Motor Size Upgrade Question

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YellowBuzzaroundEX

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Dec 19, 2021
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For my small mobility scooter...

Question: Would a larger motor increase speed/torque when going up hills (if I still use original 50A controller and 21AH AGM batteries)?

There is no available space to increase AGM battery size. I need to continue using lead AGM batteries. One reason is lead batteries (mounted in floor) are ballast to keep low enough center of gravity.

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More Background Info:

I have a mobility scooter with a 330W motor (brushed motor) and 50A controller. It's a 24V system with two 12V deep cycle AGM batteries in series.

I increased tires diameter from 7.5" diam to 10.4" diameter (thus 38.7% higher gearing than stock).

I increased the onboard controller computer program max speed setting to 100%. This increased RPM (voltage) to max that controller and batteries can deliver.

Top speed increased from 4 to 6.5 MPH on level ground. I'm happy with speed on level ground. Real world range decreased from 6 to 5 miles. I'm satisfied with range.

However, it now bogs down when going up hills. It needs slightly more torque for hill climbing.

It currently has a 330W (brushed) motor. There's a 420W (brushed) upgrade motor available that would easily bolt-in.

===

Question: Would a larger motor increase speed/torque when going up hills (if I still use original 50A controller and 21AH AGM batteries)?

There is insufficient space to increase batteries size. I need to continue using lead AGM batteries.
 
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A larger motor would help you if you're pushing your motor harder than designed.
You may also want to put more amps into said larger motor... this way you can keep it closer to it's efficiency band while climbing.
 
neptronix said:
A larger motor would help you if you're pushing your motor harder than designed.
You may also want to put more amps into said larger motor... this way you can keep it closer to it's efficiency band while climbing.
Click to expand...
The motor is being pushed harder than designed when driving up hills.

I have an easy way to increase motor size +27%, but NO practical way to increase input amps. This is due to battery size & type limitations, which are due to scooter design limitations.

Torque... Would a 27% larger motor improve speed/torque (driving up hills) if input amps remains unchanged? It sounds like you're saying "yes".

Efficiency band... I read that an electric motor is most efficient around 75% of rated load. Is that correct?

I think the motor I have is operating at more than 75% load when driving on level ground, and at 100% load when driving up hills. So I suspect that a 27% larger motor might be more efficient even without changing input amps. What do you think?

P.S. - 90% of my scooter driving is on level ground where the existing motor is marginally adequate. The other 10% of my scooter driving is on hills where the existing motor is inadequate.

I'm handicapped and unable to walk. So I rely on this scooter. The existing motor strains enough (bogs down) going up hills that it's causing me concerns about reliability as well as being too slow up hills.

Thank you for sharing your advice and expertise.
 
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If you can't increase neither voltage nor current then the total power delivered to the motor will remain the same even after switching to different motor type. But there may be differences in the RPM/torque of different motor types (however, some technical specs would be needed to tell what would be the result of switching that motor).

Anyway, you're basically at the limits of your battery capacity and motor power - 21Ah battery, 5 miles of range at 5mph -> which means the battery is discharged after 1 hour ride. This gives us power estimate around 400 watt -> which confirms that your motor is running at 100% of its rated power. And it's not a very efficient motor or drivetrain, a bit too much power is needed to just move the scooter at 5mph. So the question is - is the current motor the problem? Is the new one any more efficient than that? Or maybe the problem is somewhere else - the battery capacity is less than it says on the label, or the gearbox is really bad, or the scooter very heavy..
 
rafalg said:
If you can't increase neither voltage nor current then the total power delivered to the motor will remain the same even after switching to different motor type. But there may be differences in the RPM/torque of different motor types (however, some technical specs would be needed to tell what would be the result of switching that motor).

Anyway, you're basically at the limits of your battery capacity and motor power - 21Ah battery, 5 miles of range at 5mph -> which means the battery is discharged after 1 hour ride. This gives us power estimate around 400 watt -> which confirms that your motor is running at 100% of its rated power. And it's not a very efficient motor or drivetrain, a bit too much power is needed to just move the scooter at 5mph. So the question is - is the current motor the problem? Is the new one any more efficient than that? Or maybe the problem is somewhere else - the battery capacity is less than it says on the label, or the gearbox is really bad, or the scooter very heavy..
Click to expand...

