Battery vs controller vs motor rating limitations

[Chintan_joey]

So I have a few questions with my ebike build. I bought the 500w voilamart conversion kit off ebay, 36V 20Ah blue battery off ebay too. From initial tests, I'm getting a top speed of 24mph(throttle only) for first 10minutes after charge and then it drops to 20mph consistent. After 8-10miles of riding, the battery has drained significantly and the controller will cut off automatically. I have to turn off and on the power switch to regain motor control which again goes off in few minutes and will only work if I throttle it only slightly. The controller is rated 36V 22amps and my battery has 20A continuous discharge rate with a max. instantaneous peak of 25A.

I'm thinking of few mods here, can I upgrade the controller to a 36V 30Amps or something for this problem to not occur. Also, will changing throttle help anyways? My throttle has 2 cables and has a battery reading but I guess it's a knock off because for it to read battery, it needs to have 3 cables instead of 2.

I would appreciate some help/knowledge on upgrading motor controller and throttle for this problem to not occur. I assume with a 20Ah battery pack and less use of throttle, I should get atleast 20-25miles of range.

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[goatman]

sounds like a crappy battery, do you have a link to what you bought

 

[Chintan_joey]

sounds like a crappy battery, do you have a link to what you bought

Sure, there you go.

https://www.ebay.com/itm/293314294162

Bought it for $190 with a 2 year ebay warranty on it.

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[goatman]

it says:
Automatic Low Voltage Disconnect: 35V

so if they used cheap chinese cells with big volt sag, thats the problem. id ask for my money back

the pack is 20ah, if you go full throttle/20amps continuous you should be able to go 1hr not 10 minutes

 

[MadRhino]

+1
Your battery is cheap sh*t. It can’t even supply 20A continuous, and upgrading power to 30A would cut off right away. It is lower Amp draw, that would let you use it and improve range.

 

[amberwolf]

So I have a few questions with my ebike build. I bought the 500w voilamart conversion kit off ebay, 36V 20Ah blue battery off ebay too. From initial tests, I'm getting a top speed of 24mph(throttle only) for first 10minutes after charge and then it drops to 20mph consistent.

The short time of higher speed is likely the battery voltage being high enough to make the motor spin at a higher speed. As the battery runs down, it's voltage drops (this is how batteries work), and your speed drops. At some point it reaches the flatter part of the battery's discharge curve, and speed stays about the same, but still decreasing, until the battery is nearly empty, and then it falls off rapidly or just shuts off.

To maintain a higher speed, you'd need a higher voltage battery, if your controller is compatible with that, or a different winding of motor meant for a higher speed in the same size wheel.

It also takes more power to maintain a higher speed, so the battery (and controller, and motor) have to be able to handle the higher power continously.

The controller is rated 36V 22amps and my battery has 20A continuous discharge rate with a max. instantaneous peak of 25A.
<snip>
I'm thinking of few mods here, can I upgrade the controller to a 36V 30Amps or something for this problem to not occur.

Increasing current demand by the controller from the battery will make your problem worse, not better.

The controller is already capable of asking for more continous current than the battery was designed for. If you are using it in a way that it does this, then that would be one reason for the battery to run out sooner than expected.

If you don't have a wattmeter or ammeter (to measure the actual current pulled from the battery while you're riding), it's a useful tool for diagnosing problems and finding out your actual needs.

The battery is the heart of the system. You should use a battery that is capable of supplying *more* current and power (but just the right voltage) than your controller and motor will ever demand of it, or else you stress the battery and end up with problems varying from cutouts and shutdowns to low range to short battery lifespan.

Also, will changing throttle help anyways? My throttle has 2 cables and has a battery reading but I guess it's a knock off because for it to read battery, it needs to have 3 cables instead of 2.

I don't know what you mean by that statement.

If your throttle has a voltmeter on it, then you simply wire the two voltmeter wires to your battery wires (at the controller is the easiest spot). But you have to follow the diagram provided by the seller to know which wires those are, without taking the throttle apart to find out (they dont' go back together as easily as they come apart), and you cannot just try different wires or you risk destroying the throttle, as only the voltmeter can handle battery voltage.

Either way, changing the throttle will not help your problem.

I would appreciate some help/knowledge on upgrading motor controller and throttle for this problem to not occur. I assume with a 20Ah battery pack and less use of throttle, I should get atleast 20-25miles of range.

