I’m a total beginner here working on my first build. The bike is complete and I’m so far happy with the motor setup. I wanted a light, small motor that could accept a Shimano 1x11 drive train so I purchased the Bafang G310 (250w nominal) rear hub from Grin. I paired it with a Grin C-4820-GR_Higo 36v-52v sine wave controller. Then I purchased a 52v 13.6ah battery from EM3EV. Did I buy too large of a battery? I think the controller will handle it but I don’t want to burn up the motor. I’ve been using it and I have a lot of hills around here and it seems to be doing ok, motor case doesn’t feel hot after just warm. Also I’m using throttle only, no pedal assist.
First Ebike: Too much Battery ?
- Thread starter MacN
- Start date
markz
100 TW
:thumb: :thumb: :thumb: :thumb:
Can cause problems because of the old adage, the more wires and stuff you have the more that can go wrong. Then for a person like you, new, first ebike build, troubleshooting could be a challenge so good on you for going throttle only :thumb:
So ya just imagine if you went with a display kit like a KT, even more wires and even more stuff
Countless people coming into ES with an error code on their display.
I believe that controller is 25A, I remember looking at it or something similar yesterday browsing for a Sinewave, FOC with regen. Your battery is probably 40A so your good there.
52Vx13.6Ah=708watt-hours so depending on how much you pedal, hills, terrain, wind, your body weight, cargo, you'll probably be doing all right with range. 30wh/mile (20wh/km) will net you 23 miles or 35 km.
To convert to wh/mile you can go here https://www.aqua-calc.com/convert/electric-car-energy-economy/watt-hour-per-kilometer-to-watt-hour-per-mile
https://ebikes.ca/learn/batteries.html
Minimal Assist (using motor only on hills, slower ~30kph setup) 6-8 Wh/km
Typical Assist (~40 kph with pedaling, motor on all the time) 9-12 Wh/km
Power Hungry (either no pedaling, or hauling a load, or going really fast) 14-20 Wh/km
MacN said:
No. You can burn up the motor with a 36V battery, so ... no worries there, eh?
You might be interested to plug your numbers into Grin's motor simulator. When I do that, just guessing at some elements of your situation, I find for example that if you were on a 7% grade (pretty steep), you could take it at 21 mph, full throttle, for almost 2.4 miles before it overheats. Or you could take it at half throttle, about 12 mph, and get twice as far.
A real life 7% hill isn't going to be 2 miles long, so there's a lot more to applying this info to the real world. I doubt you're going to burn up your motor, but watch the heavy loads.
e-beach
10 MW
Just don't overheat the motor. Learn how to ride your local terrain without letting the motor get too hot. Warm to the touch, is fine. Too hot to touch is too hot.
If it's the Super Shark with 35E cells, then it seems like a good match, since the battery can provide 20A (rated conservatively by EM3EV, at 5A per cell), per EM3EV, and the controller limit is 20A as well. If you went smaller, then you would need higher output cells, which will also have less capacity/range. I don't think it would make much sense to go smaller in a 13S pack. The next smallest would be 13S3P, which could provide 20A with 35E cells, but harder on the pack, and 25% less range, or even less range using higher output cells (e.g. 30Q).MacN said:
JackFlorey
100 kW
Probably not. If you can add a temp sensor to the hub; then you will know for sure.MacN said:
MadRhino
100 GW
You never have too much battery, unless you are racing. When weight is a major factor and extra battery capacity is a nuisance.
The current fed to the motor is set in the controller program. Your battery could be too small to supply the controller setting, but it will never be too big as to cause damage to the controller or motor. It will only make more range.
It is recommended to build a bike with extra battery capacity for many reasons:
-safe range when riding conditions are adverse.
-charge and discharge safe margin for longer life
-extra power available for future upgrade.
The current fed to the motor is set in the controller program. Your battery could be too small to supply the controller setting, but it will never be too big as to cause damage to the controller or motor. It will only make more range.
It is recommended to build a bike with extra battery capacity for many reasons:
-safe range when riding conditions are adverse.
-charge and discharge safe margin for longer life
-extra power available for future upgrade.
Battery is fine, the controller is a bit of a worry without limits.
