# do I need a controller?



## boatswain2PA (Feb 13, 2020)

Haven't had any run-off this spring/summer so cattle pond is getting very low. Have old windmill well that looks like it produces about 1-2 gpm (from generator powered testing we have done) that used to dump into this pond. Windmill would be exorbitantly expensive to repair.

Looking at a 24/12 volt submersible pump that draws 4 amps at 24 volts, so 8 amps at 12 volts (96 watts...right?). Hoping to wire this and one 100 watt solar panel each directly to a 12 volt truck battery. With this set up I shouldn't ever risk overcharging the battery, but will likely end up with a dead battery every morning. 

Some questions for the experts here

1) Would it be bad on the pump when the solar panel doesn't produce the required 96 watts? I feel like the pump would just slow down, but I don't want to mess up a $150 pump.

2). If I do one panel, would the battery even do anything since the pump draws 96% of the panel's advertised output? Seems like cheap route to go would wire panel directly to pump. Sunlight = water. Less sunlight = less water. No sunlight = no water. Right?

3). If I do 2 panels, would I need a controller? Can I wire them in parallel for 16 amps/12 volt and send that directly to the battery and pump? Then when sun goes down the battery drive the pump for a while longer? 

Whether I do 1 panel or 2 panels, would I need a controller for such minimal operation?

"We should buy land and live in the country" I said...."It'll be fun!" I said.....


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## KC8QVO (Mar 22, 2011)

You bought land and live in the country. So have fun. 

You don't want to do that. I woudn't think the pump would be too much of an issue, however if your voltage is low enough to where the drag on the pump cancel out and the pump doesn't run then you basically have a resistor sucking current for no reason. There may be a possibility of over-heating the windings in the pump motor, but I am not well-versed on motor/alternator windings to give you a definitive yae/nae there on the overheating aspect. 

You will, however, destroy the battery in what you propose.

The pump motor has nothing to stop it from drawing current. The battery will push current until there is 0 voltage left in it. If you drain a lead variant battery below about 80% of charge state (20% depth of discharge) you significantly reduce it's lifespan. At 80% charge state it should still be over 12 volts which means that your pump is likely going to run. Even if the voltage goes down to, say 8 volts and your pump isn't running the pump is still drawing current which will keep on dragging the battery voltage down - until it gets down to, you guessed it... 0 volts. 

This is why you need the proper voltge regulation on your system - to both charge and prevent over-charging, as well as the reverse - prevent excessive discharge so as to keep your batteries in good health. 

Here is an example of a low-voltage cut-off device that you can use to kill the pump's power and protect the batteries. I believe there is a way that you can program the voltage of when it cuts off. It appears to be set from the factory at 11, that would probably be OK for most applications with lead batteries, but it may help to increase that to another value. 

http://www.westmountainradio.com/product_info.php?products_id=pwr_guard

The charge controller should be a given with the solar panel also. You can get them for pretty cheap at the power level you are working with. The trick is more so the low voltage side so as to get the pump to cut off. 

Another thought here is that the pump is going to be consuming power. If you don't have enough solar power to supply everything the pump draws plus enough to charge the battery your battery will never charge. This is bad. 

The PowerGuard listed in the link will cut power off on the low end. So lets say that you have a bright sunny day and the pump is running and there is enough power to charge the battery. When the sun drops to where the energy going in to the system is less than the power consumed by the pump the battery will discharge all the way down until the PowerGuard cuts off the power to the pump. There is nothing to charge the battery back up, so it sits there all night long at it's discharge state voltage. When the sun comes back up the next day the first thing that will happen is that the PowerGuard will turn on again (if you have it set to do so, otherwise it will require a manual reset) and send power to the pump. It won't be until the solar panel production is high enough to fully supply the pump with excess that the battery will begin to charge again. 

So I think, if you want your battery to last, you are going to have to give some more thought in to your system. The battery should be sitting charged - not discharged - which means that you need a way to control the pump to turn off while the battery is able to be at full charge state, not bottom end discharge state.


