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Discussion Starter #1
Please help!

I'm using a 1973 wiper motor, and my current power supply is a battery charger with 6 VDC at 6 amps. The motor runs at the speed I want, but it has trouble lifting my bride's head prop, and it gets stuck pretty easily. So now I'm looking into buying a new power supply with more amps.

The supplies I'm looking at are: 5V 8A, 5V 12A, and 5V 22A. Is it possible to have too many Amps? I'm worried about losing the motor and being stuck with a static prop.

I also just bought a DCM-249 wiper motor from All Electronics, which works great at 6VDC, but a little fast.

I want to buy a power supply for each motor, both in the 5-6 volt range, but I'm not certain what to do. Any advice would be greatly appreciated!

Michael
 

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Power supply

I don't know how good you are with wiring but You can use a PC power supply to power your props and you might have or know someone that has an old scrap PC you can pull the power supply out of.there is a 5V,12V and some in betteewn Voltage with these or you can buy them new online for about 20 bucks.the how to to make these work is online too.I forget who it is that has the how to hack for these but it is there I want to say scary terry?might be able to find it in the search here too.
 

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Discussion Starter #3
Thanks, I have looked over Scary Terry's pages. They are very informative but there isn't much mention about amps. I think the computer power supply probably doesn't give out enough amps for my needs, and I really want to push the amps as high as I can reasonably and safely go, especially since I now know 6 amps won't cut it.
 

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Insane Genius
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When it comes to power supplies you can never have too many amps, just too few, you cant overload a circuit because you have too many amps in the power supply, however, you can burn it out if your circuit draws too many amps from the power supply, so if you have an 6amp power supply just make sure that your wiring is rated to 6amps

automotive motors can draw a fair bit of power, and should not have a problem with 6amps
 

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6 amps should be enough though. I'm not experienced with the older wiper motors though. I good place to pick up a higher amp PS is any HAM radio store, they usually have a good selection.
 

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HELLoween Ubber Lord
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The older wiper motors normally use 12v right from the batt, they can handle & draw alot more amps than the new ones. Try hooking it up straight to a 12 v batt & see what your prop does,
I bet that you are not giving it enough amps to provide it the torque energy it needs to lift your prop head. I work with the older motors as we build older hot rods & muscle cars & usually have
plenty of these motors lying around for prop use.6v may be what you want speed of prop wise,but without those amps.............ain't gonna cut it.The older motors need
more amps than the newer ones now,(older models) use 8-10amps min,15 average draw with resistance applied (wiper arms with linkage, or prop pending weight of needing to be moved).
 

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Insane Genius
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yeah, I've seen a 15amp draw from a loaded wiper motor before now, this is why computer PSUs are good, they can supply that kind of power without paying a lot of money for it.
 

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I don't think amps are your problem - the Torque of the motor will drop as you lower the voltage into it. I've found that once you're under 8 volts, it will stall if the load is too heavy.
 

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Discussion Starter #10
KevinS - I did read about that on a website discussing volts vs. amps, but I couldn't really comprehend how the relationship works to create varying amps in different power supplies with the same voltage. It seems to depend on resistance, and I just don't get it.

I've been trying to learn about electronics, but as soon as they stuck amps in there (in like the first chapter) it suddenly got hard for me to visualize it.

I think I'll go with 5V 8A for the All Electronics motor and 5V 12A for the 70's motor. The All Electronics motor lifts my prop with no problem, but it's just too fast, even at 6 volts. I suppose I could try making linkages to change the speed, but that's a whole other concept that I never know how to get my desired result! It is a lot of fun building this stuff though, but time is getting short!

Michael
 

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I'm a total moron with electrical terms, but if my wall wart says 7 volt and 300 mamps, I'm guessing I'm under powered. MY FCG gets stuck every time. I ran it off a grill rotisserie last year, but it's noisy. I got 20 wiper motors for 25 bucks at the local yard. All you can carry for $25. I'm guessing I need a new wall wart with actual amps, not milliamps, correct?
 

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Insane Genius
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Yup, 300mA is barely enough to break wind!

To give you an idea of what 300mA at 12VDC is, consider a 1KW heater, that is 1000W, 300mA at 12V is 3.6W, or 0.36% of the power of a 1Kw Heater.

