2009 Ford KA car tends to cut off when warm

Car drives perfectly fine but if there’s a load on the battery tends to cut off, starts up ok ish but everytime the fan kicks in or even if I put the wipers or just the headlights it stalls. Only happens if the car is warm, So far have changed the crank sensor, throttle body, coil pack/leads and plugs , new ecu, new battery and nothing has helped. Everything Iv tried above seems to make it better for a few hours but then the problem returns. Taken it to multiple electricians but they have failed to get to the bottom of it. Can I be the the alternator even though the electricians are saying that it is functioning fine, No codes on car so hard to find the problem. It’s low mileage of 40k. Help needed plz.