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## boatswain2PA (Feb 13, 2020)

So two 12 volt 100 watt panels wired in series going to two batteries wired in series, then to this controller, then to the pump? That should keep the batteries charged, right?

Could the panels overwhelm the batteries, especially if the pump quit for some reason?


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## KC8QVO (Mar 22, 2011)

The link I posted earlier is to a device called a PowerGuard, from West Mountain Radio. It "guards" your battery from being destroyed by cutting off the draw to it. 

In the theory of using the PowerGuard and your pump - you would put the PowerGuard in-line between the battery and your pump. 

The PowerGuard is NOT a "controller" for charging - it prevents damaging batteries by too deep of discharge as it cuts the power off before you get there. 

You will need a "charge controller" to sit between the solar panels and the battery. 

However, the combination of the "PowerGuard" and a "Charge Controller" in your system is not sufficient. This is because the automation (IE - lack of manual interaction) of the system comes from the PowerGuard turning off the pump only when the batteries have reached their lowest charge state. 

You do not want the batteries sitting in their lowest charged state. You want them to sit charged. 

So that is where you need to give more thought to your system. If you set up the system with the charge controller and PowerGuard then you are going to limit the lifespan of the batteries and will need to replace them regularly. Whereas if you give more thought to the system you may be able to maintain the batteries better and make them last much longer. 

One way, off the top of my head, you may be able to set this up is to have a controller set up to also trip the pump to run. So when you have enough power from the solar panels that the controller is allowing power in to charge the battery have that also be the point where your pump runs. Then when the solar panels stop producing power have the lack of charge current going to the batteries cut off the power to the pump. 

What I can't tell you off the top of my head is how you would maintain the voltage of the battery in that application. If you had enough solar power to provide a surplus of power - beyond what the pump is using - to where the batteries can charge then the charge current will be cut off when the sun is up so as to protect the batteries from over-charge (which is the whole point of having a charge controller in the first place). If that is the point where your pump is also turned off it wouldn't make any sense - while you have a surplus of power is when you want the pump to run. 

What you don't want is the pump to run and drain the batteries to where the batteries sit dead. That is my main point in what you had proposed up front - that method (no controlling, period) will destroy the batteries from allowing them to discharge to 0 volts. 

So you need to figure out 2 things - 
1. How to regulate the charging of the battery
2. How to allow the pump to run when there is solar power; and how to disable the pump when there is no solar power. 

If you shop around I am sure there are controllers that will do exactly this - your situation could be very common. 

A water pump is going to be drawing a respectable amount of power. Batteries are rated in Amp-Hours. That is how many amps you can supposedly draw from a battery in 1 hour. Or, if you reverse the numbers - how many hours you can run with 1 amp draw. The amp-hour rating should never be taken literally. Lead-variant batteries should not be discharged below about 80%, or a 20% depth of discharge, if you want them to last. 

So your pump - if it draws 8 amps - on the surface would need an 80 amp-hour capacity battery to run 10 hours with no charge. At 20% depth of discharge this means that you need a lead battery capacity of 400 amp-hours. The PowerGuard mentioned here would be to protect the batteries at 20% depth of discharge (supposedly, if you can get the cut off point set for that voltage, I don't know what the stock 11 volt cut off is in % depth of discharge off the top of my head - better than it going down to 9 or 10 volts, for darn sure, but if that will safely prolong the life of the batteries I am not sure off the top of my head). 

When your solar panels are producing power they, in the same number scenario above, would need to replenish the 80 amp hours used at the same time as that pump is running drawing its' 8 amps for the period of light that you have available to get the batteries back up to charge before the solar production drops off. That is - if you intend for the pump to run for that same 10 hour period after solar production stops. If you have 6 hours of good solar production in a day and the pump runs for those 6 hours then your pump is consuming (8x6=) 48 amp-hours at the same time you are trying to get 80 amp-hours back in to the bank (your charge energy). So now you need to provide (48+80=) 128 amp-hours in that 6 hour period. 128 amp-hours in a 12 volt system with a 14v (illustration) peak charge state voltage is 1792 watt-hours. Divide that by 6 and you get almost 300 watts. 

