A Few More Days to Clear Sky?; A Product to Avoid

Spring progresses slowly, but it appears that next Tuesday night (today is Saturday) will finally be clear and suitably dark for testing the things I need to verify about my IFN imaging setup before it goes on the road. In the meantime I've been putting together the traveling kit so that I can have all the cables and such needed for the project ready. It's also been time to top off all my lithium batteries. 

Lithium batteries are remarkably tolerant of abuse. The can abide deep discharges if you can get them to a charger within a day or so. Almost every lithium battery of any reasonable size now includes a battery management system that prevents too-rapid discharge or overcharging. The batteries also tolerate temperatures that I wouldn't! 

Maintaining a lithium battery is easy, too, even in the seasonal sport of astrophotography. At the end of the imaging year, just make sure they're they've been discharged to about 50% capacity, then every three months bring them up to 100% and back down to 50%. When you resume imaging and their use becomes more continuous just keep them fully charged. 

Yesterday I started the springtime full charge of the battery pack I use to power my laptop, and it revealed something I should have known. The pack in question is a pair of 15 Ah batteries in parallel, so I thought to use my 10 A charger.  The pack's only port is a 12 V automotive socket and the charger was sending 10 A through a fused automotive plug. All was fine for a while, but then the charger indicated it had shut itself off and there was a faint aroma of overheated plastic. That's never good.

Inspection of the plug showed the fuse was intact, but that the coiled spring at the base of the fuse was misshapen and the plastic around it had melted. Supposedly 12 V plugs can handle 120 W (10 A @ 12 V). At the point it started to overheat it was probably being asked to handle around 135 W, which evidently was too much for it. I suspect the rating for the plug I was using was well below this; I've seen some that are only rated for 60 W. 

I use one of these plugs to run power to my laptop, another to feed the mount, and a third to power the rest--CCD camera cooling, dew preventer, and USB devices. The total of all these rarely approaches 50 W and is typically more like 25 W, with a little going to the mount and the rest pretty much evenly split between the laptop and camera plugs. Although I've never had an issue with the plugs during imaging this current limitation is something to keep in mind if I ever change equipment. 

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At first glance this Astromania dew preventer looks like a great deal. A 10-inch strap with on-off switch and easily adjustable power control. And the connections are compatible with common 12 V power sockets. What more could you want for a mere $20?

From that buildup you can probably guess it was not quite a great deal. It was a pretty bad one, really.

I connected it to my primary power box and tried it out. I started with the toggle switch off and the power control rotated to the off position. My power box reported 0 W, 0 A. Good. Then I flipped the toggle on. Immediately the Current rose to 2.1 A and the strap started to warm up. In fact, it got quite hot: too hot to wrap around a cameral lens without risking damage. Obviously the controller was somehow defective. With the Controller at it's full-on setting the current was 2.4 A. Were I not a Vine reviewer, I would have returned this immediately. 

But there was another problem, the strap itself. Most straps are very flexible and have no problem conforming to the cylindrical shape of optics. This one won't do that. The plastic lining of the strap is thick and very stiff, and even working it for a while by hand didn't get it to wrap around a 135 mm lens without a few big gaps.

So it was a complete fail and got one of my rare 1-star reviews. Setting aside the problem with the strap the only way this would function is if you could control the current with some other device. And you would want to first make sure the strap connecter would be compatible with your device's strap socket. (It couldn't work with my Pegasus Powerbox or any of my other manual Kendrick controllers, for example. Yes, you could make an adapter for this, with a 5.1x2.5x3 socket on one end and an RCAphono plug on the other. But why bother.)