Author Topic: Did low voltage kill this pump?  (Read 7718 times)

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madlabs

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Did low voltage kill this pump?
« on: July 17, 2013, 06:52:52 PM »
Hi All,

Drat! Came home to find the pump dead on the hillbilly hot tub. It had started going south last week and luckily I ordered another one. It's a Rule 2000 gpm bile pump. Upon performing an autopsy, I see that the plastic holders for the brushes got so hot they melted, allowing the brushes to lose contact. Windings seem fine.

I have had this pump tied directly to 3*55 watt, 12V panels in parallel. In the middle of the day the voltage climbs to about 16 volts, a little high. But I'm thinking with the melted brushes that we are talking too low voltage issues in the early morning and late afternoon. I've heard it growling and trying to run while taking a tub in the late afternoon. Does this seem like the probable culprit?

If so, I guess I'm going to have to make some sort of controller for it. Bummer, I was digging the easy route. I could do something like a dummy load on the NC side of a relay, use some programmable logic (PIC 12F675, I have some), when the voltage gets high enough despite the dummy load, flip the relay, lose the dummy load and run the pump.

Seems like a lot of dog though. If I do that I might as well put a temperature probe in the thermal panels and just run the pump when the panels have enough heat to make it worth it.

Anyone got a simpler way? I have a decent electronics junk box.

Thanks!

Jonathan

Frank S

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Re: Did low voltage kill this pump?
« Reply #1 on: July 17, 2013, 08:29:59 PM »
how about a battery and a 10 Amp  PWM
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OperaHouse

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Re: Did low voltage kill this pump?
« Reply #2 on: July 17, 2013, 09:38:47 PM »
AC motors suffer from brown out, I don't think that is a problem with DC.  For lower light levels a linear current booster.  That basically keeps the panels at the power point voltage which doesn't vary much with light level.  This can be done with any standard PWM chip.  As a bonus the PWM can limit the maximum voltage too.  This combined function can be easily done with a PIC or UNO with added features of temp control and timed events.

Simen

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Re: Did low voltage kill this pump?
« Reply #3 on: July 18, 2013, 02:47:04 AM »
Those bilge pumps are for intermittent use in cool bilge water, not continuous in warm water. I have used those Rule pumps in my boats, and usually have to swap them out every other season... :)
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XeonPony

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Re: Did low voltage kill this pump?
« Reply #4 on: July 18, 2013, 08:52:20 AM »
Those bilge pumps are for intermittent use in cool bilge water, not continuous in warm water. I have used those Rule pumps in my boats, and usually have to swap them out every other season... :)

thats the answer dead on, bilge pumps are to empty water in a cold surounding.

you need a proper seperated motor pump combo, or buy lots and lots of the bilge pumps!
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madlabs

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Re: Did low voltage kill this pump?
« Reply #5 on: July 18, 2013, 09:25:07 AM »
From what I read online, lots of folks use this same pump for sump pumps and put a lot of hours on 'em. Of course, that is in cold water.

So, none of you think that low voltage killed the pump? The brushes were melted right out of it. The only other time I have seen melted brushes it was low voltage caused excessive current draw. Also, it had been used for many hours on an 12VDC power supply with no problems, it was only a few weeks on the panels and then poof.

Jonathan


OperaHouse

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Re: Did low voltage kill this pump?
« Reply #6 on: July 18, 2013, 09:44:41 AM »
Higher voltage will definitely increase current and those bilge pumps are likely designed to work best when the battery is at a lower voltage.   I pump septic water with a bilge pump, that has to be tough on sealing surfaces.  Some have gone for many years and others have only lasted a month.  Certainly putting some micro smarts behind it so it only runs when it is useful will add life.

madlabs

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Re: Did low voltage kill this pump?
« Reply #7 on: July 18, 2013, 10:34:05 AM »
Wouldn't the higher voltage result in lower current?