So for the numbers outlined here with the pump running while solar production is occurring, and with the pump running for 10 hours after solar production stops, you need 300 watts of solar panel capability. This doesn't mean 300 watts of solar panels as the sticker number (IE - 3x 100 watt panels) - it means you need 300 watts produced out of the panels that you have. You likely aren't going to get 100 watts out of a 100 watt solar panel except rarely in direct sun with no visible moisture. If you figure that the panels may be 60% efficient (not ideal conditions all day) then you need "500 watts" of sticker/advertised solar panel wattage to get your 300 watts of average production. Some days more, some days less. 

If you use a charge controller and something like the PowerGuard with your proposed set up will it work? If the pump is running while the solar panels are running and you start with a fully charged battery - you will get 1 full run out of it. Then the following days the running will dwindle off quite a bit, the amount they dwindle off will be proportional to the amount of solar production you have. The reason for the dwindle - you aren't going to be able to recharge the battery if you aren't producing the power to do so (the 300 watts). So how far the battery gets charged, or shall I say, discharged, during the 1st day is going to impact how long the pump runs after the solar production stops. Day 2's pump run time will depend on how much solar production you get to run the pump, first off, but with any extra going to charge the battery - how much charge are you going to get? 

If you keep on that path the battery will always be discharged, never fully charged. That will destroy your batteries quickly.

Perhaps someone else on here has experience with exactly what you are trying to do and knows of a device that you can use to regulate the charging and discharging with an autonomous system. I just would hate to see you try something while not understanding the in's and out's of what you're doing only to have a failed system. The road you were proposing was doomed. 

You can run low wattage solar panels in to battery banks without a charge controller. This isn't the smartest idea, however if the wattage of the panel is such that its max charge current is never pushing the batteries peak charge voltage over its edge (trickle charging) then the power may cancel out. When you provide more current than what it takes to trickle charge is where you get in to destroying the battery on the high-side. And that wattage would surely be less than what it takes to run your pump = won't work in your scenario and you need a controller.


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## boatswain2PA (Feb 13, 2020)

Huge thanks for the detailed response. 

Could I just skip the battery and use two 100 watt solar panels and a controller to get water during daylight hours?


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## KC8QVO (Mar 22, 2011)

That is a good question and I am not sure how to properly answer that in a way that would communicate the right perspective to you. 

With that having been said, what does come to mind in that idea - and thanks for the idea, it shows you are thinking "outside the box" - is that a "charge controller" is to provide charge current. That means an existing voltage (battery voltage) and current sent to that voltage in an attempt to raise it. 

My charge controller is a Micro M+ for my small portable system. It samples the voltage on the output to figure out what state to put the charger in to. If you have no battery connected for it to take a sample of the voltage of then it doesn't know what to do = doesn't turn on to send charge current. 

Solar panels are unregulated voltage sources. I used the word "voltage" here, not "current". My small panels, unloaded, will produce over 20 volts. I've seen as high as 22 volts out of them. They are rated at 15 volts for use in a 12 volt system. Yet, unloaded they are pretty high in bright strong sunlight. That is the reason they are unregulated. In order to charge, however, you have to have the ability to produce higher voltage than what you are charging. 

So if you have a solar panel intended for a 6 volt system that can push 200 amps (in theory here) and the unloaded voltage of the panels peaks at 13 volts - you may have the ability to drive 200 amps from your solar array, but since the peak voltage of the panels needs to go above your at-rest battery voltage before charging occurs you are only going to get a very small amount of current - if your battery voltage sags under 13 volts and the panels peak to 13 volts. At 13 volts your batteries are not fully charged, nor will they ever get there. So your 200 amp available charge current is meaningless with the voltage mismatch because you don't have the voltage to get the batteries where they need to be. 

