Friday, November 11, 2005

Hemsworth slides

OK, I've started doing a few of my Grampa Hemsworth's slides along with the one's I'm doing for my wife's family. The scanner I'm using is a pretty decent one (prices finally came down enough!) that my M-in-Law bought to use to scan her slides. Since I have the scanner at my house, a side benefit is that I get to use it to scan my stuff as well.

Some of these are pretty old. The first slide in the first tray is a picture of my grandparents on their wedding day in May of 1939. As expected, there are quite a few of my mother and her siblings as well.

I'll get through these, but it will take me some time!

Monday, November 07, 2005

Progress report


I haven't taken Itok out for a run in a while and it's probably going to rain tonight and for a few days this week. He did get out in the front yard on Saturday while we were cleaning the garage. I thought he would stick around and play with us, but instead, he took off running (he LOVES to run). Taylor and Bryce spent about 15 minutes chasing him down. He didn't even act the least bit sorry for running off. He's going to learn how to come to a whistle no matter how many bags of doggie treats (or hot dogs) it takes!

Slide Scanning

I've done 20 boxes now for a total of just under 1000 slides (a few weren't completely full). I also scanned a bunch of documents that Janice's mom had on her pioneer ancestors that we haven't seen yet. I had intended to read some of them today while we were in Logan babysitting, but we played with the kids instead. 13 more boxes and I can start on my Grampa Hemsworth's slides.

Furniture re-arrangement

The family room was the victim this month. We moved everything (including the piano). It seems a lot bigger now at least when you stand at one end and look down to the other end (there's nothing in the way anymore).


My PocketTracker worked fairly well today on our trip with my digipeater and with the one on Shepherd Peak up in Layton but none of the others in the area seem to know what to do with it. I'll have to bring it in and look at the programming. You can follow it here on

Battery testing is progressing

Ok, so we just got back from visiting friends in Logan. It's been a long day and I want to go to sleep but I have to put just one more battery on the CBA. I'm numbering each of the batteries that I test and I'm up to 77 with this last one that I'm doing for a friend.

So far, I've found that several of my main batteries (the ones I thought were reasonably good) are actually pretty much worthless (at least for more than a few Amp hours worth). I still have 4 or 5 more to gather and test for the first time (they're in use in various places), but I've gone through most of the rest now.

I also found out that some that I thought weren't that great test out like they're brand new. Of course there are some in between that aren't totally dead yet. Like the 100Ah behemoth that came out around 80Ah even though it's been sitting for 12 months.

Thursday, November 03, 2005

Mold your own ear piece

Steve (NV7V) just sent around this link: PodFitKit Home

Sure sounds a lot cheaper than paying a professional to come and do it for you. You can mess up quite a few times and still come out ahead!

Let me know if you or anyone you know trys it. (click the comments link)

Wednesday, November 02, 2005

Voltage set points on modified APC UPS units

I have noticed now that I have modified about 8 of these units that when they are attached to a battery, they float at different voltages depending on whether the main power switch is on or off.

Typically, the powered ON voltage is adjusted for about 13.8V (a good voltage to float most VRLA batteries). However, the powered OFF voltage jumps by up to 0.5V. This is a little high to float at for lengthy periods, but shouldn't hurt anything if left for a day or so. In fact, it may be helpful to let a battery float for a little while at this voltage to help equalize the individual cells. A fully charged 18Ah battery that had been floating at 13.8V drew only 60mA or so for a couple of minutes before dropping to less than 10mA when it reached 14.3V.

Float voltage adjustment

It's also interesting that the charge rates are different depending on the power switch. With the power switch ON, these units will charge a nearly dead battery at about 350mA. With the power switch OFF it charges at around 400mA. While this isn't exactly a fast charge for an 18Ah battery, it is plenty to maintain a bank of batteries in an always ready state. If you intend to charge batteries with one of these units, I would only count on about 5Ah a day.

Tuesday, November 01, 2005

Discharge cut-off voltages for VRLA/SLA batteries

I learned today by reading the technical manual on Power-Sonic's VRLA/SLA batteries that they recommended the following cut-off voltages for batteries under load:

Load to Volts per cell = 12V equivalent @ 68 degrees F
0.05C (20 hour rate) to 1.75V/cell = 10.50V (Ah available = 100% of rated capacity)
0.10C (9 hour rate) to 1.75V/cell = 10.50V (Ah available = 90% of rated capacity)
0.20C (4 hour rate) to 1.75V/cell = 10.50V (Ah available = 80% of rated capacity)
0.33C* (2 hour rate) to 1.67V/cell = 10.00V (Ah available = 72% of rated capacity)
0.50C (80 min rate) to 1.67V/cell = 10.00V (Ah available = 65% of rated capacity)
1.00C (33 min rate) to 1.50V/cell = 9.00V (Ah available = 55% of rated capacity)
2.00C (12 min rate) to 1.50V/cell = 9.00V (Ah available = 40% of rated capacity)
3.00C (7 min rate) to 1.37V/cell = 8.22V (Ah available = 36% of rated capacity)

*This rating was not in the data from Power-Sonic - I estimated it based on the other values because I needed a load value between .2C and .5C.

Of course other manufacturers will have somewhat different specifications, but I think these are pretty reasonable numbers and I intend to use them on future tests of VRLA/SLA batteries with my new battery analyzer in place of the default setting of 11.4V.

I also found the following interesting:

  • These recommendations cover batteries ranging from 0.5AH to 100.0Ah.
  • A 1C discharge rate reduces the Ah capacity rating to about 1/2 of the 20 hour rating (which is how most batteries are marketed).
  • A 3C discharge rate reduces the Ah capacity rating to about 1/3 of the 20 hour rate.
  • In the 400VA UPS units I have been modifying, 7Ah rated batteries were used. With a full load, this corresponds to a 3C discharge rate and should last about 7 minutes.
  • Replacing a 7Ah battery in a 400VA UPS with a battery* rated at 40Ah gives 70 minutes of run-time at full load. A 10x increase in run-time in exchange for a 6x increase in rated capacity.
*I often use multiple batteries in parallel.