Jonathan

OperaHouse

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Re: Did low voltage kill this pump?
« Reply #8 on: July 18, 2013, 11:02:28 AM »
In AC motors that is true since speed remains constant.  In DC motors speed increases with voltage.  Depending on pump design, increasing speed generally increases fluid flow and therefor higher pump current.  Unless a positive displacement pump, restricting flow lowers pump power.

oztules

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Re: Did low voltage kill this pump?
« Reply #9 on: July 19, 2013, 04:48:00 AM »
I am of the opinion that the hot water was not the culprit, nor the duty cycle.
Melted brushes with good windings does not feel like heat.
50-60C water is not that far removed from 15-20 degree water, and I would expect that it would make little difference, as the water is dense and will keep the temps to not much over water temp... not enough to worry windings etc.

For me it sounds like you direct connected the thing to the panels in set and forget mode, with no current booster, and this will all but guarantee  cooked brushes, as they impart enough current to heat the armature, but not enough to turn it in low light conditions.

Use a tl494 or similar and just use the op amps to set the step off voltage, and the other to set the upper voltage. This will boost the current in low light conditions, so that the rotor WILL turn (albeit very slowly in low light), and not just sit and cook the brushes. ( you will only get 90% pwm... built in 10% dead time, but you don't need 100% anyway, and you get full control, voltage regulation, current boost, clean waveform, a precision voltage regulator built in..... whats not to like?)

Set the upper voltage of the motor to 10-11v, and it should run for a long time. The pwm combined with the freewheeling diodes and the motors inductance is what gives you the buck converter effect.

I think your initial reaction was on the money.... low light with no current booster = dead motor every time.


Thats my 2 bobs worth anyway.



...................oztules
Flinders Island Australia

madlabs

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Re: Did low voltage kill this pump?
« Reply #10 on: July 19, 2013, 11:17:06 AM »
Oz,
 I did indeed connect the panels directly to the pump in set and forget mode. It was so easy and I was so happy...

The chip you mention sounds good, but I need a little help understanding. I looked and found a schematic for motor control:

http://www.eleccircuit.com/pwm-control-speed-motor-12v-by-tl494/

So, I can use the output section of this schematic. Would I be using a pot on each of the inputs, one to set turn on voltage and the other to set turn off voltage? What did you mean by "step-off" voltage? Turn off voltage?

I'll dig around, I *might* have some kind of PWM chip kicking around. Although the one you linked is cheap and comes in DIP, so if I have to order one no big deal.

Thanks!

Jonathan


oztules

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Re: Did low voltage kill this pump?
« Reply #11 on: July 19, 2013, 10:56:08 PM »
"So, I can use the output section of this schematic. "..... yes you could, although I would prefer to see a totem pole of pnp npn transistors to drive the gate from whoa to go and back again... This will ensure proper gate turn on and turn off.

The frequency would be better at 20khz so you don't have to hear it squirm at lower light levels..... unless you want to hear it, and then go for 5khz or so.

The step off voltage I refer to is simply a poor mans mppt. The problem with solar panels is that they are essentially current sources with an internal resistance.

You will have heard on here before that if you connect a 18v panel to a 12v battery, the panel voltage will drop to meeet the battery termonal voltage, and you lose the 30% or so between 12 and 18v.

When you direct connect a panel to the motor, it does the same thing, except it has no terminal voltage, and so drags the panel down to whatever the panel can support at that light level.. The current will remain the same, but the voltage will drop..... so you throw away power, and are limited to the current dependent on the light conditions.

At low light, your motor was seeing short circuit current, but no voltage ( almost), so it sat there and cooked. On better days, this would not last long, and maybe it would start turning before the thing cooked, once away, the voltage rises, and your motor ahs back emf to balance the incoming voltage, and it runs normally. If the transition is too long for the physical mass of the motor to absorb the current before it starts to motor... then poof...

