Re-Pumping a Chiller Unit for Laser Engraver

[awemawson]

I went to use my Chinese Laser Engraver to make a label only to find that it was reporting an error on the water circulation. Now these things come as standard with a small immersible pond pump, and you provide a bucket to put it in 

Now I have to use anti-freeze as my laser is next to the roller shutter, and I didn't want an open bucket of poisonous antifreeze on the floor in case the dogs took a sip, so I got an enclosed 'Chiller Unit'. These things are essentially very simple - they have a reservoir tank, and a circulating pump that pumps coolant through the laser tube, and returns it via a pair of aluminium tube radiators. There is a thermostat controlling a fan cooling the radiators, and a flow sensor coupled to an alarm sounder. Finally there is a thermometer display showing tank temperature. They are quite expensive for what they are, but I was fortunate enough to pick a used one up for less than half price on eBay. It has served me well for a year or so until this incident.

Examining it it was obvious that the pump wasn't running. It's a brushless 24v DC 25 watt jobby. The exact identical item is available on various Chinese web sites, but at quite a price and a very long lead time.

Time to see what else will fit. Several small 24 V pump available in the UK on ebay - but with different mountings and different inlet pipe diameters, but I was sure that could be overcome 

Ordered one and the postman delivered it this morning so here goes :

First remove the old pump. Mounted nicely on a rubber vibration mount, but the wet side was intriguing to say the least. It seems they've used soft silicone tube with silicone sealant and tywraps to hold it all together

[awemawson]

The replacement pump was a nice close match in terms of its electrical characteristics and flow rate - actually it's flow rate was slightly greater. However it's mounting was completely different.

A bit of cogitation resulted in me bending up a bracket from 1.6 mm galvanised plate to adapt the new pump to the original holes that were in the chassis.

The differing input port sizes was easily overcome by a bit of reinforced pvc pipe that happened to have both the right i/d and o/d 

[awemawson]

So I popped the new pump in and re-made the electrical connections, and re-filled the tank with the antifreeze solution. Sure enough, things are back to normal, no alarms 

However I'd noticed when I drained the tank that there were bits floating about, so had filtered the coolant through a spray painting filter on the way back in, and filtered out some fibrous 'stuff' that was sufficient to block the filter. Now as the pump circulated coolant through my 'test loop' I realised that there was still quite a bit that must have been in the radiators.

Time to drain down again and re-filter 

[awemawson]

So I left it running on the test loop for a while to prove out it's potential for leaks, then put it back together and returned it to service on the laser. Perhaps I can make those labels now 

[wheeltapper]

have you taken the old pump apart? it might be the same crud stopping it working.

Roy.

[awemawson]

Oh yes I'm sure that it is.

Still on the bench awaiting investigation, though it was drawing significant current and dropping my lab supply so perhaps not too hopeful - I'll certainly pull it apart and try when time permits and report back.

[John Stevenson]

I get the occasional fault on my laser cutter as well Andrew, same model I think.
On mine it's the red water valve sticks at the back on start up and a rap with anything handy sorts it out.
I do have a new valve but not got round to fitting it yet. It only happens on start up and never faults into a cut.

[awemawson]

John is that actually a valve or a flow sensor? My Chiller has a black flow sensor, but the actual laser cutter must also have one, as when I was 'running on a pond pump' it knew if the water wasn't flowing due to a pinched pipe or whatever.

In this case it was the chiller giving an alarm before the laser had time to think about it.

[awemawson]

So as promised I've pulled the original motor apart. OK there was a bit of gunge in it, but not enough to cause problems I think. The ferrite magnetic armature spins on a ceramic shaft with ceramic bushes either end. All rather nicely made. So I gave it a good clean up and tried running it off a lab supply.

Starts to run, gets up to speed, then cuts out. At first I thought maybe it was lack of water lubrication, but I arranged a feed to the intake and it did the same.

It probably got gunged up and something on the electronics board has given up the ghost from the overload 

[RobWilson]

Afternoon Andrew

Just to save faffing with engineers clamps when closing off a hose you may want to look at these 

http://www.ebay.co.uk/itm/3pc-Flexible-Hands-Free-Hose-Pliers-Pipe-Clamp-Plier-Set-Brake-Radiator-/221525296511?hash=item3393efc57f:g:HPgAAOSwv0tU5Gp6

Cheep as chips  ( I have few sets ) , quick to clamp and they dont shag the pipe/hose your clamping    handy when working on plant fuel lines and the likes .

Rob

[awemawson]

Neat idea Rob thanks for the link