wheelcair power supply

[zotdoc]

I am working on a power chair robotics project and want to make a plug in power supply that would run 2 - 24 volt wheelchair motors as a test bed - so I can stop charging batteries all the time. The main circuit breaker in the power chair is 80 amps. does that mean I can get by with a 24 volt 80 amp power supply? any body with experience in making such a supply or any ideas?

[dacflyer]

ya you should have no problem, but i doubt you will use 80 amps, usually the motors will draw about 30 amps or so under full load.
just make sure you have very good filtering, because of the controller is very sensitive...

[haklesup]

A circuit breaker is generally chosen for a higher than normal current that will still protect some of the assembly. Its safe to say the load operates well under 80A, 30 to 40 is a good guess.

If you choose too low current, you may struggle going up slopes or starting with a heavy passenger when the motor would experience the most torque. you should still work OK on flats

[zotdoc]

thanks for the input. I have a 240 volt 50 amp circuit for a welding machine and anyone have any ideas about where toget a 240 to 24 volt transformer that will handle this much current?

[haklesup]

It's a similar problem to trying to make an AC power supply for a DC Car amplifier (which also take large DC current at 12V). The power supply would cost more than just getting an AC supplied amplifier. In your case, the power supply would rival the cost of replacing with AC motors that run at higher voltage and lower current. 50A takes a lot of copper.

A compromise solution is to leave the batteries in place and add a high current (5A or 10A) charger to keep them topped up. Can get an automotive battery charger in that range anywhere for not too much. Whether that works depends on your project and actual drain.

[zotdoc]

after looking all over the net I cant find a transformer anywhere that will handle this problem, and the idea of just keeping the batteries charged looks better and better. Thanks guys.

[jwax]

Couple of questions-
1) Electric wheelchairs are designed for very heavy loads, under very high current conditions.
(250 lb person in a 200 lb chair going up an incline heavy) Are you planning on these large loads for your project? If so, look for an 80 Amp power supply. If not, size your supply accordingly.
24 VDC at 80 Amps is almost 3 HP. Do you need that?

2) How are you controlling these motors? Relays, or solid state?

3) Do you need full speed from these motors? They will run half speed at 12 volts, and therefore half the current.

4) Running 240 VAC has its own hazards.

[haklesup]

A transformer for a linear supply for this would probably be larger and heavier than the battery if you can even find one in surplus stocks (you can definitely order one new but you don't want to know the price). A switching power supply should be available but it will cost in excess of $500 with far better regulation than you need. In many cases you can parallel the DC outputs of switching supplies to get higher current. I don't think you can parallel transformers in that way though. Phase shifts will screw you up.

[sghioto]

Check out some of those YouTube videos on rewinding the secondary of a microwave oven transformers. They claim you get about 1 volt per turn and up to 100 amps.

Steve G

[Lenp]

Zotdoc
Considering the 24 volt welding transformer, you may be able to unwind some of its secondary (24v side) to get you down to the lower voltage. I did this not long ago with a 24V fork lift charger and it was easy to get it down to about 13V. Since the winding was on the outside, I used a dremel with a cutt off wheel to cut almost through some of the windings then peeled them off. Cut and measure as you go so you don't go too far.

Or, consider ways to reduce the transformer's input, maybe a variac, or I know that a light dimmer control is not really suitable for a transformer and it might cause hum and some overheating, but it will work in many cases if you watch the line current.

Len