To stop this, we can use one of the op amps in the 494 to sense the incoming voltage. We then compare a sample of this to a fixed voltage. We can get that from the 5v regulated output from the tl494 ( pin 14 i think ). Even if it is just a 5k trim pot from 14 to ground with the slider going to pin 16 At mid point this will give you 5/2 or 2.5v on pin 16. That is our reference. Then it is a simple matter of taking the Array + and using a divider on it to give us about the 2.5v at the divider point.
Feed this to pin 15.

What should happen now, is if the motor speed control is set for say 3/4 speed (using pin one and 2 for that), if the pulse is too skinny, the pwm unit will try to widen the pulse by dropping the voltage on pin 3 ( op amp output ) As pin 3 gets driven down, the output if fed to another comparator internally, and beaten with a triangle wave.

The result is that when ever the pin3 voltage touches the triangle below it's peak, the pulse is the width of the line drawn across the triangle at that point. If pin 3 is zero, the full triangle is the pulse width... etc etc.

So at the time when it want to drive the motor up to full speed or whatever, it will try to pull 3 down, but the second comparator (pins 15 and 16) are orred with the same pin three.
In our case, we want the result from pins 15 and 16 to count... so as the voltage at pin 3 dropped by turning on the motor pulse, the flimsy panel voltage will sag... and this is caught by the pin 15 and 16 comparator. It then raises the voltage on three, and shuts the pulse width back down... so they fight over the same pin, and whomever puts the highest voltage on that point, will lower the pulse width.


What this means is that the voltage at the array will NEVER drop below what you set it for with the trim pot, as as soon as it tries, the pulse will narrow and it won't happen... no matter how hard the pin 1 and 2 comparator try to make the motor run fast, it just cant because of the voltage limit of 15,16.

This means your operating point is going to be always at or above the voltage you set. The resultant pulse width will be the compromise between what you wanted, and what can be achieved with the voltage available...... but we also get the buck converter effect. The capacitor on the array output ( yes put a cap on the input to this thing), will charge and discharge into the motor via the fets via the pulse width... so 1A @ say set to 16v will suddenly become perhaps 5A@2-3v.... so the pump will turn.... because the current is the torque, the voltage is the speed, we now have a current amplifier... it is going to turn no matter how low the light is ... until it gets very  very overcast/night..... because the cap will discharge it's energy in bursts into  a low impedance load ( locked rotor motor), so the current can get very high.... albeit wih a very low voltage.... so very low watts , but will still grunt and groan, but still turn. At low speed the pump will provide low load to it too.

The last thing to control is the max speed, so the pump runs for a long time, at reduced voltage... you can use the voltage across the freewheel diode across the motor as the reference, and this time you could use the pin 4 ( pulse width control max). I last did this a long time ago, but used a little opto isolator to look at the voltage across the motor, and then use the output to drive some of the 5v regulated into pin 4 proportionally... pin4 high, no pulse, pin4 zero, max width.

None of the above is what Elec Engineers would do, but I can vouch for the effective result. There is a 2hp solar water pumping unit here running one of these for the last few years.... probably not the right way, but a way anyhow.

I no longer have the circuit, or the board drawing, but thats how i remember it.

http://www.ti.com/lit/an/slva001e/slva001e.pdf    Use this link to learn about the chip. They are in nearly all the computer power supplies I have torn down, also KA7500 is the same thing.

Which ever way you go, you do need to control the step off point to get any useful result short of lots of sun, and you do need that for the current boosting to stop the burning smells.. The max voltage control will give your motor long life, and the speed control to give you the feeling you have some control over all this .


Someone who knows what they are really doing like Opera or Joe will be able to explain better, and may have some circuits to try.



.......................oztules


Flinders Island Australia

madlabs

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Re: Did low voltage kill this pump?
« Reply #12 on: July 20, 2013, 11:04:07 AM »
Oz,

Fantastic explanation and many thanks for the time it took to write. I have a couple of PC power supplies I could rob for a chip. One question: I'l guessing this is a circuit that doesn't bread/proto board very well, gate capacitance on the FET and so on?

