Is there any limit on how many SATA power connectors i can extend

Power distribution in any situation is like a length of chain or team sport. It is only as strong as its weakest component. For most power systems, there are 2 main elements: connectors and cable.

Each element has certain voltage and current ratings. These ratings are usually dependent on temperature. They also only apply to the brand of components you have.

So for this example, we'll use a Molex brand Molex to Sata cable. Why? Because Molex acutally bother to take the time to specify the parts that make up their assemblies. The spec for this cable is available here. We're only interested in the cable and the sata connector though.

If you look at that spec, you notice that the connector is rated to 1.5 A DC and the wire they use is 18 AWG (I'm a mm² man myself but let's roll with it). If you look up recommended wire gauge to current rating (such as here) you'll note that 18 AWG is rated to 16 A for short runs. So our connector is the weak point, more specifically the point were two connectors meet.

Now let's look at HDDs (as per your comment). Say you have a Seagate Barracuda 1 TB, when you look at its specs, it draws about 6 W under operating conditions. We'll say this is 0.5 A @ 12 V (though it is probably a combination of the rails) to simplify. This isn't the worst case though, this drive draws 2 A on start up but the connectors can handle it for a short time.

So you have 3 of these drives and you want to split them off the same SATA power point. The current will be additive so the current draw when operating will be...

0.5 x 3 = 1.5 A

However, this is when all drives are reading and writing which is unusual unless you have a RAID-1 type setup on all 3 drives.

So theoretically, yes, you could connect 3 hard drive off a single power point. More would exceed the designed limits of the connector that would connect to the PSU.

On a side note, while the start up current should be considered as a part of design (up to 6 A in this example with all 3 drives), it should also be noted that the Molex connectors have tested at higher current (7 A, see this connector spec). But if you exceed the design max and melt something, then that will be your problem and yours alone.