[onyx824]

Hi all, as you can tell from the title, I am attempting to make a go kart from an old power chair (mobility scooter). There are two large DC motors but a lot of the electrical components are missing. We have the motors and that's it. No batteries, no nothing. So how do we make them spin? Here is what I have done so far. I am looking for verification on my spotty electrical knowledge.

First, I found the chair's replacement batteries on the internet. They have 12v and about 15A. The chair is called the Jazzy Select GT if you want to verify that information. The chair takes 2 batteries in series, and the motors are parallel. Since the actual batteries for the chair are too expensive, can we get away with using these batteries?

So that covers current (kinda) and voltage, but we need to steer the think by having variable speeds in each motor independently. So we need to control each motor's speed on its own, and I was thinking of doing this by having two variable resistors. If RI=V and V is 24, we would want 50 or so Ohms of variable resistance for each side. What resistors could you recommend?

Thanks in advance for all the wonderful help!

 

[brian_]

First, I found the chair's replacement batteries on the internet. They have 12v and about 15A.

That would presumably be a capacity of 15 amp-hours (Ah), not a current output in amps (A).

The chair is called the Jazzy Select GT if you want to verify that information.

We have a mobility scooter from the same company. The setup of two 12-volt AGM batteries in series in normal in this type of device. The Jazzy Select GT manual says it uses U-1 size batteries; those are much larger than batteries in our compact scooter, and should normally have about 33 Ah capacity. The U-1 size is commonly used for the starter battery in lawn tractors.

The chair takes 2 batteries in series, and the motors are parallel. Since the actual batteries for the chair are too expensive, can we get away with using these batteries?

Get away with using what batteries - did you intend to include a link to something, or are you referring to some smaller 15 Ah batteries that you found as a replacement?

Smaller batteries would have two concerns:

1. endurance (range) will obviously be shorter
2. the maximum discharge rate will be lower - this might be enough of a limit to impede fun performance, but more information about required motor power is needed

 

[brian_]

There are two large DC motors but a lot of the electrical components are missing. We have the motors and that's it. No batteries, no nothing. So how do we make them spin?
...
So that covers current (kinda) and voltage, but we need to steer the think by having variable speeds in each motor independently. So we need to control each motor's speed on its own, and I was thinking of doing this by having two variable resistors.

If our scooter is any indication (and I'm sure it's typical), these machines normally use electronic controllers, just like the larger EVs discussed in this forum. Going back to controlling speed with a resistor would be really unfortunate. It would work; it just wouldn't be efficient, and I'm not sure it would be a lot cheaper.

If RI=V and V is 24, we would want 50 or so Ohms of variable resistance for each side. What resistors could you recommend?

How did you pick 50 ohms? Are you assuming that the battery spec including "15 A" means that each motor needs 15 amps? Even then, I don't follow how that results in 50 ohms... but that's probably just my misunderstanding.

When I had a problem with our scooter (which turned out to be wiring damage), I took it apart and had a look at the controller. It has 40 amp capacity, and in a quick online search appears to have the same current rating as the controllers used for the Jazzy Select GT. Example of online source of replacement part:
40 Amp Controller with 4-Prong Connector for Jazzy Power Chairs with the GC2 Joystick Remote
I realize that buying these controllers is not reasonable; however, the original equipment indicates the capability which is required.

 

[onyx824]

That would presumably be a capacity of 15 amp-hours (Ah), not a current output in amps (A).


We have a mobility scooter from the same company. The setup of two 12-volt AGM batteries in series in normal in this type of device. The Jazzy Select GT manual says it uses U-1 size batteries; those are much larger than batteries in our compact scooter, and should normally have about 33 Ah capacity. The U-1 size is commonly used for the starter battery in lawn tractors.


Get away with using what batteries - did you intend to include a link to something, or are you referring to some smaller 15 Ah batteries that you found as a replacement?

Smaller batteries would have two concerns:

1. endurance (range) will obviously be shorter
2. the maximum discharge rate will be lower - this might be enough of a limit to impede fun performance, but more information about required motor power is needed

Sorry about the motor link not working. Here it is: https://www.amazon.com/Razor-Electr...&pf_rd_p=b841581f-e864-5164-afa6-4c18a8348879


Regarding the current, I meant that each battery says (on its side) it has a power output of around 15 amps during cyclic motion.