Most likely you need to upgrade your battery pack, or downgrade your controller, as the battery probably simply can't handle what's being asked of it.

It is very common with cheap battery packs to not be anywhere near as good as the advertisements say they are. Many are made with literally garbage recycled cells, and those taht aren't are made with cheap cells that are not matched with each ohter, and so the cells can't all provide the same current and capacity and voltage, and they begin to unbalance (become different in voltage from each other), so the BMS turns off the pack as soon as the first cells reach the low voltage cutoff (LVC) so you don't damage the cells and have a fire.

Then when it's recharged, unless it's left on long enough to rebalance the cells (assuming it has a balancing-type BMS), the cells are worse than they were the last time, and they'll shut off earlier in the ride each time until the pack has no range at all.

Sometimes you can leave the pack on the charger for several days (or weeks, depending on how badly imbalanced it is), and it will rebalance, and then make sure that every time you use it you leave it on the charger whenever you are not actually riding, so that it can try to keep the pack in balance. This will reduce the problems, but it won't fix them, because the cause itself still exists, and it will still get worse over time--the harder it is used, the worse the problem will be.

It's possible that your pack is acutally built well enough, but that the cells are just not balanced yet, and doing the above will fix it and keep it fixed. But we've seen enough cheap battery problems here that I am skeptical.



Quoting the battery specs off that page for reference:

Charge Voltage: 42V
Battery Capacity: 20AH
Continuous Charge / Discharge Rate: 20A
Battery Power: 500W(Max)
Cell Combination: 7-parallel 10-series
Automatic Low Voltage Disconnect: 35V
Certificate: CE,RoHS,MSDS
Custom Bundle: Yes
BMS: 20A
Automatic Over Voltage Protection: 42V
Material: Lithium ion
Flame Retardant Electrolyte: Yes
Energy: Electric
Length Way Circuit Boards: Yes
Compatible Brand: Universally
Automatic Internal Cell Balancing: Yes
Brand: CAO MM
Explosion Proof Polymer Cells: Yes
Manufacturer Warranty: 1 year
Package List: 1 x battery pack;1 x Charger.
Cell Size: 18650
Compatible Battery Sizes: 36 V
Cell Quantity (parallel*series): 70pcs
Suitable for: ebike Bicycle;e bike;electrical motorbike
Charge Time under 2A Charge Curren: 8hours(Standard)
Feature: Chargable
Charge Time under Fast(5A)Charge Current: 4hours
Type: 36V 20Ah 18650 li-ion Battery
Charge Temperature Range: -20-55°C/-4-131°F
Product Type: Battery
Model: 3620
Battery Type Included: 18650
Battery Type: Rechargeable
Capacity (amp hours): 20Ah
Compatible Battery Type: Li-ion
Charger Type: 42V/2A 2.1mm DC adapter
Cell Size (L*W*T ): 200*140*70mm/ 7.9*5.5*2.8inch
MPN:
Does Not Apply
Battery Weight: About 3.8KG/8.4lb
Coin Cell Diameter: 18650
Chemical Composition: Lithium
Peak Discharge current: 25A
Voltage: 36V
UPC:
Does not apply

 

[Chintan_joey]

So I have a few questions with my ebike build. I bought the 500w voilamart conversion kit off ebay, 36V 20Ah blue battery off ebay too. From initial tests, I'm getting a top speed of 24mph(throttle only) for first 10minutes after charge and then it drops to 20mph consistent.

The short time of higher speed is likely the battery voltage being high enough to make the motor spin at a higher speed. As the battery runs down, it's voltage drops (this is how batteries work), and your speed drops. At some point it reaches the flatter part of the battery's discharge curve, and speed stays about the same, but still decreasing, until the battery is nearly empty, and then it falls off rapidly or just shuts off.

To maintain a higher speed, you'd need a higher voltage battery, if your controller is compatible with that, or a different winding of motor meant for a higher speed in the same size wheel.

It also takes more power to maintain a higher speed, so the battery (and controller, and motor) have to be able to handle the higher power continously.

The controller is rated 36V 22amps and my battery has 20A continuous discharge rate with a max. instantaneous peak of 25A.
<snip>
I'm thinking of few mods here, can I upgrade the controller to a 36V 30Amps or something for this problem to not occur.

