Power Equipment Forum banner
1 - 20 of 29 Posts

·
Registered
Joined
·
29 Posts
Discussion Starter · #1 ·
I'm curious what effect the soft start has on the upstream voltage in a house main panel while it is active during a start. It would be interesting to see how much distortion there is.

In context, people are (rightfully) concerned about generator THD, and it would be good to know if the soft start causes some funny business.

Cheers
 

·
Registered
Joined
·
5,493 Posts
it will depend on the class of the generator.
the soft starts work well for sure.

way better than a hard start on distortion down line.
 

·
Registered
Joined
·
29 Posts
Discussion Starter · #3 ·
No doubt a soft start is necessary for A/C on a generator. I'm not trying to argue against them. I use soft starts a lot in the industrial power world and they are notorious for throwing major distortion onto the line side. That's what I'm curious about for these ones.
 

·
Registered
Joined
·
29 Posts
Discussion Starter · #5 ·
You're thinking of a VFD. They also use soft starters, which use SCRs or triacs to chop the ends off the cycles. They don't have an inverter to produce a new frequency. The full name is "reduced voltage soft starter".
 

·
Registered
Joined
·
1,105 Posts
always had good luck with old fashion hard start , plus there cheap and easy to install
A hard start is the absolute opposite of a soft start, isn't it?

CMIIW but hard starts are used when you need the motor to produce more torque during startup to get things moving.... all at the expense of it requiring higher starting current. It's not typically what you want when running off of a generator.
 

·
Registered
Joined
·
8 Posts
A hard start is the absolute opposite of a soft start, isn't it?

CMIIW but hard starts are used when you need the motor to produce more torque during startup to get things moving.... all at the expense of it requiring higher starting current. It's not typically what you want when running off of a generator.
I don't claim to be the expert. But when I tested my home AC and AC,s on my RV before and after installing my hard start capacitor , it reduced starting AMPS alot. on my hone AC starting amps was around 70 , after hard start it was below 50. I do not remember now on the smaller Rv ACs how much it dropped.
from what i understand soft start is better , but I can only talk about what I have used and I remember on the RV it kept the generator from bogging down when the AC was starting.
 

·
Registered
Joined
·
1,105 Posts
Then you probably meant to say soft start.

 

·
Registered
Joined
·
772 Posts
On a few A/C units, the hard start kits actually do decrease inrush current. Most times it increases inrush though as Orly mentioned. I don't know why the difference...seems like a hard start would always result in higher inrush.

A soft start kit will decrease inrush better than a hard start kit every time. Also, they start the fan first and then the compressor which also decreases inrush for the condenser unit.
 

·
Registered
Joined
·
772 Posts
Here is an example of a hard start kit reducing inrush (video at bottom of page)...really odd.
 

·
Registered
Joined
·
8 Posts
Then you probably meant to say soft start.

no i meant hard start , i have never bought a soft start due to their cost .
 

·
Registered
Joined
·
8 Posts
no i meant hard start , i have never bought a soft start due to their cost .
hard starts work buy dumping the power stored in the capacitor to the motor that is trying to start. it monitors for a voltage drop, once triggered it dumps power to help the motor start.
they have been used for decades . soft start is a fairly new technology
 

·
Registered
Joined
·
29 Posts
Discussion Starter · #15 · (Edited)
I have never heard of a hard start kit, and when I look at info online, there seems to be a lot of explanations that are maybe right in terms of results, but wrong in terms of why. Single phase AC motors like in an air conditioning motors do not benefit from the capacitor charging up to give it an extra boost--- that's a DC thing. I think what it's actually doing is adding capacitance to the starting capacitor to put the starting/aux winding more out of phase with running winding in order to get more torque. I think that would work to a point, but it depends where the start winding is physically located compared to the run winding. Or else it's reducing the torque by throwing the angle off, so basically "reduced torque starting device" instead of a "reduced voltage starting device". If anyone has a wiring diagram or a good explanation of how they work, I'm all ears. I'm tempted to say they border on snake oil though.

From this site: What is an Air Conditioner Hard Start Kit | Day & Night

normal capacitors are excellent marathon runners, but poor sprinters. AC hard start kits are the opposite; they can handle the power surge from the first few seconds of a startup without breaking a sweat.
By storing an increased amount of electricity beforehand, hard start kits can get the compressor motor moving at an optimal speed almost instantly.
Don't they know that the polarity of the capacitor changes 120 times a second? Meaning it charges and discharges 120 times a second. It's not storing electricity for a few seconds to help start the motor. They have no idea what a run and a start capacitor are for. But you can't blame them too much, because it appears most AC websites have no idea. Take this one for example: What is the Difference Between a Start Capacitor and a Run Capacitor? . Wow, what a bunch of baloney.

