P14 Current Limit Setting

Killerchaos7

100 µW
Joined
Nov 24, 2021
Messages
8
Alright, so here's a little something to share right quick to give you guys an idea of what I've got for my ebike. I have the following:

Battery:
72V 25AH with 50A BMS
Max Continuous Discharge Current: 50A
Peak Discharge Current:150A

Controller:
48V-72V sine wave (Max 84V)
Amp Rate: 60A

26" Hub Motor:
72V 3000W (41.67 amps if you do the math with these values)

I've input the proper settings in the display to my liking and whatnot. Now as for the P14 setting, I noticed that it was set at 26 amps (the range for mine is from 1 to 50). Did a test for a couple of rides, and noticed that it's got some power to it and whatnot but it only gets up to around 36mph while not really reaching 3000W, so I changed it to 30 amps. For the next couple of rides, the power increased somewhat and now had me topped out at 44mph full speed and actually reaching roughly 2800W (though I did briefly reach 3000W for a second or two). Made one more change and put that same parameter setting to 35 amps. Another speed increase to roughly 48mph and was actually hitting 3000W (peaked at 3300-something a few times). At this point, I feel like as though this might be where I needed to set this thing to. My battery indicator shows that I still have plenty of capacity even after riding a good few miles in a suburban area with some traffic and short bursts of full throttle on open roads.

With all of the above information in mind, my question to you all is what is the absolute SAFEST MAXIMUM setting that I can use here? I rather not push that setting any further than where I already am without first finding out from the more experienced folks on here if I'm able to do so. If there's more that my set up can handle, then I'd like to know. Otherwise, I'm staying with where I am at this time. I'm well aware that setting that parameter too high is gonna spell for something to eventually fry itself to death or worse.
 
This is way out of my league, but I'm wondering just how comfortable you are with 2 things. The max amperage ratings for the battery/controller/motor you're using (knowing full well manf's have been known to stretch the truth just a bit), and the size of the wire you're using to carry this amount of power.

In my mind, you're asking "how big a bump can I hit before this dynamite goes off"? I doubt seriously there's a "safe" answer.
 
The best way is to monitor the heat of the motor, controller and wires. While it not bad to use a lot of power for a few seconds to get up to speed. Pull hills or riding into the wind at speeds higher than your setup can handle is bad.

I would start with your battery. First if it has a 50a BMS then you not going to pull 150a. Find the max continuous discharge of your battery. Above this your damaging the battery if ran more than a few seconds. If you want to make your battery last longer then farther you stay below that number the better. Then find out if your controller gets hot running them amps and if your wiring is getting hot to the point of melting. If all is well so far then just monitor your motor for heat and don't get it so hot you weaken your magnets.

The specs suggest that you can set your max setting just under 50a so it does not trip your BMS (Don't think your BMS is set at 50a). You should only need to worry on long hills or trying to ride at 40+ mph for miles. Just monitor your motor heat to see what you can get away with. Everyone rides differently and the terrain varies. I live in close to flat roads and can not keep my watts high, hit max speed then watts drop. Only way to hurt the motor is keep it loaded and heating up. Pulling hills or riding faster than it can get rid of heat.

My setup is not as robust as yours, 72V 24ah battery (max continuous discharge is 36a), 40a controller and 1500w motor. can set it at 3200w. My top speed is around 32 mph and it only takes 700w-1200w to maintain this speed. Hills would be the only way for me to over heat the motor. Have a three setting power switch. Can set it at 2000w watts and not worry about over heating. Lose some take off speed but is gentle on the battery, controller and motor.
 
Killerchaos7 said:
Another speed increase to roughly 48mph and was actually hitting 3000W (peaked at 3300-something a few times).

With all of the above information in mind, my question to you all is what is the absolute SAFEST MAXIMUM setting that I can use here?

These two sentences don't belong together. You're riding around at 48mph on a bicycle and concerned about safety?
 
AHicks said:
This is way out of my league, but I'm wondering just how comfortable you are with 2 things. The max amperage ratings for the battery/controller/motor you're using (knowing full well manf's have been known to stretch the truth just a bit), and the size of the wire you're using to carry this amount of power.

In my mind, you're asking "how big a bump can I hit before this dynamite goes off"? I doubt seriously there's a "safe" answer.

I've kept that in mind, seeing as though some of the reviews I've watched on YouTube have mentioned this a good few times about how sellers will boast that their ebike kit can do this and that when it really doesn't through proper testing. So far, what I've got lives up to what the seller marked this as, and even moreso when reading over the reviews for the kit that I bought, but yeah. That's the reason why I basically said that I stopped at 35A... I'm not risking going any higher than that until I get a definitive yes, and if I can't, then I'm willing to not push my luck any further and just enjoy the fact that I have something fun to ride.