Increasing current demand by the controller from the battery will make your problem worse, not better.

The controller is already capable of asking for more continous current than the battery was designed for. If you are using it in a way that it does this, then that would be one reason for the battery to run out sooner than expected.

If you don't have a wattmeter or ammeter (to measure the actual current pulled from the battery while you're riding), it's a useful tool for diagnosing problems and finding out your actual needs.

The battery is the heart of the system. You should use a battery that is capable of supplying *more* current and power (but just the right voltage) than your controller and motor will ever demand of it, or else you stress the battery and end up with problems varying from cutouts and shutdowns to low range to short battery lifespan.

Also, will changing throttle help anyways? My throttle has 2 cables and has a battery reading but I guess it's a knock off because for it to read battery, it needs to have 3 cables instead of 2.

I don't know what you mean by that statement.

If your throttle has a voltmeter on it, then you simply wire the two voltmeter wires to your battery wires (at the controller is the easiest spot). But you have to follow the diagram provided by the seller to know which wires those are, without taking the throttle apart to find out (they dont' go back together as easily as they come apart), and you cannot just try different wires or you risk destroying the throttle, as only the voltmeter can handle battery voltage.

Either way, changing the throttle will not help your problem.

I would appreciate some help/knowledge on upgrading motor controller and throttle for this problem to not occur. I assume with a 20Ah battery pack and less use of throttle, I should get atleast 20-25miles of range.

Most likely you need to upgrade your battery pack, or downgrade your controller, as the battery probably simply can't handle what's being asked of it.

It is very common with cheap battery packs to not be anywhere near as good as the advertisements say they are. Many are made with literally garbage recycled cells, and those taht aren't are made with cheap cells that are not matched with each ohter, and so the cells can't all provide the same current and capacity and voltage, and they begin to unbalance (become different in voltage from each other), so the BMS turns off the pack as soon as the first cells reach the low voltage cutoff (LVC) so you don't damage the cells and have a fire.

Then when it's recharged, unless it's left on long enough to rebalance the cells (assuming it has a balancing-type BMS), the cells are worse than they were the last time, and they'll shut off earlier in the ride each time until the pack has no range at all.

Sometimes you can leave the pack on the charger for several days (or weeks, depending on how badly imbalanced it is), and it will rebalance, and then make sure that every time you use it you leave it on the charger whenever you are not actually riding, so that it can try to keep the pack in balance. This will reduce the problems, but it won't fix them, because the cause itself still exists, and it will still get worse over time--the harder it is used, the worse the problem will be.

It's possible that your pack is acutally built well enough, but that the cells are just not balanced yet, and doing the above will fix it and keep it fixed. But we've seen enough cheap battery problems here that I am skeptical.



Quoting the battery specs off that page for reference:

Charge Voltage: 42V
Battery Capacity: 20AH
Continuous Charge / Discharge Rate: 20A
Battery Power: 500W(Max)
Cell Combination: 7-parallel 10-series
Automatic Low Voltage Disconnect: 35V
Certificate: CE,RoHS,MSDS
Custom Bundle: Yes
BMS: 20A
Automatic Over Voltage Protection: 42V
Material: Lithium ion
Flame Retardant Electrolyte: Yes
Energy: Electric
Length Way Circuit Boards: Yes
Compatible Brand: Universally
Automatic Internal Cell Balancing: Yes
Brand: CAO MM
Explosion Proof Polymer Cells: Yes
Manufacturer Warranty: 1 year
Package List: 1 x battery pack;1 x Charger.
Cell Size: 18650
Compatible Battery Sizes: 36 V
Cell Quantity (parallel*series): 70pcs
Suitable for: ebike Bicycle;e bike;electrical motorbike
Charge Time under 2A Charge Curren: 8hours(Standard)
Feature: Chargable
Charge Time under Fast(5A)Charge Current: 4hours
Type: 36V 20Ah 18650 li-ion Battery
Charge Temperature Range: -20-55°C/-4-131°F
Product Type: Battery
Model: 3620
Battery Type Included: 18650
Battery Type: Rechargeable
Capacity (amp hours): 20Ah
Compatible Battery Type: Li-ion
Charger Type: 42V/2A 2.1mm DC adapter
Cell Size (L*W*T ): 200*140*70mm/ 7.9*5.5*2.8inch
MPN:
Does Not Apply
Battery Weight: About 3.8KG/8.4lb
Coin Cell Diameter: 18650
Chemical Composition: Lithium
Peak Discharge current: 25A
Voltage: 36V
UPC:
Does not apply

That makes sense. This clears out a lot for me. I was skeptical but still went through with this battery but Good that I can still return it. Any recommendations on a good 36V battery? Also should I be looking at constant discharge rate of battery or the max discharge? Few good Hailong batteries that I googled had 12-15A constant discharge ( less than current battery) but at max instantaneous discharge of 30A. My controller can support 22Amps, as per the label on it.