It cruises at 6.5 mph with 5 miles range. The current motor and available upgrade motor are both brushed motors. The controller uses 24V variable frequency pulses to vary rpm/speed.
 
Correct me if I'm wrong, but I think 1 benefit of a larger motor (even with same input amps & volts) would be more durability.

I'm also interested in how it would affect torque/speed under heavy load (going up hills).

l'm also interested in how it would affect efficiency/range driving on level ground (light load) and going up hills (heavy load).
 
YellowBuzzaroundEX said:
but NO practical way to increase input amps. This is due to battery size & type limitations, which are due to scooter design limitations.
Click to expand...
Its obvious that your existing motor is not drawing anything near that 50A controller limit ( 24v x50A = 1200W ), and i suspect that is because the batteries cannot discharge at 50A .
have the batteries checked, and try to get some amper measurements under load
 
G'day Yellow.
A bigger motor will be less stressed but it won't perform any better. The problem is the batteries. They sag.
18ah SLAs in top condition can deliver 1 amp for 18 hours but not 18 amps for 1 hour. More like 18 amps for 20 minutes.
It's like this...

Inside the battery are angry pixies called Ian.
When you've charge it & there's lots of tasty electrons around, the Ians live with Annie.
When you start to use the batt, Annie starts discharging & the Ians start leaving to live with Cathie.
The more currents you draw, the more Annie discharges & the faster the Ians want to leave.
But the way to Cathie's through the wilds of Electrolyte is guarded by the evil Peukert who won't let them all through together so many get lost in the wilds of Electrolyte until you recharge & they find their way back to Annie.
If you don't try to draw too much too fast, Annie won't discharge so hard & the pixies named Ian will leave a few at a time. The evil Peukert doesn't notice so then they all get through the wilds of Electrolyte to Cathie less angry.
But seriously mate, if you're using the scooter in situations where the batteries are sagging & the motor is bogging down you're pushing it too hard.
Consider a bigger, more capable machine.

AussieRider
 
YellowBuzzaroundEX said:
I increased tires diameter from 7.5" diam to 10.4" diameter (thus 38.7% higher gearing than stock).
Click to expand...
You need to provide the specs on the two motors. My thought is it will be difficult to even regain the 38% of torque you gave up by switching to the larger wheels. Speed and torque are a trade off, so you need to decide which you want more. If you want both, then you’ll need the battery upgrade, and decide whether to increase amps or voltage.
 
AussieRider said:
G'day Yellow.
A bigger motor will be less stressed but it won't perform any better. The problem is the batteries. They sag.
18ah SLAs in top condition can deliver 1 amp for 18 hours but not 18 amps for 1 hour. More like 18 amps for 20 minutes.
It's like this...

Inside the battery are angry pixies called Ian.
When you've charge it & there's lots of tasty electrons around, the Ians live with Annie.
When you start to use the batt, Annie starts discharging & the Ians start leaving to live with Cathie.
The more currents you draw, the more Annie discharges & the faster the Ians want to leave.
But the way to Cathie's through the wilds of Electrolyte is guarded by the evil Peukert who won't let them all through together so many get lost in the wilds of Electrolyte until you recharge & they find their way back to Annie.
If you don't try to draw too much too fast, Annie won't discharge so hard & the pixies named Ian will leave a few at a time. The evil Peukert doesn't notice so then they all get through the wilds of Electrolyte to Cathie less angry.
But seriously mate, if you're using the scooter in situations where the batteries are sagging & the motor is bogging down you're pushing it too hard.
Consider a bigger, more capable machine.

AussieRider
Click to expand...
It's a travel scooter (boot scooter) that easily disassembles into 5 parts that my caregiver can put in my car trunk (boot).

A larger scooter would be too much for my caregiver to lift into car trunk and wouldn't fit in car trunk.
 