I wouldn't run my 311s at more than 5A (at 52V) without thermal roll back. I suggest 10-12A maximum with roll back. They heat up quickly. I limit mine to 80C which is on the low end of the spectrum... definitely wouldn't want it exceeding 100C. Phase Amps above 30A risk stripping gears.
I wouldn't run my 311s at more than 5A (at 52V) without thermal roll back. I suggest 10-12A maximum with roll back. They heat up quickly. I limit mine to 80C which is on the low end of the spectrum... definitely wouldn't want it exceeding 100C. Phase Amps above 30A risk stripping gears.
dogman dan
1 PW
Never can have a too big battery for the controller. Too high voltage yes, but never too much capacity for the controller. That's what it does, controls the current fed to the motor. You can have a battery that is too big to carry on the bike without being awkward. This is what pushed me toward cargo bikes eventually, I was wanting to carry 40 ah, or more for really long touring rides.
However, you did choose a smaller motor, that can be pushed to overheat. This is primarily done by too much load on it. Mostly this is in the form of weight. Ideally, you'd either weigh 150 pounds of less when climbing long steep hills, or you are fit enough to pedal harder than typical old, fat, smoked for 50 years type riders.
Just pedal hard up the hills, and you won't hurt the motor, unless you weigh a lot more than 200 pounds. If you do, you need to buy a new motor when you smoke the one you have. Try to keep your speed well above 12 mph up the hills, preferably 15 mph. If you are fit, this should be no problem. Loading the motor enough to be unable to ride 10 mph, will smoke the motor. At low rpm, under heavy load, the motor makes more of the current into heat instead of motion.
Slow riding is fine under light load, like on the flat. Its only on the hills that you have to ride 15 mph, ideally.
Also, its a long hill you can't ride up faster than 12 mph that is the problem. If you slow to 5 mph on a really steep hill, but only briefly, thats ok. The motor will get hot, but not melt it. Do that for 20 min or more up a long hill, and the motor will melt.
I did a lot of deliberate melting of motors years ago, to be able to set limits of kit warranties. We needed to know what weight limit to put on the riders, for the warranty to be valid.
However, you did choose a smaller motor, that can be pushed to overheat. This is primarily done by too much load on it. Mostly this is in the form of weight. Ideally, you'd either weigh 150 pounds of less when climbing long steep hills, or you are fit enough to pedal harder than typical old, fat, smoked for 50 years type riders.
Just pedal hard up the hills, and you won't hurt the motor, unless you weigh a lot more than 200 pounds. If you do, you need to buy a new motor when you smoke the one you have. Try to keep your speed well above 12 mph up the hills, preferably 15 mph. If you are fit, this should be no problem. Loading the motor enough to be unable to ride 10 mph, will smoke the motor. At low rpm, under heavy load, the motor makes more of the current into heat instead of motion.
Slow riding is fine under light load, like on the flat. Its only on the hills that you have to ride 15 mph, ideally.
Also, its a long hill you can't ride up faster than 12 mph that is the problem. If you slow to 5 mph on a really steep hill, but only briefly, thats ok. The motor will get hot, but not melt it. Do that for 20 min or more up a long hill, and the motor will melt.
I did a lot of deliberate melting of motors years ago, to be able to set limits of kit warranties. We needed to know what weight limit to put on the riders, for the warranty to be valid.
999zip999
100 TW
Get your hand out put your hand on the motor is the motors hot you will know it if it's warm it's okay same with the controller get your hand out put it on the controller do not overheat your controller or your motor you put your hand on there and you will know if it's too hot.
he is not going to open up the motor and put a temp sensor inside. Maybe there's a tape on thermometer that you can put on ?
he is not going to open up the motor and put a temp sensor inside. Maybe there's a tape on thermometer that you can put on ?
MadRhino
100 GW
Yep. Not a drama anyway, to fry a small hub motor. Motors are cheap. If you need to babysit your motor, it is because it is obviously too small. Then you buy a bigger one now, to have it on a shelf when the small one fries.
