Working in research and science - becoming too absorbed in a research project

I had a 34 year career in science, most of it in molecular parasitology research, but the last 10 years managing scientific facilities and services in a research institute.

I think that you have identified your major problem, not being able to say no to requests. You probably need to recognise that the interests of a supervisor and bench scientist - PhD students, technicians and post-docs - are fundamentally different. The PI wants to get as much work as they can out of their students and staff, however, the PhD student only needs to do as much work as will reasonably guarantee passing the viva, the professional bench scientist wants to do as much work as is consistent with producing publishable material, but at the same time having a social/romantic/family life, and remaining sane. Once this dichotomy of interests is recognised it becomes easier to say no to requests to do extra work. Have I done some stupid things because I was asked? Yes! 16hr long experiments through the night,  and 12 hour experiments taking samples every hour on a Sunday to name but two! However, as I worked in my field for longer, my confidence grew and I was able to politely decline such requests.

It is also useful to be able to distinguish between genuine deadlines, like writing material for a presentation at a conference, when some extra work would be of genuine use, and routine demands for working long hours which are not, certainly not for one's health. Outside working to a genuine deadline, you need to set definite boundaries on the time you spend working. I would normally work an 8:00 to 4:00 day in the lab, Monday to Friday do no more than an hour's work on any weekday evening, take Friday evening off completely, and keep my weekends free of work. If there were a genuine deadline approaching, I would work Saturdays, but never Sundays. If you set yourself definite work time and me time boundaries, you will not be sucked in to obsessive overwork.

Thank you Martin, your reply is very helpful.

I think realising that the PI and postdoc who is supervising me have different interests/priorities to me, will help. I also realised that when someone asks me if I "can/want to help out with a project" the underlying assumption for me is that the person asking expects me to do it, (otherwise they would not go through the effort of asking). However a friend recently pointed out to me that in her view that assumption is not always true and that people can and do sometimes ask without actually expecting you to agree- this has been a real revelation for me. 

I will try to put into place some more boundaries in terms of working hours (my working hours were quite crazy and just kept getting longer- and yes I have done the crazy 16 hour things or overnights in the past- but that was a bit different as I chose to do it because I really wanted those results). I find drawing up boundaries particularly difficult as I have very high intrinsic motivation (I just love science)- for example, when I started off in the lab I would sometimes go in at weekends to use the microscope because this is what I consider "fun". Reading a paper can be so relaxing. I can also get a bit overexcited about a project and try to do too much at once. However, in my current lab I never even got around to properly starting my own project (and if I did do things I was genuinely interested in it would be very late or at weekends after finishing all the other work). I hope that if I set limits on working hours, science will become more fun again. 

The postdoc who is supervising me seems to think it is normal that my main task is to help him finish off his projects (he doesn't really do any wet lab anymore) and that my project takes second place/ is to be done in spare time. I am not sure if this is normal?

I do think I have been taken advantage of (also regarding the contract I was promised), however I think I make this very easy for people as when I joined the lab, all I cared about was the science. 

Thank you so much for your advice and for sharing your experience!!

Happy to be of use. If you are working as a paid research assistant, while pursuing a PhD, then you can be legitimately asked to work outside of your PhD project. However, this work should not replace work on your project entirely, or take up the majority of your time. You need to see your PI and work out a reasonable schedule of how your project should progress, what are the milestones - such as formal reports to be examined - and, very importantly, a firm timeline for finishing. Like I said, you need only as much in the way of results as will guarantee passing the viva, while your PI wants to exploit your abilities to the greatest extent possible. Most universities appoint a PI who is not your supervisor to look after your interests, if no such person has been appointed for you ask about it, if one is in place, you can legitimately take any concerns about overwork to this person.

Yes, the insurance issue is something I also worried about. Having people work illegally and unpaid initially seems to be something that they like to do here, I found out later that they did exactly the same to the other PhD student (just worse as he worked even longer unpaid...) and there are some other dodgy things that have come to light over time. Hopefully I have learnt from this experience and will find a nice lab where I can settle down :). Thanks for all your advice! 

Yes, the insurance issue is something I also worried about. Having people work illegally and unpaid initially seems to be something that they like to do here, I found out later that they did exactly the same to the other PhD student (just worse as he worked even longer unpaid...) and there are some other dodgy things that have come to light over time. Hopefully I have learnt from this experience and will find a nice lab where I can settle down :). Thanks for all your advice!