ZeroEm said:
The best way is to monitor the heat of the motor, controller and wires. While it not bad to use a lot of power for a few seconds to get up to speed. Pull hills or riding into the wind at speeds higher than your setup can handle is bad.

I would start with your battery. First if it has a 50a BMS then you not going to pull 150a. Find the max continuous discharge of your battery. Above this your damaging the battery if ran more than a few seconds. If you want to make your battery last longer then farther you stay below that number the better. Then find out if your controller gets hot running them amps and if your wiring is getting hot to the point of melting. If all is well so far then just monitor your motor for heat and don't get it so hot you weaken your magnets.

The specs suggest that you can set your max setting just under 50a so it does not trip your BMS (Don't think your BMS is set at 50a). You should only need to worry on long hills or trying to ride at 40+ mph for miles. Just monitor your motor heat to see what you can get away with. Everyone rides differently and the terrain varies. I live in close to flat roads and can not keep my watts high, hit max speed then watts drop. Only way to hurt the motor is keep it loaded and heating up. Pulling hills or riding faster than it can get rid of heat.

My setup is not as robust as yours, 72V 24ah battery (max continuous discharge is 36a), 40a controller and 1500w motor. can set it at 3200w. My top speed is around 32 mph and it only takes 700w-1200w to maintain this speed. Hills would be the only way for me to over heat the motor. Have a three setting power switch. Can set it at 2000w watts and not worry about over heating. Lose some take off speed but is gentle on the battery, controller and motor.

You made some very good points here. Starting off with what you mentioned about the battery, that's the only information that I know of regarding its amp potential. Obviously, I can inquire the seller about the finer details, which I'll get around to doing that after leaving my replies here. Never thought about checking the wires, as I've only been able to just monitor my motor through how many watts I'm putting out at higher speeds. Anytime that I exceeded 3000, I'd quickly back off from it unless I'm performing a short burst of full throttle, which, again, makes it go a little over 3300 for my setup. It helps that where I live, it only gets into the 50s during the day and cools back down close to 40 whenever I get off from work, so there's at least that much as far as keeping things from heating up so much while I'm riding out here.

Any real steep hills that I come across, I get my bike going a good bit just before I start going up and then backing off some to where I can safely cruise while going up and pedaling some at the same time so the motor's not doing all the work for me. I also don't try pushing 40+ every so often; only when it's absolutely necessary to keep up with speeding traffic, which happens in one portion of my area whenever I'm heading to work. Before and beyond that point, I stay anywhere between 30 and 35mph for regular riding (or basically between 1200 and 2100 watts; sometimes a bit more. Kinda fluctuates a good bit, but that's a general range that I've noticed). My area is piedmont terrain, so there are flats at times but also hills here and there. Some steep; others not, and most of them are just gradual ones where I regularly ride on.

That's a good setup you've got there for what it is, and it sounds like you've got quite a bit of control over what your motor can do for ya based on your needs. Not bad at all, I say.

E-HP said:
Killerchaos7 said:
Another speed increase to roughly 48mph and was actually hitting 3000W (peaked at 3300-something a few times).

With all of the above information in mind, my question to you all is what is the absolute SAFEST MAXIMUM setting that I can use here?

These two sentences don't belong together. You're riding around at 48mph on a bicycle and concerned about safety?

I understand how ludicrous that sounds when thinking about these two things, but this wouldn't be my first rodeo. Before my conversion to electric, I was hitting 45mph with a custom-made 80cc race engine, and it had potential to rocket me up to 55mph; just never got there on account of having my carburetor screw up, which led to other unnecessary issues that made me eventually give up on trying to work on this thing after owning it for roughly 3 years.

I just don't want things to prematurely end after recently getting the opportunity to experience something new here just because I didn't know at what point I should stop with something as crucial as setting my current limit. Don't get me wrong; as much as I like to squeeze out every bit of potential power this particular motor has, I also wanna prevent myself from taking things too far with it before I end up getting myself (or others around me) hurt from some accident related to this amongst other things and/or completely screwing up this whole project that I've spent months preparing for and building.
 
Killerchaos7 said:
I understand how ludicrous that sounds when thinking about these two things, but this wouldn't be my first rodeo. Before my conversion to electric, I was hitting 45mph with a custom-made 80cc race engine, and it had potential to rocket me up to 55mph; just never got there on account of having my carburetor screw up, which led to other unnecessary issues that made me eventually give up on trying to work on this thing after owning it for roughly 3 years.

55mph "Rocket"?
As long as you don't lose sight of the fact that it's a bicycle, that goes just fast enough to kill yourself, with less horsepower than a riding lawn mower, and slower than a Toyota Prius.
 
