# The Princeton Tec EOS Diet…



## SilverFox (Dec 7, 2005)

I use a Princeton Tec EOS headlamp all the time at work. I usually set it on low and it keeps me from falling into holes and tripping over things. I use a flashlight to see and inspect with, but for general navigation, the EOS works out very well.

The EOS is regulated and seems to do a good job of sucking Alkaline cells dry. It is advertised to run about 6 hours on a set of 3 AAA cells on high. On low, I believe the advertised run time is something like 60 hours. Not bad for a set of around 900 mAh cells. Many people have been using NiMh cells and have been pleased with their performance as well. I have not tested NiMh AAA cells at 150 mA, but believe that most brands (regardless of what their label says), should come in with similar capacity.

The EOS weighs 105 grams with the strap and with a full set of Alkaline batteries.

While the EOS is fairly lightweight, I decided to put mine on a diet.

I contacted AW and found out that there are Li-Ion cells that are the same size as AAA cells (10440). Their capacity is a bit low at 320 mAh, but if you parallel them you end up with 3 cells at 4.2 volts and 960 mAh. This is pretty much a direct replacement for the 3 AAA Alkaline cells.

I ordered some cells and put them in. The middle cell has to go backwards and the negative end does not contact the metal strip. A small magnet took care of that problem, and the plastic holder of the light will keep the magnet from slipping around out of place. EDIT: You also have to jumper the contacts at the top and at the bottom. The contacts are in two pieces in both places and you need to connect them together. END EDIT

My EOS went from 105 grams to 98 grams and now is more comfortable to wear, should have the same run time, will have better cold weather performance, I am no longer concerned with self discharge, and because the batteries are rechargeable, I am still enjoying guilt free illumination… 

Now I am looking for a place to put a “Lithium Powered” sticker.

I must add that all the standard warnings concerning Li-Ion cells should be adhered to:

These cells are unprotected, so charge them often. If you run them all the way down you will destroy them.

You will need a charger than can handle Li-Ion cells and keep in mind that these are 320 mAh cells. The preferred 0.7C charging rate is 22.4 mA. I am charging at 25 mA. You will need some way to hold the batteries for charging. If you charge them in series, you should make provisions to balance them from time to time. If you charge them in parallel, things on the charging side get easier, but how to hold them becomes more of a challenge.

Don’t charge Li-Ion cells unattended.

Charge on a fire proof surface.

Tom

As a foot note…

My wife things I am a bit off because I am running around the house with my head lamp on bouncing my head back and forth trying to see how much of a difference 7 grams makes. I have two EOS headlamps, so I don’t have to change batteries all the time.

I believe there is a noticeable difference, but I also though that my truck had a little more snap to it when I replace the exhaust system and fitted it with Corvette tips…


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## cognitivefun (Dec 7, 2005)

Good post. Thanks for the idea.

You can also use NiMH which should work okay if you don't mind the self-discharge.


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## SilverFox (Dec 7, 2005)

I forgot to add that you have to be careful when replacing the cells. If you don't put them in correctly, you will probably fry the light...

Tom


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## Bogus1 (Dec 7, 2005)

I like the EOS too and was wondering about this myself. So the trick in converting it to parallel from series is to reverse the middle battery?

Thanks


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## SilverFox (Dec 7, 2005)

Hello Bogus1,

You've got it...

At first I was going to call this a mod, but it is actually more of a substitution.

The only difficult part is to get a connection between the base of the middle cell and the contact. Usually the battery nipple makes that connection, so I improvised a nipple on the base of the Li-Ion cell using a magnet.

Tom

EDIT: Please note that this information is not correct. In addition to reversing the middle battery, you also need to join the two piece connectors at both the top and the bottom of the battery compartment.


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## jar3ds (Dec 8, 2005)

i wonder what 1.5v lithiums would reduce the weight.... ? i think i'll be going more that route


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## SilverFox (Dec 8, 2005)

I have run into a problem with this project... EDIT: Problem fixed... END EDIT

I have been doing some run times and am getting similar results to what Doug (Quickbeam) got. About 2 hours regulated light on high, then things start to dim.

However, when checking the voltage of the individual cells (total system voltage was around 2.9 volts), I am finding that the two outer cells are pretty close, but the middle cell is over 4.5 volts.

Everyone knows that is not a safe voltage to be at with Li-Ion chemistry.