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[amberwolf]

I was skeptical but still went through with this battery but Good that I can still return it.

Anytime you have doubts about something, it's a good idea to entertain them and do a bit more checking to see whether they are telling you something important.

Any recommendations on a good 36V battery?

Unfortuantely good stuff seems a bit harder to find these days, with the CV precautions and personnel problems. You could check Ebikes.ca in the clearance section, or the battery section. I don't know if EM3EV still sells batteries or not (according to some reports, they've stopped selling certain kinds of motors, chargers, etc).

You could build your own using used Nissan Leaf cells, which bolt together easily. 5 modules would work, for 10 series cell groups for 36v nominal. There's a lot of threads about them if you want to research this idea. Or new EIG NMC cells, like those Jimbob01 is selling over in the for sale area of the forum.

You can build your own with other types of cells, but it's not a bolt-together process, and requires a significant amount of other knowledge to figure out what to build and what to build it with and how to do so, plus other tools that add to the cost, making a single battery more expensive than it could be.

Also should I be looking at constant discharge rate of battery or the max discharge?

For that, i refer you back to the stuff I already posted, especially the underlined/bolded part. The nonhighlighted part is because if you don't know how much current/power you're actually using, regardless of what a lable on a part says somewhere, you dont' really know how much your battery has to supply.

For instance, if you never use mroe than 10A on your rides, there's not much need for a better battery than that, if you're sure you'll never exceed that kind of load. (though if this was the case, then your present battery would be *really* poor. ).

The controller is rated 36V 22amps and my battery has 20A continuous discharge rate with a max. instantaneous peak of 25A.

If you don't have a wattmeter or ammeter (to measure the actual current pulled from the battery while you're riding), it's a useful tool for diagnosing problems and finding out your actual needs.

The battery is the heart of the system. You should use a battery that is capable of supplying *more* current and power (but just the right voltage) than your controller and motor will ever demand of it, or else you stress the battery and end up with problems varying from cutouts and shutdowns to low range to short battery lifespan.

 

[dogman dan]

FWIW, getting a better battery would help, as the others said. What happens to a weak battery is it sags voltage under load. This means not only does the battery voltage drop as you drain it,( normal) but it also drops more because of the load it can't handle. This makes it cut off before its fully empty. This is why you can restart it, and limp a bit farther.

At full throttle you likely draw about 12 -15 amps of juice, but your battery would be happier with less than 10 amps. When you use more amps, the voltage just drops to the cutoff level. Look for a battery with a higher amps rating, 30 or more.

A good 36v 20 ah battery should be taking you about 20 miles, at full throttle, slowing to 18-20 mph at the very end. So you are leaving about half your battery capacity on the table because of sag under load. Riding slower all the time would help, at 18 mph, and pedaling moderately should get you about 15 miles per ride. Just more efficient to pedal a bit more, and have less wind resistance.

To get real performance increase, a high quality 48v battery would mean more speed throughout the entire ride, but this also means a controller upgrade to 48v.

 

[donn]

To get real performance increase, a high quality 48v battery would mean more speed throughout the entire ride, but this also means a controller upgrade to 48v.

Though to be fair to the 36V alternative, the difference here is only that we're sort of arbitrarily supposing the same maximum current draw, measured in amperes - not entirely arbitrary, perhaps, given that battery construction would naturally allow that. I'm just saying, if you can somehow upgrade to a system that can sustain 30A x 36V, then it will deliver more power and go faster than a 48V upgrade that sustains 20A - 1080W vs. 960W. Or so it seems from looking at the simulations, anyway.

 

[Chintan_joey]

FWIW, getting a better battery would help, as the others said. What happens to a weak battery is it sags voltage under load. This means not only does the battery voltage drop as you drain it,( normal) but it also drops more because of the load it can't handle. This makes it cut off before its fully empty. This is why you can restart it, and limp a bit farther.

