Need power supply for a 12 vdc gearhead motor - low rpm/high torque(22 lbs-in.)

[JumboGarlic]

I'm building a conveyor that uses a 12 v dc gearhead motor. The only info I have with the motor is: 12 v dc, 30 rpm, high torque-22 lbs. per inch, 1:333 gear ratio, 0.8 w horse power. I'm not sure what the "w" in 0.8w horsepower means. It doesn't say anything about amperage.
I need a power supply/adapter just for the motor, no other circuitry involved. In-put is house-hold AC current.
Being an artist, I have no math skills, so any help would be greatly appreciated.

 

[blueroomelectronics]

Being an artist, I have no math skills

Leonardo would disagree.

 

[KeepItSimpleStupid]

whp is wheel HP defined here: Horsepower - Wikipedia, the free encyclopedia

I'd measure the no load current using a car battery and multiply by at least 1.5

I do get something like 75 amps using (746*0.8*1.5)/12. The 746 is Watts/HP, the 0.8 is the HP of the motor; the 1.5 is the fudge factor for starting current and the 12 is the voltage; P=V*Il I is current in Amps

You could also measure the DC resistance of the motor (Tough) and use that as the basis of the power supply.

Finally, you could just use a car battery under actual conditions, measure the current and multiply by 1.5.

 

[Jaguarjoe]

Old computer ATX power supplies spit out tremendous current and are either free or just about free. Two 5v/30a and one 3.3v/30a all in series will give 13.3v and 90 amps.

 

[MikeMl]

I predict that your actual running current will be much less than 75A because you are not likely to be mechanically loading the motor to anything like its rated HP. I just got through building an airplane tug that used a DC gearmotor as the prime mover. It is rated at 1/4HP, but in the final application, it takes much less than 1/4HP (186W) to keep the airplane moving once it has started to move.

 

[Diver300]

It's not lbs per inch. It's lb inches.

Anyhow, 30 lb inches and 30 rpm is only 10.65 W of mechanical power. The efficiency of the 1:333 gearing will be poor, and the motor won't be good either. If you estimate 10% overall, then the electrical power is around 100 W and you need about 8 A. However, the efficiency is a wild guess, so the power could be a lot more or less.

I have no idea where the 0.8 comes from. It's too big to be horsepower and too small to be Watts.

 

[tcmtech]

Old computer ATX power supplies spit out tremendous current and are either free or just about free. Two 5v/30a and one 3.3v/30a all in series will give 13.3v and 90 amps.​

Only in over unity land.

Everywhere else they still put out 30 amps combined.

 

[tcmtech]

Your most practical and cheapest route will be to just use a common high amp 12 volt battery charger.

 

[Jaguarjoe]

Only in over unity land.

Everywhere else they still put out 30 amps combined.

1 box at 5v/30a, another box at 5/30, and a third box at 3.3/30

 

[tcmtech]

Yes the voltages are additive when they are put in series but the current capacity is not.

Add up the individual wattages eachone produces and see what final number you get. I will bet anything you want that the end number is not 13.3 * 90 = 1197 so think about it for a while.

 

[Jaguarjoe]

OMG! I can't believe I did that. Its a good thing I only spent 5 yrs in collij.

 

[JumboGarlic]

Thanks for all the info. I was wondering about the car charger, and comp. p-supply, but I didn't want to over do it and damage the motor some how. So if the p-supply is rated higher than the motor, the motor only pulls what it needs and won't be damaged by the excess?

 

[dougy83]

the motor only pulls what it needs and won't be damaged by the excess?

Connect the motor to a power supply of the specified voltage and it will pull as much as it needs.

 

[JumboGarlic]

Connect the motor to a power supply of the specified voltage and it will pull as much as it needs.

So if I have a power supply rated at 12 v dc and 100 amps, that won't hurt the motor, even if the motor is rated at only .5 amps? It will only pull what it needs, all those extra amps the p-supply has won't cause any problems?

 

[cowana]

No. Unless you connect something wrong, or short out the leads, or stall the motor. That's when a big power supply can cause damage.

But under normal use, a 100A power supply would run a 0.5A motor fine.

 

[KeepItSimpleStupid]

Look at it this way. A house has a 200 Amp service. 120 outlets are protected such that the wiring won't overheat at 15 or 20 Amps.

The load, weather it be a toaster (1500W), TV (100 Watts), a Shaver (10W) or a night light (4 W) will only draw what it needs. Only the TV in these examples have fuses built in.

 

[JumboGarlic]

I was pretty sure that was how AC worked, but I wasn't totally clear about the DC motor and didn't want to take any chances. I know this seemed like a pretty simple question, but I have learned a lot from you guys. Thanks again for the formulas and taking a little time for a novice. I've been planning on trying some guitar effects pedal schematics, so I will probably be asking for a little more advice from you guys in the future.