How to connect a 4.2v cell to a light source using a barrel connector?

[OneBigDay]

I am hoping somebody can point me in the right direction on this.

I have a Cygolite Mitycross 350 bicycle headlight. It comes with a proprietary but standard "3.8v" enclosed waterproof battery pack. This battery pack plugs into the lamp portion of the light with what looks to me like a standard barrel type connector. The barrel is about 5mm wide, by exactly 15mm long. See photos below.



The reason for my post is that I have some 3.8v 26650 IMR cells (4000mAH) that I am using with some FM flashlight hosts, but it got me thinking I should be able to use these same cells as a backup or alternate power source for the Mitycross.

So 3 questions I guess for starters.

1) Any reasons why I should not try this or potential pitfalls
2) Is the above pictured barrel connector standard and if so where can I get one? I see some similar at batteryspace but they are only 8mm long.
3) Is there some kind of standard battery holders that are used for this type of application or am I looking at making a custom battery holder too if I go down this road?

 

[EvilLithiumMan]

I am hoping somebody can point me in the right direction on this.

I have a Cygolite Mitycross 350 bicycle headlight. It comes with a proprietary but standard "3.8v" enclosed waterproof battery pack. This battery pack plugs into the lamp portion of the light with what looks to me like a standard barrel type connector. The barrel is about 5mm wide, by exactly 15mm long. See photos below.



The reason for my post is that I have some 3.8v 26650 IMR cells (4000mAH) that I am using with some FM flashlight hosts, but it got me thinking I should be able to use these same cells as a backup or alternate power source for the Mitycross.

So 3 questions I guess for starters.

1) Any reasons why I should not try this or potential pitfalls
2) Is the above pictured barrel connector standard and if so where can I get one? I see some similar at batteryspace but they are only 8mm long.
3) Is there some kind of standard battery holders that are used for this type of application or am I looking at making a custom battery holder too if I go down this road?

1) Potential pitfall would be using an unprotected cell. Be sure you understand the care and caution required if using an unprotected cell.

2) From looking closely at your photo, it appears the connector is a 5.5mm OD (outside diameter) plug, which typically have a 2.1mm ID. This is a standard size, among the dozens, if not 100's, of standard plugs available. Do a Google search on "DC coaxial power connector 5.5mm" and you'll find many places offering these. If there is an electronics surplus store nearby, try looking there too.

3) I'm gussing you would need a custom holder. Perhaps another CPF'er with more experience will chime in here.

 

[Meterman]

The barrel is about 5mm wide, by exactly 15mm long.

The outer diameter of these plugs will be 5.5mm, but then there are two versions of inner diameter: 2.1mm or 2.5mm and the lenght may be either 9mm or 14mm.

HTH
Wulf

 

[NutSAK]

The outer diameter of these plugs will be 5.5mm, but then there are two versions of inner diameter: 2.1mm or 2.5mm and the lenght may be either 9mm or 14mm.

HTH
Wulf

Lengths of 9.5mm and 11.5mm are common in the 2.5 x 5.5mm connector size.

 

[OneBigDay]

Thanks guys, this is helpful.

Now that I know I'm looking for a "DC coaxial power connector" that makes all the difference. I can't tell if it's 2.1mm or 2.5mm inside diameter - I will just pick up a couple of each online and see which one fits.

I will start with a cheap "C" cell holder from radio shack for a proof of concept run for the holder. Cut it in half and remount at the correct spacing apart. This will work for starters.

 

[poguy]

Do you have any wall wart supplies stashed away? The 5.5mm plug is common. If you have a few you might have both 2.1 and 2.5 ID just to see what they look like.

Do you have any hamfests coming up in your area? They can be great places to find electronics-related junk.

 

[OneBigDay]

UPDATE:

First went to a local shop with a lot of stuff called AEI electronics, they had a few shorter DC plugs, but no luck. Next I ordered a couple of part # 090-499 (2.5mm x 5.5mm x 14mm DC Plug) from an online vendor called parts express. Arrived quickly and the physical plug fits into my headlight fixture. The original plug may be 1 or 2 mm longer than these, but I was still optimistic about success.

So I hooked up the new DC plug to my cell. + to the inside lining, - to the outside shell. I checked it with a multimeter and this is the same polarity as on the original battery pack. Put a DMM on the new contraption and it's getting power to the DC plug. So far so good.

But when I plug it into the headlamp. :shakehead No light, no mayhem, just deafening silence.

I'm not going to make a big project out of this, but if anyone else has suggestions, I'm listening.

 

[NutSAK]

If the connector you bought has a 2.5mm ID, and the fixture is designed for a 2.1mm ID, you would probably not get a connection at +V.

 

[OneBigDay]

If the connector you bought has a 2.5mm ID, and the fixture is designed for a 2.1mm ID, you would probably not get a connection at +V.

Good point, I bought a couple of both sizes (2.1 & 2.5) because they were only $1 each and I wasn't sure of which size I needed. The 2.1 does not fit, definitely too small.

 

[NutSAK]

Good point, I bought a couple of both sizes (2.1 & 2.5) because they were only $1 each and I wasn't sure of which size I needed. The 2.1 does not fit, definitely too small.

Well, in that case... :thinking: :shrug: