Convert 24 volt DC to 24 volts AC

[FIGJAM]

Research is not telling me how to do this.

Any ideas?

[EspressoDude]

assuming 2 12v batteries and reasonable load: use 1 12volt battery, cheepo inverter (HF) to 120AC, then step down transformer

[unjonharley]

There are 24 volt power supply plugin's to 120 volt..

As said before, To get AC from DC a inverter is needed

[FIGJAM]

I need about 20 amps, but this is not in my wheelhouse.

Been researching since 5am and I'm lost!

[unjonharley]

Google... transformer 24 volt DC to 24 volt AC inverter..

[Sham]

Do I dare ask what you are trying to power? This may help in offering a better solution than stepping up to 110VAC then back down to 24VAC.

[FIGJAM]

Jon, all that gets is inverters to get 110AC.

The carnival wheelchair of death quit on me and they don't make the control boxes or joysticks anymore.

Trying to connect direct without the CB&J gets a 1/4 turn, like hooking a DC motor to AC.

I think the control box was converting 24 VDC to 24 VAC since hooking to a 12 volt AC transformer at 2 amps got it to at least turn slowly.

Motors need about 20 amps.

I'm not certain of any of this at this point.

[some seeing eye]

The mass market is to 120v AC, even though it would be relatively easy to design and produce a 24VDC > 24VAC switching converter. Espresso's suggestion is the cheapest way to go, but few inverters like driving a pure inductive load - the step down transformer. Transformers also tend to be expensive.

This is very cool and Burningman spirit, trying to repair planned obsolescence! Can you get any numbers off the motor to find its specs/ get chair manufacturer to reveal?

There ought to be a national parting out chair website!

[FIGJAM]

These motors are very torquey and quick.

They can haul 400 pounds around easily.

They cost about $2800 apiece.

Any links to the transformer that I need?

I'll keep looking.

[SnowBlind]

If it's a motor controller, then it's possible that it's not simply converting DC to 24V AC and be done with it. Depending on the type of motor, the controller might varying the frequency to control the motor. In which case simply turning it into 24 V @ 60Hz is not going to do what you want.

[some seeing eye]

http://www.newark.com/hammond/1182s24/t ... dp/54X7550 You can wire the two 24 leads in parallel. You might see if you can borrow an autotransformer (variac) capable of 20A on the secondary to test your idea. High school or college electronics lab?

[rmc50]

Jon, all that gets is inverters to get 110AC.

Trying to connect direct without the CB&J gets a 1/4 turn, like hooking a DC motor to AC.

I think the control box was converting 24 VDC to 24 VAC since hooking to a 12 volt AC transformer at 2 amps got it to at least turn slowly.

Motors need about 20 amps.

I suspect that you would need more than just "AC" to make the motor turn properly.

How many leads come out of the motor?

I did a search on Ebay for wheelchair motors and the vast majority were 24 VDC.

A motor that has only two leads is either is either a brush / commutator style or an induction motor. Induction motors need a good sine wave AC and are not suitable for speed control. I would expect a motor with a commutator would work as well on DC as it would on AC.

It is much more likely that the motor has three leads. Such a motor requires 3-phase power, which can come from a controller. Such motors are far less sensitive to the power being a true sine wave.

What is even more common in small motors are "brushless DC" motors, which will have three main leads and usually 5 small leads. The small wires connect to sensors that sense the position of the motor shaft and tell the controller how to apply power to the three motor leads. It is possible to do away with the position sensors, using "back EMF" to sense the motor shaft position, but this doesn't work at zero speed and would be awkward for a wheel chair.

If what you have is a brushless DC motor then there are lots of controllers that are available. The most common arrangement is to have three phases, 120 degrees apart. There needs to be a current limit set and the controller has to be configured for the voltage (24, 36, 48, etc). Such controllers are sold for "E-bike" conversions and electric scooters and can be purchases for as little as $40.

If what you actually have is a DC motor then what you want is a "Pulse Width Modulator". Search Ebay for "PWM Motor Controller" and you will find suitable devices. Adapting one to fit your existing controls Joystick) might be a challenge....

Or you can search Ebay for a used controller for the wheelchair that you had. If it was a popular wheelchair then the chances are good that someone is selling the part you need.

Rod

[EspressoDude]

post a link to the motor, other wize it is all electrons in the dust trying to guess what is needed

[Sham]

I am pretty sure I can design a circuit that will use a 24vdc relay to flop the voltage back and forth and turn dc into ac by activating the relay. I am not sure what hertz cycle would come out of that, but it would be pretty fast.

[FIGJAM]

This will have to do till I get mine from the guy that was testing them.

http://www.ebay.com/itm/Invacare-Arrow- ... 19f56293fb

[FIGJAM]

This is an MKIV gearless brushless motor (part number 1079291) made for an Invacare power chair.







There are 3 large wires.

Red, black, and blue.

There are also 6 small wires.

Red, black, blue, orange, white, and green.

If I connect the large black wire to 12 vdc negative and the large red to positive, the motor will turn just a fraction.

Doing the same with the large blue wire to positive will turn the motor in the opposite direction, but just a fraction.



Electrical engineering is way out of my depth.

I had a guy with 35 years of electric motor experience trying to bench test these motors, and he got the same results, until he tested it with a transformer.

He got it to turn slowly, but his transformer only supplied 2 amps.

He said he had never seen a motor like this before, and he didn't seem sure whether the transformer was producing AC or DC current.

[EspressoDude]

http://www.wheelchairdriver.com/board/v ... 6&start=20

it appears these are 3 phase servo motors with hall effect current sensors for feedback to the servo amplifier and possibly a brake

speed is dependent on the frequency of the three phase. without the factory controller these motors are total trial and error with $$servo amplifier$$

[unjonharley]

It was so much easier when a DC motor had one brass stud and AC had a red and a black wire to hook up..

[SnowBlind]

This will have to do till I get mine from the guy that was testing them.

http://www.ebay.com/itm/Invacare-Arrow- ... 19f56293fb

Are those the ones you have? He doesn't have much detail, but I don't think those are AC motors. Actually, I think most (all?) brushless motors are DC. (I could be totally wrong though)

[FIGJAM]

Yeah, it's confusing to me too.

The mobility service people are not much help either.

They don't really have bench test equipment.

Took the whole chair in for a diagnostic and $45 later was told it was probably the joystick.

Got a joystick off ebay for $200, no go.

Took the chair back to re-diagnose with the new joystick, and after 2 days, they figured it was the control box.

Got a control box off ebay for another $200. still no go.

Sent the ebay parts back figuring I could rig my own switching system, but these motors are to esoteric for my knowledge base.

Haven't given up, but I'm getting close!

[ygmir]

extend the shaft and put a 5 h.p. gas engine on it. That will turn the motor, and thusly drive the chair.

[FIGJAM]

Why didn't I think of that!!!

[EspressoDude]

giggle search "24 volt ac brushless servo motor" and look at all the hits.

also. Invacare will be less than helpful. They have proprietary systems, and a HUGE LIABILITY if they help someone cobble something together that may be used to propel a chair. You will likely have more luck building something from industrial servo motors and drives, then figuring out how to attach wheels to it.

[Elliot]

Another thing I ran into with medical equipment, when I needed a small rubber part for a friend's racing hand-cycle: Such handcycles are usually paid for thru medical-benefit or -insurance programs, and the dealer wanted "a ton" of paperwork filled out just to sell me a $15.- part for cash. So be prepared for that.