View Full Version : Knackered soft starter - can I ditch it altogether?

24-10-2013, 12:33 PM
Hi all

I have a 7KW, single phase split in my house, which has eaten 2 soft start modules (it came with the soft starter ex factory) since we moved in.
As it's reasonably small I reckon that I will see little, if any, difference to my power bill if I do away with the soft starter.

The question is, how do I do that? It's been a long time since I had to deal in depth with single phase comps & start relays & I'm frankly unsure of the best way to go about it. :o
Can anyone help with a wiring diagram? (I'll see if I can post the existing one up tomorrow).
Advice on sizing / type of start relay?
Advice on sizing capacitors?

Thanks a lot. :)

27-10-2013, 01:11 PM
the soft starter is for limiting start up current and limiting line voltage drop due to direct line starting/
it has nothing to do with your bill.
replace it or connect directly
good luck

install monkey
27-10-2013, 01:19 PM
an 8kw 1 phase unit can pull upto 90amp on start up- this will cause ur lights to flicker/dim slightly
even a 3kw 1 phase unit again non inverter can pull 30amp and again cause lights to flicker everytime the comp starts

27-10-2013, 01:23 PM
notice he said soft starter.
inverter cards are similar but used diffrently,
good luck

install monkey
27-10-2013, 01:29 PM
soft start regulate the peak start up current - giving approx costs of around 30%- by bypassing this your increasing your start up current costing slightly more in running costs, also increasing the wear rate of the compressor,but if its zapped 2 already then its worth a try

27-10-2013, 02:54 PM
words well spoken .
i would however look for a better model soft starter , http://www.solconusa.com/low-voltage-soft-starter-rvs-ax.html (http://www.solconusa.com/low-voltage-soft-starter-rvs-ax.html)
good luck

28-10-2013, 06:46 AM
Thanks guys.

The plan is to replace this unit with ducted A/C @ some point in the nearish future, so this is not expected to be a permanent solution.

Here's the wiring diagram:

Clearly the soft starter acts as the start relay.
So, do I need to replace the soft starter with a start relay? If so, how do I select the right one?
I'm told that I can bypass the system completely by (iirc) wiring the contactor straight to the run winding, and wiring the start terminal to neutral via the run (yes run, not start) capacitor.
Since the windings are then in series instead of parallel, this sounds like it'd work.
But, how does it work?

I wish I'd managed to get all tgat electrical & motor theory into my skull way back when!! :rolleyes:

28-10-2013, 09:05 AM
G'day FreezerGeezer,

This soft starter serves two purposes

1) Soft start - gradual electronic closure of circuit for motor neutral

2) Connection of the start winding / capacitor for required duration.

The soft start function is not of paramount importance, but some method of controlling the start winding is.

Perhaps something like this might do the trick?



Many other types & styles are available, your local supplier may be able to suggest an alternative.

28-10-2013, 09:31 AM
Thanks HVACRsaurus. That'd be the go - I probably should have dropped into Actrol this arvo & asked!

Anyway, I got the weird-wiring-without-relay trick worked out this evening with my mate's help.
You connect it like this:

Live input to Common. Run to Neutral. Start to Neutral via the run capacitor.

Now the missus, having whinged about being too hot, has asked me to turn off the A/C because she's too cold! WOMEN!!!! :rolleyes: :sigh:

So - can anyone tell me how this works, please? I'd really like to understand what's happening here.

I really, really should have paid more attention in the Motor Theory classes!

07-11-2013, 10:08 AM
Sussed it. Basically I've turned a Cap. start, cap. run setup into a permanent split capacitor system.
Thanks for all the help guys. :)

13-11-2013, 09:46 AM
Sussed it. Basically I've turned a Cap. start, cap. run setup into a permanent split capacitor system.
Thanks for all the help guys. :)

Is it ok to run a cap start cap run motor with a PSC system? There must be some difference in start torque for instance ....I should have paid more attention at trade school to.
What were the running amps like -

13-11-2013, 11:59 PM
It will work fine if it starts. The problem is that starting might be unreliable. To fix that, put the start cap back in. The PTC starters are universal and would work well. They're not as good as a start relay but since it was able to start as a PSC, it's just to add more margin.

14-11-2013, 11:22 AM
Well, it starts & runs ok so far RBM. I draw is 8A. To be honest I never had a reason to check the current with a working soft start in place, but can't see that it'd be any different. I imagine the inrush I will be higher, but really we use the thing so infrequently that I'm not bothered about it.
Once it's on it tends to stay on, as it isn't capable of pulling down the whole open plan area in a reasonable time, if at all (It's a BlueWay - some cheap, badge engineered thing that a couple of other suppliers also used with their own co. names on. None of those companies survive as far as I can tell)

17-11-2013, 05:30 PM
I hope it works out for you but running a CSCR motor as PSC configured may or may not work depending on the internal structure of the stator and the start winding. It's likely to run at lower efficiency which means higher motor temperatures. Whether it will last, only time will tell. You might run into a stall/locked rotor condition if the machine ever short cycles and the compressor is started whilst still under load because it hasn't equalised. I normally wouldn't recommend you do this unless it's a last resort and you're not too worried if there's a burnout.

10-12-2013, 10:52 AM
Baie dankie Frikke.

I had figured it's more a get-out-of-the-brown-stuff solution & may not last. It's good to know why that could be.
However if it lasts through the summer I'll be happy. In the meantime, if we replace a split system with the right size soft start, I'll can cannibalise that & fix it properly.
If it does die between now & next November, hopefully I can persuade the wife to let me fit ducted throughout. Currently she wants me to put a split in the kitchen / dining area. That'd be fine except I think it'd look kak! Plus, while I can see some advantages to multiple splits, it's an untidy solution & make more maintenance work for me at home. ;)