50W discharge, 100W charge and some minor changes

[exoper]

Hi i want to mod my clone of Imax B6 50W to make maximum usage of this little thing.

TO DO:

-50W discharge (Graphic card cooler, sensing resistor, current opamp circuit?)

-100W charge (SMPS elements replacement, sensing resistor)

-individual temp and UART ports.

I alredy make some physical changes to charger, changed input connector to XT30 ( i dont think that DC jack can handle 3+ amps), chenged output connectors to XT60 (plug in battery directly to charger), some changes to balance port ( i use naw only 6S port for all bateries, 2S port is naw a temp sensor port). 

  

50W DISCHARGE

I alredy have graphic card coller and some fan, now i just have to cut a heatsink a little and mount it to charger somehow. 

For such a discharge power there will be also high current so i need to change sensing resistor from 500mΩ to something much smaller. I think that 5mΩ will be good but at small current charger could be inaccurate so maybe changing resistor in feedback of opamp? (R14 at the schematic from 2k to 5k or more?) 

 

100W charge

To achieve 100W we need to chenge transistors in SMPS, i found IRF8734PBF for N-MOSFET (30V 21A 3,5mΩ) , IRF9310PBF for P-MOSFET ( 30V 20A 4.6mΩ) and MBRF1645 for diodes. i'm not sure that inductor can handle 100W. Anything else that i need to replace to achieve 100W? 

UART / TEMP Port

ok hare i have no idea how to do this, i bet since temp sensor is analog and UART is digital, that those two are not on the same port of procesor so there is a chance to get them separably. Any schematic or idea will be priceless :) 

I will keep this tread updated :)

[diggit]

Just for reference, I made one mod too, look here. 20W power loss on that GC cooler with fan on 5V seems to be ok. It is copper heatsink with integrated fan. I placed all SMPS power components on that heatsink too. Sensing resistors were changed too.

There are several cooling mods in this group. I might help you.

You should check, that your inductor can handle such currents.

[exoper]

Thanks diggit :) 

I read your modification earlier, you give me idea of using graphic card cooler. I even bough identical cooler as yours but decided to use larger one. 

Did you expand the output power or only place SMPS power transistors on heatsink?

[diggit]

I wanted something compact and I had this one at home. It was proof of concept.

I have 5 components (TO-220) on heatsink. Load, buck, boost transistors and probably 2 diodes. IDK how much I increased output power, but something else is limiting output at ~57W (). I did this mod to increase discharging capacity. Then Turnigy 400Wx2 came to me and I lost interest.

[exoper]

Oh, ok thanks.

Meantime i trace the data transmit on the board. It looks like i need only to remove i resistor and make some type of connector for usb dongle. 

Pictures for future use :) 

[diggit]

Nice work you did there.

In src/hardware/atmega32/generic/50W/HardwareConfigGeneric.h is defined ENABLE_EXT_TEMP_AND_UART_COMMON_OUTPUT which in result disables UART when external temp. probe is used. To disable this effect, add:

#undef ENABLE_EXT_TEMP_AND_UART_COMMON_OUTPUT

to your HardwareConfig.h and recompile your FW. UART output and External temperature measurement should then work concurrently.

[exoper]

I cut a heat sink and mount it to the charger. After placing IRF44N and 7805 at heatsink I compile FW, upload and after calibration I get error wen try to discharge :( 

[exoper]

ohh and also wen compiling a new FW I chenged limits just for testing purpose. 

[diggit]

It is problem with calibration. Look here. The problem is, that max (new limit) discharge current will result in ADC saturation with your current calibration (thus can't be reached). You need to change sensing resistor (smaller value) and re-calibrate discharging current.

[exoper]

Ok, got it. Resistors and other SMPS components are i transport ( i ordered them online). Will post when they arrive. 

[exoper]

I wonder if there is a way of changing input upper limit from 18V to 24V. 

Input capacitor is for 25V (little low safty for 24V) but we can change it. 

7805 and transistors should be fine too.

I guess input voltage sensing circuit need some changes. But is there any limitation in FW? 

[diggit]

I think, that limiting is Capacitor and input voltage divider for voltage measurement. Check SMPS transistor max Uds, but I think, it should be ok. Mine 7805 was heating at 12V so I replaced it with this switched buck converter. Works fine with much higher efficiency.

Sensing resistor should be about 1/10th of original one to increase range 10 times. OP amps should handle 24V quite well.

[exoper]

Figured it out, I changed R83 from 18K to 27K allowing adc to mesure up to 27V. 

I connected a power supply and starting from 12V I slowly increased voltage up to 24V. Everything looks fine, also need to recalibrate input voltage (because we change the measuring circuit).

Before I start changing anything i checked datasheets for transistors and 7805, both transistors Uds=30V so no problem here. 7805 Uin=25V so its near its limit. Also little DC-DC converter for 5V it's a good idea.

Some photos of my work.

      

All components on 5V rail takes 62mA so at 24V power at 7805 will be P=(24-5)*0,062=1,178W. That no so much but why losing this energy, I have somewhere little buck converter, just need to find them...