Help: Smoking dimmer on Bezzera Strega pump

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ravco
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#1: Post by ravco »

Hi guys,
I tried installing a dimmer on the pump of my Strega following Tom Chips very helpful instructions as far as possible. Things looked good for a moment and I was able to regulate the pump and thereby the flow of water. But within a minute the dimmer started to smoke and stink, so I uninstalled it again. Luckily my Strega didn't seem to have got hurt. I would be very grateful for some help.

The Strega-pump is a Ulka Model E, Typ EX 5, 230V, 50 Hz using 48W. The rotary dimmer TomC recommended probably takes 150V and is only available in Germany for more than 70 $. I therefore decided to go for a single pole LED dimmer (taking 230 V, 50 Hz and up to 200W, adjustable from 4 to 230V) said to also be useable on normal lights. This dimmer only had 2 terminals, one for the hot wire and one leading to the terminal device. As far as I can make out, the component that was damaged on the dimmer might have been a varistor (small lenticular thing with two little feet, couldn't make out what was written on it). What went wrong? Any ideas? Thanks.

OldNuc
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#2: Post by OldNuc »

Without going and looking up this mod in detail there one thing that comes to mind here: light dimmers are only rated for resistive loads and that pump is an inductive load, they are not equivalent, the dimmer is probably underrated for that pump.

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ravco (original poster)
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#3: Post by ravco (original poster) replying to OldNuc »

Thanks a lot. That sounds plausible. I've ordered a dimmer for small motors up to 4000W. I will see if that works.

OldNuc
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#4: Post by OldNuc »

That should solve the problem as light dimmers tend to not play well with motors at all.

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radudanutco
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#5: Post by radudanutco »

ravco wrote:...I therefore decided to go for a single pole LED dimmer (taking 230 V, 50 Hz and up to 200W, adjustable from 4 to 230V) said to also be useable on normal lights. This dimmer only had 2 terminals, one for the hot wire and one leading to the terminal device. ...
OldNuc wrote:... light dimmers are only rated for resistive loads and that pump is an inductive load, they are not equivalent, the dimmer is probably underrated for that pump.
currently I am using 3 dimmers: one on the Strega pump, and two on my DIY roaster with air pump and heat gun element;

all are ordinary Chinese dimmers (about 3-4 euros each), with two terminals, but the two on the roaster are meant to be used on fans; one, rated for 500W, is used for the air pump (as bought), and the other one, for the heating element, has the triac changed for a 16A one, on a larger heat sync;

they are reliable enough from what I've used... I still have 4 of them to choose from, and I used several others before, on my modded popcorn roasters...

the Ulka EX5 with 48W should be quite a small a load; but possibly a LED dimmer is even smaller?

the dimmer is connected using the same spade connectors inside the machine, on the pump leg;
in my mod, the dimmer, and the switch to shortcut it are mounted outside, together with the pressure gauge and the PID, on a plate fastened to the drip tray leg:

(i know, it's not about industrial design, it was meant to be a temporary test setup, but as usual is in operation since last year...)

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ravco (original poster)
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#6: Post by ravco (original poster) »

radudanutco wrote:currently I am using 3 dimmers: one on the Strega pump, and two on my DIY roaster ...
all are ordinary Chinese dimmers (about 3-4 euros each), with two terminals ...
Thanks for the info. The dimmer I have orderd has 4 terminals, 2 for AC input and 2 for output. Do you know whether I have to jump the 2 input and output terminals for this mod?

OldNuc
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#7: Post by OldNuc »

220v is usually 2 hot wires and a neutral so you use both poles. If there is a single hot wire and a neutral then you would use only one. I do not have the schematic for your machine so I can not tell you how to wire this up. The major confusion here is that these power ratings are watts of energy consumed across a time period, in simple words it is the average power consumption and in no way reflect the max or min power rating. The MAX power consumption of the vibe pump is considerably higher than the average power and dimmers are rated for a maximum average continuous power at full output voltage. What this means if you turn it down to 1/2 voltage you now have exactly 1/2 of the original power rating.

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radudanutco
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#8: Post by radudanutco »

ravco wrote:... The dimmer I have orderd has 4 terminals, 2 for AC input and 2 for output. Do you know whether I have to jump the 2 input and output terminals for this mod?
I would have to know exactly what type, connection diagram etc. normally it comes with the unit;
however a light dimmer rated 400-800W, single pole, is all you need;

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ravco (original poster)
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#9: Post by ravco (original poster) »

Thanks. I'll wait for the dimmer to be delivered and have a look at the connection diagram.

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ravco (original poster)
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#10: Post by ravco (original poster) »

I finally found a 3800W dimmer with two terminals that seems to work https://www.amazon.de/Spannungsregler-E ... drok+dimme. I installed it yesterday night. First tests this morning with a danesi espressoblend were promising, but it will take a lot more experimenting. Thanks again for your help!

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