How does a parallel pack charge its center cell under load? :thinking: :thinking: :thinking:

I am sure there must be a good reason this is happening, but I am at a lost to explain it...

Tom


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## markdi (Dec 8, 2005)

just reversing the middle cell can not be the only mod needed to put all the cells in parallell.


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## SilverFox (Dec 8, 2005)

Hello Markdi,

Yes, you are absolutely correct. I feel like I left my brains in the ditch...

I did measure the voltage across the whole pack and it was showing 4.134 volts. From that, I thought I had everything in place. Wrong...

OK, let me try again. In order to put all three cells in parallel, you need to add a jumper wire to connect the top two battery connection pieces and another jumper wire to connect the bottom two battery connection pieces. With all of the top contacts connected together, and separately with all of the bottom contacts connected together, you can add the Li-Ion cells (taking care to make sure that you follow the orientation for the cells in slots 1 and 3, but you need to reverse the cell in slot 2) and they will be in parallel.

Things are working much better now... I am about 2.5 hours into a run time test and am still in full regulation. 

While I was checking things out, I swapped the optic for a Fraen optic that I got from Mr Bulk a while back. It makes the hot spot wider at the expense of some spill. It measures less on my light meter, but the beam shape seems more useful. I will have to give it a try and see how I like it.

Tom


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## Krit (Dec 8, 2005)

As I know, It's rather dangerous if we parallel li ion cell together. Because we don't know exactly capacity each. The high capacity cell might charge another low cell and affect to low cell. So it's rather risk when use paralell mode without control circuit for paralell propose.


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## SilverFox (Dec 8, 2005)

Hello Krit,

I have matched these cells for capacity and there is very little danger in using them this way. The problem came from me not hooking things up properly.

Another problem is that these are bare cells and I have to be on top of the discharge. When I see the light fall out of regulation, they are at about 3.0 volts per cell, and it is time to charge them back up again.

My usual habit is to recharge frequently. I am checking run times right now. After 3 hours on high, I am still at 3.65 volts and still in full regulation. This is better performance that I have observed on Alkaline cells or NiMh cells. I wonder if I can get 4 hours...

I usually use the light on low and can expect a weeks use from it between charges.

Charging in parallel also will eliminate any imbalance between the cells. It is a little tricky to set up, but is quite easily done.

Tom


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## SilverFox (Dec 9, 2005)

Well, I didn't get 4 hours...

At 3.5 hours (around 3.06 volts), the EOS dropped out of regulation. At 3.75 hours I was down to 3.0 volts and shut things down.

Doug (Quickbeam) reported 2.25 hours until the light dropped to 50% and with the Li-Ion cells in parallel, I am getting 3.5 hours. That is like a 50% increase in run time in regulation. 

Not bad.

The down side is that when the light starts to go dim, it dims down very rapidly with the Li-Ion cells. 

To lighten things up even more, you could put the jumpers in and run with one cell. I will have to try that and see what the run time is like.

Tom


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## SilverFox (Dec 9, 2005)

This is getting very interesting...

My original plan was to power this light with a single Li-Ion cell, but after realizing that the capacity for an AAA Li-Ion cell is very low, I went on to put 3 cells in parallel.

I just finished running it on one cell. 75 minutes on high until it dropped out of regulation, and quickly dove to the 3.0 volt mark in the next 5 minutes.

I have now gone from the original 105 grams to just slightly over 80 grams. That is a significant drop in weight. Although there is some loss in run time, it is not as drastic as I first thought it would be. Since I usually run the light on low, this may be the perfect way to go for me. 

I have some other headlamps around here... I may have to see what I can do with them.

Tom


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## jar3ds (Dec 9, 2005)

woudl it be possible to get a pic of exactly how your are running these in parraell?


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## SilverFox (Dec 9, 2005)

In order to complete this project, I did a run with 2 Li-Ion cells. The weight with 2 cells is 85 grams and the light ran 2.5 hours on high before dropping out of regulation.

This gives me a wide variety of ways to manage my energy needs.

I will probably start out with 2 cells in the light and carry a third for a back up.

Tom


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## SilverFox (Dec 10, 2005)

Hello Jar3ds,

Here is a picture of how things are set up. The picture shows all three cells installed, but it will run on 1, 2, or 3 cells.







Tom


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## SilverFox (Dec 13, 2005)

Update:

I ran the light with one cell on low.