 

[onyx824]

If our scooter is any indication (and I'm sure it's typical), these machines normally use electronic controllers, just like the larger EVs discussed in this forum. Going back to controlling speed with a resistor would be really unfortunate. It would work; it just wouldn't be efficient, and I'm not sure it would be a lot cheaper.


How did you pick 50 ohms? Are you assuming that the battery spec including "15 A" means that each motor needs 15 amps? Even then, I don't follow how that results in 50 ohms... but that's probably just my misunderstanding.

When I had a problem with our scooter (which turned out to be wiring damage), I took it apart and had a look at the controller. It has 40 amp capacity, and in a quick online search appears to have the same current rating as the controllers used for the Jazzy Select GT. Example of online source of replacement part:
40 Amp Controller with 4-Prong Connector for Jazzy Power Chairs with the GC2 Joystick Remote
I realize that buying these controllers is not reasonable; however, the original equipment indicates the capability which is required.

Ill definitely consider using the controller from the chair instead. I'm pretty sure I know what's what, but I might be missing parts since this chair was donated to our studio without many components (like batteries).
https://imgur.com/gallery/60b2X/

 

[brian_]

Ill definitely consider using the controller from the chair instead. I'm pretty sure I know what's what, but I might be missing parts since this chair was donated to our studio without many components (like batteries).
https://imgur.com/gallery/60b2X/

While the controller would be a prime part to strip out, apparently it was left in... that's it in the last photo.

 

[brian_]

Sorry about the motor link not working. Here it is: https://www.amazon.com/Razor-Electr...&pf_rd_p=b841581f-e864-5164-afa6-4c18a8348879


Regarding the current, I meant that each battery says (on its side) it has a power output of around 15 amps during cyclic motion.

It's rare to show a current rating on a battery, and any U1 battery can deliver a lot more than 15 amps, at least for a while. 15 amps might be a recommended maximum charging rate (although the charger which comes with the power chair trickles along at only 3 amps).

The VB1280 AGM batteries in the Amazon link don't show any current or capacity rating that I can find in the photo, but the listing includes a capacity of 7 amp-hours. Since they are wired in series the capacity of the combination is still 7 amp-hours, but at 24 volts. 15 amps might be about as much as you want for a discharge rate from something that small.

The set linked from Amazon appear to be normal AGM batteries of a common size, plus wiring set up for a specific brand of scooters. You don't need that that specific wiring, and can easily set up what you need, so any pair of 12V AGM batteries that you can find - at least that large but preferably larger - would work as well.

These "1280" (just means 12V and 8.0 Ah) batteries are very small compared to the U1 batteries that come with the power chair:

• VB1280: 15.2 x 6.6 x 9.4 cm ; 2.3 kg; 7 Ah (or 8 Ah)
• typical U1 (or "12350"): 19.8 x 13.8 x 17.1 cm; 12 kg; 35 Ah

AGM batteries are pretty good - as lead-acid goes - for high discharge rates over a short time, so if you can stand quite short kart rides (much shorter than the time that a power chair user would expect to be able to run), these small batteries might be fine. On the other hand, bigger ones would last longer, and without the wiring US$60 will probably buy a pair of twice that capacity (e.g. UB12150, 15 Ah from Universal Battery).

 

[onyx824]

It's rare to show a current rating on a battery, and any U1 battery can deliver a lot more than 15 amps, at least for a while. 15 amps might be a recommended maximum charging rate (although the charger which comes with the power chair trickles along at only 3 amps).

The VB1280 AGM batteries in the Amazon link don't show any current or capacity rating that I can find in the photo, but the listing includes a capacity of 7 amp-hours. Since they are wired in series the capacity of the combination is still 7 amp-hours, but at 24 volts. 15 amps might be about as much as you want for a discharge rate from something that small.

