# Advice on design of a two 5hp DC motor propulsion system

Discussion in 'Homework Help' started by tannerhunt5, Jul 24, 2016.

1. ### tannerhunt5 Thread Starter New Member

Jul 24, 2016
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I'm designing a propulsion system that takes a turbopump which draw air in, passes it through intercoolers and then another turbopump pushes the air out. I'm having a hard time getting my design straight and would greatly appreciate help straightening some things out.

So this is my list of items I currently have in the system:
• bank of 10 24 V Li-Ion batteries (50 Ah, 50 A max discharge rate)
• two 5hp 208 Volt motors (After inefficiencies are taken into account the power draw is suspected to be around 10 kW)
• a COTS motor controller
• some sort of battery management system
• 8 gauge wire rated at 32 amps
I need the motors to run at a constant rate of 3600 rpm for appx. 3 minutes at a time.

The math I have so far for each motor: 5 kw = (208 V)*(24 A) which checks out but I know it cant be that simple. Should the motors be in series or parallel? Or do I need a power distribution unit to distribute 240 V to each motor? Will a 50 Ah capacity be plenty?

Your thoughts and suggestions? Thank you!

Jul 24, 2016
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3. ### tcmtech Distinguished Member

Nov 4, 2013
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Are the motors DC, single phase or three phase and what controller are you using?

Also, what are you doing with this rather large battery powered dual turbopump drive being as you have linked you must have around \$12K - \$15K invested into this project?

4. ### tannerhunt5 Thread Starter New Member

Jul 24, 2016
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Just a concept for a school project! And I apologize I made a mistake in my motor selection. There are no DC motors that I can find that can deliver the power that I need so an AC motor will have to be used. I'm assuming a single phase since I only need the motor to run at one speed (correct me if my logic is incorrect).

Here is the controller I had in mind: http://www.zapiinc.com/products/motor-controller/ace-3ble-3#

Jul 18, 2013
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The motors appear to be 1phase induction motors they need to be 2pole to run at that rpm and 2 pole will run at something under 3600 (~3460) on 60Hz.
You cannot control the speed with these motors, plus those controllers appear to be for a different motor technology, BLDC etc.
You just need a power relay or contactor to switch the motor.
Max..

Last edited: Jul 24, 2016

Jul 18, 2013
15,856
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Also most countries have access to 230/240vac including N.A. you cannot run them in series!
If running them for 3 minutes what is the off time? If frequent start/stop over heating could be an issue.
Max.

7. ### jpanhalt Expert

Jan 18, 2008
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I am surprised you couldn't find a DC motor of 5HP. Model airplane motors up to 5KW continuous are available.
Why did you pick 3600 rpm, instead of something faster for your turbine?

John

8. ### tannerhunt5 Thread Starter New Member

Jul 24, 2016
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Hm, I cant seem to find any. Most 120V DC motors are in the 1-1.5 HP range. And 3600 rpm was selected from our propulsion team lead after he crunched the numbers of the quantity of air would need to be moved by the turbines.

Feb 5, 2010
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