A friend bought himself a new compressor - but this was 4hp vs the 3hp of the older one. For some reason he found it blew fuses in the plug on a fairly regular basis - and before I could get a dedicated supply wired in for him, it had melted the switch in several of his 13A sockets.I think continuing to use these devices this way will eventually give you a problem somewhere or other, lets hope it doesn't involve a fire.
Oh yes, he found it would only work when run through an extension lead - the resistance of 10 or 20m of 1.5mm cable lowered the startup current enough for it to start on a 13A fuse
As to earlier questions :
Wouldn't replacing the motor with a smaller one work out cheaper than this anyway, or is that too simplistic a view?
No, you would just overload the motor. As ericmark has already said, it's the load that determined motor power - in rough terms flow rate times pressure equals (mechanical) power, and unless you reduce one or both of flow/pressure then you won't reduce mechanical power. Electrical power is then mechanical power divided by motor efficiency - and most induction motors are sufficiently efficient that you won't get any real benefit from choosing a different design.
You could change the motor for a slower one. If the current one is 3000rpm (2 pole) then fitting a 1500rpm (4 pole) motor would give you half the flow, and after reducing the nozzle size to compensate you'd take about half the power. But you'd also only have half the cleaning power. But in a pressure washer there's a good chance it already has a 4 pole motor, and the next step would be a 6 pole motor running at a little under 1000rpm - but I don't think they are very common and certainly won't be as cheap as the common 2 and 4 pole motors you can buy for a pittance these days.
You could also enlarge the nozzle very slightly, which should lower the pressure if the system is properly balanced. Same flow rate, lower pressure = lower power. But also lower cleaning power.
Lastly, you could swap the motor for a 3 phase 220V motor and run it off a small inverter. The inverter would give soft start and almost eradicate the startup surge, and you could adjust the speed (run it a little below full speed) to reduce the flow rate and pressure - thus reducing the power, but also the cleaning ability. Ideally you would also need an unloading valve so the motor/pump can get up to speed before having to work against any pressure would be needed - but this would help with any of the above options. You will most definitely need to find someone who knows what they are doing.
Realistically, none of these options are going to end up better than buying the right machines for your situation - and by the time you've factored in the returns from selling the current ones, then replacing them will probably work out cheaper.