I also don't want the pump to run in the lowest light conditions possible. There is some heat loss in pipes and filter etc., so I am sure there could be a period where it is possible to keep the pump moving water but there isn't enough warmth in the panels to make it worth it.

It's going to take a while to experiment with your suggestion, so I spent yesterday working on a junk box kludge. Got it together enough to watch it cut off yesterday. I hope to get a proto-board version done today. It's foggy here this morning so I may even get a chance to see it turn on.

I didn't have a SPDT or any DP beefy enough for the job. SO I had to glue two relays together. Classic junk box action!

7444-0

A shot of most of the montage:

7445-1

Thanks!

Jonathan

OperaHouse

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Re: Did low voltage kill this pump?
« Reply #13 on: July 20, 2013, 11:22:37 AM »
I wrote a while back about using LM2596 module from China as a poorboy MPP charge regulator. Thread http://www.fieldlines.com/index.php?topic=146685.0   Only one panel monitoring transistor would be needed. Just set the voltage of each module to the same voltage 11-12V first and then connect all the outputs together.  Just bought another of these last week and it was only $1.70 shipped.   A fast $5 solution.  Don't have much faith in their current spec but three in parallel should run the pump.   You never specified the current rating of the pump.  I still think it was over voltage.  Three 55W panels likely put the voltage well over 16V into the motor.   

The TL494 certainly is an option.  There is one example with current monitoring.  Since the load (water) will likely always be there, you could monitor the panel voltage instead of the output voltage.  The voltage op amp + - pins would have to be reversed since it needs to shut down with under voltage.  Then just set the maximum current the motor is allowed.
« Last Edit: July 20, 2013, 11:38:32 AM by OperaHouse »

madlabs

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Re: Did low voltage kill this pump?
« Reply #14 on: July 20, 2013, 11:37:37 AM »
Opera,

The pump says 8 amps. In reality it pulls about 6 amps at 12V. I agree that high V may or could be an issue. The pump sees 14V with only two panels in full sun, so I am going to leave off the third panel.

I looked at the thread. So I see it will protect from high V and allow me to run in lower light conditions (not always good). Will it protect from the low V scenario? I want to be covered on all fronts, these pumps aint cheap.

Thanks!

Jonathan


OperaHouse

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Re: Did low voltage kill this pump?
« Reply #15 on: July 20, 2013, 11:46:40 AM »
I added some more info to the last thread.   If you would ever consider a UNO, a lot of nice features could be added to extend the life of the pump. Doing some new water heater programming this week and have a spare UNO.  Might play around with some speed control.  I snag up a UPS now and then at the town dump.  These are ready made for fun.   I have three pumps in my boat cause I don't trust them at all (and it is wood).  I was kinda surprised at the 8A,  That is bigger than I've seen.

madlabs

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Re: Did low voltage kill this pump?
« Reply #16 on: July 20, 2013, 12:16:20 PM »
What kind of features are you talking about? I took a quick look and see it has PWM, analog inputs, etc. I think I have all the same stuff in PICs and I have a bunch laying around gathering dust.

I don't think I need speed control per se. I just need to make sure there is enough juice but not too much. I just did a test as the sun came out from behind the fog and found I need to see at least 7V on my dummy load before there is any actual heat gain to be had from the thermal panels.

Thanks!

Jonathan

madlabs

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Re: Did low voltage kill this pump?
« Reply #17 on: July 21, 2013, 08:05:44 PM »
Between my last post and now I have made some progress with my junkbox controller for the hillbilly hot tub. I do intend to pursue some of the solution outlined above, but it is going to take me a while and I need my hot tub NOW!! ;-)

So, I grabbed a PIC 12f675 and soldered up a protoboard. The way it works is: NC side of a realy connects the panels to a dummy load. This clamps the voltage some so that the controller isn't fooled when the voltage climbs in the morning but can't really support a load. When the voltage gets high enough in spite of the dummy load, it flips the relay which disconnects the dummy load and connects the pump. I ended up using a battery for the logic and relay because in low light situations it is possible that starting the pump can crash the system, resulting in repeated attemps to start the pump and execessive relay chatter. So I had to add a simple LM317 battery charger circuit. Here is the brain board.