At 16 hours and 39 minutes, I noticed it getting very dim. I was below my goal of shutting things down at 3.0 volts and the voltage was at 2.5 volts. At this low current draw, it did not spring back up to over 3.0 volts, so I quickly put it on my charger. My charger complained that it was over discharged at first, but then the voltage came up and everything is fine.

I think it would be best to limit the run on one cell on low to 16 hours. That means that with 3 cells you would get around 48 hours of run time.

I now have run times on high and low. I guess I should do a test on medium...

Tom


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## SilverFox (Dec 14, 2005)

Update:

I finished the test on medium. Here is a summary of run times with this set up:

On high
1 cell gives 1 hour and 15 minutes,
2 cells give 2 hours and 30 minutes, and
3 cells give 3 hours and 45 minutes of run time.

On medium
1 cell gives 4 hours,
2 cells give 8 hours, and
3 cells give 12 hours of run time.

On low
1 cell gives 16 hours,
2 cells give 32 hours, and
3 cells give 48 hours of run time.

Once again these run times are with the unprotected 10440 Li-Ion 320 mAh capacity cells, running in parallel.

Tom


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## Krit (Dec 15, 2005)

SilverFox, Very good data on EOS. Thanks.


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## jar3ds (Dec 15, 2005)

awesome! how would you think a protected 10440 would work? 

I wonder if we could get you to do a energizer lithium 1.5v runtime test in all three modes just to compare runtimes... maybe even a NiMH? The weights of those two battery chemistries by the weights of your mod with the runtime data woudl give a ton of excellent feedback on the EOS...

i can't wait to get mine and figure out how to make it flood as much as possible... =)

the eos is such an awesome light

thanks for the thread silverfox! great mod!


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## SilverFox (Dec 16, 2005)

Hello Jar3ds,

Protected cells would work fine, but usually with protected cells you loose some of the capacity. Starting with only 330 mAh, the losses in capacity may be significant. 

I never asked AW if these came in a protected form, so I don't know if they are even available.

Since the EOS is a regulated light and doesn't have a high current draw, I am not sure there would be an improvement using Lithium AAA's in the stock configuration. However, if you were going to store it in your car for emergency use, it would be a good choice.

I remember the original Alkaline cells seemed to last forever. After I ran them out, I switched to NiMh. I never had a problem with them, but I am diligent to re-charge often.

After using this modified EOS for a few days, I find that since I changed the optic, I find that I am using medium more than before at work. With the stock set up, I would switch the light to low and go. Now, with the wider beam, I can get by with low, but prefer medium. 

However, I no longer need my diffuser to read a book. The low setting is just right.

I guess there are trade offs which ever way you go...

At any rate, using re-chargeable cells, I don't mind going up in power, I just have to re-charge a little more often. 

Tom


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## jar3ds (Dec 19, 2005)

what did you do to the optic? I'm thinking about McR-18... but I don't know if it will be better? I want a replacement reflector that gives me tons of flood/spill! The McR018 seems to be spot/spill beam like a HDS... I think I want more of a flood than a HDS style of beam... I wonder how the IMS 17mm compares to the McR-18? 

What would you recomend?


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## SilverFox (Dec 19, 2005)

Hello Jar3ds,

I just happen to have an optic on the shelf. I believe it came from Mr Bulk and was used in his Baby Pin light. It dropped right into the holder, but I don't think it sits all the way down on the LED.

It has the effect of making the spot wider, at the loss of some spill. My light meter readings dropped in half. This makes low very nice for reading without having to diffuse the beam, but makes me step up to medium for work. I am still getting good run time, and with rechargeable batteries, it's no big deal. Obviously, high will not throw as far as the original optic did, but for throw I usually have a flashlight handy...

Tom


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## jar3ds (Sep 20, 2006)

Tom,

I assume the new weight for the EOS w/ 3x10440 is the 98 grams weight... as you stated in the starting post...

however, what is the weight w/ only one 10440? Thanks

Jared


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## chesterqw (Sep 20, 2006)

to get real light weight, lithium disposable ?
or does it make no diff?


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## jar3ds (Sep 20, 2006)

well... i'm unsure of the weight of the 10440's... or the AAA lithium primary's


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## SilverFox (Sep 23, 2006)

Hello Jared,

I believe the 10440 cells are close to 6 grams each.

Tom


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## jar3ds (Sep 23, 2006)

thanks silverfox.... i'm ordering up some 10440's ...

how do *you* charge them? I'll use AW's 10440 charger to get me by for a while... however in the future...

