Soft Start add-on: possible / how much?

[drmrbrewer]

I'm considering a 4kW heat pump, which apparently has a startup current that might cause the DNO to have a fit.

The heat pump doesn't have an integral soft start circuit, so the question is:

(a) is there a simple (off the shelf) soft start circuit that can simply be placed in series with said heat pump?

(b) if so, how much money (roughly) are we talking?

OK, that's two questions I'm not planning on installing this myself, just doing some research.

Thanks.

 

[ericmark]

I used a soft start for a concrete press it was cheaper than an inverter but more expensive than star - delta start.

However it can cause problems with refrigeration units if the start process takes too long.

There was a heat problem from the soft start so a contactor bypassed it once it was running.

Thinking of small refrigeration units they often have a overload which will trip if the pressure is too high and then re-try again latter. This would be messed up with a soft start and one would need to write into the program so it's can't restart until set time has elapsed.

Not sure on price as the motor I was starting was far bigger seem to remember around 20A per phase. It was not to stop DNO worries but to reduce the start torque on the drive shaft. We had our own dedicated 500A supply transformer.

The soft start also affected the power factor however we had our own power factor correction unit so again that did not worry us.

As to soft start v resistor start I don't know where the two now stand. Costs are dropping for soft starts.

But 4kW is not really that big for a three phase motor and clearly you would not be using a soft start on a single phase motor the whole idea is to quicken the start time with them not reduce it.

It is getting more and more common to use inverters and three phase motors with single phase supplies because of the greater control giving both ramp up and down plus speed control but as an add on one has to be careful not to exceed the torque which the drive chain can cope with.

 

[drmrbrewer]

But 4kW is not really that big for a three phase motor and clearly you would not be using a soft start on a single phase motor the whole idea is to quicken the start time with them not reduce it.

This would be a single phase motor and single phase supply... just a common-or-garden domestic supply. I understand that the heat pump can draw up to 50A on startup... is that not enough to cause neighbours' lights to dim and hence make the DNO a little uppity?

 

[westie101]

This would be a single phase motor and single phase supply... just a common-or-garden domestic supply. I understand that the heat pump can draw up to 50A on startup... is that not enough to cause neighbours' lights to dim and hence make the DNO a little uppity?

More than likely, though it could be a higher current than that as the usual factor for Direct motor start is 7x running current.

 

[ban-all-sheds]

I understand that the heat pump can draw up to 50A on startup... is that not enough to cause neighbours' lights to dim and hence make the DNO a little uppity?

http://www.fastlec.co.uk/redring-powerstream-12kw-instant-water-heater-rp12-p-2154.html