The set linked from Amazon appear to be normal AGM batteries of a common size, plus wiring set up for a specific brand of scooters. You don't need that that specific wiring, and can easily set up what you need, so any pair of 12V AGM batteries that you can find - at least that large but preferably larger - would work as well.

These "1280" (just means 12V and 8.0 Ah) batteries are very small compared to the U1 batteries that come with the power chair:

• VB1280: 15.2 x 6.6 x 9.4 cm ; 2.3 kg; 7 Ah (or 8 Ah)
• typical U1 (or "12350"): 19.8 x 13.8 x 17.1 cm; 12 kg; 35 Ah

AGM batteries are pretty good - as lead-acid goes - for high discharge rates over a short time, so if you can stand quite short kart rides (much shorter than the time that a power chair user would expect to be able to run), these small batteries might be fine. On the other hand, bigger ones would last longer, and without the wiring US$60 will probably buy a pair of twice that capacity (e.g. UB12150, 15 Ah from Universal Battery).

Thanks for all the help! I think I understand the battery issue, but when I set up the circuit for the first time, how will I avoid overloading the components? Also, we have no charger, and we don't have the physical input to the motor controller. Are there any specifics on what kind of charger and controller input we should get, or does it depend on the battery?

Thanks!!!

 

[brian_]

I think I understand the battery issue, but when I set up the circuit for the first time, how will I avoid overloading the components?

You do need a fuse or circuit breaker to protect wiring and other components from overload, but you also need to design the combination of components properly: if the battery is too small to handle the motor, it will always be too small no matter how you wire it.

A fuse holder or circuit breaker is easy to include in the wiring for the batteries. It would be normal to have a large fuse in the heavy-gauge wiring from the batteries to the controller, and a smaller fuse in the lighter-gauge wiring from the batteries to a 24-volt charging power inlet.

 

[brian_]

Also, we have no charger, and we don't have the physical input to the motor controller. Are there any specifics on what kind of charger and controller input we should get, or does it depend on the battery?

For the charger:
These scooter and wheelchairs tend to use a very basic 24-volt charger, sized to be as cheap as possible while having enough output to recharge the batteries overnight. That means 3 amps for the larger chairs and scooters (with 35 Ah batteries), 2 amps for our lightweight (with 20 Ah batteries), and maybe even smaller for the tiny stuff. The batteries can stand be charged a lot faster than that, so any "24 volt" charger for AGM batteries will work.

You can also just use any modern (automatic, multistage, preferably with AGM setting) charger intended for car and similar smaller lead-acid batteries - you would just charge one at a time. If you charge them separately, be careful to charge them to the same state before using them together.


For the controller input:
I was able to find a complete wiring diagram online for our scooter. If you can find one for the power chair, it should show what each pin of each connector needs to connect to. For the connectors themselves, if they're not a common type you may need to buy some wiring sections as repair parts for the power chair.

 

[onyx824]

For the controller input:
I was able to find a complete wiring diagram online for our scooter. If you can find one for the power chair, it should show what each pin of each connector needs to connect to. For the connectors themselves, if they're not a common type you may need to buy some wiring sections as repair parts for the power chair.

I can't find one for the chair. Is there another way to change the speeds of each motor individually?

 

[brian_]

I can't find one for the chair. Is there another way to change the speeds of each motor individually?

I haven't found a detailed wiring diagram, but this parts diagram shows what cables go between the components, and which connector of the controller each plugs into; it doesn't include any detail of the wires in each cable, or the pins in each connector.
Jazzy Select Gt Replacement Parts
You could at least see if you have these cables, as a start on what you might need and what additional detail is needed.

In this case it appears that the joystick is not just a joystick: it is an electronic module with integrated joystick which communicates digitally with the motor controller.

A challenge in controlling two motors for steering is that a typical motor controller is designed so that the driver's input is treated as a request for a level of torque, but for steering you need to control the speed.
If you apply the same torque to both left and right wheels of a normally steered car it steers normally (going where the front wheels point); if you apply the same torque to both left and right wheels of a skid-steered vehicle it wanders around depending on the drag on each side and the slope of the surface. You need to control the speed of left and right wheels to be the same to go straight with a skid-steer.

