Wheel chair battery

[Ray Eyre]

I have a powered wheelchair that uses a specialised 24v Ni-Mh battery pack yamaha jwb2. Common on a lot of powered wheelchairs.

The battery pack no-longer holds any charge and it will cost over $1500.00 New Zealand to replace.

I am going to replace it with 2 x 12v 6.7Ah SLA batteries but, as the Ni-Mh fits into a dedicated slot in the wheelchair, I going to rip the guts out of the Ni-Mh battery case and wire the SLA's into the output circuit.

My only issue and the one that I need advice on is:

The electronic joystick control is powered by 4.7v taped internally in the 24v Ni-Mh battery case.

I intend to use a 12v to 5v USB power supply for the joystick circuit.

I don't think that an extra 0.3 of a volt will be an issue but I do need advice, because if I fry the joystick electronics then my chair is useless.

WILL 5V destroy the joystick circuit.

I have already mocked the circuit and given it a trial run using the 2 x 12v 6.7Ah SLA's
and using 3 x 1.2v rechargeable AA cells to power the Joystick.
The AA cells only last about 5 minutes.

Thanks in advance.

 

[Harald Kapp]

Without knowing the electronics inside the joystick controller it is impossible to answer your question with a high degree of certainty.
However, as the joystick is powered by a tap in the original battery, one can safely assume that the controller has an internal voltage regulator and that it may well withstand 5 V.
To be on the safe side, you can put a Schottky-diode in series with teh 5 V output of the USB power supply. This will drop approximately 0.3 V, leaving 4.7 V for the controller.
What is the current consumption of the controller? If 2 AAs are dead within 5 minutes there must be a considerable current. The max. current is required to select a suitable Schottky-diode.

Alternatively use an adjustable 12 V to 5 V step-down converter (example) instead of the USB power supply and set it to 4.7 V output voltage. You'll need a separate housing for the converter as these usually come as bare assembled PCBs.

 

[WHONOES]

I assume that you are aware that the method of charging the two differing types of batteries is not the same.

 

[Bluejets]

Discharge also.......

 

[Ray Eyre]

I assume that you are aware that the method of charging the two differing types of batteries is not the same.

Yes I am aware.

 

[Ray Eyre]

Discharge also.......

 

[Ray Eyre]

I have a powered wheelchair that uses a specialised 24v Ni-Mh battery pack yamaha jwb2. Common on a lot of powered wheelchairs.

The battery pack no-longer holds any charge and it will cost over $1500.00 New Zealand to replace.

I am going to replace it with 2 x 12v 6.7Ah SLA batteries but, as the Ni-Mh fits into a dedicated slot in the wheelchair, I going to rip the guts out of the Ni-Mh battery case and wire the SLA's into the output circuit.

My only issue and the one that I need advice on is:

The electronic joystick control is powered by 4.7v taped internally in the 24v Ni-Mh battery case.

I intend to use a 12v to 5v USB power supply for the joystick circuit.

I don't think that an extra 0.3 of a volt will be an issue but I do need advice, because if I fry the joystick electronics then my chair is useless.

WILL 5V destroy the joystick circuit.

I have already mocked the circuit and given it a trial run using the 2 x 12v 6.7Ah SLA's
and using 3 x 1.2v rechargeable AA cells to power the Joystick.
The AA cells only last about 5 minutes.

Thanks in advance.

 

[Ray Eyre]

The rechargeable AA cells were only 600 mAh and were taken from a solar garden light as I did not have anything else available at the time. They may not have even had a full charge.

I have 3 x 12v to 5v USB converters in my parts box and will try from the lowest output to the highest.
1 x 500 mAh
1x 1000 mAh
1 x 2000 mAh

I have various Schottky diodes in my parts boxes that are left over from previous tasks, So I will try to find one that will do the job.

I don't have any idea on how to work out the current demand of the Joystick circuitry and I guess I will use the age old trial and error method, perhaps some one can advise me on this?

I am fully aware of the different charging needs of batteries.
I have a 24v Lead Acid charger from my old mobility scooter that charges the SLA's in about 2 hours, that will be used in place of the Ni-Mh charger.