Wiper motors need lots of amps, ID suggest you start at 5A, and preferably get a lot more.
 

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Discussion Starter #13
I'm back, and a bit confuzzled still! I've been on All-Electronics.com looking at two power supllies:

- a Power-One SP637 for the newer wiper motors, which is a switching power
supply.

- an EOS VLT100-4002 for the older wiper motor, which doesn't appear to be switching. I found a datasheet for the EOS VLT100-4002:
http://www.shopeio.com/inventory/pdf/VLT100-4002.pdf

However, here's little to no information about the SP637 on the internet. Would anyone have any idea what the pinout is for the SP637? AE's site says it is clearly marked, but I like to research before I buy something.

Also, what do I do with the sense pins? Ignore them? Connect them to something or each other? Thanks for your advice!
 

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Oh yes, I pulled out an old forgotten computer and looked at the power supply: 15 Amps! I guess they DO put out enough juice! I might just use this instead! Maybe I'll try all three...
 

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the best way to think about how much voltage/amperage that any device will use is actually to use both the terms together. As was pointed out earlier you have to think of it in terms of Watts. The mathematical relationship between voltage and current for any device is dependant on its power requirements...that is in watts or kilowatts.

now for anyone versed in basic algebrais is really easy...voltage x current x a mechanical constant called "power factor" = kilowatts (or power).

if you cut the voltage down, obviously the motor has to pull more current to maintain the same power...and the motor WILL maintain the same power.

try a radio shack power supply...they sell ac to dc converters that put out 12VDC (which is what your motor is used to running off of anyway) for anywhere from $10-$100 with varying current capacities. I bought 6A power supply that will handle two wiper motors that go to my hanging corpses and they run fine all night...(and if you check the equation above you will notice that with you running your motors at 6VDC andpulling 6A...it is mathematically equivalent to running at 12VDC at 3A, both pull about 36W).

I ran my power supply off a motion detector so that when ppl approach the props they are stationary, then as they get close, the motion detector trips, the power supply gets its juice from the wall and VIOLA...the props get to moving.

happy haunting...and I hope this helped,


DannyK


oh.. and also, there is no way to buy a power supply with too many amps... Amps are drawn from the power supply as needed by the total system load, think of voltage as potential energy and current as flow. you ALWAYS have water pressure in the pipes in your house, but you dont actually SEE any water flow until you ask for it...electricity works the same way.

once again, hope this helped.

DannyK
 

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I'm sure someone knows why this wouldn't work, or would it. Can you just put a dimmer switch in line before the converter to lessen the power getting to the motor?
 

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Insane Genius
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why? do you want to reduce the speed or power (strength) of the motor?

If you want to reduce the speed then the best way of doing this is with a PWM controller, PWM has two main advantages over dimmers 1) they are far more efficient in their use of electricity and 2) they maintain the motors power

here is a sample

Electronic Kits 12VDC motor speed control
 

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You CAN use a dimmer for that, but you want to hook it up in parallel with the motor. This will have the dimmer operating as a shunt around the motor, think of it as a volume knob, fully clockwise sends the majority of the current through the motor while fully ccw will send most of the current through the resistor, thus stopping the motor. I do agree that a motor speed controller will be a better option, but they are also SIGNIFICANTLY more expensive than a dimmer.

Hope that helped,

Dannyk
 

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Thanks Danny and Phoenix. I'm not sure I see the down side of using the dimmer. I do see the upside in cost over the motor speed controller. What am I losing with the dimmer?
 

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I don't seem to be able to delete or edit my earlier post in this thread - What I stated was misleading :(

Here's how I understand this:

A DC motor will slow down when you lower the voltage because it will only accelerate to the point where the Back emf (generated by the armature spinning in the fixed magnetic field) reaches the Forward emf (Supplied by the Power supply). When you drop the supplied Voltage, you drop the max no load speed.

The amount of current it draws will increase as the load goes up. (All motors have a rating called "Stall Current", which is the draw measured when an opposing force stops it from rotating). The lower the current rating is from the supply you're using, the less the load needs to be to stall the motor.
 
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