Solar Freaks

Hi Tony et al,

I'm putting together a system for remote fieldwork - a panel in the 13W range or so, that will charge a battery (likely 12V, though possibly 24V since my computer wants 20V in, and I figure just stepping down is easier than stepping both up and down). From what I've found online, MPPTs seem geared to high-power applications. I haven't found anything that's very small and low-power, though I can't think of any reason they couldn't be made. I'm thinking an MPPT would be nice in the field, as it would squeeze what I could from as small a panel as possible, given different loadings. Sometimes it would be nice to charge the battery and run some electronics all at the same time, for example, and that would change the loading on the panel, and hence its efficiency as well. Basically, an MPPT sounds like it would be nice for maximum flexibility.

Any ideas of where to pick up a small unit that I could then attach to some portable panels? Making an MPPT myself might be an option, but perhaps more involvement than I'm really looking for.

Thanks,
Allie

hello Allie, is the panel open 13v open circuit or 13v at the mpp?

Hi Tony,

Thanks for the reply. I don't have the panel yet - i was figuring somewhere around a 13 watt system. Maybe 12 or 24 volts at the output to the MPPT. But it's all open for negotiation now, since I have bought anything. Just trying to plan it out properly.

thanks,
allie

If you computer needs a 20v input, then use a 24volt panel. That way you just need to use a buck converter, and they are very efficient if designed well. If you have trouble finding a mppt for this, i can modify a FATMAX mppt unit to run well at lower power for you.

thanks tony. the fatmax looks like it's around 100mm x 40mm? With such a low power app, one should be able to get away with a smaller footprint, no? regardless, the modified fatmax sounds like one good possible solution.

what is the most common way low-power panels regulate themselves? hard to imagine it's just a straight output from the panel to the battery...

thanks,
allie

Have you seen the Easymax, that's only 30 grams and 40mm x 30mm. For smaller panels, they dont usually run mppts, they usually match the load to the panel, but for demanding applications, they run small mppts.

Hi Tony,

The easymax looks great. One question: it seems like you have to press a button to find the MPP. I plan on having my panels sit in the sun all day under changing light conditions, with changing battery voltage as it charges, or as it's used, and even connecting other devices in parallel. Is there any way to set the easymax to find the MPP on regular intervals, rather than having to press a button?

Thanks,
Alex

Well thats what the FATMAX does, its auto tracking. But the Easymax isnt auto tracking.
Im working on an auto tracking smaller unit, but it wont be ready for another month at least.

Hey Tony,

I'm in no huge rush - let me know when the new unit is out! I hope you'll find a good market for it - I haven't found any small MPPT solutions out there yet.

Thanks,
Allie

Hi to all at the forum,
I am searching for a project that will allow to charge a lead acid battery of 6Vdc using a panel of 40 Watt.
I read on this forum that the switcher shall have a mppt function too for maximum efficiency.
I would like to know if there is a project available to me to be used a s a referece : i will like to see a PIC source code for both MPPT , switcher , PWM etc... etc . The circuit diagram will be interesting too.
The 6 VDC battery is of about 10 A/h so the power is small !
It will be an hobby project mainly used for my radios.
Thanks in advance for any assistance.
Best Regards,
Ambrogio
IW2FVO
North Italy

Hello and welcome.

Just use a standard buck converter to keep things simple,
and use the PIC to read the input voltage and current.
Then just regulate the input voltage.

Don't worry about the output unless your worried about overcharging the battery.

cheers.

Hi Tony,
Thanks very much for the reply on the matter.
Is it possible to have a schematic diagram for the converter?
Any PIC application to control the converter ?
Any suggestion is appreciated.
thanks again Tony.

Regards,
Ambrogio
IW2FVO
North Italy

Allie,

I work for a company called Genasun that specializes in low-power/light weight MPPT. Hope this helps.

Alex

thanks hay4man. What's the difference between your low-power MPPT unit and the Charge Controller with MPPT? Is one just for low power, and the other for higher power?

thanks,
allie

Yeah, the main difference is the power rating. The lower power version is also lighter and smaller.

Alex

ok, thanks. so, what is it that makes these things as big as they are? the transformers?

Your guess is pretty good. The three biggest components in the low power product are the inductor, the capacitors, and the microcontroller. The low power version is about the size of a cell phone (but twice as thick).

It's possible to make these things really small, but that requires operating at higher switching frequencies, which is in general less efficient.

ok - thanks for the info. so in the end, it becomes of question of whether getting a bigger solar panel versus using an MPPT is more space,cost and energy efficient. Any ideas about that?

If your solar panel is well matched to your battery, i.e., if the battery voltage is very close to the max power point, the MPPT may not be cost efficient, but in a majority of situations, this is not the case.

Also, using a boost MPPT allows you to use a panel with an operating voltage lower than the battery voltage.

right - i plan on connecting various devices to the panel at different times - hence different loads, and the desire for the mppt. regarding stepping up the voltage, seemed like that was only available with the special unit on your webpage, not the low-power mppt.

thanks,
alex