Here, if you want to know how start and run capacitors actually work, read this page: Why Single-Phase Induction Motors Need Capacitors | eMotors Direct
 

·
Registered
Joined
·
8 Posts
I have never heard of a hard start kit, and when I look at info online, there seems to be a lot of explanations that are maybe right in terms of results, but wrong in terms of why. Single phase AC motors like in an air conditioning motors do not benefit from the capacitor charging up to give it an extra boost--- that's a DC thing. I think what it's actually doing is adding capacitance to the starting capacitor to put the starting/aux winding more out of phase with running winding in order to get more torque. I think that would work to a point, but it depends where the start winding is physically located compared to the run winding. Or else it's reducing the torque by throwing the angle off, so basically "reduced torque starting device" instead of a "reduced voltage starting device". If anyone has a wiring diagram or a good explanation of how they work, I'm all ears. I'm tempted to say they border on snake oil though.

From this site: What is an Air Conditioner Hard Start Kit | Day & Night





Don't they know that the polarity of the capacitor changes 120 times a second? Meaning it charges and discharges 120 times a second. It's not storing electricity for a few seconds to help start the motor. They have no idea what a run and a start capacitor are for. But you can't blame them too much, because it appears most AC websites have no idea. Take this one for example: What is the Difference Between a Start Capacitor and a Run Capacitor? . Wow, what a bunch of baloney.

Here, if you want to know how start and run capacitors actually work, read this page: Why Single-Phase Induction Motors Need Capacitors | eMotors Direct
I think its waiting to see a drop in voltage below a point, then it fires off until load is reduced , but if you really never heard of them before, there is a ton of videos on youtube on hard start kits and how they work. that can explain better than I.
Soft starts seem better to me , but I was trying to convey I hard start which have been around decades longer than soft-start kits are CHEAP like I have bought them for 15$ before, you piggie back it on your start capacitor, very easy to wire like only 2 wires
and its a solution for someone that doesn't have 300$ for a softstart
 

·
Registered
Joined
·
8 Posts
good video, make sense why my Hard start worked great with my generator . I would get a voltage drop when the Ac started ( because it is not unlimited like the power grid ) the hard start would give it that extra " hand " to start it spinning and then drop out because the hard start I have ( and I guess all them) have a PCR that turns them off after the compressor starts. he said they are not to be used all the time unless ( and then he listed why ) but one of the reasons was a long run and voltage drop ( I.E. a generator in my case ) I would go from around 50 ish start amps on my RV ac to around 25 to 30 ish . But this was a good video this guy seems like a good trainer
I would love to see this guy explain soft starts and maybe VS heard starts now that would be very good video
 

·
Registered
Joined
·
122 Posts
My take on the hard start is that it corrects the phase angle shift created by engaging the compressor.

When the compressor is turned on, it introduces a substantial inductive load. When there's too much inductance, the current lags the voltage so they are no longer in sync with each other. Since the voltage no longer peaks with the current, the power is less effective, so more power is needed.

By adding another cap, the added Capacitance offsets the high inductive load keeping the voltage and current phases better in sync and maintains the effectiveness of the power during the start-up.

Once the compressor gets up to speed, it's inductive load decreases and if the cap was left connected it would would cause an unwanted phase shift (in the opposite direction i.e. current leads voltage) so a relay opens removing the cap from the circuit.

So basically, a hard start keeps the compressor more efficient during start-up. Less wasted power that causes heat.

There are a ton of factors that influence how much less current is drawn with hard start installed like age, amount of wear, design of the compressor motor, condition of wiring/relays, etc.

Saw where one guy videoed a hard start install. Peak current went from 147A to 90A.
 

·
Registered
Joined
·
488 Posts
good video, make sense why my Hard start worked great with my generator . I would get a voltage drop when the Ac started ( because it is not unlimited like the power grid ) the hard start would give it that extra " hand " to start it spinning and then drop out because the hard start I have ( and I guess all them) have a PCR that turns them off after the compressor starts. he said they are not to be used all the time unless ( and then he listed why ) but one of the reasons was a long run and voltage drop ( I.E. a generator in my case ) I would go from around 50 ish start amps on my RV ac to around 25 to 30 ish . But this was a good video this guy seems like a good trainer
I would love to see this guy explain soft starts and maybe VS heard starts now that would be very good video
Watch this video of the Micro-Air EasyStart designer explaining the benefits of the soft starter to the HVAC company owner/trainer and the benefits over a hard starter:

They compare the two technologies in detail.
 
1 - 20 of 29 Posts
Top