Halloween Forum banner

1 - 20 of 46 Posts

·
Registered
Joined
·
508 Posts
Discussion Starter #1
Hey guys-
I need to run my wiper motor fairly slow. I was thinking about 3 volts or so- according to Scary Terry, this will run it at about 10rpm, which is perfect. I'm having trouble finding a 3-4v power supply that also has a high current rating. I tried a 3v 1a and it wouldn't turn the motor on. I think it needs around 4amps to run with decent torque.

Any ideas for a CHEAP solution? Space constraints on this prop won't allow me to gear down the motor. I DO have some computer power supplies- but every time in the past I tried this method, it turned into a nightmare... trying to rig a side load circuit so that the PS stays on- it just turns into a whole 'nother project just to get the thing to work right! I'm open to trying it again, but... would prefer a simple wall wart or something.

Ideas?
Thanks!
 

·
BAD INFLUENCE
Joined
·
11,453 Posts

·
Registered
Joined
·
508 Posts
Discussion Starter #3
Dang, I was hoping to find something a little smaller/cheaper... thanks for the help! Anyone else have any ideas?
 

·
Registered
Joined
·
310 Posts
You will have a hard time finding a power supply that provides 4A for less than $20, and even a harder time finding an odd voltage like 3 or 4V. To be honest, changing the voltage for a motor may be the cheapest way to control the speed but when you use that method you also give up torque. When you are using a motor with some kind of gearhead the problem becomes even worse because the motor has to overcome that initial surge necessary to get the gears turning. The better solution is to use a speed controller which allows you to keep the voltage to the motor at the rated level and instead sends a pulsed signal to the motor. The longer the pulses the faster the motor goes. The advantage with this method is that you hardly lose any torque at low speeds. Here is a kit that you can purchase that allows you to adjust the speed and handles up to 7A.
 

·
Registered
Joined
·
508 Posts
Discussion Starter #5
LOL. Yeah, tried that kit before. It never worked. Any others out there?
 

·
Registered
Joined
·
508 Posts
Discussion Starter #7
Yeah, I have some computer power supplies. Those are always a nightmare to work with- see my above comments. UNLESS someone has an easy way to deal with them?
 

·
Registered
Joined
·
508 Posts
Discussion Starter #8
Hey AZDude-
If I use a computer PS, and use the 3v supply line- will that drop the amps/torque down quite a bit?
 

·
Registered
Joined
·
71 Posts
You may try this.

You need and old 12 volt car battery that measures well below 12 volts and a wall wart or other power supply that puts out 4 or 5 or 6 volts or so dc. If you connect the wall wart to the battery it will keep an old worn out battery charged to 4 volts. (Make sure the output is DC and you get the polarity correct) The battery will give you the ability for a few amps and the wall wart will limit the voltage the battery charges to. The battery needs to be pretty well run down and useless for a car, or it soon will be. The current the wall wart (or other power supply) can put out as well as the state of the battery will determine how long you can run the motor. Best if it is intermittent use.

Andy
 

·
Registered
Joined
·
490 Posts
Motor torque is (generally) proportional to the current passing through them. As long as your power supply is capable of delivering the voltage you need (for the speed you want) at the current required (for the load you're pushing) you should be okay.

I'd highly recommend using a PWM motor speed controller to achieve what you're looking for. This will let you use a higher battery/supply voltage, and yet still control the speed of the motor. Batteries don't like being way below their nominal charge.

Here's an interesting site I just found. Or, if you're adventurous, you could pick up a used/surplus brush motor servo amplifier on ebay. Apparently, these can go for pretty cheap (as little as $30-40).

- Hook
 

·
Registered
Joined
·
508 Posts
Discussion Starter #11
Ouch. Those are pretty expensive.

The car battery thing is pretty interesting. I actually have some old Power Wheels batteries- those battery operated cars kids drive around in. I believe they're 6v. So- you're saying to drain it, hook it up and re-charge it with a 3v wall wart? This is where you lose me- is the CURRENT that is on the wall wart going to determine the current I'm going to get out of the battery?

