Preheater Rev 2 in use

So this version never worked right, it leaked, so I gave it on it after trying to fix it.

I think the box I used for this one wasn't as good as the type used for version 1.

Preheater Rev 1 in use

Follow this link for the construction details of this preheater
How I built the Revision 1 preheater

So, how does it work.

It heats the water well, and does not leak, which were my two biggest worries
. 
Leaking was the obvious worry, but using high temp RTV to help seal the box, and the threads on the tube fittings appears to be working.  The only leak I have is coming from the thermocouple, because I used a fiberglass insulation thermocouple, the water is leaking though the fiberglass insulation.  I tried to seal the insulation inside the preheater, but I guess I didn't do a good job of that.

When I turn it on, it gets up to temp pretty quickly, in about 6 minutes it is pretty stable, and gets to within a few degrees of the boiler temp, per the PID thermocouple I have.

Issues I have with it.
The preheater temp drops pretty significantly by the end of the shot, down to about 120F, and it was around 220F when the shot started, so I lost 100F during the shot.  And, it starts to drop pretty early in the shot, and then continues to drop as the shot progresses.

Recovery time is longer then I expected.  After dropping to 120F, it takes about 5 minutes for it to get back to 220F.  Since it only took about 6 minutes to heat up initialy, I am not sure why recovery time is so long, but that is what I measured.

I warmed up the unit for about 20 minutes, and then pulled a shot.  It was a double, with around 14g of coffee, but I did not measure it.  The chart below shows how the temp varied over the shot.  I'm not sure why there was a little peak at 4 seconds, maybe a shot of steam/hot air when the shot started.
I measured by putting a thermocouple over the edge of the basket, with it close to the middle of the basket.
The shot was kind of fast, but I think it was fine for this measurement, you can see it was pretty steady until around 33 seconds, and stayed within 5 degrees until 40 seconds into the shot.

 I am building a Revision 2 preheater, to hopefully fix the issues I have, and get better performance.

Building the Revision 2 Preheater

Gaggia Preheater Construction Rev 2

There were a few things I did not like about my first preheater, so I decided to give it another try.
You can read about Rev 1 here
Revision 1 preheater construction

I hoped to reduce the recovery time, and also hoped to lower the temperature drop in the output of the preheater during the shot.

I picked a different box for the preheater, this one is thinner then the one used in Rev 1.
This is the box I used for Rev 2
Hammond 1590WG

Drawing of the box
1590G pdf drawing
This box is thinner then the first one, 0.8 versus 1.2, so it is 50% thinner, which should help the recovery time.
This box is longer then the first one.  I found a heatsink from All Electronics that happened to fit almost perfectly, when cut in half.  Just took a little filing to get them to fit right.
Heatsink
I added 7 of these inside my box, pretty much filled it up.  I measured the volume with and without the heatsinks, and surprisingly the heatsinks did not effect the volume very much, maybe a 1/4 oz at most.
I glued the heatsinks in place with food safe epoxy from Mcmaster, then used RTV to seal around the heatsinks.

For the fittings in the preheater, I decided 90 degree elbow fittings would work better then straight ones
1/8 BSPT x 6mm elbow

I also decided to use a better 6mm coupling, one that handles a higher pressure
6mm coupling
Even though the first one didn't leak, this one is better.

Few more pics.

I put a bead of RTV around the top, then put the top on, and installed it back in my Classic.

Turned the Classic on, and it looked OK at first, then I noticed water around my Classic.  After a little investigation, I found the source of the water, it was coming out of the thermocouple.  The thermocouple wirre is double insulated, so I think it was leaking out between the layers of insulation.  :(

I took the preheater apart, and stripped back the thermocouple so there was only one layer of insulation for the wire inside the preheater.

Gaggia Preheater Construction Rev 1

I am adding a preheater to my Gaggia Classic, here is my first attempt to do it.

There are some people who have done this by wrapping copper tubing around the boiler of Gaggia's. 

I was going to do it this way, I even bought the copper tubing, but when I tried to install the tubing, I found it was hard to wrap it around the boiler, so I wondered if there was another, easier way to do it.  I was also worried the copper tubing would not have enough volume.

Example 1 of copper tube preheater

Example 2 of copper tube preheater

Different way to preheat a gaggia

here a guy machined a preheater for his gaggia.  Would be the way to go, if I had a milling machine, but since I don't, I needed another approach.

I started thinking about another way to do this, then I found that a couple companies, Bud and Hammond make little, watertight boxes.  There is a flat part on the front of the boiler which I could strap this little box to.

I looked at what was available, and decided this box would fit the best

Bud AN-1301

I calculated that it will hold 2 3/4 oz of water, and there will be about 5.5 square inches of surface area where the body of this box will mate with the front of the boiler.

Here is a pic of the body of this box.

I had to do a couple things to this box to make it work.  The first was to mount a couple tube fittings in the box.  I bought these fittings from Mcmaster

6mm to 1/8 BSPT straight adapter

They have a 1/8" BSPT thread on one size, and a 6MM push to connect hose fitting on the other side.

1/8 BSPT thead taps are expensive, but you can use a 1/8-27 NPT pipe tap instead.  It is close enough, and it worked fine.

I drilled and tapped holes on both sides of the box.

The other change I made to the box was to add some internal dividers, so when cold water comes into the box, it will take a little while before it cools down the outgoing water.  I bought a sheet of thin aluminum from my local hardware store, and cut it to size, then drilled a couple holes in the ends.   When installed, the holes were put on opposite sides of the box.

These were glued inside the box, to divide it into three sections. hopefully to keep the outgoing water hot longer, as cold water comes into the box.

I used food safe high temp RTV to glue the dividers in place.  I also used RTV to seal the tube fittings, I put RTV in the holes before I screwed the fittings into place.

I also installed a thermocouple near the exit fitting, so I could measure the water temp close to where it exits the preheater.

The last thing I did was put RTV around the edge, on top, before I screwed the cover on.

To install it, you need a one more tube fitting from Mcmaster

6mm push to connect coupling

You also need some 6mm, Teflon tubing
6mm Teflon tubing

Installation is pretty simple.
You cut the tube the connects the pump to the boiler, near the pump.
You connect the tube from the boiler to the output of the preheater.  In my case, the output has the thermocouple, otherwise there is no difference between output and input of the preheater.
 
Then, you put the 6mm coupling on the tubing from the pump, and add enough 6mm tubing on the other side of the coupling to reach the input of the preheater.
 
The preheater is mounted on the front of the boiler, with a hose clamp to hold it in place.  I sanded the flat section of the boiler, to make it flater.  Before installing, I put thermal grease on the preheater, to get better heat transfer.
 
You now have a preheater.