Going back to the charge controller ability to run the pump directly - the only voltage that would be available there would be what the controller outputs. If it is like mine and needs to sense that battery voltage state to know what to do at the start you won't have it output any current = pump won't run. That is just a guess. 

On the other side of the coin, if you do away with the controller you take the brain out of the question and just run straight current - when it is available. 

There is an electronic part called a "Zener Diode". It is a passive, dumb if you will, "voltage regulator" in that it has a fence at it's nominal voltage. If you have a 14 volt zener diode it will pass voltage up to 14 volts then trim off the top. This might actually work in your scenario.

The inductive load of the motor won't care much about voltage regulation (a DC motor uses a change in voltage to change the speed, you just don't want to over-speed it or send too much voltage to it trying to overcome heavy drag as you will burn out the windings in the motor in short order - so you do need to protect the motor to some extent). The motor, in turn, will somewhat regulate the voltage of the panels. This is because the motor is going to consume current. The lower the current available the lower the voltage is going to be and the slower the motor is going to run. 

If your panels can push 12 amps, lets say (144 watts at 12 volts), and the motor is rated to 8 and under your particular load it draws 8 when running normally then you have 4 amps available from the panels that will drive the voltage of the system past 12 volts. Somewhere in that curve, if you think of it as a graph, of amperage available vs. peak unloaded voltage of the panels you will find what the operational voltage is going to be at the pump. I guarantee that is going to be beyond a safe operating level for the pump - and why you need to, at least on the top end, regulate the voltage - so you don't smoke your pump motor.

Here is an example of a zener diode. They come in all kinds of "packages" (the form factor). These are thru-hole panel/heat sink mounted. There are also TO-220 packages, among others. However, for power handling the thru-hole ones are likely going to work better. You can run them in parallel. TO-220's can also be bolted down to heat sinks and are great for power dissipation (that's what my output transistors are in my Micro M+ - TO-220 package transistors, but I don't have enough panel capacity to drive them hard so they have clip-on heat sinks instead). The main thing to look for is the power capability. The ones in the link here are 50 watt-rated ones. I would think 2 would be OK, 3 would give you head room so you aren't maxing out the dissipation. Of course, you would want to bolt them to a plate of some kind as a heat sink and ensure they have airflow.
https://www.newark.com/solid-state/1n3313b/zener-diode-50w-14v-do-5/dp/56J9299

If you aren't familiar with a basic diode - they are a "check valve" for electrical current. So, the zener diodes in this application would do 2 things. They would act as a "check valve" to only allow current to flow through the motor. They would also act as the "voltage regulator" so as to trim the voltage to 14 volts - should the output of the panels get up to it. Otherwise, they pass everything below - within reason. 

These particular zener diodes have forward bias voltage at 1.5 volts, supposedly (comment next to "Electrical Characteristics" at the top of the spec sheet PDF). That means that it takes 1.5 volts off the circuit. So if you send it 13 volts, under load, the pump motor would see 11.5 volts. If you send it 15 volts, the pump motor would see 13.5 volts. If you send it 20 volts, the pump would see 14 volts (the cut off point for the diode - it won't pass more than 14 volts, regardless of what is sent to it - until severely high voltage, thousands of volts, breaks down the diode and jumps over it). 

This sounds like an interesting project. I will have to dig around and see if I can find some zener diodes that might work and run them with a small motor and see what happens. I'm sure I have a motor around to try and I have solar panels...


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## boatswain2PA (Feb 13, 2020)

KC8QVO said:


> It samples the voltage on the output to figure out what state to put the charger in to.


So the controller really acts like a battery charger that gives the batteries the amount of amps they need to charge most efficiently?

Looks like the complete outfit I will need is about $1500 (https://shop.rpssolarpumps.com/products/rps-200-solar-well-pump-kit/)

I think you should come up with a more basic and cheaper product, market it, and become rich! lol


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## KC8QVO (Mar 22, 2011)

boatswain2PA said:


> So the controller really acts like a battery charger that gives the batteries the amount of amps they need to charge most efficiently?


