Home Page link

Hard start compressor motor applications

Home| Search | About
Login Password
Register Now! Lost Password?

HVAC Discussions - Heating, ventilation and air conditioning. 

Bookmark this page:  YahooMyWeb Yahoo!  Google Google  Windows Live Favorites Windows Live  del.icio.us del.icio.us  digg digg  Add to Netscape Netscape
Subject Author Date
Hard start compressor motor applications tree_75 08-17-2006
If you were  Registered and logged in, you could reply and use other advanced thread options
Posted by tree_75 on August 17, 2006, 10:44 am
I need someone to shed some light on the priciples of hard start kits
commonly applied to HVAC installations. I deal with industrial three
phase motors on a daily basis. For isolated, off-grid installations
(mostly offshore), we often utilize soft starters on large motors to
help reduce the required starting current capacity of generators.
While chatting with one of my neighbors who is an HVAC tech (unsure of
his competency though) I asked if there were any common modifications
to AC circuits that allowed for reduced current starting. He mentioned
"hard start kits" but could not explain the concepts involved. I'm
trying to size a generator for home use and would like to consider
means of reducing the required starting current for my AC units (4 &
1.5 ton units).

Thanks in advance for any valuable knowledge!
tree


Posted by Dido on August 17, 2006, 5:28 pm
From my experience I have found that are big variations
in starting of refrigeration compressors.
Hard start and soft start amperage will very but only for short
period, well how on the soft start amperage may be little smaller
but for longer time, in hard start amperage will be higher but for
shorter period of time, so the average current it will most likely
be very close, you will have to choose what you can with stand more,
with these phenomena you may had to experiment your self to find what
works better, remember time is milliseconds and all compressors are not
same including that some compressor may run without starting cap.
or hard start (device) and yet it could be use with both. It depend on
OEM design and how often machine start and stops.
Hard start kit takes place of starting relay and starting cap.
so if your system using starting relay and cap. you will not use
hard start kit (device) their will not be any benefit from it.
I work with all setup above and I can not see that anyone
can tell you what will work for you in your situation.
Good luck from Dido
www.cas-environ.com





>I need someone to shed some light on the priciples of hard start kits
> commonly applied to HVAC installations. I deal with industrial three
> phase motors on a daily basis. For isolated, off-grid installations
> (mostly offshore), we often utilize soft starters on large motors to
> help reduce the required starting current capacity of generators.
> While chatting with one of my neighbors who is an HVAC tech (unsure of
> his competency though) I asked if there were any common modifications
> to AC circuits that allowed for reduced current starting. He mentioned
> "hard start kits" but could not explain the concepts involved. I'm
> trying to size a generator for home use and would like to consider
> means of reducing the required starting current for my AC units (4 &
> 1.5 ton units).
>
> Thanks in advance for any valuable knowledge!
> tree
>



Posted by Dido on August 17, 2006, 5:28 pm
From my experience I have found that are big variations
in starting of refrigeration compressors.
Hard start and soft start amperage will very but only for short
period, well how on the soft start amperage may be little smaller
but for longer time, in hard start amperage will be higher but for
shorter period of time, so the average current it will most likely
be very close, you will have to choose what you can with stand more,
with these phenomena you may had to experiment your self to find what
works better, remember time is milliseconds and all compressors are not
same including that some compressor may run without starting cap.
or hard start (device) and yet it could be use with both. It depend on
OEM design and how often machine start and stops.
Hard start kit takes place of starting relay and starting cap.
so if your system using starting relay and cap. you will not use
hard start kit (device) their will not be any benefit from it.
I work with all setup above and I can not see that anyone
can tell you what will work for you in your situation.
Good luck from Dido
www.cas-environ.com





