Any advantage of 40A BMS for a 30A controller?

Obsessed biker

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Hi builders! Still pretty new here, but found great advice for my first (and only) 2 stroke build. I'm now trying to finish my first electric build. All I need now is a battery for the 48v 1000w front wheel kit i got. I'm leaning towards a 52v 20ah. My understanding is the 52v increases the max speed and won't lose as much power as the battery approaches empty. I would think that a higher voltage battery would also be less strained and therefore have longer life. Or do i have it backwards? Could it be a 48v will drain the battery to it's low voltage cutoff which is lower than what a 52v should be drained to and hence shortening it's life? Please correct me if I'm wrong.

Anyway, provided 52v will work with my controller without any problem, the ones I'm looking at are available with either a 30A or 40A continuous BMS. What I'd like to know, is a 40A helpful at all or is it unnecessary overkill when my controller says it's max draw is 30A?
 
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Street Ryderz

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Hi builders! Still pretty new here, but found great advice for my first (and only) 2 stroke build. I'm now trying to finish my first electric build. All I need now is a battery for the 48v 1000w front wheel kit i got. I'm leaning towards a 52v 20ah. My understanding is the 52v increases the max speed and won't lose as much power as the battery approaches empty. I would think that a higher voltage battery would also be less strained and therefore have longer life. Or do i have it backwards? Could it be a 48v will drain the battery to it's low voltage cutoff which is lower than what a 52v should be drained to and hence shortening it's life? Please correct me if I'm wrong.

Anyway, provided 52v will work with my controller without any problem, the ones I'm looking at are available with either a 30A or 40A continuous BMS. What I'd like to know, is a 40A helpful at all or is it unnecessary overkill when my controller says it's max draw is 30A?
A 40a bms on the battery is fine it just insures that the controller can draw it's full 30a safely and tbh the better way to go.The 52v battery is also fine since a 48v system has a peak voltage of around 56v but the cut off as mentioned above is 41-42v and that's kinda low for li ion types cells at that voltage.
 

Obsessed biker

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A 40a bms on the battery is fine it just insures that the controller can draw it's full 30a safely and tbh the better way to go.The 52v battery is also fine since a 48v system has a peak voltage of around 56v but the cut off as mentioned above is 41-42v and that's kinda low for li ion types cells at that voltage.
Thanks Street, if a 40a bms would give me more speed, longer range or battery life, then I'd think it's worth the extra $25. What I'm wondering is will it do anything that a 30a one won't do with my 30a max controller? Those bms have a much higher peak anyway. Plus I heard that 40a bms are larger so idk if that'll be noticible in a complete pre-built battery. Trying to save a little bit of cash here, but if the 10a extra is actually used and would make a noticeable difference in speed, range or batt life, then I'll pay the extra cost.

So do you think that a 52v would have a shorter life if used with 48v system? I wanted to verify that low cutoff voltage, whether it cuts out through the controller or the bms. If it's the bms then wouldn't it have a higher low cuttoff to protect the higher volt battery?
 

Street Ryderz

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Thanks Street, if a 40a bms would give me more speed, longer range or battery life, then I'd think it's worth the extra $25. What I'm wondering is will it do anything that a 30a one won't do with my 30a max controller? Those bms have a much higher peak anyway. Plus I heard that 40a bms are larger so idk if that'll be noticible in a complete pre-built battery. Trying to save a little bit of cash here, but if the 10a extra is actually used and would make a noticeable difference in speed, range or batt life, then I'll pay the extra cost.

So do you think that a 52v would have a shorter life if used with 48v system? I wanted to verify that low cutoff voltage, whether it cuts out through the controller or the bms. If it's the bms then wouldn't it have a higher low cuttoff to protect the higher volt battery?
Yes it would,the extra 10a available from battery just insures the controller can draw it's max without hurting the battery or bms or controller it is always best to have a buffer zone.
 

Obsessed biker

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Yes it would,the extra 10a available from battery just insures the controller can draw it's max without hurting the battery or bms or controller it is always best to have a buffer zone.
I get what you're saying, but isn't that what the peak discharge current is supposed to be for? It says the peak is 75a for the 30a bms and 100a for the 40a one. I can't imagine how fast I'd be going to draw 75a.
 
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Street Ryderz

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I get what you're saying, but isn't that what the peak discharge current is supposed to be for? It says the peak is 75a for the 30a bms and 100a for the 40a one. I can't imagine how fast I'd be going to draw 75a.
The peak or burst discharge is the max current available from battery pack in a momentary situation,you're motor will never draw that nor would the speed controller.Amperage is not what makes it go fast, the voltage determines the rpm/speed the amperage supports the voltage under load so as not to drop to much and keep the rpm's up.The amperages main purpose is run time and for how long it supports the voltage without to much drop,when the amperage is low under load the voltage drops dramatically and may or will fall below the cut off v so the user knows it's time to recharge.
 

Obsessed biker

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You'd be going slow under load up a hill trying to accelerate to draw 75 ramps. My 1:10 scale rc truck has 760 amp burst lol
Wow that must be some RC truck! So it sounds like it would draw more amps when it's requiring more torque? I still don't get how the controller would draw over 30a if that's it's max. 🤔
 

Street Ryderz

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Wow that must be some RC truck! So it sounds like it would draw more amps when it's requiring more torque? I still don't get how the controller would draw over 30a if that's it's max. 🤔
Same thing with the battery peak and continuous,the controller is 30a continuous and probably 40-45 peak momentary or whatever the fet's are rated for.Most ebikes don't draw more than 30a unless it's a hot rod and the average constant draw is only 6-7 amps,any higher and your run time would be pathetic.
 

Obsessed biker

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The peak or burst discharge is the max current available from battery pack in a momentary situation,you're motor will never draw that nor would the speed controller.Amperage is not what makes it go fast, the voltage determines the rpm/speed the amperage supports the voltage under load so as not to drop to much and keep the rpm's up.The amperages main purpose is run time and for how long it supports the voltage without to much drop,when the amperage is low under load the voltage drops dramatically and may or will fall below the cut off v so the user knows it's time to recharge.
Ok, that helps. And accounting for what frogslayer said, it sounds like it would draw higher amps under load like going uphill. What I don't get is that the controller determines power usage and theoretically won't go over 30a unless its short bursts. So unless I regularly hit the peak draw and the controller allows it to go over how would the extra 10 available amps be utilized? Would it actually give me more torque or speed uphill? Hope I'm not frustrating you or anything. It just has to have really solid advantages for me to not see it as redundant. Lol
 
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