VFD suggestions for compressor

[minimutly]

Wow, this is really useful information, thank you for taking the time to write it all out. The plate on the receiver dates from 1965, so towards the earlier end of the range you mentioned, if the motor is of a similar vintage. Is there any way to determine for sure the type of insulation used on these particular windings? Would a plastic burn test reveal any obvious differences between old and new style insulation? Any way to 're-impregnate' or overcoat the windings in situ?

I'll look into it a bit more, see if I can work out what the insulation is made of, and whether the motor can be configured for 230V. But it's not sounding hugely promising for the original motor. I'll probably just use the spare petrol engine I have, it's a bit of a faff to set up, but no more so than getting electric running would be by the sounds of it. I only spent £100 on the whole compressor, so don't really want spend many multiples of that on VFDs and inverters with marginal chances of success.

The day job is embedded engineering (more familiar with milli and micro amps) and I have a spare PLC lying around ear-marked for the job, so shouldn't be too difficult to set something up. I'm imagining it just needs to actuate an unloader valve, power the starter until the engine gets up to idle speed, maybe run a PID loop with a servo on the throttle control to maintain a particular RPM (or just leave it at a constant throttle position if it doesn't vary that much). Close the unloader valve until it gets up to pressure, then kill the engine, and wait for the pressure to drop below a threshold before repeating the cycle. Am I missing anything there?

It was in use until recently, so I'm hoping the receiver is usable. It has what looks like inspection covers, so I'll see if I can have a look inside, and hopefully borrow a hydraulic testing kit.

Now you're talking - proper forum engineering - and probably much more likely to succeed than trying to run that on single phase. Promise one thing - you'll start, or continue this post to let everyone know how you get on?
Re the plc control - Nudge and wait might be just as suitable as a PID block for loading the engine - maybe based on an rpm set point for pumping, with another for idling? Simpler is better sometimes.

 

[julianf]

My friend acquired a dive compressor with a 3ph motor.

As I've not completed my wadkin rebuild, I lent him my 7.5kw boost vfd (less than £100 on one of @Kram s Amazon specials! ; ) and it's doing him fine.

I forget the details on his motor but it's not pocket size...

 

[Seadog]

The plate on the receiver dates from 1965, so towards the earlier end of the range you mentioned, if the motor is of a similar vintage. Is there any way to determine for sure the type of insulation used on these particular windings? Would a plastic burn test reveal any obvious differences between old and new style insulation? Any way to 're-impregnate' or overcoat the windings in situ?

I'm running a motor of 1953 vintage on my lathe, from a VFD. It's survived since 2013. The only thing that I think that I did was to replace the tails inside.

Visit Brocott's site. They do a red lacquer for this purpose.

I'm imagining it just needs to actuate an unloader valve, power the starter until the engine gets up to idle speed, maybe run a PID loop with a servo on the throttle control to maintain a particular RPM (or just leave it at a constant throttle position if it doesn't vary that much). Close the unloader valve until it gets up to pressure, then kill the engine, and wait for the pressure to drop below a threshold before repeating the cycle. Am I missing anything there?

The unloader should be an integral part of the compressor pressure switch. When the pressure causes the switch to cut power it should open the unloader automatically. The VFD will directly feed the motor and you then use one of the pairs of power contacts in the switch to operate the stop function on the VFD.

 

[graffian]

You are going to really struggle with that on single phase and also with a vfd Or converter. I had a very twin on various types of vfd, they didn’t like it. Slowing it down won’t help - the current will just pulse less often.
My advice is to sell it and get a hydrovane. That’s what I did in the end.
Sorry

My compressor came with a 5hp motor[three phase] and I replaced it with a 5hp single phase motor.
I was told you shoudl put aprox a third more horses single phase on it, but I had the motor and it worked.
All the lights dimmed and fluorescent lights restarted, when it started. When it had some pressure the lights flikered in time with the pump.
When more hp for single phase motor was suggested doubing the hp if using a petrol engine was mentioned!
I made a rotary phase converter, after 20 years of flickering all the light on the same phase as this house. The dimming and
flickering stopped. The idler motor rocks around in time with the pump.
I tried slowing the pump and it didn't make a huge difference.