Cheap MPPT controller

[n4mwd]

Does anybody know of a cheap (< $50) MPPT-like solar charge controller? I was looking at the MPT-7210A that is all over ebay, but upon further review, it is a boost converter and doesn't work for normal buck converter operation. That is, it needs panels to be lower voltage than the batteries. In this particular application, I have a 36V panel and a 24V battery. I don't want to go PWM because it would waste half the power.

I said "MPPT-Like" above because I know getting a real MPPT controller at that price would be unlikely. So I would be happy with a buck style converter as long as it doesn't blow up my lithium batteries.

 

[Bob142]

Does anybody know of a cheap (< $50) MPPT-like solar charge controller? I was looking at the MPT-7210A that is all over ebay, but upon further review, it is a boost converter and doesn't work for normal buck converter operation. That is, it needs panels to be lower voltage than the batteries. In this particular application, I have a 36V panel and a 24V battery. I don't want to go PWM because it would waste half the power.

I said "MPPT-Like" above because I know getting a real MPPT controller at that price would be unlikely. So I would be happy with a buck style converter as long as it doesn't blow up my lithium batteries.

Can you please post the full specs or a link for the panel and battery?
There's usually a sticker on the panel that'll tell us what we need. That's sometimes true for the battery as well.

 

[n4mwd]

Can you please post the full specs or a link for the panel and battery?
There's usually a sticker on the panel that'll tell us what we need. That's sometimes true for the battery as well.

320 watt 36 volt panels. 24V Lifepo4 battery pack.

I would settle for a 10A unit and take a small loss. 10A x 24V = 240W. or 15A x 24V = 360W.

I've seen some super cheap ones on ebay that do 5A. Parameters are set by triimpots. Allegedly they do both CC and CV.

 

[gnubie]

You can be pretty much assured that the units that use trimpots have no smarts in them and will run the panel off Vmp relying on your battery's present resistance to be reasonably matched with the power from the panel to try to keep it near Vmp, ie it likely won't be anywhere near Vmp.

You might as well use a PWM controller.

 

[Bob142]

320 watt 36 volt panels. 24V Lifepo4 battery pack.

I would settle for a 10A unit and take a small loss. 10A x 24V = 240W. or 15A x 24V = 360W.

I've seen some super cheap ones on ebay that do 5A. Parameters are set by triimpots. Allegedly they do both CC and CV.

Can you please post the full specs or a link for the panel and battery?
There's usually a sticker on the panel that'll tell us what we need. That's sometimes true for the battery as well.

What's the Voc, Vmp, Isc, and Imp of the panel? (from the sticker or the specs on the website etc)

What is the Ah rating for your 24V LFP battery, max charge current etc? (a link would be helpful)

 

[shavermcspud]

Why would you spend decent money on an LFP pack and cheap out on the SCC? surely you want to protect your investment of the Batteries?

 

[n4mwd]

What's the Voc, Vmp, Isc, and Imp of the panel? (from the sticker or the specs on the website etc)

What is the Ah rating for your 24V LFP battery, max charge current etc? (a link would be helpful)

The battery pack isn't built yet, but should be about about 40AH at 24V.

The panel is Canadian Solar CS1H-320MS.

 

[n4mwd]

Why would you spend decent money on an LFP pack and cheap out on the SCC? surely you want to protect your investment of the Batteries?

To keep the cost down. I may have to use the MPT-7210A in boost mode and use a 48V pack instead.

 

[SolarQueen]

The battery pack isn't built yet, but should be about about 40AH at 24V.

The panel is Canadian Solar CS1H-320MS.

That's a 72 cell, 24V nominal solar panel, designed to charge a 24V battery. Voc of 43.3V. You can use a quality PWM charge controller for that, as long as it has the right voltage outputs for your lithium battery.

 

[Bob142]

Oh it's on now! @SolarQueen is here. Sit up straight and pay attention!

 

[Bob142]

I'm gonna throw this inexpensive Epever MPPT out there again for consideration. It's now listed at $62 but should do better than a PWM. It's the version with the lower max voltage but your panel is well below the 60V max.

20A 10A Epever MPPT Solar Charge Controller 12V/24V Battery Regulator Max PV 60V | eBay

Battery Temperature Sensor Epever Monitor Adapter RS485/USB Communication Cable. when the internal temperature reach 81â, the power reduction mode will be turned on. MPPT 1000W Grid Tie Inverter For 18V/36cells Solar Panel AC110V SolarEpic Power.

www.ebay.com

 

[n4mwd]

That's a 72 cell, 24V nominal solar panel, designed to charge a 24V battery. Voc of 43.3V. You can use a quality PWM charge controller for that, as long as it has the right voltage outputs for your lithium battery.

