Protecting unprotected cells in DIY Mods

[Rocketman]

With all the discussions about which is better;
protected Li-ion cells or unprotected IMR cells
I would like to offer an option for modders to consider.
For Big Battery 3.7 volt mods, incorporate overvoltage, undervoltage, overcurrent, short circuit protection AND the 'Safer' IMR chemistry.

Some modders use PTC fuses which adds some degree of safety, but what about the protection boards that are used on Li-ion cells sold by Ultrafire, Trustfire, and AW?
These boards come in three basic versions based on peak current but the operation is basically the same. A controller chip (6 pin chip in photos) and 1, 2 or 3 dual Mosfets (the 8 pin chips) for a max current of 3amps, 6 amps, or 9 amps (some production variability). This allows the modder to design for a max current (9 to 10 amps isn't always needed).

I use several types of unprotected Li-ion cells from laptop reclaims, cheap Chinese cells, better Japanese cells, and even IMR LiMnNi 'Safer' cells, but ALWAYS include one of these cheap protection boards. The boards do drop a little voltage. The 3 mosfet board drops the least, but even the 2 mosfet board only drops about 0.120 volts @ 3 amps. Wiring these to unprotected cells isn't difficult.

Some folks have had problems with the boards, cutting out on them and disabling the cell. But isn't that a 'Good Thing"?

Just another option for the modder to consider.

 

[Rocketman]

and don't forget to VENT your mods even with 'safer chemistry'. Know which end is the WEAK end


Here's an IMR 26650 4000mah LiMnNi with a single chp (2.5 to 3 amp) protection board for a friend that doesn't do Low Resistance. This board would obviously cutout with a 1.5 ohm atty.

You can even add protection to a pipe mod.

 

[webbcm127]

where are you getting the lil cercuit boards at?

 

[Rocketman]

DealExtreme
I think GP has them also.


oh and off the bottom of older Li-ion cells.
I never throw anything away

 

[webbcm127]

DealExtreme
I think GP has them also.


oh and off the bottom of older Li-ion cells.
I never throw anything away

ha i never thow anything away either...why didnt i think of that lol!-)

 

[Rocketman]

Here's how to wire them in.
The contact labeled -P is connected to the back plate via a row of plated thru holes. I remove some of the solder mask and solder the mod negative to that area, or directly behind it on the back plate.

 

[Deadite]

I've been using them in my mods, they take up very little space.
My only issue with them is I wish they'd regulate the voltage at 3.7v.
I get a burnt taste right after a full charge, good at about half charge, then lacking just before the battery goes dead.

 

[Rocketman]

and why not just one more tip

Look inside your metal mod, commercial or home made.
Is the inside nice shiny metal?
Is the only thing keeping the cell from shorting against the mod shell the plastic wrapper?

Maybe a trimmed business card or if there's room, some cork gasket material to protect against shorts. A protected cell (the thin metal strip that goes to the positive end) can short out because of a cut or nick in the plastic wrapper. Ever wonder why your mod overheated without an atty or the switch pressed? A shorted cell because of contact with the inside of the mod shell may bypass protection circuits, master switches, fuses, or sacrificial springs. Insulate your mod. Here's a pic of an insulated flashlight mod.