RunForTheHills
1 kW
The Grin G31X kits have a thermister in the motor. It is listed as a new feature for 2021.
https://ebikes.ca/product-info/grin-kits/geared.html
2021 Product Update
After some long drawn-out efforts with Bafang we've managed to have two significant updates made to our current supply of G310/G311 motors.
Combined Speed/Thermistor: All the G31x motors at Grin now have a dual speed/temperature signal on the extra white wire, rather than just a simple speed sensor. Our Baserunner_Z9 motor controllers decouple this signal so that you can now see motor temperature on the Cycle Analyst display and use thermal rollback to prevent the motors from overheating even when used well beyond their nominal power. The thermistor used in these motors is wired a bit differently than our standard motor thermistor. So to see accurate temperature readings it is essential to use the V3.15 CA firmware. For the temperature sensor type, select "NTC Bafang" from the menu. The standard "10K NTC" thermistor option in the 3.14 and earlier firmware will under-report the motor temperature.
Stronger Magnet Adhesive: The fast wind 8T motors had their rotor magnets glued on with a stronger and higher temperature rated adhesive to eliminate the risk of magnets coming loose at high RPM's. We tested this adhesive up to 800rpm and at over 100oC without any failures, while the stock adhesives would normally see magnets coming loose at around 400 rpm.
MTA: He does need to replace the controller with a Baserunner to use the thermister signal though.
https://ebikes.ca/product-info/grin-kits/geared.html
2021 Product Update
After some long drawn-out efforts with Bafang we've managed to have two significant updates made to our current supply of G310/G311 motors.
Combined Speed/Thermistor: All the G31x motors at Grin now have a dual speed/temperature signal on the extra white wire, rather than just a simple speed sensor. Our Baserunner_Z9 motor controllers decouple this signal so that you can now see motor temperature on the Cycle Analyst display and use thermal rollback to prevent the motors from overheating even when used well beyond their nominal power. The thermistor used in these motors is wired a bit differently than our standard motor thermistor. So to see accurate temperature readings it is essential to use the V3.15 CA firmware. For the temperature sensor type, select "NTC Bafang" from the menu. The standard "10K NTC" thermistor option in the 3.14 and earlier firmware will under-report the motor temperature.
Stronger Magnet Adhesive: The fast wind 8T motors had their rotor magnets glued on with a stronger and higher temperature rated adhesive to eliminate the risk of magnets coming loose at high RPM's. We tested this adhesive up to 800rpm and at over 100oC without any failures, while the stock adhesives would normally see magnets coming loose at around 400 rpm.
MTA: He does need to replace the controller with a Baserunner to use the thermister signal though.
dogman dan
1 PW
Melting the motor won't be a problem, unless he's a pretty big guy, and doesn't pedal much.
During all those melt the motor tests I used to do, I'd be towing a trailer, and barely pedaling at all.
Its actually pretty amazing what those little geared motors can do. But haul a 300 pound guy up and down the mountains without pedaling, no. And handle 2000w doing the same, no.
But lots of healthy riders do fine with a 500w assist, which actually feels like riding a tandem with Tadej Pocacha.
During all those melt the motor tests I used to do, I'd be towing a trailer, and barely pedaling at all.
Its actually pretty amazing what those little geared motors can do. But haul a 300 pound guy up and down the mountains without pedaling, no. And handle 2000w doing the same, no.
But lots of healthy riders do fine with a 500w assist, which actually feels like riding a tandem with Tadej Pocacha.
dogman dan said:
Maybe we're getting to his concern here. He's got a 20A controller on a 52V nominal system. They say the motor is "250W", so he's nominally 4X over powered, and the simulator says if he runs it wide open, he'll overheat in 10 miles even on the flat.
I believe it's true that if he configured the current limit down to 7 or 8 amps, he'd still get very useful performance out of it, and never overheat no matter what. Good idea?
MadRhino
100 GW
Well, one could limit the bike to the point of no concern, or keep for his own judgement the choice of extra power, how much and how long is suitable to be.
I feed almost 10 times the continuous rated power of my DD motor in a hard acceleration, but It doesn't fry, because I know how long is too much and how much is too long.
I mean, a bike need to be fun too, sometimes.
I feed almost 10 times the continuous rated power of my DD motor in a hard acceleration, but It doesn't fry, because I know how long is too much and how much is too long.
