# 12VDC >2hp electric motor

1. ### bwibwi

9
I'm looking for 12 VDC (preferred) or 24 VDC electric motor that can output >2hp (preferred 3hp) and with gear reduction to 100~150 rpm.

I've looked every where but has no luck. Can anyone help?
Thank you.

2. ### FredGarvin

5,087
For a 12VDC motor that's close to 125 amps. That's some pretty good current. Do you have power to deliver that? That is a good sized power supply.

Honestly I can't say that I have seen a higher HP motor with that small of voltage. Most of the industrial ones will be at least 90 VDC.

3. ### Mech_Engineer

2,299
Like Fred said, I doubt you will be able to find that kind of power output in a 12-24V motor; A quick search through GlobalSpec didn't turn up any results. Better up your voltage or lower your power requirement.

9
5. ### TVP45

This is a good time for my Damon Runyan quote from Guys and Dolls:
"One of these days in your travels, a guy is going to come up to you and show you a nice brand-new deck of cards on which the seal is not yet broken, and this guy is going to offer to bet you that he can make the Jack of Spades jump out of the deck and squirt cider in your ear. But, son, do not bet this man, for as sure as you are standing there, you are going to end up with an earful of cider.”

Try calculating how many amps would have to flow through those #10AWG lead wires.

6. ### bwibwi

9
Mmmm, okay I don't know how to do the calculation. But judging from what you wrote, I'll say that is not the right choice?

7. ### dlgoff

3,075
Maybe you can tell us what you are trying to do and we can make some susgestions. There is one possibility; a 12V or 24V battery with an inverter to 120vac. But it might not run a 2hp motor very long.

8. ### TVP45

1hp is equal to about 750W. Allowing some inefficiencies in a motor, make that 800W. So, 4.5hp would be 3600W. Since voltage times current = power (Watts), divide 3600W by 24V and you get 150A. I don't have my wire tables handy, but #10AWG in free air should be good for about 35A continuous.

You have to look at how the manufacturer rates the power. Is it continuous? Is it peak (for perhaps a few seconds)? Is it "equivalent"? The manufacturer talks about 570A peak for this motor and that might indeed give you the locked rotor draw of a 4.5hp motor, but the magic smoke will start leaking out very quickly. Are you looking for peak power for a very short time with a low duty cycle? This manufacturer, BTW, seems to offer a gearbox.

9. ### bwibwi

9
What I'm trying to do is get a more powerful crab/prawn puller, without going into hydraulic. Right now I have a line hauler which is only 1.4 hp running on 12VDC. Its speed when running again current and with weighted trap is just now fast enough. It's rating is suppose to be 110ft/min with 100lb limit. So ideally a 400 ft deep trap will only 4 min. However, in actual it's more like 10~15 min (with some hand pulling help). So I looking to replace the motor with something stronger. I've looked at the http://www.magmotor.com/products.html for brushless and brush motors but sorry to say my physics sucks, I can't make heads or tail out of the spec pdf this manufacturer provides.

If anyone of you can help out that's much appreciated.

Ps. Another solution I just thought of, is there such gearbox that can attach 2 motors? So if I have 2 X 1.4 hp motors would I get 2.8hp? Is there such gearbox?

Thank you

10. ### bwibwi

9
Just to post new find. I've found winch motors Ramsey winch motor. It runs on 12v. I'm thinking maybe the REP8000 or REP8.5E motor. At 2000lb load amp draw is 168 and 110 respectively. I'll only be pulling 300lb (500lb max) I figure with Nautilus Deep Cycle Battery 750amp crank power and 205 min of reserve capacity (amp capacity) I should be able to operate the motor with 300lb load (approx. 100 amp) for a good 2 hours?

11. ### stewartcs

2,284
Sounds like you are encountering some drag forces as well, which are adding to your problem. If your motor is designed to pull 100 lbf at a rate of 110ft/min (I presume in air), then it will be capable of ascending less than that in water.

12. ### Mech_Engineer

2,299
Winch motors are an excellent idea that I hadn't thought of! Remember: winches use very large cables to supply power (00-Gauge perhaps?) This of course means they pull a lot of current.

Beware, I suspect the winch may drain your battery in far less than 2 hours. You need to look at the amp-hour rated capacity of the battery and divide by the current draw of the motor at your working load. The "205 min reserve capacity" is usually a "fake" number, based on a 10 amp load. If you're looking at pulling 100 amps (or even more), your reserve will be a factor of 10 less.

The reserve rating of your battery makes me think it may not be the biggest one available. Multiplying 205 minutes by 10 amps give us about 34 amp-hours, some very large deep-cycle batteries may go as high as 75 amp-hours (but will be very large and very heavy). In the perfect case, a 34 amp-hour battery will only run a 2hp winch motor (at full power) for 16 minutes. For a 3 hp motor, it will only last 11 minutes. Even a 75 amp-hour battery will only run a 2hp motor for 36 minutes, and a 3hp motor for 24 minutes.

Also, running a battery (even a nice deep-cycle one) for 15 minutes at 124 amps (2 hp 12V motor) could possibly damage the battery, either from overheating or other possible problems. Just be careful is all.

Last edited: Nov 20, 2007
13. ### bwibwi

9
Hi Stewartct, ya water current and drag is a big problem.
Hi Mech Engineer. I've just found more info on the battery. Cranking power 750amp,
Amp Hour Capacity: 103
Reserve Capacity: 205min.

Is there a way of calculating usage length from Amp hour capacity? Oh the draw is about 100amps.

PS like you mentioned just incase too much power's been drawn. I'll have 3 batteries with me. 2 for the puller and 1 for starting up the boat.

14. ### dlgoff

3,075
"Also, running a battery (even a nice deep-cycle one) for 15 minutes at 124 amps (2 hp 12V motor) could possibly damage the battery, either from overheating or other possible problems. Just be careful is all."

