Voltage Check Issue

[requenym]

Built a 1.4u and not getting the proper voltage on VCC or VIN when powered via the transformer.

Transformer outputs ~27.2 VAC
VCC Voltage 0.350
VIN Voltage 0
Resistance Between PTC (top leg) and D1 (left leg) is .5 Ohms

Using a Fluke 12B the Diode Test mode outputs a reading of for D1 1.571

Without the transformer connected and using a USB cable VIN and VCC voltage is correct

Any guidance would be appreciated.

[Ray]

If voltages are correct under USB, that means 5V->3.3V is working fine. The problem is most likely in the 24VAC->5V conversion. The Resistance Between PTC (top leg) and D1 (left leg) doesn’t tell much because these two pins are connected by PCB trace. Here are my suggestions:
– check if you have any missing component
– did you insert IC1 (MC34063)?
– does the PTC fuse feel very hot?
it would definitely help if you can post an image of the lower-left side of your board (the 24VAC->5V conversion part).

[requenym]

Ptc is not warm
IC1 is inserted
don’t believe Im missing anything – will upload pics when i can resize them. (forum won’t allow larger then 256kb)

[Ray]

You can send the picture to [email protected]

[requenym]

Thanks, that makes things simple — just sent them.

[tudor]

Hello,

I seem to have the same issue; with USB, the VIN and VCC voltages are correct, but 24V stops after it enters D1. Any ideea?

Thanks.

[Ray]

What do you mean by ’24V stops after it enters D1′? Do you mean that on the anode of D1 there is a voltage and on the cathode of D1 there is no voltage?

[tudor]

Yes.

EDIT: VIN = 0V and VCC seems to be 0.02V

[Ray]

Are you measuring AC or DC voltage? On the anode side of D1, it’s AC power; after D1 (rectification), there is basically only DC. So if you are still using your multimeter’s AC measurement you will get a reading of 0.

[tudor]

I’m using a 24V DC power supply, so I can’t miss 🙂
If using USB, everything seems to work fine, including web interface (except valves, not tested them yet). I’ll take another look at it tomorrow, just thought this might be the same setup + problem as requenym’s (except I’m using a DC power source) and was curious about what solved his.
I’ll post what’s wrong when I find the problem.

PS: suggestions where to look for mistakes are welcome 😀 Thanks.

[Ray]

Any reason why you are using a DC power supply? Since the controller uses triac to control valves, if you use a DC power supply, you will only be able to turn on a sprinkler valve and once on it cannot be turned off (because DC does not have zero crossings).

In any case, if you are using a DC power supply, you have to observe the polarity: on the 24VAC terminal, the pin closer to the USB port is tied to ground, so you should connect that to the negative wire of your DC power supply.

[tudor]

That seems to have solved it! 🙂 My mistake for overlooking that little detail. It works now, thanks!
And I’m using a DC power supply just for testing. Thanks for the warning.

PS: just a suggestion, but maybe it would help to point this out, so other non-experts won’t make the same mistake. 😀

[Author]

Posts