Registered: Feb 2000
Location:
Posts: 5

I have noticed that whenever I replace the two batteries, one always has a much lower voltage, i.e. 0.7V vs. 1.2V. It sort of seems that the devices is pulling both at
3V and 1.5V, causing one to deplete more quickly. I wonder if anyone else can confirm this? This would mean that people who want to maximze the battery life should rotate their batteries regularly. Or, if you are too lazy, always save the one with higher voltage, and after you saved two of those, re-use them again.

Registered: Mar 2000
Location: Hermosa Beach, CA
Posts: 222

It's been awhile since I took any electrical engineering classes, but if the batteries are hooked up in a series, how can the visor "pull" more out of one than the other, all things being equal?

If you are experiencing this, I suspect the differences in the batteries themselves.

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

Are you sure that that batteries were equal when they were installed?

In series, the batteries should drain fairly equally as far as I know. Certainly I don't think there should be that much of a difference assuming they were close to begin with.

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MarkEagle - Ice is nice!

Registered: Jan 2000
Location: Monroe, Michigan, USA
Posts: 244

I had noticed this in my PalmPilot Personal. It's probably variation in the individual batteries; I don't see how the device could pull more juice from one battery when they're connected in series either.

Registered: Feb 2000
Location:
Posts: 5

Yes, it could be the manufacturing spread of batteries. However, everyone is assuming the Visor is taking juice from the 3V tap. In theory, they can tap the voltage halfway, from one battery only. In this case, one battery would burn up faster. A reason could be that they need multiple voltages, and this saves them from having to add another dc converter circuit. Given that my observations consistently show one battery being completely dead, while the other is still relatively ok, I have to wonder.

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

I don't understand how power can be pulled from one battery in the Visor. As far as I can tell, they are installed in series within the unit:

Battery 1 (+) to the Visor
Baterry 1 (-) to Battery 2 (+)
Battery 2 (-) to the Visor

< + Battery 1 - \
< - Battery 2 + /

This supplies the 3 volts the Visor needs. In this configuration, it is not possible to to pull power from one battery, is it?

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MarkEagle - Ice is nice!

Registered: Feb 2000
Location:
Posts: 5

I assume you are saying there is no third connection

Battery 1 (-) to Battery 2 (+) to Visor ?

Did you open and verified it yourself, or are you assuming? If you know indeed that there is no such third connection, then I can lay my theory to rest.

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

Yes, it is an assumption on my part. I'm not brave enough to open up the case to look inside, nor do I want to pull the batteries in order to poke around with my multimeter and face a hard reset. But, with the Ice case, I can see (albeit not too clearly) that there does not appear to be any sort of connection on the right side of the battery case (when viewed from the back), except to tie the two batteries together (+) to (-).

I did check with an EE that I work with and he tells me the following: in a "perfect" world, assuming the batteries are equally charged when installed in series, they "should" discharge equally. There are many "real" world factors that come into play, though. For example, manufacturing tolerances can cause faster rates of discharge from one battery to another, but in series the discharge should be fairly "equal". Temperature is another one of the factors batteries are affected by.

Since most battery powered devices work with the batteries connected in series, he said the Visor is probably no different. Also, he said that most of today's electronic circuits rarely use anything other than 3 or 5 volts (especially battery powered ones)

His "educated" guess to this question is that the batteries must have been at different levels to begin with. He also asked whether we were talking about regualar alkalines or rechargeables like NiCAD or NiMH. He did say that NiCAD's, with their "memory" effect, can suffer from these symptoms if not properly charged and discharged.

I'm close to needing to change the NiMH's in my IVDx. When I do, I'll note the individual battery levels at installation and check them again when they get removed.

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MarkEagle - Ice is nice!

Registered: Feb 2000
Location:
Posts: 5

Thank you Mark Eagle for all your replies.

Being an EE myself, and still doing experimental research myself, what I observe is way off the normal, which is why I brought it up in the first place.

First, everytime I did start off with fresh Alkaline Batteries, and I did measure both voltages to be close to 1.53-1.55 volts.

Having gone though about four sets, each and everytime one is consistently lower than the other. I have one of those "As Seen on TV" regular alkaline battery chargers. Even though this charger isn't as good as NimH type or rechargable alkaline, it does replenish some juice. However, everytime one
battery takes longer to charge up.

I have also gone through a pair without recharging, and the result is still the same.
When I then take out this pair, one cannot be re-charged at all, whereas the other can still be somewhat replenished.

While it is true that most circuits use 3V
or 5V, it is not out of the question that lower voltages are used for standby or coma
mode. For instance, one battery could be used at all times to keep the memory going,
whether you have the visor switched on or not.

Also note that it is not quite accurate to measure a battery with a voltmeter alone. One need to draw some current to mimick the conditions in circuit, i.e. even though the battery may measure 1.3V, with real current drawn, the voltage will always be lower.
By measuring both the voltage "open circuit", and with a load and observing the difference in the voltages, one can get a good indication of how far down the curve this battery is. Believe me, one is always way more depleted than the other. I have done similar things to batteries in remote controls, and the results come nowhere near to what I see with the Visor.

You don't have to believe me, try measuring it yourself and tell me if this is consistent and repeatable among all Visors.