The way the controller I have works is that it uses a series of transistors. The transistors are 3 pin types with a base, collector, and emitter (NPN). The base is grounded and when provided a voltage at the collector they are "turned on" = they "conduct". The output (what comes out of the emitter) is proportional to what comes in to the collector, only the transistor "amplifies" it. In the case of the charge controller - the transistors are simply used as an "on/off" switch. When they conduct they emit current. Transistors are used because they have a low power draw (think of the coil in a relay - it is generating a magnetic field to hold a plate against a spring - the relay coils take magnitudes more current than a transistor takes to "turn on"). Low power draw is especially important in low power solar systems where any power consumption is magnitudes more percentage of the amount of solar power available. 

The transistor chain in the controller does a few things. First - an IC (integrated circuit) is set up as a "comparator". This is where the voltage sensing takes place. There is a calibrated (and adjustable, to calibrate) internal voltage source. This is the base that the comparator uses. The comparator senses the battery voltage and "compares" it to the internal reference. When the sensed voltage is less than the reference the comparator sends a low-level signal to the 1st transistor in the chain which makes it conduct. That in turn sends a more powerful signal out to another transistor that turns on an LED indicator, and is also the input signal to turn on the power transistor that passes current on to the battery. 

When there is no power source that the controller is hooked to as soon as the output transistor is turned on the sense line picks up that it is at the unloaded (essentially - minus the power to run the controller) voltage of the solar panels. In my case, that could be 22 volts. So the comparator sees that 22 volts and says "HOLY MOLY! WE'RE ON FIRE!" So it instantly shuts itself off - which is its purpose in life to begin with - ensure that the voltage of the battery is kept under a safe level. 

There is a capacitor in the circuit that is used as a timer to reset the sensing period. That is about 4 seconds. There is no IC, or "brain", that controls when the sensing is done - it is an analog set up based on the charge time of the capacitor. As long as there is sufficient input voltage the 4 second cycle of sensing the battery voltage will occur (whether there is a battery or not). 

As to how much current is sent to the battery - the Micro M+ is not an MPPT controller (Maximum Power Point Tracking). All the Micro M+ is happens to be a "switch". It just allows current to flow or not. It does not regulate the current. This is less efficient than MPPT, but it is a lot simpler. As to how much current will flow - that depends on the solar panel production. MPPT would squeeze out more watts, but I don't think its that big of a deal in my particular application. 

Of note also, one of the batteries I use (most of the time now) is a Lithium Iron Phospate (LiFePO4). Lithium batteries have a much different charge algorithm than lead batteries. Lead batteries can be charged more by "current". So most chargers peak charge by pulsing current on and off. More advanced chargers will stage the current - starting out at, say 20 amps, then drop to 5 amps, then float at 1 amp. Lithium batteries charge best with a charger that will vary the current to maintain the battery voltage. They do not "pulse" current - they regulate the current so that the battery is held at a "constant voltage". 

That having been said - the "pulsing" of the Micro M+ (the 4 second cycles of sampling the battery voltage, unless the battery voltage is under the set point where it will run constantly) is not very good for the LiFePO4 batteries near peak charge. They should be held at a constant voltage. 

I will have to dig in to the circuit and see if there is a way I can add a comparator that will track the current to output a particular voltage instead. That would be possible with transistors - their output is not confined to an on/off state - the trick is the signal coming in to the collector so as to regulate what comes out of the emitter. I'm not sure how to make that happen yet. 

For the time being I can maintain the battery with a proper LiFePO4 charger at home and the times I am out and need the solar power I am at least safe from the standpoint that I can't over-charge the battery, even if I can't hold it at its charge state for it to soak up as much energy as if I could. 



boatswain2PA said:


> Looks like the complete outfit I will need is about $1500 (https://shop.rpssolarpumps.com/products/rps-200-solar-well-pump-kit/)


I would be curious how that controller works. It is listed as a "pump controller" as opposed to a "charge controller", though it shows it has a hook up for a battery as well (optional, not required). It says it can handle solar input of up to 100 volts. So that sounds similar to a charge controller but probably regulates the voltage. 