The most common type of equipment using skid steering is a small loader / equipment carrier; a very common brand is Bobcat. These use hydrostatic drives (hydraulic pumps and motors) and the control position for each side determines the speed (not the torque, not the power) of the wheels on that side. The electrically driven examples that I have found all have speed-input controllers, not torque-input controllers.

This power chair uses a single controller for both motors, and that's probably normal. The single controller presumably takes the joystick input and turns the fore-aft motion into total or average torque, but controls the ratio between left and right speeds based on the left-right motion of the joystick to determine direction of travel. The calculation and logic work may be done by the joystick module, with only the two motor speeds sent to the motor controller. If you try to do this with two separate motor controllers, they will need to communicate with each other (or be directed by a single master controller) to get the speeds right... or your input device (joystick or whatever) needs to produce signals which the controllers can interpret as speeds.

 

[onyx824]

I haven't found a detailed wiring diagram, but this parts diagram shows what cables go between the components, and which connector of the controller each plugs into; it doesn't include any detail of the wires in each cable, or the pins in each connector.
Jazzy Select Gt Replacement Parts
You could at least see if you have these cables, as a start on what you might need and what additional detail is needed.

In this case it appears that the joystick is not just a joystick: it is an electronic module with integrated joystick which communicates digitally with the motor controller.

A challenge in controlling two motors for steering is that a typical motor controller is designed so that the driver's input is treated as a request for a level of torque, but for steering you need to control the speed.
If you apply the same torque to both left and right wheels of a normally steered car it steers normally (going where the front wheels point); if you apply the same torque to both left and right wheels of a skid-steered vehicle it wanders around depending on the drag on each side and the slope of the surface. You need to control the speed of left and right wheels to be the same to go straight with a skid-steer.

The most common type of equipment using skid steering is a small loader / equipment carrier; a very common brand is Bobcat. These use hydrostatic drives (hydraulic pumps and motors) and the control position for each side determines the speed (not the torque, not the power) of the wheels on that side. The electrically driven examples that I have found all have speed-input controllers, not torque-input controllers.

This power chair uses a single controller for both motors, and that's probably normal. The single controller presumably takes the joystick input and turns the fore-aft motion into total or average torque, but controls the ratio between left and right speeds based on the left-right motion of the joystick to determine direction of travel. The calculation and logic work may be done by the joystick module, with only the two motor speeds sent to the motor controller. If you try to do this with two separate motor controllers, they will need to communicate with each other (or be directed by a single master controller) to get the speeds right... or your input device (joystick or whatever) needs to produce signals which the controllers can interpret as speeds.

Thanks for all the great advice so far! I'll send you a video once were done. A super quick question this time, would this charger work?

https://www.1000bulbs.com/product/5...2z7_KSyVBY0mzuR78i0FtTQmqEdy94shoCDa0QAvD_BwE

I gather the slower the cheaper, and I don't want to spend much money. Just confused about SLA and AGM. AGM is a subcategory of SLA, so this should work. I'll also talk to their customer support team!

 

[brian_]

... would this charger work?

https://www.1000bulbs.com/product/5...2z7_KSyVBY0mzuR78i0FtTQmqEdy94shoCDa0QAvD_BwE

I gather the slower the cheaper, and I don't want to spend much money. Just confused about SLA and AGM. AGM is a subcategory of SLA, so this should work. I'll also talk to their customer support team!

Yes, but you would be charging one battery at a time, taking a long time to do it, and ending up unsure if you had the same charge level in each battery because there is no display of voltage or charging current or completion status. A common automotive battery charger (most have an AGM setting now) would be faster and better, but of course they cost more than $7.

SLA is "sealed lead-acid", which should actually be VRLA (valve-regulated lead-acid), because all lead-acid batteries have some sort of vent. Aside from Absorbed Glass Mat (AGM), the other VRLA batteries are "gel cells", although they are no longer common. For either type, a high final charging voltage and especially the even higher voltage used in "equalization" should be avoided, so this would be okay. On the other hand, the spec chart lists this as "unregulated", so it's a pretty crude thing, as can be expected for the price.