Longevity of the battery is what some or most of us think about. It's 50% or higher total cost of the total build with a little care you can get years out of it. Abusing it can cut the life down to 1 yr or 6 months. Seems like your riding within you bikes abilities. High powered burst are not bad to get up to speed. If it's only pulling 1200-2000w continuous you should not have any worries. If it's really a 3000w motor it should handle 4-5000w for a short periods. Need a tempter thermistor inside of the motor touching it outside does not give a idea of how hot it is inside. 30 mph is not a bad speed. 40 - 50 mph is more of a motorcycle. Remember mopeds ride at 35 mph. If riding fast think about your tires get good ones.
 
Killerchaos7 said:
Battery:
72V 25AH with 50A BMS
Max Continuous Discharge Current: 50A
Peak Discharge Current:150A

Controller:
48V-72V sine wave (Max 84V)
Amp Rate: 60A

26" Hub Motor:
72V 3000W (41.67 amps if you do the math with these values)

so from reading all this post, it seems like your limiting factor is your battery, so even though you can go 50a continuous, i would go 20% less on the battery and limit it to 40a. just to be safe/comfortable on the battery and BMS and to prolong the battery life.

if we took everything at face value, 72v x 40a = 2880w of energy which should be safe for your motor if it is a 3000w motor but we have to remember that fully charged is 84v and after the first throttle run it would be more like 80v, give a volt or two, depending on sag. so 80*40 = 3200w, so should still be within safe limits.

i would say, if you wanted to test what's the safest max do this test:

1. grab an inferred temperature gun and check temp of motor and controller
2. test bike by going up to top speed (40mph) and then stopping and repeat process 4-5 times
3. take temp of motor and see how fast the motor heats up on the out side.
4. log amp setting and temps difference

if temp difference is big, use with caution as motor or controller could overheat fast.
if temp difference is little, should be safe to run as motor/controller is not heating up and your not stressing either components.

this isn't a definitive test, but doing this helped me test out my own ebike and helped me know that it's safe to run 1200w through a 500w geared hub motor. Happy testing. :thumb:

forgot to add that if i went over 1200w, motor would heat up really bad and not like it. somehow, 1250w or higher was enough to overheat it fast, but 1200w and under, the motor would be able to eat that all day long, even on steep hills.
 
ZeroEm said:
Longevity of the battery is what some or most of us think about. It's 50% or higher total cost of the total build with a little care you can get years out of it. Abusing it can cut the life down to 1 yr or 6 months. Seems like your riding within you bikes abilities. High powered burst are not bad to get up to speed. If it's only pulling 1200-2000w continuous you should not have any worries. If it's really a 3000w motor it should handle 4-5000w for a short periods. Need a tempter thermistor inside of the motor touching it outside does not give a idea of how hot it is inside. 30 mph is not a bad speed. 40 - 50 mph is more of a motorcycle. Remember mopeds ride at 35 mph. If riding fast think about your tires get good ones.
justlooking808 said:
Killerchaos7 said:
Battery:
72V 25AH with 50A BMS
Max Continuous Discharge Current: 50A
Peak Discharge Current:150A

Controller:
48V-72V sine wave (Max 84V)
Amp Rate: 60A

26" Hub Motor:
72V 3000W (41.67 amps if you do the math with these values)

so from reading all this post, it seems like your limiting factor is your battery, so even though you can go 50a continuous, i would go 20% less on the battery and limit it to 40a. just to be safe/comfortable on the battery and BMS and to prolong the battery life.

if we took everything at face value, 72v x 40a = 2880w of energy which should be safe for your motor if it is a 3000w motor but we have to remember that fully charged is 84v and after the first throttle run it would be more like 80v, give a volt or two, depending on sag. so 80*40 = 3200w, so should still be within safe limits.

i would say, if you wanted to test what's the safest max do this test:

1. grab an inferred temperature gun and check temp of motor and controller
2. test bike by going up to top speed (40mph) and then stopping and repeat process 4-5 times
3. take temp of motor and see how fast the motor heats up on the out side.
4. log amp setting and temps difference

if temp difference is big, use with caution as motor or controller could overheat fast.
if temp difference is little, should be safe to run as motor/controller is not heating up and your not stressing either components.

this isn't a definitive test, but doing this helped me test out my own ebike and helped me know that it's safe to run 1200w through a 500w geared hub motor. Happy testing. :thumb:

forgot to add that if i went over 1200w, motor would heat up really bad and not like it. somehow, 1250w or higher was enough to overheat it fast, but 1200w and under, the motor would be able to eat that all day long, even on steep hills.

Thanks for the input, guys. Definitely keeping all of this in mind. I'll be doing further testing today and see where I stand with my limitations on my build. After this, I should have a very good idea of how best to monitor things while I'm riding and exactly where the peak performance truly lies given my setup. Hopefully, all will go well when everything's finished, and I can enjoy myself more than ever on my ride. 👍
 
Just a thought. Maybe consider something WAY more than you need next time, so you can USE it at about 50%, knowing there's 50% in reserve when/if you need it?
 
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