I may very well abandon using the old/dead Ni-Mh battery case and wire directly into the base of the Ni-Mh battery cradle instead. This will be more work but the ascetics will be superior.

I feel that I must also explain that the powered wheel chair is not a standard item.
It is a dedicated wheel chair that is built by Toyota for use in their "Well Cab" range of disability vehicles. Mine doubles as the drivers seat and it is designed to look like a normal car seat.
You will note 2 x 24v Ni-Mh batteries on the back of the chair. I only have one, this picture is all I could find on the net.

 

[Bluejets]

I have doubts , as quoted, that your selected sla will be a suitable replacement for the nimh, completely different structure with many limitations.
As Harald says, difficult to say without any real spec requirements, but I think fair to say that a manufacturer would hardly supply a $1500 nimh if a $30 sla would do the same job. Physical size pf packs suggest rather large form nimh, another reason I doubt a piddly little sla will work anywhere near the same.

 

[Ray Eyre]

I have doubts , as quoted, that your selected sla will be a suitable replacement for the nimh, completely different structure with many limitations.
As Harald says, difficult to say without any real spec requirements, but I think fair to say that a manufacturer would hardly supply a $1500 nimh if a $30 sla would do the same job. Physical size pf packs suggest rather large form nimh, another reason I doubt a piddly little sla will work anywhere near the same.

Your doubts are noted.

The piddly little SLA's power my lawn-mover for nearly an hour cutting medium to heavy grass. Therefore they should be more than sufficient for 15 to 20 minutes running time on my Car's power-chair.

All I am looking to do is get from my house into my car, out again at the local shops for groceries etc, back to my car and back into my house.

If I can get 15 to 20 minutes running time I will have achieved all I need.

I am NOT looking at having a scenic tour.

I have a large Invacare TDX-SP power chair that is used for my "Scenic Tours"



As I have said "Trial and error" will take place purely as I am not willing or able to pay $1500.00 NZD plus freight and import duties on an already overpriced battery.

If I fail nothing but my dignity has been lost, If I win then $1500:00 NZD plus freight plus import duty plus tax has been saved.

It is funny how my original question "will 5v damage electronics that normally use 4.7v" has been hijacked into a case of what a battery needs by way of charging and piddly little $30:00 SLA batteries wont do the job of a $1500:00 Ni-Mh.

By the way the Ni-Mh pack contains AA diameter sized cells that are a approximately 6 Cm in length, which I believe are 4/3 A cells.

I will post again after I have either won the battle or failed miserably.

Ray

 

[Harald Kapp]

I have 3 x 12v to 5v USB converters in my parts box and will try from the lowest output to the highest.
1 x 500 mAh
1x 1000 mAh
1 x 2000 mAh

mAh is nomenclature for the capacity of e.g. a battery. I guess you mean mA as max. output current of these USB converters?

I don't have any idea on how to work out the current demand of the Joystick circuitry

Use an ammeter (multimeter in amps or mAmps range)?

 

[Ray Eyre]

mAh is nomenclature for the capacity of e.g. a battery. I guess you mean mA as max. output current of these USB converters?

Yes, Typo on my behalf

Use an ammeter (multimeter in amps or mAmps range)?

 

[Ray Eyre]

The 6.7 Amp Sealed Lead Acid batteries have been fully charged.

The Sealed Lead Acid batteries have been hooked up (temporarily), the 12-volt to 5-volt USB converter has been hooked up to the Joystick electronics (temporarily). The socket between the battery holding boxes is the 24-volt charging socket.

See the photo.


Running time under load of my body weight is 67 mins to date (I gave up going up and down the same piece of road, which include a slight hill)

No, I am not going to leave the project looking like a dog’s breakfast. The + and - wires shown twisted onto the terminals in the battery holding box will be routed to the correct positions under the battery holding box and will be soldered into place.

The 24-volt charging socket will be mounted in an easy to access position.

The batteries will be secured in place, most likely with self-adhesive Velcro.

My final opinion is these “piddly little Sealed Lead Acid’s” work will work just as well as the genuine Ni-Mh battery for my normal needs.

Thanks to Harald Kapp for his advice on how to check the current load of the Joystick electronics.