>I need someone to shed some light on the priciples of hard start kits
> commonly applied to HVAC installations. I deal with industrial three
> phase motors on a daily basis. For isolated, off-grid installations
> (mostly offshore), we often utilize soft starters on large motors to
> help reduce the required starting current capacity of generators.
> While chatting with one of my neighbors who is an HVAC tech (unsure of
> his competency though) I asked if there were any common modifications
> to AC circuits that allowed for reduced current starting. He mentioned
> "hard start kits" but could not explain the concepts involved. I'm
> trying to size a generator for home use and would like to consider
> means of reducing the required starting current for my AC units (4 &
> 1.5 ton units).
>
> Thanks in advance for any valuable knowledge!
> tree
>




Posted by Jake on August 17, 2006, 7:17 pm
tree_75 wrote:
> I need someone to shed some light on the priciples of hard start kits
> commonly applied to HVAC installations. I deal with industrial three
> phase motors on a daily basis. For isolated, off-grid installations
> (mostly offshore), we often utilize soft starters on large motors to
> help reduce the required starting current capacity of generators.
> While chatting with one of my neighbors who is an HVAC tech (unsure of
> his competency though) I asked if there were any common modifications
> to AC circuits that allowed for reduced current starting. He mentioned
> "hard start kits" but could not explain the concepts involved. I'm
> trying to size a generator for home use and would like to consider
> means of reducing the required starting current for my AC units (4 &
> 1.5 ton units).
>
> Thanks in advance for any valuable knowledge!
> tree
>

As Paul said... a Hard-Start is nothing like a soft-start.

Hard-starts are simply stored energy capacitors that inject energy
(sometimes out-of-phase) into a circuit for a very short period of time.
This gives single phase motors a little more -ommph- for staring but has
little bearing on starting current.

Soft starts a frequently 'frequency choppers', which vary the
frequency/voltage curve of three phase motors in applications like pumps
and fans... when the current draw is nearly linear to how fast the
connected load is moving.

Most AC units list something called LRA... which means 'locked rotor
amps' and is a very good indication of the current required to start the
equipment. If you have a compressor/condenser with a LRA of 42, for
example... and the supply voltage is 240 volts... then 42 times 240 =
10,080... which is roughly the watts required to start the load. Some
generator makers will supply 'surge ratings' this high in a 7500 Watt
generator. Look around.

There is no magic cure for the current requirements in starting an
induction motor. Scrimp on the capacity and you'll be sorry.

Jake

Posted by on August 18, 2006, 4:00 pm

tree_75 wrote:
> I need someone to shed some light on the priciples of hard start kits
> commonly applied to HVAC installations. I deal with industrial three
> phase motors on a daily basis. For isolated, off-grid installations
> (mostly offshore), we often utilize soft starters on large motors to
> help reduce the required starting current capacity of generators.
> While chatting with one of my neighbors who is an HVAC tech (unsure of
> his competency though) I asked if there were any common modifications
> to AC circuits that allowed for reduced current starting. He mentioned
> "hard start kits" but could not explain the concepts involved. I'm
> trying to size a generator for home use and would like to consider
> means of reducing the required starting current for my AC units (4 &
> 1.5 ton units).
>
> Thanks in advance for any valuable knowledge!
> tree

I had one of these installed to help start my 5 ton AC on a generator,
and it helped quite a bit.

http://www.kickstartoem.com/faqs/contractors.html

I also notice that the lights still dim a bit, but it is for a much
shorter period of time. Just a quick blip.

Brad


Similar ThreadsPosted
hard start August 20, 2006, 2:23 pm
Supco Hard Start failure... July 10, 2007, 6:15 pm
Re: Which is the A/C motor start capacitor? October 8, 2007, 8:19 pm
help to resolve a hard equation August 28, 2007, 10:10 pm
It's Hard To Stop A Trane February 9, 2008, 4:08 pm
Hard water & choosing an indirect water heater June 11, 2007, 7:29 am
Central Air Conditioner will not start May 10, 2007, 6:26 pm
HVAC run and start capacitors January 27, 2008, 11:38 am
A/C Repair Guide - Combination Start/Run Capacitor Replacement October 24, 2007, 2:27 pm
Black Panthers try to start some shit, bikers finish it, on camera ! December 4, 2007, 11:03 pm

Contact Us | Privacy Policy

XML SitemapXML Sitemap