18650's in parallel need multi-protection?

[cityevader]

Do each individual cells in a parallel 3.7v pack need protection, or can a single protection board be shared with all cells?

I'm resigned to using spring loaded holders glued together, with batteries removable, but I'd like to get solder tab cells to make a solid pack, but they don't come with protection it seems.

 

[clintb]

If your single protection included individual taps to each cell, then yes, you could go that route. Outside of our individual hobby cells, you'll not find many cells with protection. Laptops, power tools, etc... have a single circuit to monitor individual cells, which is probably cheaper.

 

[Bullzeyebill]

Since they are acting as one cell I would think that you would not necessarly need a protection circuit if, and I mean if, you are monitoring the voltage of the pack, or your devise has a built in protection circuit. I am sort of leary about depending on protection circuits built into individual Li-Ion cells, for my flashlight purposes.

Bill

 

[45/70]

.....I am sort of leary about depending on protection circuits built into individual Li-Ion cells, for my flashlight purposes.

I totally agree, Bill. The "homemade" protection circuits some cells have added to them, don't inspire much confidence.

Dave

 

[cityevader]

hmmm, well, during the charging phase is when the most abuse will occur, as I certainly will leave it on for longer than it should, requiring some self protection in either the charger or cells. This would be the more dangerous time I imagine.

As for discharging (bike light), it'll be on a simple amc7135 (paralleled pair of 1400ma with hi-low 1.4-2.8A) so it could get drawn down too far, however, the P7 should dim considerably by then so unless I have a breakdown or some other reason to have it on for as long as possible, it could affect the cell. But either the emergency will be bad enough not to care about a battery, or i'll get home safe and sound and charge it up right away.
Should be easy enough to get/make a "fuel level" led array to indicate charge level while riding.

 

[45/70]

hmmm, well, during the charging phase is when the most abuse will occur, as I certainly will leave it on for longer than it should, requiring some self protection in either the charger or cells. This would be the more dangerous time I imagine.

Never leave Li-Ion cells on a charger past the fully charged state. This is a really bad practice, regardless of how well/the quantity of protection you have!

What we deal with here in the flashlight/torch universe, is not the same as a cell phone or a laptop. We are stretching the limits far more than these devices which are designed, tested, tried, and proven (for the most part, however even they have been known to on rare occasions) to be safe, left on the charger. My advice is, don't do it!

I don't mean to come across as an alarmist, regarding Li-Ion safety, but there is a point when common sense should kick in, leaving cells on charge beyond the fully charged state unattended, crosses the line and is a definite no no. :shakehead

Dave

 

[cityevader]

Good point on safety...I'm clearly new, having never used Li ion before. I've read a bit on the do's and don'ts, and will continue to read further into it.

The main question wasn't about protection for safety sake, but rather for pack building. It just seems like protected cells weren't made for soldering into packs as none I've found came with solder tabs.

I went ahead and ordered ones with protection, and will just use the spring holders I got from digi-key (which seem like they'll be very difficult to remove install cells, but were cheap).

 

[45/70]

The main question wasn't about protection for safety sake, but rather for pack building. It just seems like protected cells weren't made for soldering into packs as none I've found came with solder tabs.

Yes, it's true, protected cells are not for building packs. Li-Ion cells from the manufacturers do not come with protection circuits built onto the cell. Manufacturers will not sell "loose", or "bare" Li-Ion cells to individuals. Protection circuits are added on by distributors (eg. xxxxxFire) who buy loose cells from the manufacturers. To put it another way, Li-Ion cells are manufactured for building packs only, and it is assumed that an external protection board will be included either in the pack, or in the device the pack is to be used in.

Dave

 

[Kuryakin]

They SHOULD act as a single cell. If they are truly in parallel, the voltage will be exactly the same across each cell, and they'll track together.
The real issue is, is there a protection circuit out there that can handle the current loads, both charge and discharge, of such a pack?

Do each individual cells in a parallel 3.7v pack need protection, or can a single protection board be shared with all cells?

I'm resigned to using spring loaded holders glued together, with batteries removable, but I'd like to get solder tab cells to make a solid pack, but they don't come with protection it seems.