Pump motor with diode - Page 1
Forum section: electronics / beginners

author: PetrosA
author_rank: Frequent Contributor
timestamp: January 02, 2012, 02:31:48 pm
content: I'm a little confused by this and I hope someone here can help me figure it out. I have one of these pumps in my espresso machine in the 230V 70W 50Hz version being used on US 240V 60Hz mains (that's the only 2xxV pump available here):http://www.fluidotech.com/Contents/Documents/Oscillating%20piston%20pump%20Mono%20series.pdfNow for the long-winded storyThe wiring diagram shows a diode feeding the pump. From the pump plug there is also a neutral lead coming out with a female crimp end and a female crimp end on the neutral from the mains. I had never really wondered about this before except to put a diode in line on the two leads per the diagram on that pdf (I didn't know at the time that there was one built in to the cap), but I decided to figure out what the leads were last night. I remembered that the original pump worked with the leads just jumpered and also that this pump had worked with the leads disconnected so I tested that as well. Sure enough, with no neutral connected (In this case, the second 120V wire) the pump worked like it usually does, which has been pretty weak compared to what it used to do in Poland. I figure there must be a leak to ground, so I disconnected the ground wire from the pump cap. Unbelievably, the pump still worked with just one wire connected to it. The only thing I can figure is that the pump has an internal fault to ground and was completing the circuit through the water to ground bond.The only reason I went and put the diode in a couple of years ago when I put this pump in was because it didn't work as well as the original one had in Poland and that pdf shows one should be there. I should have dug deeper then since there's also a parts list pdf on the website that mentions that the cap has a built-in diode...). In reality, I've been running the pump with two diodes on it, not knowing that there was a second one in the cap. When I jumpered the second wire again last night per the original design, it ended in catastrophic failure of the pump with smoke, stink and dismay. I suspect it must have happened at the ground fault point when it got fed 240V.So my question is this: What does a diode do for the pump motor? I've only ever seen capacitors on motors, so this has me confused. Since it's being run on US 240V with two legs instead of a hot and neutral, should it have two diodes, one feeding in, the other feeding out to maintain the same direction?Any thoughts will be appreciated.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: January 02, 2012, 04:16:21 pm
content: They use the diode probably to achieve the oscillation of the pump?

author: PetrosA
author_rank: Frequent Contributor
timestamp: January 02, 2012, 04:58:09 pm
content: I think you're right. I found something today online about cell phone vibrators using the same concept, and it makes sense. In the meantime, I replaced the 230V pump with a 120V pump. So nice to have espresso again!

author: jimmc
author_rank: Frequent Contributor
timestamp: January 02, 2012, 08:26:41 pm
content: If the pump has a soft iron piston, then without the diode, it would oscillate at twice the supply frequency since both the positive and negative half cycles would produce a force of attraction.With the diode one half cycle is suppressed and so the piston oscillates at the supply frequency.I suspect the mechanics are tuned to operate at this frequency, hence do not work well with the diode removed.Jim

author: IanB
author_rank: Super Contributor
timestamp: January 02, 2012, 11:36:42 pm
content: Electric shavers tend to suffer from this effect. If the vibrating arm is tuned to resonate at 50 Hz they don't work quite as well on a 60 Hz supply. And vice versa I suppose, though I have not tried that way round.

author: qno
author_rank: Frequent Contributor
timestamp: January 05, 2012, 06:49:58 pm
content: This is called a plunger pump. It is meant to be connected to the 230 or 120V AC.During the positive part of the sinus the internal core is pulled by the magnet and pushing out water.During the negative side of the sinus the plunger relaxes and the internal core is relaxed closing off the water supply.Ulka is a large manufacturer in Italy.