At full throttle you likely draw about 12 -15 amps of juice, but your battery would be happier with less than 10 amps. When you use more amps, the voltage just drops to the cutoff level. Look for a battery with a higher amps rating, 30 or more.

A good 36v 20 ah battery should be taking you about 20 miles, at full throttle, slowing to 18-20 mph at the very end. So you are leaving about half your battery capacity on the table because of sag under load. Riding slower all the time would help, at 18 mph, and pedaling moderately should get you about 15 miles per ride. Just more efficient to pedal a bit more, and have less wind resistance.

To get real performance increase, a high quality 48v battery would mean more speed throughout the entire ride, but this also means a controller upgrade to 48v.

Makes sense, any 36v battery suggestions?

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[MadRhino]

Good batteries are expansive, because they are made with quality genuine cells, and even more expansive since we buy/make them over spec for the power and range that we need. That is what is making them run cool, and safe from low discharge voltage.

 

[Chintan_joey]

I was skeptical but still went through with this battery but Good that I can still return it.

Anytime you have doubts about something, it's a good idea to entertain them and do a bit more checking to see whether they are telling you something important.

Any recommendations on a good 36V battery?

Unfortuantely good stuff seems a bit harder to find these days, with the CV precautions and personnel problems. You could check Ebikes.ca in the clearance section, or the battery section. I don't know if EM3EV still sells batteries or not (according to some reports, they've stopped selling certain kinds of motors, chargers, etc).

You could build your own using used Nissan Leaf cells, which bolt together easily. 5 modules would work, for 10 series cell groups for 36v nominal. There's a lot of threads about them if you want to research this idea. Or new EIG NMC cells, like those Jimbob01 is selling over in the for sale area of the forum.

You can build your own with other types of cells, but it's not a bolt-together process, and requires a significant amount of other knowledge to figure out what to build and what to build it with and how to do so, plus other tools that add to the cost, making a single battery more expensive than it could be.

Also should I be looking at constant discharge rate of battery or the max discharge?

For that, i refer you back to the stuff I already posted, especially the underlined/bolded part. The nonhighlighted part is because if you don't know how much current/power you're actually using, regardless of what a lable on a part says somewhere, you dont' really know how much your battery has to supply.

For instance, if you never use mroe than 10A on your rides, there's not much need for a better battery than that, if you're sure you'll never exceed that kind of load. (though if this was the case, then your present battery would be *really* poor. ).

The controller is rated 36V 22amps and my battery has 20A continuous discharge rate with a max. instantaneous peak of 25A.

If you don't have a wattmeter or ammeter (to measure the actual current pulled from the battery while you're riding), it's a useful tool for diagnosing problems and finding out your actual needs.

The battery is the heart of the system. You should use a battery that is capable of supplying *more* current and power (but just the right voltage) than your controller and motor will ever demand of it, or else you stress the battery and end up with problems varying from cutouts and shutdowns to low range to short battery lifespan.

https://www.ebay.com/itm/163943339328


What do you think about this battery? I read Lifepo4 are somewhat better. Also it's within my budget (~$200).

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[Chintan_joey]

Good batteries are expansive, because they are made with quality genuine cells, and even more expansive since we buy/make them over spec for the power and range that we need. That is what is making them run cool, and safe from low discharge voltage.

https://www.ebay.com/itm/163943339328


I have this in mind.

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[MadRhino]

If I wanted a battery on a 200$ budget, I would do recycling.

Lifepo4 are very good for low power requirement, because they are safe and last much longer. Still, you need to buy quality lifepo4, and enough of it to reliably supply the current that you need.

 

[donn]

If I wanted a battery on a 200$ budget, I would do recycling.

Lifepo4 are very good for low power requirement, because they are safe and last much longer. Still, you need to buy quality lifepo4, and enough of it to reliably supply the current that you need.

A123 ANR 26650's are supposed to be 50A continuous, 120A pulse. Might not be the world's best "energy density", but I guess you can't have everything.

 

[Balmorhea]

A123 ANR 26650's are supposed to be 50A continuous, 120A pulse. Might not be the world's best "energy density", but I guess you can't have everything.

Then there is the practical issue of getting that kind of power out of a cylindrical cell. Nickel strip don’t play that.