Hello folks,

Can anyone explain the voltage source of +15V of UC3845 in the Bus soft circuit in the MPPT board VMII?

I can see only the voltage 120V coming from the main board, then altered somehow in the cap C10 25V then feeding the UC3845 with +13V

What's happening on my side it is about burning out the UC3845 and the double diode under it KL4 directly when turning on the inverter.

SO I started researching on the circuit schematic and found out the above wonder scenario for me at least!

Hope the experts here can help me on getting this more obvious

Thanks

In the 5kVA MKS models, it comes from the main power supply (that provides ±12 V and +5V); one of the windings is half wave rectified and feeds the main power supply's UC3845 chip via a diode. (Another diode provides a way for the main power supply to bootstrap itself).

Edit: It could well be different in the VM III and other models; the power supply sources seems to be one area where the various models differ from each other.

 

Edited November 7, 20241 yr by Coulomb

Thanks @Coulomb,

Okay now I have a better vision on the board, still missing a point, which is the Ground related to the 15V feeding the Ground pin of UC3845 in the soft start circuit, from where is it coming? Cause the two wire coming from main board are +15V and +150V (Battery SPS output).

Nevertheless, I am still encountering problem in the MPPT board for bootstrapping, let me explain what's happening:

I starts the inverter, when the relay connected to the soft start circuit runs, the soft start transformer is making noisy sound, and after few seconds the inverter gives error 09.

I measured during this bootstrapping the BUS voltage, it is increasing slowly till reaching only around 160V before the inverter stops and gives error 09.

What probably is causing the problem? I changed almost all parts related to the soft start circuit!

On 2024/11/11 at 5:40 PM, Adnano said:

I starts the inverter, when the relay connected to the soft start circuit runs, the soft start transformer is making noisy sound, and after few seconds the inverter gives error 09.

I measured during this bootstrapping the BUS voltage, it is increasing slowly till reaching only around 160V before the inverter stops and gives error 09.

It could be that the bus soft start power supply is weak, or that there is too much load on the DC bus for the power supply to cope with in the allotted time. Both of these might cause the transformer to make an unusual sound.

On 2024/11/11 at 5:40 PM, Adnano said:

I changed almost all parts related to the soft start circuit!

I wonder if the transformer has failed: either with shorted turns, or the ferrite core has cracked and now has too much air gap (these "transformers" are supposed to have an air gap to store magnetic energy). It is possible to try a transformer from another unit?

I decoupled the MPPT board and fed the UC3845 with 15V and the transformer with 135V and shortened the Opto-coupler, the noisy sound is there.

I replaced the transformer and still same result.

The PWM is around 5.4KHz with 50% duty cycle.

I am still unable to find the issue