Or- will the battery put out higher current, but remain at the 3v rating?

This is very interesting...

Oh, btw- this is NOT for intermittent use- but continuous (it's a haunted bookshelf). However, it'll only run 4hrs a night... AND- can I leave the battery hooked up and charging off the wall wart AND run the wiper motor off the battery at the same time?
 

·
Registered
Joined
·
490 Posts
If it's for continuous use, all the current will be coming from the charger. The battery would be pretty much irrelevant. The only exception would be that the battery might help out with transients (sticky points in the rotation). However, if the battery were nearly completely discharged (1/2 or 1/4 of its normal voltage), it wouldn't be able to supply much current anyway.

I'd say check out what Brad suggested, or at least take a look at their voltage/speed table to figure out what voltage you really need.

Take a look at this 5V 11A supply for $6. This would make a great servo supply too!

- Hook
 

·
Registered
Joined
·
508 Posts
Discussion Starter #14
ok- I'm also VERY open to a different motor. I guess I feel that it's silly to spend extra money on something to reduce the speed of a good motor- why not spend the same money on a slower, high torque motor to begin with? Do you guys know anything that would work? Anything in the 3-10rpm range, high torque would be awesome. CHEAP TOO!!!
 

·
Registered
Joined
·
508 Posts
Discussion Starter #15
ok- so I'm comparing apples to apples here...

How much 'torque' or power does a wiper motor have?
 

·
Registered
Joined
·
508 Posts
Discussion Starter #16
FYI-
I have a car battery charger running at 6v right now. It's running the motor too fast, which is why I was looking for around 3-4v instead...
 

·
Registered
Joined
·
48 Posts
Are you using the motor to lift a weight? I have a prop that has a moving arm (up and down).

I'm using a wiper motor and an ATX computer power supply. I haven't had any issues with the power supply after I jumpered the "start" leads together. I'm using 3.3 volts to move the arm, at a speed that looks best. The motor was struggling some to lift the arm so I added a counter balance that weighs just under 4 lbs and the motor lifts and lowers the arm with ease. Depending on how much room you have this might be the way to solve your problem

If you have room to add the counter balance it should take care of the loss of torgue.

I also have a rotisserie motor in a spooky tree prop. The two arms (limbs) move uip and down, but with this prop I had to add 16 lbs of counter balance but it works great...
 

·
Registered
Joined
·
508 Posts
Discussion Starter #18
Nope- it's a haunted bookcase- so it's just a spinning shaft with cams on the shaft. I don't believe it needs THAT much torque to move the books in/out. No way to counter-balance anything. I'd PREFER to keep the wiper motor, since, it's already hooked up. I can try using a computer supply again- it's just always been such a nightmare.

Otherwise- maybe a motor like this would work?
https://www.surpluscenter.com/item.asp?UID=2009083118482799&item=5-1712&catname=electric
 

·
Registered
Joined
·
508 Posts
Discussion Starter #19
That motor has 120in-pounds of torque, or 10ft-pounds. I believe a wiper motor, has around 13ft-pounds, depending on the speed/gear/voltage you're using.

I'd prefer to just use the motor I already have rigged up tho.

Now- previously, when hooking up an ATX power supply... I had to get one of those LARGE resistors, hook it up across a couple wires somewhere inside the box- and jumper something else, and run a light bulb or some other mechanism on the thing just so that it would stay on. Apparently there's the power shut down mechanism to where it'll shut the PS off if it doesn't detect a load right away? Or- the wiper motor current did something funky with it, don't remember. It was a huge hassle. I wish I could just plug in a wall wart and be done with it.

Suggestions?
 

·
Registered
Joined
·
48 Posts
well they're not low voltage, but a rotisserie motor has quite a bit of torque and they are pretty compact... and turn at approx 5 rpms...

As far as your problems with the computer power supply I don't have any answers. I have two of them for power to wiper motors (one is used to rock a rocking chair) and don't have any problems.
 
1 - 20 of 46 Posts
Top