Using a Varistor to solve a back EMF problem

[cygnusv]

Update - and apology for absence! Computer failure lost me a lot of everyday data including contact details with this very useful and friendly forum. I received an email posting from the forum earlier today and was then able to get back in touch.

The pump problem described in this thread has been (apparently) completely cured and I'm doing my best to share the details with other boaters who will have experienced these problems.

My sincere thanks, Stu

 

[cygnusv]

Hi everyone

Many thanks to all and particular thanks to KrisBlueNZ for the advice and the life saver diagrams. I fitted all the bits and pieces over the weekend and operated the pump in pitch black with the switch cover off. No sign of any spark at all at the contacts!

Interesting to note is that for less than the cost of postage quoted by Mouser, I was able to pay for everything (including cost of parts with free postage) from ebay. The parts are original so hopefully, after way too long, we should have a properly working pump!

It's nice to find a bunch of experts who are prepared to take the time to help a beginner.

Thanks again, Stu

I know that this is a blast from the past and that sadly KrisBlueNZ passed in 2015 and is sadly missed. He very kindly helped me with a 24 volt pump problem. After 5 years his solution to my back emf problem still stands proud. I want to reproduce exactly the same solution to the same problem with another pump on my boat. My problem is a difficulty in getting hold of a diode I used then. I've been looking for either a VS-1N3210 or the 'R' version. Can anyone recommend an affordable common alternative? Anyone reading this original posting will realise I'm still not the brightest bulb in the forum, but bright, dim or just me I would appreciate your advice.
Many thanks in advance, Stu

 

[Harald Kapp]

"VS-1N3210" has a vendor specific prefix . The generic name of this diode is 1N3210.
1N3210 is available e.g. here.

 

[cygnusv]

"VS-1N3210" has a vendor specific prefix . The generic name of this diode is 1N3210.
1N3210 is available e.g.

"VS-1N3210" has a vendor specific prefix . The generic name of this diode is 1N3210.
1N3210 is available [URL='https://www.mouser.de/ProductDetail/GeneSiC-Semiconductor/1N3210?qs=UW%252B%252Bp%2FVkpn%252B%252BUlZKWEoSIw==']e.g. here

.

here[/URL].

Hi Harold Kapp. Thank you so much for that info. I've checked around several uk sites and struggled.
I actually did find US supplier and have ordered 2 units for about the same money as the mouser unit's single supply.
I really don't understand why the UK stocks are like hens teeth.
Thank you so much for your information. Stu

 

[WHONOES]

Have you ever considered using an old starter motor relay from a car. These have to switch hundreds of amps without failing for many years. You could probably get one from a breakers yard.

 

[cygnusv]

Have you ever considered using an old starter motor relay from a car. These have to switch hundreds of amps without failing for many years. You could probably get one from a breakers yard.

Thanks for this. In the past I used 24volt auto relays but they too failed. KrisBueNZ's solution has been a real workhorse, surviving 3 full years of full blown domestic use. My real problem now is the apparent lack of suitable diodes in the UK, I could do with a more common part.
As it is I have again, ordered diodes from the US.

 

[hevans1944]

It is possible that, knowing the diode characteristic parameters of the 1N3210 (datasheet), you could use a parametric search engine such as this one on DigiKey to find a suitable equivalent. If you use Google to find the 1N3210 on DigiKey, the splash page gives the important diode parametersunder the heading Product Attributes, but perhaps more important for you is a clickable box labeled View Similar near the bottom of that listing. This will lead you to a DigiKey page with some 56,123 diodes. Narrow your search by choosing appropriate parameters from the menu choices at the top of the page. For your application, the peak inverse (reverse) voltage or PIV capability and the forward current capability are probably most important, followed perhaps by packaging and temperature range of operation.

I am really glad for you that @KrisBlueNZ was able to help you find a durable solution to your contact erosion problem. He is sorely missed here in the forums, but the hundreds (if not thousands) of well-designed solutions he provided here will be his legacy on ElectronicsPoint. Nothing ever dies on the Internet. Once posted, it is there forever.

I don't know which Square D pressure switch you are using (they make a lot of variations), but the diaphragm-operated, adjustable pressure range and adjustable hysteresis, two-pole, single-throw version I use on my well and aerator pumps here in Florida fail about once a year when ants sneak under the plastic cover and wind up being killed under the contacts. The resulting ant goo is not electrically conductive.

I don't know what ants find so attractive about the innards of this pressure switch. I can clean the contacts with a fine abrasive and restore functionality for awhile, but the final solution may be to apply a silicone RTV (Room Temperature Vulcanizing) sealer over all the possible entrance holes. If I never have to adjust the pressure switch cut-in and drop-out pressure points, the Square D pressure switch could outlast my thirty year mortgage with "bullet-proof" sealing against ants.

 

[WHONOES]

I am surprised that the starter motor relay / contactor fails. They are required to switch up to 700A or more of start current .
An alternative could be a large or several larger MOSfet transistors.
Also, have you tried Farnell and / or RS Components web sites for some diodes. They don't have to be the specific type that you quote. They just need to be able to fulfil your requirements.
Further, I have some chunky diodes lying around doing nothing and have been for many years. They are Semikron SKKD 46/04 types rated at 400V and 250A for 10ms. They are 2 diodes in one package arranged as a half bridge. I see no reason why you could not use just one of them to snub your motor.
If you want one, it would be free issue. Have a look at their datasheet.