I mean, a bike need to be fun too, sometimes.
I don't even know for sure what my direct drive motor is rated for, or if that's even meaningful. I'm confident enough that I am not going to smoke it, but I don't really know how hot it gets. I don't get off and feel it, and I doubt it would lead to a lot of reliable insight without doing that a lot more often than I think anyone does.
If I had a small geared motor, significantly more liable to overheat than my direct drive, I suppose I'd seriously consider scaling the controller down to match it. No one gets a motor like that thinking to ride it like a stealth motorcycle.
If I had a small geared motor, significantly more liable to overheat than my direct drive, I suppose I'd seriously consider scaling the controller down to match it. No one gets a motor like that thinking to ride it like a stealth motorcycle.
dogman dan
1 PW
Tests to destruction I did ten years ago on similar size motors were powered with 48v 20 amps. The motor can handle that amps fine. It will only pull about 10 amps going 20 mph.
Scaling down the amps to the motor won't help a lot, if the rider weighs 350 pounds, and rides up steep hills.
No motor handles being overloaded, like fat guy rides up 8% hill a mile long, and won't pedal. This results in a motor rpm too low to run the motor efficiently. and then, hell yeah,, with 500w being made directly into heat it don't take long to melt a motor. Quickest I ever did one was 15 min. But typically you get more like 30 to 45 min, if the rider pedals even slightly, and the weight of the rider is under 200 pounds. So you see, even if you can't maintain 15 mph up that hill, you can get away with a lot if the hill takes only 10 min to climb.
The weight limit for this guys motor should be around 200 pounds for a hill several miles long. A 500w rated motor, DD or geared, has more copper and magnets, and thus has a weight limit closer to 300 pounds.
But more weight is possible, if the rider is very fit and can pedal up 200w for half an hour. Most of us mere mortals can do more like 100w, and then for only about 10 min. About 50w, then we last an hour or more.
Scaling down the amps to the motor won't help a lot, if the rider weighs 350 pounds, and rides up steep hills.
No motor handles being overloaded, like fat guy rides up 8% hill a mile long, and won't pedal. This results in a motor rpm too low to run the motor efficiently. and then, hell yeah,, with 500w being made directly into heat it don't take long to melt a motor. Quickest I ever did one was 15 min. But typically you get more like 30 to 45 min, if the rider pedals even slightly, and the weight of the rider is under 200 pounds. So you see, even if you can't maintain 15 mph up that hill, you can get away with a lot if the hill takes only 10 min to climb.
The weight limit for this guys motor should be around 200 pounds for a hill several miles long. A 500w rated motor, DD or geared, has more copper and magnets, and thus has a weight limit closer to 300 pounds.
But more weight is possible, if the rider is very fit and can pedal up 200w for half an hour. Most of us mere mortals can do more like 100w, and then for only about 10 min. About 50w, then we last an hour or more.
Seems like the OP may have lost interest in this thread, since the bike is running fine with no issues. The question is hypothetical, since I doubt he's going to go out and buy a smaller battery to replace the one he has, or un-buy the one he bought.
E-HP said:
The question he asked was also ill-formed, because the battery itself isn't really the problem, right? A battery of lower voltage and capacity could as easily toast his motor. So I believe that by asking the wrong question, he rescued his question from being hypothetical? If you like philosophical twists.
donn said:
Ya, but when he says "I’ve been using it and I have a lot of hills around here and it seems to be doing ok, motor case doesn’t feel hot after just warm. Also I’m using throttle only, no pedal assist." it tells me that the hills must be pretty small, if he can climb them on throttle only using a 250W motor. The hills would have to be even smaller if he were doing that and weighed 350 lbs. and not having any issues.
E-HP said:
Sorry for the misunderstanding. When I say throttle only I mean no cadence or torque sensor. I’m still pedaling and using the throttle for assist as needed.
UPDATE: While out riding one morning the gears stripped. I was just riding normally around my area, nothing crazy but possibly this little motor can’t handle the local terrain.
MadRhino
100 GW
Yep. Small geared motors are fragile. Buy a bigger one, then you will be happy that you had opted for a big battery.
