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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Is a pump a resistive or inductive load? https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1182366501 Message started by CWatters on Jun 20^th, 2007, 8:08pm

Title: Is a pump a resistive or inductive load?
Post by CWatters on Jun 20^th, 2007, 8:08pm

I've got one of these pumps in a rainwater harvesting tank.
http://www.rainharvesting.co.uk/pdfs/In%26Out%20pump.pdf

Currently it plugs into a socket but I'd like to put it on a time clock so we can set it to water the garden while we are away. The pump data says it draws 1100W / 5.3A but

Q1: does anyone know if this would present an inductive load?

5A is probably too much for most central heating timers so I'll probably have to use a relay. I'd hate for the contacts to weld themselves closed as it would cause between 4,000 and 6,000 liters or water to be dumped on the vegtables!

Q2: Are there any clever tricks that can be used to fail safe a relay? Two relay contacts in series perhaps?

Title: Re: Is a pump a resistive or inductive load?
Post by Lectrician on Jun 20^th, 2007, 8:22pm

Motors are inductive.

Use an Immersion Heater time clock - These are rated at 16amps. Either this, or for tighter control (7 day, or two week etc), get a din rail mount timer and fit it in a din rail enclosure.

http://www.tlc-direct.co.uk/Products/TCTI24.html

Crap make, but you get the idea...Flex in and Flex out.

Title: Re: Is a pump a resistive or inductive load?
Post by CWatters on Jun 20^th, 2007, 9:10pm

Ah yes. Hadn't thought of an immersion heater timer.

Title: Re: Is a pump a resistive or inductive load?
Post by sparky415 on Jun 20^th, 2007, 10:06pm

CW,
Did the pump come with a float switch (to stop the tank from running dry)? If not it might be a good idea to fit one as well

Title: Re: Is a pump a resistive or inductive load?
Post by CWatters on Jun 26^th, 2007, 12:16pm

Hi, No the pump didn't come with a float switch but it claims to have "run dry protection" and it does indeed appear to switch off when the level gets too low. I'm not sure if this feature is something I can rely on or just as a backup so I will be fitting a level switch at some point as well.

I hooked up a Smiths Timeguard Immersion heater timer over the weekend but can't get it to work at the moment. The timer is in the garage and I added a single pole single throw switch to bypass the timer on the outside near the tap. (Top circuit) The bypass switch works fine but not the timer. If I short the live in to live out terminals on the timer itself the pump runs fine so it looks like the timer is faulty.

I'm wondering if applying mains to the switch live output of the timer when the timer is off is what damaged it. I plan to try another one and change the switch to a double throw so that it selects either permanant live or switch live from the timer (bottom circuit).

Title: Re: Is a pump a resistive or inductive load?
Post by Lectrician on Jun 26^th, 2007, 9:42pm

You have put a neutral to the timer as well havn't you? you dont need to loop the neutral through the timer, but you need to put a neutral to one of the neutral terminals.

Title: Re: Is a pump a resistive or inductive load?
Post by CWatters on Jun 27^th, 2007, 8:01pm

Yes and an earth :-) Just didn't need to show it on the sketch. It's all wired ok and double checked. Just can't work out why the timer failed -it was either faulty when delivered or it didb't like having live applied to switched live output via the switch. Guess I'll have to get another and try that. No time just now.