# [PIC] Car Cooling System PSU Design Related

1. ## Re: [PIC] Car Cooling System PSU Design Related

Is this better now?

The SPV will be 20V or > that is max 35V. It is sensed by PIC. If SPV falls below threshold voltage then battery charging is stopped.

Only if SPV is sufficient and Battery voltage has dropped then after sensing them the Switchers are turned On. Switchers by default will be Off.

So, If I assume 20V nominal SPV and panel rated for 270W then

270W/24V = 11.25A

270W/20V = 13.5A

So, we need only 4A max per switcher ( 4 + 4 = 8A). The SPV will never power the load. It is only for battery charging.

Now, how big heatsink do I need for the switchers?

270W / 35V = 7.7A

7.7A / 2 = 3.86A. I guess this is sufficient for charging each 40Ah battery.

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2. ## Re: [PIC] Car Cooling System PSU Design Related

Originally Posted by baileychic
Then shall I use two switchers whose output is fixed to 14.4V and feed each 14.4V to one Battery and so the 2 switchers will be charging the batteries in parallel.
The upper switcher needs particular care about its circuit connections to the upper battery. How it's ground-referenced, whether to positive supply, and whether it's an isolated type.

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3. ## Re: [PIC] Car Cooling System PSU Design Related

Please check ECCS_4,pdf and reply whether the upper switcher's ground connections are okay.

Should I connect the upper switcher GND pin to where B1 and B2 batteries connect?

4. ## Re: [PIC] Car Cooling System PSU Design Related

I reverted back to the previous design with diodes.

Please check this. I have one question. If say B1 battery is disconnected and battery charger is On then doesn't Q2 Mosfet short the B2 battery to the ground?

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Refer BAT CHARGER.pdf and answer below question.

Will the battery charge without shorting B2 now? Will the series battery voltage be +24V while it is being charged?

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Consider only this REV3 PDF.

Is this circuit okay?

5. ## Re: [PIC] Car Cooling System PSU Design Related

Originally Posted by baileychic
doesn't Q2 Mosfet short the B2 battery to the ground?
No. D5 permits current flow only downward (charging) through B2 (lower) battery, never upward (discharging).

Refer BAT CHARGER.pdf and answer below question.

Will the battery charge without shorting B2 now? Will the series battery voltage be +24V while it is being charged?
D5 is faulty because it does not permit normal charging. B1 battery only charges while Q2 conducts. A wire needs to replace D5.

6. ## Re: [PIC] Car Cooling System PSU Design Related

respectfully, D5, etc allow charging, they are out of ckt for the 24V discharge - so Brads comments are a bit out to left field ....

7. ## Re: [PIC] Car Cooling System PSU Design Related

Diode D5 is in different positions on the two schematics. I agree with Easy, that D5 allows battery current to 24V circuitry at the right (in either schematic). In that sense it does not block discharging of batteries.

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8. ## Re: [PIC] Car Cooling System PSU Design Related

D5, ... D6 ...

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