which dc-dc buck converter? I don't want to fry my 'system'!

[richsolar]

Hey,

Looking at a quick get-around whilst I build my own system . . .

I have a Bluetti EB70 and two 230w (37 ocv) used panels (spec attached) which are not compatible, can i use a buck converter safely to reduce the voltage going into the Bluetti?

I have found these on Amazon;

https://www.amazon.es/-/pt/dp/B07CZBQ665/ref=sr_1_31?keywords=dc%2Bdc%2Bconverter%2B36v&qid=1689413662&sr=8-31&th=1

They make a 36v (max. input 50v) and a 48v (max. input 60v) setp-down converter, not sure which size will be optimal for my solar array. Which will be the two panels connected in paralel for a total of 37v ocv? Or will the voltage fluctuate somewhat i.e exceed either of the max inputs for the buck converters?

Newbie looking for reassurance.

Ta,
Rich

 

[DIYrich]

Neither. They are rated for 120 watts, and you have 230 watt panels.

5 of the 48v in parallel *might* work. You don't want to run at the limits for extended periods of time.

You might be able to use the 36v if the buck converter is never an open circuit. However it might become an open circuit in a low voltage state.

 

[Vigo]

So judging by the specs i can find, the solar mppt input can take 12-28v ocv and probably 8a max (it says 200w max solar). It also can charge a 716wh battery from a 12v power source in 7-8hrs, suggesting it will never pull more than 10a from that input, probably a bit less since it claims 100w charging from that input.

The idea of using a step down converter is fine. Probably any number of 24-12v or 48-12v models would work as long as their actual max input voltage worked with how you were wiring the panels (series vs parallel). A 48-12v may have a ‘minimum’ input voltage to consider as well if you are only feeding it 30-odd volts which pulls down under load to something lower.

If you are trying to get 200w of charging you should probably use a 24v output and feed it to the mppt rather than feeding 12v to the car port. Or, if you got a big enough 20a+ 12v converter you could parallel it to both the solar and car inputs and possibly still get 200w that way. Also, since in general 12v is less useful than 13.8v and step down converters which step down to 13.8v exist i would probably get one of those instead if you choose the ‘12v’ route over the 24v route. My .02

 

[richsolar]

Thanks guys, I will go the 24v route if possible with the panels connected in parallel to keep voltages down, otherwise I'll be reducing from 74v (series connection 37 + 37), not sure is possible then to use a converter . . .

So both those products I posted are limited to 120w, never saw that. Any suggestions on other converters or where I might find one suitable for this task?

 

[richsolar]

how about this?

https://www.amazon.es/-/pt/dp/B089LRQM9Z/ref=sr_1_14?crid=2WSOEA2FBVC7R&keywords=dc%2Bconverter&qid=1690017437&sprefix=dc%2Bconverter%2Caps%2C208&sr=8-14&th=1

only thing is input voltage range is 40-60v whereas my panels ocv is 37 . . .

 

[richsolar]

this one fits the numbers better . . .

https://www.amazon.es/-/pt/dp/B0BD4PCDRM/ref=sr_1_1?crid=2063D2XO2FN76&keywords=dc%2Bconverter%2B480w&qid=1690018024&sprefix=dc%2Bconverter%2B480w%2Caps%2C168&sr=8-1&th=1

I"m just a bit unsure if it's risky using a cheap device like this between my solar array and the Bluetti for fear of sending too higher voltage through and blowing the power station.

Perhaps I could also wire in some overvoltage protection after the dc converter?

 

[mikefitz]

Why not open the junction box on the rear of the panel and connect across 2/3 of the cells, the cells are arranged as shown,

Wiring within a PV Module and the Shading Effect | AE 868: Commercial Solar Electric Systems

Your ideas of using converters will fail.

Two new 100 watt panels would be the best option.

Mike

 

[DIYrich]

Orion IP67 24/12-20 model

Orion IP67 24/12 and 12/24 DC-DC Converters - Victron Energy

Completely encapsulated: waterproof, shockproof and ignition protected. Water, oil or dirt will not damage the Orion IP67 DC-DC Converter. Find a dealer nearby.

www.victronenergy.com

You could then use an Orion TR 12/24-10 to boost to 24v.

The problem with the Orion TR 24/24-12 to go directly from panels to bluetti is that the max input voltage is 35v, and your panels can get to 37v or more. It might be able to take it, but it is out of range.

 

[richsolar]

Why not open the junction box on the rear of the panel and connect across 2/3 of the cells, the cells are arranged as shown,

Wiring within a PV Module and the Shading Effect | AE 868: Commercial Solar Electric Systems

Your ideas of using converters will fail.

Two new 100 watt panels would be the best option.

Mike

I'm def reluctant to use the converters but I'm interested why do you think it will fail Mike?

https://www.amazon.es/Convertidor-Regulador-Impermeable-Alimentaci%C3%B3n-Converter/dp/B0BD4PCDRM?th=1

Both panels connected in parallel, so 37v going in (input range 36-48) - 24v going out at 10amps should provide 240 watts of input to the Bluetti MPPT, which will only draw 8amps so charging up to 190 watts?

But yeah think for safety I'll just get compatible panels.