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Contactor Sizing

52 Ford

Stainless
Joined
May 20, 2021
Regarding the original post... a 1.5HP motor should only pull 1.5HP or (745.7W per HP * 1.5 is 1,118.55W). I'm not an electrical (insert profession) and don't claim to be (refer to Just a Sparky and JST - I ain't learnt none that stuff proper, just hard knocks and a little reading.) Anyway, if you need a switch for a 1.5HP motor, get that. If the VFD says it wants 15A, get that. Heck, as long as it isn't a crazy difference in cost, I would buy the higher amp switch, anyway. It aught to last longer (especially with a lighter load).

Sent by telegraph using - .- .--. .- - .- .-.. -.-
 

thermite

Diamond
Regarding the original post... a 1.5HP motor should only pull 1.5HP or (745.7W per HP * 1.5 is 1,118.55W). I'm not an electrical (insert profession) and don't claim to be (refer to Just a Sparky and JST - I ain't learnt none that stuff proper, just hard knocks and a little reading.) Anyway, if you need a switch for a 1.5HP motor, get that. If the VFD says it wants 15A, get that. Heck, as long as it isn't a crazy difference in cost, I would buy the higher amp switch, anyway. It aught to last longer (especially with a lighter load).

Sent by telegraph using - .- .--. .- - .- .-.. -.-

Yah, really.. The heavier goods can actually be CHEAPER!

And it isn't as if you had to feed a production line with a large number of identical parts, and shave fifty-cents a unit, anyway, is it?

Ex:

1 each NIB Arrow Hart Contactor # ACC330UM10, 3 Pole, 600V, 40 Amps, 24 vac Coil ITEM PRICE: US $17.00

2 each NIB Duracool 30 Amp were $17.98 each.

The NIB 125 A Fuji was still only $70.

"etc."

"Remaindered" former stale stock or shelf-spares as onesies and fewsies of top specification from decent manufacturers are all over the place, cheap and cheerful.

Grab some and adapt.

:)

NNN
 

Just a Sparky

Hot Rolled
Joined
May 2, 2020
2 each NIB Duracool 30 Amp were $17.98 each.

Are we talking bridge contractors or mercury relays here? Durakool is mostly known for their mercury relays. $18 each for a 30 amp mercury relay that will last more or less forever is a pretty smoking deal. Especially if one has an inductive DC load to switch often.

...As long as you don't have to pay to dispose of them at end of life and they do in fact end up in haz-mat where they belong instead of landfill like so many mercury thermostats, PCB capacitors, etc.

Cradle-to-grave engineering, basic ecological responsibility and all that.
 

thermite

Diamond
Are we talking bridge contractors or mercury relays here? Durakool is mostly known for their mercury relays.
Nah. Not Hg displacement on those. Conventionals. Basic HVAC market goods, Mexican factory.

A lot of these 'vanilla' goods are made in India as well.
Buying from China is avoidable. Let's go Brandon.

$18 each for a 30 amp mercury relay that will last more or less forever is a pretty smoking deal. Especially if one has an inductive DC load to switch often.
They do and I do and I have a stash. But Mercury displacement units are typically $60 or so, and not as easy to find, NOS, major-maker.

In any case.. for DC, an SCR bridge matrix under "4Q" DC Drive control - or Crydom SSR "H" bridge - is better yet.

Single-phase especially, I've been using Crydom SSRs since the dawn of the 1970's.

No contactors at all, no arc at all, no braking resistors, either, vs clunky contactors with controlled & quenched arc.

I did say NO arc?

Also less space, fewer wires, easier control, neat, clean, and effective.

What's not to like about that?

:)
 








 
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