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MPPT controller for custom trike

September 13, 2024 — BarryK

The custom recumbent tadpole trike project cotinues. Here are recent blog posts:

...that last post describes the frame on which the solar panel will be affixed. There is now framework underneath on which to attach the MPPT battery charge controller.

The voltage from the solar panel is lower than the LFP battery, requiring a "boost" controller. This is the opposite of a "buck" controller, which is for charging a battery with lower voltage than the panel. The solar panel is nominally "24V" and the battery "48V" LFP.

Over the years, I have bought a lot of these controllers, both types. I have tested buck controllers that claim to be MPPT, but aren't. MPPT means "Maximum Power Point Tracking"; the peak power point, that is, the voltage and current, out of a panel varies with temperature and insolation (light intensity). That peak power voltage and current drops as temperature rises; I don't have figures off the top of my head, but I recall about 0.5% power drop for each 1 degree Celsius rise.

Over the last couple of years, I have purchased four boost controllers, and had the intention of doing a comparison test, but never got around to it. Anyway, the first one I bought is the Juntek MPT-7210A:

https://www.aliexpress.com/item/32871591762.html

img1

What raised my suspicions about this controller is that the solar panel voltage has to be set manually. I searched online and found a couple of people commenting that this is not a MPPT controller, despite the claims. Yes, it does track, but it tracks the fixed voltage; that is not MPPT. I must emphasize though, that I haven't tested it and have not verified that it is not a true MPPT controller.

I have three other boost controllers that are genuine MPPT, albeit determined from the specs and reviews, not from personal experience yet. The next one I bought, that I thought would be great for the trike as it is fully sealed, the elejoy 400W step-up:

https://www.aliexpress.com/item/1005005762970289.html

img2

Later on, found another, that I couldn't resist buying, the Lensun 550W buck-boost controller:

https://lensunsolar.com/collections/solar-controller/products/lensun-buck-boost-solar-controller

img3

...more expensive than the others; it cost me AU$130 including AU$25 shipping.

Lensun claim that this is both a buck and a boost controller. As a retired electronic engineer, I know that this is technically possible, but very unusual. Unique at that price. Again though, I must emphasize that I haven't verified the claim.

I have another boost MTTP controller, rated at 600W. Leaving that out of consideration for the trike, as the solar panel is only rated at 200W -- likely only to deliver about 160W based on past experience -- but then, this panel does look like from a reputable manufacturer and actual output might be closer to the rating.

Of the three contenders, only two of them are true MPPT controllers. I have built framework under the solar panel frame so as to be able to mount either, the elejoy or the Lensun. Might get around to comparing them, but for now, have put the Lensun controller on the trike.

A downside of the Lensun is that it is not sealed, so probably not a good idea to ride the trike while it is raining; at least, not without affixing some weather protection around the controller. Though, there would only be a problem with rain blowing under the solar panel frame while riding.

Yes, the Lensun controller is mounted under the solar panel frame:

img4

...it is mounted so that I can see the front display while seated.

Notice the switch beside the controller; that is to disconnect the solar panel. Probably not essential, but I thought might as well put it in (note, there will be a circuit-breaker between the controller and battery). Yet to be wired up; the black twin cable shown in the photo goes down the vertical tube and to the battery.

Coming along, slowly but surely!

EDIT 2024-09-14:
I posted above that the Lensun controller cost me AU$130. I wondered if it is available cheaper elsewhere. It seems that Lensun is a USA company and the controller is manufactured in China. I found it on Amazon and also another brand, "SolarEnz":

https://www.amazon.com/Controller-Lead-Acid-LiFePO4-Batteries-Electric/dp/B0B74HF4X3

...no mention of it being both buck and boost, nor mention of extended input voltage above 50V. But perhaps the external box is the same and Lensun have purchased it with different internals.

I wondered if it is available direct from China, and made an interesting discovery, this for AU$48 including postage:

https://www.aliexpress.com/item/1005007612832046.html

...notice that some labeling has been blacked out. Ha ha, I'm very curious, tempted to buy it just to see what the labeling is. Perhaps it is one of the models manufactured for a reseller and the vendor doesn't want to show that.    

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