# Pv connected with battery need a variable resistor but i have constant voltage and a changing current from the pv and battery

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Peter Lyngbye on 4 Nov 2022
Answered: Joel Van Sickel on 7 Nov 2022
Hello,i have a pv panel connected with an mppt Block and a sepia converter to generate a constant voltage with varying current depending on the irradiance… though I have a problem, because of ohms law I need to vary my load resistance in order to get a higher current when the irradiance increase… but how can I do this? I know there is a variable resistor blovk, but how do I control the resistance so my current will change when the irradiance increase :/ best regards!
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### Answers (1)

Joel Van Sickel on 7 Nov 2022
Hello Peter,
I'm not sure you should be controlling the resistance. In general, a solar panel and converter have no control over the load they are supplying, which is why MPPT is necessary to do with a dc/dc converter. The dc/dc converter can output a higher voltage to drive more current, which allows for control of power. MathWorks uses primarily boost converters for it's MPPT examples, but here is an example of a SEPIC. https://www.youtube.com/watch?v=mD-jUTDpVDg
You can achieve MPPT without varying your load resistance. However, if you want to calculate your resistance, it is P = IV, and V = IR. In your case, if V is fixed, and P comes from your MPPT algorithm, you can solve for R.
Regards,
Joel
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