E-HP said:
You need to provide the specs on the two motors. My thought is it will be difficult to even regain the 38% of torque you gave up by switching to the larger wheels. Speed and torque are a trade off, so you need to decide which you want more. If you want both, then you’ll need the battery upgrade, and decide whether to increase amps or voltage.
Click to expand...
Both motors (rated 330A & 420A) are DC brush motors. I have no way to get more motor specs because AFAIK they're not published.

With stock height tires/gearing the scooter was rated for a 225 lbs person.

I only weigh 120 lbs. I don't need to regain 38% of the lost torque. I only need to regain approx 10% because it's only slightly inadequate now.

If both motors are of the same design, and input volts and amps remain the same... Do you think a 27% larger motor would/might increase torque 10%?

However, I don't want to lose any rpm. So maybe this is an impossible situation if I can't increase current.
 
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Google AI says:

Yes, a larger DC electric motor with the same input amps will generally have increased torque compared to a smaller motor, as a larger motor can handle more power and generate higher torque even at the same current draw due to its physical design and larger winding capacity.

Key points to remember:

Torque is directly proportional to current in a DC motor: This means that for a given motor, higher current leads to higher torque.

Larger motor size means more winding capacity: A larger motor can have more wire turns in its armature, allowing it to generate more torque at the same current level.

Power remains constant: If the input amps are the same, the larger motor will likely have a lower speed to compensate for the increased torque, maintaining the same power output.

That last part ^ in bold got my attention. I don't want to lose rpm/speed on level ground.
 
YellowBuzzaroundEX said:
Both motors (rated 330A & 420A) are DC brush motors. I have no way to get more motor specs because AFAIK they're not published.

With stock height tires/gearing the scooter was rated for a 225 lbs person.

I only weigh 120 lbs. I don't need to regain 38% of the lost torque. I only need to regain approx 10% because it's only slightly inadequate now.

If both motors are of the same design, and input volts and amps remain the same... Do you think a 27% larger motor would/might increase torque 10%?

However, I don't want to lose any rpm. So maybe this is an impossible situation if I can't increase current.
Click to expand...
Not enough info. You can have the exact same motor but using a different number of turns in their windings, and one will have more speed but less torque than the other, even if both are rated the same. Speed and torque will always be a trade off, all other things being equal. If the motors are different, with different ratings, there’s no guaranty that the higher rated motor will have more torque or speed, without knowing how they are wound (what their Kv rating is).
 
OK. Thanks everyone for your advice. I'm now thinking it needs more powerful batteries and controller, or perhaps just batteries.

More powerful lead batteries is not possible due to physical space limitation. LiFePo4 batteries are not practical because the scooter uses/needs the weight of lead batteries in the floor to keep COG low to prevent rollovers.

I'm going to have to live with it as is, unless I can figure out how to have LiFePo4 battery and sufficient ballast.
 
The lifepo4 batteries will weigh the same as the smaller (16lb) stock battery, while having the same or greater capacity than the stock larger (30lb) battery. So is that scooter known for being prone to rollovers with the stock smaller battery set?
goldentech.com

Buzzaround XLS-HD 4-Wheel - Golden Technologies

This popular Buzzaround XLSHD scooter features compact portability with a heavy-duty weight capacity. It also features our Comfort Spring Suspension for a smoother ride. Standard colors are Red and Blue and optional color shrouds include Green, Tan, White, Yellow, Pink and Grey.
goldentech.com goldentech.com
 
E-HP said:
The lifepo4 batteries will weigh the same as the smaller (16lb) stock battery, while having the same or greater capacity than the stock larger (30lb) battery. So is that scooter known for being prone to rollovers with the stock smaller battery set?
goldentech.com

Buzzaround XLS-HD 4-Wheel - Golden Technologies

This popular Buzzaround XLSHD scooter features compact portability with a heavy-duty weight capacity. It also features our Comfort Spring Suspension for a smoother ride. Standard colors are Red and Blue and optional color shrouds include Green, Tan, White, Yellow, Pink and Grey.
goldentech.com goldentech.com
Click to expand...

