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How to test/characterize cheapo Chinese ‘MPPT’?

fafrd

Solar Wizard
Joined
Aug 11, 2020
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I purchased one of the super-cheap deck-of-cards-sized blue MPPT last year and sent it right back - it was clear it could never handle the 30A it was supposedly rated for.

These just showed up on Amazon and I couldn’t resist checking one out: https://www.amazon.com/gp/aw/d/B07P7GQ3MF?psc=1&ref=ppx_pop_mob_b_asin_title

This is a much more solidly built unit, only rated for 15A (and max Voc of 100V), and when I peak inside it’s got two honking-big inductors so I’m hopeful it is an actual MPPT and not a PWM.

I’ve got a month to decide whether I’m keeping it or not do I’d appreciate any advice on things to test and/or look for.

An Epever Tracer 2210AN is certainly a safer/more reliable choice, but for less than half the price, I couldn’t resist at least checking out this Jasmint Power SPT: https://m.aliexpress.com/item/32890260446.html

Long-term reliability is obviously a risk that can’t be avoided, but in terms of these cheapo MPPTs being deficient, what are some of the things to test / look for?
 
A good test is when charging with solar, you should be able to measure the PV input voltage at the terminals and see it is in the vicinity of the panel series Vmp. If it's the same or slightly higher than battery voltage, it's a lying liar who lies and is likely a PWM controller.
 
A good test is when charging with solar, you should be able to measure the PV input voltage at the terminals and see it is in the vicinity of the panel series Vmp. If it's the same or slightly higher than battery voltage, it's a lying liar who lies and is likely a PWM controller.

Yeah, I’d already thought I’d hook it up to a panel and see what it does. Seeing those 2 big inductors makes me pretty sure it is an MPPT, but that doesn’t say anything about how accurately it gets to ~Vmp.

In terms of testing whether it delivers the 15A of charge current it’s rated for, I suppose as a fall-back, I could always charge a drained battery for 2 hours during the most productive part of the day and then drain the battery to see whether it was charged to ~30Ah or not...

For the 100V Voc max, my supply maxes out at 30V, so I suppose I could connect that supply in series with a panel @ Voc of ~50V and see what happens (magic smoke or not, still functions properly afterwards or not).

The manual states that the 15A model can be connected to a PV array of up to 1152W (295% of the maximum charge power of 390W), so I suppose I could also hook up 2 380W panels in parallel and see what happens...

If I connect it to 2 380W panels, it ought to saturate at 390W (15A @ 26V) for a good 6 hours so I should even be able to see how it handles conversion from CC to CV as well as conversion from CV to Float when charging my little 90Ah 24V LiFePO4...

Might as well stress it and see whether it’s worth the $40 I paid.

Any other thoughts/ideas appreciated.
 
If you have a benchtop power supply (or a couple of solar panels) give it 50v in at 5a or so and if the output at 12v nominal is greater than the 5a incoming it has some degree of MPPT....
 
If you have a benchtop power supply (or a couple of solar panels) give it 50v in at 5a or so and if the output at 12v nominal is greater than the 5a incoming it has some degree of MPPT....

My bench supply maxes out at 30V and the only battery I have available is 24V.

But the solar panel I have available has Vmp of ~40V so if I can rig that up outside for a test, I should be able to confirm it’s a true mppt...
 
I’ve got 2 MPPTs, a 30A HQST model and now this 15A Jasmint SPT.

Comparing the manuals, the HQST has a ‘Lithium’ battery setting while the SPT only has Sealed, Gel, Flooded and User battery types.

The User type allows Equalization Duration to be set to 0 minutes so I believe it can be disabled and both MPPTs allow boost duration to be set, but are there any other specific settings I should look for to be sure this cheapo MPPT will be OK for LuFePO4?
 
For cycling operations, ANY charger can work if it can be set as follows:

14.6V max bulk/boost/absorption
13.6V max float
equalization voltage disabled OR set to same as bulk OR equalization time of 0
Absorption phase can be limited to 2-3 hours, preferably 30 minutes.

IMHO, the above is optimal. If a canned LFP program does not meet those criteria, USER settings should be used instead.
 
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