Will I Need a Battery?

[J.P.M.]

I use a solar fan for my shed. It used to be an attic fan in my last home but now works great for my 10 x 20 shed. The panel is only rated for 10 watts but the fan moves a lot of air during the day time.

The good part is that the fan and panel were a matched set so I never worried about over voltaging the fan motor.

An early thermal water heater design I worked on (as a hobby) way back in the '80's used a very early 12 V panel and a D.C. motor to power a pump. The idea was an attempt at proportional control of the flow rate. Part of the theory was sound but the available power density from PV at that time was inadequate for the flowrates required to get a turbulent Reynolds number or at least up into the transition zone. To get enough PV power at the time, the PV area would have been greater than the thermal collector area and not cost effective.

[SunEagle]

In the spirit of the KISS principle, seems like a thermostat and a fan powered off a.c. would be as good if not better for the application.

Just sayin'.

I use a solar fan for my shed. It used to be an attic fan in my last home but now works great for my 10 x 20 shed. The panel is only rated for 10 watts but the fan moves a lot of air during the day time.

The good part is that the fan and panel were a matched set so I never worried about over voltaging the fan motor.

[Ampster]

In the spirit of the KISS principle, seems like a thermostat and a fan powered off a.c. would be as good if not better for the application.

It all depends on where you are standing. In this case the thread is in the Off Grid section and the operative question was about whether the OP needed a battery. I was simply supporting the application of a Linear Current Booster which would be much simpler than adding a charge controller and battery.

[J.P.M.]

Years ago i bought something like that on Ebay that ran an attic fan. Worked great because the fan only had to work when the sun was bright.

In the spirit of the KISS principle, seems like a thermostat and a fan powered off a.c. would be as good if not better for the application.

Just sayin'.

[Ampster]

Years ago i bought something like that on Ebay that ran an attic fan. Worked great because the fan only had to work when the sun was bright.

[inetdog]

Google "Linear Current Booster" to see a circuit which is designed to provide the maximum possible pump output and avoid overvoltage, all without requiring a battery or charge controller.
It prevents the pump impedance from collapsing the pane voltage as the panel output drops below the nominal pump amperage, and instead delivers more current at a lower voltage to keep the pump running but at a lower speed. A secondary feature of many LCBs is the ability to set a maximum voltage to the pump. It may even be able to use the power from the extra voltage to produce an output current higher than the full sun panel current, Its operation is similar in some ways to a Charge Controller with Maximum Power Point Tracking.
LCBs are not cheap, but they are reliable and should have a long run cost lower than that of batteries and a CC.

[Mike90250]

Asterix - something to keep in mind, many folks visiting here need the very simplest, bare bones data. Don't assume they know what a complete circuit is, or how to safely disconnect an MC4 connector. And accurate terminology is mandatory for newcomers, so that we can all speak the same lingo. Then you mix in the RV crowd with their Converters.....

[sdold]

Given the comparative costs of buying a regulator and buying a cc, I personally would go for the CC, because it does a lot more than a regulator for a comparable cost.

A voltage regulator is part of a float charger powered by AC from a utility to maintain a float charge on the batteries for standby use during a power outage. Solar panels require a charge controller to regulate both charge voltage and current in stages. A voltage regulator isn't used as a solar charge controller.

[Asterix]

Incorrect. A charge controller is a lot more than a DC regulator. They often have several voltages they produce, at specifically timed intervals to provide the proper charging of batteries. Better ones will limit the current (amps) to prevent self destruction.

Asterix - please stop with the bad information. I don't know if you are just going on about stuff in ignorance, or trying to increase your post count, but your reputation for accuracy and safety is now Zero in my book.

Maybe I should have been more specific when writing that, a number of posts ago.

A charge controller is of course more than just a Voltage regulator, however the output/load can be considered as a regulator with safeguards. Given the comparative costs of buying a regulator and buying a cc, I personally would go for the CC, because it does a lot more than a regulator for a comparable cost.

[Mike90250]

A charge controller is a DC regulator. I tend to think a lot of people get tripped up on what they are calling
something, A charge controller is just a DC regulator rated at a certain current. ......

Incorrect. A charge controller is a lot more than a DC regulator. They often have several voltages they produce, at specifically timed intervals to provide the proper charging of batteries. Better ones will limit the current (amps) to prevent self destruction.

Asterix - please stop with the bad information. I don't know if you are just going on about stuff in ignorance, or trying to increase your post count, but your reputation for accuracy and safety is now Zero in my book.

[J.P.M.]

Next time you buy a pump, decide on the pressure required (how high you want to lift the water), and how high a flow rate will suffice, to do the job.

Power is key. An over large pump will just use more power.

I'd use pump curves that come with most any pump and don't forget to add pressure drop losses from friction to the static head.

Once head and flowrate for the application are determined, and depending on the application, some pump oversizing is often advisable and most usually/often unavoidable as exact head and flowrate capabilities of a pump will rarely both match the minimum application requirements. One or the other will be greater than required.

[Asterix]

Looks like the pump was physically damaged and had water ingress.

Next time you buy a pump, decide on the pressure required (how high you want to lift the water), and how high a flow rate will suffice, to do the job.

Power is key. An over large pump will just use more power.

[Asterix]

Well, the pump stopped working for some reason. Can't say that it blew. Before cutting it open I tested it on two car batteries and it wouldn't spin. It would spin by hand. It's marketed as a "galley" pump, so maybe it's not meant to run continuously for hours. Several days last week it did run continuously for several hours off a car battery. I was testing it to see how it would respond and what the water feature might look like. I ordered another one.
Idealy, I'll find a 12v pump that's designed as a "pond pump".

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Looks like it has disintegrated internally and has had water inside.

You really need to choose a pump for the task in hand and not do overkill. An example would be that a lot of pumps give flow rate but not head of pressure, which is the most important. No use having a high flow rate at a couple of feet, if you want to lift water 20 feet.

[Mike90250]

A galley pump is for pumping water to the kitchen sink in a boat. Usually for just a couple minutes. Something like a Bilge pump, which has an outlet hose connection, and you can dunk the whole thing in the water, is more like what you need

[LarryJ]

I am very surprised that it should blow your pump. A 12V pump should be able to withstand at least the 18V the solar panel could kick out on a very bright day.

Depends on the battery, put it across a car battery to try it out.

If you just want a solar powered pump, you could use a buck regulator, which you can pick up fairly cheap off ebay or amazon. For a 40W pump you will need to have a unit capable of 3.33A @ 12V

Well, the pump stopped working for some reason. Can't say that it blew. Before cutting it open I tested it on two car batteries and it wouldn't spin. It would spin by hand. It's marketed as a "galley" pump, so maybe it's not meant to run continuously for hours. Several days last week it did run continuously for several hours off a car battery. I was testing it to see how it would respond and what the water feature might look like. I ordered another one.
Idealy, I'll find a 12v pump that's designed as a "pond pump".

IMG_2143.JPG
IMG_2144.JPG