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current indicator

Simple indicator needed

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Gordon W05/11/2010 11:28:27
2011 forum posts
This may be off-topic, but I know there are lots of electrical/ electronic experts out there. I have a water pump 100m from house,350W motor, fed from house via fused spur and underground cable, this cable is live at all times. The pump is controlled by pressure switch on the pump and cuts in when pressure drops. I am trying to devise a simple cheap indicator in the house, preferably a lamp, to show when the pump is running ie. current is flowing in the wires. A return cable is a non-starter (u/ground) Also have compressor with the same requirement. Can anybody help?
modeng200005/11/2010 11:46:39
340 forum posts
1 photos
The electricity energy consumption meters have a current clamp that goes round either the live or neutral wires and indicate the load in watts.
 
John
john swift 105/11/2010 11:53:12
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318 forum posts
183 photos
try pluging the pump into a energy saving extension lead / adaptor
 
with the pump pluged into the master socket
and an indicator lamp in one of the slave sockets
 
you will have on of the shelf solution with no electrical or electronic knowlge required
 
In the past maplin sold a velleman kit that did what you want
 
but I expect you want the ready to go solution
 
        John
Les Jones 105/11/2010 12:44:24
2292 forum posts
159 photos

Hi Gordon,
                      If an LED indicator w ould be bright enough you could try this circuit.
 
It would be connected in series with either the live or neutral feed to the pump at the house end. The diodes need to be able to withstand the starting current of the motor. They only need to be a low voltage rating as they do not have the mains voltage across  them. You could also use a 3 volt torch bulb (Without the series resistor.) If you did this then replacing the lower diode with a string of four would make it brighter.
Les.
John Haine05/11/2010 13:29:43
5563 forum posts
322 photos
Les, an elegant solution, but shouldn't the LED be shown the other way round?
Gordon W05/11/2010 14:55:38
2011 forum posts
Thanks for all the very quick replies.I don't mind making something up, I'm not totally useless, but what do I start looking for? The diodes/LED looks good, starting load I guess will be at least 3 amp (against 30m head).Energy saving extension lead, new to me but sound ok. The Maplin kit also ok, I will look into all these, now I know what I'm looking for. I was loaned a clamp type ammeter, but only showed briefly on start-up, guess the load on run was too low.
Les Jones 105/11/2010 15:21:02
2292 forum posts
159 photos
Hi John and gordon,
                                        John, you are correct. I have drawn the LED the wrong way round. One other thing I did not mention is that the circuit as it is will not work with a white or blue LED as the requre about 3 volts.
Gordon, I would go for 10 amp diodes as the starting current on some types of motor can be very much more than the running current. The energy saving extension lead has one socket that the main load is plugged into. The other sockets are only powered up when the main load draws current. (For example a computer as the main load and monitor and printer plugged into the other sockets.) If you used this method you would plug the pump into the main socket and say a table lamp into one of the others. There are also plug in energy monitors that diplay current or power. 
 
Les.
Gordon W05/11/2010 17:46:19
2011 forum posts
Thanks again, just had a quick look on ebay, loads of diodes, remarkably cheap, but so far can only find up to 2amps. Can diodes be run in parallel? Will look into all ideas over weekend.
Les Jones 105/11/2010 22:18:36
2292 forum posts
159 photos
Hi Gordon,
                    Although  there are no suitable diodes on Ebay there is someone selling 35 amp bridge rectifiers for £1.45 Here is a modified design that can be built with two bridge rectifiers.
 

D1 only needs to carry about 20 mA so almost any diode would do. This diode is to prevent reverse biasing the LED with about 2.8 volts. 
Les.
Gordon W06/11/2010 09:56:15
2011 forum posts
Thanks Les ,thats ideal, I think, must get back into this electronics stuff, never done much since transisters were invented, and the price was 7/6d. Still don't understand how the energy saver extension leads saves energy tho'. I would go that way if I can find a cheap one with less than 5 sockets. Thanks all.
john swift 106/11/2010 10:43:55
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318 forum posts
183 photos
hi Gorden
 
just for information
Poundstretcher sell a 4 way adapter with 2 slave outlets for about £10 (I had a look yesterday)
 
the velleman kit K8034 is more expensive ! and you still need a box to put it in !!
 
going  for the diy solution
to save a component and make construction easy
you could use a two lead  bi colour led   (eg maplin QY83E)   to replace the led and D1
in les jones circuit
 
 
  John
 
 
 
 
 
 
 
Nicholas Farr06/11/2010 10:48:48
avatar
3988 forum posts
1799 photos
Hi Gordon, no I don;t understand how energy saver extension leads save enegy. Probaly just purer copper, so has a few micro omhs less resistance, which of course costs more to buy.
 
Regards Nick.
Les Jones 106/11/2010 13:01:05
2292 forum posts
159 photos
Hi Gordon,
                    I think this is the item that John mentioned.
 
Les.
john swift 106/11/2010 14:28:27
avatar
318 forum posts
183 photos
Hi
Les, thats the one
 
Gordon and Nick
for some time I've used an eight way adaptor with my pc
 switching off the pc also switches off the printer ,hub , external
hard drives and monitor
like it used to do with the older pc with a real on off switch and a mains outlet
 
any saving is due to the automatic power switching to ancillary devices
 
a lot off electrical devices never  switch off  but go into standby
think of all the set top boxes in use because analogue tv has beem switched off for example
 
 
 John
 
 

Edited By john swift 1 on 06/11/2010 14:30:32

Edited By john swift 1 on 06/11/2010 14:51:38

Les Jones 106/11/2010 14:58:55
2292 forum posts
159 photos
Hi Gordon and John,
                                      I have just re read the original post. The 100 meter run of cable  will have a significant capacitance causing some current to flow even when the pump is not running. This will probably be enough to light the LED dimly so a resistor will probably be required between the ends of the string of diodes. (I would suggest about 27 ohm as a starting point.) It may be better to use a 3 volt torch bulb instead of the LED, diode and resistor.
 
Les.
Stub Mandrel06/11/2010 20:25:03
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4318 forum posts
291 photos
1 articles
Les,
 
that's a really neat solution. Congrats!
 
Neil
Gordon W29/11/2010 17:38:43
2011 forum posts
Just a report, have built device to Les's diagram, using 2 rectifiers, after looking at drg. properly . works well, for info. V with no load 1V. with pump running 3.8V, when I can find my car will go buy a bulb or two.

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