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Thread: Reversing a used brush motor
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15th Feb 2020, 11:01 PM #1Most Valued Member
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Reversing a used brush motor
This maybe a question no one can answer but you never know your luck.
I have a 3 chamber diaphragm pump 12VDC pump that I have always suspected was wired backwards, if this sort of motor would even have offset brush timing(if that is what is is called). You cant see in the picture but the exposed pin on the lead from the battery is +, which you would have to think was wrong along with the colors changing at the plug.
I've pumped over 2000 litres without issue but now have other pumps that have the wiring done correctly. I could do without having to have different leads for each pups.
Anyone think revering revering the pump would be a really bad idea?
Might just have to cross my fingers.
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16th Feb 2020, 12:25 AM #2
So if I am understanding you correctly the positive goes to black on the motor ?
In some American wiring black is active, in which case it maybe correct.
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16th Feb 2020, 06:18 AM #3
Hi Stuart,
Its difficult to see in the picture but that looks like a flat vane type pump, not a diaphragm one, and the inlet/outlet appears to be at 90 degrees to the shaft axis. In which case it couldn't care less about which direction it runs in. The only point I would worry about is if the impeller was screwed onto the shaft, in which case running it in the wrong direction it could unscrew.
Now if it really is a diaphragm pump, motor rotation direction might not matter !
I use a diaphragm pump for the water delivery in my camper, it runs equally well in either direction.Best Regards:
Baron J.
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16th Feb 2020, 07:26 PM #4
If the unit utilises a field wound brushed motor, reversing the voltage polarity will not reverse the direction of rotation. To do that you need to reverse the magnetic polarity of the armature relative to that of the field windings, by swapping the cables between the field winding and brush holders. Simply reversing applied voltage polarity will reverse the magnetic polarity of both sets of windings and result in the same direction of rotation.
On the other hand if the motor utilises a permanent magnet field rather than a wound one, reversing the applied voltage polarity will reverse the direction of rotation, as you are reversing the armature magnetic polarity and leaving the field polarity unchanged, so you are reversing the polarity of one relative to the other.
For a diaphragm pump, direction of rotation should not affect the pump efficiency, the diaphragm simply moves in a chamber to create a vacuum and draws fluid in through a check valve, then moves in the opposite direction, which closes the first check valve and traps the fluid in the chamber and ultimately creates enough pressure in the chamber to force the fluid through a second check valve to the outlet once the chamber pressure exceeds the static pressure present at the outlet. As the pressure in the chamber reduces with fluid flowing into the outlet, the second check valve will close. Once the diaphragm reaches the end of its travel, it reverses direction again and starts to create a vacuum that will open the inlet check valve and draw more fluid in for the next pump cycle.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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16th Feb 2020, 08:31 PM #5Most Valued Member
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Hi Guys
Thanks. Looks like reversing shouldn't be an issue. I have some spraying to do tomorrow so I will get it done an let you share the blame if the pump dies. lol
Yes, But what I failed to mention is the pumps are from China and that one of the "other pumps" I mentioned is the same sprayer just wired differently(correctly?).....one of them has to be wrong
Pretty sure its a diaphragm, but pumps are not my strong point. Here is a better look.
I added a 750ml pressure tank as I didn't like the pump cycling every time I gave something a squirt.
I haven't been inside it so cant say if its permanent magnet or not.
Now off to change the wiring.
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16th Feb 2020, 11:27 PM #6
Hi Stuart, Guys,
Very difficult to tell. Really the only way would be to have a look inside.Best Regards:
Baron J.
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17th Feb 2020, 09:18 AM #7Most Valued Member
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17th Feb 2020, 06:34 PM #8Senior Member
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In the US the older standard colours for AC line cords was black active, white neutral, and green earth. As far as I recall, DC has always been red+ and black-.
Chas.
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17th Feb 2020, 08:20 PM #9Most Valued Member
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18th Feb 2020, 11:13 AM #10Most Valued Member
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A little late in on the conversation but it does seem to be a diaphram pump eventhough the shape is somewhat deciptive. The giveaway I suspect is the pressure switch. Correct me if I'm wrong but the operation of the pump cycles on and off depending on whether you have your hand on the spray trigger. Pull the spray trigger, pressure drops and the pump kicks in. It would be very unsusual to use a centrifugal pump for such a setup.
Also in operation, diaphram pumps tend to have a slightly pulsed output whereas centrifugal pumps produce a more even flow output.
Diaphram pumps work by being pushed open and closed by a rotating cam arrangement. The geometry for the cam (leading and trailing edge) may be optimised to run in a specific direction but it will still work in any direction and in any case I don't think diaphram pumps used for weed sprayers and caravans etc. are very hi tec or fussy.
Of course if it blows up then I guess it's another thing that I didn't know that I didn't know about!
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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18th Feb 2020, 07:19 PM #11
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18th Feb 2020, 10:37 PM #12
Hi Simon,
I was thinking a vane pump, more along the lines of several rigid blades running along the chamber walls. A centrifugal pump doesn't provide much pressure, where as a vane pump could, as could a diaphragm pump.
But you are right, a diaphragm pump does provide a pulsating output, hence the accumulator. I used a plastic coke bottle as one on the camper. Interesting to watch it start to fill with water and then stabilise about half full.Best Regards:
Baron J.
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19th Feb 2020, 09:21 AM #13Most Valued Member
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Morning
Yes, as supplied.
Not to any noticeable extent on this pump. But the triangular shape of the end of the pump makes me think its a 3 chamber pump. So I guess its much like the 3 phase v single phase motors the output is more stable? Though the geometry/timing of the cams would effect this.
I added the accumulator as I didn't think it was the greatest idea to be cycling the pump as often as I was(although in fairness it did put up with it for about 700 litres of spray, how every many starts that was). The only down side is if spraying a long time with a fine spray the pump cycles now and again, but its not nearly as often so I think I am much better off.
The coke bottle is a great idea. Cheaper than my $35 accumulator and no need to worry about the bladder being effected by the chemicals(which it would seem it is not, but that was a lucky guess lol)
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19th Feb 2020, 10:05 PM #14
Hi Stuart, Guys,
I notice that in the camper when you have the tap open and the pump stops, water carries on running for a short time while as the accumulator empties, the reverse happens as well. The pump runs for several seconds before the water starts to run. But it does very effectively smooth the flow. Most noticeable in the shower before fitting the coke bottle.Best Regards:
Baron J.
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24th Feb 2020, 08:08 PM #15Most Valued Member
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haha your funny
I usely dont start suspecting my pumps untill. the toilet level goes up instead of down.
equipment starts running hotter.
theres liqiud coming out of it or there is a funny noise.
.I think id just run the pump off a hand drill in fwd then rev for a bit and see if there was much difference.
but the hole time i was stuffing around with the pump. Id be wondering" does direction of rotation .make any differance""
aaron
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