PV Powered DC Pump Controller

Solar Mike

New Member
I need something to startup our solar powered water pumps in the mornings as the sun come out.
The magnetic drive pumps will be direct connected to a PV panel approx 50 - 180W and run continuously as long as the sun is shining, some run off 24v and others 12v dc; each voltage type has its own panel.

Problem is at low light levels the panel cannot supply the starting current to get them running and will sit for some time in a stalled state drawing current in one winding rather than being shared, so its not good for the pump.

There are a number of simple solutions out there on the net, using a comparator and a bank of electro's, the higher current devices are expensive and dont have any timing features, or the range of voltages, so its easier for me to just quickly throw something together and send off the gerbers along with a bunch of other boards.

Here is the schema for a simple design using a Picaxe 08M2 for pump control, will pickup any errors when the pcb is designed.

Cheers
Mike


24427
 

premelec

Senior Member
or time for a modest size ultracapacitor - I have zone valves that have worked for a decade which use ultracaps to shut when power is removed [Taco ESP] - I think they make higher voltage stacks now... or lithium battery string with BMS - I guess it could depend on how important starting in cloudy conditions is...
 
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Solar Mike

New Member
The pumps have no external power other than PV panel, they supply a wet area during the day, where the plant cuttings would suffer on a hot day. Its always cloudy here 50% of the time, but you can still feel the heat from the sun. Once a pump starts, it will still run at reduced capacity at a lower voltage, but wont start at that voltage. Water is pumped from a nearby stream through the wet area that then drains back into the same stream in purer cleaner form.
 

premelec

Senior Member
Hi Mike, I'm curious about what pump you are using.. and thinking about the reliable start under low sun conditions... perhaps using current amplifier [switching down converter for soft start]. I have some salvaged thermal panels in my yard that I am thinking of running for DHW preheat... thanks...
 

Solar Mike

New Member
Hi Mike, I'm curious about what pump you are using.. and thinking about the reliable start under low sun conditions... perhaps using current amplifier [switching down converter for soft start]. I have some salvaged thermal panels in my yard that I am thinking of running for DHW preheat... thanks...
There are a plethora of brushless DC magnetic drive circulation pumps out there, for low flow hot water applications as used in solar hot water panels this type works well TopsFlow, there are better ones around like the ELSid range made in the USA. The ones on aliexpress or Bangood are pretty cheap, we have used these in the past Link, the cheaper ones will only run to 60c or so, and are not suitable for solar heating applications, we use them for cold water. Davies Craig in Australia make a range of dc magnetic drive pumps for hot water systems in cars, they are very reliable, I have had one running 8 hrs a day for the past 10 years with no failures, pumping water though 8 Sqm panels on the roof. They have a life of 20,000 hours +.

Cheers
Mike
 

matchbox

Senior Member
@Solar Mike, nice project :)
I too had a similar issue with my solar tracker actuator drive some years back. The amount of damage solar panels can do to a motor or drive circuit is considerable, when power output is in the range where its not produce enough power to start up.

One morning after a big frost, the actuator and its motor was loaded up with ice and the panels weren't getting much sun due to cloud cover.
But there was just enough power available to heat up the drive FET's and de-solder them off the board.

I ended up re-designing the board and program, to take into account current sensing, voltage drop load, light intensity and drive time.
 

premelec

Senior Member
@mike thanks for the refs - I am impressed with the lack of data with regard to electrical inputs on small pumps - mostly just flow, head, temperature max. However a great variety of old style circulation models available at low price... empirical it is!
 

Solar Mike

New Member
Those small pumps I referred to, all draw approx 1 - 1.2 amp @12v, the Davies Craig has full spec's if you go to their web site, so are quite suited to run off a small pv panel.

About the simplest setup for a solar hot water system is connect the pump to the PV panel, whenever the sun is shining, its pumping hot water though the water heating panels into your HWC.

Cheers
Mike
 

premelec

Senior Member
Thanks... I'm thinking of a drain back system which would allow fluid flow through pump when it is OFF and establish siphon when on.
 

Solar Mike

New Member
Thanks... I'm thinking of a drain back system which would allow fluid flow through pump when it is OFF and establish siphon when on.
Those small pumps only have a head of 3m approx, which is fine in a closed loop system where the only "head" is the flow resistance in the pipes. However in a drain-back you have the initial height from the pump to the highest point of the panels, so may require a bigger pump than expected.

The suggested one way check valve isnt required on a drain-back, but is on a closed loop to prevent heat loss from the HWC at night due to reverse thermo-syphoning, the better type to use here are the brass swing valves as these have the less water resistance and work with near boiling water.

Mike
 
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