XPost: uk.d-i-y

If you coasted your time for all this, you could have bought a new one.
Brian

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"N_Cook" <diverse@tcp.co.uk> wrote in message news:ubt4ls$1caq7$1@dont-email.me...

On 16/08/2023 16:59, N_Cook wrote:

2 peltier units in one cabinet.
The lower unit lost thermostat control and on full whack continuously.
I disconected that one and run on the top unit only, but with display
panel and lower unit unpowered the top unit ran at half cock
continuously which was ok for the intended use as a non-freezer box low
power fridge.
Until , as no protection from dripping condensate , condensate drip from
the skyved heatsink physically corroded a pin of a small 78L08 100mA
volt reg., diode checking the whole board cold, main active devices
looked reasonable, fuses and low ohm Rs ok.
I had thought if that top control unit failed at any time I could swap
it for the bottom. Both are marked fanny.com.cn PCB100729K1, MP 011
Replaced the VR and no fan kick, green LED flashes on then off and red
LED on . I swapped control units and the identical green and red LED
function and no fan kick also.
No idea what to expect putting a DVM on both isolated peltier units,
top one on resistance each way was 12 ohm and -1 ohm presumably from the
dissimilar metals in series , the lower one 13ohm and -4 ohm which as
far as it goes ,are presumably ok.
Before checking out the output side of the PS active devices AZ494AP and
LM358P , conventional DIP devices, something silly I've overlooked?
I will try the lower unit in isolation tomorrow.

Very humid recently and I actually saw a drip fall from the top Peltier
unit while testing it , so a paxolin sloping roof fixed under the peltier
and over the power supply/control board.

I've decided a problem with the display board , the IC there must have 2x 7segment drivers and 2x DAC but also some sort of interconnect so you
cannot have max setting on one unit and min on the other.
Only wanted one unit being used for low power marginal chiller cabinet, no freezer box required,so low noise/vibration, hotel like, mini-fridge. Disconnecting that totally, the 3 wire connector marked NTC2 although no thermistor seen on that display board.
Now I know both peltiers and both PS/control boards work separately. Replacing the NTC2 lead with a 22K pot across its 8V supply (instead of
the DAC function of the user front panel) means low V setting gave full
power 12.5V on peltier and main fans and mains consumption of 70W with
both green and red LEds on, high V gave low setting of 4.7V and overall
mains consumption of 12W, just red LED on.
Unplugging NTC1 for thermistor inside the peltier unit and peltier+ fan
drive drops from 4.7V to 3.7V and 8W consumption.
AZ494 is the smps controller with error amps and dual op-amp LM358 , ST TO220 device is dual shottky rectifier on the LV side of the pcb.
Separate isolation Tx for the fixed 8V low power supply.

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