# Need help with understanding PMDC Motors

I'm building a crab/shrimp pot puller. I've seen the regular production models and a few home built versions. What I don't understand is how a 12v PMDC 90:1 worm drive motor can be rated at 2.3hp. As far as I can tell, it looks to be the same motor I'm planning to use, and mine is a 12v 600w 60:1 worm drive that is rated at 0.8hp.

https://www.discoverybaymarinegear.com/cgi-bin/quikstore.pl?category=powerhauler

I'm told that my motor can be increased to 48v. Other than the 90:1 gearing, I don't see how they can claim a 140' per minute pull of a 200lb weight on a 90:1 ratio of a motor speed of 3600rpm,with a drive pulley of about 12". Doing the math:

3600/90:1 = 40rpm at the drive pulley. 1'(12") x 3.14 x 40rpm = 125.6' per minute ....without load. Is this even possible?

Can I create more HP if I increase the voltage to 24v? And if so, would increasing it to 48v give me the 2.3hp their motor claims to have. Can I do that with a 900w PMDC motor?

Moreover, is it even possible to create 2.3hp from a 12v supply, especially if the motor is in a 3" x 4.5" housing?

Is the 2.3hp a rating of the actual motor or what is coming off the drive shaft?

I installed my 12" (11" internal diameter) drive pulley on, turned the motor on, and I cannot stop it. I'm guessing this will be more than adequate, ...but feel I am missing something.

• Do superficially identical looking cars both have the same top speed and acceleration? – Andy aka Jun 10 '18 at 18:08
• You are looking at the body and I am looking at the engine. Since I am ONLY looking at the engine, I can pretty much tell what the differences are. Therefore, your comment doesn't address any of my questions. Is there such a thing as a 2.3hp PMDC 12v motor in that size, and what voltage would it have to run to get that hp ....or is it even related to voltage? – Kevin D Holden Jun 10 '18 at 19:40

What I don't understand is how a 12v PMDC 90:1 worm drive motor can be rated at 2.3hp. As far as I can tell, it looks to be the same motor I'm planning to use, and mine is a 12v 600w 60:1 worm drive that is rated at 0.8hp.

200lb * 140ft/min is ~0.85hp or 630W (if motor/gearbox efficiency was 70% then it would need to pull ~900W = 12V x 75A from the battery). If your motor's 600W 0.8hp rating is output power then it may have similar performance.

Is the 2.3hp a rating of the actual motor or what is coming off the drive shaft?

Maximum output power of a PM DC motor is achieved when it is loaded down to 50% of free-running rpm, at which point it is 50% efficient so only half the input power comes out the shaft while the other half just heats up the motor. The motor could eventually overheat at this power level, so it may be 'de-rated' for continuous operation.

Horsepower is generally output power, while Watts could be input or output. Without detailed specifications you don't know what the 2.3hp refers to. In this case I suspect it is maximum output power, not continuous duty output.

At lower loading motor speed increases and efficiency improves, typically peaking at 85~90% of no-load rpm. A motor with higher efficiency has less heat to get rid of so it can be run at higher output power. It may also be more compact because it doesn't need as large a surface area to dissipate the heat.

Obtaining higher efficiency requires the use of more exotic materials (eg. Neodymium magnets, grain-orientated silicon steel) and finer construction (tighter windings, thinner laminations, better bearings etc.) which raises the price. A \$1200 package should have a high quality motor in it!

3600/90:1 = 40rpm at the drive pulley. 1'(12") x 3.14 x 40rpm = 125.6' per minute ....without load. Is this even possible?

Other than the 90:1 gearing, I don't see how they can claim a 140' per minute pull of a 200lb weight on a 90:1 ratio of a motor speed of 3600rpm,with a drive pulley of about 12"

The 90:1 geared motors are rated for up to 120ft/min, and it is not entirely clear whether they can pull 200lb at that speed. For example the 'Power Hauler HD3™ Motor Package' is...

Equipped with our powerful 2.3 hp 12 volt powerdrive with our zero maintenance 90:1 high torque oil bath worm drive gear box which provides pulling speeds up to 120 feet per minute with a 200 lbs. max load.

Note they do not say that it can do 120ft/min and 200lbs at the same time - but even if they did it could just be inaccurate paraphrasing of the actual spec.

• Excellent! Thanks, Bruce. Just a couple more questions. – Kevin D Holden Jun 11 '18 at 2:10
• @BruceAbbott -- offtopic for this question, but it seems you're probably the best person to answer this question I asked the other day; is there any chance you could have a look? Thanks. – Jules Jun 12 '18 at 3:29
• To answer your 'couple' of questions: increasing voltage increases speed and therefore hp (power = torque * rpm), but only reduces current if you reduce the load (by eg. increasing the gear ratio). The motor will have a maximum safe speed which limits maximum power output. At lower voltage the motor runs slower but still draws the same current at the same torque (of course at lower speed the torque load may be less, depending on the load's characteristics). Your motor will probably do the job if its ratings are realistic - easiest way to find out is try it! – Bruce Abbott Jun 12 '18 at 12:13