Well, today was supposed to be another USRPT set but it was just awful. This week I have really started struggling and I’m not sure I can fully explain why. In the end I abandoned trying to do the USRPT set and just swam the remaining reps on a slightly more relaxed turnaround time.
USRPT distance this year: 137,450m
Total distance this year: 141,800m
I couldn’t swim at my usual time today as the pool was unavailable, so I had to go this evening. I’ve been sniffly all day and feel as if I’m getting a bit of a sore throat, so perhaps that explains why I wasn’t really on my game yesterday.
Today was even worse. I really couldn’t find a rhythm and struggled from quite early on. I did get through the set with a number of failures, but it was really messy and I wasn’t at all happy with it.
USRPT distance this year: 137,450m
Total distance this year: 140,000m
So it comes to that time when I need to think about power. In particular 12V (or 13.8V) power to the piers to supply most of the kit that will be on them.
Initially my thoughts were to have a single PSU in the warm room to provide power everywhere, but I wasn’t really happy with a single PSU failure hitting all the mounts. That meant having multiple PSUs either in the warm room or at the pier, but multiple PSUs also seems a bit wasteful (and consumes a lot of space) and if they were on the pier then ensuring they were adequately ventilated whilst keeping the dew away from them was going to be a challenge.
Then someone suggested to me that I could use a battery wired in parallel with a PSU with fuses each side of the battery to protect everything and switches to allow circuits to be disconnected. It’s not a cheap solution, but it does mean the battery could power everything, possibly for several hours, in the event that the PSU died. I’d need to turn down the voltage a little, perhaps to 13.5V or 13.6V, but that should be fine.
An alternative suggestion was to just get two lower-rated PSUs and power some stuff from one and some from the other. That would probably cost the same as the single PSU solution without the battery.
So for the time being I’m dithering a little. I do need to make a decision very soon though.
Another decision that I think I’ve settled is cabling for the 12V supply. I’m fairly sure now that for the runs from the PSU to the pier I’ll use 2.5mm “twin and earth” as used for mains house wiring (and I have quite a bit lying about). A single run through the ducting should be good to carry perhaps as much as 25A, which should be more than I ever expect to need. At the pier I can split it into multicore cables to feed the mount and other kit. The alternative would seem to be to use a couple of runs of multicore automotive cable capable of carrying around 11A and balance the load across each, which seems a bit more awkward really.
So, need to get that power supply decision made…
New month, old set. Struggled a bit today and I’m not sure why, but I did make it to fifteen reps before my first fail and then failed again on twenty-one before swimming the set out.
USRPT distance this year: 135,800m
Total distance this year: 138,350m
I’ve used a couple of these power supplies for a few years for powering my NEQ6 and HEQ5 telescope mounts, but recently one of them just stopped working. It has been sitting in the workshop for a fair while waiting for me to do something about it and I recently “rediscovered” it, so I’d see what I could do.
Measuring the output voltage gave me something that was floating between about 9.5V and 11.5V, so I decided to open it up and see if anything obvious had failed. It has gained a few cobwebs and a bit of corrosion on the transformer core whilst it has been in the workshop.
Behind this board is at least one power transistor, and down on the base of the unit is the rectifier:
This is what I assume must be the regulator circuitry, though strangely it has an AC feed from the transformer. It has been suggested to me that it might be to feed some sort of circuit that senses when the unit is connected up, if it were to be used as a battery charger. There are plenty of components marked on the board that aren’t present, certainly.
And finally a couple of chunky smoothing capacitors.
I was expecting that perhaps one of the electrolytic capacitors might have given up, but actually they all look ok from the outside. Someone recommended that I twiddle with the two trimmer pots on the board in case they’d got failed, and to give them a bit of a clean so I did my best with that and powered the unit up again, at which point it gave me a nice steady 14.5V output.
So, the next step is to turn the voltage back down to 13.8V and see if it stabilises there. If it does then I think I’m done. Otherwise it doesn’t look like a particularly difficult job to replace the two trimmers as long as I can find out what values they need. A decent clean out probably wouldn’t hurt, either 🙂
Last swim of the month and it was completely chaotic. No lanes in the pool, people getting in the way everywhere, all a bit messy. I think I had two failed reps, but it was honestly hard to count it as a worthwhile session.
USRPT distance this year: 134,100m
Total distance this year: 136,650m
Hopefully when the sky is next clear at night I can get around to polar aligning my mounts, but before that I wanted to align the finders and main telescopes so I dug out an illuminated reticle eyepiece that I have mostly used to align targets for planetary imaging. I’ve had it quite some years and it’s very similar to the Skywatcher one:
It has a number of issues however.
The thread on the adjuster at the top of the eyepiece is quite loose and allows the top to wobble quite a bit. I found that (quite) a few turns of PTFE tape around the thread took a lot of the wobble out. I think that should be sufficient now as it feels fairly firm when the crosshairs are in focus.
The on/off switch isn’t great either. It also wobbles, and more often than not I forget to turn it off after using it. The knob is held on with a grub screw, so I undid that, pushed the knob on as far as I could and re-tightened it. That has improved the wobble, though it’s a little more stiff now.
I also discovered that it no longer works. Unscrewing the LED barrel revealed a couple of possible reasons:
I cleaned up the corrosion on the battery contact with some fine emery paper and resoldered the broken wire. Pleasingly that was all that was required to get it working again.
I am quite tempted to look at some means of fitting it with an external power supply. Having it plugged into a cable might actually make it easier for me to remember to disconnect it from the power. I need to give that some more thought though.
A more interesting day today, as whilst I was warming up someone who used to be a member of the club appeared on poolside and asked if she could join me and do my set (there was only one lane set out and I was the only one in it, so not an unreasonable call). She’s not swum much for the last six months and as it turned out we were reasonably well-matched in terms of speed over the set. I’d been hitting around 47s for most of the reps and before the last one she said “Push hard and go 46s on this one.” So I did, and touched the wall on 43s plus a few tenths, which I think is the fastest I’ve ever done a rep whilst swimming this set, regardless of target/turnaround time.
Two reps missed again, on thirteen and twenty.
USRPT distance this year: 132,400m
Total distance this year: 134,950m
An addendum to my previous design post. The builder dropped the motor units off for the stair lifts that he thought might be butchered to make an automated roof mechanism.
This first is the lighter weight one for the rack made from multiple steel plates. The pinion wheel here is the same.
The second is for the solid steel rack. This one also has lots of microswitches that are undamaged and might be useful as limit switches.
For the moment however they’re going to remain on one side. I want to get all the existing planned work completely before adding more. I just need to bear it in mind for the wiring and so on.
No swimming on the Monday thanks to the bank holiday, but same set again today. For the time being I think I’m going to keep these postings short unless there’s something new and interesting to report.
So, fails on reps fourteen and twenty today.
USRPT distance this year: 130,700m
Total distance this year: 133,250m