I agree. I've seen batteries explode. Not good.

15. ### Mech_Engineer

2,299
103 amp-hours! Now that's a beefy battery. Cranking power doesn't matter for your application, and as I said before, the reserve capacity is a sort of a "fake" number so we needn't worry about that.

The caclulation to figure out how long you can run a motor from that battery is a straightforward one. First, you figure out what power the motor is, and convert this to watts. Converting from horsepower to watts is done like so:

$$P_w = P_H_p * 746$$

Next, you need to figure out how many amps that motor will pull when powered with a 12V source. Like so:

$$I = \frac{P_w}{V}$$

Now the easy part- to find how long your battery can support that load. Just divide the amp-hour capacity of the battery by the number of amps your motor will pull.

$$t = \frac{Capacity}{I}$$

This is how long your battery will last in hours. Convert to minutes by multiplying by 60.

So for example, a 2hp motor pulls 124.2 amps. Your 103 amp-hour battery will therefore be able to support that motor for (at best) 49.7 minutes. It will probably be somewhat less due to efficiency losses, but 45 minutes would be a good estimate.

16. ### mgb_phys

8,952
Although as mech_engineer said above there is a limit on the sustained power you can draw from the battery without overheating. I would say sticking to 2hour discharge time would be better so 50A max from a 100Ah battery - the maximum power and capacity aren't really linked - it's just a rule of thumb. The maximum current you can safely pull drops with temperature how hot is it going to be where you are running this? Is the battery in moving cool air or inside th ehot engine bay of a truck?

Also mech_eng's calculation applies for deep-dischage batteries, for regular car/truck batteries you are lucky to get 50% of the rated capacity out of them.

17. ### bwibwi

9
I see. So instead of drawing from battery. May be I should consider drawing directly from alternator?

ps battery is located underdeck of my boat. So no moving air. But it's not hot either. About 12 degrees C.

One more thing, would parallel linked 2 batteries output 50amps each and I get 100amps?

Last edited: Nov 21, 2007
18. ### billblack

34
So....you are using something like the pot haulers at the top of this page?

http://www.snlcorp.com/Webpages/crabbing_supplies.htm

Interesting pot hauler motor specs here:
http://www.blueoceantackle.com/pot_hauler_info.htm
It looks like 12V and a max of 80 amps is the norm.

Is the motor you are using now getting hot under the present loading? If not, a gearing change might be a plan.
If you are using a boat powered by an inboard engine, it would seem to me that using an inverter or an engine-mounted AC generator to supply AC power to the pot hauler motor would be the most likely choice. When you look at the equation that Mech_Engineer posted:
$$I = \frac{P_w}{V}$$
it is apparent that if you replace 12V with 120V in the denominator your amperage needs fall by a factor of 10. That relationship shows why your neighbor's Prius runs on about 500V instead of 12.
Alternatively one could rectify that 120V AC to DC and use one of the many surplus 90-120V DC treadmill motors that are advertised. Cheaper is not a bad thing.
Safety note: if you use AC on or near the water, a Ground Fault Interrupter is a must.

19. ### bwibwi

9
Hi Billblack, yes it's something similar. No motor is not getting hot. I've taken apart the puller and finds the motor can run on either 12v or 24v. I'm going to try running it on 24v see if it works better. If not I've been exploring possibility of using treadmill motors but I'm kind of worried about the high voltage.

20. ### n3pla2000

1
I do NOT know how many HP it takes to power my cars air-conditioning. I have seen it quoted any where between 1 and 5 HP. I however after seeing differing answers fell it is close to around 2HP. I would like to know for sure. I will to give the following circumstances, and see if someone has access to the data I need. I need to determine if I need a 2HP, or a motor bigger or smaller than my best guess.

I must sit stationary in a vehicle for hours, in the summer heat. The vehicle interior can greatly exceed 120 degrees Fahrenheit. I therefore end up running the engine in 90 plus degree Fahrenheit temperatures. The air conditioner can be set to "Norm A/C" (which kicks the compressor on and off) or "Max A/C" (which runs the compress either continuously or nearly so). Presently I drive a Crown Victoria, I will need to switch to another vehicle in the future, possibly a Lincoln or some kind of minivan or SUV. So here is my problem.

First I need a motor to turn the compressor on a Crown Victoria up to say 10 hours (this is actually overkill as I want reserve capabilities). I need to find an appropriate power source (Lead Acid Automobile Batteries or Marine or Rechargeable Lithium) and the appropriate 12vdc motor strong enough for near continuous use. The motor (of unknown HP) will run the compressor. The air conditioner system will be rewired to allow it's use when the ignition switch is set to either "ON" or "ACC"(accessory). That means the blower motor for the fan, and adding a vacuum motor to run the vacuum line for the A/C controls.

I would use a relay to separate the electrical system for the A/C from the vehicle electrical system. Where the compressor is presently located, I would instead have a second alternator. This alternator would need to have a lamp place in the A/C control panel to indicate if this additional alternator is functional. The power from this would charge batteries in the trunk (by the spare tire). These batteries would run the ignition system when the engine is off.

The compressor would be shifted back and to the right and mounted on new brackets to allow clearance for the additional alternator, and to remove the A/C compressors clutch. The motor drive shaft will couple directly to the compressors drive shaft and the compressor relay would instead activate a solenoid that activate the motor rather than activating a clutch. If needed, I guess that I could retain the clutch, have the motor start then engage, and then engage clutch when the motor is up to speed. I however do not know how much HP the motor needs to be, or the size (in amp-hours) and count of the batteries needed. There is room by the spare for multiple batteries without reducing luggage space.

So guys... ho many HP is appropriate?