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Strange Voltage Reading - Lynx I on NiMH Batteries


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I have always lamented that none of my Lynxes (model 1) run on modern rechargeable batteries (NiMH). One is a salvaged Lynx that I modded with a McWill LCD, and another is a refurbished one from Best.

 

I always assumed this was because the Lynx was sensitive to the lower voltage of these rechargeables. So, since I had a spare Recom DC-DC converter left over from another project I decided to 5V mod my Lynx with the new LCD. This is the unit that I play the most, and that I would most appreciate being able to take away from the wall.

 

The mod went fine. My Lynx played like normal both using regular alkalines and using the power adapter. However, it still wouldn't boot when I put NiMH batteries inside. I tried this with both brand new, fully charged, Panasonic Eneloop Pro AA and Amazon Basics Pro AA batteries.

 

I opened the Lynx up and measured the voltage across the battery terminals. The reading was less than 1V. Switching to alkalines, I got a little over 9V. I put the NiMH batteries back in and measured the two sets of 3 batteries separately. I got just over 4V on each of them. However, when I measured the two sets in series... I got almost nothing.

 

What in the world is happening here?

 

The NiMH batteries themselves are fine. I can run my Gameboy, Game Gear, etc. using them without any issues. And yes, the battery polarity was correct. I swear I checked that like 20 times because I couldn't think of another reason why I was getting such a low voltage from the series cells.

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I've found the same problem trying to power my Lynx 1 using rechargeables! I assumed it must be a current related problem. Perhaps the current demand is too high, resulting in voltage drop, although from 9v to 1v seems more than you might expect!

 

It is strange and interested to understand this myself!

 

There's a switching circuit for producing the power isn't there, comprising of a 4066 and a Zener or something. Perhaps the voltage drop is sufficient to break that switching so it drops way down in voltage.

Edited by GadgetUK
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There is something strange going there but then I don't need to tell you that.

 

If the voltage across the pins is only reading 1v then I would say there a possibly a contact issue. Can you measure the voltage across the battery leads with the actual Lynx unsoldered just to rule that out?

 

NiMh batteries can supply a higher supply of current than Alkaline batteries due to their lower internal resistance so it's not that, 7.2 volts is more than enough to run a Lynx 1 or 2. I've run both Lynx 1 and 2 on NiMh batteries without issue.

 

I would also add that now that you have taken the backwards step of replacing the stock Lynx power circuit with a Recom Regulator then it won't work below 6.5volts and will drain your batteries if you leave them in even if the unit is off due to the fact that the Recom regulator is permanently powered. A much better solution is to put it back to stock, replace the FET with a modern equivalent and as a belt and braces replace the FET. It will work so much better on batteries and won't drain them when you turn it off. The stock circuit can work below 5 volts and your Lynx will still work too! And yes the stock Lynx power circuit is a very well designed high frequency switching regulator contrary to a lot of bull spouted around various forums.

 

http://atariage.com/forums/topic/247305-old-stock-lynx-vs-new-mcwill-screen-recom-power-reg-power-consumption/

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My daughter and I got sick this week, but I had another chance to look at it today. This time I removed the battery tray from the Lynx and tried measuring it all by itself.

I noticed something that I'm surprised I haven't seen mentioned here before--the Lynx I battery tray is designed in such a way that is not compatible with high capacity (~2500 mAh) NiMH batteries (or at least the 5 brands I have lying around the house).

For whatever reason, the main cylinder of these NiMH batteries is wider and taller than that of standard alkaline batteries. To compensate for the extra body length, the nub at the positive terminal is made shorter. The overall length thus stays almost the same as alkalines (but they are still fatter, which makes them more difficult to get in and out of certain devices).

In the Lynx I battery tray, there are two small tabs that stop batteries from pushing too far against the battery tray contacts. These tabs make it so that only the positive terminal nubs of batteries contact the battery tray contacts. However, the spacing between the tabs and the tray contacts was designed around the standard positive terminal nub length for alkaline batteries. Since NiMH batteries have smaller nubs, there is no continuity. I could easily fit a couple of sheets of paper in there.

So, mystery solved. I'll probably remove the tabs since that will alleviate some of the tightness in the tray when using NiMH batteries.

I would also add that now that you have taken the backwards step of replacing the stock Lynx power circuit with a Recom Regulator then it won't work below 6.5volts and will drain your batteries if you leave them in even if the unit is off due to the fact that the Recom regulator is permanently powered.  A much better solution is to put it back to stock, replace the FET with a modern equivalent and as a belt and braces replace the FET.  It will work so much better on batteries and won't drain them when you turn it off.  The stock circuit can work below 5 volts and your Lynx will still work too!  And yes the stock Lynx power circuit is a very well designed high frequency switching regulator contrary to a lot of bull spouted around various forums.
 


