Help with Water Pump

[alec_t]

@KISS

I have to hand it to you on the way you handled your recent mistake. Absolutely ingenious. You put it there on purpose

Thanks. Just testing you guys!

@Joe
The wiper won't be connected to either end leg. This time the pot is being used as a potential divider rather than a variable resistor. Like this:

 

[alec_t]

I don't know what's going on with the posts here. Yesterday I noticed that my posts #1856 and #1857 were duplicates so I edited #1857 to 'post deleted', only to find that both then read 'post deleted'! So I tried to reinstate the text of only #1856 (which is why it differs from what you may remember), but now both posts show the new text. Bizarre.

 

[salty joe]

I've had a lot of minor issues from day one, the most annoying being the inability to use the search thread function. All small stuff-this has been great.

 

[alec_t]

inability to use the search thread function

I find it gives up the ghost unless you limit the search in some way, e.g. by date range.

 

[salty joe]

I can't even get to the search thread function.

The yellow wire shows 5V when the controller is in high and 2.4V in low.

Should I connect one leg of the trimmer to the yellow wire and the other leg to ground? If so, where does the wiper go?

Or should I connect one leg of the trimmer to 24V, the other leg to ground and the wiper to the yellow wire?

 

[alec_t]

Did you check the pic in post #1861?

 

[salty joe]

Yes, I printed it. It shows a leg going to the yellow wire (which I thought was the control) a leg to groung and the wiper going to control. The pump has three wires going to it-24V, ground and the yellow wire that is 5V when pump is in high and 2.4V when pump is in low. I am sorry, I am unsure of this hookup.

 

[alec_t]

Yes, the yellow wire is the original control wire from the controller. The wire labelled 'control' is your new control wire input to the pump. Think of it as 'new yellow' .

 

[salty joe]

Now I'm really confused.
One leg of the trimmer gets connected to the original yellow wire. The yellow wire that is either 5V or 2.4V depending on if pump is in high or low.
One leg gets connected to ground.
It sounds like I need to add a fourth wire between the controller and pump?? I am still having a hard time figuring out what exactly the wiper gets connected to.

 

[alec_t]

Is this clearer?


Edit: I've shown the yellow wire as being cut, assuming the pot would be an add-on unit, but if the pot and its connections are going to be built into the controller then you would just detach the yellow wire end from the controller output socket pin and connect it instead to the pot top leg. You would then connect the pot wiper to that pin. The bottom leg of the pot is grounded.

 

[salty joe]

OK, now I get it! Thanks very much for that, I'll let you know how it works.

 

[salty joe]

I hooked up a 25K trimmer and it does work, but at the cost of a little top end speed. With the trimmer set for max speed, there were 4.77V at the control line. (versus 5V) The only reason I thought to check was I could tell by listening the pump was not going as fast. For now, I think I'll put the pump back together the way it was. If it turns out that I need to slow things down sometimes, maybe a SPDT could be installed to switch back and forth between using the trimmer and bypassing the trimmer. The ability to slow down each and every mode is a big plus-thanks for another good plan-sorry I had such a hard time wrapping my head around it.

 

[KeepItSimpleStupid]

@Joe

There might be some other ideas to try. 1) A larger size POT for instance.

Could you measure the voltage from ground to the wiper with and without the wiper connected over the range of the POT.
e.g. 0 to 5 V wiper not connected; 0-4.77 wiper connected

@Alec
Thought might be to buffer the Pot voltage with an OP amp, if the above tests are similar to the fake results above.

 

[alec_t]

@Joe
Theoretically, if the pump control input had an infinite resistance, the 25k pot would drop the 5V down to 4.8V; so your measured 4.77V suggests the input resistance is pretty high (~300k, if the trimmer is accurately 25k). That's good.
You probably have a spare 50k trimmer (50k is used in your built wave timer module). If so, try that. The 5V should then drop to nearly 4.9V, giving you almost the original max speed.

@KISS
I did consider a buffer, but if the pump input resistance is ~300k and the 50k pot raises the speed enough a buffer shouldn't be necessary.

 

[salty joe]

All this jiggling around broke a stranded wire at the board and almost broke another, but earlier, I super glued a screw that held the board down. Super glue is really good stuff.So I had to drill that screw out. I managed to get the board loose and make solid repairs without mangling anything. The best thing for me to do is be done with a soldering iron until tomorrow. Night all.

 

[alec_t]

All this jiggling around broke a stranded wire at the board

.....which is why screw-down terminals are recommended for wires which will be moved around. Obviously the manufacturer didn't intend people to be doing that . Glad you fixed it ok.

 

[salty joe]

... Glad you fixed it ok.

Thanks.
With a 25K trimmer, wiper hooked up, I got from 4.77V to 1.32V. Wiper disconnected and trimmer in same low position, 1.36V. Trimmer on high, wiper disconnected, 4.8V.

50K pot wiper hooked up, 4.87V-1.04V. Wiper disconnected, 4.9V-1.08V.

 

[alec_t]

Those figures are all consistent with the trimmer values being 'what it says on the tin' and the pump input resistance being ~300k. Was there a noticeable speed increase going from 4.77V to 4.87V? Would the 4.87V speed be ok, for leaving the 50k trimmer in place permanently? Or would you still want the SPDT switch to bypass it?

 

[salty joe]

Yeah, I could tell the pump was working harder at 4.87V. IDK how much below top speed this is, I'll have to make a comparison. I'd imagine a SPDT will be in order. I'm pretty sure I'll need heavier duty SPDT switches.
Thanks for that variable speed solution. Very cool application of a pot.

 

[KeepItSimpleStupid]

@Joe

Nah. We can use the OP amp trick to get the voltage higher if need be.