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PostPosted: Feb 13th, '13, 08:41 
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I have recently aquired some solar panels. Unfortunately they are 170w at 36v. I wish to run my pump during daylight hours using these, its 240v 100w.
I may have a chance at a DC to DC converter then use a small inverter to kick back up to 240v
Or a mppt Regulator (but I'm not sure if I can connect the small inverter directly to this)

If anyone has any thoughts on this or another way to do it I would appreciate their comments.


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PostPosted: Feb 13th, '13, 08:44 
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If the mppt controller can charge a 12v battery directly then you are laughing. If the mppt controller will output 37v the you will need a converter. I am guessing that once you put a load on that panel it will drop closer to mid 20v somewhere....

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PostPosted: Feb 13th, '13, 08:53 
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The DC to DC is a marine one for batteries or wind turbines reducing volts to 12 300w (currently on ebay)

The MPPT Regulator is designed for charging 12v-36v batteries 30 amps max (also on ebay)

I have more than one panel so upping the voltage or amperage is possible.


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PostPosted: Feb 13th, '13, 09:10 
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To be quite honest with you, if you are not planning on charging a battery i would just get the cheapest solar controller you can and run the DC to DC converter. The MPPT benefits would only be utilised for a very short period of time. You may even find that it wont work with a battery connected. My controller will not turn on till a battery is connected.

If the DC to DC converter can take a wide input voltage, say 24v - 40v and output 12v that is what i would do.

If you want your pump running at night then you will need some way to change the pump to mains at night also.

You are essentially doing what i am planning on, run on solar during the day then i will run on mains at night. My solar controller will cut off the load to protect the battery, so i am going to have a 12v contactor to switch over to mains when the controller kills the load...

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PostPosted: Feb 13th, '13, 09:42 
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Thanks rsevs3 :)

The only reason I was going to go MPPT, was the cheap controller regulators don't seem to be able to handle the higher wattage/voltage panels and seem designed for the 12 or 24v panels.
Just need to run the pump daylight hours.


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PostPosted: Feb 13th, '13, 10:55 
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I'd go solar -> mppt regulator -> battery, and also mppt load output -> 12V pump. This would be the most efficient. If you absolutely must run the 240V pump then get an inverter, but it won't work as well as a 12V pump.

The battery will help stabilize the system -- you don't need a very big one. Get one that can handle many cycles and deep discharge. The MPPT controller will protect it from over discharge.

Definitely go an MPPT controller, it's the critical part in your system.

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PostPosted: Feb 13th, '13, 12:51 
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If you have a 170W panel running a 100W load only then MPPT will do nothing for you except extend the running time marginally. If you are planning on utilising a battery then MPPT would be a worth while investment.

Although if you have more than 1 of those panels, it would be worth while considering adding some batteries. :)

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PostPosted: Feb 13th, '13, 14:06 
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rsevs3 wrote:
If you have a 170W panel running a 100W load only then MPPT will do nothing for you except extend the running time marginally.


I'm pretty sure that an MPPT controller will keep the solar panel at its peak power producing voltage, something a DC/DC converter will not do.

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PostPosted: Feb 13th, '13, 14:40 
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Not a lot of run time with that pump.... Any chance of getting a lower wattage pump?

Personally we went 12V pumping here with our system, went through 2-3 cheap inverters before giving up on 240V..

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PostPosted: Feb 13th, '13, 15:42 
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nebbian wrote:
I'm pretty sure that an MPPT controller will keep the solar panel at its peak power producing voltage, something a DC/DC converter will not do.


You are absolutely correct nebbian. My understanding is that a MPPT tracker will impedance match the solar panel. If your solar panel is already producing more than your load can use, there is no value in increasing your output. The only time the increased output would keep you running is for a while at the start and the end of the day. If you think that small amount of time is enough to justify the cost then go for it :thumbright:

If Sleepe was planning on adding batteries to the system then yes, definately get yourself an MPPT controller. He would still need a DC to DC converter, unless he can find an inverter that will run from 37v.

Here is a good video comparing them. By looking at that video, you may need a converter anyway :dontknow:



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PostPosted: Feb 13th, '13, 16:36 
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rsevs3 wrote:
He would still need a DC to DC converter, unless he can find an inverter that will run from 37v.


I think you misunderstood the video here. Those measurements were taken between the solar panel and the controller, not on the load output. Note that an MPPT controller is actually a specialised DC - DC converter, so that's how you can have a higher voltage than 14v on the solar panel without frying the battery.

Note that a 37v panel is 37v open circuit, under load it would be around 28 or so volts. The MPPT controller will turn that 28 volts into 14 volts (at higher current) for the inverter to use.

In fact you may absolutely need an MPPT controller due to the high impedance and high voltage of this panel -- you may only get 80 watts or so (less than the pump uses) if you try using any other type of regulator.

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PostPosted: Feb 13th, '13, 17:06 
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I think this qualifies as a question for the solar experts ...

My panel is 230 watt, 37v, and 8 amps acording to the specs on the back, but when that's converted to 12v, I think that's 19 amps, I've just bought a 20 amp MPPT solar charge controller , so I should be ok either way, but does that 20 amps mean I could double up on the panel, or that I'm just under the limit. ie Am I at 10 amps of 20 max, or 19 amps of 20 max?

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PostPosted: Feb 13th, '13, 18:00 
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Which brand / model is the mppt controller BW?

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PostPosted: Feb 13th, '13, 18:17 
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nebbian wrote:
I think you misunderstood the video here. Those measurements were taken between the solar panel and the controller, not on the load output. Note that an MPPT controller is actually a specialised DC - DC converter, so that's how you can have a higher voltage than 14v on the solar panel without frying the battery.

Note that a 37v panel is 37v open circuit, under load it would be around 28 or so volts. The MPPT controller will turn that 28 volts into 14 volts (at higher current) for the inverter to use.

In fact you may absolutely need an MPPT controller due to the high impedance and high voltage of this panel -- you may only get 80 watts or so (less than the pump uses) if you try using any other type of regulator.


The reason i posted the video was to show how much extra power you get from MPPT. That is an excellent video to compare them IMHO. Also, it may be a 36v panel. Sleepe measure the open circuit voltage so we know what kind of controller to help you with :)

Typically, when i was looking at MPPT i could not find one that would convert 24v down to 12v. First search today and i find one. That is one way you could go. My PWM one will output about 70W from a 110W panel. Not ideal, but less than 1/5 of the cost of a MPPT tracker too.

BW, the spec sheet for the MPPT should have a wattage rating too.

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PostPosted: Feb 13th, '13, 21:59 
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Looking...

I so* hope I haven't bought the wrong thing

This was one of those purchases that was lubricated with single malt scotch.

It seems I have also cornered the world market on blue LEDs.



*Does one put a comma somewhere, when using the word "so", in that way? :)

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