Thanks, I'm pretty sure they are 35.5 or 36V. The panel is only 9 amps so a PWM would ony give 9 amps at 29.2V (LIFE charge voltage). It might be better to go with a $15 PWM with a different panel that is better matched for 24V LIFE batteries

 

[SolarQueen]

Thanks, I'm pretty sure they are 35.5 or 36V. The panel is only 9 amps so a PWM would ony give 9 amps at 29.2V (LIFE charge voltage). It might be better to go with a $15 PWM with a different panel that is better matched for 24V LIFE batteries

The Vmp is 35.8, the Voc is 43.3V. That panel is perfectly matched to a 24V battery bank. Pay for a quality charge controller, it will be worth it. Don't cheap out on one of the most important components. PWM or MPPT will be fine for one panel, but get a quality one.

 

[Dzl]

Does anybody know of a cheap (< $50) MPPT-like solar charge controller?

I said "MPPT-Like" above because I know getting a real MPPT controller at that price would be unlikely.

I would question whether there is such a thing as "MPPT-Like"

From what I've seen, there are:
1. MPPT controllers (and within this higher and lower quality MPPT controllers)
2. PWM controllers
3. PWM controllers that slap MPPT or MPT on the label, muddying the waters and intentionally misleading customers

Is there really any middle ground here? (honest question, I suspect not, but I don't know, I haven't ever looked into the lower end of the SCC market).

 

[n4mwd]

I would question whether there is such a thing as "MPPT-Like"

I call the controllers that use a simple Buck converter "MPPT-Like". They work, but you don't get the same kind of efficiency that you would from a real MPPT controller that uses multi-step transformers. If you open one up and there is a big toroidal coil in there with two wires coming off of it, then its a buck converter and "MPPT-Like".

Buck converters can take higher panel voltages and bring them down to a proper charge voltage and increase the current, but they tend to be in the 85-90% efficiency range, whereas the real ones are in the 98-99% range.

 

[gnubie]

There is that bizarre 7210 thing. It is MPPT but not as we know it, the M stands for manual if anything.

It has all the requirements to do real MPPT but who ever bodged the bizarreness into it didn't have the nous to open up a Google search and find a free open source tracker algo and add that. It'll never be fixed (never is a long time but I'm confident based on it not being done so far) as enough people buy and believe it works, even when they can see the readings on their multimeters etc that show it doesn't.

 

[Dzl]

I call the controllers that use a simple Buck converter "MPPT-Like". They work, but you don't get the same kind of efficiency that you would from a real MPPT controller that uses multi-step transformers. If you open one up and there is a big toroidal coil in there with two wires coming off of it, then its a buck converter and "MPPT-Like".

Buck converters can take higher panel voltages and bring them down to a proper charge voltage and increase the current, but they tend to be in the 85-90% efficiency range, whereas the real ones are in the 98-99% range.

I've heard real world conversion efficiency for top quality MPPT (such as Outback, Morningstar, Victron) is in the 90-95% range, so if 85-90% is real world conversion efficiency with a simple buck converter, that ain't half bad.

 

[gnubie]

Don't forget that a regulator will not attempt to sit at Vmp. Of itself it may present 90% of what is on its input on its output, but if its input is reduced to 60% of the panel's output because it's not on Vmp and the load on the buck regulator sinks sufficient current to pull the panel down or light enough to let it float up to that point its not much chop. That's fine if the regulator is running a load that allows the panel to always produce sufficient voltage at the demanded current to run the situation but for anything else, such as battery charging, mismatched load etc, it sucks.

 

[Dzl]

Don't forget that a regulator will not attempt to sit at Vmp.

Isn't this really the primary advantage of MPPT?

What would be the advantage of a buck converter over PWM assuming matched battery and panel (like OP has)?

Wouldn't a PWM controller perform similarly to or outperform a simple buck converter (with its 5-15% conversion loss) if the buck converter can't do any MPPT'ing?

 

[n4mwd]

I've heard real world conversion efficiency for top quality MPPT (such as Outback, Morningstar, Victron) is in the 90-95% range, so if 85-90% is real world conversion efficiency with a simple buck converter, that ain't half bad.

i just looked up victron to be sure, but they claim 98% efficiency.

Both mppt and mppt-like controllers also use PWM (not PWN) internally to modulate the voltage, but the circuitry is totally different. With MPPT, you can have a series string of panels totaling 600V @ 1 amp and the controller will convert that into something like 14V @ 42 amps. With a PWM controller, the same 600V string would only give you 14V @ 1 amp.