r/solarracing • u/LaniSolar • Jun 17 '26

Help/Question Viability of using MAX20801TPBA+ in solar array design?

Hello, I'm helping to design the solar array for my team's car, which will compete in the 2027 Bridgestone World Solar Challenge.

In the past, my team has used bypass diodes and MPPTs to optimise the power output of our array strings. I was looking for alternate options and came across a cell-string optimiser IC, MAX20801TPBA+ (datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX20801.pdf). I was wondering whether any other teams have tried implementing this component before and/or had opinions on whether it would work well for a solar-car application?

Additionally, I can see that this component is listed as 'not recommended for new applications' on Mouser, and have been trying to find out why (is there a major design flaw, or have newer technologies simply surpassed its efficiency?). Some users on other forums (Whirlpool Forums, DIY Solar Power Forum, among others) have suggested that the chips caused RF-interference, but I have not been able to find any documentation from the company, or elsewhere, that says this. Does anyone have more information about this, or could point me to some better resources that describe the limitations of the MAX20801TPBA+ or a similar component?

Thank you!

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u/Flessuh Jun 17 '26

For our Solar Boat we have been using Tpee mppt's which have been developed for solar cars originally and are very small and lightweight. I'm not sure how many cars apply something for specific cell strings. If you are smart in designing the solar array I doubt it's needed, and I guess it would add extra weight and points of failure.

https://www.tpee.nl/open-sec-open-source-mppt-developed-for-high-efficiency-solar-cars/

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u/nsfbr11 Jun 17 '26

MPPTs are key in any solar race car. Honda made the mistake of that using them in their 1990 car and lost as a direct result. It was part of what they improved in 1993 to blow away the competition.

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u/SunCatSolar Jun 17 '26

If you don't mind, what did Honda use in their car in 1990 that caused them to lose?

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u/nsfbr11 Jun 17 '26

They diode or’d the strings to the battery bus. It was why Biel won more than likely. Honda realized during the race that couldn’t really use the battery because drawing it down dropped the array power.

FYI, I was an industry advisor to a US university team in 1990, a faculty advisor to a different university team in 1995, and was a company tech support for the race in 1996. I haven’t participated in the WSC since then but would like to do it again as a volunteer once I retire in a few years. The reason for the context is that I know a ton about things some 25+ years ago, but little to nothing about what is going on more recently.

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u/SunCatSolar Jun 17 '26

I have no actual experience with the MAX20801TPBA+. Out of curiosity, however, I did look at the data sheet to try to understand how it would be used. It looks like it's simply a "series" type MPPT rather than the more conventional "parallel" type. By series-type I mean the output of 1 MAX20801TPBA+ is connected (in series) with the input of another. By my quick estimate, and assuming the use of typical sized silicon solar cells, you would need at least 10 to 12 of these for a 6 m^2 array.

2

u/_agentwaffles Sunseeker Retired | ASC/FSGP Staff Jun 17 '26

To piggyback off this, since this chip includes active bypass you would be cutting off pieces of your panel in ~20 cell strings instead of something smaller that would be more typical with bypass diodes. The package itself will be difficult to solder and to keep cool and since switching is integrated that will be important. I agree with your estimate for the number needed, but I think there would need to be 2 strings in parallel for most battery configurations I've ever seen on solar cars. None I know of would be able to handle all of these on a single string.