EM set-up advice

[kingofnapier]

Hi,

I need a small portable battery powered EM that will hold about 75lbs. It is crucial that the EM and battery(s) it uses are absolutely as light as humanly possible. Will need to use it about 3 hours continuously. Battery will need to be rechargeable. Suggestions?

 

[VEBill]

"EM" = electromagnet

If it's going to be holding 75 lbs, then why does it need to be a lightweight electromagnet? Obviously the answer is 'for when it's not holding the 75 lbs.' But you can see why the designers of most such electromagnets probably don't spend a lot of time making them very lightweight.

The battery system should be easy these days. eBay is awash with inexpensive and powerful Li-ion cells, holders, rechargers, etc. You'll want to consider battery safety and cooling. Especially if this is going into a confined space along with humans, such as a mini-sub's ballast system.

Obviously, start your market search for the electromagnet. Meanwhile study the batteries on the market to coordinate their capacity.

 

[kingofnapier]

It's is not going to actually hold 75 lbs of weight, rather 75lbs of pulling force. How light of a battery can I get?

 

[VEBill]

My previous advice addressed that: "Obviously, start your market search for the electromagnet. Meanwhile study the batteries on the market to coordinate their capacity."

Finding a solenoid is probably best approached with Google.

Meanwhile, go to ebay and review Li-Ion batteries. You can use the PN 18650 as a starting point, not necessarily the optimal choice. Beware that the OEMs and sellers tend to exaggerate the mA-hours a bit.

 

[kingofnapier]

So the 3.7v battery you mention would power an EM that will have that will hold 75lbs?

 

[VEBill]

Probably not, but a bank of 'N' of them certainly would. For example, many laptop battery packs use six or nine of that exact PN of Li-ion cell. The trick is to define 'N'. For that, you need to find your solenoid. Once the solenoid is selected, then it's almost trivial to see how many batteries are needed.

That PN is just an example of a high power Li-ion rechargeable cell that is very cost-effective (often only a few dollars each) and readily available from Internet vendors. That PN is a good initial placeholder for the top of the list of possible cells, if and until you find something better.

You could look into Li-Poly cells too. They might be lighter weight per unit power since they're often not wrapped in a metal case. They're a bit more dangerous.

PS: You've slipped back to using the word "hold" again, vice "pull".