Grid-tie systems use "inverters" where they are presented DC (high voltage DC, up to several hundred volts depending on the system/controller) or AC (from inverters coming out of solar panel sets - as opposed to DC from them) then output regulated AC that is matched to the grid frequency and phase (they sample the power they are matching before "turning on"). AC is more efficient to transfer power over wires (think power lines - like high voltage AC at lower current vs low voltage AC at high current). The point is - the grid-tie inverters are providing power out as a regulated power to run equipment off of. In the case of varying power coming in to them - that is where the brains in the inverter really don't care what comes to them, as long as it is "enough power" (whether that is lower voltage, higher current, or higher voltage, lower current - doesn't matter within reason). 

The same theory is true for inverter style engine driven generators. The varying speed of the engine feeds power in to the inverter. Then only when the power consumption surpasses what the alternator is providing at idle does the engine throttle up to meet it - until it goes too high where the engine can't keep up.

So my assumption is that the pump controller runs the same way - it doesn't care what the power coming to it is (again, it is rated for up to 100 volts input). It regulates the output to a particular voltage. As to how it "knows" there is enough power coming in to turn on and run the pump - I don't know. Perhaps it uses the same sensing theory and pulses the output on. If the current draw tanks the voltage without enough power coming in to supply the current then it knows there isn't enough power? I would be curious to see. 



boatswain2PA said:


> I think you should come up with a more basic and cheaper product, market it, and become rich! lol


I'm not much of a designer for products. I like to experiment, learn, try things, and see things work. There is probably a reason why you don't see zener diodes commonly used in your application. Maybe not... Maybe it is "too simple" to be combined in to a "better product" for production. 

I bought a pack of zener diodes a while back - just real small ones. I want to say they are 5 volt zeners, only 1/4 watt or so. I will look and see if I can find them and a small motor from something. I would think the small diodes would fry pretty easy, but we'll see.


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## boatswain2PA (Feb 13, 2020)

I am thankful for people like you who can understand this stuff, and even more thankful that you spend your time trying to explain it to knuckleheads like me!


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## wy_white_wolf (Oct 14, 2004)

Your calculations are wrong. The pump will only pull 4 amps no matter the voltage. It just pumps less water.

You'll be lucky if the battery lasts the summer. 

There are setups meant to run solar direct without a battery. I'm currently running 2 such setups. One on my well to fill a cistern and one that pumps from the cistern to water the garden. Depending on the pump you are looking at you could possibly run it that way without a battery. Message the manufacturer to find out if you can.

A LCB ( linear current booster) does help in solar direct systems.

WWW


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## Heizen (Nov 7, 2020)

The solar charge controller can save your power module and system from early degradation. In its setup, it includes light-emitting diodes (LED), alarms, and beepers to notify users in the various stages of usage adequately.
Other LED components include low battery and battery full LEDs. These respectively indicate the health of the bank by lighting up low and high states of charge. A low battery LED suggests you stop or reduce the usage of the cell as soon as possible to save its eventual degradation upon drainage. Battery full LED, on the other hand, lets you know that battery is fully charged and ready to use.


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## MichaelK! (Oct 22, 2010)

Don't get a charge controller, get a pump controller, like what WWW is using. A charge controller takes solar power and uses it to charge a battery. A solar pump controller takes solar power and feeds it directly to the pump.


Amazon.com


Secondly, don't buy 12V panels designed for the automotive market. You'll get far more bang for your buck buying 24V grid-tie panels. Right now it looks like you can buy two 100W 12V panels for about 150$. I can buy 250W 30V grid-tie panels for 55$. With a MPPT charge controller, you can even use grid-ties to charge your 12V batteries. Buying 12V panels these days is a waste of money for anything that does not have wheels.


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