I'm thinking about buying a 4xAAA holder from http://www.thomas-distributing.com/battery-holders.htm

then making that holder parallel... then connecting it to my DSD (or some other charger)... I would assume if I hook up 3x10440's in parallel that the charging current of the DSD would be safe... but i'm just guessing...


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## Rudi (Sep 23, 2006)

SilverFox said:


> Hello Jar3ds,
> 
> I just happen to have an optic on the shelf. I believe it came from Mr Bulk and was used in his Baby Pin light. It dropped right into the holder, but I don't think it sits all the way down on the LED.
> 
> ...


 
Simpler and easier is to affix a UCL-LDF diffusing lens to the front of the EOS. Makes for a very nice reading beam.


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## SilverFox (Sep 23, 2006)

Hello Jared,

I charge them individually on my Schulze isl 6-330d at 0.25 amps, or all three in parallel at 0.5 amps.

Tom


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## SilverFox (Sep 23, 2006)

Hello Rudi,

I will have to check that out. My solution has been to take a white baby sock and pull it over the light.  

Tom


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## jar3ds (Sep 23, 2006)

SilverFox said:


> Hello Rudi,
> 
> I will have to check that out. My solution has been to take a white baby sock and pull it over the light.
> 
> Tom


 silverfox,

i think you'll be much better off w/ the HDS Mild diffuser... its a drop in solution w/ no perm. mod


http://www.lighthound.com/sales/hds_edc_accessories.htm


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## Pydpiper (Sep 30, 2006)

I get nervous just thinking about unprotected cells going on my nightstand, and your strapping them to your head.
Great bunch of info here!


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## SilverFox (Sep 30, 2006)

Hello Pydpiper,

Almost all of the problems associated with unprotected cells occur during charging. With this in mind, I simply use a quality charger and check the voltage before charging. If the open circuit resting voltage goes below 3.3 volts, my plan is to stop using the cell and replace it.

The next source of problems comes from physical abuse. I feel the light offers adequate protection, so no worries there.

The final thing to keep in mind is that there is not a lot of capacity to deal with. I am guessing that an "event" with a very low capacity cell will not amount to much.

All in all, I feel confident with this set up and use it freely.

Tom


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## jar3ds (Oct 2, 2006)

Thank to Silverfox for this thread and coming up with this idea. :rock:

I got ~ 1 hour and 25mins... so Silverfox's 1hour&15mins is not too far off at all! :thumbsup:

I used an McR-18 reflector that has been cut down and this is by far the best beam I've got'n out of the EOS (cheers to mosport  )...

Also, after the runtime test as soon as it popped out of regulation. I checked the heat. My star was a tad warm and SO WAS THE McR-18! So in addition to having a better beam with the McR-18 (instead of the 17mm IMS)... it aids as another area for heat to travel to... Very nice! :naughty: 

Also, using the McR-18 I find myself using the medium and low settings a lot more than when I did with my IMS 17mm. Mainly because the McR-18 seems to give me more fill beam between my spot and spill which is really important for a headlamp. So I can expect according to Silverfox, about 4 hours on medium which is quite a bit of light for a decent amount of time, all on a single 10440.

Since the original topic of this thread was the *EOS DIET*, I would say that it does lighten up the EOS a lot... it almost feels like there aren't any batties when you use just one 10440 cell. The way I have my EOS wired is so that only a single 1x10440 can be put in (in the bottom slot, perfect for weight distribution when tilted)... however, i did not need to solder anything... I just wedged a small jumper wire into the springs... So at anytime I can take out the jumper wire and go back to using normaling ~1.5v AAA's...

I will use this mod for my car. I can keep a pack of 10440's in the car w/ me and some lithium primaries. That way I have the slow discharge of LiON's and great cold weather performance, which is very important where I live. However, if I get stranded and need Gas Station replacement batteries all I have to do is take out the jumper wire and I'm good-to-go! 

The EOS is an amazing headlamp. Waterproof to 1 meter, BRIGHT mod'able Lux's, regulated, light-weight, uses the beautiful McR-18 reflector, and has a ton of battery options including li-ions!

*EDIT:* well PT's website says 105g for the EOS w/ 3xAlks... So an Alk according to Quickbeams site is 11.5g. That makes the weight w/o batteries 70.5g's... So add 6g for the single 10440 and you have a 76.5g headlamp!


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