Monday, 27 June 2011

My KH228 solder paste dispenser - Part 1 (Beware of Chinese tools)

Found this bargain on EBay - a pneumatic solder paste dispenser for around $100!

Mine came exactly like this one, except for the shot time controller - apparently mine is an Omron (or more likely a Chinese timer branded Omron!).

I always have a look inside any cheap tool that connects to the mains before I plug it in - this time my paranoia might have been justified.

I was surprised by how neat the insides are, it is a very simple device! It has nice push-in hose lock connectors for all the air hoses, a solenoid with sold metal base, a hefty looking digital timer which is connected to a re-wirable base (not soldered directly), a large relay in a base and a generic looking regulator and pressure valve. 

Pity about the wiring side of things! All parts run from 240v and none of the connectors are insulated (except for the powder coating on the case - which is very neat an thick), no chassis earth(!) and the craziest bit - the foot switch connector has easily touchable exposed pins! One of these pins connects to mains neutral, the other connects through the relay coil to active - I'll be sure to have that connector connected before I apply power!

A small mod to add a chassis earth and I'll feel safe enough to give it a bench test with the lid on (being careful of that foot switch connector!).

It works! Here it is with the timer running for a 0.32 second shot. There was no air connected for this test but I have since charged it and there are no leaks internally - the hoses that connect to the air inlet and outlet connectors did need some modifications. I've found that black polytube used for garden sprinkler lines fits the connectors perfectly and is easily heated and moulded. By scrapping the plastic connectors that come with the hoses and using this tube directly the lines hold 80PSI with no leaks.

Dispensing solder paste is now quick and fun! What a great idea!

Check back for upcoming parts on alternative pressure sources and possible upgrades / rewiring.


  1. Whats wrong with uninsulated connectors insided a screwed shut case?

    Looks like a real omron timer to me.

  2. It's dangerous if they come loose, case is metal and you won't know it's live until you touch it. It is now earthed. Timer looks real but I could only find that model on alibaba...

  3. Exposed terminals on relay bases are the norm in control cabinets. The 'Omron' timer is actually a programmable multi function or a time delay relay (TDR) and it is plugged into a relay base intended to be mounted to a piece of din rail. The way it is used there is a little questionable. However, if you had bought a panel mount version of the same part, it would have bare screw terminals on the unit itself. So it doesn't really make a difference. If there is a reasonable amount of clearance between the bottom of the TDR base and the enclosure I wouldn't worry. If the idea still bothers you, put a couple wraps of electrical tape around it. The important thing is to make sure the terminals are torqued properly.

    Same thing applies to the blade connectors.

    However, bonding the earth ground to the Chassis is a good call on your part!

  4. Looks like a great unit once fixed !
    Is that this one ?


  5. Hi Gary, thats exactly the same kit!

  6. hello,
    bought this model (KH228 solder paste dispenser), and found that actually i don't need it.
    It's still inside the manufacturers box and has been not used for any time. All brand new, just want to get rid of this.
    It's including all new nozzles, power cords, AC wires, Pedal, tubes, holders,
    if someone interested please contact me for more details
    twitter: sm0rtb

  7. Any chance you could either sketch out or take a more detailed picture of the venturi setup on this system? I'm working on my own home brew version but I'm not sure how to setup the venturi vacuum. Would really appreciate it! :)