I had read that thread (nice work, by the way). But I figured that if it addressed my problem, I was willing to put up with the Recom. I will put it back to stock.

 

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My daughter and I got sick this week, but I had another chance to look at it today. This time I removed the battery tray from the Lynx and tried measuring it all by itself.

 

I noticed something that I'm surprised I haven't seen mentioned here before--the Lynx I battery tray is designed in such a way that is not compatible with high capacity (~2500 mAh) NiMH batteries (or at least the 5 brands I have lying around the house).

 

For whatever reason, the main cylinder of these NiMH batteries is wider and taller than that of standard alkaline batteries. To compensate for the extra body length, the nub at the positive terminal is made shorter. The overall length thus stays almost the same as alkalines (but they are still fatter, which makes them more difficult to get in and out of certain devices).

 

In the Lynx I battery tray, there are two small tabs that stop batteries from pushing too far against the battery tray contacts. These tabs make it so that only the positive terminal nubs of batteries contact the battery tray contacts. However, the spacing between the tabs and the tray contacts was designed around the standard positive terminal nub length for alkaline batteries. Since NiMH batteries have smaller nubs, there is no continuity. I could easily fit a couple of sheets of paper in there.

 

So, mystery solved. I'll probably remove the tabs since that will alleviate some of the tightness in the tray when using NiMH batteries.

 

I had read that thread (nice work, by the way). But I figured that if it addressed my problem, I was willing to put up with the Recom. I will put it back to stock.

 

 

Fantastic! Always good to get to the cause of the problem. Are you going to file the tabs down so that you can fit Ni-MH batteries in? My favourite Ni-Mh batteries are the Standard Panasonic Enloops. The Pro's hold a bit more capacity but can "only" withstand around 500 charges whereas the standard is around 2100 charges!

 

Have fun! :-)

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My daughter and I got sick this week, but I had another chance to look at it today. This time I removed the battery tray from the Lynx and tried measuring it all by itself.

 

I noticed something that I'm surprised I haven't seen mentioned here before--the Lynx I battery tray is designed in such a way that is not compatible with high capacity (~2500 mAh) NiMH batteries (or at least the 5 brands I have lying around the house).

 

For whatever reason, the main cylinder of these NiMH batteries is wider and taller than that of standard alkaline batteries. To compensate for the extra body length, the nub at the positive terminal is made shorter. The overall length thus stays almost the same as alkalines (but they are still fatter, which makes them more difficult to get in and out of certain devices).

 

In the Lynx I battery tray, there are two small tabs that stop batteries from pushing too far against the battery tray contacts. These tabs make it so that only the positive terminal nubs of batteries contact the battery tray contacts. However, the spacing between the tabs and the tray contacts was designed around the standard positive terminal nub length for alkaline batteries. Since NiMH batteries have smaller nubs, there is no continuity. I could easily fit a couple of sheets of paper in there.

 

So, mystery solved. I'll probably remove the tabs since that will alleviate some of the tightness in the tray when using NiMH batteries.

 

I had read that thread (nice work, by the way). But I figured that if it addressed my problem, I was willing to put up with the Recom. I will put it back to stock.

 

Finally a logical answer =D This caused me to think there was a fault with my Lynx 1 when I first bought it since the DC PSU worked, but batteries didn't - until I tried alkalines... Great that you took the time to check that out and spot something that most of us would have missed.

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I should rephrase what I said above. I should have said that the design of some modern NiMH batteries is not compatible with the Lynx I. Not the other way around.

 

Here is another person describing the same issue. "Post" is the name of the part I was talking about.

 

http://www.candlepowerforums.com/vb/showthread.php?180797-Eneloops-Shoulder-s-to-big-for-the-MH-C9000

 

Does anyone have any recent (regular, white) Eneloops to test in a Lynx I? If these work I would prefer to use those instead of hacking up the battery tray.

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  • 3 weeks later...

This thread was a great find! I had been frustrated as to why my Lynx would work when connected through the AC adapter but not on batteries. Sure enough, when I inserted the batteries I was using, I was able to fit a sheet of paper between the positive post of the battery and the Lynx terminal. I wonder why they designed it with plastic tabs that prevent use of some batteries?

 

I went to the store and eyed the positive post length of various NiMH rechargeable batteries. I took a chance on some Energizer Recharge Power Plus AAs, since they looked like they had longer posts. Success! They work with my stock Lynx I. They are also low self-discharge and came pre-charged, so they worked right out of the box.

 

Now the only problem is that the batteries are a little larger in diameter than standard alkaline AAs, and they get stuck in the Lynx :(

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