7446-0

Here is a shot of the entire montage:

7447-1

Now the question is: Do I leave it running while I go away for my 24 hour shift? :-0

Jonathan




OperaHouse

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Re: Did low voltage kill this pump?
« Reply #18 on: July 22, 2013, 02:27:13 PM »
I was thinking that there is no need to run the pump till the fluid is up to temperature and shut it down when temp drops.  That will save running time on the motor.  Monitor panel voltage and increment up the pwm cycle up if voltage is higher than say 17V.  Limit pwm duty cycle to say max 80%.  Depending on code, any duty cycle under 25% should probably be off.  You likely have enough bits on the dac.  A .05 ohm resistor sampling current from common with 10K filter and 10uf cap will give you enough bits to have current limiting by reducing pwm number.

I began using those 8 pin microchips in commercial applications back in '99.  Made my life easier when one board could be used in multiple applications.

madlabs

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Re: Did low voltage kill this pump?
« Reply #19 on: July 22, 2013, 09:33:17 PM »
Very true. My last system had sensors in the tub, on the input and output of the thermal panels and on the wood fired section as well. So it was easy to know when to pump. In the morning and afternoons I could do what I called "hot shots", allowing the water to heat up until it was higher than the tub and then pump until the output of the panels was the same as the tub or less.

This system I was trying to avoid getting fancy. It isn't going to live where it is forever. I was so happy with the pump hooked direct to the PV. This system does have some degree of control, I can wait until the PV's read a high enough voltage against the dummy load and then pump. This morning it got going about as early as was useful. I'll just have to watch it and tweak the programming.

Dunno if the 12F675 has hardware PWM or not, don't have the data sheet here. This controller won't be in use for too long, I'm going to get to something better soon. I just needed something to get the dang thing heating again!

For even more fun, one of the thermal panles sprung a leak. So I had to break out the torch and braze it back up. The trials and tribulations of sa Hill Billy Hot tub!

Jonathan

joestue

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Re: Did low voltage kill this pump?
« Reply #20 on: July 23, 2013, 03:04:59 AM »
Opera, that's a pretty smart design you just described.

what comes to mind with the brush holder burn out is that the contact resistance between the armature and the brush is a variable. sometimes you can have really poor contact, and if there isn't enough current flowing to make the armature spin, you could get 2-20? times as much heat generated at the brush as normal.
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

madlabs

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Re: Did low voltage kill this pump?
« Reply #21 on: July 25, 2013, 10:08:52 AM »
Well, it's working pretty well so far. Had a on/off cloudy day with decent heat and the controller seemed to be making good choices, if there was heat to be had in the panels the pump was on. Improved my brazing skills and repaired a couple more panels. I think I'm going to add one more as fall approaches.

Jonathan

OperaHouse

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Re: Did low voltage kill this pump?
« Reply #22 on: July 25, 2013, 04:49:02 PM »
Are you just using two panels to solve the over voltage problem?

madlabs

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Re: Did low voltage kill this pump?
« Reply #23 on: July 25, 2013, 05:28:41 PM »
Yup. The highest voltage I have seen was 14V, which should be fine for now. I do like the idea of controlling and lowering the voltage a little, I'm sure I'll see better pump life. ALthough the flow rate I get during the day really mixes the water so no temperature gradient when you get in. And since it is pumping through the sand filter, the water is sparkling clean.

Gonna have to wait for it to cool a little tonight, the tub is on track to hit 110F or so this afternoon.

JOnathan