I have the 3 wheel version of that scooter, which I prefer (due to a much sharper turning radius). On level pavement, it goes 63% faster than stock due to 38% increased tire diameter AND I removed the speed (rpm) limiter. It's adequately stable with 30 lbs of lead batteries in the floor and careful driving.

I did lift a rear tire on a couple of occasions, but then I learned to drive more carefully and then no more scares.

I think it needs the full 30 lbs of lead batteries in the floor to help reduce risk of rollover; or 15 lbs of LiFePo4 batteries plus 15 lbs steel weight under the LiFePo4 batteries.
 
G'day again.
I get get it now, you need the portability.
I think I know that machine. It uses a Dynamic R series D 50 controller right?
Earlier you said you upped the max speed to 100% so I'm guessing you've got access to a programmer.
Did you try upping the max motor current & maybe the boost current for short, sudden increased loads?
IIRC, you'll find those parameters under motor management.
'Course, they'll cut your range a bit more.

AussieRider
 
AussieRider said:
G'day again.
I get get it now, you need the portability.
I think I know that machine. It uses a Dynamic R series D 50 controller right?
Earlier you said you upped the max speed to 100% so I'm guessing you've got access to a programmer.
Did you try upping the max motor current & maybe the boost current for short, sudden increased loads?
IIRC, you'll find those parameters under motor management.
'Course, they'll cut your range a bit more.

AussieRider
Click to expand...
Yes, it has a Dynamic R 50A controller. I do have access to program it. A year ago I increased max motor voltage to the limit of my Powersonic PDC 12200 AGM 21AH batteries can provide. I also increased max speed setting to 100%.

Max Current setting (factory default) was already set to max 40A.
Boost setting (factory default) was already set to max 10A. I have not changed it.

I'm going to try adjusting settings for: Load Compensation, Max Load Compensation, and Load Compensation Damping, etc. Perhaps that might help?
 
I realized that my issue is defineately not the motor because I also own a slightly larger and heavier scooter (Golden Buzzaround EX) which uses the same motor and transaxle, but has more powerful 90A controller and larger U1 batteries. The larger EX scooter climbs hills just fine.

Both scooters have same diameter tires and same gearing. Same top speed on level ground, but the larger scooter is faster up hills.
 
Last edited:
YellowBuzzaroundEX said:
Yes, it has a Dynamic R 50A controller. I do have access to program it. A year ago I increased max motor voltage to the limit of my Powersonic PDC 12200 AGM 21AH batteries can provide. I also increased max speed setting to 100%.

Max Current setting (factory default) was already set to max 40A.
Boost setting (factory default) was already set to max 10A. I have not changed it.

I'm going to try adjusting settings for: Load Compensation, Max Load Compensation, and Load Compensation Damping, etc. Perhaps that might help?
Click to expand...
Is this the manual?

For hills, you need higher phase current (motor current as AussieRider mentioned). Looking at the ranges for Max Current and Boost Current, those are clearly input (battery) current values consistent with the controller rating. What is your Motor Continuous Current set to? That range is consistent with phase current values (0-255A). I'd try shooting for 120, but maybe start with something smaller and test before increasing more.
 
E-HP said:
Is this the manual?

For hills, you need higher phase current (motor current as AussieRider mentioned). Looking at the ranges for Max Current and Boost Current, those are clearly input (battery) current values consistent with the controller rating. What is your Motor Continuous Current set to? That range is consistent with phase current values (0-255A). I'd try shooting for 120, but maybe start with something smaller and test before increasing more.
Click to expand...
Yes, that is the correct manual for my controller. On what page is Continuous Current?
 
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E-HP said:
Page 53
Click to expand...
I see it. I recall the scooter manufacturer (Golden) has Continuous Current set to 14A and I've never changed it. I'll try 16A for a while and see how it does. If I'm still not satisfied, I'll increase in 2A increments, test driving after each.

Should I also try adjusting Load Compensation and/or Load Damping?

I'm looking for a 10% improvement in hill climbing speed.

Thanks!
 
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