Igaging DRO problem

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homebrewed

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I recently bought a pair of igaging DROs with the stainless steel scales, a 6" and a 12" to install on my mini lathe. I made all the mounts and mods needed to install the 12" scale for the Z axis and moved on to thinking about how to attach the 6" to my cross slide. But I noticed that the batteries for the 12" went flat very quickly, in less than 1 week. I thought perhaps the batteries that came with the DRO were old to start with, so I replaced them with some I knew were pretty fresh. Well, they went flat very quickly as well.

Thinking that the problem had to be defective electronics -- either the display unit or the sensor -- I measured the supply current drawn by both units, using the 6" as a reference because it doesn't seem to have a problem. But BOTH units drew about the same amount of current, right around 70 micro-amps! I used a variable lab-style power supply and DVM to measure the current, so the batteries were removed to perform the testing. I examined the battery compartment, thinking that perhaps the problem was related to how the batteries were installed in the DRO -- but I didn't find anything obviously wrong, except that the two batteries are placed side-by-side so closely that they can touch. If the batteries were series-connected (to provide 6V) that would be a problem, but, again using my DVM, I found that the batteries are connected in parallel. So even if the batteries were touching (in this case it would be their two + terminals), that wouldn't be a problem.

BTW, parallel-connecting batteries isn't a great approach to address a capacity problem because you never want to use a fresh/old combination of batteries. The old one could potentially discharge the new one, depending on how old it is.

So at this point I don't know what's going on. Has anyone else experienced this kind of problem? If so, how was it addressed? I'm thinking the 12-incher will likely be going back where it came from, but it still bothers me as to what's wrong with it.
 
Did you try monitoring the current draw after the displays flip to sleep mode? What about when you switch them off? Perhaps there's a problem where the current draw is higher in sleep/off mode?
 
If two batteries are connected in parallel, did you try swapping the their positions to see if both were discharged? Could be that one position isn’t making good contact, putting all the load on the other one.

Tom
 
Thanks for the comments. Here's some additional info regarding the problem. This igaging version doesn't have a sleep mode -- at least, the 6" one hasn't gone to sleep yet, and it's been on for several days. When I change batteries I don't bother with just changing one of them, it's all or nothing so both should be in good shape. I didn't check to see what the supply current does when the "off" button is pushed. On these DROs I think the only thing the power button does is turn the display off, but it's worth checking.

I noticed something interesting today. After apparently going dead yesterday, this morning I saw the DRO had revived, and so far it hasn't misbehaved (but sometimes after changing batteries it's taken a few days to kick up its heels). It's starting to look more like some kind of intermittent problem. If so, those can be a real bear to track down. It also can be hard to prove to your vendor that there really is a problem.
 
That's interesting about not having a sleep mode; while I don't have their DRO scales I have been researching them for use with the TouchDRO product. I generally thought that they should go to sleep after a period of no scale activity. I just looked around and it seems you should be seeing 10-15microamps when off and 50-75microamps when on. Take with a grain of salt though; probably varies depending on specific model and whatnot.

Stupid question: did you test the batteries to ensure they are dead? Could it simply be a flaky battery connection?
 
That was not a stupid question at all, it reminded me of another test I'd done but failed to report. I did check the open-terminal voltage of the batteries and they definitely were low.

If the problem is some kind of intermittent short it could explain the quick battery drain and -- if it doesn't last too long -- the apparent recovery when the short opens back up.

I have read accounts of folks having problems when they use a combination of DROs from different vendors. Apparently some designs apply Vcc to the scale and some ground the scale. This can potentially cause a short when the scales are connected to a common ground (like the machine they're attached to). I don't see how this can apply in my case, because right now I just have the ONE scale mounted on my lathe. I ohmed things out and confirmed that the scale is connected to the minus side of the batteries (in other words, the DRO's ground). The positive side of the batteries DOES connect to the sensor (igaging calls it the "data sender"), but it's only accessible via the mini USB cable that connects the sensor and display modules.

The magnets on the back of the display module are not connected to ground or Vcc so there's no problem there. The steel mounting plate on the back of the data sender also is connected to DRO ground, not a problem since the scale also is connected to ground.

Hmm. I just realized that I could at least halve the problem space by unplugging the connector when the DRO misbehaves again. The display won't shut down if the connector is unplugged, it just doesn't produce a valid reading. If the display starts working properly then the problem is associated with the cable or data sender. That would become a certainty if the problem reappears when I plug the connector back in.
 
What battery type & make are you using? Large CR2032's or the small 376's?
And importantly, what chemistry? Lithium or Alkaline?
 
They're CR2032's. They are a 3V single cell so they've got to be lithium-based.

So far the DRO hasn't exhibited its problem again. This doesn't make it easy to track down the problem....
 
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