is designed to protect itself by shutting off.

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MadRhino   100 GW

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Re: Sabvoton controller help?

Post by MadRhino » Jan 13 2021 8:16pm

amberwolf wrote:
Jan 13 2021 6:30pm

... there is a recent thread where a BMS was advertised as a particular current rating, but it does not shut off even at several times that current.
Well, this is comforting me with the decision to avoid using any BMS, and monitor batteries by myself. Still, the power cut-off of a BMS should be obvious, and clearly displayed by the reset button. At least it would be if I was selling one.
Make it fool-proof, and I will make a better fool.
Current bikes
Street:
Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

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amberwolf   100 GW

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Re: Sabvoton controller help?

Post by amberwolf » Jan 13 2021 8:38pm

MadRhino wrote:
Jan 13 2021 8:16pm
Well, this is comforting me with the decision to avoid using any BMS, and monitor batteries by myself. Still, the power cut-off of a BMS should be obvious, and clearly displayed by the reset button. At least it would be if I was selling one.
There's a lot of things I would do different than other sellers and manufacturers, if I were selling stuff.... :/

FWIW, I don't use a BMS on my EIG packs, but I do use one on an 18650 pack I have (the one that came with it), because I "trust" the quality control of EIG, and the capability of their cells, to do what I want and to stay well-matched over time...where I cant' say the same for the 18650s that werent' designed for the use to which they are being put. But...I only know the limits of the BMS because I tested them--the place it came from didn't have the full information.

Eastwood   10 mW

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Re: Sabvoton controller help?

Post by Eastwood » Jan 13 2021 8:56pm

Update on my testing today :shock:
So I had to push the bike home 11 miles because it blew a fuse on the hot battery terminal. there’s a 50 amp fuse on the red/hot wire and as soon as I turned up the boost it popped the fused and I completely forgot there was even a fuse there because I had it inside of a project box with the charger port. It’s a BTR brand battery and I guess they added the fuse for extra protection. Makes me think the BMS might be slightly higher but they put the 50 amp fuse to avoid warranty claims im guessing. I was able to ride it down hills but my front chain ring is way too big to even ride on flat ground without battery power. Thankfully I got home installed a new fuse and everything is still working :thumb:

Well I learned something today :lol: :lol: :lol:
I am still very new to this and thankfully it didn’t mess anything up.

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amberwolf   100 GW

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Re: Sabvoton controller help?

Post by amberwolf » Jan 13 2021 9:03pm

FWIW, a 50A fuse won't just blow at 50A. It'll blow when it heats up enough to melt the wire, which means that it might blow instantly at 200A, or after an hour at 55A, or somewhere in between. You can go to the fuse manufacturer's site and find the chart for that fuse model, to see how that works for that fuse.

If you don't know how much current you were drawing when it blew, you can't find out by the fuse rating. ;)

Eastwood   10 mW

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Re: Sabvoton controller help?

Post by Eastwood » Jan 13 2021 9:14pm

Yes that’s correct it actually didn’t blow right away. I adjusted the boost to 75a and I’m guessing I rode 2 to 3 miles before the fuse popped. I will absolutely keep extra fuses with me from now on! It’s funny because I have a tool bag with basically everything I would possibly need except those darn fuses. :lol:

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amberwolf   100 GW

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Re: Sabvoton controller help?

Post by amberwolf » Jan 13 2021 10:48pm

Eastwood wrote:
Jan 13 2021 9:14pm
I adjusted the boost to 75a
If your battery was designed for only 50A, running it at 150% of it's designed limit may not be a very good idea. The BMS is obviously not going to protect it against sustained overcurrent, and the fuse isn't able to do that (it's basically there as short-circuit protection, because a BMS's FETs can fail in a way that leaves them "on"), so you should leave the controller set to not draw more than the battery is intended to supply.

Possible problems and effects, if any, depend on exactly how the battery is made, what it's made of (cells, etc), actual BMS behavior, and so on.

Just so you know what *could* happen (doesn't mean it will, and most likely you wouldnt' see any of these things without prolonged usage at such high currents), possible failure modes of a battery that's used beyond it's current-delivery abilities include, in no particular order:

--BMS FET overheating, leading to FET failure. The FETs can fail "on" so the BMS can then no longer prevent the pack from being overcharged or overdischarged.

--Cell overheating, leading to cell damage, and potentially to a fire (while fire is unlikely, it's possible, either from the overheating itself if it's severe enough, or from cumulative cell damage).

--Premature pack aging from the cell overheating; usually this becomes apparent with excessive voltage sag even under normal current usage, or

--Excessive voltage sag during high-current usage, possibly causing system shutdown while riding if it reaches the LVC (though this woudlnt' happen except when the pack was clsoer to empty than full), but causing lower total power output even if it doesn't (v x a = w).

--Insulation damage from overheating, potentially leading to a fire depending on where the failure happens and if a direct short occurs. Insulation that can be damaged this way is typically the cell wrappers. If they are in holders that wont' distort from the heat, then there is little risk of them touching each other and shorting between series cells, shorting out groups of cells, but if they are like many packs and simply pressed right against each other, separated only by the cell shrinkwrap, then if this is damaged, there's nothing to then prevent shorting them out if theyr'e in differnet groups, unless the interconnects are so solid they can't allow it. It's not a likely event...but possible.

Just some stuff to think about. ;)

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amberwolf   100 GW

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Re: Sabvoton controller help?

Post by amberwolf » Jan 13 2021 10:55pm

Eastwood wrote:
Jan 13 2021 9:14pm
I adjusted the boost to 75a and I’m guessing I rode 2 to 3 miles before the fuse popped.
Also, note that what the boost is set to, and how much current you actualy were drawing for any of that ride, aren't directly connected. You'd have to be measuring the current, preferably with a wattmeter rather than just an ammeter/multimeter (because you get other data like voltage sag, etc at the same time, which is important for seeing the effects of doing this), and noting down the results as you go, to know what's really going on.

Eastwood   10 mW

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Re: Sabvoton controller help?

Post by Eastwood » Jan 14 2021 12:11am

amberwolf wrote:
Jan 13 2021 10:48pm
Eastwood wrote:
Jan 13 2021 9:14pm
I adjusted the boost to 75a
If your battery was designed for only 50A, running it at 150% of it's designed limit may not be a very good idea.
Yes I very much agree! I wasn’t going to turn it past what the BMS could handle but the first reply was suggesting the BMS would protect the battery and turn off if there was an issue. I definitely won’t do that again so I learned from my mistake lol

Eastwood   10 mW

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Re: Sabvoton controller help?

Post by Eastwood » Jan 14 2021 12:13am

amberwolf wrote:
Jan 13 2021 10:48pm
Eastwood wrote:
Jan 13 2021 9:14pm
Just some stuff to think about. ;)
Thank you for the info!

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