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Mike, Master Electrician
Category: Electrical
Satisfied Customers: 1425
Experience:  Licensed Master Electrician - OnQ Certified Data Voice Audio Video Installer
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I am designing an industrial product and would like some help

Customer Question

I am designing an industrial product and would like some help on the electrical side of things. I’d like to be able to ask a bunch of basic questions and I’d certainly be willing to pay someone to answer them. I don’t need anyone to assume liability for their answers. If you might be able to help let me know.
I’ll give you my first set of questions here in case you’d like to look them over. You may need more info for the answers but this will give a feel for the problems I need to solve:
I wish to power two 2 hp three phase 208v and one 7.5 hp three phase 208v pump with one generator.
When the hoists are in lowering mode, they use electromagnetic braking and turn into power generators themselves. I am wondering if this will be ok for the typical generator. I am hoping that since the pump demands more power than the hoists will create, assuming the pump is always running the generator will simply use less fuel when the hoists are lowering an object. Also I’d like to know if it’s ok if the pump is not running in this scenario.
Secondly, I need to specify a gauge for the 600 ft long cables that power the hoists. Since weight is an issue I’d like to keep the gauge as small as possible. So I have an idea which may or may not be half-baked. I am thinking I can correct for a substantial amount of voltage drop, due to resistance in the cable, by simply increasing the voltage output of the generator by whatever voltage drop is occurring in the cable. The more I increase the voltage on the generator, the smaller gauge I can use (within reason). Let me know if I am off on this one. One detail I’d need to account for if I increase the voltage on the generator is I’d need some sort of resistor or transformer in order to bring the voltage back down to 208 for the pump, since there is a much shorter power cable between the generator and the pump.
Please let me know your thoughts if you are interested in helping.
Thank you,
Dan Pitbladdo
Submitted: 2 years ago.
Category: Electrical
Expert:  Phil replied 2 years ago.
This is not an answer... just some broad scale advice... you need a lot of engineering that is not covered by the deposit you made, an electrical engineering firm would charge you $4,000 to $40,000 for this work depending on the detail required, probably more like $10,000
We can't do that for $25.
Summary of the issues:
The generator must be an industrial type, and rate for 3 or4 times the wattage of all the motors put together... that will end up allowing you to run generator at 50% capacity needed for reliable long term operation and provide the 300% *higher amperage draw the motors require for the initial starting surge.
The generator needs to be 480 volts 3 phase to keep the wire size down.
If you want to harvest power from the load that is going down, that will need to be done with motors designed specifically for that purpose, and you will need need the electronics to go with it, and battery storage and an inverter to make it happen.
That approach will most likely prove to cost more than it saves, and will reduce the overall system reliability.
Depending on what you have in mind there are easier ways to do this with existing counter weighted elevator technology.

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