Do I need a charge controller?

Tim360

New Member
I want to set up a simple solar circuit to power a 12V, 70W micro diaphragm pump. This solar system will not have a battery. My intent is for the pump to energize when there is adequate voltage from a single 100W solar panel and de-energize when the voltage drops. My concern is that excessively high or low voltages will harm the pump. So, I am wondering if my concern is valid and if so, how to protect the pump? Would a charge controller serve the purpose of voltage regulation or is there a better way of going about it?
 

gnubie

Photon Sorcerer
A charge controller could certain do it, but so could a buck regulator (most SCCs are buck). Where you'll run into problems is the stall current for the motor. Solar panels are more current oriented than voltage oriented, ie open circuit it takes little sun light to bring the panel up to full voltage but in very little light there will be very little current to prop the voltage up.

A simple voltage switch would see the panel voltage rise up to its turn on point well before the panel produces enough current to run the motor. The voltage will then collapse as the motor tries to start. Rinse and repeat as necessary, all the time with the motor windings heating up as panel power increases as the sun rises. Eventually the panel would produce enough current to allow the motor's draw to not pull the voltage down below the voltage operated switch's turn off threshold and in time enough to start the motor....all the while the windings keep heating up.

There are solutions to this, load resistors and sensing current flowing across them and once it rises to a point you decide, the motor is turned on and the load resistors turned off. Of course, these things already exist.

solar fan controller
solar pump controller
 

Tim360

New Member
A simple voltage switch would see the panel voltage rise up to its turn on point well before the panel produces enough current to run the motor. The voltage will then collapse as the motor tries to start. Rinse and repeat as necessary, all the time with the motor windings heating up as panel power increases as the sun rises. Eventually the panel would produce enough current to allow the motor's draw to not pull the voltage down below the voltage operated switch's turn off threshold and in time enough to start the motor....all the while the windings keep heating up.

Thank you for the explanation, that makes a lot of sense. If I understand correctly, a charge controller would work and solar fan/pump controllers may work better. It's not clear to me if a charge controller resolves the issue of insufficient amperage or not. A cursory look at fan/pump controllers reveals that they are much more expensive than a small charge controller. The charge controllers are also much more readily available at my location.
 

gnubie

Photon Sorcerer
The SCC won't solve the current problem as it expects to be providing power to a battery where low current isn't an issue. There may be SCCs out there that can test the current and if it can't hold the voltage at the desired current turn the output off for a period and retry, but I'm not aware of them.

The solar fan / pump controllers monitor both and only turn the motor on when the power from the panel allows the controller to supply the current you set at the voltage you set. There's people on the forum that might be able to give you a specific controller to do the job that isn't as expensive so keep an eye on the thread.
 

Tim360

New Member
SCC won't solve the current problem
Hmmm, okay. Instead of trying to re-invent the wheel, maybe it's better to just use a charge controller with a battery and a timer to prevent the battery from over discharge. There may be cheaper solar fan / pump controller as you mention but it looks like I would have to import one and that essentially doubles the price and delays the project. I was hoping to keep it real basic but it sounds like life will be better with these additional components (charge control, battery & timer). Thanks for your advice and I will stand by for other ideas.
 

efficientPV

Solar Addict
100W panel is pretty light for a 70W load. At best this will run two hours a day. You must over panel to use a buck converter. Buck converters send the panel voltage into a death spiral when it asks for more power than the panel can provide. This is not a very difficult electronic problem, but probably far too complicated for about everyone. One solution is a separate pilot panel that measures sun intensity going to a voltage switch. When there is enough sun, the pump turns on.
 

efficientPV

Solar Addict
Just s 4 x 4 inch panel from an old solar garden light would be enough. It has to be loaded with a resistor to make it linear. In good sun rmeasure the voltage and add a resistor so it drops to 50-75% of unloaded reading. A cheap voltage monitor relay can be powered by the main array and the little panel goes to the sense terminals.
 

SolarQueen

Making renewable do-able at www.alteStore.com
A charge controller gets its power from the battery, it will not work without one. What you are looking for is a Linear Current Booster (LCB), or a pump controller. It will raise the current in the morning to help give it the boost it needs to get started.
 

gnubie

Photon Sorcerer
Don't forget that the panel power must be matched to a degree to the requirements of the motor to avoid excess voltage being applied. 250W of panels with a Vmp of 21V applied to a small 12V motor wouldn't end well. A regulator means less attention needs to be paid to this since it will ensure the motor never receives more than 12V.
 

Tim360

New Member
A charge controller gets its power from the battery
I hadn't considered that the charge controller gets it's power from the battery. Sounds obvious now that you mention it. My intent in this project was to keep it very simple and economical by compromising on functionality. Based on all of your advice, it now appears that a charge controller and a battery is the simple and most economical solution. Thank you for your advice and knowledge.
 

LarryJ

New Member
I want to set up a simple solar circuit to power a 12V, 70W micro diaphragm pump. This solar system will not have a battery. My intent is for the pump to energize when there is adequate voltage from a single 100W solar panel and de-energize when the voltage drops. My concern is that excessively high or low voltages will harm the pump. So, I am wondering if my concern is valid and if so, how to protect the pump? Would a charge controller serve the purpose of voltage regulation or is there a better way of going about it?

You and I have similar situations. I'm still trying to solve mine. https://diysolarforum.com/threads/electrical-control-advice-needed.12710/#post-141760 .
I'm following your thread.
 

efficientPV

Solar Addict
You can not look at panel voltage to determine if there is enough sun to run the pump. This varies too much with load current. A small loaded solar panel (like from a garden light) or a photo resistive cell must be used to determine sun intensity. Unless you only want the pump to run for two hours a day, you will need a panel four times larger than the than the pump needs. That solution is generally a grid tie panel which is also much cheaper. A buck converter will bring that down to 12V and also boost current. A very simple electronic problem, you just can't buy it from Amazon.
 

ZmAn3

New Member
Not to hijack a thread but if any of you point can me to some good videos or instructions on helping with the following. I have a extra 20 gallon water heater and I want to do pex tubing hot water floor heating under this little crappy 14ft by 14ft guest house I live in. I understand the concept of using a dc element to heat the water and a 12 volt pump to circulate it I think...., my problem is obviously you dont want to run the pump all the time how would you control that? should I find some 12 volt temp sensor so if it goes below x under the house then the pump kicks on till X? Thank you
 
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