My dad got a new lift chair, so as we were tossing out the old, I figured I'd see if there were any goodies to scavange. There was some heating pads, but too lazy to rip it apart that much, but there was a rather large linear actuator in there. Doesn't have a rating on it, but it can obviously lift quite a bit, at least 300 pounds. I've got the power supply and everything, but I'm wondering what problems I might run into if I tried to use it in a 12v application instead of the intended 24v. Would it still work? I'm guessing it would, but that it's going to run hotter as it would be drawing more current? Am I on the right track?
mmm... not really. I suggest you try it by hooking it up to a high-current 12v source (Eg, not you comp's PSU). with a fire extinguisher handy. my guess is that it will function about 50% of it's speced abilities. then again... 24v transformers are cheap.
I have a 12volt battery I was going to try it with. I have the 24v power supply for it, I was just thinking if wanted to use it in a mobile application, though can't think of anything off the top of my head, it's rather larger.
When you say linear actuator do you mean linear motor (like a maglev train) or something else? If it is the former then you will break it if you just connect a battery to it, they need a little more advanced control than that... Rod
General principles of Mr Ohm still apply, less volts = less current. If it's having to work harder the current drop won't be proportional to voltage, but it will still be less than the 24V current. At best it will run slower on 12V, at worst not get enough power to start and then you may see a high stall current. Try it with a car battery.
Thanks. Must be remembering things wrong. I thought with dc motors, that part of what limited the current was the inductance of the motor spinning which is why when they stall, the current increases. So I figured that if it was spinning slower, there would be less resistance, so higher current.
Thats probably not a good idea, the -ve voltages from a psu have very low current capabilities, something in the region of -0.5a maybe a bit more, probably less. I dont know what the actuator draws but ill bet its more than that. Moriquendi
I may have missed something, but if it turns out that 12V is insufficient to power it, and you're going to power it off a battery, (I'm assuming a car battery), then why not just put two car batteries in series? This would get you the 24V that you need. Incidentally, crudely speaking, the physics of DC motors usually works something like this: The wires in the motor will have a fixed resistance. When the motor is not turning, (ie at startup) then Since V(Voltage) = I(Current) × R(Resistance), then Current will decrease as voltage decreases. Once the motor is turning, then other forces (Electromotive forces) come into play. Not using any formulas, (keeping it simple), the rotation of the motor results in a force known as 'Back EMF', which is simply a voltage generated within the motor wiring, which cancels out the one being supplied by the battery. If there is no load on a motor, then this 'Back EMF' will eventually be almost equal to the voltage supplied from the battery, and current will fall to almost zero. It is the 'Back EMF' force, created by the motor turning, which prevents it from drawing too much current and overheating. The more load there is, the smaller the 'Back EMF', the more current is used, and the hotter the motor will run. Thus as CPEmma said, if the motor fails to start turning, disconnect it immediately to stop it overheating and melting. Otherwise, it will work fine at 12V, just with significantly less force that it would at 24V.
That's what I was thinking of. Just misunderstanding it. I was thinking that at a lower voltage, there would be less resistance, which might mean more current even at the lower voltage. I'll try it out with a 12v battery, if it doesn't work, no big deal. More a solution looking for a problem. Trying to think of something cool to do with it in the car. Wouldn't be worth the trouble to carry two extra batteries. Though I suppose I could find a dc/dc converter. I don't have it in front of me, but I think the PS supplies 1amp at 24v. I can always do something with it in the house otherwise.
Idea: use it to adjust the height of your computer chair by software. It could be done using a H bridge connected to the serial port. Imagine the look at the next LAN party when you press a shortcut on the keyboard to raise or lower the chair.
Not a bad idea, but not really into the lan scene (just finally got a half decent gaming rig after 4 or 5 years off of gamin). Though I've got a big drafting table that's been sitting in the closet for a couple of years. I'd like to use it, but don't really have the room for it. Maybe I'll mount it to the wall on a hinge and use it to lift it into position. The base is already tubular steel. Then I guess it would be just a matter of hinging it and finding the best place to pivot it from.
