Northwest Dive Club

Hey guys, I know I have made a few battery cans for heater vests and I need some info. since the battery packs have been supplied by you guys I don't know the particulars as to where they came from and the tech info. Could one of you give me some info as to source and voltage/amp rating and such.

Thanks Rich

Hey Rich,
Here is the one I brought to you, as we both discovered it was a bit low on the voltage and didn't work as well as we had expected.
https://www.batteryspace.com/li-ion-186 ... light.aspx

Most vests are 12V nominal from the motorcycle universe. So they achieve full heat output around 14 or 15V (what an alternator puts out). Li-ion is 11V nominal and under load about 10V. Hence the heat output is significantly reduced.
Xamps x 14V = 14X Watts
Xamps x 10V = 10X Watts
10X/14X = 70% of expected heat in Watts (roughly)

On the plus side they don't get so hot you need a pitkin controller or to cycle it on-off to avoid sweat.

The biggest issue with getting cells, is quality. The Chinese cells generally test far under their rating. Longevity isn't good either. I was lucky to find real Panasonic 3400's, yielding a 6 hour pack. There are many counterfeit cells.

A real panny cell tests a nominal 3200. Some fakes ones I got were 2800.

longevity can be impacted if you don't have a low voltage cutoff built into the system (either on the battery side or the heater side), as heater vests can and will deep discharge a pack. Many light packs don't have that as they are essentially system limited by the needs of the light head (HID's and LED's need a certain amount of voltage) Heated suits generally just make heat as long as some juice is flowing, it will just get less and less as the battery discharges, so when you use your unprotected light canister pack till its dead with a heating element that doesn't have a low voltage cut off don't be surprised if lifespan is shorter than expected.

That holds true for older NiMh batteries but almost all Li-on packs have built in protection circuits as they are required for safety. Once drained below a certain point Li-on batteries will not recover and are forever ruined so the manufacturers put in the low voltage cutoff as well as an over charge cut off. The down side is that when they reach the low side cutoff they simply turn off and that's it!

ps a 9Ah 14V NiMH is somewhat of a minimum as the sag on the voltage on anything smaller will trip the low voltage cutoff. I know people using 4.5Ah but they don't last most than 30mins, depending on the vest

Dusty, there is actually a way to recover a Li-ion battery that has gone to sleep.

The following video is for power tool li-ion batteries but it applies for them all: https://www.youtube.com/watch?v=3e-RwVawEOs

There's a good reason these systems are designed to not charge once the voltage gets too low, the cells become damaged. If they are damaged enough they become dangerous. Chemical changes happen within the cells to potentially make them unstable. Lots of the chargers will cease to function at 2.8-3.0v/cell. Low cut-off usually is set somewhere around 2.5-2.8v/cell. Low cut-off happens under load. Once the load is removed the voltage recovers generally within the chargers operating specifications.

It's not generally unsafe to use this technique down to 2.5v/cell. 2.0v/cell is pushing it.....do you feel lucky?
Below 2.0v/cell trying recover Li-on cells is playing with fire, literally. Just so you know.
(IMO the guy demonstrating that technique in the video is not doing people a real favor, though he thinks he is).

Li-on cells function best if the cells are balanced (evenly charged). Most protection circuits ONLY provide high and low protection, they do not balance the cells. If the cells are not well matched to start, and are not taken care of decently they get out of balance, the protection circuit starts cutting off the weaker cells and the pack effectively becomes shot. I've seen this happen in a couple packs that were acting strangely.

Fyi, Panasonic test specs are to 2.5v

Different manufacturers do have different low voltage cut-off specs. I'm not sure how much of that is actually 'good practice' or how much is so they can push the cell as far as possible to maximize capacity tests. It's been shown that keeping your cells between 20-80% charge maximizes the longevity. Keeping them stored fully charged and discharging them down to the bottom are excellent ways to create an early demise.

The 2.0v resting 'bottom' is pretty sound though. Once you get below that you are incurring permanent damage to the cell. Mostly that means you end up with a piece of junk over time. But there are incidents of more serious events from abused lithium cells.

In my own testing, from 3.0> 2.5 yielding only a small difference in numbers. I think was less than 100Ma, maybe even 1/2 that.

I dont discharge below 3v anylonger